Project : USDA ARS

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Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

2021 Annual Report

Accomplishments
1. Pesticide application in rice paddies has the potential to be harmful to ecological health of receiving water bodies. Thiobencarb is a commonly used herbicide in Northern California rice fields that may pose ecological risks to non-targeted organisms. Currently available models do not adequately represent the fate and transport of rice pesticides at watershed or basin scales. ARS researchers in Oxford, Mississippi, integrated rice pesticide transport technology at the field-scale with watershed-scale technology to follow the fate of pesticides throughout the watershed system. Application of the new technology to investigate the fate and transport of thiobencarb residues from paddy fields in the Colusa Basin, California, showed thiobencarb concentrations in both water and sediment phases were accurately captured at the edge of field. The integrated system accurately reflected both the seasonal pattern of surface runoff and the timing of monthly thiobencarb loadings downstream as well. The integrated technology successfully extends field level simulations to watershed scales while considering the impact of mixed land uses on downstream loads. This integrated modeling system provides technology to action agencies when evaluating rice pesticide load impacts as part of a basin level management approach to improve water quality.

2. Improved relationships between river planform and cross-section attributes. The understanding of the migration of river meander bends is incomplete because of highly complicated flow and sediment transport patterns, and resulting interactions between vertical and planform adjustment. Planform is typically represented by the curvature of the channel centerline, while point bars are the prominent features comprising the river bed. Combining analyses of aerial imagery and river bathymetry collected using unmanned aircraft systems and multibeam sonar, ARS researchers in Oxford, Mississippi, in collaboration with researchers from Louisiana State University and the University of Illinois developed relationships between channel centerline curvature and point bar geometry for select meander bends on the Wabash River, Illinois/Indiana, and the Pearl River, Mississippi/Louisiana. Additionally, an analytical model to estimate river bed geometry from channel centerline curvature was used to investigate the developed relationships. The temporal adjustment of planform and point bar geometry on both river systems was consistent for meander bends migrating in downstream direction. Specifically, the point bars presented a flat upper geometry, maximum migration rates occurred near the bend apex, and the bends developed a curvature comprising multiple maxima. These findings can be used in river engineering to determine rate and direction of future meander bend migration and channel depth. Action agencies will therefore be able to prioritize bank stabilization to protect farmland and irrigation infrastructure along meandering rivers.

3. Established baseline conditions for groundwater level and water quality for the Groundwater Transfer and Injection Pilot Project. The Mississippi River Valley alluvial aquifer (MRVAA) provides over 90% of the irrigation water used in the heavily agricultural Mississippi Delta region in northwestern Mississippi, with more than 20,000 irrigation wells supplying water to 1.8 million acres of cropland. Reliance on groundwater has resulted in consistent declines in MRVAA water levels over much of the region. ARS researchers in Oxford, Mississippi, developed the Groundwater Transfer and Injection Pilot Project (GTIP) to test the feasibility of withdrawing groundwater from near a large river and injecting the water into an area where the aquifer is depleted so that it can be used later for irrigation. The GTIP system was activated on April 15, 2021, and was operated continuously. Water level data from 17 monitoring wells were collected for at least nine months prior to the GTIP system entering the operational phase. Water quality data for a subset of 6 wells were collected for at least 7 months. Monthly physical samples were collected from over 20 sampling points and analyzed, including a set of samples collected just before the pumping began. A groundwater mound exceeding 6 ft formed near the injection wells, extending beyond a radial distance of 3,600 ft based on a small but steady rise in water level at this location. The data collected during this phase of the project will provide vital information needed for determining whether groundwater injection is a viable method for reversing declines in groundwater levels in the Mississippi Delta region. Agricultural producers, Mississippi Department of Environmental Quality, U.S. Geological Survey, U.S. Army Corps of Engineers, and other entities are keenly interested in the results of the project.

4. Conservation management planning agencies need information to guide planning activities and allocation of limited mitigation resources at regional scales. An integrated approach to analyze individual fields based on multiple management, landscape, and combined management-landscape conditions with links to larger scale analyses would be a valuable management tool. ARS researchers in Oxford, Mississippi, developed integrated watershed technology to characterize water and non-point source pollution at basin scales through integrated field-scale analyses providing optimization of computer resources at larger scales. The integrated technology was shown to provide similar results when applying individual simulations to smaller areas linked together compared to when simulating all the areas in one simulation. This study revealed the integrated approach is a viable option to increase computational efficiency when simulating large areas at high spatiotemporal resolutions. These tools provide capabilities to action agencies in performing national assessments of conservation practice effectiveness based on analyses of integrated results from individual agricultural fields throughout the U.S.

5. Flow history and transport of sand and gravel in streams. The rate of movement or transport of the sediment on the bottom of streams is information necessary to assess the net rate of erosion from upstream sources, determine the potential for erosion or deposition of the channel boundary, and ultimately to evaluate and predict the stability of the channel and watershed. ARS researchers in Oxford, Mississippi, conducted a series of experiments to determine the effect of recent flow history on the rate of movement of sand and gravel in a model stream channel. The effect of four different antecedent flows on the mean rate of sand and gravel transport for standard flows was evaluated and found to be related to the magnitude of the previous flow in the channel. This study indicates that the transport of coarse sediment in stream channels is not just a function of flow strength and sediment size but is also a function of flow history. Accurate bed load transport rates are critical for designing stable channels. This information is necessary for managers to evaluate and design sustainable watersheds to assure that fertility and productivity of the land is maintained.

6. Established field monitoring and experimental levee protection on irrigation reservoir. Irrigation reservoirs are a conservation practice for reducing dependence on groundwater for crop irrigation. Surface water is stored in the reservoirs during months with high precipitation and then used for irrigation in the summer, when crops need the most water. A common problem with the reservoirs is rapid levee erosion caused by wind-driven waves. ARS researchers in Oxford, Mississippi, initiated a field study at Johnson Reservoir near Shelby, Mississippi. A weather station was installed, levee cross-sections were surveyed, and geotextile bank protection was implemented for approximately 200 m of the south levee. In the near future, experimental floating wave barriers for reducing wave energy will be installed. The results of this work will be used for developing recommendations for reducing levee erosion for farmers who use irrigation reservoirs. Reducing erosion will make the levees last longer and reduce costs for levee repairs, which represent a barrier to using the conservation practice.

U.S. DEPARTMENT OF AGRICULTURE

Watershed Physical Processes Research: Oxford, MS