Mean annual runoff in the upper Ohio River basin, 1941-70, and its historic variation

A map of the Ohio River basin above the Muskingum River shows patterns of mean annual runoff for the climatologic and hydrologic reference period, 1941-70. The primary data base consisted of 98 long-term gaging-station records collected within this 27,300-square-mile headwater area of the Ohio River basin. Supplemental information was derived from 83 short-term records. Mean annual runoff is at a regional minimum of less than 12 inches in an area extending from the northern West Virginia panhandle to the headwaters of the Mahoning River in Ohio. Mean annual runoff of more than 32 inches occurs in parts of the upper Cheat River basin in West Virginia. The zone of high runoff trends northeastward along the western slopes of the Allegheny Mountains; magnitudes diminish to about 25 inches at the eastern basin boundary near Ebensburg, Pennsylvania. Runoff of this magnitude occurs also in a band across the upper Allegheny River basin in Pennsylvania. Ratios of mean annual discharge to the 30-year reference-period average were computed for each year of record for all long-term gaging stations. Annual discharges have ranged from about 30 percent to 200 percent of the 30-year mean. Graphed summaries of the annual ratios document the relative duration and magnitude of wet and dry periods during the past 65 years in the upper Ohio River basin. (Woodard-USGS)