California Department of Water Resources (DWR) | August 17th, 2017
Summary
When the 2012 Central Valley Flood Protection Plan (2012 CVFPP) and Conservation Framework were adopted by the Central Valley Flood Protection Board (CVFPB), the CVFPB co
When the 2012 Central Valley Flood Protection Plan (2012 CVFPP) and Conservation Framework were adopted by the Central Valley Flood Protection Board (CVFPB), the CVFPB considered the levee vegetation management strategy contained in the 2012 CVFPP as interim. CVFPB Resolution No. 2012-25 directed the California Department of Water Resources (DWR) to further develop the interim strategy into a more comprehensive approach. Resolution No. 2012-25 further directed that the approach be adaptive and responsive to the results of ongoing and future research regarding vegetation on levees, knowledge gained from levee performance during high-water events, and the need to conserve critical riparian habitat. The DWR vegetation management approach described in this appendix reflects efforts to develop a more comprehensive levee vegetation management strategy that consists of efforts to manage levee vegetation, channel vegetation, and invasive plants. Levee vegetation management is particularly important because levee vegetation can impede visibility and accessibility for inspections and flood fighting, and in some limited cases, it may pose an unacceptable threat to levee integrity. In channel areas in between State Plan of Flood Control (SPFC) levees, the floodplain and channel may provide opportunities for important riparian and wetland habitat, as well as agricultural operations. However, land uses in these areas also need to be managed to maintain the channel’s ability to convey high flows during flood events. Finally, invasive plants can adversely affect operations and maintenance (O&M) of the SPFC and are a documented stressor on the species, habitats, and ecosystem processes targeted by this Conservation Strategy. Management of invasive species, and eradication of them where feasible, reduces O&M needs by increasing channel capacity and provides important ecosystem benefits.
DWR water resources managers have been implementing the interim strategy to balance public safety with environmental quality. Current and future work will focus on improving public safety by providing for integrity, visibility, and accessibility for inspections, maintenance, and flood fight operations; at the same time, protecting important and critical environmental resources. DWR’s approach also includes ongoing policy discussions regarding potential compatibility with United States Army Corps of Engineers (USACE) levee vegetation guidance through recognition of regional variations and prioritization of levee remediation based on risk assessment. Retaining lower waterside vegetation is a leading example of how risk assessment is coupled with recognition that widespread loss of habitat on levees, particularly on the lower waterside slope, is unmitigable. The Conservation Framework identified roughly two-thirds of the riparian habitat that occurs on SPFC levees is found on the lower waterside slope. On-going DWR analyses are further evaluating this assumption. In addition, risk assessment has shown that removing this vegetation, and conducting required levee remediation, likely would not be a worthwhile investment of flood risk reduction dollars. On the contrary, vegetation in this area has long been recognized as offering protection to levees from wind and wave wash erosion (USACE 1955). Expending resources to address factors contributing to lower risk would have to be considered against expending these resources to address other levee conditions that pose a significantly higher risk (DWR 2011). Similarly, DWR is assessing how to identify trees that may pose an unacceptable risk to levee integrity in a manner that retains the majority of existing habitat over its normal life span. Ongoing research, as well as knowledge gained from levee performance during high water events, will continue to inform how vegetation management within and around the SPFC may continue to evolve toward meeting multiple objectives, including sustainability of critical environmental resources. DWR anticipates revising vegetation management policy and guidance as needed in the ongoing five year updates to the CVFPP.