A combined snowmelt and rainfall runoff model

Abstract

An outline description is given of the University of British Columbia (U.B.C.) watershed and flow models, which are a set of computer programs for the calculation of hydrologic behaviour of watershed and river systems. The U.B.C. watershed model calculates snowmelt and rain runoff from meteorological data for mountainous watersheds. The model can be operated continuously for any number of years without reinitialization. The watershed model can be interfaced with the U.B.C. flow model which routes and combines the flows from a complex network of watersheds through downstream channels, lakes, or reservoirs.A revised temperature index for the calculation of snowmelt is presented and illustrated. In addition to using the mean daily air temperature, use is made of the diurnal temperature range to describe additional radiant energy input and the minimum temperature is used to approximate dewpoint and vapour exchange.The enhanced watershed response resulting from high intensity rainfall is examined and it is shown that this enhanced watershed response can be described by one additional parameter which modifies the normal watershed calibration. This additional parameter changes the normal infiltration behaviour of a particular watershed by a certain percentage, and, is found to be a stable parameter capable of describing a range of high intensity rain events.Application of the watershed and flow models for streamflow forecasting and planning studies are described. An outline is given of operational forecasting for the Fraser River system and of planning studies on the McGregor River. In the study of the McGregor River, streamflows were calculated for a 12 year period from meteorological data. Comparison with observed monthly flows showed a correlation coefficient of 0.96.The computer programs and documentation are available from the authors.