Wetlands Operation and Maintenance guide
Contents
1. too close to Should have been designed to suit Well placed baffles or islands in wetland may inlet preventing treatment of water before redirect and slow flows to increase treatment between inlet and outlet points discharge TROUBLESHOOTING cont WETLANDS STORMWATER DEVICE INFORMATION SERIES Wetland plants are growing over the edges and across surface of the pond Wetland plants are growing in shallow edges of pond e Constructed wetlands are designed to have plants growing large fringes across pond No action required unless plants are affecting pond function for instance clogging outlet structure Pond banks are eroding Water flowing down pond banks is eroding soils Stormwater outlet pipes direct flow at banks e Minor erosion can be repaired by replacing soil and stabilising with planting or other methods e Cause of erosion from direct discharge may be repaired for instance by extending pipes down into pond Extensive erosion due to continuing discharge may require erosion protection such as rip rap geotextile Water is leaking from the wetland and through the banks along pipes Leak collars around pipes have failed or have not been fitted correctly or at all This can lead to failure of banks Failure of pond banks can cause major damage at pond and downstream so qualified construction contractors should make immediate repairs This usually requires pond to be drained banks excavated2. WETLANDS Auckland Council 17 Te Kaunihera o Tamaki Makaurau What are constructed wetlands Constructed wetlands are large shallow planted ponds that filter stormwater runoff slow flows and help control flooding downstream Similar to natural wetlands they look attractive and provide home and shelter to wildlife Constructed wetlands help remove sediments nutrients and contaminants from incoming stormwater before discharging to downstream stormwater system or waterways This guide offers a general description of constructed wetlands Each constructed wetland is specifically designed to suit a particular site so construction details will be on design and site construction plans Correct construction levels are crucial for supplying suitable drainage for wetland plants How and when should maintenance be carried out Constructed wetlands need to be maintained in two main ways Firstly so they continue to work as designed filtering stormwater slowing flows and controlling downstream flooding and secondly to look attractive A full inspection of constructed wetlands should take place a year after construction is completed This may be carried out by the construction contractor to coincide with the end of the defects liability period The tables below give only typical timelines and actions for maintaining constructed wetlands This is a general guide each wetland should have its own detailed maintenance plan to suit the
3. abilise erosion Check energy dissipaters are adequate Inspect wetland plants for exotic or invasive nuisance water species and remove Control may be done manually or with appropriate herbicide by properly licensed and registered professional Follow up inspections may be needed during growing season e Check pumps and valves if present are functioning properly e Check moving parts for corrosion and lubricate if required 2 Years Wetland liner Sediment forebay e Inspect liner for leaks and fix as per manufacturer s or design specifications e Check the forebay for accumulated sediment In general the forebay should be dredged if sediment fills over 50 of design volume Test sediments for contaminants eg heavy metals PAHs prior to dredging and dispose of sediment to landfill or similar suitable for contaminant levels TROUBLESHOOTING Wetland water levels remain high Wetland is dry Stormwater discharging from the wetland looks dirty muddy or dark WETLANDS STORMWATER DEVICE INFORMATION SERIES hdl dlrs thi rev ca dk The outlet riser openings may be too e Unless water levels remain high for more than two days or flooding is a threat narrow to allow fast draining after a storm action may not be necessary Refer decision to supervisor if necessary Outlet structures are clogged e Check outlet structures and openings for blockage by debris or sediment and clean as necessary Invasive plants suc
4. d with swamp treated runoff Risers may have scruffy bottom Separated from sGithvaauaticenecies Fine species submerged at times dome to trap debris or baffles skimmer to main pond by a bund or di q i b Plants take up nutrients prevent water life and debris from flowing low dam SA NAE mains nitrogen and phosphorous downstream Some risers have drain down and contaminants such as oil p as well as slow flows valve for maintenance and grease break down and trap sediment ve VALE nf slow flows Debris screens forebay if included ies racks capture Forebay helps slow runoff pean and sediment drops to the 3 Main wetland Shallow wide pond of variable depth to 1m planted WETLANDS STORMWATER DEVICE INFORMATION SERIES MAINTENANCE SCHEDULE e Inspect and remove rubbish and debris from inlets Inlet e Check area around inlet especially energy dissipation rip rap structures for erosion and cracking and if present repair Trash racks and debris screens Inspect and clear all litter including leaves rubbish branches and any other if fitted material that would block flows Check racks for corrosion and replace if necessary Sediment forebay e Check the forebay for accumulated sediment In general the forebay should be dredged if sediment fills over 50 of design volume e Test sediments for contaminants eg heavy metals PAHs prior to dredging and dispose of sediment to landfill or similar suitable for contaminant l
5. evels Following Bund e Check for erosion or instability and repair if required storms Risers control structures grates outlet pipes Inspect control structures weirs orifices outfall pipes for leaks and blockages skimmers weirs and orifices Blockage could be sediment build up floating debris rubbish e Control structures could be overgrown with vegetation e Clear and remove all blockages to avoid local flooding Areas around control structure need to be clear of vegetation and rubbish to maintain stormwater flow A boat may be required to access the outlet Inspect outflow pipes for leaky joints or soil piping erosion e Check if anti seep collars need repair or replacement e Check outfall and water discharge areas for erosion and restore and stabilise erosion e Check energy dissipaters are adequate Emergency overflow or spillway e Check emergency overflow path remains clear of debris and blockages and remove any blockages Check flow path for erosion and repair as necessary Structural repairs must be repaired immediately to avoid catastrophic failure MAINTENANCE SCHEDULE cont Erosion and bark stability Following Water body storms Wildlife Soil Monthly pi Trash racks and debris screens if fitted WETLANDS STORMWATER DEVICE INFORMATION SERIES Inspect banks for settlement erosion scouring cracking sloughing seepage and rilling e Remove woody vegetation growth unless species specificall
6. h as raupo clogging pond 7 Remove plants by hand do not use herbicides area A maintenance valve is open e Check drain valves and shut if open Water leaking from cracks in outlet structure Inspect for cracks and repair as necessary Inspect for leaky joints at outlet pipes and repair Wetland in area of changing groundwater e Pond will remain dry as long as groundwater levels are low levels e Design for pond should have taken this into account so this may be normal for this wetland Ground water levels have dropped due to e Drought conditions cannot be solved until wet season restores wetland pond drought conditions levels Use drought opportunity to clean sediments from forebay and repair stormwater infrastructure High concentration of sediments washing e Check catchment for erosion areas including construction works into wetland especially silts and clays due to Check erosion controls are in place Add or repair erosion control as required erosion or construction in the catchment area Forebay full of sediment e Forebay usually needs more frequent clearing of sediment than wetland pond Dredging required when forebay water storage is around 50 of total volume Local works disturbing soils with rain washing Check erosion and sediment controls in place on local construction sites these into wetland Repair if necessary and stabilise areas of exposed soil where erosion occurring Wetland outlet constructed
7. leak collars repaired and pond banks reconstructed to original design specifications Dead or dying birds Botulism is a common killer of pond birds Birds ingest toxins produced by the bacteria Clostridium botulinum either from the water or by eating maggots or other infected food sources Botulism can occur when water levels are low often mid to late summer when pond water stagnates It can also appear after algal blooms when water oxygen levels are low e Remove all dead birds and animals from the area to reduce the spread of Botulism Avoid algal blooms see below e Maintain flows through the ponds to avoid stagnant water Improve shading over the water TROUBLESHOOTING cont Algal blooms Yellow green red or blue green coloured scum on the surface of the water Algae is naturally present in waterways Algal blooms occur in good growing conditions including stagnant or slow moving water high levels of nutrients and warm and sunny weather Animal pests present Dense plant cover and abundant food supply in wetlands supports many animals including pest species Plants are suffering extreme wet and dry Plants on edge of conditions pond dying WETLANDS STORMWATER DEVICE INFORMATION SERIES e Avoid blooms by reducing nutrients entering the wetland for instance controlling fertilizers from the surrounding area and by maintaining water flows Although there are a number of suggested ways
8. n may only access reproduce and use the publication in a secure digital medium or hard copy for responsible genuine non commercial purposes relating to personal public service or educational purposes provided that the publication is only ever accurately reproduced and proper attribution of its source publication date and authorship is attached to any use or reproduction This publication must not be used in any way for any commercial purpose without the prior written consent of AC AC does not give any warranty whatsoever including without limitation as to the availability accuracy completeness currency or reliability of the information or data including third party data made available via the publication and expressly disclaim to the maximum extent permitted in law all liability for any damage or loss resulting from your use of or reliance on the publication or the information and data provided via the publication The publication and information and data contained within it are provided on an as is basis
9. particular catchment size pollutant loads and inflows WETLANDS STORMWATER DEVICE INFORMATION SERIES WARNING CONTAMINATED SOIL Constructed wetlands treat stormwater run off so will collect contaminants in the sediments of the pond and forebay All material removed from these sites should be tested for contaminants before being disposed of at a suitable secure landfill Eight key components of a constructed wetland 5 Plants STORMWATER DEVICE INFORMATION SERIES Usually native plants in the pond and on littoral shelf Species chosen to suit various water level zones in wein aka For suitable species and planting guidelines refer to ARC kali ray Technical Report TR2009 083 Landscape and Ecology Values KIA within Stormwater Management Gng a 7 Emergency overflow Structure to allow extreme f NAA d Cel AG heavy rain flows to bypass Nana kn i wetland and drain downstream Caos sc to prevent overtopping of ee TAREN wetland banks May be in A aot nt eo eo outlet riser or separate aai 8 Anti seep collars p7 KA Collars are fitted to all pipework to prevent pond leakage and ae aa TN cay A en potential bank collapse from a oe AN Hay H erosion Erosion controls at inlet eee e anes eee e eee eT SY rip rap energy dissipaters 2 Sedimentation 4 Shallow wetland area 6 Risers outlets Littoral shelf Shoreline of the Outlet riser pipe or weir for discharge of pond plante
10. plit grass around pond monthly Schedules may vary depending on seasonal growth e Remove rubbish and other floating debris from wetland pond Inspect for algal blooms usually dense water discolouration or surface scum or fish kills these could indicate water has extremely low levels of oxygen eutrophication or high nutrient loads or pollutants Test water quality if these problems suspected MAINTENANCE SCHEDULE cont WETLANDS STORMWATER DEVICE INFORMATION SERIES Wildlife Soil Control pest species so they do not threaten birds and aquatic life of the wetland Remove dead animals especially water birds to prevent disease spread e Wet areas where mosquito mosquito larvae could breed need careful maintenance e Inspect for loss of soil on wetland banks from erosion If plants are struggling to grow soil fertilizer may be required but extra care must be taken to prevent fertilizer from entering wetland and local waterways 6 Monthly Bund Risers control structures grates outlet pipes skimmers weirs and orifices Littoral zones e Check area around inlet especially energy dissipation rip rap structures for erosion and cracking and if present repair e Check for erosion or instability and repair if required Inspect outflow pipes for leaky joints or soil piping erosion e Check if anti seep collars need repair or replacement e Check outfall and water discharge areas for erosion and restore and st
11. to deal with blooms few are proven to work The use of barley straw bales in the pond may work in some cases e Thin out vegetation where possible Set traps and poison in the area using recommended procedures such as careful poison placement and providing warning signs e Choose plant varieties suitable to local conditions e New plants need watering until established e Replace unsuitable varieties WETLANDS STORMWATER DEVICE INFORMATION SERIES Quick maintenance checks Avoid Do not let erosion go unchecked Repair and replace erosion A Check for leaks and erosion on and around banks controls if necessary especially at leak collars A Regularly clear rubbish and dead vegetation around outlet structures trash racks and forebay Do not let forebay volume reach over half full of sediment Dredge and dispose of to suitable landfill x Remove dead birds in case of botulism especially in hot humid conditions Prevent fertilizers pesticides and herbicides entering the pond to avoid algal blooms and polluting downstream waterways A Keep new plants watered and control weed species Do not ignore algal blooms and unusually dirty or dark pond water These can affect the health of the wetland and downstream waterways XxX X X X Disclaimer This publication is provided strictly subject to Auckland Council s AC copyright and other intellectual property rights if any in the publication Users of the publicatio
12. uctures grates outlet pipes skimmers weirs and orifices Emergency overflow or spillway Monthly Erosion and bark stability Landscaping Water body WETLANDS STORMWATER DEVICE INFORMATION SERIES e Inspect control structures weirs orifices outfall pipes for leaks and blockages Blockage could be sediment build up floating debris rubbish Control structures could be overgrown with vegetation e Clear and remove all blockages to avoid local flooding Areas around control structure need to be clear of vegetation and rubbish to maintain stormwater flow e Boat may be required to access outlet e Check emergency overflow path remains clear of debris and blockages and remove any blockages e Check flow path for erosion and repair as necessary Structural repairs must be repaired immediately to avoid catastrophic failure Inspect banks for settlement erosion scouring cracking sloughing seepage and rilling e Remove woody vegetation growth unless species specifically included in pond planting plans to avoid future root damage to banks Removal will require bank material replacement and repair compacted to design specification of maximum 90 dry soil density Inspect for pedestrian and cycle traffic or pathways on banks e Either restrict traffic by closing paths off or provide suitable resistant ground cover to avoid erosion from traffic e Clear wetland plants of weeds and prune and replace three monthly Mow s
13. y included in pond planting plans to avoid future root damage to banks Removal will require bank material replacement and repair compacted to design specification of maximum 90 dry soil density Inspect for pedestrian and cycle traffic or pathways on banks Either restrict traffic by closing paths off or provide suitable resistant ground cover to avoid erosion from traffic e Remove rubbish and other floating debris from wetland pond e Inspect for algal blooms usually dense water discolouration or surface scum or fish kills these could indicate water has extremely low levels of oxygen eutrophication or high nutrient loads or pollutants e Test water quality if these problems suspected Control pest species so they do not threaten birds and aquatic life of the wetland e Remove dead animals especially water birds to prevent disease spread Wet areas where mosquito mosquito larvae could breed need careful maintenance Inspect for loss of soil on wetland banks from erosion If plants are struggling to grow soil fertilizer may be required but extra care must be taken to prevent fertilizer from entering wetland and local waterways e Inspect and remove rubbish and debris from inlets Inspect and clear all litter including leaves rubbish branches and any other material that would block flows e Check racks for corrosion and replace if necessary MAINTENANCE SCHEDULE cont TIMING COMPONENT Risers control str
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