Community Partner

Columbia River Fish Program Office of the US Fish and Wildlife Service

First Advisor

Yangdong Pang

Date of Award

Fall 2009

Document Type

Project

Degree Name

Master of Environmental Management (MEM)

Department

Environmental Science and Management

Language

English

Subjects

Hydraulic gates -- Environmental aspects -- Lower Columbia River (Or. and Wash.), Water temperature -- Lower Columbia River (Or. and Wash.), Hydraulic gates -- Evaluation, Tides -- Columbia River Estuary (Or. and Wash.), Salmon -- Habitat -- Columbia River Estuary (Or. and Wash.), Estuarine restoration -- Lower Columbia River (Or. and Wash.)

DOI

10.15760/mem.26

Abstract

Dramatic declines in salmon populations in the Pacific Northwest have brought new attention to the importance of estuarine rearing habitats. Levees and tide gates used to convert estuarine wetlands into farmland have reduced available habitat by more than half of historical levels. Recent efforts to restore estuarine habitats include tide gate replacement, though this method has been poorly studied. As a key indicator of salmon habitat suitability, temperature was used to evaluate the effects of tide gate replacement in a tidally influenced freshwater slough in the Lower Columbia River estuary. Three tide gates in the largest slough on Tenasillahe Island were replaced in 2007 with side-hinged aluminum gates. As managed during the data collection periods, the new tide gates did not allow tidal inflow into the slough. The study employed a Before-After, Control-Impact (BACI) approach, collecting data seasonally two years before and after replacement at the impact site and at the control site, a relatively unaltered slough on nearby Welch Island. Randomized Intervention Analysis and Monte Carlo tests revealed no significant difference in slough water temperatures after tide gate replacement, although minimum temperatures dropped up and downstream of the tide gates. Although the new tide gates did not have a significant effect on water temperature, the lower minimum temperatures may have been caused by a slight increase in tidal circulation. This result suggests that slough temperatures would decrease if the tide gates were managed to increase tidal inflow, and thus improve the quality of salmon rearing habitat.

Rights

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Comments

A project report submitted in partial fulfillment of the requirements for the degree of Master of Environmental Management.

Persistent Identifier

http://archives.pdx.edu/ds/psu/15772

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