Aspects of the hydrology of the Browney basin North East England

Abstract

A hydrological study was undertaken to investigate precipitation, evapotranspiration and runoff in the Browney basin, north-east England. The areal and seasonal distribution of precipitation during the period 1968-1972 were analysed and frequency analysis were carried out on the amount of rainfall and the number of raindays per month during the period 1939-1973 at Durham Observatory. There was a high correlation between yearly precipitation and altitude. October and September were the driest months of the year while February was the wettest month. The relatively high intensity rainfall in the late summer months gave evidence for the occurrence of convectional rain during this time of the year. A wide range in the amount of rainfall and in the number of rain-days for any given month at Durham Observatory was observed. To measure evapotranspiration two sets of evapotranspirometers were installed at two locations just outside the extreme eastern and western margins of the catchment. Other methods for measurement for estimation of evapotranspiration in the catchment were also used. These were the Penman and Thornthwaite formulae, the catchment water balance method and simple hydraulic lysimeters. The results of measured evapotranspiration at the two locations indicated greater evapotranspiration at the higher elevation. The use of simple hydraulic lysimeters for the measurement of actual evapotranspiration was discarded because of significant differences in the results of the replicates. A comparison of the catchment water balance evapotranspiration with the results from the other methods revealed that there was some moisture deficit in the catchment especially during the late summer months. Studies of runoff data from the catchment showed significant variations in the yearly, seasonal and short term patterns. These differences were explained by the differences in the amount and distribution of precipitation, evapotranspiration and antecedent soil moisture conditions. The overall hydrology of the catchment was studied by the simulation of the flow records during the period 1969-1973, using the Stanford Watershed Model IV. The results obtained revealed high correlations between the monthly recorded and simulated flows. The mean monthly recorded flow during the five year period exceeded the simulated flow by 2 percent. The actual evapotranspiration and groundwater components of the hydrologic cycle where also studies using the results of the simulation method.