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.