Location: Watershed Physical Processes Research
2020 Annual Report
Objectives
1. Develop acoustic and orthogonal geophysical methods to characterize and monitor surface and sub-surface soil properties and processes that contribute to water driven erosion and transport of soil and to assess the potential for dam and levee failures.
1.A-1. Develop seismic instrumentation and methods for characterizing subsurface soil mechanical and hydraulic properties in the vadose zone.
1.A-2. Develop a combined seismoelectric technique and high frequency-MASW (HF-MASW) method to measure subsurface soil hydraulic properties.
1.B-1. Geophysical monitoring and surveying of dams, levees and streambanks within the agricultural watershed.
1.B-2. Conduct laboratory studies to investigate the correlation between geophysical properties and the physical state of a soil.
1.B-3. Investigate wind induced ground surface vibration as a source for measuring the mechanical properties of the ground.
2. Develop and deploy acoustic measurement systems across a watershed to provide improved data collection of sediment flux for decision makers.
2.A. Interpreting the acoustic environment of natural fresh-water gravel-bed channels for use in monitoring bedload flux.
2.B. Advance the application of multiple acoustic surrogate techniques to monitor suspended sediment transport.
Approach
There is a continuing need for better methods to non-invasively measure sediment transport and soil properties in situ. Furthermore, the Nation’s aging dams need to be assessed for structural integrity. Acoustic and orthogonal geophysical techniques will be developed for measuring the mechanical response of soil to remedial measures for upland erosion, autonomous monitoring of sediment transport in streams, and imaging the internal structure of earthen dam and levees. Shear wave propagation can be used to map spatial distributions of subsurface soil mechanical and hydraulic properties, and field experiments will be used evaluate their use for detecting compaction and the extent of plow-pans. A modified shear wave acquisition system will be developed to measure temporal changes in the shear wave velocity profile to infer variations in water potential and water content. The results will be correlated with information from time domain reflectometers (TDR) buried in the test site at different depths to measure water content, a tensiometer to measure water potential, and a rain gauge to measure precipitation. In exploratory work, a laboratory study will be conducted under controlled conditions to establish a relationship between seismoelectric signals and soil hydraulic properties. We will investigate the use of wind-induced vibrations to determine mechanical properties of soil. The method does not need high-energy acoustic/seismic signals, making it suitable for remote field sites. We will perform geophysical site characterization at dams or levees showing signs of internal erosion or seepage during visual inspection. The same procedures will be applied to groundwater recharge zones and streambanks. In order to facilitate the integration of geophysical and geotechnical information, laboratory measurements of compressional and shear wave velocities and electrical resistivity will be conducted on synthetic, remolded soils and field cores. Acoustic methods can be used to improve the accuracy and effectiveness of sediment monitoring programs, but they are in need of continued development. Multiple acoustic methods will be deployed across a watershed to improve the integration of technologies and interpretation of acoustic data. The movement of coarse particles along the stream bed is particularly difficult to measure. Sound generated by coarse particle movement in streams will be used to improve the measurement of bed load transport. The focus will be on separating the sound made by moving particles from other sounds, such as bubbles and other extraneous environmental noise. Through collaborative efforts with soil scientists, hydrologists, and agricultural engineers, the new measurement technology will facilitate more comprehensive studies on sources of sediment, sediment transport and deposition in streams and lakes, and stability analysis of earthen dams and stream embankments.
Progress Report
Progress was made on the two objectives and their subobjectives, all of which fall under National Program 211 (Water Availability and Watershed Management), Component 2 (Erosion, Sedimentation and Water Quality Protection).
Progress on Objective 1A relating to the development of acoustic methods to characterize sub-surface soil properties is as follows.
A laser doppler vibrometer (LDV)-based system using a phase locking-in technique has been developed and a surface sealing/crusting test was conducted in Holly Springs, Mississippi. The results of the high frequency-multichannel analysis of surface waves (HF-MASW) method were compared with penetration and shear vane tests. The crusted soil presented high shear wave velocity (around 300 m/s) in the frequency range from 1700 Hz to 3500 Hz, whereas the non-crusted soil presented low velocity (around 150 m/s) in the frequency range from 510 Hz to 1300 Hz. The results demonstrated that the LDV-based HF-MASW method can non-invasively evaluate the surface soil properties such as surface sealing/crusting.
A simultaneous multi-channel data acquisition system for HF-MASW tests has been built that consists of a geophone array to simultaneously measure surface vibrations, from an electrodynamic seismic source. This system is monitoring the instantaneous responses of soil profiles to rain events. The obtained soil profile image reveals the temporal variations of soil profiles before, during, and after rainfall events. In 2020, the summer data will be collected and analyzed.
A laboratory measurement system that combines the HF-MASW method and the seismo-electric technique is under construction to explore soil profiles under controlled hydraulic conditions. The system includes a LDV vibration detector and an electrode array placed on the soil surface to record electrical signals induced by seismic waves. The measurement system is still under construction due to some technical difficulties. It is expected that at the end of September, preliminary data will be collected and analyzed.
Progress on Objective 1B relating to the development and application of geophysical methods to assess the potential for dam and levee failures is as follows.
A study on the application of geophysical mapping of internal soil pipes was conducted at Goodwin Creek Experimental Watershed located in Panola County, Mississippi. The study site, currently used as a pasture field, is substantially affected with gully erosion. Ground penetrating radar (GPR) and electromagnetic induction (EMI) surveys were conducted perpendicular to soil pipes connecting gully windows. Results from the study showed that diffractions from GPR measurements are effective indicators of soil pipes whereas; the EM38 can provide zoning of soils with varying degrees of soil pipe susceptibility.
Establishing a connection between geophysical and traditional soil properties are necessary in order to utilize geophysical information. Electrical resistivity and seismic wave velocity as well as various geotechnical parameters were measured in the laboratory on the same proctor compacted soil samples. An artificial neural network (ANN) model was developed to predict geotechnical parameters from electrical resistivity and seismic wave velocity.
Determining soil profiles based on its mechanical properties requires a source of mechanical (seismic) excitation. Our research is focused on wind-induced ground vibrations. In a literature search on the coupling of wind generated pressure fluctuations into seismic noise, it was noticed that the expression for the angular tilt induced by pressure fluctuations in the seminal paper by Sorrells was only valid at the surface. We developed the correct expression for effective measured displacements and an approximate expression analogous to those of Sorrells. A paper has been submitted to Journal of Geophysical Research: Solid Earth.
As we explore the use of wind generated ground vibrations for soil characterization, our field measurements do not agree with theoretical predictions. We have constructed an apparatus consisting of twelve microphones to measure the correlation length of the wind pressure both in the direct and cross-line to the prominent wind direction. This correlation length will be compared with the correlation length of the wind velocity measured using a sonic anemometer located 2m above the surface.
Another experiment has been designed using 16 -3C geophones. These geophones will be buried flush with the surface of the ground in a linear array. The data will be used to study the correlation of wind induced seismic signals, to confirm previous seismic measurements of horizontal and vertical components of the velocity field, and to provide information for comparison to the dynamic cone penetrometer test (DCPT).
Progress on Objective 2A relating to measurement methods for monitoring sediment flux is as follows.
The noise due to flowing water around the hydrophone must be addressed. Experiments in flumes and in rivers have shown that the noise can be reduced by placing the hydrophones in low-flow areas or by allowing the hydrophone to move with the water. Laboratory experiments have shown that rudimentary attempts to streamline the hydrophone do not reduce the flow noise sufficiently. Allowing the hydrophone to move with the water presents logistical challenges and is labor-intensive. There is no single analysis technique that addresses all of the problems of flow noise and impact identification, making collection of raw acoustic data necessary. This means that a long-term deployable system would need to record at a rate of at least 50 kHz, which will generate a large amount of data that must be stored in a large hard drive or uploaded to an online server. In addition, it is possible that collecting data in short bursts may be necessary to decrease the data storage requirements.
Progress on Objective 2B relating to surrogate techniques to monitor suspended sediment transport is as follows.
Subsequent acoustic data sets from the San Acacia, New Mexico site were analyzed to test the correlation between the attenuated signal and the suspended sediment concentration < 62 microns. The peer reviewed Bureau of Reclamation report titled “Field Deployment of a Continuous Suspended Sediment Load Surrogate” indicated that the acoustic signal has a relationship with U.S. Geological Survey (USGS) physical samples as well as other diurnal variables (i.e. water temperature). A long-term deployment of a multi-frequency acoustic surrogate device was deployed in the Goodwin Creek Watershed, Mississippi in conjunction with USDA Agricultural Research Service National Sedimentation Laboratory.
Hydraulic data analysis will be conducted using the multi-frequency acoustic surrogate device in the Goodwin Creek Watershed, Mississippi, in conjunction with USDA. Acoustic fit will also incorporate a relationship between acoustic signals and physical samples once a sample analysis has been completed by USDA. The refinement of acoustic fit is ongoing.
Accomplishments
1. The processes of raindrop impact, drying, and clogging of pores creates a mechanically hard top layer that exhibits high stiffness, mechanical strength, and a reduced infiltration rate. The existence of these soil surface seals and crusts affects both infiltration and surface runoff of rainwater as well as the mechanical strength of the soil surface and therefore influences upland soil erodibility. The University of Mississippi, in collaboration with ARS researchers in Oxford, Mississippi, and Pontotoc Ridge-Flatwoods Branch Experiment Station, Mississippi State University, Pontotoc, Mississippi, have developed an acoustic method to evaluate soil surface sealing/crusting layers. The basis of the method is that these surface layers, having high stiffness and mechanical strength, will also have high acoustic velocity. This method records vibrations at various distances from a vibration source (small mechanical shaker) using a non-contact optical vibration sensor, a laser Doppler vibrometer (LDV), in order to not disturb these thin layers. The instrumentation can produce higher frequencies with appropriate vertical resolution, and results are presented as soil profiles in terms of soil stiffness. The sealed/crusted top layer presents a significant increase in the acoustic velocity as compared with that of a non-sealed/crusted soil. This effort provides agricultural engineers and soil scientists with a non-destructive field tool for surface sealing/crusting assessment that will be helpful for assessing soil erodibility.
2. The measurement of sediment transported on and near the bed of streams and rivers is an important need for river management, particularly when dams are removed. The measurement of sediment transported on and near the bed of streams and rivers is an important need for river management, particularly when dams are removed, which creates a need for measuring the release of stored coarse sediments. The collection of bed load samples is very difficult and expensive, making the continued development of instrumentation necessary. ARS researchers in Oxford, Mississippi, are using underwater microphones to record the sounds of rocks impacting one another is a promising, low-cost method that may lead to a useful measurement technique for bed load measurement. The work described here is the detailed development, testing, calibration, and deployment of a system for recording the sound that gravel particles make when they hit each other in a stream. The only way to ensure that the data can be compared is by carefully calibrating the acoustic system to known standards. The goal of the work is to provide guidance for others who are studying the use of sound for bed load measurement so that data collected by different groups will be comparable. The U.S. Bureau of Reclamation has actively supported this work, since it aids efforts to improve the ability to monitor the movement of coarse sediments in streams.
Review Publications
Goodwiller, B.J., Wren, D.G., Surbeck, C. 2019. Development and calibration of an underwater acoustic data collection system for monitoring coardse bedload transport. Applied Acoustics. 155 (2019):383-390. https://doi.org/10.1016/j.apacoust.2019.06.019.
Kuhnle, R.A., Wren, D.G., Hilldale, R.C., Goodwiller, B.T., Carpenter, W.O. 2017. Laboratory calibration of impact plates for measuring gravel bed load size and mass. Journal of Hydraulic Engineering. 143(12), 06017023 doi:10.1061/(ASCE)HY.1943-7900.0001391.
Lu, Z., Wilson, G.V. 2017. Imaging a soil fragipan using a high-frequency multi-channel analysis of surface wave method. Journal of Applied Geophysics. 143:1-8. doi:10.1016/j.jappgeo.2017.05.011.
Lu, Z. 2017. Practical techniques for enhancing the high-frequency MASW method. Environmental and Engineering Geoscience. 2(I,2):197-202. doi:10.2113/JEEG22.2.197.
Lu, Z., Wilson, G.V., Shankle, M. 2019. Measurements of soil profiles in the vadose zone using the high-frequency surface waves method. Journal of Applied Geophysics. 169:142-153. https://doi.org/10.1016/j.jappgeo.2019.07.002.
Mohammadi, M., Hickey, C.J., Raspet, R., Naderyan, V. 2019. Wind-induced ground motion: Dynamic model and nonuniform structure for ground. Journal of Geophysical Research: Solid Earth. 124(8):8478-8490. https://doi.org/10.1029/2019JB017562.
