Topography and Hydrology

The Orontes, a complex river

Mohamed Al Dbiyat, Bernard Geyer

The Orontes is the Levant’s greatest river. It drains northern Beqaa, a portion of mainland Syria and of the Turkish Hatay, from the slopes of Lebanon to the foothills of the Taurus, over a stretch of nearly 610 km. Its watershed covers more than 24,870 km² with 2205 km² in Lebanon (9%), 17,110 km² in Syria (69%) and 5552 km² in Turkey (22%). Its waters, though scarce but perennial, have carved one of the most characteristic landscapes in Syria, “the Orontes gardens”.

Shaped by Tectonics

The Orontes River has been shaped by tectonics (Weulersse 1940, p 11.): its course – and the same is true of the Litani and the Jordan – corresponds to the great Syrian ditch, with a North-South axis, located on a transform fault that is part of the Red Sea rift system, which extends from the Gulf of Aqaba to the Amanus. From the Orontes headwaters in the Beqaa, down to the Amouk depression in the Province of Hatay through the Al Ghab depression, the river flows along this major tectonic axis and into the Mediterranean, below the city of Antakya.

Its longitudinal profile reveals a complex geological history and is characterized by long stages, covered with alluvial floodplains or uplands carved out by the river and connected by abrupt gradient changes marked by rocky sills (Weulersse 1940, p. 15, fig. 4). The upper Orontes, upstream the Aïn ez Zarqa spring, 650 m high, is very similar to a “wadi”, a seasonal stream, or even a temporary one, whose thalweg (main channel) is not clearly defined. Actually, the river source is a little above Hermel, where the karstic springs of Aïn ez Zarqa (the blue spring) gush out, and where, carving its way across an arid plateau, it winds through a steep and narrow, yet lush, valley. Shortly afterwards, it then reaches its first level, at about 500 m above sea level, where both Lebanon’s mountain ranges disappear, giving way to the “Homs Gap” and the fertile Tell an Nabi Mindu plain it flows across. Basalts, which occupy most of the Homs gap and the Jabal al Hulw region, have squeezed the river into flowing further away to the North-East. When flowing out of the plain, its embankment steeps deeply into the basalt Homs plateau, resulting in a new break in slope, which remains steep all the way to Ar Rastan. There, it leaves the basalt and flows across soft senonian chalk, and the valley widens – though it is still carved across a plateau. The barrier of the basaltic Jabal al-Ala mesa forces the river to again change its course, to the northwest this time, towards Hama. Close to the Al Lataminah village, the next break in slope occurs, resulting from the very low basic level of the Al Ghab tectonic rift. Its gorges are steep, and they carve out the hard Cenomanian limestone down to the citadel of Shayzar where, thanks to a fault-line, the greatest step can begin. Indeed, from Shayzar à Qarqur, there stretches out a two-fold flat landscape, which for a long time remained largely unhealthy marshlands: the plains of Al ‘Asharinah and Al Ghab, which correspond to rift valleys. In Qarqour, a break in slope closes the Ghab with a basaltic sill. From there, the Orontes flows down the slopes to Darkush and reaches the plain of Amouk, its last stage, which it crosses all the way to Antakya where the last break of slope leads it to its Mediterranean outlet.

A Complex Watershed

The Orontes watershed, a vast and complex one, can be divided into well-differentiated sections:

- Upstream to the plain of Homs, can mainly be found glacis systems whose surfaces are topped with conglomerates, and are marked with arid climate and soils, all the more so as they lie in the vicinity of Mount Lebanon highlands, which drastically ward off incursions of moist air masses. Yet, those highlands – and their, albeit lower, counterparts: the Anti-Lebanon – are at the origin of the karstic supply provided by the abundant springs that generate the Orontes and feed the large Northern Beqaa “oases”: Baalbek, Laboue, Hermel, but also the smallest oases of Younine of Fakehe or Ras Baalbek. The progressive broadening of the Beqaa towards the north has enabled the establishment of a parallel network – in the Qaa “drainpipe”, which collects the waters in the north-west of the Anti-Lebanon though it is no longer functional (Besançon and Sanlaville 1993, p. 14).

- The Tell an Nabi Mindu plain, which hosts Lake Qattinah (or Lake of Homs) is a large Neogene outcropping generated, behind basalt flows, by a once very large body of water. The presence of the “Homs Gap” between Mount Lebanon to the south and the Syrian coastal mountains enables the flow of moist air thwarted elsewhere by the barrier of mountain massifs. Hence, the plain benefits from a climate favorable to rain-fed crops, but irrigation is nonetheless widely developed there, again thanks to waters drawn from the river and springs. This accounts for the agricultural wealth of the region, where cereal crops and orchards are widely developed and gardens are concentrated around urban areas.

- Between the Tell an Nabi Mindu plain and the one of Al ‘Asharinah and of the Al Ghab, the river flows through several, first basalt then limestone plateaus, through very steep-sided valleys. The often bare surfaces of these plateaus, now reclaimed by fruit trees, traditionally used to host rain-fed grain farming. Contrary to these areas where edaphic aridity still has some impact, the bottom and alluvial terraces were the domain of waterwheels and occupied by lush crops, thanks to irrigation: this is an oasis economy, based on gardens, and which supplements the large grain economy. Most Orontes River tributaries converge toward that area. The most important ones are the Wadi Maydani, which drains all the northeast of the Anti Lebanon up to the Yabrud highlands, and the Wadi Al Kafat Who, flowing from Salamiyah, marks the foray of the basin into the arid eastern margins, up the Jabal al-Bil ‘as, a part of the Palmyrean chain to the north (about 100 km from the Orontes).

- The Al Ghab corresponds to a rift valley where sediment transported by the river is trapped. It is actually composed of two compartments, the Al ‘Asharinah low land the Al Ghab itself. The Orontes travels through the first from east to west before flowing around the rocky outcrop of Al Asharinah and through the Ghab from south to north. The whole area, naturally poorly drained and also fed by powerful springs from the coastal mountains and Syrian Jabal az Zawiyah karsts, has long been unhealthy and swampy. The Al Ghab, 80 km long and some 15 km wide, enjoys a very gentle slope (0.1 ‰); so, it has a very flat surface and the river, due to the rise of its bed, used to make a slight relief. In those days, these bank-lifts were the only inhabitable areas; there also, and only in the highest parts, lived Bedouin or mountain people in semi-lacustrine villages, relying mainly on fishing (Weulersse 1940, p 73.), buffalo breeding and small sorghum crops.

- The Qarqur-Darkush narrow pass, which contributes to the river flow thanks to springs fed from the Jabal Kosseir and Jabal al-Wastani and from the Rug depression of tectonic origin between Jabal az Zawiyah and al Wastani (Besançon et Geyer 1995) has also been completely transformed by development work on the Al Ghab (Mazloum 1954). To achieve the draining of marshes, the basalt Qarqur lock was removed; besides, the course of the Orontes was deepened from 4 to 6 m and widened from 11 to 30 m over the 5 km between the villages of Kufayr  and Qarqur (Métral J. and Métral F. 1979, p. 308).

River Catchment and Regime

The Orontes is different from the other Levant rivers because it flows almost from end to end in sub-humid Mediterranean bioclimatic region; therefore it enjoys significant precipitations (typically between 400 and 500 mm per year), which contribute to increasing its flow rate from upstream to downstream. But it is fed primarily from steep mountains, mainly limestone, which, well watered as they are, play the role of water towers, surrounding it almost all along its course, supplying many powerful springs, in all seasons. That is when it acquires its karstic nature together with the relative regularity of its flow throughout the year – further accentuated by the regulating role of the alluvial plains it flows across.

Weulersse J. (1940, p. 50) characterizes the river by the “abundance of its mean flow, the regime regularity, the absence of devastating floods and the fixity of its bed.”

In Lebanon, ¾ of the flow rate is due to inputs from the Aïn ez Zarqa springs with an average flow of around 11 m3/s, at an altitude of 650 m. Thus, the river regime in Al Qusayr, a small town located just upstream of the Qattinah dam lake, has all the characteristics of a mainly karstic watercourse regime. It has little inter-annual variations (the ratio between wet and dry years is 2 only). During the 1965-1973 period (dams have since profoundly disrupted the regime of the river), the minimum average annual river flow rate was at 14.8 m3/s, while the maximum mean annual rate was only 17.2 m3/s (Kerbé 1979). High waters start in June, averaging 16.5 m3/s, with a nearly four-month delay relatively to maximum rainfalls occurring in January-February; this is partly due to the melting of the snow on the Lebanon Mountains that feed the karstic springs. The Orontes then experiences the most marked arid climate in its course, which is part of the explanation for the preponderance of karstic inputs. Low waters, meanwhile, occur in September, with an average flow of 12.6 m3/s – still remarkably high because it is still supported by karstic inputs.

The area from Al Qusayr to Lake Qattinah is very little fed by inputs from tributaries that drain the southern and southeastern basin, located on the Anti-Lebanon eastern slopes and glacis. In this part, real tributaries have all but disappeared, due to the region’s marked aridity, sheltered as it is by the mountains: as a result, it receives less than 200 mm of precipitation per year. The Wadi Ar Rabi'ah is the biggest one, which drains the Qara and Hisya regions, and flows into the Orontes south to Al Qusayr. The southernmost part, fed by small karstic springs in the Anti-Lebanon, is traversed by the Al Majarr main wadi. The latter drains the Asal Alward area west of Rankus up to Yabrud and An Nabk. It then nearly dries up more or less in the arid lands of Northern Sadad and ends up in the Maydani wadi. The latter opens into the Orontes northeast of Ar Rastan and thus drains all the northeast of the Anti-Lebanon as well as the arid areas located east of Homs. Like in the area east of Al Qusayr, the intake is low here as it mainly depends on rainfall, already reduced over most of this region.

Flow measurement stations are rare on the river and no other data is available down to Shayzar. Reports then show lower intake with a specific module from 5.4 l/s/km2 at the entrance of the  Lake of Homs, only 2.77 l/s/km2 to the Al ‘Asharinah plain (Besançon and Sanlaville 1993, p. 17). However, it is worth pointing out that, though there are many tributaries on this section (on the left bank, the Nafseh and the Nahr as Sarut Wadis that flow down the Jabal al Hulw; on the right bank, the Maydani Al Kafat and Al Durat Wadis), their inputs are mostly due to the surfaces that lie there and add on to the main catchment basin, more so than to seasonal if not temporary flow-rates – always rather slow compared to yearly averages. In addition, springs, essentially from the Hama plateau drainage, are less numerous here. Consequently, the river regime is, in this section, more substantially marked by seasonality. Note that, on this plateau, some valleys have been barred with small dams, in order among other things to store water during seasonal runoffs, so as to sustain irrigation and groundwater supply. This is the case of the Al Kafat dam on the eponymous wadi, and of the one built across Zayzun on the eastern slope of the Al Ghab. There are 40 dams in the Orontes basin, almost all located in Syria (only the Tahtaköprü dam on the Kara Su and the Yarseli one on a tributary of the Orontes are in Turkey. In Lebanon, a dam has been scheduled downstream of the Aïn ez Zarqa springs). Two of them, among the biggest ones, are designed for energy production (Ar Rastan and Muhradah), while the Qattinah dam, along with 20 others, provide irrigation water. The others are used to control the flow. These are built across wadis, to store water, like the Zeita dam, whose particular feature is to be fed by the river also, just before the Orontes flows into Syria, through a canal. The three major dam storage capacity – Ar Rastan, and Muhradah Qattinah – is 200 to 500 million m3 per year.

Just after flowing past the Shayzar gorge and into the Al ‘Asharinah plain, its regime is again dominated by karstic inputs, and integrates waters from the great Tall Al’Uyun spring. The river flow is then set at 18 m3/s on average and is inflated due to the large number of springs flowing on the edges of the Ghab, fed from the coastal range on one hand and the Jabal az Zawiyah on the other. These springs average flow-rate is estimated at 13 m3/s (Abdulsalam 1990, p. 50). The mean annual flow rate of the river, out of the Ghab plain is about 40 m3/s. During wet years, the average maximum flow can reach 102 m3/s (1968-1969) while it may come down to 23.4 m3/s in dry years (Kerbé 1979). It should be noted that it is at high water (April-June) that agriculture water needs peak.

But the plentiful and relatively regular Orontes waters are not only beneficial. They also have a downside, in this region marked by the great number of depressions, rift valleys and deep depressions, where, due to poor drainage, water can accumulate, creating vast marshy wetlands that are repulsive until they have been drained. Even today, the drainage of the Ghab remains difficult during very wet years, despite all the work that has already been done (Besançon and Sanlaville 1993, p. 19). Finally, the Qarqur-Darkush narrow pass also brings its contribution to the river flow through sources fed from Jabal al Kosseir, Jabal al Wastani and the polje Ruj. It is through these gorges that the Orontes flows out of the area under study.

The volume of the Orontes waters, as it exits Lebanon, is estimated at 403 million m3, of which 80 Mm3 are allocated to Lebanon according to the Syro Lebanese water sharing agreement . The total water resources in the Orontes basin are estimated at 2340 Mm3/year, including inputs from Afrin and Kara Su. Where the Orontes flows into Turkey, the annual potential is 1400 Mm3/year (Droubi 2012).

The Orontes River accounts for about 13% of water resources in Syria, estimated at a total of 18,134 m3/year.

Groundwater Input

The Orontes basin is characterized by a complex geological structure and lithology. Rocks are generally very permeable, and deeply karstified: limestones and dolomites of the Jurassic and Cretaceous chalky limestone of the Paleogene. Even basalt, as it is fractured, feeds the groundwater. Fractures facilitate the resurgence of springs, especially on both sides of ditches.

The estimate of available groundwater in an aquifer is based primarily on estimating the recharge of these waters by precipitation or directly from rivers. Due to average (400 to 500 mm/year) rainfall inputs, (except in the east of the Hama Salamiyah axis, where the basin sinks into arid margins in the northern Beqaa and in the south-eastern Syria part in the region of Al Yabrud and An Nabk) and the good permeability of geological formations, most groundwater in the Orontes basin may be considered as renewable. Indeed, a recent study (ACSAD, 2012) estimated the recharge of groundwater at about 2,441 Mm3/year.

Springs total flow-rate is estimated at 275 Mm3/year. The Al Ghab region is considered the richest in groundwater throughout the Orontes area basin. It receives about 782 Mm3/year in renewable recharge, in addition to about 568 Mm3/year lateral flows from surrounding areas. In total, groundwater resources are about 1350 Mm3/year (ACSAD, 2012).

Therefore, groundwater is said to feed about 90% of the total runoff of the Orontes basin, mainly thanks to karstic springs, the main one being the Aïn ez Zarqa spring, but also the Al Ghab springs; these gush out at the foot of the eastern slopes of the coastal range, the biggest ones being Nab` al Barid (0.94 m3/s) and Ayn al Fawwar (0.93 m3/s). Finally, groundwater is deemed able to provide approximately 56% of water needs for agriculture in the whole basin of the Syrian Orontes, where the irrigated area is estimated at about 85,000 ha (Alchami, 2000). 


References

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