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The effect of depth-velocity correlations on aquatic physical habitat usability estimates




Prewitt, Charles G., author
Carlson, Clarence A., committee member
Stalnaker, Clair B., committee member

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Recent developments in instream flow evaluations have resulted in a variety of assessment methodologies. Of these, the Instream Flow Incremental Methodology permitted consideration of both physical habitat parameters (e.g., depth, velocity, substrate and temperature) and preferences for certain values of these parameters by selected organisms. This methodology was based on the PHABSIM (Physical HABitat SIMulation) computer system, which allowed 1) prediction of depths, velocities and associated substrates at a stream reach; 2) determination of weighting factors for the predicted values from preference curves constructed for each organism or group of organisms; and 31 application of a joint weighting factor (obtained by multiplying the individual weighting factors) to the surface area of the stream reach to obtain weighted usable area (WUA) for that reach. WUA is an indicator of the extent of available preferred physical habitat and a valuable tool in streamflow assessments. Calculation of joint preference factors by multiplication was statistically permissible only if the variables were uncorrelated. Using the original calculation approach, variable correlations were assumed to be zero, but might actually be quite high. To test the hypothesis that two variable (depth-velocity) correlations greater than zero did not significantly affect WUA results, a study was designed to account for effects of increased levels of correlation upon WUA calculated using various preference curves in a variety of stream types and channel characteristics. In the entire data set, the hypothesis was supported only to a correlation level of .2, a level unlikely to occur. However, results were more consistent in medium and large streams than in small streams. Further, in medium and large streams with complex channel configuration, users could expect independent depth-velocity curves to give results similar to correlated curves even if the actual correlation level was 0.4 or in many cases 0.6. Indicators of simple and complex channel conditions and discharge ranges of small, medium and large streams were given. Ecological (niche and guild theory) inferences related to habitat requirements and impact analysis were briefly discussed, and hypotheses regarding habitat diversity and stability presented. Definition of a fundamental niche using a multivariate statistical approach was suggested as a tool in predicting effects of environmental changes upon usable habitat.


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Fishes -- Habitat
Fishes -- Effect of water levels on
Streamflow velocity


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