Darryl Murray Hicks
Published: 1985
Total Pages: 468
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The delta was studied to determine the time scale and mechanisms by which river sand was incorporated into the longshore transport regime. The results are pertinent to sediment management on coasts with Mediterranean type climates and drainages. On such coasts, generally, rivers supply most of the littoral sand yet the bulk of this supply accompanies large infrequent floods. In contrast, the nearshore transport processes operate with much greater continuity and regularity. The delta studied was built by a 30-year return period flood at the mouth of the San Lorenzo River. The peak discharge at the river mouth during this flood was about 1,100 cu m/sec. The river drains an area of 357 sq km on the northern shore of Montertey Bay. There, most wave energy arrives as swell from the northwest and, except during brief flood periods, it dominates the river outflow. As a result, the San Lorenzo delta is an ephermeral feature. The study extended two years: in both years the river's supply of sand and gravel was about 300,000 cu m ten times its mean annual supply and equivalent to almost twice the mean annual net longshore transport past the mouth. Methods of investigation included: surveys of nearshore topography, estimates of the river's littoral sediment yield using river flow data and river channel surveys, and estimates of the longshore variation in longshore-transport potential using a wave refraction program. The surveyed sand level changes provided a means of tracing bulk sand movements. The longshore transport predictions were used to confirm the direction of sand movement.
