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39. The Arkansas River In Colorado Is often dry or nearly so, except In the headwater reaches, becaus~ the normal streamf low is dI- verted for Irrigation purposes. When tributary streams are in flood they discharge large quanti ties of sed I ment I nto the ma I n stem and, unless the river Is at high stage, the peak of the tributary flood Is rapidly diminished by valley storage an~ the sediment load Is deposited in the channel. The result Is an accel~ratlon of aggradation which causes channel changes, creates sandbar~, and reduces the channel capacity. The reduction In channel capacity Increases the damages from bank caving during minor floods of frequent occurrence and from Inun- dation by less frequent floods. . 40. The aggradation of the streambed of the Arkansas River and the accompany I ng rise in the water tab I,e have created major dra I nage problems, particularly in the vicinity ,of Florence and from Pueblo downstream to the Colo.-Kans. State line. Other drainage problems have developed throughout most of the ~asin because of ponding of floodwaters where the outlets to strearjls and drainage ways are inadequate. According to previous stu~les conducted by Federal and state agencies to establ Ish an overall! basin plan, there are about 243,000 acres of land in Colorado on which optimum agricultural pro- ductivity Is not attained because of ppor drainage faci Iltles. Of this total, there are 76,000 acres of highly productive lands which require drainage for continued high productivity; 95,000 acres of haymeadow, pasture, and partly cultivated land wh'ich are moderately-to-severely affected by adverse dra i nage cond it i on's but cou I d be improved and put' to a higher order of use if properly drained; and 72,000 acres of low- grade pasture and meadow land which, although not suitable for culti- vation, could be improved through drai!nage. All of the 243,000 acres have inadequate local drainage faci Iltles and of 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 all led to agriculture is seriously affected by' the v ic I ssltudes of the weather. Crop fa I lures may occure ither asa result of severe droughts or because of major floods. Fortunately, about 75 percent of the average annuail prec I p I tat i on fa II s dur i ng the grow i ng season but I tis sel dom suft H:; I ent for max I mum crop product ion. There have been years of shortage when less than 25 percent of the water requ I red for fu II crop product i:on has been ava I I ab Ie. The longest periods of drought, In order of sevehlty, were from 1888 through 1897, 1931 through 1939, and 1949 through 11956. . Our I ng recent years the spread of water-consuming vegetation ;has become a severe prOblem because of the water used and the ch~nnel aggradation caused b1 trapped sed i mElnt . 42. Depletion of the streamf loviby man-made diversions and from natural sources characteristic of semiarid regions has created serious water pollution problems. A progres!?ive deterioration of the water . 14