PWA teamed with H. T. Harvey & Associates (HTH) and the San Francisco Estuary Institute (SFEI) to provide a preliminary design for river and wetland restoration across the area known as Soap Lake, a 9,000-acre floodplain on the Santa Clara and San Benito County border. Soap Lake is the floodplain of the Upper Pájaro River and functions as a natural detention basin that greatly reduces the peak of floods many miles downstream in the towns of Watsonville and Pájaro. It is a natural (though degraded) migration corridor for animals and birds moving between the Santa Cruz Mountains and the Mount Hamilton Range. San Felipe Lake, a central feature of the floodplain, has been recognized by the Audubon Society as a “globally-important” site for birds.

The project goal is to preserve and restore a habitat corridor along the Pájaro River, spanning the southern Santa Clara Valley, and connecting wildlife populations in the Santa Cruz Mountain Range to those in the Hamilton Mountain Range. The objectives include the preservation and restoration of Soap Lake to an approximation of its historic condition which would involve the restoration of extensive freshwater/alkali wetlands (up to 308 ac) and riparian habitat (up to 381 ac) along the historic floodplain of the Upper Pájaro River, Tequisquita Slough and lower Pacheco Creek.

PWA and HTH performed a detailed assessment of opportunities and constraints for restoration at Soap Lake. PWA performed topographic surveys on site to enhance our hydrologic and hydraulic analyses of existing and proposed floodplain inundation in Soap Lake. HTH conducted an assessment of existing soil salinity, depth to groundwater, invasive plant species, poison hemlock, Japanese knotweed, Hoary cress, giant reed, steelhead and special-status vernal pool plant species.

In collaboration with The Nature Conservancy, PWA and HTH developed three conceptual restoration design alternatives including an explanation of the expected biological and hydrologic conditions. The restoration design is complementary and synergistic to many other local and regional planning efforts and to the goals of public and private entities.