Section 105.96. Outlet works

(a) Dams must include a device to allow the complete draining of the reservoir unless the Department determines that an outlet works is not feasible for a specific dam. At minimum, the device must be sized to pass a minimum of 70% of the highest mean monthly inflow at the site plus the capacity to drain the top 2 feet of reservoir storage below normal pool in 24 hours. The highest mean monthly flow shall be determined from statistics of an appropriate stream gage, as approved by the Department, transferred to the dam site by the ratio of the drainage areas. The Department may require an increased size to provide for the integrity of the dam and to protect life and property with an adequate margin of safety.

(b) In determining the reasonable time period for drainage of the reservoir, the dam owner, the dam owner’s engineer, and the Department may consider, without limitation, the following factors:

(1) The damage potential posed by possible failure of the dam.

(2) The risk and nature of potential failure and the time likely to be available to avert the failure after notice of conditions threatening the safety or stability of the dam.

(3) The purpose of the dam and reservoir.

(4) The capacity and stability of available drainage courses to convey the waters released from the reservoir in the event of emergency drainage.

(5) The influence of rapid drawdown on the stability of the dam, its appurtenant works and the upstream natural slopes of the reservoir.

(c) Under normal conditions, the maximum rate of drawdown for reservoirs impounded by earthfill dams should not exceed 1 foot per day without prior approval by the Department. Under emergency conditions, the maximum rate of partial or complete drawdown of reservoirs must be approved by the Department, when feasible.

(d) Each outlet works must include upstream closure, trashrack, and a means of dissipating the energy of flow at its outlet to assure conveyance of flow without endangering the safety and integrity of the dam or the natural environment of the stream.

The provisions of this § 105.96 adopted September 26, 1980, effective September 27, 1980, 10 Pa.B. 3843; amended January 7, 2011, effective January 8, 2011, 41 Pa.B. 219. Immediately preceding text appears at serial page (207721).

Notation

Authority

The provisions of this § 105.96 amended under section 5 of the Dam Safety and Encroachments Act (32 P. S. § 693.5).