Lower Columbia River Sand Supply and Removal: Estimates of Two Sand Budget Components

Long-term changes in the sand balance of a river-estuary system can strongly affect navigation and ecosystems. Here, we examine two sand budget components in the lower Columbia tidal river, fluvial supply and human removal. Rating curves were used to estimate daily sand input between 1900 and 2010. Publications, interviews, and data analyses were used to evaluate sand removal by dredging and mining. Comparison between sand input and removal indicates that a sand deficit has existed for $>50$ of the last 85 years. Since 1962, the deficit has averaged $4.62\hspace{0.17em}(\pm 1.74)\times {10}^6\hspace{0.17em}{\text{ts-yr}}^{-1}$. Although historic sand transport to the ocean cannot be estimated, it is now small. Several factors contribute to the sand deficit: dredging, sand mining, flow regulation by dams, and climate change. The sand deficit documented here has likely contributed to the lower water levels in the tidal river observed in recent decades, which decreases habitat availability during high flows and channel depths during low-flow periods.