QUANTITATIVE ESTIMATE OF SAND AND GRAVEL RESOURCES ABOVE THE WATERTABLE IN SOUTHERN NEW HAMPSHIRE

Good quality sand and gravel are needed for a variety of construction purposes. Because sand and gravel operations have both economic and environmental consequences and are often considered undesirable in or near urban areas, information on the location of sand and gravel resources are of increasing interest in New Hampshire and elsewhere. Because many of the sand and gravel deposits are important groundwater aquifers, knowledge about the watertable is also important. Ready availability of good quality digital elevation data and reasonably detailed data on land use have made it feasible to apply GIS analysis techniques to quantitatively estimate sand and gravel resources above the watertable in southern New Hampshire. Information on the elevation of the watertable obtained from water well and stream data allow calculations of the elevation of the surface of the watertable over large areas. The grid of watertable elevation is subtracted from the grid of digital elevation to calculate the amount of material above the watertable. Grids of areas of sand and gravel from a geologic map and of land use were used to define areas of sand and gravel that occur on land identified as forested or agricultural. The resulting grid of sand and gravel thickness above the watertable was used to calculate volumes of sand and gravel within counties in the study area and a map showing locations where significant volumes of sand and gravel resources may be present.