The Instream Flow Incremental Methodology (IFIM) using the Physical Habitat
Simulation (PHABSIM) system, has seen increasing application to the assess
ment of changes in aquatic habitats in the UK over the last 10 years. In pa
rticular, the model has been applied operationally to chalk streams (e.g. t
he Rivers Allen and Piddle) in southern England for the alleviation of low
flow (ALF) problems. More recently, the model has also been used to examine
the effect of changes in channel morphology upon aquatic habitats, such as
those that occur during flood defence, or river channel restoration, schem
es. 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 met
hodology: (1) choice of representative study sites and habitat variation at
the reach and sector scale; (2) modelling of time series and interpretatio
n of alternative water management regimes; and (3) the development of rapid
assessment techniques based upon the transfer of standardised relationship
s bf tween available habitat and discharge. Copyright (C) 1999 John Wiley &
Sons, Ltd.