Location: Watershed Physical Processes Research
2017 Annual Report
Objectives
1. Develop new knowledge and methodologies to quantify soil detachment and sediment transport, transformation, storage, and delivery.
1a: Determine functional relations among variables (i.e., rainfall, soil moisture, soil texture, bulk density, organic matter, vegetation) with soil erosion.
1b: Quantify the surface and subsurface processes controlling erosion and depositional features.
1c: 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.
2a: Quantify processes governing groundwater recharge and sustainable groundwater use for aquifers in agricultural watersheds.
2b: 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.
2c: 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.
3a: 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.
3b: Develop technologies and tools to evaluate the benefits of conservation practice plans within and among fields, streams, and watersheds.
3c: 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.
4a: 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.
4b: 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.
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
This report documents progress for Project Number 6060-13000-026-00D, which started in March 2017, and continues research from Project Number 6060-13000-023-00D, entitled “Technologies for Managing Water and Sediment Movement in Agricultural Watersheds.” Progress has been made on all four objectives and their subobjectives.
Under Objective 1 we made progress on quantifying the fundamental interactions between rain drop impact, soil erodibility and erosion mechanics both in the laboratory and the field (Subobjective 1a), which was facilitated by being able to collect large quantities of high-resolution topography using unmanned aerial vehicles. The instruments for monitoring flow rates and sampling sediment concentrations in selected soil pipes in the field have been installed and data are being collected in situ (Subobjectives 1b and 2c). The laboratory facilities and methods to study soil pipe morphodynamics experimentally (Subobjective 1c) have been fully developed and are being used. Tests have been conducted under three different flow rates with a complete range of sediment input rates for fine sand size sediment. Additional tests are being conducted with silt size sediment followed by gravel size aggregates. Regarding the research on mixed sand and gravel transport, a series of experiments documenting the effect of a range of sediment transport rates on the roughness of the bed surface has been completed in the 30-m flume (Subobjective 1c). Other goals of the experiments consisted of collecting gravel bed load transport data for calibration of impact plates and sediment generated noise. These surrogate bed load transport measurement techniques show promise for improving the quality and quantity of bed load transport data collected in gravel-bed streams. Data from this study is currently being analyzed. Sediment transport and bed topography data for a range of unsteady flows were collected (Subobjective 1c). Dune topography and sediment transport data were combined in a study of sediment transport following a sudden drop in water depth and velocity. The analysis of the data is ongoing and is focused on finding predictive relationships for sediment transport in step-down and step-up unsteady flow conditions.
Under Objective 2 we made progress in developing a regional database of groundwater levels for the Mississippi River Valley alluvial aquifer to serve as an authoritative data set among federal, state, and county agencies and stakeholder groups in developing sustainable groundwater management for the region (Subobjective 2a). We also initiated a series of research projects in the region to quantify aquifer properties and begin to address the potential for aquifer storage and recovery in the region for enhancing groundwater supply. To 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 we installed particle settling traps in Beasley and Roundaway lakes (Subobjective 2b). It is too early to know if important trends are present, but the sedimentation rate varies with season and is higher in Roundaway lake.
Under Objective 3 we made progress on both further improving the USDA, ARS natural resources computer models AnnAGNPS, CONCEPTS, EphGEE and RUSLE2, and their integration. The AnnAGNPS and RUSLE2 programs were successfully linked enabling results from RUSLE2 to be used within AnnAGNPS for watershed simulations and conservation practice evaluation (Subobjective 3a). Significant progress has been made toward the development of a web-based portal for the modeling of environmental processes. Websim (http://websim.rusle2.org) was created as a software platform to integrate and facilitate the use of natural resources modeling tools developed by ARS scientists at Oxford, Mississippi, and collaborators. Its first web app allows modeling of runoff and soil erosion in agricultural fields using the RUSLER (Rusle2-Raster, the 2D version of RUSLE2) and EphGEE models. The AnnAGNPS model was enhanced to integrate the characterization and evaluation of ephemeral gullies, riparian buffers and constructed wetlands, as well as sheet and rill erosion (Subobjective 3b). This provides assessments of the most efficient combination of conservation practices applied within watershed systems needed in conservation management planning. Improvements were made to the channel evolution computer model CONCEPTS to handle nearly dry beds and to increase its robustness for supercritical flow conditions, which is required to simulate hydraulics and sediment transport in urbanizing, rural watersheds where mixed earthen and concrete channels may occur. Further, a conceptual model was developed to estimate channel erosion by localized structures at the reach scale. New methods were developed for EphGEE to estimate the growth of gully channels for a series of storm events. Channels deepen and widen simultaneously according to local storm runoff and soil erodibility characteristics. EphGEE has new methods to estimate the seasonal variation of erosion susceptibility of a soil according to the erosion depth. These changes improve the performance of the model, especially for no-till fields. The application of the RUSLE2 soil erosion model using more detailed topographic description of hillslopes revealed some limitations of the model’s original erosion calculation methodology. New methods were introduced to RUSLE2’s 2017 version to remedy those problems. RUSLE2 performs well independently of terrain topography. Calculation methods for sediment deposition patterns at narrow filter strips and locations sudden decrease in transport capacity continue to be enhanced for a future software update.
Under Objective 4 we made progress in developing the Lower Mississippi River Basin (LMRB) 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.
Accomplishments
1. Enhanced erosion prediction technology for gully formation. Assessing the impact of agricultural practices on reducing gully erosion requires knowing where gullies will form. ARS scientists at Oxford, Mississippi, developed enhanced erosion prediction technology for the USDA-ARS Annualized Agricultural Non-Point Source pollution model (AnnAGNPS) to predict where gully channels begin and their characteristics within the landscape. Observations of gully formation at experimental sites in mixed urban and rural watersheds in Mexico showed that the new technology accurately delineated the gully network and indicated that sediment production from gully erosion exceeded that of sheet and rill erosion. Utilizing improved gully identification and erosion assessment technology can provide action agencies with management tools needed to assess ephemeral gully erosion control practices critical in the development of effective management plans that reduce sediment loads within watershed systems.
2. Launched the soil erosion modeling website http://websim.rusle2.org. An erosion-prediction system that encompasses all of the necessary databases and decision-making capabilities is needed to provide planners with the tools necessary to place effective conservation practices at all scales within a watershed system. ARS researchers at Oxford, Mississippi, developed a software-as-a-service platform and website to facilitate the integration and application of USDA, ARS soil erosion modeling tools. The website provides a map-based interface and a collection of tools that allow users to define areas for study and perform watershed-scale soil erosion and sediment transport simulations. Its first application employs RUSLE2 and EphGEE technologies to produce soil erosion maps using high-resolution terrain data. It provides automated procedures to retrieve and process all required data for modeling, including access to the SSURGO soil database and a locally-hosted national RUSLE2 database. Simulations are performed on a dedicated high-performance server using cloud technologies and virtualization. The web applications provide technical data for evaluation of erosion problems and evaluation of the performance of soil conservation measures that are critical to developing management plans for conservation practice implementation by natural resource action agencies.
3. Optimizing watershed simulation delineations improves watershed management plan development. Optimizing the level of watershed subdivision into homogeneous areas for watershed simulations improves the runoff and sediment yield results needed in watershed management plan development. ARS scientists at Oxford, Mississippi, developed an optimization approach that was integrated with a watershed pollutant loading management model using landscape characterizations describing topographic, soil, and management information to minimize the number of watershed subdivisions. Thus, the approach improved the simulation results while reducing the computational effort required for the simulations. This study provides an approach that can be used as a guideline describing watershed landscapes when applying watershed technology in developing management plans for conservation practice implementation by action agencies.
