Geologic System Approach to Assessment of Continental Shelf Sand Deposits

Abstract

ABSTRACT Public works projects for beach repair and hurricane protection are important issues in several U.S. Atlantic and Gulf coastal areas. However, the need remains to identify suitable sources of sand for possible use in public works projects. The continental shelf contains sand resources that could be used to support such projects. The Department of the Interior (DOI), Minerals Management Service (MMS) provides guidance for development of the sand resources located on the Federal portion of the continental shelf or the Outer Continental Shelf (OCS), generally extending 3 nautical miles and farther offshore. Through MMS cooperative studies with several coastal states, continental shelf sand deposits are identified and evaluated and the indigenous geologic environments are assessed. Results of the analyses are used to determine the potential of the resources as sources of sand for public works projects. The MMS/State cooperative programs use a geologic system concept as a framework for the studies and to determine the suitability of deposits for development. This paper discusses the basis and applicability of the geologic system concept to assessment of the sand resources located on the Federal portion of the continental shelf. The cooperative programs with State of Alabama and the Commonwealth of Virginia are presented as models for using this approach to assessments of continental shelf sand resources. Furthermore, the geologic system approach to resource assessment is presented as in philosophical agreement with the U.S. Army Corps of Engineers (USACE) to regional sediment management approach as applied to the U.S. coasts and river systems. INTRODUCTION Urban development along the U.S. Atlantic and Gulf coasts has increased interest in public works projects designed for beach repair and hurricane protection. Simultaneously, abundant onshore sources of sand suitable for such projects have become scarce due to deposit depletion, competing end uses, and urban development. Onshore and shoreface zone (< 30 foot water depth) sand deposits are generally found to be less satisfactory than more offshore nearshore zone (> 30 foot water depth) sand deposits for use in beach-related public works projects. The basis for this generality reason is routed in several factors related to the petrology of the deposits, the modern geologic environment, and often the engineering methods used for development. In preparation to meet future demand for beach quality sand, MMS and several States along the Atlantic and Gulf coasts are joined in cooperative programs to assess the potential of sand deposits located on the OCS. The water depths of the OCS portion of the continental shelf generally correspond with nearshore zone water depths, although many continental shelf areas within state boundaries are in water depths in excess of 30 feet and thus are also classified nearshore zone. Deposits located on the continental shelf are known to generally consist of sediment with properties such as, grain size and sorting similar to adjacent coastal sediments. In general, the petrologic properties of the nearshore deposit sands satisfy geologic and coastal engineering design specifications required for public works along adjacent coasts within the region.