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WWRC 96-01
Fiscal Year 1995 Program Report


Three research projects were funded under the FY95 program, as well as information transfer activities. These three research projects relate to important water issues in the State of Wyoming and the region.

River Bed Modification and Sediment Transport by Anchor Ice Events in Wyoming Rivers. Maintenance of river conditions and instream flows (or environmental flows) must be balanced against heavy demands for offstream water usage. There is a general understanding of the instream flow requirements needed to assure the maintenance of fish and wildlife habitats. Minimum instream flows are needed to supply sufficient sediment transport to scour encroaching vegetation and to remove fine materials from the stream bed. However, recent observations that have been made on the Big Laramie River have shown that a heretofore largely ignored process may be very important in Wyoming rivers. High sediment transport rates resulting from daily detachment of anchor ice from the stream bed have been observed. Anchor ice is an accumulation of ice on the bed of a stream, under the flowing water. Wyoming has an ideal climate for extensive and repeated anchor ice formation. Clasts ranging from cobbles down to silts and clays have been observed in transport, with concomitant modification of the stream bed, both at the site of erosion and at the downstream site of deposition. Sediment transport by anchor ice has received little but anecdotal attention in the literature. Although this phenomenon is virtually unstudied, preliminary observations indicate that it has the potential to be a major modifier of the beds of Wyoming rivers.

Modeling of Groundwater Transport and Biofilm Growth in Porous Media. This project will produce information on the behaviour of biofilms in porous media. This knowledge can then be used to design strategies for their use in preventing contamination of aquifers and also to clean them. This information will also be useful to the petroleum industry in enhanced oil recovery projects. In this project, numerical methods are used to simulate the interaction of water flow and biofilm growth and transport in a porous medium. The modeling of water flow is based on Darcy's law. The transport and dispersion equations model the movement of dissolved or suspended substances such as nutrients and microbes in the water. A local biofilm growth model that considers several types of bacteria and nutrients will be implemented. It is based on Monod kinetics together with attachment and detachment. The output of the biofilm growth model yields the size of the biofilm at the microscale, which can be used to compute changes in macroscale porosity and permeability via scale-up techniques. This information can then be used to determine the feasibility of using biofilms to act as local plugs and/or biodegrade contaminants.

Critical Groundwater Hydroperiods for Maintaining Riparian Plant Species. Today's water management reform efforts are using riparian wetland health as a central theme for promoting a change in the way water resources and rangelands are used and managed in the West. These efforts require specific information to help predict how altered hydoperiods might affect riparian ecosystems. Resource managers also require this information to design hydroperiods for constructed and restored riparian wetlands. This study was designed to help address this immediate need for critical groundwater hydroperiods by comparing controlled experiments to field data from montane meadows in Southeastern Wyoming. These field data suggest that Nebraska sedge (Carex nebrascensis), tufted hairgrass (Deschampsia cespitosa) and Kentucky bluegrass (Poapratensis) have different optimum hydroperiods. The overall objective of this study was to provide factual and reliable information on the critical plant tolerance of these three riparian species to the rate of water-level decline and the maximum water table depth by using simulated groundwater hydroperiods. Specific research objectives were to: 1) Evaluate the response of three important, but morphologically dissimilar, riparian plant species to specific groundwater hydroperiods designed to simulate dewatering of riparian zones, 2) Continue to describe the seasonal dynamics of surface water stage and groundwater elevation in subalpine and montane riparian wetlands, and 3) Compare depth to groundwater duration curves developed from periodic measurements with curves developed from continuous data.

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