Location: Watershed Physical Processes Research2012 Annual Report
1a. Objectives (from AD-416):
Assisting agricultural landowners to produce food and fiber in an economically and environmentally sustainable manner requires an integrated approach to land management practices, and protection of streams and impounded waters. This project contributes to those goals by developing and testing practices based on a scientific understanding of hydrologic, erosion, and sedimentation processes. This project also contributes to the Conservation Effects Assessment Project (CEAP) with the goal of quantifying effects of conservation management in selected CEAP watersheds, two of them managed within this project. To meet these challenges, the focus of all the proposed research activities has been chosen to evaluate innovative practices and to fill knowledge gaps in watershed models currently in use. This is realized by: (1) developing databases of weather, soil, land use, soil conservation practices, runoff, sediment yield, and nutrient data for assessing the impacts of conservation practices on the Goodwin Creek and Topashaw Creek CEAP watersheds; (2) evaluating relative magnitudes of sources and fates of sediment in CEAP-benchmark and other watersheds, and develop methodologies to establish criteria for identifying agricultural watersheds impaired by clean-sediment loadings; (3) quantifying and validating the uncertainties of model predictions at field, farm, and watershed scales for Yazoo River Basin CEAP sub-watersheds; (4) conducting field and laboratory studies to quantify the surface and subsurface flow processes governing the initiation, development and migration of ephemeral gullies and the effect of conservation management practices on infiltration, erosion, and transport; (5) conducting field and laboratory studies to improve the understanding of stream channel processes including channel evolution, sediment transport, protection of erodible embankments, edge-of-field gullies, and sediment deposition in impounded waters for CEAP and other watersheds; and (6) improving models to identify sources of sediment, determine their fate and transport within watersheds with complex channel drainage networks, and evaluate watershed water quality impacts in terms of implementation of land conservation and stream rehabilitation practices.
1b. Approach (from AD-416):
An extensive body of literature exists that describes plot or field-scale conservation practices aimed at reducing soil erosion or enhancing water conservation. However, results from plot- and field-scale studies are limited in that they cannot capture the complexities and interactions of conservation practices at the whole-farm level or at the watershed scale. Soil erosion and sediment movement processes involve the interactions of land management practices with climate, weather, soil, and landscape properties. Concentrated runoff and subsurface flow results in rill and gully erosion thus increasing soil losses and downstream sediment loads leading to increased costs of crop production, ecological degradation, and impairment of water supplies. This research focuses on 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 stream waters to help establish total maximum daily load requirements. New methods to measure and characterize changes in runoff, gully and stream channel erosion, and sediment deposition rates utilizing hydrological, geomorphic, and hydraulic engineering principles, and remote-sensing techniques will be tested in CEAP watersheds within the Yazoo River Basin, and in other watersheds when appropriate. Improved computer models and assessment tools will be provided to evaluate the impact of land conservation and stream rehabilitation practices in the most efficient manner to assist watershed managers achieve sustainable crop production systems and targeted reductions of sediment loadings.
3. Progress Report:
This is the final report for the project 6408-13000-018-00D terminated in March 2012. There was a period between the beginning of FY 2012 and the termination date for the project occurring in fall and winter. All planned research was completed prior to the start of FY 2012; no research was initiated in this timeframe which corresponded to this project. Substantial results were realized over the 5 years of the project on the technologies for understanding, assessing, and controlling sediment movement with conservation practices in agricultural related watersheds. This project contributed to the Conservation Effects Assessment Project (CEAP) by quantifying the effects of conservation management in two watersheds managed within this project. As a result of the research activities, enhancements to field, watershed, channel, and bank models have been implemented that provides evaluations of innovative practices needed by action agencies for effective watershed management needed to control erosion. The effect of soil texture and subsurface pore-water pressures were found to greatly affect soil erodibility, headcut migration rates, scour depths, and sediment delivery. To understand the growth, development and evolution of rill erosion networks, studies were completed to quantify the formation of rills subjected to various rainfall and downstream flow controls. Rill networks migrated upstream by headcut erosion where peaks in sediment transport occurred periodically and were linked to downstream water levels. Enhanced technology for evaluating the affect of conservation practices on ephemeral gully erosion at the field scale was completed with the release of the Revised Universal Soil Loss Equation, (RUSLE2 2.0), including a perennial plant growth model that predicts the management effects on forage availability and biomass for runoff and erosion. Dominant sources of sediment in agricultural watersheds were found to be important for designing practices that will reduce sediment loads to streams using naturally occurring radionuclides to track sediment on CEAP watersheds. Most of the sediment in the studied watersheds was derived from channel sources. Ephemeral gully erosion has been shown to be a significant source of sediment from many agricultural fields as a result of soil disturbing tillage operations through the use of enhanced technology incorporated into the USDA Annualized Agricultural Non-Point Source pollution model (AnnAGNPS). Evaluations of agricultural practices have been performed using AnnAGNPS in watersheds throughout the United States as part of the CEAP project as well as watersheds in Spain, Italy and China for their effect on sediment delivered from sheet and rill erosion, as well as from ephemeral gully erosion. The overall impact of the accomplishments is that important technology and research has been developed for action agencies, such as USDA-Natural Resources Conservation Service, to evaluate the effect of agricultural conservation practices at field or watershed scales and implement cost effective conservation programs targeted to the most appropriate sources of sediment.