Location: Watershed Physical Processes Research2012 Annual Report
1a. Objectives (from AD-416):
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). Sub-Objective 1a: Develop acoustic and orthogonal geophysical methods for rapid non-invasive assessment of internal structure of earthen dams and levees in agricultural watersheds. Sub-Objective 1b: Develop an intelligent sensor based system for continuous monitoring for dam and levee structures in agricultural watersheds. Sub-Objective 1c: Develop an acoustic based method for the non-invasive rapid estimation of soil surface erodibility with and without grass cover. 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). Sub-Objective 2a: Utilize acoustic attenuation and backscatter measurements as a surrogate technique for monitoring suspended sediments. Sub-Objective 2b: Investigate the use of various passive and/or active acoustic techniques to characterize bedload transport. 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). Sub-Objective 3a: Conduct a systematic lab study of the measurements of P-wave and S-wave velocities, nonlinear acoustic parameter, and electrical resistivity as a function of density, water content, water potential, compaction, and soil textures. Sub-Objective 3b: Develop and use in-situ non-invasive acoustic/seismic techniques to characterize and visualize the properties and processes of surface and subsurface soils. Sub-Objective 3b-1: Develop a Laser Doppler Vibrometer (LDV) based, in- situ, noninvasive, acoustic/seismic surface wave technique to characterize and visualize the properties of surface and subsurface soils. Sub-Objective 3b-2: Using high frequency Multi-channel Analysis of Surface Wave (MASW) technique to characterize soil surface properties such as sealing and crusting effects. Sub-Objective 3b-3: Measuring and characterizing soil sub-surface properties with the MASW method. Applications include layer delineation, and high velocity zones (plow-pan/fragipan) localization, and compaction effects study. Sub-Objective 3b-4: Measuring and characterizing soil sub-surface hydraulic properties in terms of soil water potential, water content, and infiltration rate with the MASW method. Sub-Objective 3b-5: Develop acoustic techniques for the detection and characterization of soil pipes and preferential flow pathway in associated with internal erosion.
1b. Approach (from AD-416):
1. Developing methodology and protocols for the rapid assessment of earthen embankments using non-invasive geophysical techniques will extend the application of geophysical methods by investigating the simultaneous use of seismic and electrical resistivity tomography to detect compromised zones within earthen embankments. Design and install a remote monitoring system of geophysical and geotechnical sensors in an earth embankment dam. The goal is to design and install the first remote real time continuous monitoring system in an earthen dam. The acoustic interaction with the soil medium depends upon mechanical and hydraulic properties of the soil surface that also influence soil surface erodibility. Therefore, acoustically measured properties can be used as a proxy for estimating soil surface erodibility. The first step in testing the hypothesis of this objective is to determine the experimental configuration and optimal range of acoustic frequencies. A numerical model based on existing theories of sound interaction with soil will be used to predict the acoustic response. The parameter space for the model will be constrained based upon typical soil characteristic (porosity, shear modulus, permeability, bulk density, elasticity) for a realistic range of erodibilities. 2. A design effort to advance the state of the art in the use of ultrasonic backscatter and attenuation to measure suspended sediment flux, developing a technique to evaluate the concentration and particle sizing of fines (0.1–100 µm) suspended in water, could be achieved by using either a single frequency acoustic system utilizing attenuation from forward propagation in conjunction with back-scattered signals or utilizing backscatter from multiple high (2-20 MHz) frequencies. Also, a design effort will be made to advance the state of the art in the use of kinetic energy impact plates instrumented with geophones or accelerometers to monitor bedload movement of gravel or sand. Under a parallel research effort, the NCPA has been working with the BOR to instrument a set of kinetic energy plate impact sensors to monitor bedload gravel movement as part of the Elwha River dam removal in the Olympic National Park in Washington State. The effort provides an opportunity to expand the state of the art for monitoring gravel bedload movement across other watersheds that are of interest to the USDA. 3. A seismic technique known as the multi-channel analysis of the surface wave (MASW) method has been developed at NCPA to obtain soil profile data at depths from a few centimeters to a couple of meters. A lab-scale test will be conducted. The MASW procedure consists of an acoustic/seismic excitation, a stepper motor controlled LDV for multi-points surface vibration measurement, a spectrum analysis to convert collected time-domain signals into the frequency-phase velocity domain, and an inversion process. Applying the MASW method to field soil, time/climate-related variations will be used for calculating the infiltration rate. Additional testing will consist of two parts: (1) lab tests with an acoustic transmission method and (2) field tests using MASW setup and dynamic move-out technique.
3. Progress Report:
This is the in-house project for Congressionally mandated pass-through project 6408-13000-022-02S. Highlights of the progress are listed below, but full details of the 2012 progress can be found in the Progress Report of project 6408-13000-022-02S. 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 2D and 3D numerical finite element (FE) embankment models. A quarter-scale earthen embankment dam was constructed at the USDA-ARS Hydraulic Engineering Research Unit (HERU), Stillwater, OK, research facility with known internal flaws. Compression wave (P-wave) and shear wave (S-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 MHz Digital Signal Processing (DSP) based sand system to operate at 20 MHz 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 National Center for Physical Acoustics (NCPA) 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.
1. Sensors capable of measuring moisture and temperature installed. Sensors capable of measuring moisture and temperature were installed at five locations in an earthen embankment at the USDA-ARS Research Facility in Stillwater, OK, and connected to a continuous monitoring computer. Data was collected and transmitted to Urbanflood in the Netherlands via the internet. Urbanflood scientists were able to continuously monitor changes in soil water content and soil temperature of the test embankment during its failure by internal erosion.
2. Field study detects presence of fragipan. A field study was conducted which showed the capability of detecting the presence of fragipan in a 2D soil profile image with the Laser Doppler Vibrometer Multichannel Analysis of Surface Waves (LDV-MASW) system.
3. Hydrophone array tested. A portable four channel hydrophone array to listen to the sounds of gravel collisions at a distance in rivers and streams was assembled and flume tested. This system was used in the field on an allied project on the Trinity River in California. Preliminary data suggests that the sound levels from gravel collisions increased as the peak flow condition was reached.