John R. Ritter


Tidal flow and suspended-sediment discharge were measured in or near the inlet to Bolinas Lagoon through seven ebbtides and six floodtides. The highest flows and suspended-sediment discharges occurred during the major daily ebbtide. Most transported sediment was sand and most sediment deposited in the lagoon was sand. Computations from a relation of suspended-sediment discharge and tidal range indicated that the annual suspended-sediment discharge of ebbtides exceeded that of floodtides by 9,000 tons. The highest concentration of suspended sediment occurred near the east shore of the inlet, which is at the end of a sand spit. The measured volume of water moved by a tide ranged from 180 to 2,740 acre-feet and the maximum flow measured was 7,900 cubic feet per second. The highest average velocity for a measurement was 4.9 feet per second. The maximum average velocity in the inlet occurred within an hour after midtide during a floodtide and usually at about one-third tide during an ebbtide. The relation of average tidal velocity (ut) to tidal range (R), was ut = 1.21R'50°; the average flow for a tide can be estimated by multiplying this calculated average velocity by the average cross section of the inlet.


tidal flat; sediment transport

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