Napa County Erosion Control Plan CEQA Initial Study

Long Properties Vineyards Projects, Lake Hennessey, Napa County

Client:  Napa County / Lamphier-Gregory Associates

Questa completed a soils, hydrologic, and geomorphic analysis of the proposed Long Properties vineyard development project.  This project consisted of five different parcels totaling approximately 211 acres, with vineyards to be established on 87 acres. The project involved conversion of oak savannah, grasslands, and chemise chaparral plant communities to wine grapes.  Since there are several older inactive landslides near the project area, and many of the streams draining the property to Lake Hennessey have steep gradients, geologic and geomorphic stability proved to be an important issue to evaluate. The hydrologic analysis included a characterization of the existing hydrologic setting and described potential hydrologic/runoff impacts of vineyard conversion.

Questa’s soils/geologic analysis involved compiling information of the soils and geology/slope stability of the project area, including an air photo review to examine surficial geologic instabilities. Questa also conducted geomorphic reconnaissance of the creek system in the greater project area, which involved mapping existing bank erosion and creek instability areas and evaluating reference creeks in areas below existing vineyards to provide a qualitative understanding of potential geomorphic impacts of vineyard conversion.