Specials Environment

Updated April 1999

Special: Remote Sensing for Decision-makers

Groundwater exploration

Pilot study in the Syrian Arab Republic


Introduction | Aquaculture | Forest management | Rangeland assessment | Groundwater exploration | Forest fire management | Forest decline assessment | Crop information systems | Inventory and monitoring of shrimp farms


Groundwater exploration over vast areas by traditional means (geological studies and geophysical investigations) may require extensive human and financial resources and considerable time. Yet agricultural development through irrigation of underexploited lands and the provision of drinking-water to rural areas are often urgent tasks requiring rapid identification of water resources and particularly groundwater.

The integration into a geographic information system (GIS)2 of data extracted from earth observation satellites with those traditionally gathered, coupled with selected field investigations, provides a rapid and powerful tool in the search for groundwater.


High-resolution satellite imagery

The operational availability of high-resolution satellite imagery, namely Landsat Thematic Mapper, SPOT, Soyouz, ERS-SAR and others, opens up new possibilities for the assessment of groundwater resources. Compared with information acquired by traditional methods, these data offer a number of advantages:


Case study in the Syrian Arab Republic: locating potential drilling sites

In view of the distinct environments occurring in the country and in order to test new approaches and methodologies fully, two different hydrogeological environments were selected.

Basaltic terrain of southern Syria.

Since groundwater storage and transmission in this hard rock terrain are related to the basalt cracks and joints caused by cooling and, particularly, to tectonic fractures, remote sensing data were basically used for mapping the fractures that occur there. These were later statistically analysed to identify the tensional "open" fractures, the most promising for the storage and transmission of groundwater. The integration by GIS of satellite-derived information with other data such as the location of springs and wells with above-average production and the drainage network resulted in the identification of several potential drilling sites, which were subsequently positively tested by georesistivity investigations. A well was then drilled at one of these sites, with positive results.

Coastal area.

It is well known that abundant springs occur along the Syrian coast and that freshwater sub-marine springs, often discharging huge quantities of water, exist on the seabed not far from the shore. Large quantities of freshwater are thus lost to the sea.

The 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. Digital enhancements of the thermal band of Landsat Thematic Mapper allowed for the identification of large, cold anomalies in the sea, usually at 1-2 km from the shoreline.

Fractures were then identified, also from satellite data interpretation, on the coastal carbonate landmass. The integration of these data in a GIS indicated that the cold anomalies (sub-marine springs) were on the seaward extension of well-defined fractures. A drainage network layer was also inserted into the GIS to eliminate anomalies caused by river discharge at sea. Having identified the "waterways", potential drilling sites were selected 2-3 km inland and positively tested by georesistivity investigations.


Thermal anomalies at sea north of Tartous

  

GIS overlaying of wells, springs and lineaments


Landsat Thematic Mapper, 174/37, of 18 May 1996, FCC 453 (RGB)


Evaluation and recommendations

Costs and delivery times

 Costs (US$/km2)Time (months)
Acquisition of satellite data1.01.0
Image processing and interpretation0.82.0
GIS0.51.0
Ground survey0.50.5
Geophysical investigations0.30.5
Map preparation/reporting0.61.0
Total3.76.0

A cost-effective technique

The greatest part of the time was dedicated to the development of appropriate methodologies and to testing the relevant image processing techniques. This part can be shortened in subsequent applications. We estimate that under operative conditions costs may be in the range of US$2.5-3.5/km2, depending on the difficulties presented by the area under investigation. This low-cost approach is further enhanced by the accuracy of the results and by the great reduction, compared with traditional techniques, of ground survey and geophysical investigations.

Recommendations

The methodologies developed by the pilot project in the Syrian Arab Republic may be operationally applied in other similar environments of the country as well as in other countries where the geological factors affecting groundwater storage and transmission are comparable.

This project was carried out by the General Organization of Remote Sensing (GORS) of the Syrian Arab Republic, assisted by the FAO Environment and Natural Resources Service, in the framework of project TCP/SYR/6611.