Hydrology and Sedimentation 4
HYDROLOGY AND SEDIMENTATION 4 The Laguna de Santa Rosa watershed, set in a Mediterranean climate, has a complex and variable hydrology. The watershed includes numerous tributary streams, the majority of which drain west from the Sonoma Mountains across the Santa Rosa Plain towards the northwest trending Laguna wetland ecosystem (see figure 4-1). The uplands are drained by high-gradient, high-energy, coarse-bedded mountain channels, which flow down the hillsides to the broad, flat, vernal pool-dotted Santa Rosa Plain. The main stem Laguna is a slow-moving channel that has a unique character, which was once described as: “neither river, nor pools, nor floodplain, nor marsh, nor vernal pool – but with the characteristics of all, plus other characteristics, and a distinct type of watercourse related to physical feature, but a rare one” (LAC, 1988). The character of Laguna watershed channels reflects underlying geological structures. The Santa Rosa Plain is surrounded by two actively uplifting ranges: The Santa Rosa block in the east (underlying the Mayacamas and the Sonoma Mountains) and the Sebastopol block in the west (underlying the Gold Ridge). The boundary between these two blocks is the western edge of the Laguna floodplain, near Sebastopol. The blocks are oriented on roughly a northwest-southeast axis, and both tilt towards the Laguna (Hitchcock and Kel- son, 1998). The Santa Rosa block has a major laterally displaced slip-strike fault system (the Mayacamas-Rodgers Creek faults) that forms the topographic boundary between the gen- tly sloping Santa Rosa valley and the steep slopes of the Mayacamas and Sonoma Moun- tains.
[Show full text]