Tamir Grodek

• PhD
• Researcher lecturer at Hebrew University of Jerusalem

The deterioration of check dams and other flood prevention measures, combined with storms breaking historical records, has created an immediate risk of floods and debris flows breaching urbanized alluvial fans. In this study, we reevaluate these flood and sediment prevention measures and propose a different flood prevention paradigm. Flood defense...

Overlooking the Red Sea, the desert cities of Eilat (Israel) and Aqaba (Jordan) are located in a strategic, economic, and trade junction. The cities were built on a series of alluvial fans and a playa in-between; the only gentle slopes between the steep mountains and the sea that can accommodate large urban settings. Nevertheless, flash floods, whi...

Arid ecohydrology relies on sporadic seasonal rainfall and flooding to sustain linear river oases, which are crucial for supporting flora and fauna during prolonged dry seasons and droughts years. Growing demands for irrigation, human settlements and energy have led to the construction of reservoirs as a vital water resource. However, large dams ca...

We present the Satellite Vegetation Index Time Series model for detecting historical floods in ungauged hyperarid regions (SatVITS‐Flood). SatVITS‐Flood is based on observations that floods are the primary cause of local vegetation expansion in hyperarid regions. To detect such expansion, we used two time‐series metrics: (1) trend change detection...

We present the Satellite Vegetation Index Time Series model for detecting historical floods in ungauged hyperarid regions (SatVITS-Flood). SatVITS-Flood is based on observations that floods are the primary cause of local vegetation expansion in hyperarid regions. To detect such expansion, we used two time series metrics: (1) trend change detection...

Study region A flood study was performed in the ephemeral Ugab River in the arid north-western part of Namibia. The headwaters of the river lie on the higher Namibian plateau, where most floods are generated and propagate west, through the Namib desert, to the Atlantic Ocean. Study focus Estimation of a 1 % Annual Exceedance Probability (AEP) floo...

Flood-fed aquifers along the sandy lower reach of the Kuiseb River sustain a 130-km-long green belt of lush oases across the hyperarid Namib desert. This oasis is a year-round source for water creating dense-tall woodland along the narrow corridor of the ephemeral river valley, which, in turn, supports human activity and fauna including during the...

Abstract Ephemeral rivers in dryland regions exhibit a high interannual variability of streamflow regime, mainly dominated by floods. In these environments, floods are a water resource and a potential hazard with important socioeconomic implications. The Fish River (86,600 km2) is the largest ephemeral stream in Namibia and, recently, also the focu...

Quantitative geomorphic field studies and modeling efforts have focused on the margins of southwestern Africa as an example for landscape evolution in prolonged aridity conditions and tectonic quiescence of passive margins. These efforts concluded that this region is a prime example of a steady state landscape, in which relief changes extremely slo...

https://www.youtube.com/watch?v=qmblBaTt-bs from: http://onlinelibrary.wiley.com/doi/10.1002/2016JF004081/abstract

The geomorphic response of channels to base-level fall is an important factor in landscape evolution. To better understand the complex interactions between the factors controlling channel evolution in an emerging continental shelf setting, we use an extensive dataset (high-resolution digital elevation models, aerial photographs, and Landsat imagery...

Photograph from a helicopter of the incising channel of Nahal HaArava (~18m depth in 2014), near its mouth in the salt delta, the Dead Sea.

The largest Kuiseb River floods initiate at the basin’s semi-arid headwater. Downstream, along the hyperarid Namib Desert, these floodwaters are feeding shallow alluvial aquifers, the only available water for human activity and for the natural ecology. Here, we characterize the largest floods and their changing frequency and magnitudes using palaeo...

Identification of a geomorphic index to repre-sent lower thresholds for minor flows in ephemeral, allu-vial streams in arid environments is an essential step as a precursor for reliable flash flood hazard estimations and es-tablishing flood warning systems. An index, termed Alluvial wadi Flood Incipient Geomorphologic Index (AFIG), is pre-sented. A...

Identification of a geomorphic index to represent lower thresholds for minor flows in ephemeral, alluvial streams in arid environments is an essential step in reliable flash flood hazard estimations and establishing flood warning systems. An index, termed Alluvial wadi Flood Incipient Geomorphologic Index (AFIG), is presented. Analysis of data from...

A comprehensive investigation of rainstorms and their consequent impacts on landscape evolution is geomor-phologically important, but only scant information may be available on exceptional events, because parame-ters on synoptic conditions, rainstorm, landforms and hydrology for such events may be incomparable with previous knowledge. We studied an...

In their seminal paper in 1979, Bull and Schick proposed a conceptual model for the geomorphic response to Pleistocene to Holocene climate change, based on the hyperarid Nahal Yael watershed in the southern Negev Desert. In this model, the change from semiarid late Pleistocene to hyperarid early Holocene climates reduced vegetation cover, increased...

In the Middle East, water is scarce and population growth causes a rapid rise of urban centers. Since many towns of the Palestinian Authority (PA) suffer from water shortage, the use of rainwater harvesting (RWH) as an alternative to conventional water supply has gained increasing interest among water resources planners. This study quantifies actua...

In the Middle East, water is scarce and population growth causes a rapid rise of urban centers. Since many towns of the Palestinian Authority (PA) suffer from water shortage, the use of rainwater harvesting (RWH) as an alternative to conventional water supply has gained increasing interest among water resources planners. This study quantifies actua...

Understanding recharge mechanisms and controls in karst regions is extremely important for managing water resources because of the dynamic nature of the system. The objective of this study was to evaluate water percolation through epikarst by monitoring water flow into a cave and conducting artificial irrigation and tracer experiments, at Sif Cave...

The Gihon Spring, Jerusalem, is important for the major monotheistic religions. Its hydrogeology and hydrochemistry is studied here in order to understand urbanization effects on karst groundwater resources, and promote better water management. High-resolution monitoring of the spring discharge, temperature and electrical conductivity, was performe...

Soils in similar geomorphic settings in hyperarid deserts (< 50 mm yr−1) should have similar characteristics because a negative moisture balance controls their development. However, Reg soils in the hyperarid southern Negev and Namib deserts are distinctly different. Soils developed on stable alluvial surfaces with only direct input of rainfall and...

The Mediterranean climate together with the type of urban setting found in mountainous Middle Eastern cities generate much lower runoff yields than previously reported and than usually estimated for urban design. In fact, a close analysis shows that most of the rainwater remains within the cities as a possible source for urban groundwater recharge....

To investigate processes of water percolation, the drip response of stalactites in a karstic cave below a 143 m2 sprinkling plot was measured. The experiment was conducted in Mount Carmel, Israel, at the end of the dry season and intended to simulate a series of two high-intensity storms on dry and wet soils. In addition to hydrometric measurements...

This paper summarises innovative research into the assessment of long-term groundwater recharge from flood events in dryland environments of the Kuiseb (Namibia) and the Buffels (South Africa) rivers. The integrated water resource management (IWRM) policies and institutions affecting the exploitation of groundwater resources in each of these develo...

The Gihon Spring, Jerusalem, is important for the major monotheistic religions. Its hydrogeology and hydrochemistry is studied here in order to understand urbanization effects on karst groundwater resources, and promote better water management. High-resolution monitoring of the spring discharge, temperature and electrical conductivity, was performe...

The Mediterranean climate together with the type of urban setting found in mountainous Middle Eastern cities generate much lower runoff yields than previously reported and than usually estimated for urban design. In fact, a close analysis shows that most of the rainwater remains within the cities as a possible source for urban groundwater recharge....

Quantitatively estimating rainfall–runoff relations in extremely arid regions is a challenging task, mainly because of lack of in situ data. For the past 40 years, rain and floods have been monitored in the Nahal Yael catchment (0.5 km2) in southern Israel, providing a unique data set of runoff hydrographs and rainfall in a hyper-arid region. Here...

Flood water infiltrates ephemeral channels, recharging local and regional aquifers, and it is the main water source in hyperarid regions. Quantitative estimations of these resources are limited by the scarcity of data from such regions. The floods of the Kuiseb River in the Namib Desert have been monitored for 46 years, providing a unique data set...

An upper limit for long-term scour in ephemeral streams has not been studied, although it is necessary to know it for flow regime determination, paleohydrology, and sediment budget evaluations. The available data on scour derive from short investigations lasting a few decades at most, but these are not representative of long-term processes, which a...

Processes of infiltration to groundwater in a karstic area were studied by monitoring and sampling cave drips during 2004-2008 at two sites with different lithologies: dolomite of the Yagur Fm. and crystalline limestone of the Muhraqa Fm., in Mt. Carmel, Israel. Two tracer tests under different antecedent moisture conditions and "rainfall" intensit...

A paleoflood study in the Gardon River gorge in southern France identified extreme floods larger than any modern or historically gauged flood. During the course of our study, an extreme flood on the 8–9th of September 2002 claimed the lives of 21 people and caused millions of Euros worth of damage to the towns and villages along the river. The magn...

The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine...

Multidisciplinary research in the hyperarid Kuiseb River, Namibia provides the necessary information to determine (a) long-term floods occurrence and aquifer recharge events and (b) flood routing and transmission processes along the river course. Together they assist in estimating water resources along the river. The only source of water along the...

A study for monitoring water percolation in the epikarst is carried out at Sif cave in Wadi Sussi (Israel). The research is based on continuous direct measurement of the rainfall outside the cave and water percolation in the cave chamber. The water is collected by three large sheets which integrate the drips from three different areas (16 m2, 56 m2...

Analysis of extreme hydrometeorological events is important for characterizing and better understanding the meteorological conditions that can generate severe rainstorms and the consequent catastrophic flooding. According to several studies (e.g., Alpert et al., 2004; Wittenberg et al., 2007), the occurrence of such extreme events is increasing ove...

Stratigraphic studies conducted on the alluvial fill of several ephemeral stream channels in the southern Arava Valley, Dead Sea Rift, indicate the existence of a calcic ‘soil’ developed 50–100cm beneath the channel surfaces. This anomalous calcic ‘soil’ does not fall within the categories of any standard soil or paleosol definition and thus has be...

Hyperarid ephemeral streams have limited floodplains. However, when the do form they, together with active channels edges have crucial role in establishing riparian ecosystems. Large floods (a) can continually accrete floodplains or destroy them, (b) recharge shallow alluvial aquifers that maintain vegetation during dry periods, and (c) allow veget...

[1] Better understanding of flood occurrences and long-term, floodplain planning, and flood risk assessment is achieved by integration of gauged, historical, and paleoflood data. The Ardèche River is ideal for this historical flood-paleoflood study because its historical flood levels record dates back as early as A.D. 587 and useful data date back...

In October 2002 experimental field work on runoff generation has been initiated near the city of Modiin, Israel. In a small limestone headwater catchment two representative hillslope types are selected: a) a rocky hillslope with only patchy soil cover and b) a terraced slope with abundant vegetation. Rainfall is recorded by a tipping bucket and a n...

A study of paleofloods in the Gardon River in southern France reveals the occurrence of past extreme floods that were larger than any observed historically. From 8 to 9 September 2002, during the course of the study by a complete coincidence, an extreme flood claimed the lives of 21 people and caused millions of dollars worth of damage to the towns...

On many alluvial fans in the drier parts of the world, urban settings have replaced natural areas, which in the past had been the domain of stream channel wandering, sediment deposition, and attenuation of flow energy. Due to very long intervals between flood events, little attention had been paid to these natural processes, resulting in a fallacio...

The natural array of processes conveying water and sediment from arid mountain catchments, through alluvial fans, into the base level below is affected by human intervention to an extent unknown until a few years ago. Previously permeable fan terrain has now been replaced by paved impermeable surfaces whose drainage becomes problematic. This proble...

On many alluvial fans in the drier parts of the world, urban settings have replaced natural areas, which in the past had been the domain of stream channel wandering, sediment deposition, and attenuation of flow energy. Due to very long intervals between flood events, little attention had been paid to these natural processes, resulting in a fallacio...

The 1996 Biescas flood in the Central Pyrenees, Spain, caused the loss of 87 lives in a camp site located on an active alluvial fan. The flood destroyed 31 out of a series of 36 dams and a canal which were built between 1926 and 1943 to protect the highway from threatening floods. During the flood, the sediments stored by these dams were moved down...

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...

Tracer techniques were used to study infiltration losses into a dry wadi bed. In order not to be fully dependent on rarely occurring natural flood events, an artificial flash flood was studied in a small arid stream channel, Nahal Shahmon, Israel. A reservoir was built, filled with water (550 m3) and breached artificially. Three different artificia...

Dealing with the sediment problems associated with floods poses difficult challenges to planners and managers of desert towns. Infrequent but powerful floods from even small catchments generally contain 5-10% of sediment by weight, most of it bed material. As shown by several case studies, corroborated by a simulated flash flood experiment, this se...

Geomorphological evidence and recent trash lines were used as stage indicators in a step-backwater computer model of high discharges through an ungauged bedrock channel. The simulation indicated that the peak discharge from the 26.7 m2 catchment was close to 150m3s−1 during the passage of Hurricane Charlie in August 1986. This estimate can be compa...

The height and spacing of channel bed-steps formed in boulder and bedrock in the ephermeral channels of the Nahal Yael watershed show a strong correlation with the channel slope. The distance between steps is inversely proportional to slope at slopes of 0 to 20%, but then remains fairly constant at higher slopes. Step height increases proportionall...