SEDIMENT TRAP

Definition

A temporary sediment control device formed by excavation and/or an embankment with an approved outlet used to intercept sediment laden runoff and to retain the sediment.            

Purpose

The purpose of a sediment trap is to intercept sediment laden runoff and trap the sediment in order to protect drainageways, properties, and rights-of-way downstream of the sediment trap from sedimentation.

Conditions Where Practice Applies

A sediment trap is installed at points of discharge from a disturbed area.

Wet and Dry Storage

The storage requirement for sediment traps I, II and IV is 3600 cubic feet per acre of contributory drainage area. The sediment trap storage volume of 3600 cubic feet minimum per acre shall be divided equally into “dry” or dewatered storage and “wet” or retention storage. The traps will be dewatered to the wet pool elevation corresponding to 1800 cubic feet of storage per acre of drainage. Sediment trap III consists of only “wet” storage and the volume required is 5400 cubic feet per acre of drainage area.

Types of Traps

1.   Pipe outlet sediment trap ST-I: The outlet for the trap is through a perforated riser and a barrel pipe through the embankment. Max. drainage area: 5 acres

2.   Stone outlet sediment trap ST-II: The outlet of this trap is over a stone section placed on level ground. Max. drainage area: 5 acres

3.   Rip-rap outlet sediment trap ST-III: The outlet for this trap shall be through a partially excavated channel lined with rip-rap or recycled concrete equivalent. Max. drainage area: 10 acres

4.   Stone/rip-rap outlet sediment trap ST- IV: The outlet for this trap shall be through a partially excavated channel lined with rip-rap and containing a stone or recycled concrete equivalent outlet structure. Max drainage area: 10 acres

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