Location: Watershed Physical Processes Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1: Develop, adapt and evaluate, and integrate non-invasive geophysical methods and complementary modeling efforts, in support of a comprehensive earthen dam interrogation and monitoring program (2.4.1). Objective 2: Develop acoustic hardware and measurement techniques for non-experts to improve the monitoring of suspended and bedload sediment transport. (2.2.1, 2.2.2) Objective 3: Develop non-invasive acoustic/seismic techniques and orthogonal geophysical methods to characterize surface and sub-surface soils as well as visualize and monitor subsurface pedological features affecting erosion processes (2.1.1, 2.1.3).
1b. Approach (from AD-416):
This project concerns the development, application, and use of geo-physically based acoustic/seismic technology in agricultural watersheds in particular of how these techniques can be used in predicting bank stability, dam and levee failure, and to assess the effectiveness of remedial measures and the development of early warning systems of impending catastrophic events that threatens life and property in agricultural watersheds. Specifically, the first objective concerns the development, adaptation, and evaluation of non-invasive acoustics/seismic techniques to monitor the integrity on a momentary and continuous basis of dam and levee structures in agricultural watersheds (NP211 Action Plan, 2.4). The second objective relates to the development of hardware and techniques to detect, improve, automate the measurements of suspended and bed-load sediment movement in the stream system of agricultural watersheds (2.2). The third objective relates to the developments of techniques that allow the visualization of pedological soil profile features and characteristics that affect soil erosion on upland areas such as the presence of hardpans, and water transport limiting profile features using the non-invasive acoustic/seismic technology (2.1)
3. Progress Report:
Current geophysical techniques used in the assessment of the interior of earthen embankments include: acoustic/seismic, electro-magnetic and resistivity, gravity, optical sensing, and radar. The dependence of the seismic response on embankment soil compositions and soil water content, size and depth of the seepage zone, presence of water in the reservoir, and shape of embankment was studied via 2-dimensional and 3-dimensional numerical finite element embankment models. A quarter-scale earthen embankment dam was constructed at the USDA-ARS Hydraulic Engineering Research Unit, Stillwater, OK, research facility with known internal flaws. Primary-wave and secondary-wave seismic refraction measurements were conducted on these dams at different stages from the start of construction up to failure. Numerous standard geotechnical instrumentation measuring ground deformation and soil water content are being installed in earthen dams. In May 2012, an additional five sensors capable of measuring soil water content and temperature were installed in the dam and connected to a continuous monitoring computer. We are currently designing an experiment and associate apparatus for measuring the acoustic to seismic transfer function and erodibility of soils. New transmitter components to modify the 1 mega Hertz digital signals processor based sand system to operate at 20 mega Hertz were constructed and tested along with the existing receiver components at the new higher frequency with good results. An impact plate system that mimics those built by the Bureau of Reclamation and installed on the Elwha River was built at the University of Mississippi National Center for Physical Acoustics (NCPA) in Oxford, MS, to investigate the sounds of gravel collisions in a controlled laboratory setting. The Laser Doppler Vibrometer Multichannel Analysis of Surface Waves (LDV-MASW) system has been improved greatly in terms of sampling speed, signal to noise ratio, and accuracy by adding one reinforcement beam and improving signal processing algorithm.