Detention Ponds And Basins - Missouri
Chapter 5Detention Ponds and BasinsPracticeDescriptionA dam designed to hold stormwater runoff and release the water slowlyto prevent downstream flooding and stream erosion. Detention pondsand basins are an extremely effective water quality control measureand significantly reduce the frequency of erosive floods downstream.Ideally, a detention pond will store at least the first 1/2 inch of runofffrom the design storm and release the remainder at the predevelopmentrate. Their usage is best suited to larger, more intensively developedsites of over 20 acres.Regular detention ponds have less storage and different outlet conduitsthan extended detention ponds. Both can have permanent pools of water or be designed as dry basins. Both can be designed to hold sediment.RecommendedMinimumRequirementsC. Rahm, NRCS. Platte Co.Detention pondsare designed tohold excessstormwater runoffand release itslowly to avoidfloodingdownstream areas.Prior to start of construction, detention ponds should be designed bya registered design professional. Plans and specifications should bereferred to by field personnel throughout the construction process.The detention pond should be built according to the planned gradesand dimensions.217
Detention Ponds and Basins218 Drainage Area: 20 to 50 acres Structure Life: 10 years or more Detention: 24 to 48 hour detention of runoff from the designstorm Trap efficiency: The length to width ratio of the basin should be2:1 or greater; 5:1 is optimal to capture fine sediments.Inlet: Locate as far upstream as possible from the outlet.Collector Channels: Leading to the detention pond should beconstructed of riprap, concrete or paved material to routewater to the detention pond. Anti-seep Devices: Either of the following is recommended: At least two watertight anti-seep collars should be used aroundthe outlet conduit; collars should project 1 to 3 feet from thepipe, or a sand diaphragm (see Glossary) Embankment Slopes: 2.5:1 or flatter; 3:1 where maintained bytractor or other equipment. Basin Slopes: No steeper than 3:1 and no flatter than 20:1 Vegetative Buffer: A minimum width of 25 feet around thepond (see Filter Strips) Settlement: Allow for at least 10% of extra fill Site Access: Reserved for bringing in heavy maintenanceequipment and to remove and dispose of sediments
Chapter 5Figure 5.43 Typical Detention PondConstructionSitePreparationLocate the detention pond as close to the stormwater collection system aspossible, considering pool area, dam length and spillway conditions. Locate all underground utilities. Clear, strip and grub the dam location,removing all woody vegetation, rocks and other objectionable material.Follow all federal, state and local requirements on impoundment sites.Dispose of trees, limbs, logs and other debris in designated disposalareas.Excavate the embankment foundation (outlet apron first), stockpilingany surface soil having high amounts of organic matter for later use.PrincipalSpillwayClear the sediment pool to facilitate sediment clean out.Situate the spillway pipe and riser on a firm, even foundation. Prepare the pipe bedding.Place around the barrel a 4-inch layer of moist, clayey, workable soil(not pervious material such as sand, gravel or silt), and compact withhand tampers to at least the density of the foundation soil. (Don’t raise219
Detention Ponds and Basinsthe pipe from the foundation when compacting under the pipe haunches.)Perforate the top 12 inches of the riser with 1/2-inch diameter holesspaced 3 inches apart. Set the top elevation of the riser to allow thedetention pond to store the first 1/2 inch of basin runoff in this 12-inchperforated zone, or according to the design plan.Embed the riser at least 12 inches into concrete (which serves as ananti-flotation block). The weight of the concrete should balance thebuoyant force acting on the riser.Buoyant Force Volume of Riser x 62.4 lbs/ft3Surround the base of the riser with 2 feet of clean uniformly gradedstone.Place a trash rack around the riser inlet. The trash rack should have 4to 6-inch square openings.At the pipe outlet, install a riprap or concrete apron at least 5 feet wideand 10 feet long to a stable grade.Optional: A slotted or V-notch weir, constructed within an open channel spillway, can be used in place of a riser and conduit as a principalspillway.EmbankmentScarify the embankment foundation before placing fill.Use fill from predetermined borrow areas. It should be clean, stable,mineral soil free of organic material, roots, woody vegetation, rocksand other debris; and must be wet enough to form a ball without crumbling, yet not so wet that water can be squeezed out.Place the most permeable soil in the downstream toe and the leastpermeable in the center portion of the dam.Compact the fill material in 6- to 8-inch continuous layers over thelength of the dam. (One way is by routing construction equipmentover the dam so that each layer is traversed by at least one wheel of220
Chapter 5the equipment). Tracked construction equipment does not provideadequate compaction.Protect the spillway barrel with 2 feet of hand tamped, compacted fillbefore traversing over the pipe with equipment.Place a stake at the height sediment must be cleaned out of the basin(50% of design elevation).EmergencySpillwayConstruct the spillway in undisturbed soil around one end of the embankment and locate it so that all excess flow will return to the receivingchannel without damaging the embankment.ErosionControlStabilize the spillway with vegetation as soon as grading is complete;or install paving material to finished grade if the spillway is not to bevegetated.Minimize the size of all disturbed areas. At the completion of each phaseof construction, vegetate the disturbed areas to minimize erosion.Use temporary diversions to prevent surface water from running ontodisturbed areas.Divert sediment-laden water to the upper end of the sediment pool toimprove trap effectiveness.Direct all runoff into the pond at low velocity.Stabilize all disturbed areas (except the lower one-half of the sedimentbasin) immediately after construction.SafetyBecause detention ponds that impound water are hazardous, the following precautions should be taken: Avoid steep slopes; cut and fill slopes should be 2.5:1 or flatter;3:1 where maintained by tractor or other equipment. Fence area and post with warning signs if trespassing is likely.221
Detention Ponds and Basins Provide a means of dewatering the basin between storm events.ConstructionVerificationCheck the finished grades and configuration for all earthwork. Checkelevations and dimensions of all pipes and structures.TroubleshootingConsult with registered design professional if any of the followingoccur:Maintenance Seepage is encountered during construction; it may be necessaryto install drains. Variations in topography on site indicate detention pond willnot function as intended. Design specifications for fill, pipe, seed variety or seeding datescannot be met; substitutions may be required. Unapprovedsubstitutions could lead to failure.Inspect the detention pond after each storm event.Remove and properly dispose of sediment when it accumulates toone-half the design volume.Periodically check the embankment, emergency spillway and outletfor erosion damage, piping, settling, seepage or slumping along thetoe or around the barrel; and repair immediately.Remove trash and other debris from the riser, emergency spillwayand pool area. Clean or replace the gravel around the riser if the sediment pool does not drain properly. Remove nuisance vegetation onembankment.Remove rodents that burrow into the dam.222
Chapter 5CommonProblemsPiping failure along conduit; caused by improper compaction, omission of anti-seep collar, leaking pipe joints or use of unsuitablesoil—repair damage, check pipe joints and seal leak if necessary. Usesuitable soil for backfill. Consider installing anti-seep collar.Erosion of spillway or embankment slopes; caused by inadequate vegetation or improper grading and sloping—repair damage and establishsuitable grade and/or vegetation.Slumping and/or settling of embankment; caused by inadequate compaction and/or use of unsuitable soil—excavate failed material andreplace with properly compacted suitable soil.Slumping failure; caused by steep slopes—excavate failed material andreplace with properly compacted suitable soil. Consider flattening slope.Erosion and caving below principal spillway; caused by inadequate outlet protection—repair damaged area and install proper outlet protection.Basin not located properly for access; results in difficult and costlymaintenance—relocate basin to more accessible area or improve access to site.Sediment not properly removed; results in inadequate storage capacity—remove sediment at regular frequent intervals and after major storms.Lack of anti-flotation; results in riser damage from uplift—install antiflotation structure.Lack of trash guard; results in the riser and barrel being blocked withdebris—remove blockage and install properly designed trash guard.Principal and emergency spillway elevations too high relative to topof dam; results in overtopping—lower principal and emergency spillway elevations to decrease overtopping potential.Sediment disposal area not designated on design plans; results in improper disposal of accumulated sediment—locate acceptable disposalarea and indicate location on plans.223
Detention Ponds and BasinsSafety and/or health hazard from pond water; caused by gravel clogging the drainage system—clean out clogged drainage system onregular basis.Principal spillway too small; results in frequent operation of emergency spillway and increased erosion potential—consider increasingcapacity of principal spillway, install supplemental spillway or installsuitable erosion protection in emergency spillway.Stormwater released from pond or basin too rapidly; caused by spillway pipe sized too large—consider resizing spillway pipe.224
Chapter 5Extended Detention Ponds and BasinsPracticeDescriptionA dam designed to hold stormwater runoff for a prolonged time andrelease the water slowly to prevent downstream flooding, stream erosion and pollution. Extended detention ponds and basins improvethe quality of runoff by retaining chemical-laden sediment. They alsosignificantly reduce the peak flow rate from flood events, thus reducing the frequency of erosive floods downstream. Ideally, an extendeddetention pond will store the first 1 inch of runoff and release the remainder at the predevelopment rate. Their usage is best suited to large,intensively developed sites of over 20 acres.Extended detention ponds differ from regular detention ponds by having additional storage. Both can have permanent pools of water(retention basin) or be designed as dry basins. Both can be designedto hold sediment.RecommendedMinimumRequirementsR. Braun, NRCS. St. Charles Co.Extended detentionponds are designedto hold excessrunoff. Theyreduce the impactof increasingimpervious surfacesin the watershed.Prior to start of construction, extended detention ponds should bedesigned by a registered design professional. Plans and specificationsshould be referred to by field personnel throughout the constructionprocess. The extended detention basin should be built according toplanned grades and dimensions.225
Extended Detention Ponds and Basins226 Drainage Area: 20 to 100 acres Structure life: 10 years or more Detention: 24 to 72 hour detention of runoff from the designstorm Extended Detention Control Device: Usually consists of asmall drawdown pipe or a subsurface drain Collector Channels: Constructed of riprap, concrete or pavedmaterial to route water to the detention pond. Locate collectorchannels as far upstream as possible from the detention pondoutlet. Anti-seep Devices: Either of the following is recommended: At least two watertight anti-seep collars should be used aroundthe outlet conduit; collars should project 1 to 3 feet from thepipe, or a sand diaphragm (see Glossary) Embankment Slopes: 2.5:1 or flatter; 3:1 where maintained bytractor or other equipment Basin Slopes: No steeper than 3:1 and no flatter than 20:1 Vegetative Buffer: A minimum width of 25 feet around thepond (see Filter Strips) Settlement: Allow at least 10% of extra fill Site Access: Reserved for the passage of heavy equipment andto remove and dispose of sediments Location: As close to the stormwater collection system aspossible, considering pool area and spillway conditions
Chapter 5ConstructionSitePreparationLocate all underground utilities.Follow all federal, state and local requirements.Clear, grub and strip the dam foundation removing all woody vegetation, rocks and other objectionable material.Dispose of trees, limbs, logs and other debris in designated disposalareas.Excavate the principal spillway area (outlet apron first), stockpilingany surface soil having high amounts of organic matter for later use.Clear the sediment pool to facilitate sediment clean out.PrincipalSpillwaySituate the spillway pipe and riser on a firm, even foundation. Prepare the bedding for the pipe.Place around the barrel a 4-inch layer of moist, clayey, workable soil (notpervious material such as sand, gravel or silt); and compact with handtampers to at least the density of the foundation soil. (Don’t raise thepipe from the foundation when compacting under the pipe haunches.)Figure 5.44 Typical Extended Detention Pond227
Extended Detention Ponds and BasinsConstruct an orifice hole in the riser at normal pool or connect a 6-inchdiameter low level drawdown pipe to the riser with the pipe inlet atthe normal pool elevation. Set the normal pool elevation to allowenough storage between the pipe and the top of the riser for the firstinch of runoff, or according to the design plan.Embed the riser at least 12 inches into concrete (which serves as ananti-flotation block). The weight of the concrete should balance thebuoyant force acting on the riser.Buoyant Force Volume of Riser x 62.4 lbs/ft3Place a trash rack around the riser inlet. The trash rack should have 4to 6- inch square openings.At the pipe outlet, install a riprap or concrete apron at least 5 feet wideand 10 feet long to a stable grade.Optional: A slotted or V-notch weir, constructed within an open channel spillway, can be used in place of a riser and conduit as a principalspillway.EmbankmentScarify the embankment foundation before placing fill.Use fill from predetermined borrow areas. It should be clean, stablesoil free of organic material, roots, woody vegetation, rocks and otherdebris; and must be wet enough to form a ball without crumbling, yetnot so wet that water can be squeezed out.Place the most permeable soil in the downstream toe and the leastpermeable in the center portion of the dam.Compact the fill material in 6- to 8-inch continuous layers over thelength of the dam. (One way is by routing construction equipmentover the dam so that each layer is traversed by at least one wheel ofthe equipment). Tracked construction equipment does not provideadequate compaction.Protect the spillway barrel with 2 feet of compacted hand-tamped fill228
Chapter 5before traversing over the pipe with equipment.Place a stake at the height sediment must be cleaned out of the basin(50% of design elevation).EmergencySpillwayConstruct the spillway in undisturbed soil around one end of the embankment and locate it so that all excess flow will return to the receivingchannel without damaging the embankment.Stabilize the spillway with vegetation as soon as grading is complete;or install paving material to finished grade if the spillway is not to bevegetated.ErosionControlMinimize the size of disturbed areas. At the completion of each phaseof construction, vegetate the disturbed areas to minimize erosion.Use temporary diversions to prevent surface water from running ontodisturbed areas.Divert sediment-laden water to the upper end of the sediment pool toimprove trap effectiveness.Direct all runoff into the pond at low velocity.Stabilize all disturbed areas (except the lower one-half of the sedimentbasin) immediately after construction.SafetyBecause extended detention ponds that impound water are hazardous, the following precautions should be taken: Avoid steep slopes; slopes around the extended detention pondshould be 2.5:1 or flatter; 3:1 where maintained by tractor orother equipment. Fence area and post with warning signs if trespassing is likely. Drain the basin to normal pool elevation between storm events. Determine effect on life and property in case of dam failure.Alter design to incorporate necessary safety.229
Extended Detention Ponds and BasinsConstructionVerificationCheck the finished grades and configuration for all earthwork. Checkelevations and dimensions of all pipes and structures.TroubleshootingConsult with registered design professional if any of the followingoccur:Maintenance Seepage is encountered during construction; it may be necessaryto install drains. Variations in topography on site indicate detention pond willnot function as intended. Design specifications for fill, pipe, seed variety or seeding datescannot be met; substitutions may be required. Unapprovedsubstitutions could lead to failure.Inspect the extended detention pond after each storm event.Periodically check the embankment, emergency spillway and outletfor erosion damage, piping, settling, seepage or slumping along thetoe or around the barrel; and repair immediately.Remove trash and other debris from the riser, emergency spillwayand pool area.Clean or replace the gravel around the riser if the sediment pool doesnot drain properly.Remove rodents that burrow into dam.CommonProblems230Piping failure along conduit; caused by improper compaction, omission of anti-seep collar, leaking pipe joints or use of unsuitablesoil—repair damage, check pipe joints and seal leak if necessary. Usesuitable soil for backfill. Consider installing anti-seep collar.
Chapter 5Erosion of spillway or embankment slopes; caused by inadequate vegetation or improper grading and sloping—repair damage and establishsuitable grade and/or vegetation.Slumping and/or settling of embankment; caused by inadequate compaction and/or use of unsuitable soil—excavate failed material andreplace with properly compacted suitable soil.Slumping failure; caused by steep slopes—excavate failed material andreplace with properly compacted soil. Consider flattening slope.Erosion and caving below principal spillway; caused by inadequate outletprotection—repair damaged area and install proper outlet protection.Basin not located properly for access; results in difficult and costlymaintenance—relocate basin to more accessible area or improve access to site.Sediment not properly removed; results in inadequate storage capacity—remove sediment at regular frequent intervals and after major storms.Lack of anti-flotation; results in riser damage from uplift—install antiflotation structure.Lack of trash guard; results in the riser and barrel being blocked withdebris—remove blockage and install properly designed trash guard.Principal and emergency spillway elevations too high relative to topof dam; results in overtopping—repair erosion damage and reevaluate spillway design.Sediment disposal area not designated on design plans; results in improper disposal of accumulated sediment—locate acceptable disposalarea and indicate location on plans.Safety and/or health hazard from pond water; caused by gravel clogging the drainage system—clean out clogged drainage system onregular basis.231
Extended Detention Ponds and BasinsPrincipal spillway too small; results in frequent operation of emergency spillway and increased erosion potential—consider increasingcapacity of principal spillway, install supplemental principal spillwayor install suitable erosion protection in emergency spillway.Stormwater released from pond or basin too ra
Detention Ponds and Basins 218 Drainage Area: 20 to 50 acres Structure Life: 10 years or more Detention: 24 to 48 hour detention of runoff from the design storm Trap efficiency: The length to width ratio of the basin should be 2:1 or greater; 5:1 is optimal to capture fine sediments. Inlet: Locate as far upstream as possible from the outlet.
Spa Ponds was purchased FTNCG by in May 2014, and in March 2015 the deeds (Title number NT502006) were registered in the name of the Official Custodian for Charities. Figures 1a and 1b. Spa Ponds Nature Reserve Map and Aerial View Habitats at Spa Ponds include: semi-natural broadleaved woodland, freshwater ponds, and a section of the River Maun.
8/1 8/16 9/1 9/16 10/1 10/16 80 60 40 20 0 Embanked ponds Creek-fed ponds A. B. A. C. B. D. C. Both cells lack a nucleus. D. Both cells undergo meiosis. Infection in embanked ponds increased during the sampling period. Both cells contain a mitochondrion. Protozoans were more common in creek-fed ponds than embanked ponds. Both cells contain .
into the design of the retention basins and have become standard with these constructions today. The electronic capture of the basins is conducted by Graz University of Technology, Institute of Hydraulic Engineering and Water Resources Management. The aim of this work is to create a tool for optimizing the management of the basins.
and how many fish you can harvest each year. Most farm ponds in Texas are built for livestock watering and are less than 1 acre in surface area. Although owners of small ponds traditionally want “bass in their tanks,” these small ponds are really not suited for bass
ponds that breed tropical fish that are used as pets commonly known as aquariums instead of ponds, and ponds that breed fish for food. Our focus in this paper are the ponds that bread fish for food, typically
method of decreasing both field erosion and sedimentation. If your future plans include water drawdown for pond reconstruction, now is the time to plan for drainpipes, risers, valves, etc. Stormwater Ponds Urban stormwater ponds, technically called wet detention areas, have the primary purpose of flood control.
Caltrans Stormwater Quality Handbooks Detention Basins Design Guidance December 2020 . . AASHTO American Association of State Highway Transportation Officials . ASTM American Society of Testing and . removal effectiveness for nutrients as noted in TC-22 of the California Stormwater Quality Association (CASQA) manual (CASQA 2003). They are .
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