The Columbia River estuary serves as an important migration, rearing, and transition environment for juvenile anadromous salmon before they enter the sea. Historical modifications to the estuary, including diking of peripheral wetland and floodplain habitats, modification of the tidal regime, and regulation of river flows by dams, have reduced salmonid access to shallow rearing habitats and may have eliminated sources of macrodetritus that fuel the estuary's food webs. Although emerging evidence suggests that these estuarine changes are limiting juvenile salmon production and life history diversity, lack of information about historic and modern habitat conditions in the estuary, or the ecological consequences of habitat change, undermine existing salmon recovery efforts of the Columbia Basin Fish and Wildlife Program. This contract continues the Portland State University component of a BPA-funded study to address specific information needs identified in an interdisciplinary assessment of the hydroelectric system's impacts on estuarine habitat opportunity and capacity to support diverse life histories of juvenile salmon. The work elements addressed by this sub-contract include: (1) contributing to retrospective analyses that reconstruct historic bathymetric features and tidal processes and assess effects of climate and river flow on the extent and distribution of shallow water, wetland and tidal-floodplain habitats; and (5) examination of effects of alternative flow-management and habitat-restoration scenarios on habitat opportunity and the estuary's productive capacity for juvenile salmon.