Location: Watershed Physical Processes Research2018 Annual Report
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:) Removed per approved Ad-hoc approval July 2018. See approved post plan. (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. (5a:) and (5b:) See approved post plan.
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.
We selected a soil erodibility testing method to measure the erosion resistance of soils in the laboratory and in the field. Monte Carlo simulations are being conducted to explore the contributions of various soil properties to erosion resistance. Laboratory and field facilities are being retrofitted to begin experiments to quantify the equilibrium width of ephemeral gullies for different soils and conservation practices. The experimental approaches for the laboratory experiments on the impacts of combined pipeflow and surface runoff on headcut migration were designed and existing facilities were modified accordingly. All experiments were completed as planned for conditions of runoff alone, pipeflow alone, and pipeflow with runoff under free drainage conditions and seepage conditions. The laboratory facilities to measure sediment transport capacity of soil pipes were developed and experiments were conducted on medium sized sand. Additional experiments are planned for transport of very fine sand, silt, aggregates and mixtures of particle sizes. Regarding the research on mixed sand and gravel transport, the first series of experiments on the effect of flow strength on the structure of the bed surface have been completed. Additional experiments are in progress to explore the relation between flow history of a gravel and sand bed and the transport of bed load sediment for a given flow. Several runoff events were sampled using the elutriation system in the Goodwin Creek Experimental Watershed (GCEW), Mississippi, during the past spring. These storms ranged widely in the characteristics of the hydrograph and the amount of sediment that was collected with both an optical system and the elutriation system. Data collected from these runoff events are currently being processed and analyzed (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, resembling the recession of a flashy runoff event. Data analysis was completed, including the derivation of a relationship linking dune evolution metrics to sediment transport rates. An additional series of experimental runs was completed to bolster the above-mentioned relationship and expand the range of hydraulic conditions. We monitored particle settling traps at three locations in Beasley and Roundaway lakes in the Yazoo River Basin to evaluate the use of floodplain water bodies for providing ecosystem services in order to support their use as a sustainable source of water for agriculture. The research on perched water tables and pipeflow has been completed and a paper published. Our soil-pipe field research sites in the GCEW were instrumented and numerous flow events were sampled for pipeflow rate and sediment concentrations. We made progress on further improving the USDA, ARS natural resources computer models AnnAGNPS, CONCEPTS, EphGEE and RUSLE2, and their integration. The AnnAGNPS and CONCEPTS programs were successfully linked enabling results from AnnAGNPS to be used within CONCEPTS for watershed and channel simulations and evaluations. 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. This provides assessments of the most efficient combination of conservation practices applied within watershed systems needed in conservation management planning. Further 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 near localized hydraulic structures and in urbanizing, rural watersheds where mixed earthen and concrete channels may occur. A comprehensive set of localized streambed and streambank erosion data was compiled from published research, which will be used to test a conceptual model, developed earlier, that estimates channel erosion by localized structures at the reach scale. 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.
1. Measurement of gravel transport using impact plates. Accurate knowledge of the rate of gravel movement in streams is necessary to assess the stability of the channel boundary and its potential for instability and erosion. This is particularly true when coarse sediment, which has been stored in a reservoir for 100 years, has the potential to be entrained following the removal of a dam and potentially cause channel instability and capacity issues downstream. A series of impact plates were installed in the Elwha River to monitor the transport of gravel following the removal of two dams in 2012 and 2014. ARS researchers at Oxford, Mississippi, conducted experiments in a laboratory flume to calibrate replica impact plates of the ones installed in the Elwha River. The plates were successfully calibrated to allow measurement of the number and mass of gravel particles in motion using the experimental data. Methods to adapt the calibrations to the Elwha River have been developed. Calibration relations for the impact plates on the Elwha River will allow river managers to adaptively manage the removal of the impounded sediment in a more informed and environmentally sensitive manner.
2. Analysis of irrigation reservoir levee erosion at Lonoke Demonstration Farm, Arkansas. Wind-driven waves erode earthen levees, causing significant maintenance costs for irrigation reservoirs and aquaculture ponds. ARS researchers at Oxford, Mississippi, measured levee erosion for a wide range of levee configurations and surface treatments on the Lonoke demonstration irrigation reservoir, Arkansas. Among the tested treatments, soil cement, fly ash, and geo-textiles were the most effective for reducing levee erosion by wind-driven waves. Slope and berm treatments, which modified the geometry of the levees, were not effective, with severe erosion on all sections. The most important characteristic associated with erosion was the distance across the reservoir in the direction of prevailing strong winds. The results of this work will be used to design reservoirs and wave-reduction technologies to make surface water storage more economically sustainable and to extend the life of aquaculture ponds.
3. Linkages for water flow from hillslopes to streams includes surface and subsurface flow pathways. For watersheds with networks of preferential flow paths, such as subsurface soil pipes and surface features such as edge of field gullies, the hydrologic response of the watershed can depend upon their hydrologic connectivity. ARS researchers at Oxford, Mississippi, determined the relationships between perched water tables on hillslopes with flow through soil pipes along with the thresholds for their hydrologic connectivity for two catchments in the Goodwin Creek Experimental Watershed, Mississippi. Perched water tables developed on hillslopes during a wetting up period (October – December) and became well connected spatially across hillslope positions throughout the high flow period (January – March). The water table was not spatially connected on hillslopes during the drying out (April-June) and low flow (July-September) periods. However, even when perched water tables were not well-connected, water flowing through soil pipes provided hydrologic connectivity between upper hillslopes and catchment outlets. This connectivity can result in flashy stream response, decrease in groundwater recharge, and potential by-pass of the capacity of soil to filter runoff waters of impurities.
4. Targeting conservation practice placement in watersheds by tracking and identifying sediment sources from fields. Watershed-scale simulation technology can be used to identify and track sediment loads that originate in fields and are then routed downstream. This technology allows for quantification of the impact of individual and/or integrated management practices throughout the watershed. ARS researchers at Oxford, Mississippi, used watershed simulation technology to simulate the erosion from all fields in the watershed with the highest erosive fields identified for further study with advanced field erosion technology. Using an integrated modeling approach, these targeted fields can be analyzed based on multiple management, landscape, and combined management-landscape conditions. The erosion from these targeted fields can then be integrated back into the watershed simulations to quantify the overall effect of enhanced field characterization on sediment loads at the field and watershed scales. Methods for identification of critical sediment producing areas using integrated field erosion and watershed sediment transport models can be used to support the development, evaluation and implementation of conservation management plans impacting the entire watershed by action agencies.
5. Improved soil erodibility formulation. Recent enhancements to USDA-ARS soil erosion models employ more physically-based descriptions of erosion processes, which require the parametrization of soil properties, land use and land management, and hydrologic variables to calculate soil erodibility. Such information is lacking. ARS researchers at Oxford, Mississippi, tested three soils, ranging in clay and sand content, to develop a prediction tool for agricultural erosion. The results suggest that soil erodibility is impacted by the initiation of particle movement, clay content and the void ratio, while results for critical shear stress testing suggest that silt, void ratio and water potential best indicate the initiation of motion. These findings were recently implemented within the Revised Universal Soil Loss Equation 2 (RUSLE2), which is used by USDA for improved conservation planning.
6. Effects of in-channel structural measures on urbanizing watershed sediment management in developing countries. Many studies have documented the impact of urbanization on stream channel erosion and its relationship to watershed characteristics and proximity to hardpoints like road crossings or bridges. However, very few studies have been conducted in semi-arid climates in developing countries experiencing rapid population growth, unregulated urban development on erodible soils, and variable enforcement of environmental regulations. ARS researchers at Oxford, Mississippi, in collaboration with researchers at San Diego State University, the U.S. Environmental Protection Agency, and the Ensenada Center for Scientific Research and Higher Education, Mexico, investigated urbanization and stream channel erosion in Tijuana, Mexico, through a mix of field topographic survey methods, and a comparison of channel geometry to undeveloped and urbanized watersheds in southern California. Proximity to upstream hardpoint, and lack of riparian and bank vegetation paired with highly erodible bed and bank materials were found to be the main cause of channel instabilities. Channel erosion due to urbanization accounts for approximately 25-40% of the total sediment budget for the watershed, and channel erosion downstream of hardpoints accounts for approximately 1/3rd of all channel erosion. This research has provided local and state watershed managers with improved guidelines to reduce sediment loads and yield through focusing on stabilizing the stream channel downstream of hardpoints, especially in areas with urban development adjacent to the stream channel.
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