Historic Habitat Opportunities and Food-Web Linkages of Juvenile Salmon in the Columbia River Estuary and Their Implications for Managing River Flows and Restoring Estuarine Habitat, Physical Sciences Component, Progress Report.

Long-term changes and fluctuations in river flow, water properties, tides, and sediment transport in the Columbia River and its estuary have had a profound effect on Columbia River salmonids and their habitat. Understanding the river-flow, temperature, tidal, and sediment-supply regimes of the Lower Columbia River (LCR) and how they interact with habitat is, therefore, critical to development of system management and restoration strategies. It is also useful to separate management and climate impacts on hydrologic properties and habitat. This contract, part of a larger project led by the National Oceanic and Atmospheric Administration (NOAA), consists of three work elements, one with five tasks. The first work element relates to reconstruction of historic conditions in a broad sense. The second and third elements consist, respectively, of participation in project-wide integration efforts, and reporting. This report focuses on the five tasks within the historic reconstruction work element. It in part satisfies the reporting requirement, and it forms the basis for our participation in the project integration effort. The first task consists of several topics related to historic changes in river stage and tide. Within this task, the chart datum levels of 14 historic bathymetric surveys completed before definition of Columbia River Datum (CRD) were related to CRD, to enable analysis of these surveys by other project scientists. We have also modeled tidal datums and properties (lower low water or LLW, higher high water or HHW, mean water level or MWL, and greater diurnal tidal range or GDTR) as a function of river flow and tidal range at Astoria. These calculations have been carried for 10 year intervals (1940-date) for 21 stations, though most stations have data for only a few time intervals. Longer-term analyses involve the records at Astoria (1925-date) and Vancouver (1902-date). Water levels for any given river flow have decreased substantially (0.3-1.8 m, depending on river flow and tidal range), and tidal ranges have increased considerably (by a factor of 1.5 to 4 for most river-flow levels) since the 1900-1940 period at most stations, with the largest percentage changes occurring at upriver stations. These changes have been caused by a combination of changes in channel roughness, shape and alignment, changes in coastal tides, and (possibly) bed degradation. Tides are growing throughout the Northeast Pacific, and Astoria (Tongue Pt) has one of the most rapid rates of increase in tidal range in the entire Eastern Pacific, about 0.3m per century. More than half of this change appears to result from changes within the system, the rest from larger scale changes in coastal tides. Regression models of HHW have been used to estimate daily shallow water habitat (SWHA) available in a {approx}25 mile long reach of the system from Eagle Cliff to Kalama for 1925-2004 under four different scenarios (the four possible combinations of diked/undiked and observed flow/ virgin flow). More than 70% of the habitat in this reach has been lost (modern conditions vs. virgin flow with not dikes). In contrast, however, to the reach between Skamokawa and Beaver, selective dike removal (instead of a combination of dike removal and flow restoration) would suffice to increase spring SWHA. The second task consists of reconstruction of the hydrologic cycle before 1878, based on historic documents and inversion of tidal data collected before the onset of the historic flow record in 1878. We have a complete list of freshet times and peak flows for 1858-1877, and scattered freshet information for 1841-1857. Based on tidal data, we have reconstructed the annual flow cycles for 1870 and 1871; other time periods between 1854 and 1867 are under analysis. The three remaining tasks relate to post-1878 hydrologic conditions (flows, sediment supply and water temperature), and separation of the human and climate influences thereon. Estimated ob-served (sometimes routed), adjusted (corrected for reservoir manipulation) and virgin (corrected also for irrigation diversion) flows for 1878-2004 have been compiled for the Columbia River at The Dalles and Beaver, and for the Willamette River at Portland. Sediment transports for the ob-served, adjusted and virgin flows have been calculated for 1878-2004 for the Columbia River at Vancouver and Beaver, for the Willamette River at Portland, and for other west-side tributaries seaward of Vancouver. For Vancouver and Portland, it has been possible to estimate sand trans-port (including gravel), fine sediment transport and total load. Only total load can be estimated at Beaver, and only fine sediment transport can be determined for the west-side tributaries, except for the post-1980 period influenced by the 1980 eruption of Mt St. Helens. Changes in flows and sediment transport due to flow regulation, irrigation diversion, and climate have been estimated.

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