Permits_and_Sediment_Discharge.pdf

Permits and Sediment Discharge

The Forest Service is currently applying for a 404 permit from the Army Corps of Engineers and a 401 permit from the State Water Resources Control Board. The proposed work is generally as follows.

1. The Forest Service will open the 36” diameter outlet valve in mid-September and drain the lake down to the top of the inlet of the outlet works, which is about 20’ above the bottom of the dam and the outlet pipe. This is the normal outlet path of water from the lake and shouldn’t cause any downstream water quality issues. This will leave up to 8’ of water and sediment around the extension of the inlet pipe and approximately 12’ of soil and mud around the lower inlet pipe; based on review of the Final Construction Report from 1984 (also furnished to interested contractors).

2. The contractor is responsible to finish dewatering and clearing the work area along the front of the dam and outlet works, completing the specified rehabilitation of the dam, and managing water flow through the work area from the lake and source streams. It is recommended that a lined coffer dam be constructed with an outlet pipe draining into the inlet pipe of the outlet works. Soil for construction of a coffer dam may be excavated from the lake bed from within the project limits shown on the drawings. Mud and muck from the area around the outlet works could be contained in basins in the lake bed. Contractors must propose a plan of work for this site preparation and water diversion work to be approved by the CO; and may propose other methods and materials for the coffer dam, and other methods and materials for mud and muck disposal to protect downstream water quality.

3. The constraints and limitations of permits which may be issued are unknown at this time.

However, we expect to limit site work and sediment management to areas within the lake bed, to maintain minimum down stream flows (assuming feeder streams have inflows to the lake) except for short disruptions such as for coffer dam construction, and to minimize sediment release downstream.

4. Once the work area is dewatered and cleared, and adequate provisions are in place to protect the work area and manage downstream flows, the remainder of the project work will be completed.