HYDROLOGY OF SPRING-DOMINATED STREAMS IN THE OREGON CASCADES

Spring-dominated streams in the Oregon Cascades are often characterize d by nearly constant discharge and by peak flows that occur in late su mmer or fall, several months after the annual snowmelt. A model is pre sented that can account for the temporal variations of discharge and t he delay between snowmelt and the period of peak streamflow. Springs a re assumed to be fed by an unconfined aquifer that is recharged by the annual snowmelt. Model results depend primarily on the effective perm eability and the dimensions of the aquifer. Four spring-fed streams in the Deschutes River basin in the Oregon Cascades are studied. The eff ective permeability of the young (<2 Ma) volcanic rocks that comprise the aquifers is inferred to be O(10(-11)) m(2).