Bed Load Sediment Transport in an Ephemeral Stream and a Comparison with Seasonal and Perennial Counterparts

Abstract

Bed load sediment flux in an ephemeral channel, the Nahal Yatir, is shown to be a comparatively simple function of stream power and to reach levels that are several orders of magnitude higher than maxima measured at similar levels of stream power in perennial counterparts. Channel average submerged unit flux rates are recorded as high as 4.3 kg s−1 m−1, while at the center of the channel, the highest rate recorded is 6.5 kg s−1m−1. Transport efficiency is at least an order of magnitude higher than in other channels for which there are comparable data and, on average, as much as 400 times that of Oak Creek. These differences are explained by the fact that the bed of the Yatir is not armored. It is surmised that the unvegetated nature of this desert watershed provides ample supplies of sediment of all sizes and that this, together with the rapid recession of the flash flood hydrograph and the extended periods of no flow, discourages the development of an armor layer. The flux rates are not sediment supply‐limited, as they are in perennial channels. Nahal Yatir and Oak Creek represent two ends of a spectrum, between which come seasonal and less well armored perennial streams. Transport efficiency is shown to vary considerably for each stream and from one stream to another, suggesting that it may not be possible to incorporate it easily into bed load equations in order to improve levels of prediction.

Evolution of bed load grain size distribution with increasing flow strength and the effect of flow duration on the caliber of bed load sediment yield in ephemeral gravel bed rivers

“…It is possible to fit a bed load function such as that of Parker [1979] with some confidence and to use this in conjunction with a flow duration curve to arrive at credible estimates of yield. However, the high degree of scatter in the bed load/shear stress relation that is typical of many perennial streams of similar size [Reid and Laronne, 1995] makes a similar analysis for these somewhat less prospective. The application of the flow duration/sediment transport method provides a further indication of the difficulties of attempting to link sediment transport and channel crosssectional form in concepts such as "effective" and "dominant" discharge [Graf, 1988;Knighton, 1998].…”

“…This is part of a wider investigation of sediment transport processes in dryland ephemeral streams [Laronne and Reid, 1993;Laronne et al, 1994;Reid and Laronne, 1995;Reid et al, 1996Reid et al, , 1998b. The data have been collected using a permanently installed sediment transport monitoring station.…”

Understanding the influence of slope on the threshold of coarse grain motion: Revisiting critical stream power

“…Although a power law provides the best fit to the empirical data observed within this study, it is likely that, 463 at extremely low slopes, the critical Shields' parameter will become asymptotic to a constant value (R. I. 464 by Reid and Laronne (1995), the primary effect of the increased flow resistance at high slopes is to shift the 503 position of a bed-load rating curve toward higher mean bed shear stresses, a pattern which is evident in the 504 flume data analysed here (Fig. 5).…”

A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

“…The spotty, episodic precipitation patterns often lead to a lack of base flow (unless groundwater influences are present) and, as a result, decreased incision of Arid West channel forms. The lack of consistent flow in conjunction with the immature and poorly formed/consolidated soils typically found in arid systems make both the channel morphology and the channel position highly variable and generally reduce the growth of channel-armoring vegetation (Reid and Laronne 1995, Millar 2000, Lichvar and Wakeley 2004.…”