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Title: Bedform morphology of salmon spawning areas in a large gravel-bed river

Abstract

While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwestern region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bed form types at the pool-riffle scale. A bed form differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool-riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool-riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (Chi-square=152.1, df=3, p<0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at a vertical location within 80% ofmore » the nearest riffle crest elevation. The analyses of bed form morphology will assist regional fish mangers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.« less

Authors:
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
903242
Report Number(s):
PNWD-SA-7419
Journal ID: ISSN 0202-7224; GEMPEZ; TRN: US200719%%521
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geomorphology, 86(3-4):529-536; Journal Volume: 86; Journal Issue: 3-4
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; SEA BED; HABITAT; GEOMORPHOLOGY; RIVERS; SALMON; channel morphology; Chinook salmon; river bed form

Citation Formats

Hanrahan, Timothy P. Bedform morphology of salmon spawning areas in a large gravel-bed river. United States: N. p., 2007. Web. doi:10.1016/j.geomorph.2006.09.017.
Hanrahan, Timothy P. Bedform morphology of salmon spawning areas in a large gravel-bed river. United States. doi:10.1016/j.geomorph.2006.09.017.
Hanrahan, Timothy P. Tue . "Bedform morphology of salmon spawning areas in a large gravel-bed river". United States. doi:10.1016/j.geomorph.2006.09.017.
@article{osti_903242,
title = {Bedform morphology of salmon spawning areas in a large gravel-bed river},
author = {Hanrahan, Timothy P.},
abstractNote = {While the importance of river channel morphology to salmon spawning habitat is increasingly recognized, quantitative measures of the relationships between channel morphology and habitat use are lacking. Such quantitative measures are necessary as management and regulatory agencies within the Pacific Northwestern region of the USA, and elsewhere, seek to quantify potential spawning habitat and develop recovery goals for declining salmon populations. The objective of this study was to determine if fall Chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Snake River, Idaho, USA, were correlated with specific bed form types at the pool-riffle scale. A bed form differencing technique was used to objectively quantify the longitudinal riverbed profile into four distinct pool-riffle units that were independent of discharge. The vertical location of thalweg points within these units was quantified with a riffle proximity index. Chinook salmon spawning areas were mapped and correlated with the pool-riffle units through the use of cross-tabulation tables. The results indicate that 84% of fall Chinook salmon spawning areas were correlated with riffles (Chi-square=152.1, df=3, p<0.001), with 53% of those areas located on the upstream side of riffle crests. The majority of Snake River fall Chinook salmon spawning occurred at a vertical location within 80% of the nearest riffle crest elevation. The analyses of bed form morphology will assist regional fish mangers in quantifying existing and potential fall Chinook salmon spawning habitat, and will provide a quantitative framework for evaluating general ecological implications of channel morphology in large gravel-bed rivers.},
doi = {10.1016/j.geomorph.2006.09.017},
journal = {Geomorphology, 86(3-4):529-536},
number = 3-4,
volume = 86,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
  • The flow magnitude and timing from hydroelectric dams in the Snake River basin of the Pacific northwestern United States is managed in part for the benefit of salmon. The objective of this research was to evaluate the effects of current Hells Canyon Dam discharge operations on hydrologic exchange flows between the river and riverbed in Snake River fall Chinook salmon spawning areas. Interactions between river water and pore water within the upper 1 m of the riverbed were quantified through the use of self-contained temperature and water level data loggers suspended inside of piezometers. The data were recorded at 20more » min intervals over a period of 200 days when the mean daily discharge was 218–605 m3 s–1, with hourly stage changes as large as 1.9 m. Differences in head pressure between the river and riverbed were small, often within ±2 cm. Measured temperature gradients in the riverbed indicated significant interactions between the surface and subsurface water. Neither hydraulic nor temperature gradients at most sites were significantly affected by either short- or long-term changes in discharge operations from Hells Canyon Dam. Only 2 out of 14 study sites exhibited acute flux reversals between the river and riverbed resulting from short-term, large magnitude changes in discharge. The findings suggest small-scale piezometric head differences play a minor role in the hydrologic exchange between the river and riverbed at the study sites. The processes controlling hydrologic exchange at the study sites are likely to be bedform-induced advective pumping, turbulence at the riverbed surface, and large-scale hydraulic gradients along the longitudinal profile of the riverbed. By incorporating the knowledge of hydrologic exchange processes into water management planning, regional agencies will be better prepared to manage the limited water resources among competing priorities that include salmon recovery, flood control, irrigation supply, hydropower production, and recreation.« less
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