Final environmental statement: Maintenance dredging, Petaluma River, Sonoma and Marin Counties California

FINALENVIRONMENTAL STATEMENT MAINTENANCE DREDGING,PETALUMA RIVERSONOMA AND MARIN COUNTIES, CALIFORNIA August 1975 Prepared byU.S. Army Engineer District, San Francisco, Corps of EngineersSTATEMENT OF FINDINGS MAINTENANCE DREDGING, PETALUMA RIVER SONOMA AND MARIN COUNTIES, CALIFORNIA 1. I have reviewed and evaluated, in light of the overall public interest, the documents concerning the proposed action, as well as the stated views of other interested agencies and concerned public, relative to the various practicable alternatives in accomplishing the program for maintenance dredging in Petaluma River. 2. The possible consequences of the Petaluma River maintenance dredg­ing have been studied according to environmental, social well-being, and economic effects, including regional and national development, and engineering feasibility. 3. In evaluation, the following points were considered pertinent: a. Environment.il Cans iderations (1) Dredging Effects: (a) Dredging the Petaluma River will increase the average depth, hence the capacity of the river channel. This will alter the present flow and sediment transport regimens making the project area susceptible to higher average Salinity and increased shoaling rates upstream. The project may alstj cause the existing salt water wedge to intrude further upstream of the project .area than it now does. On the other hand, the project will improve the flushing efficiency of the river and provide greater capacity for flood control purposes. Because the upper reach of the project area is already under tidal influence, the biological response to these physical changes 'would be minimal. (b) As with nearly any dredging project the subject dredging will remove the existing interface between the water and bottom substrate which is an area of nigh biological activity. Benthic organ­isms inhabiting the sediment column to the two-foot overdepth dredged level would not only be destroyed in themselves, but also lest relative to their function