1020.pdf

Reach 1 (estuary to Highway 101 bridge) contains 297,000 yd³ sediment above present thalweg, with 195,000 yd³ active. Reach 2 (Highway 101 bridge to McArthur Creek) holds 785,000 yd³, of which 265,000 yd³ is active. Gravel and sand occur in terraces, point bars, mid-channel bars, and side bars. Terraces and point bars are stable bed forms that should not be disturbed; vegetated bars should also remain untouched. Unvegetated sediment is easily mobilized. Preliminary survey identifies orange-marked areas potentially excavatable without stream damage. Sediment size distribution analysis shows median particle sizes ranging from 0.5 to 32mm across sites. Lithology consists of 30-70% schist (average 50%), sandstone (30-60%), and chert, quartz, greenstone, and conglomerates (about 10%). The largest particles are sandstone; fine fraction (<8mm) primarily derives from schist. This represents an initial survey, not approval for gravel excavation.