SPATIAL AND TEMPORAL PATTERNS IN FLOODING OF US WEST COAST RIVERS

Long term water discharge records were examined for more than 40 rivers stretching from the US-Canada Border to the US-Mexico Border. Analysis shows that flood discharges from many rivers are strongly correlated on varying time and spatial scales. The episodic delivery of freshwater and sediment from these rivers is strongly controlled by the storm tracks, storm frequencies and intensities. This may result in hourly, daily or seasonal differences in flood timing and may lead to large differences in the sediment transport on the shelf and therefore the fate of the sediment.

The fate of the sediment in the coastal oceans is driven by the physical processes acting to move the sediment from the river mouth. This could be as sediment near the water surface (buoyant plumes), within the water column (suspended sediment) and/or near the seafloor (dense underflows). The timing of the sediment delivery with relation to the fluctuations in wave energy is important in determining the fate of the material. Suspended sediment data is not extensively available for many small rivers draining the coastline. However, since the sediment flux is closely coupled with freshwater flux, and long-term freshwater discharge data is available, a detailed investigation into the timing of flood delivery of sediment from these rivers is possible. The coherence between the Fluvial and the Oceanographic Processes determines the fate of the material discharged to the shelf on varying timescales.