Lithologic control of bedrock meander dimensions in the Appalachian Valley and Ridge province

Abstract

Marked differences in bedrock meander dimensions in the Appalachian Valley and Ridge province, at times in adjacent reaches of a single stream, are related to differences in relative erodability of the bedrock. Meanders cut in thick-bedded to massive lithologies, typically carbonates, are distinctly smaller overall than meanders cut into shaly lithologies.Empirical relations developed from meander geometry measurements and estimated bedrock erodability for 78 bedrock meander reaches, containing a total of 1089 individual meander loops, show that meanders cut in shaly lithologies (ML = 105 QF.50, where ML = meander length and Qf = most probable annual flood) are about twice the length of meanders cut in non-shaly lithologies (ML = 39.3 Q:.s6). The valley floor width of the meanders cut in shaly bedrock (VF = 28 QF"' ) is two to three times wider than the valley floor width of the meanders cut in the more resistant non-shaly bedrock (VF = 8 Q:.'"). The mean and median meander length values for individual reaches typically differ by less than 10 per cent.Other factors that could affect bedrock meander dimensions were considered and none appeared to offer any help in explaining the dimensional differences observed above.In plateau regions underlain by essentially horizontal strata, the meander form characteristic of one lithology may become superimposed upon another as incision progresses, producing anomalous relationships between bedrock meandel dimensions and lithology.

Knickpoint evolution in a vertically bedded substrate, upstream-dipping terraces, and Atlantic slope bedrock channels

“…At the drainage-basin scale, south of the glacial boundary, Appalachian rivers are generally well adjusted to rock type and structure and have formed graded, concaveup longitudinal profi les within broad, long strike valleys in relatively soft rocks, parallel to fold axes, or along dominate joint orientations. Similarly, at shorter reach scales, as in the case of tight meander loops, channels are controlled by bedding, foliation, or related structures of the bedrock (Braun, 1983 fl ow perpendicular to the prevailing structural grain of the orogen across steeply dipping or foliated rocks (Fig. 3), such as the Susquehanna, Potomac, and James Rivers as they carve gorges across the Piedmont and Fall Zone ( Fig.…”

Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars

“…However, channel w:d and Lm have been observed to diminish with increasing channel boundary resistance (Braun, 1983;Harmar and Clifford, 2007). Abrahams (1985) reasoned that along channels of mixed boundary resistance, the varying return interval of formative discharge, as a consequence of changing resistance, dominates Along the lower Suir, 11 pools are scoured into the bedrock floor of the valley (Fig.…”

Discriminating between the roles of late Pleistocene palaeodischarge and geological‐topographic inheritance in fluvial longitudinal profile and channel development

“…Present day analogues can be seen where pool spacing is adjusted to differing channel width via the discharge-width to meander wavelength relationship (Soar and Thorne 2001), over channel boundaries of differing resistance. However, channel w:d and L m have been observed to diminish with increasing channel boundary resistance (Braun 1983;Harmar and Clifford 2007). In relation to stable alluvial channels, Schumm (1967) concluded that, in addition to discharge, the other independent variable determining L m is sediment load type, particularly the balance between the sand-gravel and silt size fractions.…”