A Novel Approach to Flow and Sediment Transport Estimation in Estuaries and Bays

Abstract

Reliable estimates of river discharge and sediment transport to the ocean from large tidal rivers are vital for water resources management, efficient river and harbor management, navigational purposes, and climate analyses. Due to the difficulties inherent in measuring tidal-river discharge, hydrological and sedimentological records are typically too short to adequately characterize long-term (decadal) trends. Also, uncertainties associated with observation and calibration of hydrological models suggest a need for more accurate methods based on longer records of hydrodynamic parameters (e.g. tides). Tidal theory indicates that tides and river discharge interact through quadratic bed friction, which diminishes and distorts the tidal wave as discharge increases. In this study, using tidal constituents, astronomical forcing and a model of the frictional interaction of flow and tides, I propose a novel Tidal Discharge Estimate (TDE) to predict freshwater discharge with an approximate averaging interval of 18 days for time periods with tidal data but no river flow records. Next, using continuous wavelet analysis of tidal properties, I develop a method of estimating river discharge using tides measured on multiple gages along tidal rivers to improve the time-resolution and accuracy of TDE. The applicability of the Multiple-gauge Discharge Estimate (MTDE) is first demonstrated in the two largest tidal-fluvial systems of the Pacific Northwest, the Columbia River Estuary (CRE) and Fraser River Estuary (FRE). A numerical model of an idealized estuary with similar forcing as the FRE and CRE is next run under different hydrologic and morphologic scenarios to evaluate the effect of convergence, friction, and river flow variations on the applicability of MTDE. The TDE method was applied to the San Francisco Bay, using the continuous hourly tide record available since 1858. Results show that TDE reproduces known San Francisco (SF) Bay delta inflows from 1930-present with a Nash-Sutcliffe coefficient of 0.81 and is a useful method for hindcasting historical flows from 1858 - 1929, a period that predates direct measurement of delta discharge. I also recover and digitize ~80 years of Sacramento River daily water level data between 1849 and 1946, from which river discharge to SF Bay is estimated on a daily basis, after adjusting for changes to the river channel. This discharge combined with Net Delta Outflow Index estimates (1930 - 2011) and flow estimates from tidal data (1858 - 2011) provides a more accurate version of SF Bay historic daily inflows from 1849 - 2011. Next, the history of sediment transport and