Water-resources investigations in Wisconsin, 1999

Abstract

The statewide average precipitation of 31.23 inches for the 1998 water year was 0.42 inches less than the normal annual precipitation of 31.65 inches for water years 1961-90. Average precipitation values ranged from 69 percent of normal at both the Willow Reservoir WVI weather station in north central Wisconsin and Crivitz High Falls WPS weather station in northeast Wisconsin to 141 percent of normal at the Dodgeville 1 NE WWTP and Muscoda weather stations in southwest Wisconsin (from tables provided by Lyle Anderson, Program Assistant, UW-Extension, Geological and Natural History Survey, written commun., 1999). Runoff differed for rivers throughout the State and ranged from 54 percent in northwest Wisconsin to 146 percent in southeast Wisconsin. Runoff was lowest (54 percent of the average annual runoff from 1975-98) for the Nemadji River near South Superior and highest (146 percent of the average annual runoff from 1976-79, 1981-98) for the Underwood Creek at Wauwatosa station which monitors a small urban basin (drainage area is 18.2 square miles) in southeastern Wisconsin. Departures of runoff in the 1998 water year as a percent of long-term average runoff in the State (determined using stations with drainage areas greater than 150 square miles and at least 20 years of record) are shown in Figure 4. Annual discharges for the individual water years (1916-98) at the Oconto River near Gillett, Jump River at Sheldon, and Sugar River near Brodhead are shown in Figure 5. The comparison of monthly and annual discharges for the 1998 water year to discharge for a 83-year base period at the same three gaging stations are shown in Figure 6. Low flows occurred at 21 gaging stations where the annual minimum 7-consecutive day average flows (Q7) had recurrence intervals of 5 or more years. Precipitation was well below normal from July through September in northern Wisconsin. Monthly precipitation values were 4.46, 5.69, and 4.24 inches below normal in northwestern, north central, and northeastern Wisconsin, respectively, in the July through September period (from tables provided by Lyle Anderson, Program Assistant, UW-Extension, Geological and Natural History Survey, written commun., 1999). The precipitation for the April to October period was