A Groundwater Extraction

Total Groundwater Extractions (AF)

Water Use Sectors

B Groundwater Extraction Methods

Meters

City of Porterville and community of Ducor production well meters

Routinely maintained and calibrated by the City of Porterville or Ducor Community Services District

Electrical Records

Land Use

Groundwater Model

Other

Back calculated from remotely sensed satellite ETc data and irrigation efficiency estimates based on CDWR land use maps or field surveys

ETc data been proven to have approximately 90% accurrate based on pilot studies performed within ETGSA.  Irrigation efficiencies are subject to error being they are derived from outdated CDWR land use data and correlated to common irrigation methods for any given crop.

C Surface Water Supply

Total Surface Water Supply (AF)

Methods Used to Determine

Imported CVP - USBR Central Valley Operations Reports. Local Supplies- Flow meters at district diversion points. Recycled - Estimated & metered. Precipitation - CIMIS weather stations and Groundwater Flow Model estimates on precipitation.

Water Source Types

Total Precipitation

D Total Water Use

Water Source Types

Total Precipitation

Water Use Sectors

E Change in Storage

Method used to calculate change in storage

The change in storage estimate for this annual report is specific to the Upper aquifer. The calculations were made using a Geographic Information System (GIS) map of the Tule Subbasin discretized into 600- foot by 600-foot grid cells to allow for spatial representation of aquifer specific yield and groundwater level change. Although the storage change in the Lower Aquifer is expected to be significantly less than the Upper Aquifer due to its confined nature, future annual reports will include storage change from the Lower Aquifer as well. 

The areal distribution of specific yield for the Upper Aquifer is based on the values obtained from the updated calibrated groundwater flow model of the Tule Subbasin. 

The areal distribution of change in hydraulic head across the Tule Subbasin was estimated by plotting the difference in groundwater level at wells that were measured in both fall 2020  and fall 2021 and then interpolating the subbasin-wide changes in groundwater levels in GIS using a kriging algorithm. Change in hydraulic head (groundwater level) at any given location was assigned to the overlapping grid cell. 

The  change  in  groundwater  storage  was  estimated  for  each  grid  cell  by  multiplying  the  change  in groundwater  level  by  the  specific  yield  and  then  by  the  area  of  the  cell.  Recent  dry conditions have resulted in more  limited surface water supplies and higher groundwater pumping relative to  previous years, which has contributed to the negative groundwater storage change in the 2020/21 water year.

F Monitoring Network Module

G PMA Module