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^~!-i)l U !,..HJ;j ~. CHRONOLOGY OF THE 1976-77 DROUGHT 35 subnormal again in June over most of Montana and Wyoming. Except for an area in northern Montana, rainfall in July and August was generally above normal. The same was true for September, but the deficient area moved to Wyoming. Precipitation for the rest of the year was mostly above normal, but monthly amounts were generally less than 2 in. The water content of the snowpack in the vicinity of Helena, Mont. was only 10 percent of normal on May 1, 1977 and presaged very little runoff for the usual snowmelt period in May and June. Soil moisture, in both the topsoil and in the subsoil, was deficient in most of the counties in North Dakota during April 1977. Rains early in May in South Dakota brought topsoil moisture up to "adequate." Mid-June rains in southwestern North Dakota increased the soil moisture to more than it had been in over a year. By mid-March 1977, flows in the Yellow- stone and Marias Rivers in Montana and the Cannonball River in southwestern North Dakota had receded to the below normal range. Abnormally heavy rains in South Da- kota in March increased the flow of the James River at Huron from zero to 1,700 ft 3/s. There had been no flow at Huron since July 1976, the longest period of no flow since the 10-month stretch in 1959-60. Flow ceased again early in May 1977 and did not occur again until late December, another no-flow period of almost 8 months. The James River is regulated; therefore, the long periods of no flow at Huron reflect the increased needs for diversions upstream. Warm weather late in April 1977 increased the snowmelt runoff enough in Montana to bring streamflow up close to normal or above normal and brought storage in most reservoirs above normal for May 1. Most streams in Montana peaked about a month earlier than usual because of the poor snowpack. The flow of the Marias River was down to 16 percent of normal in May. Flow of the Cannonball River for the first 7 days of June was down to only 3 percent of the normal for June, but heavy rains of up to 7 in. in south- western North Dakota during the following week increased the average flow from 7 ft 3/s to 340 ft 3;s which is 125 percent of normal. Monthly flows for June 1977 of the Yellow- stone River at Corwin Springs just north of Yellowstone National Park were the lowest since 1941 and at Billings they were the lowest since 1934. Monthly and minimum daily dis- charges on the Marias River near Shelby in June were the lowest since records began in 1911. Very high temperatures during the first half of July and below normal rainfall reduced flows in many Montana streams to near record lows. Storage in Fresno Reservoir on the Milk River in north-central Montana decreased to 35 percent of normal in May 1977 which was the lowest for May since 1961. Only May 1941 was lower. By mid-July Fresno Reservoir storage was down to 14 percent of normal. Contents in many reservoirs in Montana set or were near record lows by the end of July. Some of the records start between 1930 and 1947. A small pie-shaped part of Montana near Glacier National Park is actually part of the Saskatchewan River basin, but it has been in- cluded as the northwest corner of this region. Usable contents of Lake Sherburne in Glacier National Park were depleted by mid-JUly 1977. Normally the July contents are near 55,400 acre-ft. Contents increased by mid-August to 5,300 acre-ft which is 20 percent of normal for August. Ground-water Conditions The general pattern of changes in ground- water levels was one of decline in 1976 and much less than the usual recovery or no recovery in the following winter and spring. The decline continued in the summer of 1977 in some wells but not in others. More permits than usual were issued for new wells, and ground-water withdrawals increased in both 1976 and 1977. Records for a well in western North Dakota started in 1968, and a new record low level was reached in May 1977 when the water surface was 18.7 ft below land surface and 0.3 ft lower than the previous low of record which was in 1969. This well reacts quickly to rain- fall; therefore the rains in June 1977 raised the water level 1 ft, and it remained well above previous minimum levels for the rest of the year. A large increase in irrigated acreage oc- curred in South Dakota between 1976 and 1977 when dry land acreage was converted. Deep