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1. MER ET ES ESSE SSeS __ Linkeroever 77 Zomerbed 99 Oeversectie 0 Rechteroever 1113 Linkeroever Rechteroever Stroomv Stroomb Stroomv Stroomb Breedte uiterwaard 77 767 346 Breedte aangetakte plas sen n a n a n a n a Breedte niet aangetakte plas sen n a n a 3 7 Breedte gebied achter primaire kade n a n a 2 n a Breedte gebied achter secundaire kade n n a n a n a n a Overzicht SOBEK profiel 1 Maas 16 40 16 80 Borgharen versie 1998 1 CROSS 33 TABULATED 99 109 WS 99 DA 44 45 44 026 0 35 52 22 22 38 82 59 59 38 11 88 86 3940 91 91 40 69 99 991 4211 109 109 4SUB1 42 89 156 169 43 87 221 234 44 45 508 44 46 528 45 45 46 45 48 45 540 I DIKET 551 WDIKE2 B33 1137 B33 1179 834 1182 50 45 835 1185 52 45 836 1180 52 72 837 11901 80 2 mm Rijkswaterstaat RIZA figure 26 Example profile description SOBEK compartment compartment 33 Page 69 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 8 Glossary SOBEK GIS terminology English German Duth Definition lt 1 lt 1 D model 1 D model Arc Info Bank line Bank section BASELINE Calibration Connected lake dAf Decision Support System DSS Design water level DIGIPOL Digital Terrain Model Dike segment Floodplain Floodplai
2. 37 Example boundary flow conveying flow storing S RR 38 Creating the boundary flow conveyance flow 40 Overview methodology flow conveyance flow 42 Example dike elements ne 44 Overview proces creating dike elements RP den 46 Overview methodology SOBEK summerdikes eese ene 47 example lakes ER DU FPE OS VUE NO TEE NEU dE 48 overview methodology lake file i ARAS CUu c cM Location detailed figures of the southern tenen ACIE 64 Elevation floodplain nva wore teens wav 22 00 Example profile description SOBEK compartment compartment da ceo Re eS GUN 69 Example Neckar V SEEN EVER A 75 Page 4 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 1 Introduction 1 1 General The use of GIS in designing model schematisations has been widely extended the last few years In this way GIS has been succesfully applied to the modelling of the main Dutch rivers using the 1 D model SOBEK Geodan Geodesie 1996 a and b RIZA 1996 a A GIS application has also been used in modelling a part of the German river Rh
3. 1 Determination of flow conveying areas using the flow velocity criterium 2 Flooding free areas are interpreted as flow storing 3 Visual interpretation and conversion of the grid file to a polygon It should be kept in mind that the main channel and bank section are always flow conveying 4 Determination of flow conveyance per compartment and conversion to BASELINE figure 19 Creating the boundary flow conveyance flow storage Page 40 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam If there are no WAQUA or other 2 D results available the boundary flow conveyance flow storage has to be defined on the basis of expert judgement The different points of attention as defined in paragraph 3 6 1 have to be kept in mind As guideline should be taken that about 90 95 of the discharge is transported by the flow conveying part of the floodplain Streamline maps discharge lines and slope maps can be used for this purpose In figure 18 the above described proces is illustrated Page 41 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam verview creation SOBEK flow conveying flow storage file WORK AROUND With WAQUA results Without WAQUA results Calculate the average of the square flow velocties per SOBEK compartment floodplain only and determination of the fiowconveyance criterium for each compartment Excecute the query
4. 5400 L L 1 ol Y qd Ww Actual data Schematised data aan a os x 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 Distance figure 5 Example of actual and schematised profile 2 2 Concepts GIS application SOBEK profiles in BASELINE BASELINE has built in functionality to calculate representative SOBEK profiles from real geographic information A SOBEK profile is generated from a number of grids and an ASCII text file with additional information The method for creating these files will be explained in later chapters The application to generate SOBEK profiles is based on the following principles A distiction is being made between main bank and floodplain section Every section is limited by a highest and a lowest level and a number of intermediate levels By executing logic queries on the input grids the number of grid cells under a certain level can be counted and mulitplied by the area of one grid cell In that way for each level flow conveying and flow storage areas are calculated which can converted to widths by dividing them by the compartment length These widths can be found in the resulting SOBEK profiles For a detailed description of the application and its algo
5. Boundary flow conveyance flow storage Location and elevation of summerdikes Topographic background of the digital river map Soil roughness types These figures have been created on a scale of 1 25000 In these figures a for SOBEK relevant interpretation of spatial data is displayed It may be that the data slightly differ from the information in the SOBEK profile In the figure the location of lakes the SOBEK compartment boundaries and compartment numbering are displayed An example of a figure with the elevation of the floodplain is displayed in figure 25 Page 65 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Hi Hoogteligging winterbed Maas Kaartblad 3 ED UA A Legenda 34 8 m NAP 48 m NAP Schaal 1 25 000 30 Sep 98 SE qe 2 Rijkswaterstaat RIZA figure 25 Elevation floodplain Page 66 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 7 5 Description SOBEK profiles 7 5 1 Design of the figure The presentation of SOBEK profiles actualy consists of three steps which are also taken in the schematisation The header of the figure which SOBEK compartment and which schematisation version is concerned In the top sub figure a top map view of the SOBEK compartment is displayed The middle sub figure is actually translating the top figure into a 1 D river schematisation The distinction i
6. Square flow velocty criterium interpretation and conversion to BASELINE format Deternine the boundary flow conveying flow storage using expert knowledge Generating SOBEK input using the function Model Conversion SOBEK in BASELINE E figure 20 Overview methodology flow conveyance flow storage Page 42 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 7 Summerdikes 3 7 1 Definition The floodplain is subdivided in areas which can freely be flooded and areas which are protected by summerdikes This does not only include actual summerdikes which frequently occur in many river systems but all elements which result in a declining terrain situation with respect to the main channel This could be for example bank dikes roads or any other high elements in the floodplain Besides a threshold elevation a dike type has to be specified for each dike element e Adike element is called primary if the dike element is the only dike element in a SOBEK compartment or if there are multiple dike elements in the compartment but the dike element has the greatest influence on the water movement The threshold elevation of the primary summerdike can be found as Hop in the resulting SOBEK profile e Adike segment is called secundary if there are more dike segments in a SOBEK compartment but the dike segment does not have the greatest influence on water movement The GIS app
7. e The 9996 exceedance level is determined for all elevations in the bank section s For relevant river stretches from measuring to measuring point these 99 exceedance levels are plotted against the length of the river axis e Through these points a regression line is fitted e Atthose places where groynes are abundant h8 is derived from the regression line The elevations have to be specified in centimeters Important conditions for Hsub1 are Hsub1 HsubO Hsub1 Hkrib 5 10 Groyne elevations 5 10 1 Definition The groyne elevations Hkrib are defined as the average elevations of all groynes in a compartment If multiple elevations are available for one groyne a weighted average is calculated 5 10 2 Function In the elevation model there is no information about groynes For this reason the groyne elevations are defined in the ASCII text file The read groyne elevation corresponds to level h7 in the SOBEK profile Page 55 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 5 10 3 Creation The following methodology can be used The groyne elevations are digitised from a digital river map or topographic map If a weighted average is calculated multiple elevation points per groyne the groynes also need to be digitised as lines e combining the elevation points with the compartment file the average values compartment can be calculated The elevations hav
8. No groynes summerdikes Both the determination of the elevation levels as the labels behind the levels are dependent of the situation For each situation described above a theoretic profile layout is displayed in figure 7 Page 16 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Default layout SOBEK profiles Profile layout with groynes without summerdikes H1 Minimum level main section H2 H1 025 H5 H1 H3 H1 050 H5 H1 H4 H1 075 H5 H1 H5 Maximum level main section f SUBO Groynes not flooded H7 0 10 H7 Bevation of groynes KRIB H8 Groynes just flooded H7 0 10 5081 H9 HS 1 7 15 HB H10 H8 2 7 H15 H8 H11 H8 37 H15 H8 LEVI H12 H 4 7 15 8 H13 H8 5 7 H15 H8 H14 HB 6 7 H15 H8 HIS Maximum elevation floodplain M SUB2 royne Floodplain Profile layout without groynes without summerdikes H1 Minimum level main section MAIN H2 H1 025 H5 H1 H3 H1 050 H5 H1 H4 H1 075 H5 H1 HS Maximum level main section SUB0 HG H5 033 HB H5 H7 H5 066 Ha H5 H8 Maximum elevation groyne section S SUB1 HS HB8 1 7 H15 H8 H10 HB 2 7 H15 HB H11 HB 37 H15 HB LEV 1 H12 4 7 H15 H8 H13 HS 5 7 H15 H8 H14 HS 5 7 H15 H8 H15 Maximum elevation floodpiam SUB2 Main royne Floodpiain Section Section Profile layout with groynes and summerdikes H1 Mi
9. applicatie Software developed with an existing GIS surrounding aimed at a specific user group GIS application Grid Raster Grid A data storage structure storing a continuous phenomenon by means of a regular grid Rooster schematisatie Raster Diskretiserung Designing a model by super imposing a grid on different input themes Grid schematisation Groyne elevation Buhnenh he Krib hoogte The average elevation of a groyne Buhnenbereich Krib sectie See bank section Groyne section Htop minus the average difference in terrain elevation from Htop of all dike elements in a SOBEK compartment hase Npase The threshold elevation of the primary summerdike SOBEK compartment hiop hiop Isolated lake Nichtangeschlosse Geisoleerde plas ner See Open water in the floodplain which is isolated from the main channel Lakes Seeen Plassen All open waters in the floodplain of the riversystem Lateraler Zuflu amp Addition or extraction of water from the river system Lateral flow Laterale instroming Main channel Mittelwasserbet Zomerbed Main channel and bank section together Main section Hauptstrombereich Geul sectie That part of the river which is between the normal lines Location on the river where water levels and or discharges are
10. by winterdikes the model boundary can be determined by generating water level contours at a very high discharge e g design water levels E Another options to digitise landscape elements which have a flood defensive function Page 24 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 4 The three files have to be converted to BASELINE formats and have to be placed in the appropriate directories in the BASELINE data structure This is elaborated in the BASELINE data conventions CSO ESRI 1998 The model boundary file should also be converted from a line file to a polygon file The file should contain an united polygon describing the model boundary The upper and lower boundary should intersect with the normal lines and the bank lines 5 With function Tools Generate Sections the section file can be generated This file is a basic SOBEK file Since it is also used for WAQUA the file is stored in a general data directory which is used for both models 6 Eventually the input grid file for the SOBEK application can be generated using the function Models Conversion SOBEK 3 3 4 Work around With this work around a basic SOBEK file is generated which is already in BASELINE format and can be directly used by the function Models Conversion SOBEK In that case step 5 as described above has to be conducted manually It is up to the user to decide whether the input grid should be generated either in A
11. compartment boundary file With the function Models Conversion SOBEK the file can be converted to SOBEK input grids This method is illustrated in figure 14 Page 34 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam No Data Model boundary Como floodplain iso ines Comp main channel figure 16 Creation compartment boundaries floodplain Page 35 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 5 4 Work around Compartment boundaries main channel The compartment boundaries of the floodplain have to be created outside BASELINE in Arc Info In paragraph 3 5 1 the conditions to which these boundaries have to pertain are formulated The creation of the compartment boundary file in the main channel consists of the following steps 1 Determine the length of a branch using the river axis and calculate the length of the compartment for the branch of interest by dividing by an integer This should be done for all model branches 2 first compartment boundary is located at half a compartment length after the node and the last compartment boundary is located hal a compartment length before the second node The compartment boundaries ca be defined by digitising nodes on the river axis 3 compartment boundary should be placed on the upper and lower model boundary by digitising nodes on the river axis 4 Ifthe compa
12. e BASELINE manages both data for 1 D models 2 D models In most cases the same data are used but sometimes the data are used differently for SOBEK and WAQUA schematisation respectively Another problem is that both models require the same type of data but in a different format and not all data in BASELINE are used for both models This may cause uncertainties about the data to be used e Especially data applied for SOBEK require preparations of the basic data to be able to implement 3 D river characteristics in a 1 D model For the main Dutch rivers these procedures have been standardised For other rivers however these methods have to be applicable using the same model philosophy This manual illustrates the methods of using spatial data and BASELINE and how they can be applied to SOBEK modelling The ins and outs of the Dutch situation will be extensively described and methods on how to prepare other datasets for use in BASELINE will be presented Knowledge of GIS hydrology and BASELINE manuals is however inevitable Collecting the required spatial data to build a model will remain a labour intensive task involving many different sources This manual aims at the application of GIS to SOBEK modelling Step by step the proces from raw data to data which can be read by the SOBEK model will be described The use of the GIS appplication BASELINE will have an important role in this manual Workarounds which illustrate Page 5 Report GIS a
13. geometry contants and several start and boundary conditions have to be specified depending on the objective of the model Transitions to areas outside the model boundary conditions and the starting point of the calculation start condition are hereby defined Using this input together with Page 9 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam constants unkown values like waterlevels and flow velocities can be calculated on the grid points in an iterative way figure 3 Example grid schematisation WAQUA The same constraints to the stability and accuracy as for SOBEK calculations basically pertain of the WAQUA calculations In practice however the stability of the calculations can only be granted by using sufficiently small time steps For 2 D and 3 D models an accurate schematisation of the geometry is also essential To obtain reliable model results it is necessary to convert the 3 D geometry in a responsible and reproducable way to a model schematisation Using spatial data stored in a GIS database 2 D model schematisations of the large Dutch rivers are currently developed Page 10 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 1 4 Data collection The information in this report specifically has a spatial character It should be kept in mind however that not all the information is digitally available when setting up a sche
14. is based on the physical characteristics of the river system The use of GIS can be of great value in determing this In the main channel tables specifying the relation between Ch zy values and local discharge for river stretches can be used In addition seperate stretches can be defined if necessary for those locations in the river where solid layers or other forms of bottom protection occur For the bank section a fixed K Nikuradse value is used which is applied seperately for each branch On the basis of experiences with the SOBEK model for the river Meuse a K Nikuradse value of 0 50 can be used initially For the floodplain a method is developed for the Dutch rivers which calculates the roughness as K Nikuradse on the basis of ocurring ecotypes in the floodplain This method is succesfully applied for the SOBEK models of the river Rhine and the SOBEK model of the the river Meuse RIZA 1996a en RIZA 1998a An important advantage of this method is that the roughness of the floodplain is reproducable and well argumented At the same time it is possible to simulate the effect of modifications in ecotypes in the floodplain due to adaptations For determing the roughness of the floodplain the river can be subdivided into stretches taking into account the following points of attention e length of the stretches is equal to ten times the compartment length This is determined by the demand of enough detail without compromising the 1 D c
15. maximum K Nikuradse will be calculated In the calibration the maximum K Nikuradse value can be used as initial roughness for the floodplain It is assumed that local disturbances such as tree rows small roads etc are averaged out By using a maximum calculated K Nikuradse value these additional roughness is automatically taken into acount Page 60 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam For more infomation about the use of ecotope maps for the determination of roughnesses in the floodplain reference is made to RIZA 1996a RIZA 1996b RIZA 1998a RIZA 1998b and HKV 1996 6 6 Structures In SOBEK structures are weirs locks bridges etc They have a special position For schematising weirs in a river there are two options The weirs can be schematised in a way which resembles the actual geometry as closely as possible An advantage of this method is that the fysical layout of the weir is still recognizable A disavantage is that it is more difficult to control the weir Due to valve flowing at low discharges a second controlable stucture with a small threshold has to be schematised in order to simulate weir management properly e The weirs can also be schematised as plain pour over thresholds An advantage is that the upper water level is not influenced by the lower water level at small discharges In that case only one controlable structure is enough A disadvantage is t
16. one for the main channel and bank and one for the floodplain section This seperation is made because elevation data for the main channel are often available in greater detail compared to the floodplain In figure 13 an example is given of an elevation model Elevation in cm figure 13 Example digital elevation model 3 4 2 Function Elevation data are the basis for the calculation of the SOBEK profiles The elevation levels and widths in the profiles calculated by the GIS application are based on elevation data of the digital terrain model The elevation model is also very important in assigning threshold elevations for dike segments see paragraph 3 7 and lake elevations see paragraph 3 8 The elevation model is also used as a tool in generating other relevant SOBEK data Page 27 Report GIS and SOBEK modelling Date 03 06 99 For RIZA Geodan Geodesie B V Amsterdam 3 4 3 Creation in BASELINE BASELINE has extensive functionality Tools Generate elevation model to create an elevation model with a triangular irregular network TIN using a number of different input files Elevation data main channel Elevation data floodplain Elevation data banks Elevation data lakes Model boundary Boundary of an area of interest optional For a description of this BASELINE function and the file formats of the input files reference is made to the BASELINE user manual CSO ESRI 1999 and the BASELINE data conventions
17. should be possible to present additional information for each profile The data should be accessible on a PC with Windows 95 The documentation has to be specifically for SOBEK for individual rivers With this application it is possible to deliver the documentation with each schematisation on CD In this chapter the design of the documentation application is presented together with the data which can be presented is discussed An user manual for the software necessary to use the CD is delivered with each first CD of each schematisation 7 2 Design of the presentation The presentation application is designed in three levels Firstly a number of figures is presented which give a general overview of the river and the locations of the extends for which overview figures have been created With more detailed figures information about a river stretch of approximately 5 kilometers can be displayed It does not only concern information which is important for each SOBEK compartment but the elapse over the river stretch can give insight of how it was modelled One could think of elevation data flow conveyance etc Within a detailed figure it is possible to zoom in on specific characteristics of SOBEK profiles For these figues additional information is available about lateral inflow Q h curves structures etc Besides these spatial figures there is also schematisation specific data available This mainly concerns the branch division the exact locatio
18. slo EET 12 2 2 Concepts GIS application SOBEK profiles in BASELINE 14 Cuin gross M oo 15 ol i510 ijjj Matta SS O 18 S OD BUE ouai RIEF I o ERA GERD Ea QVENM DE EYES EEN UTERUS NUN SER ASR VGICY E RE 20 2 1 IOI DEC FE ASI RO 20 TARNO eo de cans FE NL SUV 21 32 4 BOMMEN 21 322 CARON IN BASELINE sesinin a N 21 323 WOIK GEOUEM au ia senva serene deerne 21 7 seen 23 a3 T RERUM RS RM 23 3 92 FUCO EPA 24 3 3 2 Creaton In BASELINE orasaun es AN AANSEN 24 3 9 8 e T e A 25 E 27 3 4 1 BORON 27 Sid FUNCION uu ismscec ene ux SEN xe CU RE DNA x AES URSREEFEAEA NUEVA T 27 3443 CARTON in BAGELINIS eei sasszeazQEvEke nux VE Ea E xx Ud GR NOR EX Fa S OR Chao Aq ran docu 2
19. 5 10 1 Definition ater vannesa lenie 55 FUOD aenema 55 5 10 3 Ga nasaan deventer 56 5 11 Threshold elevations of lakes E PE A E E AA A ETE 56 6 GIS independent SOBEK data nnee 57 BT IUBE N ECE SIMI MR er uu b bu EE A 57 PE Mo BIL Deeds Ue ID BL iere IR EUER emer T D PR enn 57 BL SEL AN een nente RM OR Doer Me 58 6 4 Boundary conditions model boundaries O ERES gt 6 5 Soil roughnesses n 60 gd en 61 7 Presentation SOBEK input Gale onciau 62 E tss rio HERE ETT meenen B Y a Design ofthe presentatoren de 62 OVerview TIOHI eB co cii I SEE tenet ns arne gg 7 4 Detailed figures Moi es RN INNEREN IMMO MEI D DM DE 65 7 5 Description SOBEK wen RR 67 7 5 1 Design of the figure BORSA RN A NEQU UM RA 67 7 5 2 Top sub figure SUM ASE ORE E Me c EI D 0 67 7 5 3 Middle sub figure dara wonnen 67 1 5 4 Lowest Sub HULS nissen 68 8 Glossary SOBEK GIS terminology vases es ao LO ADS senteren te en ta ne sE Page 3 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Figures hours 1 Example queryind an
20. 8 34 4 WOERDEN Liu varen aszavevexcsu uz PE a CEN S ua ers hide 30 3 5 SOBEK Co pare fDuu i oseenoseesesa osean dann 32 S B T VENE Wa NIT 32 ee 33 25 9 Groatot BASELINE a asceciszeacseusazcazsuzasvbsaauutus uud aera vod on a o eV S OR MEN Re ineens 34 3 54 10 ok pF DEAF ES FE eu ERROR Ca S KG VaE Ck Cue S QS KR TE A EDGE E 36 3 8 Flow CONVEYING TOW SIOrBg BI BB iiid eise ciss snae to v eren ra o apii va erae PER CUR M Ven 38 25 1 ENOR eos aa E VERE GEQ CEA uA MUS RE OE GV ADAM ES neske 38 AGE FUflCBON uisi scu narra e Ue D uS RER a da CUvaRrR REV C c QU R CE LV ER OD MEL 39 3 5 3 Gato In BASELIWI 7 cii ia iT 39 2 8 4 VORKEN iie opcris GER OCEAN 39 ST Summe 2a ecsoiscex sace ra vna CuscP cu a E a NR Veg gura U CUR sen 43 STA DOO uasa insti MAN UVEEU SENS EXER S ERE EQYQUVAS VU BUE Ree oda Uy cu qu caa vac 43 d a FUNGO uiae vera kd overeenstem wiers CX Maz QR EEUU VUE 44 S 7 9 Qrealon in BASELINE ernorm sees VERE SEEN UU du VUES OE 45 3 744 WON TORING onverveerd NEU ERREUR N 45 SJ LS ucro FIR A OS ASN ISEE NER VERIS EARS ERE RA dA TE 48 DOUG us tena EE venne SENATE NER GEO 48 39 8 2 FUBGI
21. CSO ESRI 1998 The created TIN can be converted to SOBEK input grids one for the main channel and banks and one for the floodplain using the function Models Conversion SOBEK The most important task is to obtain reliable elevation data for the main channel the banks the floodplan and lakes in the floodplain They will be briefly discussed Main channel in the Netherlands depth sounding data collected by the survey department of the directorate general of public works and water management RWS is usually used These data are often in a cross section format with a fixed interval e g 100 meters After conversion of these data to BASELINE point coverages they can be directly used in building the digital terrain model Potential problems may occur in the neighbourhod of weirs and bridges where no accurate elevation data are available Experience has proven that SOBEK is very sensitive to lack of data The only solution to fill the gaps is to add additional data or to interpolate Bank section The elevation of the bank section forms the transition zone between the main channel and the floodplain In the Netherlands water level fixations are available with a fixed interval of 75 meters These can also be directly used in generating the TIN after conversion to BASELINE format Quit often elevation data in the bank section is unreliable or lacking Page 28 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V A
22. DT 364320 GIS AND SOBEK MODELLING A manual for constructing schematizations RIZA Working document 99 121X Authors F Hoefsloot W W Immerzeel Geodan Geodesie U Pakes R van der Veen RIZA Arnhem Amsterdam june 1999 C 26969 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Version management Author s F Hoefsloot W W Immerzeel U Pakes van der Veen Documentnumber wi G9019 Projectnumber G9019 Status Final version Document date Number of pages 76 Released Signature Datum Omschrijving 31 05 99 First draft english 03 06 99 Final version English Versie den cod Mimi Page 1 j 51 4 Dn m PT m i m es ee t DU eU fa TE VATE I P ul pe Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Table of contents QW 0 9 P 4 Ee O 5 fs 2000 P mamatt 6 DEDI AEON M P 9 1251 OOo RES RGC VARGAS AN GM GDDHE ROAD E CO 9 TA EBD Facius GO EREN DAN FCACHLUHOAICE AERE GR Rc CR oc 9 TA DR ec rei 11 2 Application of GIS concepts in SOBEK modelling eorr erret tror norton nnne n nous 12 Ser o s oo
23. K Maas Versie 1998 1 Veen van der R Pakes U Essen van J en Schutte L rapport nr 98 038 ISBN 9036951895 13 RIZA 199628 Calibratie SOBEK Rijntakken versie 1996 0 Veen van der R Pakes U Essen van J en Schutte L rapport nr 97 034 ISBN 9036950805 14 RIZA 1996b SOBEK Maas 1998 1 Beschrijving Geografische gegevens en GIS applicatie Veen van der R Pakes U Essen van J en Schutte L rapport nr 98 053 ISBN 9036950805 Page 74 Se Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam B1 Neckar case Deutsche Grundkarte 1 5000 84 Rechts 82 Hoch Neuostheim Bia sot 7 7 eru T E 4 NEE a gt e wenden MM PARI 1 A joi te ae A Vera dee ahem Naueirheur node 4 7 EIT 5 Rig Q brhellungl EE j el figure 27 Example Neckar Page 75
24. OBEK modelling This chapter will deal with the underlying principles of the SOBEK profiles calculated with GIS Besides these principles a number of quidelines for generating representative profiles pertaining to the GIS files will be presented In defining those guidelines the different user potentials for the SOBEK model were kept in mind Understanding of the above described matters is essential for a correct construction of a SOBEK schematisation 2 1 Representative profiles A SOBEK profile is an as accurate as possible schematic display of the river on a certain location Instead of positioning a real geometic profile on a certain location on the river compartments with a variable length along the river axis which contain both the main channel and the floodplain are used For each compartment an average profile is calculated taking into account all relevant information within the compartment A profile contains information about storing and flow conveying widths from the lowest point in the main channel to the highest point in the floodplain These flow storing and flow conveying widths are calculated using information about summerdikes lakes terrain elevation geometry and information about the location of flow coveying and flow storage areas This method has several advantages compared to locating an actual geometric profile on the river E All the available information in a compartment is averaged to a profile and there for is a more
25. OD uoo HW OE AREE newsservers nen a sessies 48 3 8 3 Creo n BASELINE ornamentele nes 49 VOrkEROUNG icu vec aA Vena o RR REA NOVA ARR ennen 49 Report GIS and SOBEK modelling _ Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam AAE SR eeen eere ee 51 4 1 Soil rougnesses floodplain based on ecotopes 51 dn 51 ENA EEN eren beende oen berend se 51 eA Ea pi alaani e Dl p 51 4 5 Upper and lower model DOUNCQFIBS eee erret ert tita eie nr denn 51 SASL uu uc ica tnr axi eee ener AN RN DEA eee ER MSS EDEN 52 BET UFICIOPE missers dave UPC CUP APR Rd CU QE S DU ASRS 52 Do unice opa er tas vene 52 5 3 River name siti FEVER e SEV VR Qe HE voL oc Fe EO 5 4 Location compartments sinatra ac EA 53 5 5 Nearest settlement LRE 53 5 6 Compartiment lenglh v VE EC RE ener nere tens dra 5 7 Version NAMEN aco serere 5 8 Maximum elevation main channel OSEE ERO DUI das aD RUE 54 5 5 t BERNO serre nnee 54 5 8 2 Fonol wrevel 54 SES raven EN weten 54 5 9 Maximum elevation bank section nende enen te 55 5 8 BENE ennen reen 00 5 9 2 Function vennen eenn SER TET EET UT SSS Creation EL rv e dansten www 5 10 Groyne GlEVaON S aisinn mms 55
26. SELINE figure 14 Overview methodology elevation model ee ee in Page 31 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 5 SOBEK compartments 1 3 5 1 Definition For the schematisation and calculation of SOBEK profiles the river system both the main channel bank and floodplain is subdivided into compartments A SOBEK compartment is a river stretch for which one representative cross profile is calculated The SOBEK profile calculation point is located in the centre of the compartment When defining the SOBEK compartments a distinction should be made between compartments in the main channel and compartments in the floodplain In figure 15 an example is given of the SOBEK compartment coverage SOBEK compartments Legend gt SOBEK compartments main channel EN SOBEK compartments floodplain 0 1000 2000 Meters figure 15 Example SOBEK compartments Page 32 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Compartment boundaries main channel The compartment boundaries in the main channel have to pertain to the following demands e compartment boundaries are always perpendicular to the river axis e A weir is always a compartment boundary e The compartment length of consecutive compartments is approximately equal If the model is also required to make morphologi
27. SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam If there are WAQUA results available the following method can be used E Inundation maps can be generated using the water level fields and the digital elevation model e With the different inundation maps it can be determined whether an area is protected by a summer dike E These areas have to be digitised and converted to BASELINE format CSO ESR 1998 e The ASCII text table and the eventual dike element file can be generated using the water level fields the elevation model and the compartment boundaries figure 20 Overview proces creating dike elements In figure 21 the above described proces is illustrated Page 46 Report For By fields GIS and SOBEK modelling RIZA Geodan Geodesie B V Amsterdam Overview creation SOBEK summerdikes file WORK AROUND EE VIES ESMEE iT j 4 m M es T tal elevation model digital iver map 1 t BONUM P N ee HER LT Dad 5 d Je inundaron mi h scharges i rc us soma Lat Waterleval fields Ss a eee figure 21 Overview methodology SOBEK summerdikes Date 03 06 99 Topographic mans and Page 4 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 8 Lakes 3 8 1 Definition All waters in the floodp
28. The bank or groyne section is defined as the area between the bank and normal lines The bank line is the line which seperates the floodplain from the bank If there are groynes it is the line connecting the groyne toes An example of the section file is displayed in figure 10 The section division of a part of the Rhine between Andernach and Lobith is displayed SOBEK sections figure 10 Example SOBEK sections Page 23 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 3 2 Function The SOBEK section file has multiple functions In the GIS application different calculation algorithmes are used for each section In the main channel section a maximum and minimum elevation is determined using the digital elevation model and the section file Between the maximum and minimum level a number of intermediate levels are defined based on linear interpolation In the bank section the choice of elevation levels is depending on the presence of groynes and in the floodplain section the presence of lakes and dike segments play an important role E It regularly occurs that different data densities are used in the main channel and floodplain Oftenly elevation data are available in a higher density in the main channel than in the floodplain By using a subdivision between main channel bank and floodplain it is possible to specify different grid cellsizes when generating SOBEK input grids E A value
29. about 8096 The determination of compartment boundaries in the main channel has to be done manually for the time being but will be automised in the near future This is further elaborated in paragraph 3 5 4 Compartment boundaries floodplain Using the function Tools Files SOBEK Compartment Boundaries the compartment boundaries in the floodplain can be created This function requires the following input files Compartment boundaries main channel Water level field at a high discharge calculated with WAQUA Model boundary File with the boundary left bank right bank For a detailed description of the input file formats functionality and principles reference is made to the user manual and the technical documentation Geodan Geodesie en HKV 1998 b en c The left bank right bank input file can be easily created in Arc Info by combining the river axis and the model boundary The function generates a preliminary compartment boundary file by generating iso water level lines The function results in four output files Preliminary compartment boundaries Water level grid iso water level lines Grid with water level leaps in the floodplain The preliminary compartment file has to be adapted manually in Arc Info resulting in a closed compartment boundary file which pertain to the file format as specified in the BASELINE data conventions The water level grid the water level lines and the file with water level leaps can be used to edit the preliminary
30. accurate display of reality e SOBEK profile is relatively insensitive for the local situation of the place where the profile is positioned e All available information in a SOBEK compartment is actually used e The length of a SOBEK compartment is arbitrary The location of the profiles can however be specified by the user for example one profile each river kilometer s The sensitivity to errors in measurements in a SOBEK compartment is considerably reduced because an average value is calculated making the profile less suspectible to errors in individual measurements Page 12 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam An example of the conversion of real information to profile information is displayed in figure 4 It should be kept in mind that in a 1 D model it is not possible to distinguish between the different banks In figure 4 however this is done for illustrative purposes as opposed to the use in SOBEK figure 4 Conversion of real terrain information to a representative profile The fact that all available data within a SOBEK compartment are averaged to one profile also has a number of disadvantages X All data of two different banks are averaged to one floodplain section which results in unrecognizable terrain features By averaging data in SOBEK compartment field measurements be hard to recognize In figure 5 an example is given of differences which ma
31. an Geodesie B V Amsterdam 3 4 4 Work around It is not necessary to generate the elevation models for the main channel and floodplain by using a TIN in BASELINE There is a variety of interpolation techniques which can be applied in a general GIS environment for example Inverse distance interpolation e When creating the elevation models outside BASELINE it is important that e appropriate grid cellsizes are applied for the main channel and floodplain respectively e There are no No Data values in the elevation models e outer extend of the elevation model of the main channel is in conformity with the boundary of the bank section e outer extend of the elevation model of the floodplain is in conformity with the model boundary e Arc Info grids are conform the BASELINE format ie integer grids with elevations in centimeters CSO ESRI 1998 In figure 12 the above described methodology is illustrated Page 30 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Overview creation elevation model Dutch sduation Conversion to BASELINE format WORK AROUND Creation of elevation model in GIS using a different interpolation technique and conversion to BASELINE format Creation ofthe TIN using Tools Creation elevation model Generating SOBEK input using the function Mode s Conversion SOBEK in BA
32. anch positive x direction is from start node to end node If parallel stream channels occur and are relevant to the objective and scale of the model these have to be schematised as seperate branches A node is defined as a location where two or more branches coincide Special nodes are nodes which are only connected to one branch These are located at the model boundaries At those nodes the model boundary conditions have to be specified In order to obtain a good SOBEK model it is important to choose the model boundaries appropriately On the nodes which are located on the model boundaries the boundary conditions for the model are specified therefore it is of great importance that they coincide with location in the system where measuring data are available Q h relations and or water levels Within the system to be modelled nodes have to be defined at least at relevant seperation points or confluences Finally nodes can be placed at those locations where in time will be a connection with other models 6 2 SOBEK calculation grid The SOBEK calculation grid is a network of points on a branch for which calculations are executed The calculation point is the heart of a SOBEK compartment and the point where the SOBEK profile is located which is calculated with the GIS application On the calculation points simulations with SOBEK are executed By situating the SOBEK calculation grid on the banches a numer of things has to be taken into account Calcul
33. as value equal to one when the lake is connected and a value of two when the lake is isolated The lake elevation which is usually assigned to the lake corresponds to the surrounding terrain elevation The elevation of elements in the neighbourhood of lakes which are influencing flow conditions have to be taken into account though The elevations of the lakes can be assigned to the lakes using the digital elevation model and a buffer function It is important to verify if the specified lake elevations are not lower than the maximum elevation of the bank section because his is not allowed The maximum lake elevation should at least be 10 centimeters higher than the maximum bank elevation The file format of the lake file is described in the BASELINE data conventions CSO ESRI 1998 In figure 23 the above described method is illustrated Page 49 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Overview creation SOBEK lakes file WORK AROUND Generating of polygon file with the outer boundaries of the lakes Determine whether a lake is connected or isolated and assigning of codes Conversion to BASELINE fomat Assign the average elevation of the field around lakes to the individual lakas Generating SOBEK input using the function Modeis Conversion SOBEK in BASELINE figure 25 overview methodology lake file Page 50 Report GIS and SOBEK modelling Da
34. ata are als lacking in these cross profiles This can be solved Wi s described ab above Another problem when using cross profiles may t be that the available dat tireh cove ver the model area This can be solved by digitising additional elevation Benten maps A common problem in using elevation data from cross section is that the density of measuring points on the cross sections is often much higher than the point density between the cross sections This may cause problems in the interpolation E The errors between the cross sections are much higher than on the cross sections E Because of the large differences in point densities it is difficult to interpret which points are actually used in the interpolation method E When interpreting gully structures it may occur that points from the bank of the gully are taken into account when interpolating the centre of the gully These factors may cause major anomalies in interpolating curved and gully river stretches It is therefore recommendable to interpolate these data to a regular grid of points outside BASELINE using different software which takes the direction of the channel into account Interpolation can be executed using SURFIS Fioole 1998 or AMOR RWS It is always recommendable to check the digital terrain model on discontinuities in terrain elevation Page 29 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geod
35. ation points are always located at the up and downstream sides of a structure The distance between one and another is approximately 1 meter At the beginning and at the end of a branch there is always a calculation point For the stability of morphological calculations it is very important that there is a SOBEK profile on each calculation point Besides that it is also very important that the variation in length measured along the river axis is not too large It is estimated that for morphological calculations the maximum variation between consecutive compartments may not exceed 30 This also implicitly defines the SOBEK compartment length The number of calculation points on a branch is depending on the objectives of the model Flooding prediction short calculation times accurate calculated water levels at MSW measuring points and river kilometers Page 57 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam E Calculation of design water levels short calculation times many different calculations e Policy analytical studies Short calculation times calculation of differences between reference and different cases of major river adaptations e Morphological studies stability of calculations equal length interval detailed enough to display morphological changes e Water quality studies short calculation times less accurate calculation of water levels These demands can be partial
36. cal calculations consecutive compartment lengths should not vary more than 30 The compartment boundaries at the upper and lower river boundaries are determined by the model boundary e Atan intermediate node half a compartment length is defined both upstream and downstream which do not have to be equal At branches which connect to a seperation point the calculation point is located at length interval from the node These length intervals do not have to be equal for consecutive branches In this way the location of the profiles is approximately equal to the beginning cq end of the branch e measuring point is located the middle of a compartment on a SOBEK calculation point e The compartments are logically and subsequently numbered Compartment boundaries floodplain The compartment boundaries in the floodplain connect to the compartment boundaries of the main channel on the one hand and on the model bounday on the other An important principle of 1 D hydraulic modelling is that the water level in the floodplain is equal to the water level in the main channel Leaps in waterlevels in the floodpiain principly are therefore compartment boundaries Compartment boundaries in the fioodplain be defined as water level iso lines following the water level at the intersection of the main channel and the compartment boundary in the main channel for the left and right bank respectively The water level field to be used can be obtain
37. d seleclirig ooo tee hl ER IRE F X ERR EN NR AE SR XR tasten sans 7 figure 2 Example creating elevation model in T2500 Tedere en aus 8 figure 3 Example grid schematisation WAQUA eee voren 10 figure 4 Conversion of real terrain information to a representative POMC sis oor res oves 13 figure 5 Example of actual and schematised profile eerte erano eon tu renun rne nue 14 figure 6 Example profile SERRA DR E SECONDI EQ QM Nc figure 7 Example situations TN ee sian med 17 figure 8 example river axis and kilometers en C M S RENS XN E EHE stem NE figure 9 Example SOBEK SI TIEN IN RES eni seen 23 figure 10 Overview methodology sections REIR etende Serene mantel 26 figure 11 figure 12 figure 13 figure 14 figure 15 figure 16 figure 17 figure 18 figure 19 figure 20 figure 21 figure 22 figure 23 figure 24 figure 25 figure 26 figure 27 Example digital elevation model eneen pepers 27 Overview methodology elevation R P E 31 Example SOBEK Compal TENS mieren ter ttiv nba anna Ens a 32 Creation compartment boundaries floodplain 35 Overview methodology SOBEK
38. d the creation in BASELINE and a work around outside BASELINE will be discussed The following GIS files will be consecutively discussed river axis sections SOBEK compartments boundary flow conveyance flow storage summer dikes and lakes The terminology used in this report and relevant to hydraulic modelling and GIS is summarized in the glossary at the end In annex 1 an example is given of how a topographic map can be used for the construction of the model The different themes are drawn in different colors for a map of the Neckar a Page 2 Report GIS and SOBEK modelling ate 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 2 River axis 3 2 1 Definition The river axis is a virtual line through the heart of the river An example of the river axis is displayed in figure 8 figure 8 example river axis and kilometers 3 2 2 Creation in BASELINE In the current BASELINE version there is no functionality to generate the river axis file 3 2 3 Work around In the Netherlands the river axis is defined by the survey departent of the directorate general of public works and water management RWS as a series of straight and curved line parts If there is no river axis available it can be digitized using topograhic or digital river maps It is important that the line through the heart of the river is used and not for example the shipping lane The river axis plays an important role in defining SOBEK compartment boun
39. daries in the main channel and in calculating exact lengths of SOBEK compartments This length is read from an ASCII file and used in the BASELINE application SOBEK profiles which generates the SOBEK cross profiles Therefore it is of utmost importance that the river axis accurately describes the length of a river stretch bottleneck in the SOBEK modelling of the main channel can be that the seperation point of river branches does not necessarily confluence with the hydraulic seperation point of the river branches For the determination of the SOBEK compartments this is however very important and should be taken into account Page 21 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By _ Geodan Geodesie B V Amsterdam Ideally both seperation points should coincide For the file format of the river axis file reference is made to the BASELINE data CSO ESRI 1998 Page 22 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 3 River sections 3 3 1 Definitions The GIS application seperates between the following river sections E Main channel section gt Bank or groyne section E Floodplain section The main channel section is defined as the area between the normal lines The normal line is the line which defines the boundary between the water of the river and the land If a river has groynes the normal line is defined as the line which connects the heads of the groynes
40. e a weir or an intersection with tributaries A schematic display of the river at a certain location It is the input element for SOBEK describing the river geometry dimensions The description of a river system for the SOBEK model using averaged cross profiles of a certain length along the river axis Part of the floodplain of the river that only contributes to the storage of water in the SOBEK model The flow storing area is determined for each compartment and does not necessarily coincide with the legal boundary of flow storing areas Spatial element which up to a ceratin water level has a resisting influence on the flow of water into the floodplain In SOBEK these dikes are not always recognizable in the field The determing elevation of a summerdike from whereon it will start flooding Data storage structure which describes a continuous phenomenon by connecting measuring points by triangles resulting in a continuous surface Hydrodynamic simulation model for the calculation of water movement water quality salt movement temperature and sediment transport in two or three dimensions Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Page 73 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 9 Literature 1 CSO ESRI in opdracht van RIZA 1999 Gebruikershandleiding BASELINE Geldermans S en Meulen van der M S rapport n
41. e in calibrating the model These points usually can be derived from the digital river map if available For the file format reference is made to the BASELINE data conventions CSO ESRI 1998 4 4 Location of structures The location of structures bridges weirs and locks are very important because they have a great influence on the water movement The location of weirs is also important in determing the compartment boundaries in the main channel For the file format reference is made to BASELINE data conventions CSO ESRI 1998 4 5 Upper and lower model boundaries It is important to have the upper and lower model boundary digitally available as an aid in determing the compartment boundaries in the main channel Up to now the model boundaries are not yet available in BASELINE Page 51 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 5 ASCII data 5 1 Function Besides the GIS files described in chapter 3 the GIS application SOBEK profiles in BASELINE also requires an ASCII table as input from which the different fields are read by the application The first line for example contains information about the location of the profile and the nearest settlement A number of important elevations are also read from the ASCII file In the near future the ASCII file can be partly generated automatically 5 2 Fileformat The ASCII file is a comma delimited text file with the following fields R
42. e proces it is assumed that the extractions Page 58 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam are minimal at discharges higher than the perannual average discharge 3 Limitations drainage to the river Generally this pertains to sub watersheds which can freely drain water to the river but which can not drain anymore due to high water levels in the river In order to model the discharge proces it is assumed that the drainage capacity of sub watersheds starts to decrease from discharges higher than the level from where the floodplain will start to flood onwards 4 Maximum limitations drainage to the river Generally this also pertains to sub watersheds which can freely drain water to the river but which can not drain anymore due to high water levels in the river In order to describe the discharge proces it is assumed that the drainage capacity is minimal at discharges where the entire floodplain is flooded The boundaries between the situations are debatable Besides they will vary from sub watershed to sub watershed For water movement models there is a need of one unambiguous estimate of lateral flows in different hydraulic situations The following points of attention should be taken into account when making the estimate e Based on physical parameters as far as possible e Suitable for flood forecasting models limited on line data e Suitable for calibration and verification ca
43. e to be specified in centimeters If there are no groynes the No Data value 9999 has to be filled in Important conditions for the groyne elevations are Hkrib gt HsubO Hkrib Hsub1 For the format of the groyne file reference is made to the BASELINE data conventions CSO ESRI 1998 5 11 Threshold elevations of lakes The application adds the contribution to storing widths of connected lakes to the lowest level in the main channel by default It is however possible to set this level by specifying a threshold lake elevations in the ASCII text file In reality the lake will start storing when the elevation of the bottom of the lake is exceeded by the water level If the default level lowest point level in the main channel has to be used the No Data value of 9999 has to be filled in which also holds when there are no lakes in the compartment Important condition for the threshold elevation of lakes is Lowest level in the main channel x threshold elevation lakes x Hsub0 Page 56 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 6 GIS independent SOBEK data 6 1 SOBEK branches A SOBEK branch is an element of the SOBEK schematisation A branch is defined as a river stretch between two nodes A branch has the following characteristics Start node End node Length Geographic ori ntation optional The geographic ori ntation can vary within a branch the direction of the br
44. ecessarily constant in time and space Much attention should be paid to the magnitude of the inflow Important fields of attention are the objectives of the model the available data for calibration and the available data when the model is operational In general measurements are required for large lateral inflows For operational use in for example a flood forecasting model these inflows have to be calculated based on precipitation discharge models Smaller inflows for which usually no data are available have to be derived unambiguously from the data which are available One could thnink of relations on the basis of areas and charateristics of sub watersheds As far as the local hydraulic situation along the river to be modelled is concerned it can be assumed that the discharge at the upper boundary is a measure for the drainage or extraction capacity Based on the discharge at the upper boundary 4 hydraulic situations can be distinguished as far as lateral flows are concerned 1 Maximum extractions from the river In general this situation will coincide with long dry summer periods with low river discharges Especially water supply for agricultural application is of great importance in these periods In order to describe the discharge proces it is assumed that discharges are maximal at very low discharges 2 Minimum extractions from the river Generally this pertains to fixed drinking water extractions form the river To describe the discharg
45. ed by using WAQUA results at a high water discharge This method may result in high differences in areas between consecutive compartments in the floodplain If the slope of relatively large areas is small the entire area is assigned to one compartment These are usually storing areas behind dikes or old river branches At the same time this also implies that compartment areas can be relatively small at places where slopes are high for example at bridges or bottle necks This proces of defining compartment boundaries using iso water levels has been automised for the most part If there are no WAQUA results available the compartment boundaries have to be defined with expert judgement using the same principles 3 5 2 Function The SOBEK compartment boundaries file has multiple functions Firstly a SOBEK compartment is the principle schematisation unit for which the river characteristics are averaged For each compartment a SOBEK profile is calculated by the GIS application Secondly it is of utmost importance for 1 D hydraulic modelling that a compartment describes an area of approximately equal water level which is garanteed when the method described above is used Page 33 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 5 3 Creation in BASELINE In the current version of BASELINE the generation of SOBEK compartment boundaries in the floodplain using a WAQUA water level field is automised for
46. eedance level is lowered until it is just below the lowest individual gryone elevation in the river stretch e maximum level of the main channel is than determined according to the translated regression line through the 1 exceedance levels The elevations have to be specified in centimeters Important conditions for Hsub0 HsubO0 lt Hsub1 lt Hkrib 10 Page 54 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 5 9 Maximum elevation bank section 5 9 1 Definition The maximum elevation of the bank section Hsub1 is also read from the ASCII text file en returns in the SOBEK profile as level 8 If there are groynes in the compartment the elevation is defined as the weigted average of all groyne elevations plus 10 centimeters If there are no groynes the 1 exceedance level of the elevations in the bank sections is selected 5 9 2 Function To ensure that the location of the bank lines is in agreement with elevations in the elevation model and that the maximum elevation of the bank section is lower than the average groyne elevation a maximum bank elevation is defined 5 9 3 Creation If there are groynes in a compartment the maximum elevation is determined by calculating the weighted average per compartment of all groyne elevations plus 10 centimeters Reference is made to paragraph 5 10 If there are no groynes in the compartment the following method can be used
47. eshold elevations to individual dike elements The following steps should be taken e Adike segment file has to be specified as described in paragraph 3 7 4 e An ASCII file has to be generated with the fields segment number compartment number type and threshold elevation as defined in 3 7 1 For the appropriate file format and location in the BASELINE data structure reference is made to the BASELINE data conventions CSO ESR 1998 Using the function Files SOBEK Dikes the SOBEK basic dike file be generated With the function Model Conversion SOBEK the dike types and the threshold elevation can be converted to SOBEK input grids which can be read by the application The dike types and dike elevations are assigned using the ASCII table pecause in that way it is possible to modify the SOBEK compartment file without important consequences for the SOBEK summerdike file 3 7 4 Work around The dike segment file can be generated in different ways If there are 2 D model results available it is recommended to use them If this is not the case the dike segments can pe determined using digital river maps and topographic maps Together with the elevation model it is possible to determine which areas are protected by dikes where the flooding point is and what the elevation threshold is When this information is avaliable it is possible to generate the ASCII text file as described in paragraph 3 7 3 Page 45 Report GIS and
48. haracter of the SOBEK model e Stretch boundaries on the basis of upper and downstream compartment boundaries Branch compartments define the boundary for a roughness stretch in the floodplain On the basis of ecotope maps as many as possible ecotopes with similar effects on water movement should be clustered For the calculation of K values per river stretch the following procedure should be followed For each clustered ecotope the average waterdepth is determined in the flow conveying part of the floodplain flow conveying according to the SOBEK delimitation of flow conveying flow storage On the basis of a table with depth depended K values a K value can be determined for each clustered ecotype The different clustered ecotopes have to be merged for each stretch in order to determine a representative K Nikuradse value How the total K value for each stretch is determined is further elaborated in RIZA 1996b Basically two extremes can be distinguished The vegetation is flowed through in longitudinal direction In a stretch there are different vegetation types alongside The vegetation type with the lowest resistance will draw most of the water Therefore a minimal K Nikuradse will be calculated for the stretch The vegetation is flowed through in cross direction In a stretch different vegetation types are located behind one another In this situation all occuring vegetation types either smooth or rough are flowed through Therefore a
49. hat the physical lay out is less recognizable As far as bridges and ferry ponds are concerned it is proposed to use pour over constructions in the main channel and floodplain For the pass through widths and threshold elevations the physical dimensions of bridges and ferry ponds should be used initially If data are available the pass through widths will be adapted according to 2 D calculated slopes so that they can be reproduced by SOBEK Page 61 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 7 Presentation SOBEK input data 7 1 Introduction Besides the use of GIS to generate input for SOBEK GIS can also be applied to present all the used data for documentation A presentation application has been developed by RIZA which uses the same data as the application to generate SOBEK profiles in BASELINE With this presentation application it is easy to make the used data accessible Using the application it is easy to generate and present a large number of figures Besides data for SOBEK it is also possible to determine and present other characteristics of the river system For the delivery of a model inclusive documentation it has been decided to have a presentation application developed which presents the spatial data for a number of reasons Because of the great number of figures it is desirable to present the data digitally It should also be able to visualize the data without Arc Info It
50. he SOBEK and WAQUA models for the Dutch Rhine branches and the river Meuse is finalized The SOBEK data for the German Rhine form Andernach to Lobith have also been embodied in BASELINE In close co operation with the Bundesanstalt f r Gew ferkunde BfG in Koblenz about 800 km German rivers are modelled Initially these rivers will only be modelled using SOBEK Finally BASELINE will be multilingual and adapted to the Windows NT platform in the near future For an extensive description of BASELINE functionality reference is made to the user manual CSO ESRI 1999 1 3 Models 1 3 1 SOBEK SOBEK is a numeric program aimed at simulating water movement sediment transport water quality and salt movement in schematised open watercourses The water system has to be defined as a scheme of logically connected nodes and branches Within the branches there are calculation points which are connected to data When simulating water and sediment movement cross profiles soil resistance initial waterlevels or depth or discharge and characteristic grain diameters are required as data The distance between the calculation points numeric step length Ax is connected to the numeric time interval At The relation Ax At has to pertain to two criteria stability and accuracy These criteria put constraints on the maximum step and time interval Stability is garanteed in SOBEK by the implicit application of the Preissman scheme of water movement The propagat
51. here the streamline direction differs much from the model direction are flow storing e objective is to define the boundary flow storage flow conveying in such a way that about 90 95 of the discharge in a SOBEK compartment is assigned to the flow conveying part of the floodplain In figure 16 an example is given of the boundary flow conveying flow storage Strovoer Flow conveying _ Storage igure 16 Example boundary flow conveying flow storing Page 38 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 6 2 Function The amount of water which can be discharged by the floodplain is to a high degree depending on the flow conveying area The flow conveying area is mainly determined by local terrain features In the SOBEK profile therefore there is a distinction between flow conveying widths and flow storing widths 3 6 3 Creation in BASELINE In the current version of BASELINE there is no functionality to determine the boundary flow conveying flow storage automatically This will however change in the near future Because this functionality has not yet been implemented the methodology will be illustrated in paragraph 3 6 4 The location in the BASELINE data structure as well as the required file format are illustrated in the BASELINE data conventions CSO ESRI 1998 With the function Tools Conversion SOBEK the file can be converted to a SOBEK input grid 3 6 4 Wo
52. iderably It is possible in BASELINE to generate grids at different spatial resolutions using the same input data Page 19 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 GIS data 3 1 Introduction In this chapter the GIS files which are directly used by the BASELINE application to generate profiles will be discussed Files which are not directly used but which are important when constructing a SOBEK model are described in chapter 4 The basis for obtaining useful data is usually the digital river map DTB Of course there is a wide variety of other input data sources which are especially important for generating the essential GIS files in foreign countries e g ATKIS Digitale Bundeswasserstralfbekarte The GIS file which describes the river axis will also be discussed in this chapter The river axis is however not directly used by the GIS application but serves as the basis for the schematisation and is therefore discussed primarily Within short notice the river axis will however play a crucial role in automatically generating the SOBEK compartment boundaries in the main channel This option will be imlemented in the next BASELINE release It is recommended to follow the order of this chapter in setting up a schematisation The first step in setting up a schematisation is however the definition of the model lay out see chapter 6 For each GIS file the definition the function an
53. ine Because of the succes of the application of GIS for 1 D models an application is being developed which can also be used in hydrological modelling using the 2 D model WAQUA The use of GIS in hydrological modelling requires expert guidance in both the fields of hydraulics and GIS GIS has to be used as a tool to implement changes in river geometry In order to manage large amounts of spatial data and to facilitate database control the GIS application BASELINE has been developed BASELINE enables hydrologists without profound GIS knowledge to design model schematisations using GIS A short description of BASELINE SOBEK and WAQUA is presented in paragraphs 1 2 and 1 3 BASELINE enables to create the spatial component of a model schematisation from a predefined GIS format The use and implementation of BASELINE outside RIZA has shown that there were still a number of problems concerning BASELINE and the BASELINE application SOBEK profiles Therefore it has been decided to develop a manual aiming at potentials in the used methods Incentive to the devlopment of this manual is the implementation of BASELINE at the Bundesanstalt f r BfG in Koblenz Germany The problems mainly concern e The data in BASELINE is very divers and may originate from many different sources The data have to be converted to certain predefined formats before they can be put in BASELINE This requires profound knowledge of both GIS and hydraulics
54. ion of physcial disturbances in the system which need to be modelled accurately determine the step and time interval An essential part of model schematisations is the display of the river geometry This 3 D geometry has to be converted responsibly and reproducable to representaive cross profiles of river stretches along the river axis Using spatial data stored in BASELINE and the BASELINE application SOBEK cross profiles the cross profiles can be generated in a format which can be directly read by SOBEK Therefore the river is subdivided in compartments and along the length x measured along the river axis an average profile is generated Combining these profiles with characteristics like soil roughnesses lateral inflow weirs etc a SOBEK model can be build Currently profiles are generated in an ASCII format which can be directly read by SOBEK version 1 0 1 3 2 WAQUA WAQUA is a hydrodynamic simulation system for the calculation of watermovement water quality temperature and sediment transport in two or three dimensions The software is commonly used for the calculation of one or more of the above mentioned transports in large water bodies like seas lakes or rivers To calculate with the software the reality has to be simplified schematised to a 2 D or 3 D grid schematisation see figure 3 In that way the river geometry is principally schematised by a detailed elevation model and a model for hydraulic roughness After defining the
55. ion supporting system which may result in a more directed decision taking proces The at the cross profile location operating basis for the design or construction elevation of a flood defence which serves as the basis of the construction calculation of the design profile Interpolation software of the survey department aimed at the interpolation of data in the main channel A model describing the terrain elevation in a certain data format That area in the floodplain which can not be freely flooded from the river because of a relatively higher element in the floodplain See floodplain section That part of the river which is located between the model boundary and the bank lines Page 70 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Stroomvoerend gebied Durchstr mter bereich Part of the floodplain of the river that at least at high water contributes to the discharge of water The flow conveying area is determined for each compartment and does not necessarily coincide with the legal boundary of flow storing areas Flow conveying area Geographic Geographisches Geografisch A structurized collection of computer hardware software Information System Informationssystem Informatie systeem and geographic data designed to efficiently capture GIS analyse and display geographically referenced data GIS Anwendung GIS
56. isation to be build the actual length interval has to be determined It is however possible to determine an upper and lower boundary E Due to simplification in a 1 D model the length interval can not be to small A length interval smaller than the width of the main channel only introduces fake accuracy Especially for 1 D models it is of great importance that hydraulic parameters elapse fluently from one profile into another If small length intervals are used this is difficult to obtain e When a large length interval is used many details of the river geometry will be lossed which have to be compensated during model calibration If a length interval of more than twice the width between the winterdikes is used a lot of information will be lost In the flooding prediction model Andernach Lobith the demands for calculation times and accuracy were fullfilled using a length interval of 1000 meters For the SOBEK models of the Dutch Rhine branches and the river Meuse a length interval of 500 meters was used Most important are the demands of policy analytical studies and morphological studies For an appropriate display of morphological and hydraulic interventions it is important to have six to seven calculation points within the river stretch where the interventions are undertaken When a length interval of Page 18 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam approximately 500 meters is used it is
57. iver stretch name Compartment number Location compartments Nearest settlement Groyne elevation Version number Compartment length Maximum elevation main channel Maximum elevation bank section Threshold elevation lakes In Table 1 an example is given of the ASCII table The first line is a header line which is not used by the application but which is required elevation PH jetemen elevation Jenga branch settlement elevation length MK Boan Mn Bene WE uus Andemach 79795 frenes _ NN A 5351 SISSSITS ON 501 5954 9 NN OL 2 E sper e em Een Table 1 Example ASCII table pm dl o EE pe 1 8 NEL mee du dk Oe Ls NE MN laoreet Page 52 For RIZA By Geodan Geodesie B V Amsterdam 5 3 River name The name of the river is used in order to be able to distinguish between different rivers It can be decided to specify a river branch in this field instead of only the river name For each calculated profile this name is read and can be found in the first line of the SOBEK profile This name should not contain comma s since that is the seperator character 5 4 Location compartments The location of the compartments is specified with a start and end kilometer of the SOBEK compartment This field serves however only as identification of the profile so no exact river kilometers have to be specified This field i
58. lain which are not part of the main channel are treated as lakes in SOBEK This includes gravel pits harbours canals and oxbow lakes Besides the location of the lakes it is important whether a lake is connected to the main channel or isolated Lakes which are disconnected by a weir lock or valve are also defined as isolated lakes A connected lake connects at the bankline An elevation is also assigned to the individual lakes This eleveation corresponds to the average terrain elevation around the lakes In figure 22 an example is given of the lakes file figure 22 example lakes file 3 8 2 Function The distiction between isolated and connected lakes is made in order to ensure that the lakes will contribute to the storage at the appropriate time An isolated lake contributes to the storing widths as soon as the lake elevation is exceeded in the SOBEK profile A connected lake however contributes to the storing widths from the lowest point in the profile onwards If a lake is located in the flow conveying part of the floodplain it also contributes to the flow conveying widths By default it is assumed that flow conveying lakes flow over an additional depth of two meters This only Page 48 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam occurs if the lake elevation is exceeded This holds for both isolated and connected lakes If there are no summerdikes in a compartment but there are one
59. lculations automatic definition of boundary conditions e Suitable for use in a decision support system DSS From a practical point of view it is recommended to cluster lateral inflows from many different sources to one large unit e g between two measuring points In this way the actual inflow at a certain location is not appropriately modeled it is however a very good description of later inflows for an entire river stretch For the determination of the location and areas of sub watersheds the use of GIS can be extremely helpfull For the time being the necessary files and routines have not been integrated in BASELINE and therefore the calculations have to be executed manually 6 4 Boundary conditions model boundaries In order to prevail that the model results are influenced by the chosen model boundaries it is important to always choose the model boundaries outside the area of interest In the determination of the spatial extend of the model boundary at the up and downstream boundaries it is imporant to take a potential combination with other sub models into account If possible the model boundary is defined by a compartment boundary of the model to be connected Overlap between the model can than be prevailed Page 59 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 6 5 Soil roughnesses In SOBEK roughnesses can be specified for the three different sections If possible the roughness
60. ld elevation has to be determined This threshold elevation corresponds with the determing crown elevation of the dike This is the location where the dike will flood and the area behind the dike will start flowing cq storing In order to achieve that the entire dike segment will start flooding at the appropriate moment the dike segment is intersected with the SOBEK compartments and threshold values are assigned according to the slope of the river to each dike element per SOBEK compartment This can be accomplished by assigning threshold elevations to the upstream and downstream compartments which correspond to the waterlevel at the discharge where the threshold elevation at the flooding point is exceeded If this is ignored it may be possible that for example if the flooding point is located upstream the downstream part of the dike segment is already flooded before the Page 44 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geadesie B V Amsterdam threshold elevation of the flooding point is exceeded because it is lower due to the slope of the river 3 7 3 Creation in BASELINE the current BASELINE version there is no functionality yet to automatically generate dike segments For the time being this file has to be generated outside BASELINE using 2 D model result if available Within BASELINE it is however possible to automatically intersect the dike segments with the SOBEK compartment boundaries and assign thr
61. lication calculates areas which are protected by a dike and not with the location of the dike it self For each SOBEK compartment a threshold value is assigned There for a dike boundary is usually placed on the boundary of SOBEK compartment and dike segment This boundary does not have a physical meaning but is applied for application technical reasons In figure 19 an example is given of the dike elements coverage Page 43 Report GIS and SOBEK modelling pate 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam sobekkade 1 E Primary summerdike __ Secundary summerdike figure 21 Example dike elements coverage 3 7 2 Function Because there are areas which can not freely be flooded the dike elements file is used in order to model this 2 D phenomenon in a 1 D model The SOBEK model can only calculate with inclining profiles In other words declining situations can not be modelled which is not desirable In order to Solve this a parameter AA is defined which is equal to the through flow area of all declining situations in a SOBEK sompartment A distiction is made between flow conveying flow through area AAf and storage flow through flow area AAt These AA s are added to the profile after the water level has exceeded Hop In a SOBEK schematisation dike segments are schematised This means that the entire area which is protected by the summerdike is stored as a polygon in a GIS file For each dike segment a thresho
62. llers All BASELINE functionality is menu driven This functionality enables potentials for management and maintenance consulting and selecting implementation of changes and conversions to model schematisations BASELINE also has functionality for presentation of spatial data All functions aim at facilitating the conversion from spatial data to model schematisations By formalising procedures and a well described data model a high degree of reproducibality of schematisations has been obtained while at the same time the modeller is enabled to implement necessary changes In the following paragraphs BASELINE functionality will be briefly summarized The navigation and maintenance functionality enables the user to easily copy basic data to projects or variants to define the structure for a new schematisation or area and copying moving or deleting of data Page 6 Report GIS and SOBEK modelling Date 03 06 99 For RIZA E Geodan Geodesie B V Amsterdam Baseline figure 1 Example querying and selecting Data can be displayed and queried on screen using management and querying functionality This can be done both spatially using the mouse as on the basis of attribute characteristics Selected data can be saved as a seperate data set The change button enables the user to actually modify the data Both location and attribute values can be modified in this way When one or more files are displayed on the screen there is menu d
63. ly conflicting When building the model it can be of great importance to pay a lot of attention to the positioning of the calculation grid It is important to realise that a SOBEK profile is the smallest unit in which adaptations in the river system can be shown For an appropriate display of the effect of measures it is important that in a stretch where measures are taken at least 6 to 7 calculation points should be defined With a length interval of 500 meters measures at floodplain level ca 3000 meters can be schematised If a larger length interval is used it is not longer possible to consider measures at floodplain level This results in the fact that measures on a scale smaller than 6 times the length interval are difficult to model using a 1 D model Usually such local measures are modeled using 2 D models 6 3 Lateral inflow At the different locations in the river water can be extracted or added to the river This inflow can be either natural tributaries streams or artificial drinking water and industial water extractions sewer overflows pumping stations A lateral inflow can be defined at every location in the model If a hydraulic model is anticipated for a certain inflow it is recommendable to define a node at the location where the inflow confluences with the river When this extension of the model is not foreseen then there is no need to strain the model with unneccesary nodes with no specific function Lateral inflow is not n
64. matisation for a new river stretch It is up to the modeller to creatively deal with the available datasources Some examples are E Drawing on analogue maps followed by digitising e Use of binary data from other software packages in formats which are supported by Arc Info see Arc Info manual e Use of tailor made software to convert data to ASCII formats which are supported by Arc Info and BASELINE E Use of aerial photographs satellite imagery and other digital maps E Etc Besides information needed to build the model there is also a lot of data required for the calibtaion and verification of the model in a later stage This mainly concerns Data to define initial values waterlevels discharges roughnesses Measuring series of waterlevels and or discharges Q h relations Data on lateral inflow The main part of this information can most likely be retrieved from the same data sources which also supply the spatial data Therefore it is recommended to start thinking about the use and desired accuracy of the model Tuning of data needed for model development and model calibration in this stage easily is achievable The data for building and calibrating the modei can than be collected simultaneously which improves efficiency and shortens the period needed to build and calibrate the model Page 11 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 2 Application of GIS concepts in S
65. measured Measuring point Mefipunkt Meetpunt Modelgrenze Modelgrens The line describing the area to be modelled Model boundary The downstream model boundary This is where the boundary conditions are imposed at the calibration Untere Modelgrenze Model lower Model ondergrens boundary Obere Modellgrenze Mittelwasserlinie Model upper Model bovengrens The upstream model boundary boundary Normal line The boundary between the water of the river and the land If there are groynes it is the line connecting the groyne toes Normaallijn Prim rer Primair kade Sommerdeich That dike segment having the greatest influence on water movement Primary summerdike Hauptsommerdeich Q h relatie Data for describing the relation beween discharge and waterlevel Q h relation Q h Beziehung Page 71 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam River axis River geometry River kilometer River sections Roughness Secundary summerdike SOBEK branch SOBEK calculation grid SOBEK compartment SOBEK nodes SOBEK profile schematisation Storage area Summerdike Threshold elevation Triangular Irregular Network TIN WAQUA FluBachse FluR amp geometrie Fluf amp kilometrierung Flu amp bereich Rauheit Sekund
66. msterdam Floodplain and lakes Elevation data from the digital river map DTB can be use to build the DTM of the floodplain in the Dutch situation These data have a density of approximately 1 point per hectare and can be directly used in building the TIN after conversion to BASELINE format In the past years modern data collection techniques like laser altimetry have increased in popularity At this moment a digital terrain model of the netherlands is build by the survey department of the directorate general of public works and water management RWS with an average point density of one point per 16 m In the near future these data will probably be also available for this kind of applications Elevation data of lakes refer to the average elevation of the terrain around lakes In the paragraph about lakes 3 8 it is specified how the lake elevations are assigned to the individual lakes When the data are converted to SOBEK input files the lake elevation are embedded in the elevation model There is a file in BASELINE with the depths of the lakes This file is important in WAQUA schematisation and is not relevant for SOBEK but can however work confusing It is also possible that elevation data of the floodplain are available a as cross profiles with a fixed interval 100 200 meter which describe the geometry After c conversion c of these cro S eto BASELINE point coverages they can be directly used i in the creation of N No lake d
67. n of profiles and other characteristics on the branches Page 62 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 7 3 Overview figures In order to give a general overview of the river the river is subdivided into a number of overview maps The figure displays the main channel and floodplain together with the location of the SOBEK compartments For ori ntation the names of a number of settlements along the river are displayed in the figure The red rectangles and numbers display the location and numbering of the sub areas For theses sub areas a detailed figure can be generated of specific elements of the river In figure 24 an example is given of an overview map of the southern part of the river Meuse Page 63 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 4 Bladindeling detailkaarten MAAS Km 2 Km 95 Zuid Schaal 1 275 000 28 Sep 95 figure 24 Location detailed figures of the southern Meuse Page 64 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 7 4 Detailed figures On a more detailed level different data are available In order to gain insight in how the different elements are modelled it is not only important to have insight in the seperate profiles but also in the elapse of information along the river for example Elevation floodplain Elevation main channel
68. n section 1 D model 2 D model Arc Info Uferlinie Uferbereich BASELINE Kalibrierung Angeschlossener See dAf Decision Support System DSS Bemessungs Hochwasser DIGIPOL Digitales Gel ndesmodell DGM Deichsegment Hochwasserbett berflutungsbe reich Vorlandbereich 1 D model 2 D model Arc Info Oeverlijn Oever sectie BASELINE Calibratie Aangetakte plas dAf Decision Support System DSS Maatgevend Hoogwater MHW DIGIPOL Digitaal Terrein Model DTM Kade segmenten Winterbed Uiterwaard sectie Model that simulates the hydraulic characteristics of a river in one direction Model that simulates the hydraulic characteristics of a river in two directions Mainstream GIS software package developed by the Environmental Research ESRI The boundary between the bank and the floodplain If there are groynes it is the line connecting the goyne heads That part of the river which is located between the bank lines and the normal lines GIS application in Arc Info for the management analysis and presentation of river related data Calibration Open water in the floodplain which is connected to the main channel The flow conveying through flow cross profile of areas behind summerdikes within a SOBEK compartment in m The total flow storing and flow conveying through flow profile behind summerdikes within a SOBEk compartment in A decis
69. nction of elevation In the first column the elevations are displayed the second columns contains the flow conveying widths and the third column contains total widths all in meters e in line 3 indicates the lowest level if there are no connected lakes in the compartment e in line 3 indicates that there is a connected lake in the compartment The width of the lake area compartment length is added to the total width at the lowest level in the main Page 15 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam section The difference between flow conveying width and total width should comply to the width of the connected lakes in the compartment e 50 0 indicates the highest level in the main section Level to 7 therefore describe the main section e KRIB indicates the groyne level The elevation of this level complies to the groyne elevation in the SOBEk compartment given that there are groynes e 50 1 indicates the highest level in the bank section Level 8 to 10 thus describe the bank section 0 1 indicates the elevation of the primary summerdike in the compartment e DIKE2 indicates the level where the primary summerdike is flooded e 50 2 indicates the highest level in the floodplain section figure 7 shows that the application distinguishes between 4 types of situations Groynes no summerdikes No groynes no summerdikes Groynes summerdikes
70. nd SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam how to prepare the data outside BASELINE however will also be discussed These work arounds will result in data in BASELINE format which can be converted directly to SOBEK input data This manual will also focus on the concepts of using GIS in SOBEK modelling as well as the presentation of SOBEK relevant data This report is aimed at hydrologists with basic GIS knowledge who want to build a SOBEK schematisation using GIS 1 2 Baseline The use of spatial data and GIS methodology has played a key role in modelling large rivers in the past years One of the consequences of this development is that the amount of required data may increase rapidly To manage the development of GIS technology in the future the river department of RIZA had developed BASELINE BASELINE is a GIS database and application which facilitates the creation of the spatial component of modelschematisations for SOBEK and WAQUA The development of BASELINE is based on a number of starting points A lot of data are collected edited and saved for both SOBEK and WAQUA This may cause data redundancy and may cause that the models are based on different data In BASELINE the spatial data are saved in a way to ensure an appropriate area description This area description can than be converted using a number of conversion tools to a schematisation for SOBEK or WAQUA BASELINE is a GIS tool to be used by mode
71. nimum level main section MAIN H2 H1 025 H5 H1 H3 H1 050 H5 H1 H4 H1 075 H5 H1 HS Maximum level main section 5080 HG Groynes not fooded H7 0 10 H7 Gevation of groynes KRIB Groynes just flooded H7 10 SUB 1 HJ H8 05 H10 HB8 H1D Elevation of pimairy summerdike BIDIKE 1 HIT 10 05 Witt WI 10 WIDIKE 2 H12 H11 0 25 H15 HB H13 HIT 0 50 HIS H8 HI4 HIJ 0 75 H15 H8 HIS Madmum elevation fioodplain 5082 n floodplain Floodplain after summerdike Section Section Profile layout without groynes with summerdikes H1 Minimum level main section MAIN H2 H1 025 H5 H1 H3 H1 050 H5 H1 H4 H1 075 H5 H1 H5 Maximum level main section SUBO HG HG H5 033 H amp H5 H7 HS 066 HB H5 H8 Maximum elevation groyne section 5081 H9 8 05 10 H8 H10 Elevation of pimairy summerdke htop DIKE1 HIT 10 0 05 Wf11 Wf 10 I oIKE2 H12 H11 0 25 H15 HB H13 H11 0 50 H15 H8 H14 H11 075 H15 H amp H15 Maximum elevation floodplain S SUB2 n Groyne Floodplain Floodplain after summerdike Section Section figure 7 Example situations Page 17 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 2 4 Guidelines The representativeness of the profiles is depending on The chosen compartment length This length determines over which length along the river axi
72. nto two banks howewver still exists In the lowest figure the actual SOBEK input is presented in table format together with an overview of where on the river the profile is located In an example of a profile description is displayed In the following paragraphs the different elements of the sub figures are discussed 7 5 2 Top sub figure In the top sub figure a top map view of the SOBEK compartment is displayed In this sub figure the boundary of the SOBEK compartement is displayed with a dotted red line The number and river kilometers are also displayed The backgound of the figure consists of the main channel and floodplain of the river If there are lakes and or summer dikes than they are are also displayed in the figure 7 5 3 Middle sub figure One of the characteristics of a 1 D model is that there is no distinction between elements which are located on the left or right bank respectively Therefore it is often diffictult to assess the actual effect of individual elements on the profile It is tried to solve this problem in the middle sub figure In this figure the relevant geographic elements in a SOBEK compartment are translated to a 1 model and displayed as areas per bank In the figure the area weighted part of the main channel is displayed In the floodplain the lakes and flow conveyance is also shown In a vertical frame the length of the SOBEK compartment is displayed In the table the calculated widths per bank of the different part
73. of zero should be assigned to the section file if areas inside the winterdikes are not part of the model E In a later stage a soil roughness is assigned to each section 3 3 3 Creation in BASELINE The SOBEK sections file can be generated in a number of steps 1 Outside BASELINE the normal lines file as defined in paragraph 3 3 1 is generated There are several options e Digitising the normal lines using analogue river maps e Selecting normal lines from a digital river map e g DTB river 1 5000 and convert them to Arc Info format E Digitising a line connecting the groyne heads E Generating water level contours using 2 D model results at a chosen discharge 2 Outside BASELINE as well the bank lines file as defined in paragraph 3 3 1 is generated in approximately the same way as the normal lines Digitising the bank lines using analogue river maps Selecting bank lines from a digital river map e g DTB river 1 5000 and convert them to Arc Info format e Digistising the line connecting the groyne toes e Generating water level contours using 2 D model results at a chosen discharge 3 Outside BASELINE the model boundary file as defined in paragraph 3 3 1 has to be generated The model boundary is determined by E Digitising the line connecting the toes of the winterdikes from analogue maps e Selecting the lines describing the wintedike from a digital river map e g DTB river 1 5000 If the floodplain is not delimited
74. ons CSO ESRI 1998 The above described proces is illustrated in figure 15 Page 36 Report GIS and SOBEK modelling Date 03 06 99 For RIZA B Geodan Geodesie B V Amsterdam Overview creation SOBEK compartment file WORK AROUND Creation compartments in BASELINE using ToolsiFies SOBEK compartment boundaries Manual creation of compartment boundaries main channel in Arcfinfo and conversion to BASEUNE format Manual creation of compartment boundaries floodplain based on expert judgement Combining compartments main channel and floodpian Conversion to BASELINE format Manual changes in compartment boundary file Ganerating SOBEK input with the function Models Conversion SOBEK in BASELINE figure 17 Overview methodology SOBEK compartments Page 37 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 6 Flow conveying flow storage areas 3 6 1 Definition The boundary between flow conveying and flow storing areas in SOBEK indicates which parts of the floodplain at a very high discharge contribute to flow conveyance and which parts only have a storage function Between bank ful discharge and the maximum discharge this boundary is defined by the elevation model and local geometry The following guidelines can be used whene determing the boundary e The main channel and the bank section are always flow conveying e Areas w
75. or more partly flow conveying lakes then the Hip of the profile is equal to the lake elevation If this occurs it is recommendable to assign equal lake elevations to all the lakes in the compartment However if there are dike elements in a compartment than Hip is equal to the threshold elevation of the primary summerdike 3 8 3 Creation in BASELINE The basic lake file has to be created outside BASELINE It is however possible to generate the SOBEK input grids lake elevations and lake code isolated connected with function Models Conversion SOBEK 3 8 4 Work around The outer extent of the lakes can be derived from digital river maps or can be digitised using topographic maps A problem which may occur is that either digital rivermaps or a topographic maps are based on data which are collected at different times e g aerial photographs Because of differences in waterlevels differences may also occur in the outer extent of the lakes When generating automatically the lake file it may happen that many surface waters with a very small area are selected Most likely they do have a very small influence on the water movement Therefore it can be decided to remove waters from the lake file which contribute less than 1 meter lake area compartment length to the width in the profile Whether a lake is connected or isolated can usually also be derived from the digital rivermaps ot the topographical maps The lake file has an item code which h
76. possible to model interventions at floodplain level approximately 3000 meters When using a larger length interval it is not possible anymore to model interventions at floodplain level The chosen cell size For the generation of SOBEK profiles the different SOBEK vector themes have to be converted to grids which have a specified grid cellsize This cell size is depending on the detail of the input data It may for example occur that elevation data of the main channel have a greater detail than the elevation data of the floodplain In that case a smaller grid cellsize can be specified for the main channel than for the floodplain A maximum grid cellsize of 10 of the average width of a section can be used as an indication This indication garantees sufficient detail in the the cross direction of the river even if the data are averaged For the bank section the same grid cellsize is used as for the main channel If the bank section is relatively small and if there are no groynes the grid cellsize of the main channel should be sufficiently small to generate a representative part of the profile for the bank section It can be decided to decrease grid cellsize or distinguish between main channel and floodplain if the quality of the input data allows it It should however be taken into account that by increasing spatial resolution the needed calculation time of the SOBEK profile application and storage capacity in the BASELINE database will increase cons
77. r 99 163 2 CSO ESRI in opdracht van RIZA 1998 Protocol basis bestanden BASELINE Meulen van der M S rapport nr 98 624 3 Geodan Geodesie in opdracht van RIZA 1996 a Schematisatie voor het SOBEK model Nederlandse Rijntakken Zeeman M 4 Geodan Geodesie in opdracht van RIZA 1996 b Schematisatie voor het SOBEK model Grens en Plassenmaas Zeeman M 5 Geodan Geodesie en HKV in opdracht van RIZA 1997 SOBEK model Andernach Lobith Phase2 Data collection and processing Zeeman M en Hoefsloot F V J rapport nr PR 042 6 Geodan Geodesie en HKV in opdracht van RIZA 1998 a Applicatie SOBEK profielen Technische Documentatie Hoefsloot F Nijssen Immerzeel W en Weidema 7 Geodan Geodesie en HKV in opdracht van RIZA 1998 b BASELINE application cross sections user manual rapport nr PR 192 10 8 Geodan Geodesie en HKV in opdracht van RIZA 1998 c BASELINE applicatie SOBEK vakgrenzen technische documentatie Hoefsloot F Bottelier Immerzeel W en Weidema P 9 Geodan Geodesie en HKV in opdracht van RIZA 1998 d BASELINE applicatie SOBEK vakgrenzen gebruikershandleiding rapport nr PR 222 10 10 HKV in opdracht van Riza 1996 Analytisch model hydraulische ruwheid overstroomde vegetatie 51 D Klopstra H J Barneveld en J M van Noortwijk rapport nr PRO51 11 RIZA 1998a Ecotopenkartering Rijntakken oost rapport nr 98 054 ISBN 9036952085 12 RIZA 1998b Calibratie SOBE
78. rc Info or in BASELINE see step 6 paragraph 3 3 3 When the input grid is created in BASELINE the file should pertain to the BASELINE data conventions The following steps should be taken 1 The normal lines bank lines and model boundary should be generated in the same way as described in the steps one to three in paragraph 3 3 3 2 different line elements should be merged in an Arc Info coverage Then the section polygons should be created with item definitions as described in the BASELINE data conventions CSO ESRI 1998 3 This file should be converted to a SOBEK input grid This can be done in Arc Info or in BASELINE In figure 10 the methods described above are illustrated in a flowchart Page 25 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Overview creation SOBEK section file WORK AROUND CEU En RE Whe Cr ME hu figure 12 Overview methodology sections Page 26 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 3 4 Elevation data 3 4 1 Definition Elevation data give an as accurate as possible display of the terrain elevation of the river basin It is of great importance to build an appropriate digital terrain model DTM because a well described geometry is the basis for the quality of the model The eventual digital elevation model consists of two regular grids with elevations in centimeters
79. rer Sommerdeich Untergeordneter Sommerdeich SOBEK SOBEK zweig SOBEK rechengitter SOBEK rechen element SOBEK knoten SOBEK profil SOBEK Diskretiserung Nichtdurchstr mter bereich Sommerdeich berstr mh he Unregelmafige Dreiecksverma schung TIN WAQUA Rivier as Rivier geometrie Rivier kilometrering Rivier secties Ruwheid Secundair kade SOBEK tak SOBEK rekengrid SOBEK vak SOBEK knoop SOBEK profiel SOBEK schematisatie Stroombergend gebied Zomerkade Instroom hoogte Triangular Irregular Network TIN WAQUA Virtual line on the axis of the river The spatial description of a river system The ocation of the main channel floodplain and lakes file displaying the river kilometers projected on the river axis Distinction between main channel bank section and floodplain in a river system Parameter used to describe the resistance against flowing in SOBEK A dike segment not having the greatest influence on water movement in a SOBEK compartment Numeric program for simulating water movement sediment movement water quality and salt movement in schematised open waters A river stretch between two nodes A network of points for which SOBEK performs calculations A compartment with a fixed length along the river axis A point in the SOBEK schematisation which describes the end or the beginning of a SOBEK branch This could b
80. ritmes reference is made to the user manual Geodan Geodesie et al 1998 b and the technical documentation Geodan Geodesie 1998 a of the application SOBEK profiles in BASELINE For more information about the concepts of the GIS application reference is made to the reports of the SOBEK model 1998 1 of the Meuse RIZA 1996 b and the SOBEK model Andernach Lobith Geodan Geodesie en HKV 1997 14 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 2 3 Profile layout In figure 6 an example profile is displayed The first line of the profile contains a number of administrative data of the profile Name of the river stretch Start and end kilometer of the SOBEK compartment Name of the nearest settlement Version number In the second line a number of SOBEK parameters are displayed CROSS TABULATED WS and DA are SOBEK keywords SOBEK compartment number Width of the main section Combined width of the main and bank section Sediment transporting width Elevation of the primary summerdike in the SOBEK compartment in m Elevation of the primary summerdike minus the average terrain elevation behind all summerdikes in the SOBEK compartment Flowconveying area behind the summerdike in m in the SOBEK compartment Total area behind the summerdike in m in the SOBEK compartment From line three onwards the flowconveying widths Wf and total widths Wt are displayed as a fu
81. riven functionality to zoom in zoom out and pan This is illustrated in figure 1 Page Report GIS and SOBEK modelling LS Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam By using different tools in BASELINE basic information can be converted to information which can be used in the creation of model schematisations On the basis of elevation data it is for example possible to create an elevation model see figure 2 Another example is to determine an initial soil roughness of the floodplain using ecotype maps Creation of a water level model using WAQUA output is also possible Model schematisations based on spatial data can be created using the model button For the time being a connection is made to SOBEK and WAQUA The number of models can however be further elaborated BASELINE can exchange data by a number of import and export functions Using these options all BASELINE data can very easily be exchanged between different parties It has to be kept in mind when importing data that BASELINE requires specific formats and names of files and items There is a limited potential to create maps in BASELINE for visual data checks If fancy presentations are required it is easy to create those in Arc Info or ArcView because of the standardises names and formats of the BASELINE files Page 8 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam At this moment data entry for t
82. rk around If WAQUA results are available the following methodolgy can be applied A flow velocity grid can be generated which belongs to a design water level discharge For the determination of the boundary flow conveying flow storage only the floodplain is important It is assumed that every cell contributes to the loss of energy in the floodplain The energy loss for flowing can be described as dH 2 9 loss constant V flow velocity g gravitation constant For each cell in the floodplain from the square flow velocity and from the sum of the square velocities the average square flow velocity per SOBEK compartment is calculated Empirically it has been determined that a square flow velocity smaller than half the average square flow velocity is an appropriate criterium for the boundary flow storage flow conveyance RIZA 1996 a Lakes in the floodplain can however contribute considerable at lower flow velocities because they flow over a larger depth For lakes in the flow storing part of the floodplain it is therefore seperately determined whether they should be assigned to the flow conveying part of the floodplain on the basis of the discharge pattern In this way sheltered areas behind dikes bridges and dry areas are appropriately modelled mmm Page 39 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam In figure 19 the different steps are schematically displayed
83. rtment lengths in consecutive compartments differ more than 30 the number of compartments in a branch should be optimised in order to minimise differences in compartment lengths 5 Combine the normal lines see paragraph 3 3 and the river axis file with the digitised nodes There have to be drawn lines which intersect the normal lines and the digitised nodes and are perpendicular to the river axis 6 The normal lines and the drawn lines have to be converted to a compartment polygon file which is correctly numbered Besides the compartment number the compartment file also has attribute indicating whether a compartment is located within the floodplain or the main channel The required formats are specified in the BASELINE data conventions CSO ESRI 1998 Compartment boundaries floodplain If there are no WAQUA results available the boundaries have to be defined based on expert judgement The following steps have to be taken 1 The compartment boundaries of the main channel and the modelboundary should be combined 2 From the intersection normal lines compartment main channel lines should be drawn up to the model boundary for both the left bank and the right bank It should be kept in mind that the water level in the main channel should be equal to water level in the floodplain 3 Polygons should be created and correct attribute values should be assigned For the appropriate file formats reference is made to the BASELINE data conventi
84. s also taken up in the first line of the SOBEK profile 5 5 Nearest settlement This field contains the name of the nearest settlement to the profile The generation of the name might be automised using a settlement map and the SOBEK compartment file It also only serves as identification of the profile and can be found in the first line of the profile This name should not contain comma s since that is the seperator character 5 6 Compartment length This is a very important parameter The calculated widths in the SOBEK profile are directly depending on this length By means of different selections areas are calculated by the application which are divided by the SOBEK compartment length resulting in the widths of the profile The compartment length is defined as the length along the river axis from compartment boundary to compartment boundary These lengths can be calculated by combining the compartment files and the river axis In the near future this will be automised 5 7 Version number In this field the version number of the schematisation is noted Both the year and the versionnumber are defined for example 1998 3 This name should not contain comma s since that is the seperator character Page 53 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 5 8 Maximum elevation main channel 5 8 1 Definition In the table there is a field which contains values which are in agreement with the ma
85. s an average profile is calculated The choice of compartment length is determined by the objectives of the model to be build The following user possibilities should be taken into account For policy analytical studies calculation time has to be kept When differences between a reference situation and a scenario are calculated the compartment length should be sufficiently small in order to see the results of the different interventions For morphological calculations the stability of the calculations equal length interval than 30 difference between consecutive compartments and enough detail to show morphological changes have to be taken into account gt For flooding predictions short calculation time a limited number of calculations and an accurate calculation of waterlevels at measuring points and other relevant points river kilometers have to be taken into account For the determination of hydraulic limiting conditions for constructive purposes short calculation times large numbers of calculations and smaller degree of detail should be kept in mind e Water quality studies have to pertain to short calculation times less accurate calculated water levels and a smaller degree of detail The different users partially have conflicting demands On the basis of the desired calculation time the length interval is inversely proportial to the calculation time and the user objective of the schemat
86. s are shown The table also contains the widths of are behind the summerdikes in a compartment The table shows the widths of the different elements on both banks as well as total widths Page 67 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 7 5 4 Lowest sub figure In the lowest sub figure the actual SOBEK input is given For each compartment if available additional information is shown This information is integrated in the graphical presentation of a SOBEK profile The following information is presented if available General data Profile number Branch number Location of the profile on the river indication Version number of the profile G Structure A structure is only schematised when the effects of the structure is not modelled accurately enough through the geometry or roughness Only these structures are taken into account in the presentation If there are structures in a SOBEK compartment the following information is presented name location river kilometer E Lateral inflow Name Location river kilometer Meetlocaties Name Location riverkilometer bank Type E Qh curve Name E Particularities of the schematisation a Potential manual adaptations in the profile etc Page 68 GIS and SOBEK modelling RIZA By Geodan Geodesie B V Amsterdam _ Report a NN Date 03 06 99 Indicatieve breedtes per oever Lengte 395
87. te 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam 4 Additional GIS data Besides the use of GIS for simulating the river geometry for SOBEK other input for SOBEK can also be generated with geographic information 4 1 Soil rougnesses floodplain based on ecotopes In SOBEK it is possible to define a soil roughness for the floodplain for a certain river stretch This roughness is predominantly determined by the occuring vegetation types ecotopes The roughnesses per river stretch can be calculated using an ecotope map How this map can be used to calculate the roughness is further elaborated in paragraph 6 5 In chapter 7 an illustration is given of an ecotope map of the river Meuse 4 2 Rivier kilometers The file with river kilometers has predominantly an administrative purpose The exact length of the SOBEK compartments can be determined with the river axis file The file with river kilometers can be used when defining the SOBEK compartment boundaries and for generally locating the profiles The file can be created by making selections in a digital river map or by digitising river kilometers from a topographic map For the fileformat reference is made to the BASELINE data conventions CSO ESRI 1998 4 3 Measuring points Another useful aid in defining the compartment boundaries in the main channel are the measuring points the locations where water levels and or discharges are measured These locations als have great importanc
88. ximum elevation of the main channel HsubO This elevation corresponds to the elevation of level 5 in the SOBEK profile by default This level is defined as the 1 exceedance value of the elevations in the main channel However if there are groynes in a compartment which have elevations lower than the 196 exceedance level the groyne elevations are used To minimise the effect of outliers regression calculations are used 5 8 2 Function For the determination of the maximum level of the main channel Hsub0 it has be taken into account that the elevation is in agreement with the location of the normal lines The level should be chsoen high enough to ensure that at least 99 of the gridpoints between the normal lines are lower than the chosen elevation Besides that the maximum level of the main channel always has to be lower than the elevation of the groynes in the SOBEK compartments Hkrib and the maximum elevation of the bank section 5 8 3 Creation For the determination of the maximum elevation level of the main channel the following procedure can be used For each SOBEK compartment the 196 exceedance level is determined On relevant stretches from measuring point to measuring point this 1 exceedance level is plotted against the length of the river axis in a graph In this graph the groyne elevations are also plotted Regression lines are fitted through the groyne elevations and the 1 exceedance levels The regression line through the exc
89. y occur between reality and the schematised profile In this figure a geometric profile which is manually drawn through the heart of the compartment is compared to the calculated SOBEK profile Differences are caused by the following factors e SOBEK profile has only one bank from the lowest point in the main channel onwards Therefore it seems that the profile is constructed from the centre of the main channel The geometric profile starts at the boundary of the floodplain on one bank and ends at the boundary of the floodplain at the other bank The widths in the SOBEK profile are determined by dividing the area of the selected grid cells by the length of the compartment These widths can therefore differ from actual widths on a certain location in the SOBEK compartment In SOBEK profile all data within a SOBEK compartment are used The big difference between maximum elevation is caused by a relative high area close to a weir This area is located within the SOBEK compartment but falls outside the line drawn for the geometric profile E In a SOBEK profile the succeeding levels have to increase in height Therefore it may be that relatively low parts of the floodplain are embodied in the profile too soon These situation are corrected by defining dike segments see paragraph 3 7 Page 13 Report GIS and SOBEK modelling Date 03 06 99 For RIZA By Geodan Geodesie B V Amsterdam Height in cm NAP

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