Location: Watershed Physical Processes Research2011 Annual Report
1a. Objectives (from AD-416)
The objective of this effort is to assess the processes associated with ephemeral gully development through the study of: ephemeral gully evolution pertaining to ephemeral gully widths and networks; soil resistance to gully erosion; and the effect of agricultural practices on gully erosion across a range of temporal and spatial scales including the influence of above and below ground biomass. These studies will lead to new or enhanced algorithms for use in ephemeral gully erosion models. Ephemeral gully erosion represents an important and often dominant sediment source within watersheds in the U.S. and worldwide that is often overlooked when evaluating the effect of conservation practices in controlling erosion.
1b. Approach (from AD-416)
Develop and execute novel experimental programs to understand the processes leading to the initial growth and development of gullies under varying hydrologic and topographic conditions. Define the key pedologic, hydrologic, and hydrodynamic parameters that control the magnitude, morphology, and rate of soil loss, gully erosion, and landscape degradation due to gully development. Develop theory and equations to predict soil loss and gully erosion on hillslopes and agricultural fields under different management practices and integrate these into USDA watershed and soil erosion models.
3. Progress Report
Flood control reservoirs designed and built by federal agencies have been extremely effective in reducing the ravages of floods nationwide. Yet some structures are being removed for a variety of reasons, while others are aging rapidly and require either rehabilitation or decommissioning. A journal paper was written to summarize collaborative research activities to assess sedimentation issues within aging flood control reservoirs and to provide guidance on such tools and technologies. Ten flood control reservoirs located in Oklahoma, Mississippi, and Wisconsin have been examined using vibracoring, stratigraphic, geochronologic, geophysical, chemical, and geochemical techniques and analyses. These techniques and analyses facilitated (1) the demarcation of the pre-reservoir sediment horizon within the deposited reservoir sediment, (2) defining the textural and stratigraphic characteristics of the sediment over time and space, (3) the accurate determination of the remaining reservoir storage capacity, (4) the quantification of sediment quality with respect to agrichemicals and environmentally-important trace elements over both time and space, and (5) the determination of geochemical conditions within the deposited sediment and the potential mobility of associated elements. Stream restoration is a general term used for the wide range of actions undertaken to improve the geomorphic and ecologic function, structure, and integrity of river corridors. While the practice of stream restoration is not new to geomorphic, ecologic, or engineering communities, the number of restoration activities and their associated costs has increased dramatically over the last few decades because of government policies intended to protect and restore water quality and aquatic species and their habitats. Because technology transfer is an important activity in scientific discourse, a book chapter was written to provide a comprehensive, integrative, and interdisciplinary synthesis of process-based approaches, tools, and techniques currently used in stream restoration, as well as their philosophical and conceptual foundations. A common goal of stream restoration projects is to limit channel migration and streambank retreat through bank stabilization practices. Bioengineering with various types and species of vegetation is a widely used technique due to its natural aesthetic and low costs, but has lacked quantification for design purposes. The need to improve design and better understand the impacts of riparian vegetation on streambank stability has prompted many research initiatives, although very few studies have focused specifically on the impacts of vegetation growth on the bank-toe, a crucial surface for streambank stability. A series of flume experiments was conducted to better understand how the flow regime and distribution of boundary stresses are impacted by bank-toe vegetation and to test the hypothesis that during high flow events, certain configurations of vegetation growth may enhance erosion potential on streambank and bank-toe surfaces. Monitoring activities included face to face meetings, phone calls, and e mail messages.