Alameda Creek Watershed Sediment Forum

About Alameda Creek

Introduction

Alameda Creek is the largest watershed in the Bay area draining approximately 650 square miles of the East Bay interior hills and valleys, including the Livermore-Amador and Sunol valleys. The creek then cuts through the East Bay Hills via Niles Canyon before flowing across its large alluvial fan and floodplain complex, ultimately discharging into the southern portion of the San Francisco Bay. Average annual rainfall in the watershed varies from 24 inches on Mt Hamilton at an elevation of 4,400 ft above sea level to 15 inches near the Bay margin in Fremont. In addition to the growing urban areas of Livermore, Dublin, Pleasanton and Sunol where collective population has risen from 70,000 in 1970 to 170,000 in the 2000 census, the watershed is managed for grazing, equestrian facilities, nurseries, and, more recently, vineyards. There are three major reservoirs (San Antonio, Del Valle, and Calaveras that collectively store 225,000 acre-feet) in addition to a groundwater recharge and pumping complex downstream that relies on the Niles Cone aquifer. All together, about 3,000,000 residents of the Bay Area rely on Alameda Creek for clean drinking water. The wide range of topography and climate provide for the beneficial uses of agriculture, groundwater recharge, fisheries (cold water, warm water, spawning, and migration), rare and endangered species, recreation, and wildlife habitat.

The Sediment Dichotomy

A combination of eroding soils, landslides and debris flows, and incising and widening channels annually supply large volumes of sediment to the Creek. Coarse sediment is positive for the creek segments managed for spawning and rearing habitat for salmonids. However, those same coarse sediments can fill reservoirs and the downstream flood control channel in Fremont, impact bridges, and impair regular operation and maintenance of groundwater pumping and percolation facilities. Fine sediment is generally deleterious to all the beneficial uses of the Creek. However, once both types of sediment have passed through the flood control channel and into the Bay, they are valuable as the supply for the biological and physical material necessary for wetlands on the Bay margin. Hence, agencies managing different parts of the Creek system face a dichotomy of competing needs with regards to coarse and fine sediment.

Developing Information and Coordination among Groups

Agencies, stakeholders, and land owners have begun the process of learning about where sediment comes from, what kinds of sediment are in the Creek (coarse versus fine), what measures may be affective to protect channels, how it moves through the system, how it collects behind structures and in channels, and how much of it moves through to the wetlands on the Bay margin. Presently, much of this information is being collected in isolation by agencies in response to their individual needs and goals. However, due to a common regulatory framework, there are likely instances where sharing information or perhaps even developing joint monitoring, research, or modeling projects would reduce overall costs and increase the usefulness of the information generated.