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A TOOL FOR EVALUATING. FLOW REQUIREMENTS. IN FLORIDA STREAMS?. Florida Fish and Wildlife Conservation Commission. Eric Nagid and Gary Warren. PHABSIM:. P hysical HAB itat SIM ulation System. Combines hydrological and biological models
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A TOOL FOR EVALUATING FLOW REQUIREMENTS IN FLORIDA STREAMS? Florida Fish and Wildlife Conservation Commission Eric Nagid and Gary Warren PHABSIM:
Physical HABitat SIMulation System • Combines hydrological and biological models to predict changes in habitat area over a range of discharges. • Is a component of the Instream Flow Incremental Methodology (IFIM). • Is the most widely used model for deductive estimation of biological effects of stream flow alteration. • Has been successfully defended in court.
Biological • Habitat Preference Criteria – for each life stage. • velocity • depth • substrate / cover Primary Components of PHABSIM • Hydrological • Field measurements of physical habitat conditions • along transects. • velocity • depth • substrate / cover 2. Hydrological modeling of flow / stage relationships.
PHABSIM Output Weighted Usable Area • The usable area of habitat available, in a stream reach, to a given species at a given discharge. • The product of velocity, depth, and substrate/cover preferences multiplied by cell size. • WUAs are summed over an entire reach and used as an index of habitat quality and availability.
Limited range – SSC Recreationally important Easily sampled Flow sensitive Sessile Easily sampled Biological Suspectsfor the Suwannee River Basin Suwannee bass (Micropterus notius) Net-spinning caddisflies (Hydropsychidae), Mayflies (Baetidae)
Little evidence that fish populations actually respond to changes in weighted usable area. • Does not perform well in soft-bottomed, shifting sediment streams. • PHABSIM is unidimensional. Locally: • Fish in peninsular Florida, particularly Centrarchids, are ubiquitous. Therefore, HSC may be vague and uninformative. Criticisms of PHABSIM General:
Evaluation of Stream Flow Models Selecting and Modifying the Most Appropriate Model for Florida Streams • PHABSIM / IFIM • River 2D • Channel Units / Channel Types (CU / CT) • Indicators of Hydrologic Alteration (IHA) • System Impact Assessment Model(SIAM)