Geographic Setting and Natural Conditions
The Dead Sea is part of the Jordan Rift Valley (JRV), which extends from Lake Tiberias in the north to the Gulf of Aqaba in the south. The bottom of the Dead Sea is, at 790 metres below sea level (m bsl), the lowest point in this valley and the shoreline, at about 420m bsl, is the lowest land surface on earth. The shores on the eastern and western sides of the Dead Sea rise sharply, to about 1,000m over a distance of 15-20km. This striking topography developed because the JRV is an active tectonic boundary of the Arabian Plate. The Dead Sea Transform Fault is characterized by both spreading and lateral movements along the JRV. This results in a considerable risk of earthquakes. In spite of the absence of seismic activity for the past 500 years or so, this risk has a large influence on the structural design and cost of the RSDS Project.
During the Pleistocene period, the JRV was covered by one large lake that extended from Lake Tiberias to some 35km south of the Dead Sea. The highest water level (180m bsl) was reached around 25000 BCE. The sediments deposited at the bottom of the lake are marls, consisting of loam and calcareous silt loams which are mixed with salts and gypsum. These formations are known as Lisan deposits. The land tongue that now separates the deep northern part of the Dead Sea from the shallow southern part where the potash industry is situated is known as the Lisan Peninsula (from the Arabic word lisan, ‘tongue’). Below these deep alluvial deposits, the underlying rocks are faulted by the tectonic activities along the JRV.
The Dead Sea region is of major historical, cultural and religious significance and includes important archaeological sites. With its therapeutic spas and healing waters, the Dead Sea attracts many local and international tourists. The RSDS Project area also includes sensitive regions (e.g. for migratory birds) and nature reserves (e.g. the Dana Nature Reserve).
The area between the Dead Sea and the Red Sea is sparsely populated, with densities of 10 to 50 inhabitants per km2 or less. The main population centres are located in the Aqaba/Eilat area and on the shores of the Dead Sea.
The climate is subtropical, with maximum temperatures varying from 40oC in July to 23oC in December and minimum temperatures from 30oC to 13oC. The average annual rainfall is less than 50mm, and the average number of rainy days is about 15. At 400m bsl the atmospheric pressure is 5% and the oxygen content 4% higher than at sea level, while there is less solar ultraviolet radiation. Modelling and desk studies of climate change suggest that, by 2100, the average temperature may rise by 3-6oC and the precipitation may decline by 30%. The greater intensity of rainfall events may also result in a 30-50% decrease in runoff and aquifer recharge by 2100. However, like other wadis draining directly into the Dead Sea, the side wadis that flow into Wadi Araba/the Arava Valley south of the Dead Sea are prone to occasional large flash floods. These floods strongly influence the design of RSDS Project infrastructure.
Until 1978, the Dead Sea was composed of two stratified water layers with different temperatures and salinities (meromictic state). However, in the winter of 1978-79, a complete turnover occurred, when the density of the upper layer became greater than that of the lower layer. Presently, seasonal stratification results in an annual turnover, creating a monomictic state of the Dead Sea. The homogeneous water contains 343 grams per litre (g/L) of dissolved salts and has a density of 1240g/L. Compared to sea water, Dead Sea water is richer in chlorides (Cl), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca) and bromide (Br) and is deficient in sulphates (SO4). The chemical industry annually extracts 650MCM from the Dead Sea and returns 250MCM of brine. It appears that this activity changes appreciably the chemical composition of the Dead Sea by increasing the concentrations of Mg, Ca, Cl and Br, while the concentrations of Na, K and SO4 are decreasing. Recent indications suggest that the very saline and dense deep layer formed by chemical industry return brines will continue to develop.
In addition, the hydrodynamic equilibrium between the surrounding fresh groundwater and the salt water of the Dead Sea has been affected by the decline in water levels. The interface between the two has begun to readjust to a new equilibrium state through a seaward movement of the fresher groundwater. Accordingly, groundwater levels in the surrounding areas have dropped, as large amounts of fresh and brackish groundwater have flowed into the Dead Sea in partial compensation for its declining level.