EVALUATING SALTWATER-FRESHWATER INTERFACE USING TRANSIENT ELECTROMAGNETICS (TEM) IN THE MATHESON WETLANDS PRESERVE, MOAB UTAH

The Scott and Norma Matheson Wetlands Preserve ecosystem is a rare wetland adjoining the Colorado River that supports an important diversity of flora and fauna in an arid part of the Colorado Plateau. The Matheson Preserve is the main discharge zone of the larger Moab-Spanish Valley groundwater and surface-water system. The water supply and ecological health of the Matheson Preserve are therefore tied to changes in the larger groundwater and surface-water system.

The Utah Geological Survey has been conducting detailed work on the sources of water to the Matheson Preserve and changes in wetland health over time, particularly focused on a shallow underlying brine layer. The brine layer mixes with the freshwater sources, creating adverse conditions for life in the preserve. As a part of a broader wetland health study, we used Transient Electromagnetic (TEM) resistivity measurements to evaluate the position, seasonal and long-term fluctuations, and source of the brine layer which underlies the fresh water that sustains the wetlands. Saline water is typically easy to detect against a background of fresh water due to the large contrast in electrical resistivity. The TEM surveys produce a series of resistivity depth-slices through the wetland that constrain the movement of the brine layer.

As Colorado River flow rates continue to drop due to climate change and increasing water use, it is important to understand the role that the brine layer plays in this wetland environment. The relationship between brine and freshwater has implications for threatening vegetation health, wildlife habitat, and overall water quality of the preserve. The data provided in this study will help wetland managers and local and state water managers make decisions to ensure the long-term survival of the Matheson Preserve.