Fluvio-pedogenic processes in an ephemeral stream channel

Judith Lekach, Rivka Amit, Tamir Grodek, Asher P. Schick

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

A detailed stratigraphic survey conducted in the alluvial fill of the channel of Nahal Yael - a small catchment in the Southern Negev Desert - indicates the existence of a continuous, compacted, red-colored unit at an average depth of 50 cm beneath the surficial grey non-cohesive alluvium. Granulometric distinction between the grey and the red alluvium is evident only within the fine (<0.063 mm) fractions; the clay content in the red alluvium, though less than 5%, is more than double in the grey alluvium. Cementation by calcium carbonate causes the hardening of the 'red' unit. Reddening is due to small amounts of iron oxide coatings. While the upper contact of the 'red' unit is abrupt, the compaction and coloring diminish gradually downward, forming a diffuse lower boundary. The structure controlled infiltration rates into the upper grey alluvium exceed by an order of magnitude those into the 'red' unit, but are two orders of magnitude less than the velocity of the flood front, indicating that the flood fronts progress over unsaturated alluvium. The proposed model is one of a dual component flow within the alluvial fill: a longitudinal flow within the upper active layer, proceeding mainly along structure determined paths, and a vertical flow which affects the whole alluvial fill. The former of the 'red' unit is tied to the cumulative influence of persistent differences in water availability to various parts of the channel before and during flood events. The 'red' unit forms at the lower limit of the contemporary scour and fill processes, and therefore, its depth reflects the contemporary hydroclimatic regime. Its identification as a partial buffer to floodwater infiltration offers new insights into the problem of the generation of desert floods and the mechanism of transmission losses in ephemeral streams.

Original languageEnglish
Pages (from-to)353-369
Number of pages17
JournalGeomorphology
Volume23
Issue number2-4
DOIs
StatePublished - Jun 1998
Externally publishedYes

Bibliographical note

Funding Information:
This study benefited from a research grant from EARTHWATCH for two field seasons, granted to A.P. Schick. The authors are grateful to the 40-odd EARTHWATCH volunteers, whose contribution to the study was invaluable. Review of an earlier manuscript by D.H. Yaalon and his contribution to the definition of the term Fluvio-Pedogenic-Unit is much appreciated. Thanks to Aaron Yair and to Ian Reid for their comprehensive reviews, and to Michal Kidron (Cartographic Laboratory, Hebrew University) for drawing the figures.

Funding

This study benefited from a research grant from EARTHWATCH for two field seasons, granted to A.P. Schick. The authors are grateful to the 40-odd EARTHWATCH volunteers, whose contribution to the study was invaluable. Review of an earlier manuscript by D.H. Yaalon and his contribution to the definition of the term Fluvio-Pedogenic-Unit is much appreciated. Thanks to Aaron Yair and to Ian Reid for their comprehensive reviews, and to Michal Kidron (Cartographic Laboratory, Hebrew University) for drawing the figures.

FundersFunder number
Earthwatch Institute

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