INCOH/SAR-1/95-Long term baseflow studies

Abstract

The flow in the rivers during the lean period i.e. winter and summer season is called low flow and when there is no effective rain fall and snow melt and the entire flow originates from the groundwater it is called baseflow. The release of water from the groundwater reservoir into the river channels is controlled by the drainage and the geotechnical properties of the river basins. Low flow is defined on a seasonal basis and is linked with the annual solar cycle and its regional or even local climatic effects. A simple regime, such astropical regime, has only one dry season during which there is only one period of low flow. An equitorial regime on the other hand is marked by two rainy seasons and two dry seasons, usually of unequal length. Seasonal irregularities and hence the severity of low flow differ considerably according to a basin's physiography and its climatology.

The connection between quantitative and qualitative aspect of water resources is especially sensitive during low water periods. For various reasons (health, environmental conditions) it is necessary to maintain a minimum discharge in rivers, consequently this water is not available for other water users. The question of quality of the environment often depends on the availability of low river flows, particularly in areas of urban living, or on problems of public health, such as combating endemic diseases, as well as for thermal or chemical pollution.