Figure 8A-12D: Inlet Protection (Type 4)

8A.04.4Sediment TrapFigure 8A-13: Sediment TrapA sediment trap consists of a small, temporary ponding area with a rock weir or perforated riser pipeat the outlet formed by excavation or by constructing a weir. The sediment trap serves drainageareas five acres and smaller and has a design life of approximately six months.A. Applications1. Drainage areas which are 5 acres and smaller.2. Sites in proximity to rivers/streams, wetlands, or phosphorus-sensitive water bodies.3. Sites where major clearing and grading is likely to occur during the wet season.4. Sites with downstream erosion or sedimentation problems.5. Downslope of disturbed areas.B. Combining with Permanent Drainage Facilities1. If a project includes a permanent storm water retention/detention pond, the rough gradedor final-graded facility could function as a trap during construction. Design features ofthe permanent structure, such as surface area, retention time, and outlet control, shouldmeet the design requirements of the temporary facility. Completion of the permanentfacility should occur only when all upstream control structures are in place andstabilization of contributing drainage areas is complete.2. If a project includes an infiltration facility, the roughly excavated facility could be usedas a trap or basin the facility provides the surface area and retention time required by thetrap or basin. Excavate the sides and bottom of the facility to a minimum of two feetabove final grade with a backhoe working at "arms length" to minimize disturbance andcompaction of the infiltration surface.Section I - DESIGN STANDARDS 8A - 47 EDSP 2002