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Say it ain’t Flow

The Delta Stewardship Council held its January meeting on the 27th and the 28th, before comments from two weeks of January scoping meetings could be compiled, condensed and processed for consumption.  They have a Delta Plan to complete by January 2012.

On the first day of the DSC meeting, Independent Science Board Lead Scientist Cliff Dahm made a presentation to the Council on Setting Flow Criteria for Estuaries and Rivers.  He cited firsthand accounts, published scientific literature, and other data used in analyzing, quantifying, and setting flow criteria.  He gave examples from Texas, Australia, South Africa, and Florida, where a 15% reduction in flow threshold has been designated as a point where “considerable harm” may be done to the ecosystem.

Dr. Dahm cited conjunctive groundwater use as an effective measure to reduce surface diversions in Florida. He made it as clear as he could that “FLOW is recognized widely as a critical driver in estuary systems.”  He suggested that our export regimen be overhauled in such a manner that we may more easily mimic the natural flow regime of our system,  and he demonstrated graphically how we have been violating this 15% or even 25% threshold for decades, especially in times of low flow when irrigation demands are highest.

(Historically in California, we actually divert more surface flow in dry years than in wet years, and most experts in Aquatic Ecology would argue that proportionately larger exports during periods of low flow cause “considerable harm” to the ecosystem.)

Dr. Dahm used actual historic data from the Bay-Delta estuary to support his assertion that if we were able to capture and convey this water during peak flows, California could expect only minor, if any, reduction in Delta water supply.  And we would have that supply without harm to the ecosystem.


Hydrologist Dr. Lucas Paz spoke on the subject of flows and used more pliable flow charts and less demonstrative graphics.  But the message was the same: Flow is a major determinant in estuarine health. Both scientists said that exports should not be taken in a long, slow “suck” but should be “gulped” from the system or not taken at all.If we hope to restore populations of native keystone species, such as Chinook Salmon and Steelhead, as much effort as possible should be made to mimic the natural hydrology of the System.

Devil’s advocate questioning from the Council failed to undercut the scientists’ message on the importance of flows of clear, clean, cold water.

(Gary Bobker of the Bay Institute notes that “Flow is necessary, but not sufficient,” adding that reductions in point source pollution need to be made as well.)

Byron Buck. Executive Director of the State and Federal Contractors Water Agency, admitted that previously, population indexes of certain key species showed a correlation between species decline and export levels, but more recently those correlations seem to have disappeared.  Mr. Buck and his associates may be making a statistical error known a Type II correlation error.

This type of error occurs when there are so few of the selected representative species present in the system that the numbers are not sufficient to demonstrate a correlation between two variables.  The analysis will contain failed alarms or false negatives. The alarm may fail purely by chance: the effect is present in the population, but the sample you drew doesn’t show it.

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  • February 14, 2011, 10:38 pm

    We must not make the same mistakes and we must save the Delta from Big Ag, developers and the big city of LA. Proper water flows must be maintained if we are to have a healthy delta and SF Bay! Cities must be a part of this. Like Bay-Friendly which educates professionals about proper water control on land the cities can coordinate with such entities in getting Architects, developers, Land Management personnel and home owners/property owners to understand the importance of water conservation and control. Another diversion no matter what it is called isn’t what is needed here!
    More coordination between cities and counties in planning where to build new structures and how to implement real water conservation is needed. Our water resources are limited and we all need to act like we recognize that fact and plan accordingly.