The spatial and temporal variability of stream flow challenges
scientists' ability to inventory in-stream habitats and assess their sensitivity to environmental
changes. This document describes a method for in-stream physical habitat inventory
based on two-dimensional finite element hydraulic modeling, a Froude number and depth
based habitat classification system, and a Geographic Information System. The
approach is applied to the Ratcliff Ford reach of the Jacks Fork River, Missouri, USA in
order to assess the sensitivity of in-stream habitats to climatically induced hydrologic
variation. Modeling results for 31 discharges (0.4-78.5 cms) are presented in three
ways: as plan-view maps of depth, velocity, Froude number, and habitat distribution; as
contour plots of bivariate distributions of depth and velocity, and as summations of
habitat abundance in wet and dry climatic regimes. Modeling results indicate
non-linear, divergent relationships between discharge and habitat areas. Race-like
conditions with intermediate Froude numbers (Fr# = 0.2-0.4) dominate channel conditions at
higher discharges while pools and glides (Fr# = 0.1-0.2) dominate channel area at lower
flows. Comparisons of habitat duration curves for wet and dry climatic regimes
suggest that most of the net loss of habitat area in dry years is accommodated at Ratcliff
Ford by a loss of race and riffle habitat. Pool and glide habitats may be
less sensitive to hydrologic variability because the canyon-like nature of the Ratcliff
Ford reach maintains deep, narrow pools over a wide range of discharges. |