A high magnitude storm and flood in a hyperarid catchment, Nahal Zin, Negev Desert, Israel

Abstract

Abstract:In October 1991 a high magnitude rainstorm¯ood, estimated return period 40 years, occurred in Nahal Zin, a 1400 km 2 catchment in the hyperarid Negev Desert. The meso-scale structure of the storm was a curved squall line that developed from a thunderstorm in accordance with the topography of the catchment divide, by which it was strongly aected. Tropical moisture reached the area via the subtropical jet stream, in conjunction with a lower level northward intrusion of the Red Sea trough (RST-N) into the Mediterranean Sea. Rainfall, as measured at the few and sparse gauging stations, was much too small to account for the resulting large¯ood. Peak¯ow and other hydraulic characteristics of the¯ood were indirectly reconstructed. The techniques of palaeo¯ood hydrology used were based on sedimentological evidence of ®ne-grained¯ood sediments deposited in back-¯ooded tributaries, as well as on other stage indicators. The HEC-2 procedure was employed to determine water surface pro®les.The spatial and temporal characteristics of the event were studied through a combination of rainstorm analysis, remote sensing, hydrological and sedimentological data; they jointly explain the magnitude and timing of tributary contributions producing the integrated¯ood in the main channel. The¯ood as reconstructed reveals a three-peak hydrograph: two peaks were generated by the same storm but had dierent¯oodwave arrival times in the main channel; the third resulted from a local rainstorm which occurred on the following day and covered only one tributary.The curved structure of the storm and its dynamics in relation to catchment orientation resulted in storm movement in tandem with the¯oodwave. The synchronous contribution from all main tributaries preserved evidence of the¯oodwave both in stage and volume by replacing the transmission losses in the sections with thick alluvium.Other high magnitude¯oods on record for the large Negev Desert catchments are caused by a cold upper air incursion associated with the RST-N. Most of them occur in the autumn and are caused by storms with highintensity rainfall. This is in stark contrast with the¯ooding behaviour of the semi-arid zone further north, which is linked primarily to the core of the Mediterranean winter. The complexities involved in the generation of a large desert¯ood, as revealed by this study, illustrate the fallacy of applying routine hydrological modelling to such events, and underline the need to study the processes involved in adequate detail. #

Flood events in Mediterranean ephemeral streams (ramblas) in Valencia region, Spain

“…The real time detailed information networks like SAIH are of vital importance in facilitating the recognition and monitoring of the processes that generate floods with response times of a matter of hours, as is the case for Mediterranean ephemeral Ž streams. However-as is noted by many authors Pilgrim et al, 1988;Greenbaum et al, . 1998 -the analysis of the spatial variability of the hydrological behaviour requires the existence of a denser network of rainfall and stream discharge gauges in a single basin, in order to evaluate better the mechanisms that generate floods.…”

Red Sea Trough flood events in the Negev, Israel (1964–2007)

“…Abramski, 1983, Inbar, 1987, Schick andLekach 1987, Greenbaum et al 1998, Krichak and Alpert 1998, Ben David-Novak et al 2004, Dayan and Morin 2006.…”

Integration Techniques for Environmental Impact Assessment of Industrial Pollutants

“…Many researchers have described flood hydrographs and the recession limb as part of flood-routing procedures [16,[19][20][21][22][23]. In general, flood hydrograph analysis provides a simple method for estimating runoff volume in a watershed in response to storm patterns [24][25][26][27] or physical characteristics of the drainage area [10,11,15,28,29]. However, in both cases, there is a need for many variables and complicated equations.…”

“…The YP is dominated by the Subtropical ridge (latitude of [20][21][22][23][24][25][26][27][28][29][30] 0 N), and is classified as arid zone. The YP has been designated as a national radioactive waste site for the last approximately 50 years.…”