Posted December 1998
Remote Sensing Officer
Environment and Natural Resources Service (SDRN)
FAO Research, Extension and Training Division
with the cooperation of
General Organization of Remote Sensing
Syrian Arab Republic
from "Groundwater exploration by satellite remote sensing in the Syrian Arab Republic", RSC Series 76, FAO 1998
< continued from Part 1
For the purpose of this study, the coastal area is the landmass occurring between the Syrian mediterranean coastline in the west and the depression of Al-Ghab in the east, southward it is bounded by the Lebanese border and in the north by the Eskandaron region. The area considered has an approximate length of 140 km in the N-S direction and of 40 km across, thus covering 5600 km2.
Its morphology varies widely from place to place, but the main features are the coastal alluvial plain, quite wide south of Lattakia; the low basaltic hills in the south and along the coast near Banyas; the gently undulating marl hills; the dissected ophiolitic plateau north of Lattakia (not studied by the project); and the rugged carbonate mountainous terrain. Deep valleys criss-cross the area, usually related to faulting. The coastal area has an average elevation of 1200-1300 m in its eastern border (maximum elevation 1 520 m) and a general dip westward, that is toward the coastline.
Geologically, the coastal area is an uplifted block (monoclinal) bounded on its eastern side by the north-trending faults separating it from the vast depression where the fertile, recently reclaimed Al-Ghab Plain occurs. The abrupt escarpment separating it from the plain (elevation 170 m asl) rises in two or three steps to an average height of 1300 m. Considering the lithologic sequence and the thickness of the marls (300 m) which have been eroded away, the total throw of the fault system is estimated to be around 1 400 m.
The landmass, however, is not a unique block, as other regional faults, mostly trending NE, have subdivided it into smaller blocks, each with its own general dip. This subdivision should be properly considered when reconstructing groundwater movement, as each block is a separate unit.
Rainfall is concentrated in the winter months and increases eastward, as to be expected considering the morphology of the area, from 800 mm near the coast to 1400 mm in the mountainous area.
From a lithological/stratigraphic point of view, the landmass is made up of a very thick carbonate sequence, capped by basalts in its southern half and transgressively overlaid by marls in its northern half. A clear tectonic line, trending NE, subdivides the landmass in roughly two equivalent portions.
The carbonate sequence which constitutes the core of the landmass and defines its main morphological aspects, consists of an alternance of dolomite, dolomitic limestone and limestone, usually thick bedded to medium bedded with flint nodules on some formations, ranging in age from Mid Jurassic to Mid Cretaceous. Thickness averages 1 200 meters. Some marl horizons, sometime of considerable thickness, occur in the formations of Mid Cretaceous and thick basalt and tuff interbeds in Lower Cretaceous. Those marl and basaltic interbeds, where occurring, define the lower surface of localized aquifers and consequently numerous springs occur along their contact.
Upper Cretaceous and Eocene are essentially made up of marls, with limestone intercalations. These are outcropping in the central-coastal portion of the landmass with a general dip seaward, as because of the westward tilting of the uplifted block, they have been eroded away at the higher elevations. Thickness of the marls averages 250-300 meters. This stratigraphic situation creates the conditions for the occurrence of confined aquifers, however, as will be reported later, much better possibilities for groundwater extraction are available in the area.
Finally, Pliocene consists of basalt, basaltic tuff lava and volcanic breccia, of an average thickness of 100 meters, occurring in the southern part of the coastal area toward the border with Lebanon and along the coast, mainly near Banyas.
Extensive karst phenomena are evident in all areas where limestone and dolomite outcrop. As a consequence, notwithstanding the considerable amount of rainfall, water is scarce to unavailable in the rugged mountainous terrain of the interior, with the exception of the places where springs occur at the contact between the basalt or the marl interbeds with the overlaying limestone/dolomite sequences.
The coastal area, as described above, offers to the hydrogeologist a variety of different scenarios for groundwater search. However, as the purpose of the study was the development of remote sensing/GIS methodologies suitable for this kind of terrain, the team concentrated its activities in two sectors, namely 1) the possibility of exploiting the large amounts of fresh water now lost to the sea from springs on the seabeds not far from shore; and 2) the carbonate interior.
Landsat TM data, acquired at the end of the summer were preferred to reduce the masking effect of the vegetation cover. ERS-SAR data were interpreted for terrain and lineaments analyses.
|Landsat TM||path/row||acquisition date|
|174/35||21 September 1995|
|174/36||21 September 1995|
|ERS-SAR (geocoded)||track/frame||acquisition date|
|078/2889||14 July 1996|
|078/2907||14 July 1996|
It is well known that large springs occur along the shoreline and that fresh water springs exist on the seabed, not far from shore. Large amounts of freshwater are thus lost to the sea. Objective of the activities was, therefore, to identify the "waterways" and indicate the most promising sites for drilling inland, so that water can be tapped before it is lost. To achieve this, as a first step it was thus necessary to identify the fresh water springs on the seabed.
Digital enhancements of the thermal band of Landsat TM showed large, cold anomalies in the sea, usually at 1-2 km from the shoreline. Although the thermal channel of Landsat TM was not the most suitable for this kind of work, due to its large resolution (120 m.) and hour of acquisition, the phenomena were evident on the September data. To enhance those features a mask was thus created and only the thermal data of the sea portion were stretched. Pseudo-colour density slicing followed, to evidentiate the coldest anomalies. Field interviews with local fishermen confirmed that the anomalies correspond to large submarine freshwater springs.
Lineaments analysis was thus performed on Landsat TM data, both visually on 1:100 000 scale prints of FCC 453 (RGB) or directly on the computer screen on a series of data, such as the above FCC and single near-mid infrared bands (bd. 4-5). Routine enhancements were applied. ERS-SAR data were also used for lineaments detection, however lineaments detected through radar data were later reported on TM images, due to the lay-over of the radar data and thus their geometric distortion in the mountainous terrain. The full collection of lineaments, as obtained from the above analyses, was thus compiled on one map after checking and removal of the questionable lineaments. This was thus inserted into the GIS as "lineaments layer".
Having located the submarine springs and inserted this information into the GIS ("thermal layer"), the information on lineaments extracted from analysis of Landsat TM and ERS-SAR was superimposed ("lineaments layer"). As expected, a complete correspondence was found between submarine springs and lineaments, the springs being located on the seaward extension of well defined lineaments identified inland.
A "drainage layer",created with information essentially extracted from topographic maps, was also available in the GIS and used in conjunction with the "thermal layer" to eliminate anomalies due to river discharge into the sea. However, in late September only a few rivers carry enough water to the sea to cause substantial cold anomalies.
To avoid any problem due to changes in scale, all GIS layers were at the same scale of 1:100 000.
To tap the water now lost to the sea it is thus just needed to drill along selected lineaments, our "waterways". Consequently potential drilling sites were selected 2-3 km inland, located by GPS and field tested by geo-resistivity investigations (Schlumberger method).
|1||Sheikh Saad||34 55 80||35 55 33|
|2||Sheikh Saad||34 55 63||35 55 33|
|3||East of Tartous||34 55 12||35 54 24|
|4||East of Tartous||34 55 82||35 53 63|
|5||Zamrin||35 00 63||35 54 55|
|6||Banyas||35 13 45||35 58 20|
All tests indicated the occurrence of large amounts of groundwater in the fracture zone. Many other sites resulted as good potential drilling places, but the objective of the study was only to identify and field test a methodology, the operative implementation of it being left to the relevant government departments.
The correlation between cold anomalies in the sea (submarine springs) and lineaments is thus permitting the identification of drilling sites inland to tap and thus use the water before it is lost .From the size and number of the thermal anomalies, it is assumed that huge amounts of water are now discharging to the sea.
In September 1997 a Russian company under contract with GORS has completed a low altitude thermal scanning along the Syrian coastline. This method permits quantification of discharge. All cold anomalies have been thus mapped in a very accurate and detailed way and by applying the methodology indicated by this project it will be possible to identify many more sites suitable for drilling. Comments
In the Tartous area large alluvial fans occur at the lower portion of each valley which then overlap to form a large alluvial deposit. This is recharged by groundwater moving in large quantities in fracture zones and also through karst channels. Farmers have drilled innumerable wells in the alluvial deposit, with very good results, for irrigation during the dry months. Outside the alluvial area, wells drilled to supply water to towns have very good production and not level fluctuation even if pumped continuously when they happen to be on a fracture zone ("waterway"), otherwise they are dry or almost dry. The vast majority of the wells in the area has, and is, drilled wildcat. Information on wells number, location and production is scanty or lacking altogether.
Just south of Banyas, the limestone dipping toward the sea is capped by thick basalt. The large aquifer occurring in the limestone (karst channels and fractures) is thus confined in this area. Many private and highly producing artesian wells with an average depth of 120 m exist in this area. Seaward, several submarine springs and corresponding thermal anomalies occur.
Northward, the large alluvial plain south of Latakia, extensively used for agricultural production (citrus, vegetables, etc.) is dotted by thousands of private wells used for irrigation during the dry months. Again, number, location and production of wells is practically unknown.
Large springs, clearly related to faulting, occur at the foot of the carbonate sequence, not far from the coast, such as the Banyas (2 000 l/s), Surit, Sanet Springs and the huge Es Sinn Spring of an average discharge of about 12 000 l/s. Water from this spring is piped to supply the towns of the area and the excess is used for irrigation of the adjacent plain.
From the above, it is evident that the seashore area has already the necessary water resources for domestic and irrigation purposes, with the exception of a few well defined areas. Still the huge amounts of water presently lost to the sea can be tapped to supply the thirsty carbonate interior and/or rationalize the present water distribution system.
Severe problems of sea water intrusion occur in the Hamidyeh coastal plain, near the border with Lebanon, and north of Lathakia. This is due to uncontrolled over-exploitation of the limited aquifer occurring there by the farmers and also to the fact that boreholes are dug in a wildcat fashion. Without adequate action, land degradation (salinization) will reach a level in which agricultural production will be severely impeded. The project has identified in the Hamidyeh area a "waterway" which may supply the necessary irrigation water, thus eliminating the above problems. Further field investigations and test drilling should thus be carried out in this area. The project has not studied the area north of Lathakia, but it will clearly be worthwhile to apply the same methodology there.
As indicated, the rugged mountainous terrain of the coastal landmass is made up of an alternance of dolomite, dolomitic limestone and limestone, with marl interbeds mainly in the upper part of the lithological sequence. Thick marl horizons in Mid Cretaceous and basalt and tuff interbeds in Lower Cretaceous define the lower surface of localized aquifers and cause numerous springs. Permanent surface drainage usually rests on those impermeable beds. Extensive karst phenomena are widespread in the limestone and dolomite outcrops with typical surface expressions such as lapiez, dolines, etc. Water infiltration is consequently very high. Towns and villages occur around the springs indicated above, but usually water availability is limited due to the karst phenomena.
It is well known that fracture traces and lineaments are important in rocks where secondary permeability and porosity dominate and where intergranular characteristics combine with secondary openings influencing weathering and groundwater movement.
Latthman and Parizek (1964) established the important relationship between the occurrence of groundwater and fracture traces for carbonate aquifers and in particular that fracture traces are underlain by zones of localized weathering and increased permeability and porosity. Fracture traces and lineaments are likely to be areas of secondary permeability and porosity development in carbonate rocks. The fracture zones form an interlaced network of high transmissivity and serve as local groundwater conduits from massive rocks in interfracture areas. Thus, as fracturing greatly increases the solution of limestone and dolomite, creating preferential avenues for groundwater movement, there is not a real need, in theory, to discriminate among lineaments; the basis for the selection, in a carbonate area, of a suitable place for groundwater development, including the necessary field investigations, is the occurrence of a well defined lineament along which topographic lows should be selected, according to accessibility and local water needs. The above concept should be, of course, adjusted to local situations. For the study of the carbonate interior, the greatest part of the needed information was already stored in our GIS, namely the lineaments ("lineaments layer") and the surface drainage ("drainage layer"). Three new layers were added to the system to have the basic information necessary for selecting promising areas for further field investigations, namely the "geology layer", the "blocks layer" and the "towns and village layer".
The "geology layer" was compiled from the geological maps of the area at scale 1: 50 000, extracting only the boundaries between the main lithological sequences (limestone/ dolomite, marl, basalt). As the stratigraphic position of each unit was known, the purpose of this GIS layer was to visualize the rocks outcropping in each area.
The "blocks layer" constituted probably the most important input into the GIS for the task of locating promising drilling sites. As indicated in paragraph 3.1 Area description, the coastal landmass, an uplifted block with a general dip westward, is not an unique block, as other regional faults, mostly trending NE, have subdivided it into smaller blocks, each with its own general dip. Thus, lineaments trending according to the dip of the block are evidently the most suited for subsequent investigations as they constitute the preferential avenue for groundwater movement, further they should collect all groundwater moving along the other lineaments they intersect and also from eventual surface drainage they intersect at higher elevation. All groundwater moving along the above lineaments should then reach the regional faults bordering the block and precisely the one which constitutes the topographic low of the system (Fig.5).
Fig. 5: Tectonic "blocks", southern portion
In this scenario, this fault is a real "waterway" as it drains all groundwater moving in the block and is, thus, the best place for groundwater search. This working hypothesis is confirmed by the occurrence of the huge Es Sinn Spring (average discharge 12 000 l/s) resting on one of these main faults and by the presence of the largest thermal anomalies on the seaward extension of the border faults.
The "blocks layer", as input into the GIS, included the regional faults bordering the blocks and the general dipping of each block, this last evaluated by remote sensing data and/or extracted from geological maps.
The "towns and villages layer" was included into the GIS to facilitate the work. It represented the location of towns and villages in great need of water supply, thus the search for promising groundwater sites will be concentrated only around them.
In selecting the above towns and villages, those in the eastern part of the landmass, that is not far from the escarpment, were not included for technical reasons, although they are in dire need of water. Actually, several faults and fractures, orthogonal or inclined in respect to the main tensional fault system trending approximately NS which has uplifted the coastal landmass, with the increased weathering and solution of the carbonate rocks along them constitute preferential avenues for the groundwater movement and drain the area toward the lowlands of the Al-Ghab Plain. As a result large springs occur at the foot of the escarpment and in the fault-controlled valleys intersecting it. In this framework, there is no possibility of locating good groundwater sites around the above towns and villages, which should be supplied by pumping up the water from the springs at the foot of the escarpment, as it is correctly being done.
By combining, on a place to place basis, the information contained in the GIS layers it was possible to locate preferential sites for further field investigations around selected towns and villages. Sites were selected either on major lineaments trending according to the dip of the block in which they occurred, downward of intersection with other main lineaments or surface drainage, or on the main lineaments bordering the lowest side of the blocks, our "waterways".
Once the potential drilling place was selected, a further evaluation of it was done by checking on topographic maps at 1: 100 000 scale the site accessibility. All potential sites of difficult accessibility were then disregarded. The finalized list of sites selected for geophysical investigations is reported in Tab. 5.
|1.||East of Ain Al-Tahon||34 50 28 75||35 58 09 70|
|2.||Al-Qounsieh (A)||35 01 21 37||36 02 41 84|
|3.||Al-Qounsieh (B)||35 01 01 84||36 02 39 87|
|4.||Jebab||35 03 32 55||36 01 11 37|
|5.||Al-Qadmos||35 05 48 28||36 09 03 17|
|6.||Al-Hataniah||35 09 00 33||36 04 25 64|
|7.||East of Mailas Khirbet||35 18 46 22||36 11 02 11|
|8.||Saker House p.||35 18 49 48||36 07 00 26|
|9.||Al-Qardaha||35 27 53 06||36 01 47 05|
Geo-resistivity tests orthogonal to the lineament trace, undertaken according to the Schlumberger method at Al-Qounsieh (A and B) provided very good results. Climatic conditions impeded the undertaking of geo-resistivity tests in the other sites. These will, however, be effected as soon as possible.
The project, through cooperative arrangements with local institutions, was supposed to have two/three test wells drilled at sites selected according to the methodology previously indicated. This, however,did not happen for time constraints. Well drilling will most probably be done in the near future, too late to be reported here.
Well drilling, in case of positive results, will have proven beyond doubt the correctness of the approach followed. The positive results of the geo-resistivity tests in Al-Qounsieh provide, however, a good indication of the expected drilling outcomes.
Furthermore, two wells drilled by a private company in Lower Cretaceous basalt outcrops at sites selected by the project according to a slight variation of the methodology indicated, were highly successful. There is thus scope to be confident that the wells when finally drilled at the sites indicated will be positive.
An important issue which should be properly considered by the relevant authorities is the safeguard of the aquifers of the area from pollution. In the heavily fractured karst terrain of the carbonate interior, groundwater moves, sometimes in large quantities, along karst channels, caves and fissures often occurring as the result of preferential weathering and solution of carbonate rocks along faults and fractures. Infiltration is mainly from sinkholes, solution cavities and fissures in the rocks. In this situation groundwater can be easily polluted by incorrect waste disposal or by untreated sewage from towns and villages, with subsequent severe sanitary risks.
The project has developed, tested and finalized groundwater search methodologies suitable for three different environments and based on satellite remote sensing, GIS and field investigations, including geophysical tests.
In the basaltic terrain of southern Syria, where morphological expressions of faults and fractures are rare, satellite data acquired in spring and summer allowed for the mapping of many lineaments believed to be associated with near vertical faults and fractures and thus with groundwater movement. The statistical study of the lineaments indicates that the greatest part of them trend N65-70E. This is likely to be a direction of tensional fracturing and, thus, of "open" fractures along which groundwater moves.
Overlaying of location of springs and wells producing above average to the above lineaments shows an almost perfect coincidence. Following the methodology indicated in paragraph 2.2, the project has identified a large number of potential drilling sites, but preference has been given to the Assuwayda Province, where the difficulties of locating groundwater are greater and the water supply is short..
Along the Syrian coast, large freshwater springs occur in the seabed not far from shore and thus large amounts of water are lost to the sea. The study of the thermal anomalies caused by the occurrence of these springs permitted their identification. It was noted that these submarine springs rest on the seaward extension of lineaments mapped inland and consequently potential drilling points were identified on these lineaments to tap the water before it is lost to the sea. From the number and size of the thermal anomalies it is estimated that huge amounts of freshwater are now lost to the sea that may be tapped to supply the towns in the thirsty carbonate interior or to rationalize the present water distribution system.
Finally, the project developed a methodology to locate promising groundwater sites in the central-western part of the coastal carbonate interior, to supply towns and villages of this region with the necessary water. The working hypothesis of the "blocks" constitutes the core of the methodology, but it should be field checked and confirmed by further investigations.
Over-exploitation of the aquifer by farmers in the Hamidyeh coastal plain is inducing saline water intrusion with negative effects on the agriculture being experienced and with much more disastrous effects in the future (soil salinization) if the trend is not reversed. The project has identified in the area a "waterway" along a lineament which may provide the needed irrigation water. Further study is thus recommended for the above.
Groundwater moving in fractures, joints and fissures in the southern basalt area and in the karst channels and fissures in the coastal carbonate landmass may be easily polluted by waste disposal and defective sewage systems of towns, as well as by herbicides, pesticides and fertilizers in the agricultural areas, with resulting severe health risks for the users. A monitoring system of water quality is thus recommended, as well as a survey of the main pollution sources.
In studying the southern and coastal areas we saw an incredible number of wells drilled by farmers and other users according to their specific needs. On the other hand, information on wells is rather obsolete, incomplete or missing altogether. In this framework it is time-consuming and possibly inaccurate to estimate the water balance of the aquifers through indirect extrapolations, further, over-exploitation of the underground water resources is a concrete risk. The sharp decrease of the discharge of the Mouzerib Spring near Daraa in the last years clearly indicates an increased and uncontrolled water tapping through wells upland in the basin. It is thus necessary to make a new inventory of all private and public wells, mainly in the southern basaltic area, collecting all relevant information such as location, use, depth, depth of water table, average production, etc., in order to quantify the groundwater resources available and thus prepare a master plan for their rational utilization.
The methodologies developed by the project and described in this report may be further applied in similar environments in Syria, as well as in other countries where the geological factors affecting groundwater storage and transmission are comparable.
This study undertaken in Syria clearly indicates that the integration into a GIS of data extracted from satellite imagery interpretation with those traditionally gathered, coupled with selected field investigations and the geological knowledge of the area under investigation, provides a powerful tool in groundwater search.
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