WSP08775 - Laserfiche WebLink

Home Browse Search

I'io!'H;I.\l~' li '-; 1;.,;' V c..d ~'~ CHRONOLOGY OF THE 1976-77 DROUGHT 75 Stream flows in Maryland and Delaware were below normal during the summer of 1977 and generally were the lowest since 1970, but they were well above the minimums of record, many of which occurred during the summer of 1966. The exception was the Choptank River near Greensboro, Md., 65 mi east of Washing- ton, D.C. where new monthly minimum flows occurred in May, June, and July 1977, and the flows were in the deficient range for 7 months from February to August 1977. There was much publicity and concern in the Washington, D,C, area when the flow of the Potomac River near there dropped to 40 percent of normal during May and June 1977. However, enough rain fell in the basin during the summer to maintain the flow at more than three times the diversion rate for municipal supplies. The drought in Virginia was the most severe in the north, central and eastern parts of the State in 1977. The September runoff of the Rapidan River near Culpeper, about 65 mi southwest of Washington, D,C., was the sixth lowest flow for September since records began in 1930. The lowest September flow occurred in 1954 when it was a fourth of that in 1977. In North Carolina the drought was not con- tinuous, but the eastern half of the State was affected in both 1976 and 1977, Streamflow was below normal from March through Sep- tember 1976 and was near the minimum of the last 50 years, Deficient streamflow occurred again from April through mid-August 1977. Flows of some streams in South Carolina in July 1977 receded to the level where the 7-day average flow reached recurrence intervals of 2 to 6 years, Runoff and precipitation in New Mexico are not very high in normal times, but the be- low normal precipitation and runoff reduced the storage in major reservoirs that provide water for irrigation to less than 50 percent of average in December 1977, Ground-water Conditions In several States, some wells went dry or did not yield enough water, but the main prob- lems were related to the wells rather than the ground-water supply. Wells were not deep enough, or not in a very good location, or had not been developed correctly after they were drilled, Water levels in North Carolina were gener- ally below normal from June through Septem- ber 1976 and about the same period in 1977, However, no serious ground-water deficiencies developed. The use of ground water for irrigation in Georgia is a "whole new use" of that resource according to the State Geologist. Some shallow wells in southern Georgia went dry when overpumped. Therefore, the Governor ordered a survey of ground-water consumption as an early step toward the development of a coordinated water and land use policy. There was also concern that the large number of new wells drilled and the increased withdrawals might overtax the ground-water resource, Water Quality The severe winter of 1976-77 in the eastern United States coupled with below normal run- off caused an increase in the ice cover on streams and lakes--both in thickness and areal extel)t. Fish kills occurred in some ice covered streams and stock ponds. These factors also affected the flow of the lower Mississippi River and the position of the freshwater-saltwater interface which is where the chloride concentration reaches 5,000 mg/L. At Baton Rouge, La., the discharge dropped to 175,000 ft3/s in October 1976, but this was 100,000 ft 3/s more than the minimum flow of record in 1939. On October 6, 1976, the leading edge of saltwater had intruded 57 mi up the Mississippi River to Myrtle Grove, but increased flows pushed the leading edge downstream 24.5 mi by October 20 and 46 mi by November 12. With flows under 200,000 ft 3/s starting on November 20, 1976, the lead- ing edge moved back upstream 14 mi by mid- December and reached a point 47 mi above Head of Passes by mid-August 1977. It receded to river mile 11 again by Septem- ber 28, 1977. The penetration of saltwater as far as Myrtle Grove has a mean recurrence interval between 5 and 10 years, Communities along the lower reach of the Mississippi River that use river water for their supply had to import freshwater to dilute their supply to acceptable levels. Activities Resulting from the Drought Crop damage in Virginia was high, and municipal water supplies were dangerously