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~ 39. The Arkansas River in Colorado is often dry or nearly so, except in the headwater reaches, because the normal streamflow is di- verted for irrigation purposes. When tributary streams are in flood they discharge large quantities of sediment into the main stem and, unless the river is at high stage, the peak of the tributary flood is rapidly diminished by val ley storage and the sediment load is deposited in the channel. The result is an acceleration of aggradation which causes channel changes, creates sandbars, and reduces the channel capacity. The reduction in channel capacity increases the damages from bank caving during minor tloods ot trequent occurrence and trom inun- dation by less trequent floods. '. 40. The aggradation of the streambed ot the Arkansas River and the accompanying rise in the water table have created major drainage problems, particularly in the vicinity ot Florence and trom Pueblo downstream to the Co!o.-Kans. state I ine. Other drainage problems have developed throughout most ot the basin because ot ponding of floodwaters where the outlets to streams and drainage ways are inadequate. According to previous studies conducted by Federal and State agencies to establ ish an overall basin plan, there are about 243,000 acres ot land in Colorado on which optimum agricultural pro- ductivity is not attained because of poor drainage faci lities. ot this total, there are 76,000 acres ot highly productive lands which require drainage for continued high productivity; 95,000 acres of haymeadow, pasture, and partly cultivated land which are moderately-to-severely affected by adverse drainage conditions but could be improved and put to a higher order ot use if properly drained; and 72,000 acres ot low- grade pasture and meadow land which, although not suitable tor culti- vation, could be improved through drainage. AI I ot the 243,000 acres have inadequate local drainage faci I ities and ot this total, 78,500 acres also have inadequate major outlets. 41. Since agricultural activities in the Arkansas River Basin in Colorado are so dependent on irrigation, the economy of those portions of the basin closely al I ied to agriculture is seriously affected by the vicissitudes ot the weather. Crop tai lures may occur either as a result ot severe droughts or because ot major tloods. Fortunately, about 75 percent of the average annual precipitation fal Is during the growing season but it is seldom sufficient for maximum crop production. There have been years of shortage when less than 25 percent of the water required for ful I crop production has been avai lable. The longest periods of drought, in order of severity, were trom 1888 through 1897, 1931 through 1939, and 1949 through 1956. During recent years the spread ot water-consuming vegetation has become a severe problem because of the water used and the channel aggradation caused b1 trapped sed i ment. 42. Depletion ot the streamtlow by man-made diversions and from natural sources characteristic of semiarid regions has created serious water pollution problems. A progressive deterioration ot the water 14