LAND-USE CHANGES IN THE BALQUHIDDER CATCHMENTS SIMULATED BY A DAILY STREAMFLOW MODEL

The development of a model for the simulation of streamflow using only rainfall and evapotranspiration inputs at daily intervals presents special difficulties when using the data from the Kirkton and Monachyle catchments. The complex vegetation distribution in the Monachyle and the upper areas of the Kirkton, and the problems associated with the winter dormant grass made it necessary to modify the conceptual model which has been developed at the Institute of Hydrology for estimating the effects of land-use changes. Despite these difficulties, simulation of the streamflow in the calibration period produced volume agreement with observed values within 1% on the Monachyle and 4% on the Kirkton, and close agreement in the time distribution except during the few major snow accumulation episodes. Cumulative water use predicted by the model was in reasonable agreement with the catchment water balance estimates. A comparison of model estimates of soil moisture deficits with those observed by soil moisture neutron probe during plot studies produced a good correlation, providing further evidence of the validity of the model concepts. During the subsequent period, when the land use was being changed, the model also performed well. Simulating these changes in the model produced streamflow volume agreement with observations within 0.2% in the Monachyle and 0.8% in the Kirkton. This performance gave confidence in the use of the model to generate extended data sets for use in assessing the effects on water resources of various levels of afforestation in this environment.