Instream flows: Five features of effective summer flow strategies

By Ann Willis

As summer begins and stream flows drop throughout California, concerns resurface about whether there’s enough water to support critical ecosystems. Environmental flows have long been a contentious issue, often presented in conflict with existing water use. But there are five key ideas worth remembering as water users and regulators throughout the state consider how best to support environmental objectives during these periods of naturally low stream flows within the framework of existing water laws and desired water use.

  1. Location matters.

Reduced cold water habitat during the summer is a common concern in a state that supports a number of cold water species, including spring-run Chinook and coho salmon. But while warm water or dewatered streams may appear alarming, they can be part of a stream’s natural condition. Smaller, headwater streams are more likely to have cooler water (assuming there’s snowmelt, rainfall runoff, or groundwater-fed springs to wet the channel).

But larger streams, areas that are far downstream from headwater sources or groundwater contributions, or streambeds of porous gravels are naturally warmer or even dewatered during the summer. These seemingly undesirable, intermittent flow conditions play an important role in supporting biodiversity. Providing instream flows to support cold-water species in these areas won’t overcome natural limitations to desirable habitat, and may promote undesirable, non-native species over native ones.

  1. Objective matters.

Instream flows are often proposed as a way to address a regulatory objective, like recovery of a target species. But each species has different needs at different life stages, so clearly identifying the objective for instream flows is important. Is it to reduce or maintain desirable water temperatures? Ensure passage upstream? Improve or sustain physical habitat? Different objectives have different flow and water quality requirements. Knowing what you’re planning for helps identify when, where, how much, and what quality of water is useful – or not.

  1. More water is not (necessarily) better.

When stream flows are reduced by diversions or regional groundwater use, and degraded ecological conditions also exist, it’s logical to conclude that adding water to the stream will resolve those ecological impairments. Except sometimes it doesn’t.

In general, if stream water is already warm, or the contributing sources are warm, adding water will not cool the stream down. But there are other situations where increasing stream flow can help. Studies show that adding water tends to have the greatest benefit when it’s used to address extreme low flow or water quality conditions – in the right location (see #1).

In the Shasta River, habitat conditions for fall-run Chinook improve the most when water is added to the lowest observed seasonal flows, when fish return to the system, but show little to no effect as these flows increase.


Additional streamflow improved available pool habitat in the Shasta River the most when water was added to the lowest baseflows. From Willis et al. (2015)

In an on-going study of oversummering habitat for coho salmon, preliminary results similarly show that additional water tends to have the greatest benefit when water temperature conditions are at their warmest and stream shade has yet to fully develop. But aside from those extreme conditions, adding water provides marginal, if any benefit. These unexpected findings have important implications, most notably that:

  1. Land and water use do not equal ecological degradation.

Over 80% of the Earth’s land is influenced by humans. Agriculture accounts for almost 70% of human water use. Given the extent of our footprint, achieving conservation goals by reserving habitat from human use or eliminating water use is insufficient and infeasible. Large-scale conservation efforts must consider how to create sustainable

A rice farm in the Yolo Bypass near Sacramento. Photo by Carson Jeffres

A rice farm in the Yolo Bypass near Sacramento. Photo by Carson Jeffres

biodiversity within human-dominated landscapes. This is reconciliation ecology.

Studies show that successful reconciliation is possible. In California’s Central Valley, rice farmers cooperate with water managers, scientists, and regulators to provide floodplain habitat on rice fields for juvenile Chinook salmon, creating some of the most successful growing conditions outside of hatcheries.

Photos by Carson Jeffres, UC Davis

Big Springs Creek in 2008, the year before fencing (left), and six months after cattle exclusion. Photos by Carson Jeffres, UC Davis

In the Shasta Valley, The Nature Conservancy demonstrated how to operate a cattle ranch – including diversions for irrigation –  while restoring and sustaining Big Springs Creek, the largest and most robust cold-water stream

Orchards of walnuts (above) and almonds (below) may be viable sites for groundwater recharge, though the potential for water damage to such high-value crops adds risk.

Orchards of walnuts (above) and almonds (below) may be viable sites for groundwater recharge, though the potential for water damage to such high-value crops adds risk. Photo by David Doll

for juvenile coho salmon in the lower Klamath Basin. Researchers are exploring how flooding fields can promote groundwater recharge while maintaining agricultural activities. These projects show the importance of reconciling land and water use with environmental objectives, as well as their potential for success.

So how do you design a management strategy for a stream system that reconciles ecological and water use objectives?

  1. Focus on QQST – Quantity, Quality, Space, and Time – to achieve long-term, viable, multi-objective water use.

Water management frameworks should explicitly recognize that realistic potential exists to support multiple and competing water uses (i.e., “co-equal goals”) when a stream exists in a reconciled state. QQST is a guiding principle to this framework that provides a method to efficiently identify competing water demands and develop flexible solutions.

Conceptual figure

A conceptual diagram of a stream system as it transitions from a baseline state, through a degraded condition, and into recovery with the implementation of interim, transitional, and long-term measures. From Willis et al. (2013)

Using the QQST principle, three types of management strategies can be developed to achieve established co-equal goals: interim (or “emergency”), transitional, and long-term measures.

Each management strategy is implemented depending on the condition of the aquatic ecosystem, which can be defined in various stages of degradation, recovery, or reconciliation.

Recent actions by the State to curtail water restrictions during the California’s severest drought conditions, and then ease water restrictions while implementing long-term policies to sustain California’s water resources (e.g., the Sustainable Groundwater Management Act) are good examples of the various types of interim, transitional, and long-term measures that can be used.

As the concepts of co-equal goals and reconciled ecosystems become more widely applied, approaches like QQST can help guide water users, resource managers, and agencies to effective and sustainable water management strategies.

Ann Willis is a staff researcher with the Center for Watershed Sciences. Her work focuses on management strategies to balance water resources to achieve co-equal goals of human and environmental water use.

Further reading

Willis et al. 2013. Water resources management planning: conceptual framework and case study of the Shasta Basin.

Willis et al. 2015. Instream flows: New tools to quantify water quality conditions for returning adult Chinook salmon. Journal of Water Resources Planning and Management.

UC Davis Center for Watershed Sciences. Nigiri Project: Growing Rice and Salmon on a floodway.

Bachand et al. 2015. Capturing El Nino for the underground. California Waterblog.

Yarnell et al. 2015. Functional flows in modified riverscapes: hydrographs, habitats and opportunities. Bioscience.

Allan JD and Castillo MM. 2007. Stream Ecology.

Rosenzweig ML. 2003. Reconciliation ecology and the future of species diversity

Sanderson et al. 2002. The human footprint and the last of the wild

Cosgrove and Rijsberman. 2014. World water vision: making water everybody’s business

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2 Responses to Instream flows: Five features of effective summer flow strategies

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  2. Joseph Rizzi says:

    Very nice article Ann. Your “Orchards of walnuts” reminds me that we should be planting more trees along or in the Rivers to add shade and keep the water cooler. Also Deeper rivers and/or pockets of pools along the rivers will help keep the water cooler. Keeping in mind that sediment makes rivers shallower over time so to keep the cold balance strategic deepening (not to increase flow speed but volume of water in river) is one of the best ways to help our friendly fish.

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