UGS Matheson Wetland and Northern Spanish Valley Groundwater Resources Report

June 1, 2024

Kathryn Ladig of the Utah Geological Survey gave a 40 slide presentation on her almost 100 page report on the Matheson Wetlands and Northern Spanish Valley Groundwater Resources. The report contained four areas of specific research: groundwater resources, a water budget for the wetland, brine characteristics under the wetland, and a plant/water evaluation and trends.

Groundwater Resources: The groundwater resource section indicates that water coming from the monitored springs, the two horizontal wells and Water Cress, has remained steady over the last two years of her study. She also reported that water from Skakel springs and the northern Duck puddle spring travel north ward after entering the ground. It also appears that groundwater elevations in the Wetlands are more closely related to the level of the Colorado River and not Mill Creek or precipitation in the wetlands. This finding is also supported by the groundwater levels in the wetlands which actually increase near the edge of the wetlands by the Colorado River. It also appears that flood events in the wetlands from the Colorado River do add a lot of water to the wetlands for a small amount of time, but that water is lost quickly after the flooding event. Mill Creek is not gaining or losing water after it enters the wetlands.

Water Budget: The water budget for six years was evaluated and the average of those six years was about 1050 acre-feet of water. However, the water budget can vary up to 25% some years. The majority of the inflow to the water budget is precipitation, accounting for over half of the inflow. The majority of the outflow is evapotranspiration which also accounts for over half of the outflow.

Brine Layer: This investigation didn’t solve all the mysteries associated with the brine Layer, but it did answer some questions. First as we already knew the brine water is older than the fresh water. There does appear to be some mixing of the brine with freshwater as the brine is much saltier than the fresh, but not as salty as the paradox formation. It also seems clear that the brine layer does not “change” seasonally. Questions still to be answered are why is the brine layer closer to the surface in the north than the south, does the brine actually travel in any direction, and if all the fresh groundwater was eliminated, would the brine reach the levels where it would directly discharge to the Colorado River.

Remote Sensing and Wetland Changes Over Time: The vegetation in the wetlands has changed over the last 30 years, we all know that. The greenness index over the last 30 years has increased in a large portion of the wetlands, but in the last 10 years the greenness index has decreased almost throughout the entire wetland. There have been significant changes to the vegetation in the wetlands during that time. Perennial forbs and grasses have declined whereas annual forbs and grasses seem to be increasing. Most of the vegetative changes are probably tied to human and “event” activities, namely the introduction of the tamarisk beetle and subsequent fire dramatically changed the wetland vegetation. The wetlands have also seen a significant decrease in surface water over the last 30 years.

Recommendations for Further Wetland Evaluation: The study based numerous recommendations on their results. The first, which has been recommended by other scientists in other publications more than once, is flow monitoring of the City of Moab’s water supply coming from Skakel Spring. The study also recommended the continuation of “continuous” groundwater level monitoring that has been occurring in the wetlands. There were several suggested activities associated with the answering of questions we still have about the brine layer. Some of those included different monitoring methods as well as efforts to categorize the subsurface physical components. There were also recommendations to directly monitor and categorize vegetation and subsequent changes as well as continue remote monitoring. Finally, there were some monitoring suggestions directed at figuring out why the wetlands are drying up.