Location: Watershed Physical Processes Research2013 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:
To characterize the properties and processes controlling sediment detachment by water, progress has been made on refining and transferring technology on soil erodibility testing methodology. Use of photogrammetry has been adapted to provide detailed data on the erosion of soil by flowing water. Progress has been made on constructing a large scale surface erosion apparatus in the laboratory. Experiments on the erosion of sediment by waves are continuing. Preliminary trial experiments where waves impact an earthen levee are progressing using natural soil materials. The methodology required to prepare the earthen levees is under development. 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 erosion of sand from a gravel bed are in progress. Preliminary data indicate that sand may be eroded more deeply from a gravel substrate than prior work has indicated. Laboratory equipment for rapid scanning of the substrate and techniques to characterize sand beds with dune forms have been developed as the first phase of the conduction of unsteady flow experiments with sand transport. To quantify and predict erosion and morphologic adjustment of channels from pore to river scales, improvements of channel reach bed and bank erosion models have continued with the addition of multiple dimensional capability and improved bed material sorting algorithms to channel stability simulations. Improvements have been made on the ability to assess and simulate the location and processes associated with ephemeral gullies on agricultural fields. 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. Analyses are under way on the 30-year rainfall record from Goodwin Creek. A novel technique to use cesium and lead to arrive at sedimentation rates in the late twentieth century was developed and applied. Three new edge-of-field stations have been added to expand the range of spatial scales represented in the runoff and sediment datasets. New experiments have been initiated on the dynamics of soil piping in a pasture collocated with one of the new edge-of-field sites. In addition, tests are being conducted using real-time in-situ grain-size analysis technology to investigate the dynamics of suspended sediment transport and flocculation during a runoff event. New quality control protocols have been established for the Goodwin Creek Experimental Watershed. Historic datasets have been revised subject to rigorous quality control standards in preparation for a publishable final historical dataset.
1. Improved prediction of transport rates of sands released from reservoirs. Prolonged erosion of farm fields and hill slopes has greatly reduced the storage capacity of reservoirs and the structural integrity of dams. Common mitigation measures concern removal of dams or flushing of stored sediments, which releases sands into sand-deprived river reaches. Current relations to calculate the downstream transport rates are not accurate as they assume that the released sediments are available on the riverbed. ARS scientists at Oxford, Mississippi, developed a new transport relation by conducting laboratory experiments of sand transport over immobile gravel and cobble beds typically found downstream of dams. The new relation uniquely links sand transport to the surface characteristics of the gravel and cobble riverbed, which not only improves predicted transport rates but also the resulting riverbed and flood elevations. The U.S. Bureau of Reclamation and the U.S. Army Corps of Engineers have been provided with a tool to develop and evaluate more accurately dam removal and sediment flushing alternatives.
2. Gully formation in agricultural fields identified and characterized. Knowledge of where gullies form can be used by watershed models to assess the impact of agricultural practices that reduce gully erosion. Results from Kansas and Mississippi experimental sites indicated the capability of enhanced technology developed within the USDA-ARS Annualized Agricultural Non-Point Source pollution model (AnnAGNPS) to predict the locations of gully channel initiation points, characterize properties of the gully, and simulate sediment loads from gully sources. Utilizing improved gully identification technology can provide action agencies with enhanced information and management tools to assess ephemeral gully erosion control practices critical in the development of effective management plans that reduce sediment loads within watershed systems.
3. Adequacy of existing precipitation data for climate change studies of within-day dry periods. The National Weather Service (NWS) maintains a large data base of short-time increment precipitation data that can be used for climate-change studies. These data often have mixed depth resolutions of 0.1 inch and 0.01 inch. Approximately 60 years of high temporal (minute resolution) and depth (0.01 inch) resolution data from an experimental watershed in Ohio (3 gauges) and NWS resolution Ohio-area data (15 gauges) were used to evaluate if there was an effect of climate change on dry periods and whether high resolution records were required. It was found that mixed and uniform resolution NWS records were not sufficient to identify climate changes in subdaily times between storms. High resolution Ohio data showed a significant change in climate only in November (shortening of sub-daily dry periods). Other NWS data did not conclusively show a similar effect. The study is providing guidance for climate change studies when using the larger geographically available data set and for further evaluating effects of climate change on storm characteristics for storm modeling.
Davidson, G., Rigby Jr, J.R., Pennington, D., Cizdziel, J. 2013. Elemental chemistry of sand-boil discharge used to trace variable pathways of seepage beneath levees during the 2011 Mississippi River flood. Applied Geochemistry. 28:62-68.