WSP06216 - Laserfiche WebLink

Home Browse Search

2-18 I I I I I I I I I I I I I I I I I I I average of about 65 million acre-feet of natural flow annually at the mouth of the Missouri River near St. Louis, Missouri, exclusive of evaporation and consumptive uses attributable to water resource project developments. Under 1970 conditions of development and utilization, the net average annual outflow from the basin was estimated to be 53.6 million acre-feet.l Recent appraisals, based upon an aggregation of basin State estimates of water use, indicate a 1975 average annual flow of 49.4 million acre-feet at the mouth of the Missouri River near st. Louis. Abnormally high and low streamflows are not uncommon in most parts of the basin. Indicative of the drought potential is the fact that natural runoff as low as half the mean has occurred in nearly 10 percent of the years of record. At the other extreme, severe flooding caused by snowmelt, spring rains, and thunderstorms, is common in many drainages throughout the basin. Surface Water 9uality Overall, the water quality of the basin's waterways can be classed as fair. In the western portions, in their headwaters many of the mountain streams remain pristine and pollution-free. Sediment and dissolved solids concentrations became major problems in the rivers as they flow across the plains. In areas where irrigation is practiced, return flows from croplands are often laden with fertilizers, pesticides, and herbicides, degrading nearby watercourses. Runoff containing high concentrations of organic wastes from animal feedlots is another major agriculture-related water quality problem. Finally, municipal and industrial wastes continue to pollute many of the basin's major and minor streams, although ongoing plans and programs are striving to alleviate many of the problems.