Seepage beds, often called " Dutch drains", are gravel-filled 

 ditches that dispose of stormwater by ground infiltration (Figure 38). 

 They can reduce total runoff volume and diminish local flood peaks in 

 any area where soil porosity is at least 0.12 foot per day. Seepage 

 pits and seepage beds are often used together. 



Figure 38. Samole infiltration system for runoff water showing the 

 design for (A) receptacle, (B) seepage pit, and (C) Dutch drain 

 (Source: Reference 71). 



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 TILE DRAIN 



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Like seepage drains, seepage pits are usually gravel -filled 

 structures that collect runoff and allow percolation into the soil (see 

 Figure 38C). Seepage pits, however, hold the runoff long enough to allow 

 filtration before release. As a result, they are more likely to become 

 clogged with sediments than are Dutch drains. A properly designed seepage 

 pit (also called a "dry well") will maintain infiltration at pre- 

 development levels and enhance the local water supply, provided that soil 

 porosity is at least 0.15 foot per day. It can be located centrally in a 



152 



