The Offshore Sand Resources Study
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The first objective of the Offshore Sand Resources study was to locate sand deposits in federal waters off the Maryland coast. Our search for sand resources was based on the Quaternary stratigraphic model of Maryland's inner continental shelf, developed by Toscano and others (1989). The model suggests that significant quantities of sand suitable for beach nourishment would be found in surficial Holocene deposits. Sand is found in a variety of Holocene features on the inner continental shelf. Sheet sands are common off the Delmarva coast. These deposits are highly variable in thickness, areal extent and grain size. Such characteristics can make sheets sands difficult to dredge. Sand may also be found as fill in paleochannels. The channels were formed by rivers and inlets, and have subsequently filled with sediment. However, channels are limited in size, and are usually buried under a significant thickness of overlying sediment. Like sheet sands, these qualities make channel deposits difficult to dredge.
Linear sand ridges are common on the Maryland shelf. The ridges, or shoals, often contain large quantities of sand, and are located in relatively shallow water. More than twenty shoals can be found within 24 km of the Maryland coast. These factors make shoals a potentially valuable source of sand. Linear sand ridges share several common features. Duane and others (1972) characterized these features:
- ) Linear shoal fields occur in clusters, or fields, from Long Island, New York to Florida.
- ) Shoals exhibit relief up to 30 ft, side slopes of a few degrees, and extend for tens of miles.
- ) The long axes of linear shoals trend to the northeast and form an angle of less than 35 degrees with the shoreline.
- ) Shoals may be shoreface-attached, or detached. Shoreface-attached shoals may be associated with existing barrier island inlets.
- ) Shoal sediments are markedly different from underlying sediments. Shoals are composed of sands and generally overlay fine, occasionally peaty, sediments.
The linear sand ridges observed on the Maryland shelf have developed in surficial, late Holocene deposits. These sand bodies are thought to have been formed as sea level rose at the end of the last ice age. Based on the Toscano stratigraphic model, Kerhin (1989) concluded that significant sand resources on Maryland's inner continental shelf would be confined to linear sand ridges. From this conclusion, we limited our search for offshore sand to the shoal fields east of Fenwick and Assateague Islands.