Dane County Stormwater Manual

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dewatering [2022/05/13 09:51] – created admindewatering [2023/11/21 15:26] (current) – admin
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 The selection of the dewatering practice depends upon the predominant soil texture encountered at the dewatering site.  Refer to Figure 1, the USDA Soil textural triangle, to assist with classifying the soil of the site.  Figure 2, Dewatering Practice Selection Matrix, illustrates acceptable dewatering options and their effective ranges.  Pumping rates, volumes, and device effectiveness must also be considered when selecting a practice. The selection of the dewatering practice depends upon the predominant soil texture encountered at the dewatering site.  Refer to Figure 1, the USDA Soil textural triangle, to assist with classifying the soil of the site.  Figure 2, Dewatering Practice Selection Matrix, illustrates acceptable dewatering options and their effective ranges.  Pumping rates, volumes, and device effectiveness must also be considered when selecting a practice.
  
-[{{ :wiki:images:usda_soil_texture.png?600 |Figure 1: USDA Soil Textural Classification}}]+[{{ :wiki:images:usda_soil_texture.png?500 |Figure 1: USDA Soil Textural Classification}}]
  
 =====Practices===== =====Practices=====
 Dewatering can be preformed in a variety of ways and should be selected based upon the individual site characteristics.  The accepted dewatering practices are geotextile bags, gravity based settling systems, passive filtration systems, and pressurized filtration systems. Dewatering can be preformed in a variety of ways and should be selected based upon the individual site characteristics.  The accepted dewatering practices are geotextile bags, gravity based settling systems, passive filtration systems, and pressurized filtration systems.
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 +[{{ :wiki:images:dewatering_matrix.png?800 |Figure 2: Dewatering Matrix}}]
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 ====Geotextile Bags==== ====Geotextile Bags====
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 Portable sediment tanks are intended to settle only sands, loamy sands, and sandy loams.  If polymer is added, these tanks will additionally be appropriate for settling loams, silt loams and silts.  Portable sediment tanks should be at least three feet deep and have a minimum of two baffled compartments.  The inlet and outlet pipe should be a minimum diameter of three inches.  To account for the settling of suspended sediments, one must determine the appropriate size of a tank.  Multiply the pumping rate (gallon per minute) by 1.83 (a factor that includes the conversion from gpm to cfs and the particle settling velocity for Soil Class 1) to calculate the surface area of a tank in square feet. Portable sediment tanks are intended to settle only sands, loamy sands, and sandy loams.  If polymer is added, these tanks will additionally be appropriate for settling loams, silt loams and silts.  Portable sediment tanks should be at least three feet deep and have a minimum of two baffled compartments.  The inlet and outlet pipe should be a minimum diameter of three inches.  To account for the settling of suspended sediments, one must determine the appropriate size of a tank.  Multiply the pumping rate (gallon per minute) by 1.83 (a factor that includes the conversion from gpm to cfs and the particle settling velocity for Soil Class 1) to calculate the surface area of a tank in square feet.
  
-[[sediment trap|Sediment traps]] and [[sediment basin|basins]] are temporary sediment control devices, while [[wet basin|wet detention basins]] are generally permanent structures designed to address post-construction pollutant reduction requirements.  The design, installation, and operation of sediment traps and basins should meet WDNR requirements.+[[sediment trap|Sediment traps]] and [[sediment basin|basins]] are temporary sediment control devices, while [[wet pond|wet ponds]] are generally permanent structures designed to address post-construction pollutant reduction requirements.  The design, installation, and operation of sediment traps and basins should meet WDNR requirements.
  
 ====Passive Filtration Systems==== ====Passive Filtration Systems====
  
-Passive filtration systems also rely on filtration as the main means of removing sediment.  The distribution of particle size in the stormwater influences sediment removal efficiency.  Manufactured filters should be sequenced from the largest to the smallest pore opening.  Available are sand media filters with automatic backwashing features that can filter to 50 μm particle size, screen or bag filters that can filter down to 5 μm, and fiber wound filters that can remove particles down 0.5 μm. +Passive filtration systems also rely on filtration as the main means of removing sediment.  The distribution of particle size in the stormwater influences sediment removal efficiency.  Manufactured filters should be sequenced from the largest to the smallest pore opening.  Available are sand media filters with automatic backwashing features that can filter to 50 μm particle size, screen or bag filters that can filter down to 5 μm, and fiber wound filters that can remove particles down 0.5 μm. 
  
-Other practices include filter tanks, filter basins, [[vegetated buffer strip|vegetative filters]], grassed swales, and filtration fabric and should be installed, operated, and maintained according to manufacturer recommendations and WDNR.+Other practices include filter tanks, filter basins, [[buffer strip|buffer strips]], grassed swales, and filtration fabric and should be installed, operated, and maintained according to manufacturer recommendations and WDNR.
  
 ====Pressurized Filtration Systems==== ====Pressurized Filtration Systems====
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 =====Method to Determine Practice Efficiency===== =====Method to Determine Practice Efficiency=====
 Dewatering practices reduce the amount of suspended sediment in water that must be removed from a site through filtering methods.  The efficiencies for these practices vary by the type of device used and soil texture, pumping rates, volumes and device effectiveness.  Devices that are constructed on site will have an efficiency that is determined by calculating the settling efficiency for the device. Dewatering practices reduce the amount of suspended sediment in water that must be removed from a site through filtering methods.  The efficiencies for these practices vary by the type of device used and soil texture, pumping rates, volumes and device effectiveness.  Devices that are constructed on site will have an efficiency that is determined by calculating the settling efficiency for the device.
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-[[File:/Images/Dewatering Matrix.PNG]] 
  
 ==References== ==References==
-  *[[https://dnr.wi.gov/topic/stormWater/documents/Dewatering_1061.pdf|Wisconsin DNR Dewatering Conservation Practice Standard 1001]]+  *[[https://dnr.wisconsin.gov/sites/default/files/topic/Stormwater/1061Dewatering.pdf|DNR Dewatering Conservation Practice Standard 1061]]
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