4 research outputs found
Development and Application of Hydraulic and Hydrogeologic Models to Better Inform Management Decisions
Water is one of the most important and limited resources in regions with little rainfall. As populations continue to grow, so does the need for water. Individuals in water management positions need to be well informed in order to avoid potential negative effects concerning the overall quality and amount of water available for both people and the environment. In order to provide better information for these individuals, computer models and mathematical relationships are commonly developed to estimate the outcome of different situations regarding surface water and groundwater. Along these lines, this study focused on two modeling studies that provide information to managers regarding either stream restoration techniques or the amount of groundwater available.
The first study investigated the effects that beaver dams have on streams. In order to do this, a computer model was developed to represent a section of stream with beaver dams and a section without. The model provided information regarding changes in the average depth, width, and velocity of the stream as a result of having beaver dams. We also measured changes in sediment size distributions between the two stream sections to confirm that beaver dams additionally impact sediment movement and channel shape. Results indicated that only a few dams are actually needed to achieve many of the desired changes in stream restoration.
The second study involved testing an equation that was used to predict how much precipitation would become groundwater in a Midwestern watershed. Variables in the equation included measurements of natural or developed land, movement of water through soil, the depth of the water table, and hillslope steepness. We tested the equation in two western watersheds to determine if variables used in the earlier study remain relevant when applied under different conditions. The independent application of the method to each western watershed stressed the importance of meeting simplifying assumptions and developing more complete datasets. We also found that the application of existing simplified empirical relationships may not be suitable in estimating groundwater recharge in mountain watersheds
Stream Centric Methods for Determining Groundwater Contributions in Karst Mountain Watersheds
Climate change influences on mountain hydrology are uncertain but likely to be mediated by variability in subsurface hydrologic residence times and flow paths. The heterogeneity of karst aquifers adds complexity in assessing the resiliency of these water sources to perturbation, suggesting a clear need to quantify contributions from and losses to these aquifers. Here we develop a stream centric method that combines mass and flow balances to quantify net and gross gains and losses at different spatial scales. We then extend these methods to differentiate between karst conduit and matrix contributions from the aquifer. In the Logan River watershed in Northern Utah we found significant amounts of the river water repeatedly gained and then lost through a 35âkm study reach. Further, the direction and amount of water exchanged varied over space, time, and discharge. Streamflow was dominated by discharge of karst conduit groundwater after spring runoff with increasing, yet still small, fractions of matrix water later in the summer. These findings were combined with geologic information, prior subsurface dye tracing, and chemical sampling to provide additional lines of evidence that repeated groundwater exchanges are likely occurring and river flows are highly dependent on karst aquifer recharge and discharge. Given the large population dependent on karst aquifers throughout the world, there is a continued need to develop simple methods, like those presented here, for determining the resiliency of karst groundwater resources
Persistent Urban Influence on Surface Water Quality via Impacted Groundwater
Growing urban environments stress
hydrologic systems and impact
downstream water quality. We examined a third-order catchment that
transitions from an undisturbed mountain environment into urban Salt
Lake City, Utah. We performed synoptic surveys during a range of seasonal
baseflow conditions and utilized multiple lines of evidence to identify
mechanisms by which urbanization impacts water quality. Surface water
chemistry did not change appreciably until several kilometers into
the urban environment, where concentrations of solutes such as chloride
and nitrate increase quickly in a gaining reach. Groundwater springs
discharging in this gaining system demonstrate the role of contaminated
baseflow from an aquifer in driving stream chemistry. Hydrometric
and hydrochemical observations were used to estimate that the aquifer
contains approximately 18% water sourced from the urban area. The
carbon and nitrogen dynamics indicated the urban aquifer also serves
as a biogeochemical reactor. The evidence of surface waterâgroundwater
exchange on a spatial scale of kilometers and time scale of months
to years suggests a need to evolve the hydrologic model of anthropogenic
impacts to urban water quality to include exchange with the subsurface.
This has implications on the space and time scales of water quality
mitigation efforts