Posted by: Deirdre Des Jardins | August 6, 2019

DWR rescinds engineering performance standards for Delta tunnel

The Department of Water Resources delegated the design and construction of the WaterFix project to the Delta Conveyance Design and Construction Authority in the October 2018 Joint Exercise of Powers Agreement.   The Joint Exercise of Powers Agreement included performance standards for the engineering design of the project. The performance standards included requirements that the Delta conveyance be designed to withstand a maximum earthquake, and to have a 100 year lifetime.

The June 2019 Amendment to the Joint Exercise of Powers Agreement rescinded the engineering performance standards.  This should be of concern to water agencies evaluating whether to participate in the Delta conveyance project.

The requirement for a 100 year design lifetime is particularly important because of sea level rise. The impact of sea level rise on the North Delta intakes was last evaluated in 2010.   The hydrodynamic modeling assumed 55 inches of sea level rise by 2100, which is about half that of current maximum estimate of 10 feet.

SLR 2200

US Army Corps of Engineers   Sea level rise in the Delta through 2200

The 2010 modeling also evaluated the impacts of widespread levee failure, but used a grid from the Delta Risk Management Strategy modeling that only went as far north as Isleton and Bouldin Island.   So the modelling implicitly assumed that only levees in the South Delta would fail.

grid

 Grid used for modeling of salinity intrusion for DRMS and North Delta intakes

For these reasons, California Water Research  has recommended that more hydrodynamic modeling be done to assess the impacts of extreme sea level rise on the previously proposed North Delta intake locations.

The Delta Independent Science Board made similar recommendations in their 2014 review of the Delta conveyance project, stating,

If the effects of major environmental disruptions such as climate change, sea-level rise, levee breaches, floods, and the like are not considered … one must [not] assume that the actions will have the stated outcomes.

Without such an assessment, there is insufficient information for decision makers to evaluate the Delta tunnel as a water supply project.


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