The Turlock Irrigation District and Modesto Irrigation District, acting jointly, hereinafter called the Districts, shall operate Don Pedro Dam and Reservoir in the interest of flood control, and the City and County of San Francisco, hereinafter called the City, shall operate Hetch Hetchy Dam and Reservoir and Cherry Valley Dam and Reservoir in the interest of flood control all as follows:

(a) Storage space in Don Pedro Reservoir shall be kept available for flood-control purposes in accordance with the Flood-Control Storage Reservation Diagram currently in force for that reservoir, except when storage of floodwater is necessary as prescribed in paragraph (d) of this section. The Flood-Control Storage Reservation Diagram in force as of the promulgation of this section is that dated 4 April 1956, File No. TU-1-26-7, and is on file in the Office of the Chief of Engineers, Department of the Army, Washington, D.C., in the office of the Turlock Irrigation District, Turlock, California, and in the office of the Modesto Irrigation District, Modesto, California. Revisions of the Flood-Control Storage Reservation Diagram may be developed from time to time as necessary by the Corps of Engineers and the Districts. Each such revision shall be effective upon the date specified in the approval thereof by the Chief of Engineers and by the presidents of the Districts and from that date until replaced shall be the Flood-Control Storage Reservation Diagram currently in force for the purpose of this section. Copies of the Flood-Control Storage Reservation Diagram currently in force shall be kept on file in and may be obtained from the office of the District Engineer, Corps of Engineers, in charge of the locality, the office of the Turlock Irrigation District, Turlock, California, and the office of the Modesto Irrigation District, Modesto, California.

(b) Storage space in Hetch Hetchy Reservoir shall be kept available for flood-control purposes in accordance with the Flood-Control Storage Reservation Diagram for that reservoir currently in force, except when storage of floodwater is necessary as prescribed in paragraph (e) of this section. The Flood-Control Storage Reservation Diagram in force as of the promulgation of this section is that dated April 4, 1956, File No. TU-3-26-1, and is on file in the Office. Chief of Engineers, Department of the Army, Washington, D.C., and in the office of the Public Utilities Commission of the City and County of San Francisco, California. Revisions of the Flood-Control Storage Reservation Diagram may be developed from time to time as necessary by the Corps of Engineers and the City. Each such revision shall be effective upon the date specified in the approval thereof by the Chief of Engineers and by the Public Utilities Commission of the City and County of San Francisco, California, and from that date until replaced shall be the Flood-Control Storage Reservation Diagram currently in force for the purpose of this section. Copies of the Flood-Control Storage Reservation Diagram currently in force shall be kept on file in and may be obtained from the office of the District Engineer, Corps of Engineers, in charge of the locality, and the office of the Public Utilities Commission of the City and County of San Francisco, California.

(c) Storage space in Cherry Valley Reservoir shall be kept available for flood-control purposes in accordance with the Flood-Control Reservation Diagram currently in force for that reservoir except when storage of floodwater is necessary as prescribed in paragraph (e) of this section. The Flood-Control Storage Reservoir Diagram in force as of the promulgation of this section is that dated April 4, 1956, File No. TU-2-26-6, and is on file in the Office, Chief of Engineers, Corps of Engineers, Department of the Army, Washington, D.C., and in the office of the Public Utilities Commission of the City and County of San Francisco, California. Revisions of the Flood-Control Storage Reservation Diagram may be developed from time to time as necessary by the Corps of Engineers and the City. Each such revision shall be effective upon the date specified in the approval thereof by the Chief of Engineers and by the Public Utilities Commission of the City and County of San Francisco, California, and from that date until replaced shall be the Flood-Control Storage Reservation Diagram currently in force for the purpose of this section. Copies of the Flood-Control Storage Reservation Diagram currently in force shall be kept on file in and may be obtained from the office of the District Engineer, Corps of Engineers, in charge of the locality, and the office of the Public Utilities Commission of the City and County of San Francisco, California.

(d) Any water temporarily stored in the flood-control space indicated by the Flood-Control Storage Reservation Diagram currently in force for Don Pedro Reservoir shall be released as rapidly as can be accomplished without causing flows in Tuolumne River below LaGrange Dam to exceed 7,000 c.f.s. during rain floods or to exceed 9,000 c.f.s. at all other times.

(e) Any water temporarily stored in the flood-control space indicated by the Flood-Control Storage Reservation Diagrams currently in force for Hetch Hetchy and Cherry Valley Reservoirs shall be released as rapidly as can be accomplished without exceeding the respective safe channel capacities, and without materially contributing to major encroachment into the flood-control space at Don Pedro Reservoir. Such releases shall be proportioned between Hetch Hetchy and Cherry Valley Reservoirs in such manner as to assure that the percentage of encroachment into the flood-control space at the two reservoirs will tend toward equality insofar as possible. Whenever the storage space in Don Pedro Reservoir is less than 90 percent of that indicated by the Flood-Control Storage Reservation Diagram currently in force for that reservoir, releases from Hetch Hetchy and Cherry Valley Reservoirs shall be restricted to those required in connection with the generation of hydroelectric power in the power system of the City and in connection with diversion into the water supply system of the City.

(f) In the event that the water level in Don Pedro Reservoir rises above elevation 605.55 at the dam (top of spillway gates), subsequent operation of the dam shall be such as to cause downstream flows to exceed as little as possible the criteria prescribed in paragraph (d) of this section, and in no event to cause the maximum subsequent release from the reservoir to exceed the estimated maximum subsequent inflow to the reservoir.

(g) In the event that the water level in Hetch Hetchy Reservoir rises above elevation 3806 at the dam (top of spillway gates), subsequent operation of the dam shall be such as to cause downstream flows to exceed as little as possible the criteria prescribed in paragraph (e) of this section, and in no event to cause the maximum subsequent release from the reservoir to exceed the estimated maximum subsequent inflow to the reservoir.

(h) In the event that the water level in Cherry Valley Reservoir rises above elevation 4700 at the dam (spillway crest), subsequent operation of the dam shall be such as to cause downstream flows to exceed as little as possible the criteria prescribed in paragraph (e) of this section, and in no event to cause the maximum subsequent release from the reservoir to exceed the estimated maximum subsequent inflow to the reservoir.

(i) Nothing in the regulations of this section shall be construed to require dangerously rapid changes in magnitudes of releases from any of the reservoirs.

(j) The Districts shall procure such current basic hydrologic data, make such current determinations of required flood-control storage reservation in Don Pedro Reservoir, and current calculations of permissible releases from Don Pedro Reservoir as are required to accomplish the flood-control objectives of the regulations of this section.

(k) The City shall procure such current basic hydrologic data, and make such current calculations of permissible releases from Hetch Hetchy and Cherry Valley Reservoirs as are required to accomplish the flood-control objectives of the regulations of this section.

(l) The City shall keep the District Engineer, Corps of Engineers, in charge of the locality, and the Districts currently advised of reservoir releases, reservoir storages, basic operating criteria which affect the schedule of operations, and such other operating data as the District Engineer, Corps of Engineers, may request for Hetch Hetchy, Eleanor, and Cherry Valley Reservoirs.

(m) The Districts shall keep the District Engineer, Corps of Engineers, in charge of the locality, and the City currently advised of reservoir releases, reservoir storages, basic operating criteria which affect the schedule of operations, and such other operating data as the District Engineer, Corps of Engineers, may request for Don Pedro Reservoir.

(n) The flood-control regulations of this section are subject to temporary modification by the District Engineer, Corps of Engineers, if found necessary in time of flood emergency. Request for and action on such modifications may be made by any available means of communication, and such action shall be confirmed in writing under date of same day to the operating agency for the reservoir affected.