Quantitative Modeling of Channelized Flow Within a Karst Stream

Colorado State University, Fort Collins CO

Investigators

Abstract

0000725 Wohl Physical and chemical erosion processes are rarely considered in tandem. Physical erosion processes have received rigorous, quantitative treatment in surface channels where on-going research has begun to integrate studies of reach-scale processes with landscape evolution and morphology. Chemical erosion processes have received considerable attention in karst terrains, but have yet to be fully integrated into studies of surface channels. Combining studies of physical and chemical erosion is desirable and is most needed in terrains where both may be of equal importance. The latter include fluviokarst where streamflow processes and landscape evolution are intimately linked to fluvial and karst processes. Using techniques initially developed for surface channels, open channel flow will be examined in an internally drained fluviokarst basin, Buckeye Creek, in southern West Virginia. Closed conduit flow will be examined using a quantitative model developed expressly for this project. Quantitative modeling of surface and subsurface flood flows will provide direct insight into the mechanisms by which fluviokarst streams erode while simultaneously transporting insoluble sediment derived from resistant strata in the headwaters of the basin. The latter processes must diverge from those in typical surface streams due to intermittent closed conduit flow in the cave(s) and backflooding upstream of cave entrances and passage constrictions. Although backflooding has the effect of increasing head and possibly flow velocities within constrictions, flow velocities and shear stress must decline upstream, with the result being a relative decrease in physical erosion and sediment transport above some threshold. The manner by which constrictions and their affected reaches are coupled is of direct relevance to mixed alluvial-bedrock streams. In both cases, the manner by which reaches with relatively high and low stream powers form continuous profiles despite dramatic differences in transport processes and capabilities is unknown and will be studied by quantifying flow properties in each type of stream segement. Simultaneously, the relative roles of chemical and physical erosion in shaping reach-scale and basin-scale stream morphologies and profiles will be addressed by numerical estimation of the ability of the surface and cave streams to abrade, pluck, and quarry, by direct measurement of sediment transport rates, and by directs measurement of solute transport in the cave stream.