A habitat assessment approach to the management of groundwater dominated rivers

The Instream Flow Incremental Methodology (IFIM) using the Physical Habitat Simulation (PHABSIM) system, has seen increasing application to the assessment of changes in aquatic habitats in the UK over the last 10 years. In particular, the model has been applied operationally to chalk streams (e.g. the Rivers Allen and Piddle) in southern England for the alleviation of low ¯ow (ALF) problems. More recently, the model has also been used to examine the e�ect of changes in channel morphology upon aquatic habitats, such as those that occur during ¯ood defence, or river channel restoration, schemes. The paper outlines some of the issues related to the application of the model to groundwater dominated rivers, such as chalk streams, and provides examples of the application of the model to a water resource issue and to assess a habitat restoration scheme. The paper also reports on three areas of recent research to improve the methodology: (1) choice of representative study sites and habitat variation at the reach and sector scale; (2) modelling of time series and interpretation of alternativewater management regimes; and (3) the development of rapid assessment techniques based upon the transfer of standardised relationships between available habitat and discharge.