For the purpose of this subchapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
CAVE DRIPLINE. The beginning of a cave, defined as a line on the ground at a cave entrance, formed by drips from the rock above at the outermost point of the entrance’s overhang.
CLOSED DEPRESSION. A karst geologic feature; a distinct bowl-shaped depression in the land surface; size and amplitude are variable; drainage is internal. Naturally occurring closed surface depressions found within karst landscapes are called SINKHOLES (see below).
GEOLOGIC FORMATION. The basic or fundamental rock stratigraphic unit in the local classification of rocks, consisting of a body of rock (usually a sedimentary stratum or strata but also igneous or metamorphic), generally characterized by some degree of internal lithologic homogeneity or distinctive lithologic features (such as chemical composition, structures, textures, gross aspect of fossils, or time of deposition); typically used for mapping the geology of an area.
GEOLOGIC MEMBER. A rock stratigraphic unit which is subordinate (a subject) of a formation; this unit is not necessarily mappable and is usually a unified subdivision of local extent that may or may not be contained in more than one formation.
GROUNDWATER DRAINAGE BASIN. An area of the landscape that drains through the subsurface to a spring or other component of a karst drainage system such as a cave stream of karst window. This term is analogous to CATCHMENT for surface drainage systems, in which case it denotes an area of the landscape that drains to a river confluence or other point in a surface drainage system. In contrast to surface CATCHMENTS, karst GROUNDWATER DRAINAGE BASINS generally cannot be determined by topographic maps, and thus must be delineated by other methods, primarily dye tracing.
EPHEMERAL LAKE. A body of standing water occurring in a sinkhole of a karst region that is usually visible after sufficient precipitation has occurred. They may form from slow permeability of soils, rises in the water table, or the development of a natural liner of slow permeable clays or soils.
KARST. A terrain, generally underlain by limestone or dolomite, in which the topography is chiefly formed by the dissolving of rock and which may be characterized by sinkholes, sinking streams, subterranean drainage, and caves.
KARST FEATURE BUFFER. A buffer area around a sinkhole collapse feature, the extent of which is established in the field by a licensed geotechnical engineer. The purpose of the BUFFER is to minimize the exposure of impervious surfaces such as structures to sinkhole subsidence.
KARST GEOLOGIC FEATURES. Geologic features that develop on karst terrain. Examples of KARST GEOLOGIC FEATURES are sinkholes, caves, sinking streams, and karst springs.
KARST SPRING. The discharge points for underground streams.
KARST SURVEY. A survey of property located within karst prone areas of the county, as depicted on the karst prone areas map. The survey of a property within this area is required prior to development review.
SINKHOLE. Any closed depression in soil or bedrock formed by the erosion and transport of earth material from below the land surface, which is circumscribed by a closed topographic contour and drains to the subsurface. The SINKHOLE boundary is described as an area bounded by a projected line demarcating a change in slope from toward the center of the sinkhole to away from the sinkhole which represents a local drainage divide. Precipitation falling on the surface sloping toward the sinkhole is likely to run into the sinkhole throat or infiltrate the soil and move through subsoil conduits to the throat. This includes areas which contribute surface water to a SINKHOLE via streams.
SINKHOLE COLLAPSE FEATURE. Sometimes called COVER COLLAPSE SINKHOLE, a relatively steep-side, “throat-like” sinkhole typically within a larger sinkhole and typically with rock or soil walls formed by the erosion and transport of earth materials into the subsurface in a manner such that the expression of this transport has propagated to the surface.
SINKHOLE WATERSHED. An area bounded by a projected line demarcating a change in slope from toward the center of the sinkhole to away from the sinkhole which represents a local drainage divide. Precipitation failing on the surface sloping toward the sinkhole is likely to run into the sinkhole throat or infiltrate the soil and move through subsoil conduits to the throat. This includes areas which contribute surface water to a sinkhole via streams.
SINKING STREAM SINKPOINT. The location where a surface stream disappears into the subsurface karst aquifer, either at a discrete point such as a cave entrance, or gradually along the reach of a stream channel.
STRATIGRAPHIC UNIT. A stratum or body of strata recognized as a unit in the classification of the rocks of the earth’s crust with respect to any specific rock character, property, attribute, or for purposes such as description, mapping, and correlation.
(LDC § 4.9)