Methods for Successful Construction of Vernal Pools - Case Studies in the Sacramento Valley.

ABSTRACT: “Methods for Successful Construction of Vernal Pools – Case Studies in the Sacramento Valley” In the Sacramento Valley, naturally occurring vernal pools are typically found on very old terraces with restricting claypans and/or duripans (hardpans) that have been dated from 30,000 to more than 500,000 years old. These depressional seasonal wetlands are regulated by the Clean Water Act. The conversion of natural landscapes into economically profitable leveled agricultural fields has resulted in loss of many habitat types, including vernal pool complexes. Since restoration to an exact pre-disturbance condition is usually not feasible for many leveled agricultural sites due to the drastic changes to the landscape and underlying hydrological processes, mitigation efforts in these areas typically focus on landscape-level restoration to achieve an optimal mix of uplands and wetlands . One method to compensate for the loss of these wetlands is to construct new vernal pools that replicate natural functions. Identifying appropriate soil types and their respective landscapes, especially in soils leveled for agriculture, are critical to successfully constructing or restoring vernal pools. These soil factors are instrumental in the design process, development of vernal pool construction plans, and the implementation of such plans. This presentation details examples of landscape characteristics and soil properties of pre-construction soil pits used to guide the conceptual design of constructed vernal pools, as well as implementation. Final habitat design is based upon shallow subsurface soil investigations of water restricting horizons -- i.e., claypans and/or duripans (hardpans) -- and analysis of existing vernal pools shapes and sizes. An example of one case study illustrates the construction of 327 vernal pools on about 80 hectares of irrigated pasture in southeastern Sacramento County, CA. Models depicting natural and altered soils and landscapes at the mitigation site are provided to illustrate the relationships of the depth of restricting layers to constructed vernal pools. Establishment of the proper relationship between the vernal pool bottom and the restricting layer is a critical step in successfully restoring this at-risk wetland habitat. This presentation provides results from several landscape and geomorphic analyses that demonstrate how the restoration objectives were achieved and the resulting alteration of the landscape. PRESENTER: Terry D. Cook, Soil Consultant 3214 Lillard Drive Davis, CA 95618 Ed Armstrong, David Burns, Christian Carleton, Sandy O’Bleness, Kenneth D. Whitney, PhD, Foothill Associates 590 Menlo Drive, Suite 1 Rocklin, CA 95765. TOPIC SELECTION: National Society of Consulting Soil Scientists ESTIMATED TIME: 1/2 hour PREFERRED PRESENTATION FORMAT: Podium