Measuring flood output from 110 coastal watersheds in California with field measurements and SeaWiFS

The 1300-km-long California coast receives output from watersheds that rang e from similar to 10 km(2) within the coastal mountain ranges to similar to 120 000 km(2) for the drainage basins of the Sacramento and San Joaquin Ri vers, Results from a combination of field and remote-sensing data, modeling , and digital techniques show that during the El Nino winter of 1998, the i mpact of sediment and water transport on nearshore waters from coastal wate rsheds was spatially extensive, varied with depth, and was comparable to th e impact of output from large rivers, The mass of sediment estimated from S eaWiFS data for 25 discrete and coalesced buoyant river plumes emanating fr om 110 watersheds was 2.2 x 10(6) t, Although the mass of all of the plumes represents only 1%-2% of the total sediment output from the rivers, the pl umes covered an area of 29 500 km(2) of coastal waters. An important cautio nary note is that the surface plumes visible in the remote-sensing data (ev en though nearly coincident with flooding) do not represent mass output fro m the rivers.