1. WATER SUPPLY ASSESSMENTS IN ARID
ENVIRONMENTS-
INNOVATIVE WEATHER DATA/GIS APPROACH
CALCIMA 2014 Annual Education Conference
November 5, 2014
San Diego, California
Joe Zilles, P.G.
GIS by Alex Makovics

2. WATER SUPPLY ASSESSMENT
FRAMEWORK
CALIFORNIA REGULATORY ENVIRONMENT
 SB221/610
 CEQA
 Local Kern County Policy 41
 Review of development proposals
 Evaluation of substantial groundwater depletion

3. REGIONAL SETTING

4. SITE SETTING
 Location: Western Mojave Desert
 Southeast of Tehachapi Mountains
 Project: Approximately 7,700 acres
 Project Demand: 41 acft/year (O&M)
 Annual Precipitation – 6.1 to 11.4 inches/year
 Evaporation Rate – 57 to 66 inches/year
 Current Local Demand: 2,555 acft/year (commercial,
residential, agricultural)

5. CHALLENGESs
 Low Rainfall/High Evaporation
 Define the Supply Regime
 Show Project Demand Does Not Exceed
Available Supply
 Make a Connection Between Published
Data and the Project Demand

6. ESSENTIALS TO CALCULATING
WATER SUPPLY ASSESSMENT
 Precipitation
 Evaporation
 Run-off /Recharge
 Underflow (Groundwater)
 Predicted Future Water Use
 Normal, Single Dry and Multiple Dry Years
Impacts

7. STARTERS
 Precipitation 6.1-11.4 inches/year
 Evaporation 57-66 inches/year
 Irrigation returns (30% of total irrig.
demand 2,362=709 acft/yr/project
area) (USGS, 2003)
 Mountain Front Recharge (Upper
Alluvial Fan and fractured bedrock) =
40,700 af/yr (USGS, 2003)
 Bedrock Recharge Efficiency (Maxey-
Eakin, 1949)
 2, 3, and 8% depending on
elevation = 176 af/yr/project area
 Current Area Demand = 2,555 af/yr

8. Watershed
Defined
 27,000 Acres
 Acreage per
500 foot
elevation
contour

9. Rainfall Data Re-Examined
 Detailed GIS
Weather Data
(Prism Climate Group, Oregon State
University, 2010)
 Rainfall Data
per 800 meter
grid
 Data recorded
per month
 Data recorded
back to 1971

10.  Rainfall
per grid cell
averaged from
1971-2000(Prism 2010)
 November-
February

12. Rainfall totals within 1,000
foot elevation contours
 5000-6000 feet-4,144 acft
 6000-7000 feet-2,677 acft
 7000-8000 feet-1,407 acft
 Total Rainfall 8,228 acft

13. Mountain Front Recharge
Watershed
Elevation
(feet msl)
Average
Precipitation
Nov-Feb
(acft)
Bedrock
Recharge
Efficiency
Loss
(%-acft)
Mountain Front
Recharge (less on
site bedrock
recharge) (acft)
5000-6000 4,144 2%-83 4,061
6000-7000 2,677 3%-80 2,597
7000-8000 1,407 8%-13 1,294
8,228 176 Total 8,052

14. Outcome
Recharge
Source
Normal Year Single Dry Year Multiple Dry Year
Mountain Front 8,052 4,239 6,646
Irrigation
Percolation
709 709 709
Total Recharge 8,761 4,948 7,355
(ET) 4,493 4,493 4,493
Net GW Recharge 4,268 455 2,862
Future
Demand=2,633
Recharge
>Demand
Recharge
<Demand
Recharge
>Demand

15. THANK YOU
Joe Zilles, P.G., Principal Geologist
(916)366-1701jzilles@kleinfelder.com