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Show ment is not known so that measures cannot be taken to increase it. Data on the quantity and safe yield of ground water are badly needed, as are also data on its quality. It is known that in some areas, ground water is so highly mineralized as to be unfit for use. (See table 5, chapter 3, and Problem A-4.) Water yields and losses.-Much opposition to plans for Missouri Basin improvements grew out of fear that upstream demands for irrigation water would prevent navigation in the downstream reaches, or vice versa. Hydrologic data did not permit a firm determination of the availability of water at any given point because of inadequate precipitation and stream-flow records, inadequate analysis of climatic data, especially of evaporation, amount of water loss by plants, losses due to changes in agriculture, especially dry land to irrigation, or added increments to stream flow due to forest practices. There is a general lack of information as to the most efficient use of water when applied to land. Under present irrigation practices, especially flood irrigation, much water is wasted. Some studies have been made to determine more efficient and less costly practices, but most of these relate to only a few types and crops. Considering the vast area with its varied soils and climates and its many different crops, only a beginning has been made. Vegetation of different types and evaporation withdraw soil water in different amounts accord- ing to rooting characteristics, density, exposure, and soil type. As irrigated crops replace native vegetation or dry land crops, water requirements will increase materially. The difference between supply and consumptive use in a drainage is avail- able for replenishing surface or underground waters. Only limited estimates are presently avail- able as to this balance, although many estimates have been made as to the amount of water avail- able after upstream demands have been met. Estimates of the consumptive use of water, espe- cially by riparian vegetation, are generally unsat- isfactory. The many thousand acres of such vege- tation in the basin consume large amounts of water, much of which might be recaptured. If adequate information were available, it is possible that the designs of reservoirs and costly spillways could be altered and that water programs would be modified. Under some circumstances increased stream flow can be made available by forest and range practices which reduce evaporation and other losses. Their value needs to be demonstrated on a sufficient scale. Research is also needed on other watershed man- agement methods to govern rates and amount of water flow and to control sediment production. Soils.-About one-third of the basin has been covered by detailed soil surveys. These cover essentially all of the basin area in Iowa, Missouri, and Nebraska, and small sections-less than 10 counties in a State-of tihe other States. Only about one-third of these soil surveys can be con- sidered adequate for planning purposes. About half are sufficiently accurate for generalized use, but not for detailed planning as for irrigation or other proposed land use clianges. Some 12 mil- lion acres of lands either no^v irrigated or scheduled for early application of water should be mapped in sufficient detail to permit satisfactory farm plan- ning. On new projects, the detail of soil mapping and classification should provide the essential in- formation required by all the agencies working in the area. Such surveys of public lands are particu- larly needed as a basis for good management. Soil analyses are needed to determine amounts and kinds of soluble salts, presence of alkali, and physical soil properties, to assure effective planning for irrigation, drainage, farm lay-outs, and cropping systems. Such surveys are currently in progress. About 3 million acres need surveys to appraise their irrigation potentialities before irrigation projects are undertaken. These studies must precede engi- neering plans for water use. Lack of soils information may also be held re- sponsible for the lack of sedimentation data. In recent years, the sediment problem has been recog- nized as a very important one in the Missouri Basin in view of the large sediment loads carried by the river and the problems such as accumulation of sediment in the reservoirs or the degradation of parts of the alluvial valley by the clear water re- leased from the reservoirs. Recent developments in sediment sampling and analysis have resulted in more dependable records of sediment load. These records are available for only a relatively short period. However, the sediment program, which has been under way for a relatively long period, pro- vides data which give a good indication of sediment load which has been used for a conservative estimate of the sediment storage required in reservoirs. The mechanics of sediment transport are, as yet, not fully determined. These Inadequacies in basic records and techniques provide probably the great- est opportunities for advancement in the near future in the field of basic data. Maps.-Topographic maps of a high standard 196 |
