The Competing Needs of Development and Resources in the Karst Terrain of the Lehigh Valley, Eastern Pennsylvania

摘要

A large percentage of the Great Valley (locally the Lehigh Valley) is underlain by thick sequences of deformed Cambro-Ordovician age carbonate bedrock that is a valuable mineral resource. The weathering of these rocks along bedding discontinuities under temperate climatic conditions over long periods of geologic time has produced a karst surface that is generally hidden from view by a variable thickness of glacial and alluvial/colluvial sediments. Karst subsidence features such as sinkholes and surface depressions have propagated up through these sediments, but more often than naught; the land surface can leave very few clues to the casual observer of processes that may be occurring at depth. The dissolution of carbonate bedrock has resulted in a natural plumbing system of pipes and drains that directly affects the distribution of surface and ground waters. Variations in water volume coincident with seasonal fluctuations in precipitation or by the alteration of drainage patterns through changes in land use can ultimately affect the rate at which sinkholes occur or generate problems of ground-water contamination and localized flooding. The close proximity of the Lehigh Valley with respect to the New York and Philadelphia metropolitan areas is a major factor in the attraction of people and businesses. Population, households, and employment are all projected to increase by approximately 8% over the next 25 years (Lehigh Valley Planning Commission). On a par with an increase in land development is an increase in utility and transportation infrastructure and increasing demands on water and mineral resources. Cultural migration can become problematic in karst areas. Oftentimes the application of standard land development practices, developed in non-karstic regions, simply does not apply in karst areas. From the initial concept through the engineering and construction phases of a project, karst areas require special consideration, particularly in infrastruture design and storm water management. This paper will discuss the general impact of land-use change on karst terrain but will focus on a recent case in the vicinity of Stockertown Borough, Northampton County (see Petrasic, these proceedings). Its story is unique with respect to the relatively short period of time involved and the degree of significant damage to public and private property.