How Water Use Affects Nooksack Streamflows

by Eric Hirst

Editor’s Note: a longer, more detailed version of this article is available at: 
https://whatcomwatch.org/wpww2/wp-content/uploads/2025/02/Effects-of-Human-Water-Use-on-Nooksack-Streamflows.pdf

Climate change is dramatically affecting seasonal flows of water throughout the Nooksack River watershed, with substantial declines in summer flows. These declines are virtually certain to continue for the next few decades. (1) We need to better understand how these much lower flows will affect fish and other wildlife as well as water use, especially agriculture.

Climate change also increases the need for irrigation because summers are hotter and drier. We need to better understand how these temperature and rainfall changes affect irrigation.

The water rights adjudication now underway will, within a decade or two, determine who has the right to use water, when, where and in what amounts. This legal process should be informed by the current and projected relationships between available supplies and demands.

When the Washington Dept. of Ecology (Ecology) issued its instream flow rule in 1985, it was officially clear that water supplies in the Nooksack River basin were limited. (2) Since then, the relationships between out-of-stream water use and streamflows in the watershed have been an important issue. In particular, summer streamflows are often insufficient to meet Ecology’s minimum flows, worsening conditions for salmon and other wildlife.

I explore the relationships between streamflows and out-of-stream water use for the mainstem Nooksack River at Ferndale and for Fishtrap and Bertrand creeks near their confluences with the mainstem. I chose these locations because the mainstem at Ferndale is only five miles from the river’s outlet in Bellingham Bay; thus data from this location roughly represent the watershed as a whole. Fishtrap and Bertrand creeks are at the other end of the spectrum, small tributaries to the mainstem, dominated by agricultural irrigation.

I focus on summer (July, August, September) because that is when flows are the lowest and human use of water is the greatest. (3) The lack of data on irrigation water use and complexities of groundwater flows limit the accuracy of results developed here. (4)

Nooksack River

I analyzed monthly data from the U.S. Geological Survey (USGS) gauge for the period 1967 through 2024 (58 years). I converted the measurements from cubic feet per second to acre-feet per month to allow comparisons with estimates of water use. As discussed elsewhere, the trends for summer flow are downward. (5) During the last 15 years (2010 – 2024), flows declined by almost 4 percent per year.

Monthly flows vary greatly (Fig. 1), with summer flows averaging about 60 percent of annual flows. (6) The figure also shows estimated monthly consumptive water use. (7) For most of the year, human water use is a small fraction of instream flow (1.1 percent on average), but during the summer months, water use averages 5 percent of flow, reaching a peak of 8 percent in August. (8)

Fishtrap Creek

Data for Fishtrap Creek are available for 26 years, 1999 through 2024. (9) Here, too, the trends in streamflow are negative: -7.6 percent per year for summer flow over the past 15 years. Monthly flows vary much more than for the mainstem: the volume flowing during the summer is only 16 percent of the yearly average (Fig. 2).

Averaged over the full year, out-of-stream water use is 10 percent of instream flow. But during the summer, human use (primarily irrigation) is almost two-thirds of the total water available (water use plus actual streamflow). And in August, water use is three-fourths of total water.

Bertrand Creek

Data for Bertrand Creek are available from an Ecology station for the 22-year period from 2003 through 2024. Summer flows declined at 2.3 percent per year.

Interpretation

As expected, results for these three water bodies are quite different. In a sense, the mainstem at Nooksack represents, at least roughly, the entire watershed, both in terms of water supply and water demand. Fishtrap and Bertrand creeks, at the other end of the spectrum, represent small tributaries with substantial amounts of water use, primarily for agricultural irrigation.

The amount of water flowing through Fishtrap, averaged over the year, is 2 percent of the Nooksack volume. During the three summer months, the Fishtrap volume is only 0.6 percent of the Nooksack volume. The comparable numbers for Bertrand Creek relative to the mainstem are 2.4 percent and 0.5 percent. Thus, Fishtrap and Bertrand flows are much more variable than are mainstem flows. Because of this larger seasonal variation in the two tributaries, the eff ects of water use on summer fl ows are much greater in the two creeks than in the mainstem; compare Figs. 2 and 3 with Fig. 1.

Conclusions

Based on these three locations, the relationship between streamflows and human water use varies dramatically throughout the Nooksack watershed. In the basins where farms predominate, the effects of water use on summer streamfl ows are substantial. In other basins, water use probably has only modest effects on instream flows.

The results presented here should be replicated for several other sub-basins within the Nooksack watershed, both to verify the findings developed here and to better understand the relationships between water use and water supply. Such an analysis is important because:

• Climate change is dramatically affecting seasonal flows throughout the watershed.
• These declines are virtually certain to continue for the next few decades.
• Climate change is increasing the need for irrigation as summers become hotter and drier.
• Agricultural irrigation needs to become much more efficient; and society should encourage, require, and help farmers adopt modern wateruse efficiency practices and technologies. This likely will require changes in state water law to encourage, rather than discourage, efficiency.
• The Nooksack adjudication should be informed by the relationships between available supplies and demands.

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Eric Hirst has a Ph.D. in engineering from Stanford University, worked at Oak Ridge National Laboratory for 30 years as a policy analyst on energy efficiency and the structure of the electricity industry. He moved to Bellingham 22 years ago and remains active on local environmental issues.

 

Sources Cited

1. E. Hirst, Climate Change and the Nooksack Adjudication, April 2024.
2. Washington State Dept. of Ecology, Instream Resources Protection Program—Nooksack Water Resource Inventory Area (WRIA) 1, Chapter 173-501 WAC, June 9, 1988.
3. Human water use means all out-of-stream uses, including residential, commercial, industrial, and agricultural uses.
4. See the Appendix of E. Hirst, Effects of Human Water Use on Nooksack Streamfl ows, Feb. 2025, for an explanation of the assumptions and estimates used in this analysis. https://whatcomwatch.org/wpww2/wp-content/uploads/2025/02/Effects-of-Human-Water-Use-on-Nooksack-Streamfl ows.pdf
5. E. Hirst, “Nooksack Watershed Summer Water Temperature Trends,” Whatcom Watch, 33(12), Dec. 2024. During recent years the downward trend in summer flows throughout the watershed has accelerated, worsening conditions for salmon.
6. For consistency across the three watersheds, comparisons use fl ow data from the last 15 years only, 2010 – 2024.
7. Consumptive water use is the amount of water withdrawn or diverted that is not returned to aquifers or streams. Consumptive use for irrigation is caused by evaporation and transpiration.
8. The effects of water use on streamfl ows may be less than shown here because parts of Whatcom County lie outside the boundaries of the Nooksack watershed, such as Dakota and California creeks and Lake Whatcom. As a counter, RH2 Engineering estimated 2020 consumptive water use for all of WRIA 1 as 116,400 acre-feet, more than double the estimate used here (RH2 Engineering, Regional Water Supply Plan – Phase 2 Report, Jan. 2023).
9. Unlike the mainstem, which is fed by glaciers and snowfall, Fishtrap and Bertrand creeks flow south from lower British Columbia and are affected strongly by human and natural actions there.