HR: 0800h
AN: H31A-1275    [Abstracts]
TI: Physical modeling of transverse drainage mechanisms
AU: * Douglass, J C
EM: john.douglass@pvmail.maricopa.edu
AF: John Douglass, Paradise Valley Community College 18401 N. 32nd St., Phoenix, AZ 85032-1210 United States
AU: Schmeeckle, M W
EM: mark.schmeeckle@asu.edu
AF: Mark W. Schmeeckle, Arizona State University PO Box 870104 , Tempe, AZ 85287-0104 United States
AB: Streams that incise across bedrock highlands such as anticlines, upwarps, cuestas, or horsts are termed transverse drainages. Their relevance today involves such diverse matters as highway and dam construction decisions, location of wildlife corridors, better-informed sediment budgets, and detailed studies into developmental histories of late Cenozoic landscapes. The transient conditions responsible for transverse drainage incision have been extensively studied on a case-by-case basis, and the dominate mechanisms proposed include: antecedence, superimposition, overflow, and piracy. Modeling efforts have been limited to antecedence, and such the specific erosional conditions required for transverse drainage incision, with respect to the individual mechanisms, remains poorly understood. In this study, fifteen experiments attempted to simulate the four mechanisms and constructed on a 9.15 m long, 2.1 m wide, and 0.45 m deep stream table. Experiments lasted between 50 and 220 minutes. The stream table was filled with seven tons of sediment consisting of a silt and clay (30%) and a fine to coarse sand (70%) mixture. The physical models highlighted the importance of downstream aggradation with regard to antecedent incision versus possible defeat and diversion. The overflow experiments indicate that retreating knickpoints across a basin outlet produce a high probability of downstream flooding when associated with a deep lake. Misters used in a couple of experiments illustrate a potential complication with regard to headward erosion driven piracy. Relatively level asymmetrically sloped ridges allow for the drainage divide across the ridge to retreat from headward erosion, but hindered when the ridge's apex undulates or when symmetrically sloped. Although these physical models cannot strictly simulate natural transverse drainages, the observed processes, their development over time, and resultant landforms roughly emulate their natural counterparts. Proposed originally from an extensive literature search, most of the criteria that indicate the expected evidence associated with each mechanism following transverse drainage incision were replicated for antecedence, overflow, and piracy. Two superimposition experiments failed to replicate the mechanism and test the associated criteria. Following experimentation, the criteria were applied in a cursory fashion to twenty randomly selected sites in the southwestern USA. Development of first order hypotheses were ranked on a confidence scale tied to individual criterion noted in the field, literature, and DEMs for each site. The results indicate a possible link between the dominant tectonic regime and the proposed mechanisms; and highlight the importance of short-lived fluvial instabilities in relation to understanding long-term drainage development.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1815 Erosion
DE: 1821 Floods
DE: 1824 Geomorphology: general (1625)
DE: 8122 Dynamics: gravity and tectonics
SC: Hydrology [H]
MN: Fall Meeting 2005