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

This paper examines evidence for the occurrence and causes of low flows, an d strategies for their mitigation, in two regulated, chalk-fed streams. The rivers occupy adjacent catchments of similar topography, have long histori es of water exploitation and land-use change, and are subject to conflictin g demands of water resource development and increased pressure for environm ental improvement. In one case, a strategy of low-flow mitigation based upo n reduced groundwater abstraction has been proposed. Although flows are sho wn to be declining through time, and low flows are more common over the las t decade, analysis of rainfall records and groundwater levels produce incon clusive evidence for the causes of low flows. Despite their natural similar ities, 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 change s over a longer time period provides the best rationale for these sensitivi ties and contrasts. The study illustrates the potential danger of starting with a solely climatic-hydrological perspective to low flows which then pro gresses to a hydrological 'solution'. Consideration of catchment land-use h istory, and of the importance of water quality, suggest limited applicabili ty of reduced abstraction in mitigating low-flow problems in these kinds of environments. The study reinforces calls for further studies of groundwate r-surface water interaction as essential inputs to appropriate and sustaina ble water resource management strategies. Copyright (C) 2000 John Wiley & S ons, Ltd.