Basinwide instream flow assessment model to evaluate instream flow needs

Quantification of sufficient or minimum flows needed to sustain the aquatic habitat is necessary for satisfactory resolution of water use conflicts and planning of water allocation strategies. The Instream Flow Group (IFG) of the U.S. Fish and Wildlife Service has developed a methodology to gage the quantity of suitable habitat in a stream. Application of the methodology requires information on the local variations of depth and velocity in a stream reach. Conventional flow models are inadequate for this application, and evaluation of aquatic habitats requires extensive field work. Results obtained in a study reach cannot be applied to other reaches with dissimilar areas. To address the problem of defining the local variation of depths and velocities for regional habitat evaluation, a probabilistic flow model is developed. The probabilistic model incorporates hydraulic geometry relationships to evaluate average flow parameter values without the necessity of field observations. Local variations of depth and velocity values are evaluated from probability distribution models developed from field data collected on the Sangamon and South Fork Sangamon River basins. The flow model simulation for calculating stream habitat suitability with the IFG methodology is illustrated.U.S. Geological SurveyU.S. Department of the InteriorOpe