The Bureau of Reclamation, or its designated agent, shall operate the Twin Buttes Dam and Reservoir in the interest of flood control as follows:
(a) Whenever the Twin Buttes Reservoir level is between elevations 1,940.2 (top of conservation pool) and elevation 1,969.1 (top of flood control pool) the flood control discharge facilities shall be operated under the direction of the District Engineer, Corps of Engineers, Department of the Army, in charge of the locality, so as to reduce as much as practicable the flood damage below the reservoir. All flood control releases shall be made in amounts which, when combined with releases from San Angelo Reservoir on the North Concho River and local inflow below the dam, will not produce flows in excess of bankful capacities on the South Concho and Concho Rivers downstream of the reservoir. In order to accomplish this purpose, flows shall not exceed a 22.5-foot stage (25,000 c.f.s.) on the USGS gage on the Concho River near San Angelo, Tex. (river mile 60.9); or a 22.8-foot stage (25,000 c.f.s.) on the USGS gage near Paint Rock, Tex. (river mile 19.6).
(b) When the Twin Buttes Reservoir level exceeds elevation 1,969.1 (top of flood control pool), releases shall be made at the maximum rate possible and continued until the pool elevation recedes to elevation 1,969.1 when releases shall be made to equal inflow or the maximum release permissible under paragraph (a) of this section, whichever is greater.
(c) The representative of the Bureau of Reclamation in immediate charge of operation of the Twin Buttes Dam shall furnish daily to the District Engineer, Corps of Engineers, Department of the Army, in charge of the locality, a report, on forms provided by the District Engineer for this purpose, showing
(1) for Twin Buttes Reservoir, the elevation of the reservoir level; number of river outlet works gates in operation with their respective openings and releases; uncontrolled spillway releases; storage; reservoir inflow; available evaporation data; and precipitation in inches; and
(2) for Nasworthy Reservoir, the elevation of the reservoir level; irrigation outlet works and controlled spillway releases; storage; tailwater elevation; and reservoir inflow. Normally, one reading at 8 a.m. shall be shown for each day. Readings of all items except evaporation shall be shown for at least three observations a day when the Twin Buttes Reservoir level is above elevation 1,940.2. Whenever the Twin Buttes Reservoir level rises to elevation 1,940.2 and releases for flood regulation are necessary or appear imminent, the Bureau representative shall report at once to the District Engineer by telephone or telegraph and, unless otherwise instructed, shall report once daily thereafter in that manner until the reservoir level recedes to elevation 1,940.2. These latter reports shall reach the District Engineer by 9 a.m. each day.
(d) The regulations of this section insofar as they govern use of the flood control storage capacity in Twin Buttes Reservoir above elevation 1,940.2 are subject to temporary modification in time of flood by the District Engineer, if found desirable on the basis of conditions at the time. Such desired modifications shall be communicated to the representative of the Bureau of Reclamation in immediate charge of operations of the Twin Buttes Dam by any available means of communication and shall be confirmed in writing under date of the same day to the Regional Director in charge of the locality, with a copy to the representative in charge of the Twin Buttes Dam.
(e) Flood control operation shall not restrict releases necessary for municipal, industrial, and irrigation uses.
(f) Releases made in accordance with the regulations of this section are subject to the condition that releases shall not be made at rates or in a manner that would be inconsistent with emergency requirements for protecting the Twin Buttes Dam and Reservoir from major damage or inconsistent with safe routing of the inflow design flood (spillway design flood).
(g) The discharge characteristics of the river outlet works (capable of discharging approximately 32,470 c.f.s. with the reservoir level at elevation 1,969.1) shall be maintained in accordance with the construction plans (Bureau of Reclamation Specifications No. DC-5274 as modified by revised drawings and criteria in Designers' Operating Criteria, Twin Buttes Dam, dated February 1963).
(h) All elevations stated in this section are at Twin Buttes Dam and are referred to the datum in use at that location.
[31 FR 12521, Sept. 22, 1966]