Trends and Sustainability of Groundwater in Highly Stressed Aquifers (Proc. of Symposium JS.2 at 207 the Joint IAHS & IAH Convention, Hyderabad, India, September 2009). IAHS Publ. 329, 2009. Transforming a desert into a food basket: quantitative and qualitative effects of agricultural development on a unconsolidated brackish environment MATHIAS TOLL & MARTIN SAUTER Applied Geology, University of Göttingen, Goldschmidtstr. 3, D-37077 Göttingen, Germany [email protected] Abstract In semi-arid areas groundwater systems are frequently not sufficiently characterized hydrogeo- logically and long-term data records are generally not available. However, long-term time series are necessary to design future groundwater abstraction scenarios or to predict the influence of future climate change effects on groundwater resources. To overcome these problems, an integrated approach for the provision of a reliable database based on both hard quantitative and sparse and fuzzy data was taken and developed further. This developed integrated approach is demonstrated in the lowermost area of the Jordan Valley/Jordan. The Jordan Valley was rapidly transformed from a barely inhabited area into the “food basket” of Jordan. As a result, hundreds of shallow wells were drilled and large amounts of groundwater were abstracted, since groundwater is the major source for irrigation. Consequently groundwater quality decreased rapidly since the 1960s and signs of overpumping and an increase in soil salinity could clearly be seen. A numerical 3-D transient model integrating all important features of the hydrogeological system was developed and tested against stress periods depicted during the historical review of the test area (model period: 1955–2001). These stress periods include periods of intense rainfall, of drought, and of anthro- pogenic impacts, like building of storage dams and the influence of violent conflicts. Recommendations for future sustainable groundwater abstractions are given. Key words stressed-aquifer system; unconsolidated aquifer; qualitative data; numerical modelling; Jordan Valley INTRODUCTION This study focuses on the effect of increased anthropogenic activities on a previous natural unaltered groundwater system in an arid environment. A frequent problem in semi-arid to arid areas is the poor data situation. An integrated approach was used successfully to set up a numerical steady-state 3-D groundwater flow model. This integrated approach combines recorded data (e.g. water levels, chemical analyses of well waters, geophysical data, remote sensing data) with soft and fuzzy information (e.g. questionnaires, reports). The integrated approach used is described in detail by Toll (2008). On the basis of the steady-state model a transient 3-D groundwater flow model was set up that simulates the impacts of anthropogenic development on the groundwater resources from a natural system to a highly stressed groundwater system. STUDY AREA Geography and climate The research area is located in the lower Jordan Valley/Jordan (Fig. 1). The centre is located at WGS84 coordinates 31°52′N and 35°36′E, and has an area of 150.66 km2, and an average elevation of 270 m below mean sea level (b.m.s.l.), and, compared to the bordering area to the east, a very smooth average slope of one to two degrees. The lowest point is located at the Dead Sea shore in the south, with an elevation of 420 m (measured in 2006; as of today the current drop rate of the Dead Sea level is 1–1.3 m/year) below mean sea level (the elevation depends on the water level of the Dead Sea), and the highest point at the fan apex of Wadi Hisban with 160 m b.m.s.l. The detailed study area includes the unconsolidated strata of lower Jordan Valley and extends from the Dead Sea in the south, to the town of Karameh in the north, from the Jordan River in the west to the margin of the western hills of the East Bank in the east. The maximum extension is 14 km east–west and around 20 km north–south. The hydrology of the unconsolidated Copyright © 2009 IAHS Press 208 Mathias Toll & Martin Sauter (a) (c) (b) Fig. 1 Location of the study area. (a) Middle East; (b) study area in the regional context; (c) study area. strata, the focus of this study, can only be understood by including the slopes and highlands of the East Bank located in the east of the study area, because it is considered that the major part of recharge and of sediment supply to the unconsolidated aquifer derives from this area. Two major cities are located 10 and 20 km to the east of the study area: the city of As-Salt and the capital Amman. The deeply incised valleys of Wadi Kafrein carry perennial flow. However, during and after the rainy events, they also drain floodwater down to the Jordan Valley. The flood- water carries sediments, and sometimes even rocks, forming fan deposits in the Jordan Valley. According to Köppen (1931) the study area can be classified as a Group B Dry (arid and semi- arid) climate, since precipitation is less than the potential evaporation. Morphology has the largest influence on the prevailing climate. A subdivision into three different climatic zones can be made: the Highlands area, the Western Slopes of the East Bank, and the Jordan Valley. The climate in the Highlands is of Mediterranean type. It is characterized by long, hot, dry summers and short, cool, rainy winters. Towards the west, the climate undergoes a rapid change to semi-arid and arid climate in the Jordan Valley. The western Slopes act as a transition zone between the Mediterran- ean climate along the Highlands in the east and the arid climate in the Jordan Valley in the west. Rain only falls during the winter months. The climate changes abruptly from dry hot summer conditions to humid, cold, and stormy conditions. Usually it starts to rain in November and rainfall continues until the end of April, and 70% of the annual precipitation falls between November and February. Snow falls once to twice a year in the Highlands. The average annual precipitation on the western ridges of the Highlands (Jordan University, Amman) is around 505 mm/year, on the eastern part of the Western slopes (Naur) 395 mm/year, and in Jordan Valley (South Shuneh) the long-term average is around 166 mm/year (MWI open files). Thus a strong correlation with altitude and climate data exists for the area. Geology and hydrogeology This study deals only with the unconsolidated Jordan Valley aquifer system. Therefore, only the unconsolidated rock column will be discussed below. The Shagur Formation is believed to be the Transforming a desert into a food basket 209 oldest formation deposited in the Jordan Valley (Upper Pliocene–Lower Pleistocene). The Shagur Formation consists of massive, crudely bedded fluvio-limnic conglomerates that alternate with crudely bedded travertine and marl or claystone. This unit overlies unconformable older consolidated rocks. Clasts are angular to subangular and siliceous cemented. In the type localities in the east and south the terrestrial to fluvio-limnic Shagur Formation has a thickness of approx. 75 m. However, thickness changes significantly within the different facies types (Bender, 1968). While the Shagur Formation crops out in the east and southeast of the study area, it was not reported, neither in the deep oil wells Jordan Valley 1 and 2, nor in the wells drilled by the Ministry of Water and Irrigation (MWI). During Pleistocene times, three members can be distinguished. The three members (the coarse clastic, the silt and the lacustrine) are a vertical and lateral facies succession from terrestrial/flu- vial, to deltaic/limnic and limnic/brackish lake environments. The “Pleistocene aquifer” consists of the coarse clastic and the silt member. However, exploitable water resources are principally restricted to the coarse clastics member. The lacustrine member consists of marl, gypsum and silt, and is generally considered an aquiclude, void of exploitable water. It crops out mainly in the west of the study area. Since the Lisan Lake reached an elevation of –180 m above mean sea level, its sediments can be found in incised channels of the major wadis up to the margin of the Jordan Valley. Its total thickness is around 40 m. The coarse clastic member consists of gravel, inter- bedded with clay, sand and marl horizons. Both, the coarse clastic and the silt member underlie, overlie, or interfinger with the Lisan Formation. The youngest unit is built up of sub-recent terrigenous sediments deposited along the outlets of major wadis. These alluvial fans are still accumulating as a result of large floods. They consist of debris from all neighbouring lithologies and are deposited according to their transport energy. The biggest components are found close to the apex and the smallest close to the fan margin. The transport normally takes place along alternating channels or after very heavy rain storms as sheet, or debris flow. Thus permeable horizons alternate with less permeable lithologies within these deposits. It is believed that the thickness maximum is near the valley margins, thinning out towards the centre of the basin. Well depth is rarely beyond several tens of metres. Often the alluvial aquifer directly overlies the Pleistocene gravel aquifer and because of that is hydraulically interconnected with this aquifer. The unconsolidated material of the Jordan Valley aquifer system deposited on consolidated material, mostly limestone, dolimitic limestone and to a lower extent sandstone. These consolidated rock columns make up the major aquifer systems (Upper aquifer, Lower aquifer and the Kurnub Group aquifer) of the western slopes and the highlands of the East Bank. These consolidated aquifer systems carry freshwater towards the Jordan Valley aquifer system. By the multilayered nature of these consolidated aquifers and aquitards it follows that many aquifers are confined, and so it seems likely that the unconsolidated sediments of the Jordan Valley aquifer system are infiltrated from beneath via consolidated layers dipping into the Jordan Valley.