RSS FeedsGroundwater Hydrology
This chapter of the BDR describes groundwater in Napa County, documents the groundwater system, and describes the methods used to determine existing groundwater hydrology and the policies that apply to groundwater in Napa County. This chapter also describes the approach and data used in developing a local integrated surface water and groundwater model. The Groundwater chapter is complementary and builds on the general surface water hydrology discussion presented in Chapter 15, Surface Water Hydrology, of the BDR. A supporting technical report (Napa BDR Groundwater Hydrology Modeling Report) was developed and includes a more complete documentation of the groundwater model construction, calibration, sensitivity analysis, and presentation of results. Consulting hydrologists from DHI Water & Environment led the surface hydrology, groundwater, and water quality tasks of the BDR (Chapters 15, 16, and 17, respectively), working collaboratively with other specialists from the Jones & Stokes/EDAW project team.
A physical-based integrated surface water/groundwater (ISGW) numerical model was refined for the groundwater resources chapter. The MIKE SHE/MIKE-11 groundwater model builds on the surface model described in the surface water quality chapter of the BDR, expanding the original model’s capabilities to analyze groundwater resources as well. To facilitate the analysis of groundwater resources, the County was divided into 11 evaluation areas. Extent of the groundwater analysis focuses on the aquifers underlying the 11 evaluation areas. The resultant MIKE-SHE ISGW model represents the subsurface domain (saturated zone) as a single- or multi-layered two-dimensional model, depending on the geological and hydrogeological description.
Review of existing documents and collection of data was undertaken to support the development of the MIKE-SHE ISGW model. From the literature review, no regional groundwater studies or models that address the groundwater resources comprehensively across the County were found. USGS produced a groundwater model in the Lower Milliken-Sarco-Tulucay Creek area to examine groundwater resources in that subregion of the County. This document provides valuable information on the aquifer dimensions and properties in this area. Several regional studies of the groundwater resources studies and records from the California Department of Water Resources provide pumping rates throughout the evaluation areas. Well hole logs with geological information are also being investigated to construct the subsurface model.
The MIKE-SHE ISGW will allow the County to examine surface and groundwater use in the 11 evaluation areas. Specifically, the groundwater chapter of the BDR includes a technical report with estimated groundwater usages, water balances, groundwater elevation trends, appropriate maps, timeseries graphs, and other graphics for each evaluation area. The following maps, at a scale of 1:12,000, are included in the groundwater resources chapter.
- Groundwater basins/recharge areas map showing well locations, groundwater flow patterns, recharge areas, discharge areas, and zones of influence
- Groundwater elevations/depths map
- Groundwater short areas map.
In addition, time-series graphs of water level conditions and derived information will be provided.
