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Hydro-Alteration in Rivers and Streams --- Can We Estimate It Using Field Measures of Channel Habitat from EPA’s National Aquatic Resource Surveys?
Citation:
Kaufmann, Philip R, D. Carlisle, AND Marc H Weber. Hydro-Alteration in Rivers and Streams --- Can We Estimate It Using Field Measures of Channel Habitat from EPA’s National Aquatic Resource Surveys? National Water Quality Monitoring Conference 2019, Denver, CO, March 25 - 29, 2019.
Impact/Purpose:
Flow alterations in rivers and streams continue to be a major cause of habitat degradation and impairment of water quality and biotic integrity in the U.S. and worldwide. Unfortunately, EPA’s National Aquatic Resource Surveys (NARS) do not yet have direct measures that would allow us to monitor the status and trends in this important stressor. The authors propose a practical approach for regional and national scale assessment and monitoring of hydrologic alteration. A critical requirement of their approach is an evaluation of the precision and accuracy of flow estimates calculated from channel habitat data routinely collected by NARS at thousands of stream and river sampling sites throughout the U.S. The authors compare summer low flow and bankfull flow estimated from channel size, slope, wood, and residual depth measured by NARS with long-term flow measurements from closely-matched USGS gauge locations in the U.S. Current results suggest that indicators for assessment of hydro-alteration within the rigorous NARS statistical design may be ready for application for the next rivers and streams assessment. Because these indicators are based on physical habitat data currently collected by NARS, we expect that analytical ability to examine status and trends from 2008-09 through 2018-19 will be ready for EPA’s next National Rivers and Stream Assessment.
Description:
Flow alterations in rivers and streams have great potential to adversely affect physical habitat, water quality, and biological assemblages. The magnitude, frequency and timing of stream flows can be altered by flood and low flow management, changes in drainage basin impervious area, extraction of surface and groundwater, and by natural or anthropogenic changes in precipitation or evaporation. We calculated several indicators of hydro-alteration using field measurements of channel morphology routinely collected at sites sampled by the USEPA’s National Aquatic Resource Surveys (NARS), in combination with long-term flow measurements at USGS gauges. The accuracy of the estimates based on channel morphology is critical to the application of these indices. We tested the accuracy of a published hydraulic resistance formula in modeling discharge, using low flow and bankfull stage channel size, slope, wood, and residual depth measured by NARS. Our predictions of low-flow discharge had SE’s less than 0.4 order of magnitude compared with actual low flow discharge measurements (m3/s and m3/s-km2) ranging over six orders of magnitude at >300 closely-matched USGS gauge locations in the U.S. At the same locations, we predicted bankfull floods that recur at intervals ranging between 1.3 and 2.5 yr, with SE’s of 0.20 to 0.27 orders of magnitude. Based on these findings, we propose a practical approach for regional and national scale assessment and monitoring of hydrologic alteration and its effect on physical habitat in streams.