Project Overview

Project Summary

Hyporheic exchange, the temporary storage of surface water in stream bank sediments, affects the transport of solutes, including nutrients, through watersheds. Water diverted into the hyporheic zone has a longer residence time and more interaction with biogeochemically active sediments than water in other flow paths. Hyporheic flux rates and geochemistry have not been studied in semi-arid intermountain watersheds, transitional in climate between alpine catchments and desert lowlands. Hyporheic exchange in watersheds in humid regions is enhanced by stream meanders, variable flow rates, and sediment hydraulic conductivity. In water poor regions other geomorphic characteristics, particularly beaver dams, may equally influence hyporheic exchange.

We are completing an intensive study of hyporheic interaction and nitrogen uptake potential in an intermountain semi-arid watershed with significant beaver activity. The study includes field experiments and numerical hydrologic models designed to 1.) identify and quantify hyporheic pathways and fluxes of water and dissolved solutes across the surface-groundwater interface and 2.) the causes of hyporheic flux variability. We are testing whether in-stream flow obstructions, particularly small beaver dams, enhance extent of the hyporheic zone along semi-arid streams compared to the effects of other geomorphic and hydrologic controls. We use inverse modeling of in-stream tracer tests to characterize hyporheic storage parameters along various reaches of Red Canyon Creek, Wyoming. We also plan to use observations of tracers at near-stream wells to independently test the results of the in-stream tracer tests.

We are testing the hypothesis that reaches with a greater degree of hyporheic interaction have a greater potential for uptake of nitrate. Dissolved nitrate has been paired with the conservative tracers during in-stream tracer tests. Using the rate of decline of nitrate concentrations downstream and an exponential nutrient uptake model, we have quantified nitrogen uptake lengths along Red Canyon Creek and compared results with hydrologic measures of hyporheic exchange.

Results of in-stream tracer tests are empirical in nature, and therefore difficult to generalize to other sites. For this reason, we have also used three-dimensional numerical computer models of near-stream flow paths to evaluate the physical processes controlling the aerial extent and flux of water through hyporheic zones. These groundwater flow models will be integrated with surface runoff models to assess the impact of watershed scale changes in hydrologic conditions on reach scale fluxes of water through the hyporheic zone. Our model will explore the relative influences of stream characteristics and hydrologic conditions on hyporheic interaction, allowing for better generalization of experimental results.

Site Instrumentation

Parshall Flume

We recently installed a flume on-site to record the streamflow rates over time. The flume is located near the bottom of the watershed, where Red Canyon Creek joins the Little Popo Agie. The flume is equipped with two pressure transducers, located within the long, white PVC pipes installed on the side of the flume (only one is shown in this photo).

Stream water samples are collected weekly at this site and at two sites farther upstream, at the confluence of Red Canyon Creek and its tributary, Cherry Creek. We also collect precipitation after storm and snow events. Chemical analyses of these waters will be used to do chemical budgets for the watershed.

Site Surveying

The well field has been very well surveyed to obtain a detailed three-dimensional map of the site. This information will be used to generate surface water profiles along the site during different discharge events. The surface water profiles will then be incorporated into our groundwater simulations (in MODFLOW) to see the affect of changes in discharge on surface-groundwater interactions along the creek.

Temperature Data Collection

We have installed several iButton temperature data loggers to collect profiles of stream temperature in the streambed along Red Canyon Creek. Temperature profiles are used to assess the degree of surface-groundwater interaction.

Detailed Streambed Characterization

We have installed several mini-piezometers (~30) along a section of Red Canyon Creek to better understand how surface-groundwater interactions can be characterized using hydraulic properties, water chemistry and temperature. We are also interested in how the small dam shown here impacts the exchange of surface water with the hyporheic zone.

Well and Piezometer Field

The segment of Red Canyon Creek shown here is located in the lower part of the watershed, near the confluence with the Little Popo Agie River. Note the gravel road to the right side of the smaller image, for scale. This reach along Red Canyon Creek has been very well instrumented as the site for the Univ. of Missouri's Branson Geology field camp hydrology course. Each year, students install additional wells as a part of their course work (more on the camp can be found here). This site has been the subject of several in-stream tracer tests and MODFLOW models aimed at measuring and predicting the degree of hyporheic interaction along Red Canyon Creek.

The Nature Conservancy of Wyoming

The Nature Conservancy (TNC) of Wyoming owns most of the Red Canyon Creek watershed, as shown by the yellow outline below. The accompanying photograph is a view of the watershed taken from a scenic overlook. TNC raises cattle on the rangelands using an innovative grazing management plan that mimics the use patterns of historic ungulates by moving livestock in herds across the landscape. TNC's progressive management strategies include encouraging the local beaver colony to populate streams and create small debris dams to pool water and resaturate near-stream riparian wetlands and meadows (see photo above). In addition, TNC has created anthropogenic debris dams and small concrete dams to mimic the effects of natural beaver dams.