Location: Watershed Physical Processes Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Characterize the properties and processes controlling sediment detachment by water. (2.1.3). 1a: Determine functional relations among variables (i.e., rainfall, soil moisture, soil texture, bulk density, organic matter, vegetation) and their effects on soil detachment and erodibility. 1b: Improve estimates of eroded sediment aggregate size distribution and composition. 1c: Quantify particle detachment by wave-impact energy. Objective 2: Improve the understanding and quantification of sediment transport in channels. (2.2.1) 2a: Quantify the effects of mixed particle-sizes on sediment transport. 2b: Quantify sediment transport and bed evolution under unsteady flow conditions. 2c: Quantify sediment transport capacity downstream of headcuts. Objective 3: Quantify and predict erosion and morphologic adjustment of channels from pore to river scales. (2.1.1, 2.2.1). 3a: Quantify and predict the location, magnitude, processes, and controls of ephemeral gully erosion. 3b: Quantify and predict the role of morphological channel adjustment and riparian zone management on resulting watershed sediment load. Objective 4: Integrate research and technology to quantify management and climate effects on watershed physical processes. (2.1.1, 2.2.1, 3.1, 3.2, 3.3, 4.1, 4.2, 4.3). 4a: Quantify impacts of climatic variability and land management on sediment and water yield under current and future climate scenarios. 4b: Quantify watershed-scale rates of erosion and related management effects using integrated sedimentation records in receiving waters. 4c: Develop a GIS-based erosion prediction management system that facilitates database acquisition and input file development, and supports multiple scales of focus, including: watersheds, farm fields, and streams.
1b. Approach (from AD-416):
Soil erosion and sediment transport processes involve the interactions of land management practices with climate, weather, soil, and landscape properties. An extensive literature exists that describes plot-scale research into soil erosion processes and the effects of conservation practices in reducing soil erosion or enhancing water conservation. However, plot-scale studies are limited in that they cannot fully capture the complexities and interactions of conservation practices in complex topographies. Some processes such as concentrated flow erosion and stream channel flow only emerge at larger scales. Concentrated runoff and subsurface flow result in rill and gully erosion. Channel erosion and associated soil losses and sediment loads within streams and impounded waters lead to increased costs of crop production, ecological degradation, and impairment of water supplies. Accurate measurements, interpretations, and predictions of total load in streams and rivers are critically needed for watershed management and stewardship. Total sediment load is commonly used to assess the impacts of agricultural activities on sediment yield from watersheds, to identify unstable drainage networks, to determine the efficacy of restoration programs, best management practices, and engineering techniques, to document the impact of land use changes through time, and to assess water body impairment. In addition, sediment has been identified as a cause of impairment on aquatic life, habitat, habitat resources, and industrial and municipal uses of water. This research will focus on quantifying watershed processes resulting in soil erosion and deposition, and developing tools and techniques to quantify the impact of implementing conservation practices within a watershed in the most efficient manner to achieve sustainable and targeted reductions of sediment loadings to the nation’s streams and impounded waters. New methods will be tested to measure and characterize changes in runoff, gully and stream channel erosion, and sediment deposition rates utilizing hydrologic, geomorphic, and hydraulic engineering principles, and related acoustic, seismic, and remote-sensing techniques in watersheds throughout the U.S. and abroad when appropriate. Improved computer models and assessment tools will be provided to evaluate the impact of land conservation and stream- and reservoir-rehabilitation practices in the most efficient manner to assist watershed managers to achieve sustainable crop-production systems, targeted reductions of sediment loadings and improvement of aquatic habitat.
3. Progress Report:
This report documents progress for Project Number 6408-13000-023-00D, which started in March 2012, and continues research from Project Numbers 6408-13000-018-00D, entitled “Integrated Assessment and Analysis of Physical Landscape Processes the Impact the Quality and Management of Agricultural Watersheds” and 6408-13000-020-00D, entitled “Technologies for Assessing Sediment Movement & the Integrity of Flood Control Structures, Streambanks, & Earthen Pond Levees & Embankments.” Progress has been made on all four objectives. To characterize the properties and processes controlling sediment detachment by water, progress has been made on determining the functional relations among key variables. Experiments on the erosion of sediment waves are continuing. Preliminary trial runs, where waves impacted an intact section of marsh grass, were completed. The marsh grasses were established on a packed-in-place soil substrate to approximately replicate the sediments that are beneath natural grasses. It was found that a naturally-shaped soil profile leading up to the marsh edge was necessary for realistic wave interactions and that the processes are highly dependent on the water level. Towards improving the understanding and quantification of sediment transport in channels, experiments on the transport of sand over immobile gravel are continuing with new emphasis on more detailed collection of velocity data and the nature of the transition to a fully sand covered bed. Experiments on the transport of sand over cobbles have been completed and data are being analyzed and interpreted. The first phase of expeiments on the transport of sand gravel mixtures in channels has been completed and results are being written up. Laboratory equipment and plans are being made for the conduction of unsteady flow experiments. To quantify and predict erosion and morphologic adjustment of channels from pore to river scales, improvements of channel reach bed and bank erosion models has continued with further improvements to lateral channel migration algorithms. Experiments on ephemeral gully widening and migration processes have been ongoing. A database of practices associated with ephemeral gullies has been developed. Towards the integration of research and technology to quantify management and climate effects on watershed physical processes, development of the gully routine on field and watershed simulation models has continued. Geographical Information Systems (GIS) are being used to develop prediction management systems to work on watersheds, fields, and streams. Research on the effects of the impacts of climatic variability on land management and sediment and water yield have begun. Sediment cores were collected from four locations in Beasley Lake, Mississippi. Each location has a unique land use, which we hope to link to local sedimentation rates. The sediment cores have been sectioned, dried, weighed, and crushed for analysis. The samples are now being counted for Lead-210 and Cesium-137 in the gamma spectrometer and should be complete in winter 2012-2013.
1. Improved prediction of lateral channel migration using floodplain-soil resistance-to-erosion properties. Laterally migrating, meandering streams erode large quantities of fine-grained bank soils, which adversely impact downstream aquatic resources. Tools have relied on observed migration from historical aerial images to predict future migration patterns, which introduces great uncertainty. ARS scientists at Oxford, Mississippi, with collaborators at the Universities of Illinois and Pittsburgh co-developed a new computer model that employs the resistance-to-erosion properties of floodplain soils in combination with a meandering channel flow model to predict channel migration rates. The new technology not only improves predicted migration rates but also the planform pattern of meandering streams. The U.S. Army Corps of Engineers and natural resource agencies in various states have adopted the model to design, locate, and prioritize bank protection and stream restoration works.
2. Gully database established. A database was established of topography, soil properties, land use, and management practices associated with ephemeral gullies under different climate and geographical settings across the United States and in China by scientists from ARS in Oxford, Mississippi, and Beijing Normal University, China. Topographic survey data were collected for selected watersheds with ephemeral gullies under different management and land use conditions and an extensive variety of soil properties were determined at known gully locations. The database will be used to improve technology to predict the location of gullies for use in watershed erosion models and allow watershed managers to develop improved plans for preventing erosion problems.
3. Evaluating levee integrity with rapid water chemistry analysis. The Mississippi River alluvial plain in Mississippi is an intensive agricultural region protected from flooding by an extensive network of levees. During large floods such as the Mississippi River flood of 2011 the levee system can be put under considerable stress. One visible feature of this stress is the presence of “sand boils” on the dry side of the levee where the pressure of river water has created a conduit through the soil that goes under or through the levee itself. If the water is traveling through the levee or only very shallowly beneath it, there is an increased chance of levee failure and resulting damage to property and crops. If the pathway is deep beneath the levee base the risk of failure is much lower. ARS researchers at Oxford, MS, in partnership with the University of Mississippi and the Yazoo Water Management District showed that the elemental chemistry of water from sand boils can be used to separate the sand boils into different classes based on their degree of interaction with deeper groundwater. This work will help the U.S. Army Corps of Engineers rapidly prioritize potential weaknesses in levees during flood events.
4. Developing simple models of evaporation and precipitation. The region of the atmosphere within a few kilometers of the earth surface known as the “atmospheric boundary layer” is the dynamic layer responsible controlling evaporation, cloud formation, and precipitation. Every climate model must account for the dynamics in this region, and the manner in which each does so is important for the resulting predictions of global climate patterns. Locally this layer is important for predicting the spread of airborne pollutants and the formation of thunderstorms. Researchers at the USDA-ARS in Oxford, MS, in collaboration with researchers at Duke University have developed a mathematical model for the temperature, moisture content, and height of this region as it develops during the day. This model may be used as an efficient method of accounting for the boundary layer in larger scale climate models and will allow for improved predictions of climate change and lead to better scenarios for dealing with these changes.
5. Gully formation and erosion contribution in Conservation Effects Assessment Project (CEAP) agricultural fields identified and characterized. Knowing where gullies form and their contribution to total sediment load within watersheds is critical in assessing the impact of agricultural conservation practices to reduce gully erosion. ARS scientists in the National Sedimentation Laboratory at Oxford, Mississippi, obtained results from CEAP and international experimental sites to locate and evaluate the impact of gully erosion on total watershed load. Enhanced technology was developed and applied within the USDA-ARS Annualized Agricultural Non-Point Source pollution model, AnnAGNPS, to: predict the location of gully channel initiation points; characterize gully properties; and assess gully conservation practices to reduce sediment load at these sites. Utilizing improved gully identification and assessment technology has provided action agencies, such as adoption by USDA-Natural Resources Conservation Service state offices in Ohio and Kansas, with enhanced information and management tools to evaluate gully erosion control practices critical in the development of effective management plans that reduces sediment loads within watershed systems.Romkens, M.J. 2011. Calculation of exit gradients at drainage ditches. Landform Analysis. 17:151-153.