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Hydraulic microhabitat assessment is a category of environmental flow tools (e.g., Physical Habitat Simulation system and other methodologically similar software) that, at its core, uses habitat suitability criteria (HSC) to link values of point hydraulic variables (usually depth, velocity, and substrate/cover) to habitat values for target life stages. Although this assessment tool has been used worldwide for decades, the history of the HSC curve is relatively unknown because the foundational information is predominantly contained in obscure and often unpublished reports. We review the history of the HSC concept in applied aquatic ecology to clarify its scientific pedigree, ensure its proper use, and build a foundation for future research. We begin the review with the formative decades of the 1950's through the 1970's, when consumptive‐based western USA water law conflicted with conservation traditions and natural resource management objectives, although water allocation issues date back at least to the 19th century. By analysing the history of the HSC concept, we aim to establish the biological, hydrologic, and geomorphological conditions that must be met for the HSC concept to be successfully employed. In spite of its documented assumptions and limitations, the HSC concept will likely continue to be a useful tool to help address water resources allocation issues in defined hydrologic and geomorphic settings. We conclude that HSC‐based methodologies should be considered as one of several environmental flow approaches involved in sustainable water resources management.

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Figure 11. Annual channel maintenance capacity index (ACMCI) for the Klamath River below Iron Gate Dam, California. The equation for the index is cmci = (QD ^0.87-5000 ft 3 /s ^0.870/(10000 ft 3 /s ^0.87). Data for 1924-1960 were for the streamgage below Copco Dam a short distance upstream from the present streamgage and at a location within the Iron Gate reservoir.

SUMMARYThis report presents the results of a field study of the precision of various roughometers and profilometers for predicting serviceability.Forty-five pavement sections of three types (flexible, rigid and overlay) were rated by a lay panel, the AASHO Road Test panel and the HighwayResearch Board Committee on Pavement Condition Evaluation. These same pavements were evaluated using the roughness and profilometer equipment.Statistical relationships, following techniques adopted at the ASSHO Road Test, were developed between rating and objective measurements.The lay panel tended to rate the pavements higher than the professional panels. The results indicated little difference regarding the precision of the various instruments in so far as predicting serviceability is concerned. The data suggest that the BPR type roughometer can be used successfully for predicting serviceability.Data from this study were combined with those from the AASHO Road Test and serviceability equations were developed for these combined data on the basis of the Slope Profilometer. Correlations between roughometers and the Slope Profilometer were presented. Equations are presented which should permit engineers who have past records of roughometer readings to interpret these data in terms of Present Serviceability Indices.