EARLY DEVELOPMENT OF KARST SYSTEMS .2. TURBULENT-FLOW

A simulation model developed to explore patterns of fracture enlargeme nt within incipient limestone karst aquifers has been extended to turb ulent flow. In contrast to the highly selective passage enlargement th at occurs early in cave network development under laminar flow, the tr ansition to turbulent flow results in more general passage enlargement , leading to maze networks when initial fractures are large and hydrau lic gradients are high. These results support previously published hyp otheses for the development of maze patterns, including formation with in structural settings that have created initially large fractures or within flow systems periodically inundated by flooding. Maze developme nt is also favored under turbulent flow when passages are entirely wat er filled, and where the groundwater flow system is long-lived. By con trast, branched patterns are most common when passages become free-sur face subterranean streams, because depression of the piezometric surfa ce along main passages, downcutting along main passages, and possible infilling with sediment of side passages limit the sharing of discharg e among interconnected fractures or bedding planes that promote maze d evelopment.