USGS Washington Water Science Center
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9722-DUP - Flood-Carrying Capacity and Sedimentation Trends of the Lower Puyallup River System - Phase I - Completed FY2010
Problem - Recent flooding in the Lower Puyallup River System, due in part to sediment aggradation in sections of river channel, has renewed interest in knowing the current flood-carrying capacity of the main stems of rivers in the Lower Puyallup River System and the flood-carrying capacity for different river-system management options. Sediment was commonly removed from the river until about the mid-1990s, when this practice largely ceased to protect aquatic habitat. It is not known how the change in sediment management has impacted the long-term aggradation/degradation trends and flood-carrying capacity of the lower Puyallup River system as a whole. A previous study evaluated the effects of potential new setback levees on aquatic habitat and function and the flood-carrying capacity of the system in Pierce County but did not include sediment management as a potential management option. Some stakeholders in the basin are considering both levee setback and sediment-management river-system management options to reduce flooding and increase habitat and want to know the likely impact of these potential options. As a result, a subset of the stakeholders, including the Puyallup and Muckleshoot Tribes, Pierce County, King County, and Pierce Conservation District have asked the USGS to assist in evaluating river-system management options. This study, conducted in cooperation with Pierce County, emphasizes trends in sedimentation and flood-carrying capacity for different river-system management options and represents a first step in the river-system-management-evaluation process.
Objectives - The general objectives of the study are to better understand the current flood-carrying capacity of the Lower Puyallup River System, the flood-carrying capacity for different river-system management options, and the long-term sedimentation trends of the system.
Relevance and Benefits - This study addresses issues related to flooding in a populated area of the Nation that also provides important habitat for endangered salmonids. The study is consistent with the USGS strategic science direction, "A National hazards, risk, and resilience assessment program: ensuring the long-term health and wealth of the Nation," identified in the strategic Science Plan of the USGS (U.S. Geological Survey, 2007).
Approach - The objectives will be met by a series of tasks, including 1) measuring channel cross sections in the Lower Puyallup River System; 2) analyzing changes in the sections since 1984; 3) analyzing historical changes in cross-section elevations at four USGS gages; 4) analyzing historical flood-carrying capacities at the same gages; 5) constructing a one-dimensional, steady-state hydraulic model and using the model to estimate current flood-carrying capacity; 6) conducting grain-size analyses of bed material along selected cross sections; 7) expanding the model of Task 5 to include a sediment-transport model and using the model to evaluate the impacts of potential river-system management options; and 8) documenting the study results in a report.
9722-EAF - Geomorphic Analysis of the Fluvial Response from Sedimentation Downstream from Mount Rainier, Washington - Phase II - Completed FY2012
Problem - Sediment input to the river systems draining Mount Rainier, Washington, has resulted in high rates of aggradation on selected reaches of the Carbon, Nisqually, White, and Puyallup Rivers, increasing channel migration and reducing the flood-carrying capacity (Czuba et al., 2010). Moreover, the listing of Puget Sound Chinook salmon and steelhead as threatened under the Endangered Species Act complicates river-management options available to resource managers when addressing increased flood risk. In addition, an apparent increase in the rate of aggradation along rivers within Mount Rainier National Park in the past two decades (Beason, 2007) may portend increased rates of alluvial aggradation in lowland rivers as sediment pulses move downstream.
Objectives - The objectives of the study are to estimate sediment input from the upper watershed of rivers draining Mount Rainier and estimate downstream transport of this sediment through the Puyallup River network (Puyallup, Carbon, and White Rivers) and along the upper Nisqually River upstream from Alder Lake.
Relevance and Benefits - This study addresses issues related to flooding in a populated area of the Nation that also provides important information explaining habitat for endangered salmonids. The study is consistent with the USGS strategic science directions "A National hazards, risk, and resilience assessment program" and "Climate variability and change" identified in the 2007-17 science strategy of the USGS (U.S. Geological Survey, 2007).
Approach - Analysis of the geomorphology of the rivers draining Mount Rainier will rely on published literature, unpublished data and expertise from professional colleagues, field-collected data, historical data, topographic data, hydraulic modeling, and the application of geomorphic principles of the downstream movement of sediment pulses in river networks.