Applying spatial hydraulic principles to quantify stream habitat

Flow complexity plays an important role in stream ecology. Yet, a paucity of research exists with regard to quantifying flow complexity and relating it to the habitats that aquatic organisms utilize. Here we provide a generalized example of how two-dimensional (2-D) numerical hydraulic models and spatial hydraulic metrics can be used to simulate and quantify biologically important flow patterns within streams. A detailed topographic survey, incorporating meso-scale topographic features (e.g. exposed boulders and bedrock outcrops) is performed for a small urbanized stream. The 2-D hydraulic model RMA2 is then used to model the flow conditions within the stream reach. Model results demonstrate that the meso-scale topographic features create highly complex flow patterns of potential biological importance. Recently developed spatial hydraulic metrics, based on hydraulic engineering principles (vorticity, circulation and kinetic energy gradients), are then used to quantify the various types of flow complexity found within the stream reach. In particular, spatial hydraulic metrics are used to quantify the stream reach's overall flow complexity and the flow complexity surrounding three chub mounds. A method for uniquely characterizing circulation zones is then developed and applied to five circulation zones within the study reach. The principles used in performing this study's topographic survey, spatial explicit hydraulic modelling and spatial hydraulic analyses, form a general framework for quantifying flow complexity in any stream. The ways in which using hydraulic models and spatial hydraulic metrics can help establish better habitat suitability criteria and design best management practices for use in stream and catchment area restoration projects is discussed. Copyright (c) 2005 John Wiley & Sons, Ltd.