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Using ground-penetrating radar to determine the quantity of sediment stored behind the Merrimack Village Dam, Souhegan River, New Hampshire

By
David J. Santaniello
David J. Santaniello
Department of Earth and Environmental Sciences
,
Boston College, 140 Commonwealth Avenue
,
Chestnut Hill, Massachusetts 02467
,
USA
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Noah P. Snyder
Noah P. Snyder
Department of Earth and Environmental Sciences
,
Boston College, 140 Commonwealth Avenue
,
Chestnut Hill, Massachusetts 02467
,
USA
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Allen M. Gontz
Allen M. Gontz
Department of Environmental, Earth, and Ocean Sciences, University of Massachusetts–Boston
,
100 Morrissey Boulevard, Boston, Massachusetts 02135
,
USA
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Published:
January 01, 2013

Abstract

We investigated the viability of ground-penetrating radar (GPR) as a method to estimate the quantity of sediment stored behind the Merrimack Village Dam on the Souhegan River in southern New Hampshire. If the predam riverbed can be imaged, the thickness and volume of the reservoir deposit can be calculated without sampling. Such estimates are necessary to plan sediment management after dam deconstruction. In May 2008, we surveyed six cross sections with a Mala Geosciences ProEx 100 MHz GPR. In a related study, topographic surveys were conducted in 2008–2009 to monitor the sediment flux associated with the removal of the Merrimack Village Dam in August 2008. Within a month of the removal, these surveys mapped the predam riverbed in the uppermost cross sections in the former impoundment. We compared these surveys to our interpreted GPR images for one cross section to determine a calibrated velocity for the impounded sand of 0.043 ± 0.020 m/ns. We also estimated the radar velocity of the deposit by analyzing hyperbolic reflections in the GPR images, and found a similar result (0.039 m/ns). Using the calibrated velocity, we estimated a total volume of sediment stored behind the Merrimack Village Dam of 66,900 ± 9900 m3, which compares well to a previous estimate (62,000 m3) based on a depth-to-refusal survey. Our findings indicate that GPR is a useful technique for quantifying impounded sediment prior to dam removal in reservoirs containing 1–10 m of sand overlying a coarser predam riverbed, but it may be less effective in settings with finer and/or thicker impounded sediment.

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Contents

GSA Reviews in Engineering Geology

The Challenges of Dam Removal and River Restoration

Jerome V. De Graff
Jerome V. De Graff
U.S. Department of Agriculture Forest Service Clovis, California 93611 USA
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James E. Evans
James E. Evans
Department of Geology 190 Overman Hall Bowling Green State University Bowling Green, Ohio 43403 USA
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Geological Society of America
Volume
21
ISBN electronic:
9780813758213
Publication date:
January 01, 2013

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