Project : USDA ARS

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Research Project: Managing Water and Sediment Movement in Agricultural Watersheds

Location: Watershed Physical Processes Research

2020 Annual Report

Objectives
1. Develop new knowledge and methodologies to quantify soil detachment and sediment transport, transformation, storage, and delivery. 1.a. Determine functional relations among variables (i.e., rainfall, soil moisture, soil texture, bulk density, organic matter, vegetation) with soil erosion. 1.b. Quantify the surface and subsurface processes controlling erosion and depositional features. 1.c. Quantify the effects of mixed-particle sizes and bed forms on roughness and sediment transport. 2. Improve knowledge of processes controlling surface and groundwater movement in agricultural watersheds, and their associated quantification. 2.a. Removed per approved Ad-hoc approval July 2018. See approved post plan. 2.b. Assess the use and management of floodplain water bodies for providing ecosystem services in order to support their use as a sustainable source of water for agriculture. 2.c. Quantify the processes partitioning components of the water budget in upland catchments of the Lower Mississippi River Basin. 3. Translate research into technology to quantify and evaluate management effects on watershed physical processes. 3.a. Develop a GIS-based erosion prediction management system that facilitates database acquisition and input file development, output visualization, and supports multiple scales of focus, including: watersheds, farm fields, and streams. 3.b. Develop technologies and tools to evaluate the benefits of conservation practice plans within and among fields, streams, and watersheds. 3.c. Develop new computer model components to simulate non-uniform sediment transport and stream morphologic adjustment at subreach scales. 4. As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in the Midsouth region, use the Lower Mississippi River Basin LTAR site to improve the observational capabilities and data accessibility of the LTAR network and support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the Midsouth region. Research and data collection are planned and implemented based on the LTAR site application and in accordance with the responsibilities outlined in the LTAR Shared Research Strategy, a living document that serves as a roadmap for LTAR implementation. Participation in the LTAR network includes research and data management in support of the ARS GRACEnet and/or Livestock GRACEnet projects. 4.a. Develop the Lower Mississippi River Basin LTAR location addressing issues of long-term agroecosystem sustainability specific to the region, participating in the Shared Research Strategy, and contributing to network-wide monitoring and experimentation goals. 4.b. Enhance the LMRB CEAP watershed long-term data sets and integrate with other long-term data sets in the LMRB to address agroecosystem sustainability at the basin scale. 5. Increase knowledge and understanding of the processes governing movement, storage, and quality of water in the Mississippi River Valley Alluvial Aquifer, and develop technologies to enhance the sustainability of water resources for agriculture. 5.a. and 5.b. See approved post plan.

Approach
In the Lower Mississippi River Valley, groundwater extraction for irrigation has outpaced aquifer recharge, and precipitation is expected to fall in fewer, higher intensity events, thereby increasing runoff and stream peak discharges. This will impact erosion patterns and rates, destabilize streams with consequent loss of arable land, adversely impact ecosystem services, and reduce reservoir usability. These are not only regional but also national concerns. There is a critical need for improved understanding and quantification of the processes that control: the movement of water across the landscape; the detachment and transport of soil and sediment; and the morphologic adjustment of channels. This research will use an integrated approach to watershed management through the development and testing of innovative practices and computational models based on a scientific understanding of hydrogeomorphic processes at the test-plot, farm, watershed, and river-basin scales. Field and laboratory, short- and long-term experiments will be conducted to fill technology and knowledge gaps in USDA erosion models concerning: ephemeral gully and soil pipe erosion; transport of eroded sediments and of sediments introduced by reservoir sediment management actions; and stream system physical integrity. Findings will be used to develop new computer modeling components to optimize conservation measure design and placement for the RUSLE, AnnAGNPS, and CONCEPTS computer simulation models. Long-term monitoring combined with new field experiments will investigate the long-term sustainability of surface and groundwater resources in the Lower Mississippi River Valley.

Progress Report
Progress was made on all five objectives and their subobjectives, all of which fall under National Program (NP) 211. The construction of a new laboratory soil erodibility testing method is nearing completion. The field site flume retrofit and laboratory rainfall collection system to study gully erosion processes and control is ongoing. All measurement equipment has been tested and is operational. The laboratory experiments and field monitoring of the combined impacts of soil pipeflow and surface runoff on headcut migration were completed and fully analyzed, which culminated in two journal publications. The studies’ results confirmed and quantified the processes involved in internal erosion of soil pipes such that the controlled field experiments planned for next year were deemed unnecessary. A series of experiments were initiated on the calculation of bed load in sand-bed streams using the rate of modification of the bed forms on the stream bottom. This cooperative study with researchers from the U.S. Army Corps of Engineers-Engineer Research and Development Center in Vicksburg, Mississippi, will provide information to quantify confidence intervals of the bed load calculation procedure. A new series of experiments was begun to further explore conditions of sand clean-out over immobile gravel beds. Data from a previously conducted series of experiments concerning the effect of antecedent flows on the movement of bed load in a gravel bed channel were analyzed and a manuscript was prepared. Analysis of sediment transport data from step-up experiments was completed, and a manuscript on the results was submitted to the Journal of Hydraulic Engineering. The manuscript contains final results for the experiments, which were focused on the effects of rapid increases in flow discharge and depth on sediment discharge magnitude and lag. Monitoring of particle settling traps at three locations in Beasley Lake was continued during FY2020. A new design for compact sediment traps that work in shallow water was completed, and it is being used alongside existing, much larger, traps in Beasley Lake. Three new sediment traps for shallow water conditions were deployed at Roundaway Lake and monitored. We published results of monitoring sedimentation rate, along with a model for the observed intra-annual variability, in a peer-reviewed journal article. We made progress on further improving the USDA, ARS natural resources computer models AnnAGNPS, CONCEPTS, EphGEE and RUSLE2, and their integration. The integrated capabilities of AnnAGNPS to characterize and evaluate ephemeral gullies, riparian buffers and constructed wetlands, as well as sheet and rill erosion were completed and released as AnnAGNPS Version 5.51 in December, 2019. This provides critical management tools to evaluate the most efficient combination of conservation practices applied within watershed systems needed in conservation management planning. The conservation planning tool RUSLE2 has been transformed into a web platform with improved dynamic erodibility and carbon sequestration computations. The RUSLE2 ephemeral erosion calculator (EphGEE) has been modified and is currently under calibration review using remotely-sensed centimeter-scale imagery. To improve the interoperability of the CONCEPTS channel evolution computer model with other federal natural resources computer models, its use online and on high-performance computing platforms using languages such as Python, the code of CONCEPTS is being refactored following Basic Model Interface standards developed by the Community Surface Dynamics Modeling System. We made progress in developing the Lower Mississippi River Basin (LMRB) Long-Term Agroecosystem Research (LTAR) site through participation in national network activities, the establishment of new flux tower sites, and further development of the Common Experiment design for the LMRB site. The Water Information Systems by KISTERS (WISKI) is being used to enhance the collection, management, and analysis of precipitation, runoff, and sediment concentration data from the ARS Conservation Effects Assessment Program (CEAP) Goodwin Creek Experimental Watershed. We continued development of a novel pilot project for investigating managed aquifer recharge in the Mississippi Valley Alluvial Aquifer. Construction of the system is nearing completion, and a draft monitoring plan is being circulated to the agencies involved in the project. Observation wells are online. A rigorous routine of sensor calibration and cleaning was establishment to prevent fouling of instruments. Water quality and water level from 6 of the 12 observation wells is automatically telemetered to the National Sedimentation Laboratory and archived by WISKI. The 2009 lidar dataset of the Yazoo River Basin was corrected for topographic discontinuities along flight line edges. Lentic surface water bodies have been delineated in the Yazoo River Basin utilizing the 2009 lidar data and these are currently being compared to manually delineated water bodies from three HUC-10 watersheds and to the National Hydrography Dataset Plus High Resolution (NHDPlus HR). A database with these water bodies is under development and includes surface area, precipitation, estimated evaporation, and will include estimated average depth and volume. Centerlines of lotic water bodies in the HUC-12 Roundaway Bayou watershed were delineated showing significant deficiencies in NHDPlus HR for application to the Yazoo River Basin with respect to lotic ecosystems.

Accomplishments
1. Assessing RUSLE2 and WEPP differences as a conservation planning tool. To streamline delivery of conservation assistance to farmers, the USDA Natural Resources Conservation Service (NRCS) will be transitioning from using the Revised Universal Soil Loss Equation 2 (RUSLE2) to the Water Erosion Prediction Project (WEPP) in order to guide conservation planning regarding erosion by water. However, there is a concern that estimated erosion rates may increase as a result of the transition, thereby adversely impacting farmers’ conservation compliance. ARS researchers in Oxford, Mississippi (RUSLE2 Team), and West Lafayette, Indiana (WEPP Team), conducted almost 40,000 simulations covering different climate, soil, land management, terrain, and crop yield conditions for counties in Illinois and Iowa. The soil loss estimates for about 50% of the simulation scenarios were statistically different between RUSLE2 and WEPP. In comparable scenarios, the primary differences were related to model soil erodibility characterization, slope length effects, no-till management and cover crop managements. WEPP was sensitive to the quality of climate inputs; future work should therefore include comprehensive evaluations of different climate scenarios, and data precision, gaps and resolution. The performed assessment is vital to conservation management planning provided by NRCS and farmer’s conservation compliance under specific provisions of the 2018 Farm Bill.

2. Interagency study to assess measuring techniques for soil erosion-resistance. Agencies across the federal government use various techniques to measure the erosion-resistance of soils, which is critical information for estimating soil loss from cropland or determining the integrity of earthen dams, levees, roads, and streams. Federal agencies have documented significant differences in erosion-resistance measured by jet erosion test (JET), erosion function apparatus (EFA), borehole erosion test (BET), and other technologies for same soils. As part of an interagency effort, ARS researchers in Oxford, Mississippi, in collaboration with the U.S. Army Corps of Engineers (USACE), U.S. Geological Survey (USGS), and Texas A&M University-Texas Transportation Institute used laboratory and field BET, EFA, and JET methods to measure erosion resistance of clay, silt, silty sand, and sandy soils at or collected from 18 sites near Sacramento, California. Measured erosion-resistance differed significantly between these three methods using their standard data processing procedures. It was found that the estimation of the applied forces acting on the eroding soil surface was responsible for the discrepancies. Improved procedures were developed that ensured consistency of assessed erosion regime and estimation of applied forces among the methods, which resulted in statistically equivalent soil erodibility values though the parameterized force at which erosion commences presented small differences. This study has provided USACE, USDA, and USGS new insight and confidence in using a range of soil erosion-resistance measuring techniques critical to managing our Nation’s infrastructure and conservation of our Nation’s natural resources.

3. Subsurface flow through soil pipes below gullies accelerates gully headcut migration. Formation of gully headcuts and their rate of migration upslope is often mistaken as the sole result of overland flow without realizing the role of flow through soil pipes below the gully or into the headcuts. Failure to understand the controlling processes can lead to inappropriate models, erroneous predictions of soil losses and invalid applications of conservation practices. ARS researchers in Oxford, Mississippi, conducted the first-ever controlled laboratory experiments involving flow through soil pipes simultaneous with concentrated channel flow on headcut migration under conditions with and without seepage. Subsurface flow through a soil pipe below the gully caused erosion inside of the soil pipe at the same time that channel flow caused headcut scour hole development. When the headcut extended to the depth of the soil pipe, surface runoff entering the scour hole interacted with flow from the soil pipe also entering the scour hole. This interaction dramatically altered the headcut processes, greatly accelerating the headcut migration rates and sediment concentrations. This study confirmed that pipeflow dramatically accelerates headcut migration especially under conditions of shallow perched water tables and highlights the importance of understanding these processes in headcut migration processes. This work led to the development of a state-of-the-science flow and sediment transport model for internal erosion of soil pipes that was published in the Vadose Zone Journal and featured in CSA News and will eventually contribute to the next generation of gully erosion models.

4. Validation of novel method for computing bed load from river topography data. Measuring sediment transport in large rivers is problematic due to high water depth, large bed forms of different geometry and sediment concentrations that vary greatly in time and space, which make it difficult to obtain numerous accurate physical samples near the bed of the river where most sediment is transported. In order to overcome these issues, repeated multi-beam acoustic surveys of bed topography can be used to arrive at reach-averaged sediment transport rates. An established methodology for converting repeated bed topography measurements to sediment load is the U.S. Army Corps of Engineers' ISSDOTv2 model, which stands for Integrated Section, Surface Difference Over Time; however, there is a need for establishing error bounds and further developing the methodology. Since it is nearly impossible to collect enough physical samples to validate the method in a river, ARS researchers in Oxford, Mississippi, conducted laboratory experiments to estimate error bounds for the ISSDOTv2 method, to continue development of the method, and to evaluate its performance in unsteady and spatially variable sediment transport scenarios. The ISSDOTv2 method produced sediment loads that were from -29% to +6% with a mean error of -6% relative to independent total load measurements made during the study, which is considered to be good agreement due to the difficulty of obtaining sediment transport measurements, even in laboratory experiments. The work is providing the only validation data set for the ISSDOTv2 method, which is being applied in larger river systems of national concern, such as the Mississippi and Ohio rivers. Bed load transport rates are important for assessing the stability of rivers and for determining impacts on river navigation and morphology.

5. Riparian buffer technology developed to assess soil loss reductions as a result of edge of field vegetation. In agricultural watersheds, natural or constructed vegetated riparian buffers can promote sediment deposition and nutrient filtering that enhances downstream water quality. ARS researchers in Oxford, Mississippi, developed watershed pollution modeling components to estimate sediment load reductions from riparian vegetation at field to watershed scales. Spatially distributed information describing riparian vegetation physical characteristics were incorporated into the model, including buffer width, slope, vegetation type, and consideration of concentrated flow paths through the riparian zone that may decrease the capability of riparian vegetation to effectively filter sediment. The model provides capabilities to evaluate various levels of conservation management with and without the contribution of riparian vegetation. This framework serves as an effective spatially distributed approach to assessing the impact of riparian buffers on watershed sediment loads and downstream water quality by action agencies, such as Natural Resources Conservation Service (NRCS), to support the development and evaluation of conservation management plans impacting the watershed.

6. Bed surface structure and its effect on the transport of coarse sediment in streams. Accurate knowledge of the rate of movement of the sediment on the bed of streams is necessary to assess the net rate of erosion for the watershed upstream of the channel, to assess the stability of the channel boundary, and its suitability as habitat for aquatic organisms. ARS researchers in Oxford, Mississippi, conducted experiments in a laboratory channel to determine the effect of flow strength on the structure of a sediment bed consisting of a mixture of sand and gravel. Details of the structure of the channel bed were found to change with increasing flow strength such that corridors of sand formed on the surface of the stream bottom at lower flows and evolved into wider corridors with increasing flows which affected the movement of sediment, the roughness of the channel bed surface, and the depth of flowing water. An understanding and predictive capability for the evolution of the bed surface structure is important for improving the generally poor performance of sediment transport prediction methodologies. Information of this type will be useful to develop improved tools to predict bed material transport and the stability of channel boundaries. This capability will allow watershed managers to more effectively manage sediment in agricultural watersheds in an environmentally sensitive manner to facilitate the design and maintenance of stable channels and contribute to the preservation of soils and sustainable agriculture.

U.S. DEPARTMENT OF AGRICULTURE

Watershed Physical Processes Research: Oxford, MS