Managing source water for maximum benefit in a challenging climate

By Amber Lukk and Ann Willis

Figure 1. A site in the study reach of the Little Shasta River during summer baseflows. (Image credit: Amber Lukk).

In drought-prone northern California, limited water resources, private water rights allocations, and inefficient transport and use of water resources causes tension between freshwater conservation and private landownership (Garibaldi et al. 2020, Vissers 2017). In the face of a changing climate, drought curtailments will likely become more frequent, ratchetting stress on all water users (Vissers 2017). From an engineering perspective, efficiently managing water rights as arid landscapes become drier and less predictable will be essential to preservation of working landscapes and the environment.

Water purchases and leases are a common tool for securing water rights for environmental purposes. California recently considered a budget proposal to allocate $1.5 billion to buy-back private agricultural water rights to mitigate drought and support ecological uses (Bork et al. 2022). However, water right purchases can be incredibly expensive, and understanding which water rights are most likely to achieve maximal environmental benefit is vital for optimized management. Especially in coldwater habitats, the quality of water sources included in buy-backs will determine success of such efforts.

In our recent study (Lukk et al. In Press), we explore these concepts using a case study of a stream where water rights affect both spring-fed and surface water sources. The study focused on restoration of a portion of the Little Shasta River (Siskiyou County, Northern California) through reconnection of Evans Spring. This natural coldwater spring was historically a tributary to the Little Shasta, but is currently diverted for agricultural use. In the study, we explore effects of increasing stream flow using alternative water sources (e.g., in-stream runoff versus off-channel springs) to enhance coldwater habitat along a working cattle ranch.

Of the simulated scenarios, piping water directly from Evans Spring to the Little Shasta showed the greatest thermal benefits, with a maximum temperature reduction of 2.7°C. This scenario (Piping Scenario B) would provide substantive ecological benefits, especially for salmonids of conservation concern. The addition of surface water runoff, however, did not provide thermal benefits to the Little Shasta River. But while piping spring water provided the largest temperature benefit, this same strategy sacrifices potential benefits of off-channel habitat and restoration of the historical spring-fed channel. The trade-offs associated with piping versus historical channel restoration are important, as one option provides immediate benefit to existing habitat during current conditions when extreme low flows and warmer stream temperatures occur during the summer; the other reflects a more long-term conservation strategy.

No matter which option is pursued, the implications of these findings are that the source of water transfers is vital to success of an environmental water dedication. Water management practices aimed at increasing quantity of water dedications often overlook water quality in favor of an emphasis on quantity alone. When planning water inputs to a coldwater ecosystem, especially for the purposes of conservation, the water quality of the source water should be taken into consideration. Natural coldwater sources have considerable value for California’s native ecosystems, whereas their thermal quality is of little value for agricultural uses (Garbach et al. 2014). In contrast, other dedications may increase the amount of water available to streams, but result in little benefit because they have marginal ecological quality.

Figure 2. Results from the temperature model showing the differences in water temperature between the baseline measurement and the projected values from each alternative management scenario.

With the challenging unpredictability of freshwater resources, understanding the best possible uses for high-quality coldwater sources may provide the greatest benefits to the environment as well as adjacent working landscapes. For coldwater ecosystems, preservation of natural thermal regimes will be key to conservation efforts in the face of a changing climate (Willis et al. 2021). Prioritizing different water sources and when to use them may provide considerable benefits for the future of water resource and stream management in California.

Amber Lukk is an Assistant Specialist at the Center for Watershed Sciences. Dr. Ann Willis was a Senior Research Engineer at the Center for Watershed Sciences and is currently the California Regional Director at American Rivers; her research focuses on water management for stream conservation in working landscapes.

1 Response to Managing source water for maximum benefit in a challenging climate

Tom Cannon says:

December 4, 2022 at 8:21 am

The free-flowing sections of the little Shasta River should be a coho salmon sanctuary. In wet years adult coho can repopulate the sanctuary. In dry years eggs or fry can be transported from the Klamath Hatchery down the hill to the sanctuary. Winter flows would allow yearling coho to emigrate down to the Klamath.

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