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USGS: Evaluation of Groundwater Resources in Spanish Valley Watershed, Grand & San Juan Counties, Utah

August 23, 2019
by John Weisheit

Release Date: AUGUST 16, 2019

Melissa Masbruch, Hydrologist
US Geologic Survey, Utah Water Science Center
Email: mmasbruch@usgs.gov
Phone: 801-908-5068

Click here to read the summary, the report, and to view three plates (graphics and maps)

A new assessment of groundwater resources in the Spanish Valley watershed in southern Utah shows an amount that is about 30–40% lower than previously reported, according to a U.S. Geological Survey report.

Future growth in the Moab, Utah, area is dependent on adequate water resources. With surface waters fully appropriated, water needs to support future development must be met with groundwater resources. The last assessment to determine how much groundwater is available in the Spanish Valley area was completed in the 1970s.

“These findings will be useful to local and state water managers in evaluating how much additional development can be sustained in the Moab area with the groundwater available,” said lead author and USGS scientist Melissa Masbruch. “This information can also help decision-makers make informed choices as they develop a future groundwater management plan.”

The total amount of groundwater entering and leaving the aquifer system within the Spanish Valley watershed is estimated to be 13,000 to 15,000 acre-feet per year. This estimate is based on the amount of groundwater flowing out of the aquifer, which provides a more robust assessment of how much water is in an aquifer system than recharge measurements. This current estimate is about 30–40% lower than the 1971 estimate of 22,000 acre-feet per year.

The Spanish Valley watershed includes the valley-fill and Glen Canyon Group aquifers. Results show that there is no significant groundwater inflow from the Glen Canyon Group aquifer to the valley-fill aquifer. Rather, inflow to the valley-fill aquifer was found to come from the Pack Creek watershed. This is in contrast to findings from the 1971 assessment’s assumption that 14,000 acre-feet per year of groundwater enters the valley-fill aquifer from the Glen Canyon Group aquifer. Findings also show a groundwater outflow of 300 to 1,000 acre-feet per year from the watershed to the Colorado River. This amount is much lower than the 1971 estimate of 11,000 acre-feet per year.

For this study, scientists collected water-quality, water-level and flow data from wells, springs and streams in the Spanish Valley watershed from 2014 to 2016. Water-quality and water-level data were used to determine the sources of groundwater recharge and flow throughout the aquifers. Flow measurements helped to assess groundwater discharge to streams and springs and were used to determine inflow and outflow to the aquifers.

This study was done in cooperation with the Utah Division of Water Rights, City of Moab, Grand and San Juan Counties, Grand Water and Sewer Service Agency, Utah School and Institutional Trust Lands Administration, The Nature Conservancy, Utah Division of Wildlife Resources, Living Rivers, San Juan Spanish Valley Special Service District, U.S. Bureau of Land Management and the U.S. Forest Service.

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MOVING FORWARD: Suggestions from Canyonlands Watershed Council

  • A watershed-wide monitoring program is of utmost importance: Climate variability and water demand hardening (development that is not sustainable) must not impair the water security of this community, nor should it degrade the riparian values of Mill Creek, Pack Creek, and the natural flow of perrennial springs; this heritage is cherished by residents and visitors.
  • Compromising the safe-yield is unacceptable: Should the data analysis of the monitoring plan indicate that community values are in jeopardy, the response by the planning agencies must be transparent and the decision process must include a solution that has long-term sustainibility.
  • Continue to collaborate with the regional agencies of the National Oceanic and Atmospheric Administration (NOAA): Our community needs the best science for our specific community as it relates to the trend (1906 to 2019) of diminished precipitation, dry soils, increased evaporation and plant transpiration.
  • Invite the regional science community to provide presentations: Usa adequate venues on dates and times that will accommodate good attendance by the city and county planning agencies and the stakeholders of this communtiy.

DO NOT WASTE TIME & MONEY ON WATER DIVERSION PROJECTS FROM THE COLORADO OR GREEN RIVERS:

  • The annual average yield (supply) of the Colorado River Basin at Lee's Ferry, AZ in 1922 (the year of Colorado River Compact negotiation) was 18 million acre-feet (MAF).
  • The current annual average yield (1906 to 2018) is now 14.8 MAF, a cumulative loss (112-years) of -3.2 MAF.
  • From 2000 to 2017, the annual average yield at Lee's Ferry, AZ was 13 MAF.
  • From 2000 to 2017, the current annual average total consumptive use (demand) of the Colorado River Basin above Lee's Ferry, AZ was 4.7 MAF.
  • From 2000 to 2017, the current annual average flow below Lee's Ferry, AZ was 8.9 MAF.
  • From 2000 to 2017, the total annual average demand for the upper and lower basins was 13.6 MAF, a deficit of -600,000 acre-feet per year.
  • In the year 2060, the projected imbalance between supply and demand (using the data between 1906 and 2010) is estimated to be -3.2 MAF.
  • Further reading, and a document archive, can be found HERE

NEWS
  • Click here to read this story by Moab Sun News called "USGS Study Shows Less Water Than Previously Reported"
  • Click here to read this story by Dennis Webb in the Grand Junction Sentinel about how the Western Slope of Colorado and Grand County, Utah are warming at a faster pace than the rest of the USA
  • Click here to read this story by Carter Pape of Times Independent called "Moab Watershed 30 to 40 Percent Smaller Than Previously Reported"
  • Click here to read this story by Carter Pape of Times Independent called "How Water Ends Up In Moab"
  • Click here to read this story by Carter Pape of Times Independent called "USGS Confirms Valley Water Budget"

 

DOCUMENTS

  • Click here to read the summary, report and to view three plates (graphics and maps)

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