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Alternative title

Hyporheic Temperatures, Cool-water Refuge, and Hope for Chinook Salmon

Date of Award

Winter 2023

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Sciences

Degree Name

Master of Science (MS)

Department

Environmental Sciences

First Advisor

Helfield, James M.,

Second Advisor

Sobocinski, Kathryn L.

Third Advisor

Bodensteiner, Leo R., 1957-

Abstract

This thesis project is part of an ongoing study assessing the effectiveness of a potentially innovative habitat restoration strategy for Pacific salmon in thermally impaired rivers. This strategy uses engineered log jams (ELJs) to create pockets of cool-water refuge by forming deep scour pools and promoting localized upwellings of shallow subsurface (i.e., hyporheic) water. This project seeks to characterize the relationship between hyporheic temperature and overlying surface stream temperature to elucidate the extent to which hyporheic upwellings can deliver cool water to ELJ-formed pools during the summer low-flow season. Among six sites within a 2.7 km-long study reach on the South Fork Nooksack River, I found that one had hyporheic temperatures that were consistently colder than the overlying surface stream (categorized as “cold”), two had hyporheic temperatures that were variable but buffered relative to the overlying surface stream (categorized as “cool”), and three had hyporheic temperatures that were not buffered relative to the overlying surface stream (categorized as “warm”). The daily maximum and seven-day average of daily maximum temperatures at the cool sites were >1.5°C cooler in the hyporheic zone than the overlying surface stream, and at the cold site, the daily maximum was >8°C cooler. Yet the warm sites exhibited no meaningful differences between hyporheic and surface temperature. Similarly, the observed daily range in temperature was significantly smaller in the hyporheic zone at the cold and cool sites, but not at the warm sites. Habitat mapping around my study sites suggests it might be possible to identify well-buffered hyporheic flowpaths based on specific combinations of channel geomorphic units, which influence the length, extent, and depth of hyporheic flow paths. Building engineered log jams closer together and subsequently promoting closer spacing of scour pools has the potential to greatly increase the extent of cool-water hyporheic upwellings in the South Fork. Conclusions drawn from this research can inform and improve the design of future habitat restoration efforts in a way that maximizes their benefit and promotes climate adaptation for salmon populations in thermally impaired rivers.

Type

Text

Keywords

hyporheic, engineered log jams, South Fork Nooksack River, temperature, restoration, Chinook salmon, ELJs, cool-water refuge, climate adaptation, Pacific salmon

Publisher

Western Washington University

OCLC Number

1411753939

Subject – LCSH

Hyporheic zones--Washington (State)--Nooksack River; Engineered log jams (Hydraulic engineering)--Washington (State)--Nooksack River; Water temperature--Washington (State)--Nooksack River; Chinook salmon--Washington (State)--Nooksack River

Geographic Coverage

Nooksack River (Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

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