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