Missouri is a state with rich karst terrain. Geotechnical evaluation of foundation design for bridges and dams requires an understanding of the characteristics of subsurface geological environment, including sediments, bedrock and benthic habitat. It is crucial that the community empowers itself with the knowledge of the karst system's characteristics in order to potentially use it as a source of water and drainage, but also to avoid the disaster of building constructions too close to vulnerable land on top of massive karst caverns. Electrical resistivity tomography profiling (underwater cables), and continuous resistivity profiling (towed cable) surveys were conducted to characterize the lake sediments (rock and soil) beneath the man-made Little Prairie Lake, in Central of Missouri State, United States. Electrical resistivity (with marine cables and towed cable) was used to determine variability in the lithology and thickness of sediments (soil and rock) beneath the lake with conjunction of echo sounder in order to calculate water depth. Side scan sonar was used to map the variations in the lithology/nature of exposed lakebed sediments and to locate the potential hazard of trees. On land, electrical resistivity tomography was used with multi-channel analysis of surface wave method to determine sediments, joints, and the depth of bedrock. Analyses of the acquired data revealed the location and orientation of the original stream channels (prior to the construction of the earth fill dam). Underwater electrical resistivity tomography and continuous resistivity profiling determined joints, sediments, and bedrock underneath water bodies. Integrated marine geophysical tools help to evaluate the subsurface prior to any construction project (dam or bridge), are useful in determining the characteristics of lithology (fractured rock, intact rock and soil), and make it possible to map benthic habitat and the submerged potential hazards of trees on the lakebed as well as accurately measuring water depth.
Side scan sonar, sub bottom profiling and electrical resistivity tomography (marine cables) were used to characterize the lake sediments (rock and soil) beneath the manmade Little Prairie Lake, central Missouri. Sub bottom profiling and electrical resistivity tomography (with marine cables) were used to determine variability in the lithology and thickness of sediments (soil and rock) beneath the lake, while side scan sonar was used to map the variations in the lithology/nature of exposed lake bed sediments.Analyses of the acquired data revealed the location and orientation of the original stream channel (prior to the construction of the earth fill dam). The side scan sonar was also used to map variations in the biomass at the bottom of the lake. AbstractSurvey efforts in complex areas present a challenge. This talk will explain the collection, processing and presentation of point cloud data collected underwater with multibeam sonar systems (RESON 7125 and BlueView 5000), as well as 3-D laser scanner collected above the water. Example data from mapping and inspections of dams, pipeline crossings, and cable routes will be presented in the form of integrated point clouds, digital terrain models (DTM), charts, solid models and movies. AbstractOver the past two years, the Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) has imaged the subsurface at five CZO's: Calhoun, Boulder Creek, Eel River, Reynolds Creek, and Southern Sierra. Techniques applied include seismic refraction, electrical resistivity, downhole logging, ground-penetrating radar, magnetic gradiometry, EMI, and surface NMR. We will present results from these sites that demonstrate the following: (1) The base of the Critical Zone may be defined as the depth to which fractures remain open (thus allowing pathways for meteoric water), and this depth is likely controlled by the near-surface stress distribution.(2) In areas characterized by regional compressive stresses, intact bedrock shows an inverted topography relative to surface topography, with bedrock "ridges" under stream valleys.(3) Seismic refraction velocities provide information on weathering zone thickness and can be inverted for estimates of bulk porosity that match measured porosities from coring. (4) Geophysical imaging provides a way to map the top of fractured bedrock (base of weathering) across landscapes. (5) Snow GPR data can provide estimates of snow-water equivalent over large mountain watersheds.
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