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--- infiltration_basin [2022/05/06 10:52] – admin
+++ infiltration_basin [2025/09/30 14:48] (current) – admin
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 ====== Infiltration Basin ======
+:!: The current version of WinSLAMM (10.5.0) overestimates evapotranspiration (ET) volume. Until a fix is implemented, ET may not be turned on in the model. :!:
 Infiltration basins are depressions that collect and store stormwater until it can infiltrate into the subsoil.  Sediment settles out in the device, and nutrients, metals, and organic material are adsorbed by the soil as the water infiltrates.  Infiltration basins may also be designed to reduce peak flows from a site if the storage capacity of the device is increased and a stable outlet structure is included in the design.
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   *Reduces thermal impacts of runoff
-Disadvantages
+**Disadvantages**
   *Limited functionality with frozen ground
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   *Requires frequent maintenance
   *Not applicable on sites with high sediment loads or sites with large concentration of hydrocarbons
+{{ :wiki:images:schematics:infiltration_basin_schematic.png?1000 |}}
 =====Design=====
-Infiltration basins are depressions that collect and temporarily store runoff and should be designed to drain within 48 hours.  To prevent erosion of the basin and to increase the infiltration capacity of the practice, they should be lined with vegetation that is tolerant to frequent inundation (refer to [[Seeding]] or [[Native Plants]]).  The effective infiltration area must receive runoff that has been pretreated.
+Infiltration basins are depressions that collect and temporarily store runoff and should be designed to drain within 24 hours.  To prevent erosion of the basin and to increase the infiltration capacity of the practice, they should be lined with vegetation that is tolerant to frequent inundation (refer to [[Seeding]] or [[Native Plants]]).  The effective infiltration area must receive runoff that has been pretreated.
-Stormwater must be delivered to the basin from pretreatment devices at non-erosive velocities to prevent erosion of the structure.  The pretreatment device must provide TSS reduction of 80% for a 1-year, 24-hour storm event.  Pretreatment for oil and grease separation may be necessary depending on tributary source areas.  Basins receiving runoff from rooftops only do not require pretreatment.
+Stormwater must be delivered to the basin from pretreatment devices at non-erosive velocities to prevent erosion of the structure.  The pretreatment device must provide TSS reduction of 60% for residential development and 80% for commercial, industrial or institutional development. Pretreatment for oil and grease separation may be necessary depending on tributary source areas.  Basins receiving runoff from rooftops only do not require pretreatment.
-The depth of the basin is dependent upon the infiltration rate of the soil and the retention time of the structure, and should have a length to width ratio of 3:1.  The bottom of the basin must be at least 3 feet above the seasonally high water table to prevent groundwater contamination.  Side slopes must be 3:1 or flatter to promote uniform infiltration and safety while making maintenance tasks, such as mowing, easier.  A drawdown device must be included to provide winter pass through, and allow for timely maintenance.
+The depth of the basin is dependent upon the infiltration rate of the soil and outlet design, but may not exceed 2 feet.  The bottom of the basin must be at least 3 feet above the seasonally high water table to prevent groundwater contamination.  Side slopes must be 3:1 or flatter to promote uniform infiltration and safety while making maintenance tasks, such as mowing, easier.  A drawdown device must be included to provide winter pass through, and allow for timely maintenance.
 In order to prevent channelized flow and extended localized ponding, large basins should be divided into multiple cells.  Level spreaders that distribute the runoff over the effective infiltration area of each cell should be utilized.  A drawdown device must be included for each cell in the basin.
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 =====Method to Determine Practice Efficiency=====
-If the basin includes a forebay that is used for sedimentation, the sediment removal efficiency calculations on the [[basin efficiency]] page may be used to calculate the level of pretreatment.
+[[http://www.winslamm.com/|WinSLAMM]], [[https://dnr.wi.gov/topic/stormwater/standards/recarga.html|RECARGA]] or other approved model must be used to determine the performance of this practice.  Additional information on the modeling of infiltration practices is found on the [[Infiltration Guidance]] page.
-In order to determine the infiltration performance of this practice WinSLAMM, RECARGA or other approved models may be used.  Additional information regarding acceptable modeling of infiltration practices is found on [[infiltration modeling]] page.
 ===References===
-[[https://dnr.wi.gov/topic/stormwater/documents/1003InfiltrationBasin.pdf|Wisconsin DNR Infiltration Basin Technical Standard 1003]]
+{{ :wiki:flyers:infiltration_basin_flyer.pdf | Infiltration Basin Guidance for Owners}}
+[[https://dnr.wisconsin.gov/sites/default/files/topic/Stormwater/1003InfiltrationBasin.pdf|DNR Infiltration Basin Technical Standard 1003]]