Sediment Retention Structures

Reservoirs used to store runoff will trap a large portion of suspended sediments in the runoff. Criteria and general procedures needed to determine the volume required for sediment accumulation and its allocation in the reservoir are contained in the USDA-NRCS National Engineering Handbook-3 (NEH), Sedimentation. NEH-3 includes procedures for determining:

1. sediment yield for present and future conditions after planned land treatment measures are applied in the drainage area of the dam;
2. trap efficiency of the reservoir;
3. distribution and types of sediment expected to accumulate;
4. proportion of submerged and aerated sediments; and
5. sediment densities and compaction.

If the amount of sediment accumulation calculated exceeds two watershed inches in 50 years for the uncontrolled drainage area of the dam, it will be necessary to reevaluate the entire watershed to determine if more economical methods of reducing sediment yield or trapping sediment may be feasible and applicable.

The following information is extracted from the NRCS TR-60 publication -
Earth Dams & Reservoirs (July 2005).

Example of an entire sediment retention structure
Example of a discharge structure within a sediment retention reservoir

Photo acknowledgements to Dennis Hoffman, BREC.