A Groundwater Extraction

Total Groundwater Extractions (AF)

Water Use Sectors

Rural Residential

B Groundwater Extraction Methods

Meters

Metered Municipal Wells

Metered connection maintained by City of Corning and Hamilton City

Electrical Records

Land Use

Land use estimates were derived from crop mapping and CropScape survey results

Typical uncertainty for water balance calculation

Groundwater Model

Other

Rural residential groundwater extraction is estimated based on City of Chico-Hamilton City District's 2020 Urban Water Management Plan 2020 usage of an average per capita water use of 181 gallons per capita per day. Population data from the 2020 census was coupled with water district boundary data to identify total population not serviced by municipal supplies

Uncertainties are from population estimates and gallon per capita per day estimates

C Surface Water Supply

Total Surface Water Supply (AF)

Methods Used to Determine

Diversions for local supplies are estimated based on historic State Water Resource Control Board eWRIMS (Electronic Water Rights Information Management System) data for total diversions. Surface water delivery estimates are based on historic deliveries in the area that have occurred in dry and critical years

Water Source Types

D Total Water Use

Water Source Types

Water Use Sectors

Rural Residential

E Change in Storage

Method used to calculate change in storage

The spatial distribution of estimated changes in groundwater storage for the period from spring 2023 to
spring 2024 are shown in Figure 4-2. Since groundwater storage is closely related to groundwater levels,
measured changes in groundwater levels can serve as a proxy for and be utilized to estimate changes in
groundwater storage. Groundwater level data obtained from the DWR Water Data Library (DWR, 2025)
were generally recorded on a monthly to quarterly basis. For Water Year 2023?2024, a raster surface
representing seasonal high groundwater level changes was generated by spatially interpolating (kriging)
data from selected wells across the subbasin. These seasonal high changes were calculated by subtracting
groundwater levels recorded in the spring of 2023 from those recorded in the spring of 2024.
The selected wells represent sites with groundwater level records that are considered representative of
subbasin conditions. In areas?mostly near the subbasin boundaries?where polygon-specific groundwater
data were unavailable, interpolated raster pixel values from the selected wells were used for groundwater
storage change calculations. In cases where multiple groundwater level records existed within a single
polygon, an average groundwater level was assigned to that polygon. Groundwater storage change was then
calculated by multiplying the change in seasonal high groundwater level (2024 minus 2023) by the specific yield (Sy) value assigned to each polygon, and by the polygon area (in acres), resulting in groundwater
storage changes from 2023 to 2024 expressed in acre-feet.
It should be noted that the groundwater model as described in the GSP was not used to estimate storage
changes for WY 2021 through WY 2024. (Figure 4-1). The approach of using measured groundwater
elevation changes to estimate storage changes is considered reasonable and cost-effective for the
purposes of the annual report.
Negative changes in storage values indicate lowering groundwater levels and depletion of groundwater
storage, whereas positive changes in storage values represent rising groundwater levels and accretion of
groundwater storage. As shown in Figure 4-2, change in storage within each polygon ranged between -
160 and 1,400 AF. When compiled, the total change in storage in the aquifer is approximately 20,900 AF
between spring 2023 and spring 2024. The central portion of the Subbasin had the smallest positive
change in storage, while the surrounding portions, especially the southeastern and northwestern portions
of the Subbasin, experienced the largest positive change in storage.

F Monitoring Network Module

G PMA Module