addressing climate change adaptation in regional transportation plans

Setting and HistoryThe California Delta is the center of a vast river network that drains the centralvalley of California, receiving roughly 80 percent of the water in the state (DeltaVision, 2008). The Delta is fed by several rivers, the largest being the SacramentoRiver and the San Joaquin River, in addition to the Mokelumne, American, andCalaveras rivers. These rivers empty into the low-lying basin of the Delta, whichoutlets to San Francisco Bay and then the Pacific Ocean.Before the 1850s, the Delta was nourished by semi-annual flooding and theaccompanying sediment deposits, making for vast wetlands of channels andislands. As the sediment supply was curtailed through flood control and theland was converted to agriculture, the elevation of large portions of the Deltadropped below sea level making this area prone to more frequent flooding.Levees were constructed to protect the agricultural and residential areas onwhat are now below-sea-level islands. The drop in elevation continues, resultingin a need for increased levee height over the roughly 2,000 kilometers of leveesthat continuously hold back water in the low-lying areas(see Figuire 8).The state water system (Central Valley Project and State Water Project) relies onthe Delta as the conduit for water exported from the north to the south. In itsentirety, the Delta is home to over half a million people, yet more than 23 millionpeople rely on water that travels through the Delta, and one sixth of all irrigableland in the United States is in the Delta watershed (PPI, 2007). Conditions in theDelta have been altered dramatically from its pre-developed state. These changeshave endangered many native species and created habitat for even more nonnativespecies.The water supply, economic viability, and environmental resources of the Bay-Delta region are critical to the state.Climate Change Impacts in the Lower Bay-DeltaClimate change is expected to result in the following impacts in the lower Bay-Delta:• Higher temperatures and increased storm/wind activity may exacerbatedrops in elevation of low-lying areas.• Changes in the magnitude of precipitation and precipitation/snowmelt runoffintensity may reduce control of the salt water front that is artificially helddownstream of water export pumps.• Sea level rise is not expected to have an appreciable impact on the seismicvulnerability of the lower Delta.APG: UNDERSTANDING REGIONAL CHARACTERISTICS PAGE 52