Anthropogenic accommodation space, or that space in the Delta that lies below sea level and is filled neither with sediment nor water, serves as a useful measure of the regional consequences of Delta subsidence and sea level rise. Microbial oxidation and compaction of organic-rich soils due to farming activity is the primary cause of Delta subsidence. During the period 1900-2000, subsidence created approximately 2.5 billion cubic meters of anthropogenic accommodation space in the Delta. From 2000-2050, subsidence rates will slow due to depletion of organic material and better land use practices. However, by 2050 the Delta will contain more than 3 billion cubic meters of anthropogenic accommodation space due to continued subsidence and sea level rise. An Accommodation Space Index, which relates subaqueous accommodation space to anthropogenic accommodation space, provides an indicator of past and projected Delta conditions. While subsidence and sea level rise create increasing anthropogenic accommodation space in the Delta, they also lead to a regional increase in the forces that can cause levee failure. Although these forces take many forms, a Levee Force Index can be calculated that is a proxy for the cumulative forces acting on levees. The Levee Force Index increases significantly over the next 50 years demonstrating regional increases in the potential for island flooding. Based on continuing increases in the Levee Force Index and the Accommodation Space Index, and limited support for Delta levee upgrades, there will be a tendency for increases in and impacts of island flooding, with escalating costs for repairs. Additionally, there is a two-in-three chance that 100-year recurrence interval floods or earthquakes will cause catastrophic flooding and significant change in the Delta by 2050. Currently, the California Bay-Delta Authority has no overarching policy that addresses the consequences of, and potential responses to, gradual or abrupt landscape change in the Delta.

California is home to 64 military facilities, more than any other state. All four military service branches, in addition to the US Coast Guard, operate facilities in California. More than half of California's military facilities are located within, at the edge of, or within a stone's throw of major metropolitan areas.

California is also home to more than 34 million people, most of whom live in metropolitan areas. By 2020, the California Department of Finance projects, California's population will grow to 45 million. If past trends continue, the majority of this growth will occur at the edges of existing metropolitan areas, nearby or adjacent to active military facilities.

Many military facilities conduct operations that extend beyond their perimeter boundaries and generate significant aircraft and artillery noise. As California's population grows, the number of people living near military facilities and impacted by facility operations will also grow.

Without some degree of forward planning to reconcile the space needs of California's growing population with the operational needs of the military, the encroachment of urban growth on California military installations may significantly compromise the presence, functions, and missions of the military in California.

This report provides information regarding the potential encroachment effects of projected population growth and urban development on California military installations. It also presents and evaluates alternative planning and policy approaches for dealing with current and projected encroachment issues. Finally, it develops a web-enabled spatial database for use by civilian land use planners and military operations planners in analyzing encroachment issues and undertaking future encroachment zone studies.