OCR Text |
Show ing the capacity available for low-flow seasons and low-flow "years; (b) water requirements of the watershed management program; (c) water re- quirements in the lower basin for other uses, such as sanitation; and (d) possible adjustments in the design ancd operation of navigation works so as to reduce wa, ter requirements. Reservoir operation and navigation.-The ex- pected navigation season on the Missouri is about 8 months. During this period a constant sustained flow of ad equate amount is most desirable for navi- gation. Reservoir control of floods tends to assist this objective by storing excess flows during flood periods for later release. Normally, floodwaters stored in the flood control portion of a reservoir are released immediately after the flood period at maxi- mum safe rates. However, when flood periods are seasonal sis they are on the upper Missouri main stem, wheie high flows occur during the March and June rises, it is possible to make joint use of the flood control portion of reservoirs by storing excess flows and holding them for release later in the year. Thus, in the main stem reservoirs there is a top zone of storage reserved exclusively for flood con- trol. Below it there is a joint use zone, which is used for flood control and which also is useful for other purposes. If flood flows are stored here they are re- leased later for various purposes, including naviga- tion. The space available which may benefit navi- gation therefore is greater than it could be under a different hydrologic regime. As details have not been fully planned, studies on the operation of the system of reservoirs are in progress. The latest series of studies, based on current estimates of irrigation and related deple- tions, have started with Fort Peck Reservoir, which is now operating, expanding to include the sit- uations expected as each succeeding reservoir is added to the system. This procedure is being fol- lowed to provide an integrated operation pattern, under which these reservoirs must be operated for efficient multiple-purpose use. The studies are being undertaken jointly by the Corps of Engineers, Bureau of Reclamation, and Federal Power Com- mission. Navigation also can be made compatible with hydroelectric power production. Although energy production will not be as great as if the reservoirs were operated for power production alone, a large energy output will be obtained. Main stem hydro- electric power plants are being installed to a capac- ity which, can utilize the flow for navigation. The proposed downstream Gavins Point Reservoir is large enough to permit daily and weekly reregula- tion of the releases from upstream power plants and even the flows. However, operation for navi- gation and for downstream pollution abatement requires larger releases during the 8-month summer season and smaller releases during the rest of the year, a variation of releases at odds with power requirements, impairing the character and value of power at some main stem projects.3 Later requirements of the watershed manage- ment program.-The proposed watershed manage- ment program of the Department of Agriculture may make important subtractions of water from the total available for all other uses in the middle and upper basin States. Some estimates suggest that as much as 5J/2 million acre-feet may be consumed in farm ponds, for water spreading, and other pur- poses. A study is currently in progress by the De- partment of Agriculture and the Corps of Engi- neers to estimate the amount of water required for on-the-farm and other uses contemplated in the agricultural program. This study is scheduled for completion early in 1951. Water requirements in the lower basin for pur- poses other than navigation.-Whether or not there is a navigation program, releases of water for sani- tation and domestic water supply in the lower basin will be essential. The Public Health Service esti- mates that the minimum required releases for these purposes during the navigation season are 20,000 cubic feet per second. This amount of water is a large percentage of that required for open-channel navigation, tentatively estimated at 25,000 to 30,000 cubic feet per second. As minimum re- quirements for sanitation and domestic water sup- ply on the lower river are likely to receive high priority in water allocation, navigation is assured of a significant percentage of the water needed to operate the proposed open channel. Adjustments possible in the design and operation of navigation works so as to reduce water require- ments for navigation.-Within the limits of ac- curacy of available basic hydrologic data, estimates of annual discharge on the Missouri show the fol- lowing average flows at Sioux City, Iowa: * 51-year period (1898-1948), 24.2 million acre- feet. * In coordinated operation of the reservoirs it is antici- pated that those upstream from Fort Randall can be operated as the power load requires. * Corps of Engineers. 199 |