Ground-penetrating radar (GPR) and continuous seismic-reflection<br>profiling (CSP) on shallow rivers, lakes, and ponds are efficient and<br>economical ways of obtaining subsurface hydrologic and geologic information<br>for environmental and engineering studies. These methods are similar in<br>that they produce continuous subsurface profiles, are easy to use, and the<br>records can be straightforward to interpret. They are dissimilar in that GPR<br>cannot penetrate electrically conductive water or subsurface sediments, and<br>CSP usually cannot operate in water less than 5 ft (feet) deep.<br>GPR records collected on a lake in New Hampshire have been interpreted<br>to estimate the depth to bedrock and to evaluate the grain-size<br>characteristics of the underlying stratified drift at the lakeshore<br>boundary. In a pond in Massachusetts, CSP and GPR were used to determine<br>the depth to bedrock and the grain-size characteristics of the subbottom<br>materials in part of the pond. Water-column multiple reflections, depth and<br>conductivity of water and subsurface materials, and diffractions degraded<br>the quality of the GPR records.<br>CSP records collected in the Connecticut River near Hartford,<br>Connecticut were used to estimate the depth of till and bedrock interfaces<br>and to evaluate the grain-size characteristics of subsurface materials.<br>Interpreted CSP records also can indicate bedding planes within consolidated<br>rock units. Water-column multiple reflections and very shallow water<br>degraded the quality of the CSP records.<br>GPR and CSP methods have been used to delineate infilled scour holes<br>near bridge piers. Scour holes that have been filled with up to 8 ft of<br>loose sand have been mapped during engineering-scour studies near a bridge<br>in Connecticut.<br>Because GPR and CSP operate on different principles, the two<br>geophysical methods complement each other. Depending on the required depth<br>of penetration and the degree of resolution needed, one or both of these<br>methods can be used to acquire accurate and reliable subsurface hydrologic<br>and geologic information critical to environmental and engineering studies.


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