Skip to main content


Title: Further Validation of PHABSIM for the Habitat Requirements of Salmonid Fish
Author: M Dunbar
Author: A Ibbotson
Author: I Gowing
Author: N McDonnell
Author: M Acreman
Author: A Pinder
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1262, Representation ID: 422, Object ID: 2472
PHABSIM (the Physical Habitat Simulation system) is a set of hydraulic and hydroecological models that define changes in physical habitat availability for target species given a change in river flow or channel geometry. The PHABSIM methodology was conceived and developed by the US Fish and Wildlife Service and has been further developed for use in the UK by the Institute of Hydrology (now CEH Wallingford). It has been used at more than 76 sites on 44 rivers in the UK. About half of these have been applied studies to determine the potential impacts of abstraction and channel restoration, and half have been research studies. In particular it has been its use by the Environment Agency for assessing the effect of groundwater and river abstraction on salmonid habitat availability. To support the application of PHABSIM to these issues, the Environment Agency established a programme of research and development entitled “Ecologically Acceptable Flows” (EAF). Phase I of the programme included a wide ranging review of how the PHABSIM models works and confirmed its general applicability to rivers of England and Wales, where management objectives relate particularly to salmonid fish or coarse fish with particular depth and velocity requirements. During the EAF programme, PHABSIM was applied on a range of rivers, both Chalk and upland, and the results were generally accepted as informative and useful to the Agency in defining ecological impacts of water resource schemes. Training courses were run and a field guide produced. The overall objective of the project was to test PHABSIM further as a tool for assessing water resources issues, specifically assessing prescribed minimum flows with the aim of setting river flow objectives. Specific objectives were to evaluate: 1. the use of site specific Habitat Suitability Indices (HSIs) versus generalised HSIs 2. PHABSIM predictions of physical habitat, 3. the relationship between brown trout/salmon populations and physical habitat availability. These objectives were tested on four target areas: two upland rivers (River Walkham, Devon and River Senni, South Wales) and two Chalk streams (Rivers Piddle and Frome, Dorset). In this way it was possible to compare results between sites, that would traditionally be considered as similar in “type”, and between rivers of different types. In summary, the EAF programme has produced a formalised Environment Agency version of PHABSIM that has been rigorously tested, a software manual, field application guide and training courses. It has confirmed the use of PHABSIM as a tool for assessing water resources issues, specifically assessing prescribed minimum flows with the aim of setting river flow objectives.
Publisher: Environment Agency
Subject Keywords: RiversGroundwaterSalmon fisheriesHabitatsFlow rateWater levelsEnvironmental impact
Geographic Keywords: FromePiddleDorsetDevonWales
Taxonomic Keywords: Salmo salarSalmo trutta
Extent: 226
Total file downloads: 299

Download PDF    Display PDF in separate tab