Location: Watershed Physical Processes Research
2024 Annual Report
Objectives
1. Develop and implement acoustic based methods for measurement and interpretation of sediment transport in streams.
1.A. Develop novel methods for data analysis and visualization to aid interpretation of acoustic sedimentation data while continuing to develop sediment transport measurement technologies.
1.B. Engage in CEAP/LTAR research by implementing existing acoustic sediment monitoring technology in CEAP/LTAR watershed.
2. Develop and adapt acoustic and geophysical methods for characterizing soils and monitoring processes within the agricultural watershed.
2.A. Develop an acoustic based soil water status assessment tool for improving water management and irrigation and rain fed decision support systems.
2.B. Develop rapid and noninvasive agrogeophysical methods for mapping and monitoring erosional processes (e.g., soil pipes in relation to gully erosion) in agricultural landscapes.
2.C. Application of geophysical measurements for estimating groundwater flow, aquifer parameters, and aquifer thickness.
2.D. Development of relationships between soil properties and geophysical attributes using machine learning.
Approach
Development of acoustic and geophysics technology addressing gaps in the USDA's suite of tools to map and monitor hydraulic processes over a range of time and space scales will consist of: theoretical and modeling efforts, controlled laboratory experiments, and field measurements using the newly developed hardware and techniques. Theoretical and modeling efforts establish the feasibility and sensitive of acoustic attributes to soil processes and sediment transport. Laboratory measurements help to better understand the physics of soils and its interaction with water and determine optimal sensor configurations, data quality requirements, and data processing schemes. Field measurements provide the final proof of concept design and incorporation into USDA applications. The first objective relates to the development of novel methods for data analysis and visualization to aid interpretation of acoustic sedimentation data while continuing to develop sediment transport measurement technologies. The second objective relates to acoustic and geophysical methods that can monitor and evaluate the performance of agricultural irrigation, drainage, and rain-fed systems, improve technology for studying soil pipe development, and to assess suitable sites and monitor the efficacy of surface water to groundwater interaction. Both parties are actively engaged in independent research projects related to the development and use of acoustic/ seismic technology for water resources applications. The parties agree that meeting the objectives of this project will expand the suite of tools, technology, and sensors for acquiring data to support science-based decision support systems.
Progress Report
Laboratory experiments were conducted at the National Center for Physical Acoustics to isolate the effect of algal concentration on the Single Frequency Acoustic Attenuation System since acoustic observations at the University of Mississippi Biological Field Station limno-corrals and the Rio Grande deployment in San Acacia, New Mexico, had regular daily variations in acoustic signals. Analysis of the acoustic data alongside the available ancillary data indicated multiple parameters that may influence the acoustic signal, primarily light intensity, temperature, and dissolved oxygen. Algae populations were measured in a 10-gallon fish tank with a dissolved oxygen sensor, thermometer, and the Single Frequency Acoustic Attenuation System. Aquarium lights on timers simulated the daily solar clock, and heaters were used to regulate water temperature. A growth medium was added to the tanks to encourage algal growth. Physical samples were extracted and placed in a Turner Designs Trilogy Laboratory Fluorometer to measure the relative fluorescence units in relation to the co-located acoustic signals. From these laboratory tests, it was determined that neither light intensity nor dissolved oxygen has an independent influence on the acoustic signal. No conclusion can be made regarding the effect of algae on the acoustic signal, and our current work has raised questions about other experiments to try. A correction is still needed to account for the change in acoustic signal. For this reason, researchers have requested to change the future milestones for Objective 1A to provide revised and expanded laboratory algae experiments that are needed for interpretation of the acoustic data.
A site was selected at Goodwin Creek Station 2 to deploy the Single Frequency Acoustic Attenuation System. This site is instrumented with numerous measurement systems and will provide more parameters to compare with the acoustic signal. Following instrument maintenance and laboratory calibration, the Single Frequency Acoustic Attenuation System was also returned to Goodwin Creek Station 1. During Fiscal Year 2024, the two systems have collected acoustic data over six high-flow events spanning approximately nine days, which has been a dry year to date. Researchers are awaiting the 2024 data from the physical samples collected by partners at the National Sedimentation Laboratory in Oxford, Mississippi. The raw acoustic data has been processed, timestamped, and uploaded to a database so that it can be compared to parameters such as flow discharge, stage height, and measured sediment concentration. While additional ancillary data is needed before a conference presentation can take place, a publication is still planned before the end of the performance period.
During this reporting year, several improvements were made to the mobile/portable high-frequency multichannel analysis of surface wave prototype’s hardware system, including improved de-coupling of vibration between the geophones and their supporting frame, improved geophone insertion method, and improved protection of the geophones. Several improvements in signal processing and data analysis algorithms were also made with smart LabView-software-based algorithms/computer codes to compensate for drastic soil condition changes automatically. The measurement system is automated, and repeat measurements can be taken at a predefined time interval to capture the instantaneous soil responses to irrigation and rainfall. The system can measure soil profiles up to 2 meters below the surface.
The improved system was used to measure instantaneous variations of soil profiles during irrigation and rainfall on the University of Mississippi campus. Three sprinklers were installed at the site for controlled irrigation. The measurements were conducted continuously before, during, and after irrigation under different initial soil conditions. The obtained temporal variations of the shear wave velocity profiles were used to assess the initial soil conditions and ongoing soil responses to irrigation and drainage processes. The study demonstrated that the method can capture the temporal variations of the soil profile in response to irrigation procedures.
A systematic comparison between the results of the improved mobile system and field-measured moisture content variations at different depths during irrigation and rainfall during different seasons and soil conditions was not completed due to a moisture meter probe malfunction. However, a new moisture probe has been purchased and installed, and irrigation and rain-fed studies are ongoing. A database of the high-frequency multichannel analysis of surface wave test results of irrigation and rainfall and moisture probe data is being established.
An electromagnetic induction survey using a GeonicsTM EM31 was conducted on a large area at Goodwin Creek survey site, a site that has documented soil pipe collapse features. Previous studies at Goodwin Creek have shown that soil pipe-affected zones are located within low apparent electrical conductivity zones. Results from the EM31 survey indicated that sections of the field with low apparent electrical resistivity could be susceptible to soil pipe formations. A section of the larger area covered by EM31 with low apparent electrical conductivity was selected, and high-resolution ground penetrating radar surveys with 500 megahertz and 200 megahertz antennas were conducted. In addition, high-resolution 3-dimensional electrical resistivity measurements were conducted between two gully windows at Goodwin Creek. These surveys were conducted to identify the attributes of well-established soil pipes on 3-dimensional electrical resistivity tomographs. High resistivity anomalies on the 3-dimensional tomograms indicated the pathway of the soil pipe between the known collapse features. This result shows that high-resolution surface-based geophysical methods can successfully map the pathways of internal soil pipes. A plan is underway to incorporate topographic information from drone elevation data or publicly available digital elevation data to generate improved internal soil pipe zoning maps.
A study was conducted at Goodwin Creek Experimental Watershed in Panola County, Mississippi, where two surface-based geophysical methods, electrical resistivity tomography, and electromagnetic induction, were used for subsurface characterization and delineation of aquifers. A 501-meter-long electrical resistivity tomography survey at 3-meter electrode spacing was conducted to characterize the subsurface heterogeneity and delineate the depth and thickness of the aquifer. An electromagnetic induction survey was conducted using a GeonicsTM EM31 instrument over a larger area to provide greater spatial coverage of the site.
A comparison of electrical resistivity tomography and electromagnetic induction results showed consistent results where high resistivity values on the electrical resistivity tomography were indicated with low conductivity on the electromagnetic induction map. The electrical resistivity tomography result showed that the aquifer is relatively thin (<10 meters) near the creek and thick (>30 meters) under the pasture. The depth to the top of the aquifer is variable, outcropping or thinly confined over a short distance (<10 meters) in the pasture but confined on both sides of the outcrop. Grain size analysis on soil samples collected at the outcrop location indicated sand soil, consistent with the high resistivity values on the electrical resistivity tomography and electromagnetic induction results. Soil samples collected away from the outcrop consisted of clayey soil consistent with low electrical resistivity values from the electrical resistivity tomography and electromagnetic induction results.
Results from this study showed the advantages and capabilities of surface-based geophysical methods to delineate aquifers and identify optimal well locations. These methods would improve groundwater management and minimize well failures due to poor placement.
Apparent electrical conductivity data was collected using a GeonicsTM EM38 at Beasley Farm, a 186-acre farm in Sunflower County, Mississippi. The data covered a larger area than what was covered by a 2022 Veris apparent electrical conductivity survey conducted by the United States Department of Agriculture. The 2022 Veris data was collected using a configuration with a depth response of 60 centimeters. The EM38 data was collected in a horizontal dipole configuration with a depth response of 0.75 meters.
Correlation analysis of apparent electrical conductivity and soil properties was conducted using clay and water content data from a 2022 United States Department of Agriculture soil physical properties measurement conducted at the farm. The analysis showed that apparent electrical conductivity measurements from EM38 and Veris showed good correlations with measured clay content (R2 = 0.49). However, the correlation between apparent electrical conductivity and water content was low (R2 < 0.3). Multiple regression analysis using apparent electrical conductivity and trend surface components most accurately estimated clay content (R2 = 0.55, r = 0.82).
For areas of Beasley farm where soil property data was unavailable, a clay content map was generated using the multiple regression analysis correlation obtained using EM38 apparent electrical conductivity and coordinate location data. The map showed soil texture variability with pockets of high and low clay content areas. By establishing strong correlations between soil properties from field samples and geophysical measurements, maps with better-detailed field variability can be generated for improved soil and crop management decisions.
Accomplishments
1. Determination of the effects of light intensity and dissolved oxygen on the Single Frequency Acoustic Attenuation System. The goal of this project is to create a system that provides an accurate estimate of suspended sediment transport with high temporal resolution. While suspended sediment is typically the dominant factor in the Single Frequency Acoustic Attenuation System’s estimate, there are other parameters that can have secondary effects on the acoustic signal. To address these effects and further improve the sediment concentration measurements, ARS researchers at Oxford, Mississippi, designed and conducted laboratory experiments in clear still water to control these variables and better understand the correlation to acoustic signals. From these experiments, researchers determined experimentally that light intensity and dissolved oxygen do not directly impact acoustic signals, which infers a likely correlation between algal bioactivity and acoustic signals by process of elimination. Once a correction can be made for algal bioactivity, this improved estimation will allow stakeholders such as researchers, scientists, and government agencies to accurately assess the concentration of fine suspended sediments.
2. Multiple station deployment of Single Frequency Acoustic Attenuation System at Goodwin Creek for long-term operation. Monitoring the suspended sediment transported in rivers and streams can be difficult and expensive, resulting in very temporally coarse measurements. The Single Frequency Acoustic Attenuation System collects near-continuous acoustic data that can be used to estimate the concentration of suspended sediment. While the continued deployment of this system provides data to help improve the predictive capabilities, the second deployment of an acoustic surrogate in the watershed allows ARS researchers at Oxford, Mississippi, an opportunity to form potential relationships and investigate hydraulic trends between both stations in the watershed. The high temporal resolution of these deployments has provided data that indicates significant sediment transport that the pump sampler underrepresented because of longer times between each measurement. This improved estimation allows stakeholders such as researchers, scientists, and government agencies to accurately assess concentrations of fine sediments in stream channels.
3. An improved portable soil profiler for near-surface soil exploration. In agricultural applications and farmland soil management, it is important to have a non-invasive tool to measure the soil’s mechanical and hydrological properties and map/monitor its temporal and spatial variations. To achieve this goal, an acoustic surface wave technique, the high-frequency multichannel analysis of surface wave method, has been developed by ARS researchers at Oxford, Mississippi, to noninvasively measure soil profiles using the shear wave velocity as a function of depth, up to 2 meters below the surface. This technique was significantly improved by building a portable device that can be employed in the field for rapid surveys. Improvements in the system include improved de-coupling between geophones and the supporting frame, improved geophone insertion method, better protection of the geophones, and enhanced signal processing/data analysis algorithm. This technique can be applied to many agricultural applications, including determining near-surface soil profiling, studying weather and seasonal effects, monitoring rainfall events, detecting fragipan layers, studying surface sealing/crusting, implementing farmland compaction studies, and evaluating irrigation performance. The potential users could be soil scientists, farmers, environment/civil engineering researchers, and military personnel.
4. Mapping internal soil pipe susceptibility using geophysical methods. Identifying the network of soil pipes in agricultural fields is challenging but essential to estimating their contribution to total fertile soil loss. One challenge is that soil pipe formations occur in the subsurface and are often covered by crops and vegetation, making remote sensing and photogrammetric detection difficult. Geophysical methods such as electromagnetic induction and ground penetrating radar provide a means to non-invasively map agricultural fields' internal structures. These methods can quickly generate soil pipe susceptibility maps of vast agricultural fields. In this study ARS researchers at Oxford, Mississippi, showed the application of an electromagnetic induction survey to identify locations susceptible to soil pipe formation. Ground penetrating radar survey is used for high-resolution mapping of the subsurface. In addition, a three-dimensional electrical resistivity survey is conducted to visualize the pathway of soil pipes. The results from this study will aid farmers and landowners in making informed and timely decisions to mitigate soil loss from soil pipe formations.
5. Groundwater aquifer characterization using geophysical methods. Excessive groundwater extraction for agricultural and industrial use threatens future water availability worldwide. Complex hydrogeological formations and high spatial variability due to various geological processes make groundwater exploration challenging. These challenges increase the need to improve the characterization of subsurface heterogeneity and identify optimal locations and approaches for the placement of groundwater extraction and monitoring wells. In this study ARS researchers at Oxford, Mississippi, showed the successful application of ground-based, non-invasive geophysical methods for identifying and characterizing an aquifer’s thickness and extraction depth. The approaches in this study can be used to identify optimal well locations for irrigational or other uses, minimizing well failures due to poor well placement. The results from this study will provide farmers, hydrologists, engineers, and state leadership with actionable information for better exploration, exploitation, and remediation of groundwater resources. A paper titled " Integrating Electrical Resistivity Tomography and Self-Potential Techniques for Enhanced Characterization of Aquifer and Investigation of Surface-Groundwater Interactions” has been accepted for publication in Groundwater.
6. Spatial soil properties mapping using rapid geophysical methods. In agricultural fields, collecting and processing soil samples provide the most accurate data on soil properties such as clay content, moisture content, nutrient level, and pH. However, they are usually collected in a coarse grid, time-consuming to process, and could miss variabilities between sampling locations. On the other hand, geophysical measurements such as electromagnetic induction (EMI) surveys can be done at a much higher sampling rate and provide high-resolution spatial maps with detailed field variability. A better understanding of the correlation between geophysical and soil properties is required to interpret geophysical results better and generate maps of soil variability. ARS researchers at Oxford, Mississippi, used results from laboratory measurements on soil samples from agricultural fields are correlated to geophysical attributes to convert geophysical maps to spatial maps of soil parameters. This study showed that the application of rapid geophysical methods and establishing strong correlations with soil properties could lead to better soil and crop management decisions for farmers and landowners through the identification of farm field variability, improved soil sampling as opposed to grid-based soil sampling and generating spatial variability maps of parameters relevant to plant growth such as clay content, soil salinity, soil texture, soil moisture.