Effects of Interannual Variation of Precipitation on Stream Discharge from Rhode River Subwatersheds1

The purpose of this study was to determine the relationships between precipitation at the seasonal and annual scale and water discharge per surface area for seven contiguous firstand second-order tributaries of the Rhode River, a small tidal tributary to Chesapeake Bay, Maryland, USA. The goal was to quantify the effects of a wide range of precipitation, representative of interannual variations in weather in this region. The discharges measured included both overland storm flows and groundwater, since the aquifers were perched on a clay aquiclude. Precipitation varied from 824 to 1684 mm/yr and area-weighted Rhode River watershed discharge varied from 130 to 669 mm/yr with an average of 332 mm/yr or 29.1 percent of average precipitation. Average annual dis. charges from three first-order watersheds were significantly lower per surface area and varied from 16.0 to 21.9 percent of precipitation. Winter season precipitation varied from 125 to 541 mm. Areaweighted Rhode River winter discharge varied from 26.3 to 230 mm with an average of 115 mm or 43.9 percent of average precipitation. Spring season precipitation varied from 124 to 510 mm and watershed discharge varied from 40.0 to 321 mm with an average of 138 mm or 46.9 percent of average precipitation. In the summer and fall seasons, watershed discharge averaged 40.6 and 40.9 mm or 13.5 and 14.3 percent of average precipitation, respectively. Except in winter, the proportion of precipitation discharged in the streams increased rapidly with increasing volume of precipitation. Stream order showed a higher correlation with volume of discharge than vegetative cover on the watershed. (KEY TERMS: surface water hydrology; precipitation; land use; long-term; forest; cropland; coastal plain.)