Controls on bedrock channel incision along nahal paran, Israel

Abstract

Nahal Paran drains 3600 km2 of Egypt's Sinai peninsula and Israel's Negev Desert. Much of the channel is alluvial, but a canyon 105 km long has been incised into Late Cretaceous chert and dolomite in the lower portion of the basin. Slackwater deposits and paleostage indicators preserved within the canyon record approximately 10 floods of 200 to 2500 m3 s-' over a period of at least 350 years.Step-backwater simulations of flood-flow hydraulics indicate extreme variations in stream power per unit area along the length of the canyon, and associated variability in energy expenditure and sediment transport. These variations reflect channel cross-sectional morphology. The greatest values of stream power occur along the lower half of the study reach, in association with three pronounced knickpoints and an inner channel. The locations of these features reflect the exposure of thick, resistant chert layers along the channel. The presence of several similar, but buried and inactive, knickpoints along the upper study reach indicates that the locus of most active channel incision has shifted with time, probably in response to baselevel changes associated with tectonic activity along the Dead Sea Rift. Thus, the rate and manner of channel incision along the canyon of Nahal Paran are controlled by lithologic variability and tectonic uplift as they influence channel morphology and gradient, which in turn influence hydraulics and sediment transport.

Bedload transport controls bedrock erosion under sediment-starved conditions

“…For comparable situations where mean values of bedload volumes and erosion rate on bare bedrock sections are available, this model can be easily calibrated by adjusting its prefactor K. Potential applications are steep bedrock channels in detachment-starved catchments (e.g., Wohl, 1998Wohl, , 1999, channel knickpoint sections with exposed bedrock such as waterfalls (e.g., Miller, 1991;Wohl et al, 1994;Cook et al, 2013;Mackey et al, 2014;DiBiase et al, 2015), high lateral bedrock sections above the channel or its banks (e.g., Hartshorn et al, 2002;Turowski et al, 2008) or even hydropower facilities that have to cope with natural sediment flux such as sediment bypass tunnels (Jacobs and Hagmann, 2015).…”

Knickpoint initiation and distribution within fluvial networks: 236 waterfalls in the Waipaoa River, North Island, New Zealand

“…One might anticipate that at any given time, even migrating knickpoints would most likely appear to be "hung up" on hard bedrock ribs or at tributary junctions where there is a step decrease in sediment and water discharge. As a consequence, the very idea of knickpoint migration has been challenged and debated episodically for over 100 years (Gilbert, 1896;Penck, 1925;von Engeln, 1942;Leopold et al, 1964;Gardner, 1983;Higgins and Gardner, 1984;Wohl et al, 1994). Because this conceptual model allows knickpoints to form and degrade multiple times during their translation through the downstream reaches, it is likely that multiple small pulses of incision or even steady base level fall would be held up at a resistant substrate and collect into a single step.…”

Scale Dependence of Lithological Control on Topography: Bedrock Channel Geometry and Catchment Morphometry in Western Scotland

“…This latter type is our focus (fig. 4), though all knickpoints are probably substrate dependent to some degree (Holland and Pickup 1976;Gardner 1983;Wohl et al 1994;Weissel and Seidl 1997;Bishop et al 2005;Jansen 2006). All knickpoints involve predominantly detachmentlimited bedrock erosion and so are characterized by thin, discontinuous alluvial cover.…”