1. Creating a Generalized Hydrologic Water Budget for Cache Valley, UT/ID
Presented by Tom Nelson
November 29, 2007
GIS-Water Resources Final Project

2. Background
Groundwater flow model developed for Cache Valley by Kariya et al, but does not account for subsurface inflow
As a result, unrealistic boundary conditions applied to achieve model calibration

3. Background Karst Topography
Landscape shaped by the dissolution of carbonate rocks (e.g. limestone)
Interconnected subsurface channels that allow for rapid water transport

4. Objectives
1) Find the storage flux of Cache Valley aquifers by creating a generalized hydrologic budget for the watersheds that contain Cache Valley, UT/ID using the following equation:
Aquifer Storage Flux = Stream Outflow + Evapotranspiration + Well Discharge – Stream/Spring Inflow - Precipitation
2) Compare results with water budget generated by Kariya et al model

5. Methods
Obtain stream discharge data to determine stream inflow/outflow
Determine area of Cache Valley watersheds using GIS analysis
Download and correct annual precipitation data
Add precipitation gage points onto map to perform a spatial analysis
Estimate an appropriate evapotranspiration rate for the valley
Obtain well discharge records for Cache Valley

6. Stream Inflow/Outflow
Cache Valley is contained within two watersheds:
1) Middle Bear Watershed (northern half of valley)
2) Middle Bear-Logan Watershed (southern half of valley)
Stream flow (Bear River) into the valley through the Alexander Dam
Stream flow (Bear River) out of the valley through the Cutler Dam

7. Inflow at the Alexander Dam
19 years worth of Bear River daily discharge data available from Idaho Dept. of Water Resources
Average annual discharge of x10^11 cubic meters

8. Outflow at Cutler Dam
Stream flow leaves Cache Valley through Cutler Dam
Discharge of Bear River measured approximately 0.25 miles downstream from Cutler Dam at 3 gages near Collinston, UT
4-10 years of daily discharge data available
Combined Annual Discharge of x10^11 cubic meters

9. Precipitation
Daily precipitation measurements from 9 stations in or near the Cache Valley watersheds
Correction factor applied due to missing data points in the data sets
A=(sum of existing values)/(total days of existing values)
Yearly Average=(A*total days in data set)/(total years in data set)

10. Precipitation
Precipitation stations added to GIS map as a feature dataset
Spatial Analysis performed using kriging interpolation method
Mean precipitation value of inches across the watersheds
Analysis of combined watershed drainage area gives an area of kilometers squared
Therefore, average annual precipitation in Bear Watersheds = x 10^9 cubic meters

11. Evapotranspiration
Monthly reference evapotranspiration data available for from a climate station in North Logan
Estimating actual evapotranspiration:
Actual ET = (Multiplier) x (Sum of Reference Evapotranspiration for non-winter months (April-November))
Actual ET = (0.5) x ( meters) = meters/year
Total annual volume = (Actual ET) x (Area) = x 10^9 cubic meters

12. Well Discharge Utah annual well discharge from Cache Valley
average annual well discharge = x 10^7 cubic meters (Burden, C.B., et al)
Idaho annual well discharge from Cache Valley
Year 2000 annual well discharge = x 10^8 cubic meters (
Combined annual well discharge from Cache Valley = x 10^8 cubic meters

13. Final Hydrologic Budget
Aquifer Storage Flux = Stream Outflow + Evapotranspiration + Well Discharge – Stream/Spring Inflow – Precipitation
Aquifer Storage Flux = Subsurace Inflow – Subsurface Outflow
Annual Cache Valley Aquifer Storage Flux = x 10^11 cubic meters per year

14. Comparison with Kariya et al Groundwater Model
Kariya’s model assumes that nearly all of the aquifer recharge is due to seepage from irrigation canals and precipitation
This causes a lack of recharge into the valley, and as a result, the annual aquifer recharge is only 65% that of the annual aquifer discharge
In 2003, Myers showed that aquifer recharge from streams is negligible
From estimated water budget:
Precipitation – Evapotranspiration = E+09 cubic meters
Assuming 50% runoff and 50% infiltration:
Infiltration from precipitation = E+08 cubic meters
If parameters of Kariya’s model were followed in this case, there would be a recharge discrepancy of E+11 cubic meters

15. Conclusions
The average annual storage flux for the aquifers of Cache Valley is approximately x 10^11 cubic meters per year, although a more intensive study would have to be conducted to obtain a truly reliable value
The assumption of Kariya et al’s groundwater model for the valley, that the aquifers are recharged primarily through seepage from canals and precipitation, appears to significantly underestimate the volume and source of recharge

16. References
Burden, C.B., et al, 2006.Ground-Water Conditions in Utah, Spring 2006: Utah Department of Natural Resources, Water Resources Division, Report 47.
Kariya, K.A., Roark, D.M., Hanson, K.K.. Hydrology of Cache Valley, Cache County, Utah, and Adjacent Part of Idaho, with Emphasis on Groundwater. USGS Technical Pub. No
Myers, Barry. Simulation of Groundwater Flow in Cache Valley, Utah and Idaho. Utah State University Master’s Thesis