At an October 27, 2016 meeting of the Delta Stewardship Council, John Leahigh, Department of Water Resources chief operator for the State Water Project, briefed the council on Water Year 2016. Precipitation-runoff and reservoir storage were up considerable compared to 2014 and 2015.  However exports were lower than expected, with reduced deliveries – only 5 to 75% – to south of Delta water contractors.

Mr. Leahigh attributed lower Delta exports to several factors:

• A concerted effort to conserve Shasta storage (for winter-run salmon) at the expense of water deliveries, mainly to south-of-Delta contractors.
• Higher summer Delta outflow that was needed to repel saltwater intrusion into the Delta caused by higher-than-normal tides associated with the warm-water “blob” along the coast. (This outflow served the dual purpose of reducing the salinity of Delta export water and allowing the water projects to meet salinity standards for Delta agriculture – see previous post.)
• Lower San Joaquin River Delta inflow that “creates a dynamic in the Delta that makes it difficult to move stored water from the Sacramento basin to the south Delta”.
• An inability to export Valley stormwater in winter-spring: “If we don’t pick it up, it ends up in the Bay and into the ocean.”  (This is a not-too-subtle reference to winter-spring export restrictions for endangered fish and pitch for the proposed Delta tunnels.)

Mr. Leahigh concluded:  “I think the key messages would be flexibility, nimbleness, and the fact that we have processes in place that would help us react to whatever we end up seeing in the coming year; there’s always a new challenge with respect to the hydrologic pattern and the regulatory environment, so just having those processes in place puts us one step forward.”

The important lesson here is that the state and federal water projects are flexible and nimble when it comes to water exports and deliveries.  When it comes to the short-term needs of the fish and their habitat, not so much.  The projects are ready with Temporary Urgent Change Petitions to benefit water deliveries, but not the environment.

In the coming months and years, regulatory processes involving water rights, water quality, and endangered species will determine the future of Central Valley fishes.

To protect and enhance these fish populations, these processes will need to address four fundamental needs:

1. River Flows
2. River Water Temperatures – holding, spawning incubation, juvenile rearing and migration.
3. Delta Outflow, Salinity, and Water Temperature
4. Valley Flood Bypasses

In the previous Part 1a post, I discussed river flows during fall.  In this post, I discuss river flows during winter.

Winter Flows

Winter is the season of high river natural flows.  Even in drought years, Sacramento River flows measurably spike during storms that provide stormwater runoff from numerous undammed tributaries and local sources (Figure 1).  On the mainstem Sacramento River and those of its tributaries that also feature rim dams, most of the stormwater inflow is captured and stored for spring-fall water supply.  On the San Joaquin River, all the major tributaries and mainstem have large storage reservoirs that capture Sierra and upper Valley runoff, so there is limited controlled winter runoff (Figure 2).

Winter flows are needed to attract adult winter-run and spring-run salmon, smelt, steelhead, and sturgeon to upriver spawning grounds.  Winter flows also carry young salmon and steelhead to the Delta, Bay, and ocean by providing velocity, water temperature, and turbidity conditions that speed migration and deter predation by birds and fish.  Winter flows stimulate food production and availability.  Winter flows and associated high water levels provide access to off channel and floodplain rearing areas that provide refuge and food.  Winter flows clean substrate and wash gravels, and thus improve spawning conditions.  High winter flows wash sediment, nutrients, and organic material into the estuary that stimulate Bay-Delta productivity.

On the Sacramento River, winter flows carry juvenile winter-run, spring-run, late-fall-run, and fall-run salmon through up to 200 miles of rivers and the Delta to the Bay and ocean.  Much of the route is leveed and channelized, with little cover/refuge and abundant predators.  Higher flows provide turbidity and lower water temperatures that deter predation.

In the San Joaquin River watershed downstream of the rim dams, flows are minimal in the absence of flood flows and dam spills.  Thus, de facto drought conditions persist downstream of San Joaquin watershed dams in all but the wettest years.  Recruitment into the salmon populations is confined to San Joaquin offspring produced in wet years, augmented by hatcher strays, since there is minimal juvenile survival to the ocean in other years because of low flows.

In the non-flood years where reservoirs capture most reservoir inflow during the winter, supplemental releases from Central Valley reservoirs should be considered to piggy-back on and enhance natural flow pulses to benefit salmon and other native fish.  Such action would most benefit salmon populations below rim dams.  Such releases can be prescribed as a portion of the natural or unimpaired inflow to the reservoirs.

Figure 1. Daily average Delta inflow from the Sacramento River 2012-2016 as measured at Freeport. Red circles denote winter-spring flow pulses that support important ecological processes such as salmon migration. Water years 2012-2015 were drought years; 2016 was a below-normal water year.

Figure 2. Delta inflow from the San Joaquin River 2012-2016 as measured at Vernalis. Prescribed fall and spring flow releases from reservoirs for salmon migrations dominate the hydrograph in these drought years. Winter flow pulses were lacking with the exception of 2016. Water years 2012-2016 were drought years in the San Joaquin watershed.