Identifying and alleviating low flows in regulated rivers: the case of the rivers Bulbourne and Gade, Hertfordshire, UK.

This paper examines evidence for the occurrence and causes of low flows, and strategies for their mitigation, in two regulated, chalk-fed streams. The rivers occupy adjacent catchments of similar topography, have long histories of water exploitation and land-use change, and are subject to conflicting demands of water resource development and increased pressure for environmental improvement. In one case, a strategy of low-flow mitigation based upon reduced groundwater abstraction has been proposed. Although flows are shown to be declining through time, and low flows are more common over the last decade, analysis of rainfall records and groundwater levels produce inconclusive evidence for the causes of low flows. Despite their natural similarities, the catchments are shown to have very different sensitivities to low flow. When concentrating upon quantity of low flow, the River Gade appears to be most compromised, but when consideration is taken of water quality, the Bulbourne is more severely affected. An examination of catchment changes over a longer time period provides the best rationale for these sensitivities and contrasts. The study illustrates the potential danger of starting with a solely climatic–hydrological perspective to low flows which then progresses to a hydrological ‘solution’. Consideration of catchment land-use history, and of the importance of water quality, suggest limited applicability of reduced abstraction in mitigating low-flow problems in these kinds of environments. The study reinforces calls for further studies of groundwater–surface water interaction as essential inputs to appropriate and sustainable water resource management strategies. Copyright © 2000 John Wiley & Sons, Ltd.