oa Using GIS to Quantify Change in the Groundwater Levels in Qatar Between 1980 & 2009

Since early 2000s Qatar has been relying heavily on desalinated water from the Arabian Gulf as the main source of fresh water. In the case of natural disasters in the Gulf such as the red-tide phenomenon, or man-made disasters such as oil-spills, Qatar would not be able to desalinate water even for days never mind the months that some disasters would bring about. Qatar is very vulnerable to such disasters, and at present does not have the strategic reserves of fresh water. The current reserve capacity is for only two days. Two days is definitely not enough. For example, in the case of the oil spill in the Gulf of Mexico it took 36 days to clean the water before it could be usable. Another example is the 2008–2009 red-tide natural disaster that lasted for more than eight months and forced the closure of desalination plants in the region for weeks.

In addition the groundwater systems in Qatar are heavily exploited mainly for irrigation purposes. The over-abstraction has resulted in the deterioration of water quantity and quality (due to seawater intrusion). Therefore, groundwater in its current state would be unusable in the event of water shortages caused by disasters in the Arabian Gulf. Large scale artificial aquifer recharge plans have been proposed in order to provide strategic reserve in emergencies. The goal of this plan would be restore the 1980s groundwater levels, through artificial recharging.

GIS is used in this study to map change in the levels of the groundwater between 1980 and 2009, using potentiometric surface data, in order to identify potential recharge zones/areas. Such information is key in any aquifer recharge project that aims to restore the aquifers and use them as strategic water reserve in the event of water shortage emergencies. This study focuses on the upper aquifer in Qatar - the Al Damman aquifer.

The environment of Qatar is desertic with no surface water and very little rainfall. In 2014 the average natural water resources from rainfall was less than 29 cubic meters per year per capita (m³/y/ca), compared to the global average of 6,000 m³/y/ca, and a water poverty line of 1,000 m³/y/ca. However, Qatar per capita water consumption is among the highest in the World, reaching more than 500 liters per person per day, whereas the global average is about 160 liters per person per day. This high per capita consumption in Qatar is attributed to rapid urbanization and changes of living standards since the early 1980s. Qatar's Gross Domestic Product (GDP) has increased from 23.5 billion USD in 2003 to 211.8 billion USD in 2014. This economic boom that has put tremendous pressure on the groundwater resources, as population increased. This pressure was caused by the rapidly increased farming activities embarked upon in order to meet the food demand of the rapidly rising population. Another reason for the increase in farms is a consequence of it reflecting the social status of its owner. Qatar's population increased almost five times from 0.37 Million to 1.74 Million between 1986 and 2010, and six times between 1986 and 2014. Groundwater withdrawal by irrigators has occurred. Figure 7 shows abstraction for irrigation increasing from 100.3 Mm³/yr in 1983 to 248.73 Mm³/yr in 2009. The groundwater abstraction rate highly exceeds the natural replenishment rate of 58 Mm³/yr from rainfall, hence groundwater levels drop.

In 2009, about 99.9% of the total potable water, produced by the Qatari water company (KAHRAMAA), was desalinated while only 0.1% was from groundwater. Desalinated water production has increased four-fold between 2003 and 2011 (from 0.44 to 1.48 million m³/day).

To identify change in groundwater level two potentiometric iso-maps of the Al Dammam aquifer for the years 1980 map were acquired in a hardcopy format. The two maps were first converted from hardcopy format to digital format by scanning, in order to enable manipulation in the GIS system. The two scanned digital images were then geo-referenced to the Qatar National Grid 1995 (QNG 1995) coordinate system, using known ground control points and ArcGIS system. Then the images were digitized by tracing the potentiometric contours/isolines in each map, converting them into vector lines. Potentiometric values were assigned to their respective vector lines. The line-or vector -is then converted to point data. Interpolation techniques enabled the generation of a continuous surface (raster) to be able to compare the cell values of the same location of the two data sets.

Spatial interpolation techniques were used to create continuous raster surfaces in order to compare the two datasets from 1980 and 2009. Two main groups of surface interpolation techniques are available in the GIS environment: deterministic; and geo-statistical. Deterministic interpolation techniques create surfaces from measured points, based on either the extent of similarity or the degree of smoothing. While geo-statistical interpolation techniques utilize the statistical properties of the measured points. Geo-statistical techniques quantify the spatial autocorrelation among measured points and account for the spatial configuration of the sample points around the predicted locations.

Based on the nature of the data available for this study and its spatial distribution geo-statistical interpolation was preferred over deterministic techniques. The Ordinary Kriging method of geo-statistical interpolation was chosen as it provides accurate interpolation with minimum standard error. Two potentiometric raster surfaces for 1980 and 2009 were interpolated. The 1980 surface was then subtracted from the 2009 surface in order to calculate the change in groundwater level between the two years.

Two potentiometric raster surfaces for 1980 and 2009 were interpolated. The 1980 surface was then subtracted from the 2009 surface in order to calculate the change in groundwater level between the two years. The difference map shows areas where groundwater level dropped between 1980 in 2009.

To help better interpret the results, the map was overlaid over a 2013 Landsat 8 satellite image, from the Enhanced Thematic Mapper Plus (ETM+). The overlay showed major level increase in and around Doha, is clearly caused by: seepage from unlined treated sewage water dumping lagoon at Abu Nakhlaa- south-west Doha; and leakage from water distribution network in Doha. Some increase also identified in south Qatar due to pivot-irrigation systems using recycled treated water.

Areas with groundwater falls in level by 4 meters and more were considered as having high artificial injection potential. The 4 meter drop was selected to avoid possible Land-Surface Deformation (LSD) by having enough space for the recharge. A few centimeters of LSD could have serious consequences for high rise buildings in Doha City, Such deformation causes cracks and damage to these buildings if the ground moves. LSD also damages water and sewage network pipe-joints and fittings, exacerbating the water-leakage problem in Doha, resulting in the water-table rises in the city. The rising water table in Doha has become a serious issue as it impedes the digging of foundations. Expensive de-watering procedures are required and special coating for the foundations which add to the construction costs. Furthermore, water leakage implies more desalinated water needs to be produced in order to substitute for the lost waters, and hence more vulnerability to disasters in the Arabian Gulf.

Some central areas, despite the high potential recharge volumes, are suggested to be excluded from the recharge, to avoid raising the groundwater levels in Doha City. In Qatar, groundwater flows radially outwards from recharge areas, centered over the higher Qatar Anticline land that plunges to the north and to the south with a surface expression of a broad shallow dome. The water discharges into the adjacent low-lying land along the coast and the Arabian Gulf. Recharging these areas will increase the flow towards Doha, down the groundwater gradient.

Another reason for excluding these central areas is that the area has a large number of sink-holes. These karst features are produced by the dissolution of subsurface gypsum beds during humid and wet periods in the Pliocene and Pleistocene period. Filling these gypsum formations with freshwater is very likely to cause re-dissolution, and hence the collapse of ground surface.

The results present essential information that could be further refined through field work and groundwater survey. Further modeling of the groundwater movement and dynamics using monitoring wells data will also be completed.

Soil permeability and soil types analysis in the area are need to carry out the analysis of the recharge areas.

It is also recommended that an interferometry study, using polaromteric RADAR surveys, be completed before, during and after the artificial recharge in order to monitor possible land surface deformation.

GIS proved to be a very effective tool in assessing disaster preparedness, management, and prevention as it helped in determining the potential recharge areas that could be used for strategic water reserve.