Page 3 of 3 Previous 4. Major fault structures, since a linear river system controlled by graben-like structures is more likely to contain thick, multi-layered reservoirs, particularly if it sits downstream from a source of gravel or water-storing material. The ideal scenario is an old, well-framed riverbed with reliable and unchanging watercourse, downstream from a high-quality reservoir feeder. Figure 3 shows the distinct fault structure that frames the Wadi Dalal.  Fig 3 - Processed image showing the course of the Wadi Dalal framed by a distinct fault structure, several kilometers long. The campsite is now located on a platform capable of hosting 30,000 refugees safely above the seasonal flood plain. 5. Slope of upstream wadi course, since the optimum riverbed slope needs to be between 0.1% to 0.4%, in order to ensure sufficient vertical recharge of reservoirs within wadi courses (Ragot 2004). (Too shallow a slope, and the reservoir can be prone to excessive silt accumulation, compromising its ability to store sufficient water reserves. Too steep a slope, and the reservoir can be prone to the erosion of the gravel bed that must recharge during the rainy season.) As illustrated in Figure 4, the Wadi Dalal has an average slope of 0.218% over its course upstream of the reservoir.  Fig 4 - SRTM-derived slope profile of the Wadi Dalal Once the five parameters listed above were understood, it was then possible to make an overall assessment of the most promising sites. In order for these areas to be suitable for UNHCR camps, RTF considered the implications of refugee resettlement near areas of existing cattle ranching, crop farming, and indigenous settlement. UNHCR-mandated restrictions on resettlement (within 50 km of the Sudan border) were buffered, and sites that were close to roads and wood fuel sources were prioritized. Reservoirs with high suitability were then examined to ensure close proximity to a suitable camp platform, since the Sphere Humanitarian Charter recommends that refugees be within 500 meters of at least one water point (The Sphere Project 2004).  Fig 5 – Total collapse of well infrastructure due to seasonal flood erosion, near the village of Abdi in eastern Chad. This can be prevented by locating production wells outside of a wadi, along fractures fed by the wadi’s deep reservoir. The final step of the analysis was to identify drilling locations around high quality sites that were away from the central aquifer and towards the edge of the containment fracture. As illustrated in the above photography, the construction of well platforms directly in the path of wadi flow can be disastrous. Well damage due to flood erosion can be avoided by mapping the fault structure immediately adjacent to an aquifer but away from the wadi channel, and locating well platforms away from actual river flow. Results This project demonstrates that geospatial analysis, when merged with geological and hydrological exploration methods, enables the water potential in arid and semi-arid regions to be accurately estimated. It also minimizes the need for costly, time-consuming, and often hazardous ground surveying. Based upon approximately 540 drilling sites throughout Ouaddaï, RTF’s WATEX process could have theoretically improved drilling success rates from 42% to 89% if it was available during earlier water exploration programs in the region. (Calculated by comparing WATEX-derived “high potential areas” with the water drilling results of the Chad Hydrological Survey and various NGOs in the past (Ragot 2004).) Key evidence of the efficacy of the process is the UNHCR’s selection of a new location to construct a major refugee camp along the Wadi Dalal, based upon the analysis provided (Chamberlain 2005). The Wadi Dalal settlement of Gaga is about 60 km east of Abéché, and was recommend because of its exceptional combination of characteristics.  Fig 6 – Location of the three exploration wells drilled in March 2005. Based upon the actual well productivity, the UNHCR decided to resettle up to 30,000 refugees to the area. As predicted, drilling confirmed that it contained a thick, high-quality gravel reservoir fed by a large volume of water. In February 2005, prior to the UNHCR’s decision to begin construction of the new refugee camp, RTF estimated that at least 20,000 people could be situated on a platform adjacent to the potential reservoir, based upon estimated water reserves (Gachet 2005). OXFAM, who carried out the drilling, confirmed RTF’s prediction with three successful exploration wells drilled in March 2005, and in May 2005 the UNHCR resettled 200 refugees to the newly-established camp, announcing that the site had the capacity to shelter up to 30,000 refugees to the area (IRIN 2005). Although the above results are impressive, a comprehensive empirical study of the efficacy of WATEX has not yet been undertaken, primarily due to the practical limitations in carrying out such an assessment in an area as remote and insecure as eastern Chad. It is also important to remember that WATEX dramatically reduces but does not eliminate the need for in situ geological survey. Ground penetrating radar, test drilling and field survey are still important elements in the groundwater exploration process. Conclusions WATEX is an innovative, holistic approach to groundwater exploration, involving a fusion of humanitarian intelligence, hydrology, geology, and geospatial analysis. This interdisciplinary approach significantly reduces the risk and cost of water exploration, and limits ground survey to only areas with high water potential. There is always, of course, some level of risk in water exploration even with extensive geophysical investigation; but in conditions of humanitarian urgency, scarce resources, and inaccessible and massive areas of interest, WATEX has a demonstrated ability to enable humanitarian agencies to identify suitable areas for resettlement and meet international standards for water access. The overarching goal of this project was to discover major water reserves on potential campsites capable of hosting up to 200,000 refugees. And while it is too early to know if that goal will be fully achieved, the experience to date with Wadi Dalal is extremely encouraging. Future applications could include irrigation planning and micro dam construction, which are symbiotic with the methodology employed by the process described in this article and in support of longer-term resettlement initiatives. Acknowledgements The authors dedicate this article to the late William B. Wood, Deputy Assistant Secretary of the US Department of State and The Geographer of the United States. Dr. Wood was a major source of inspiration and motivation during the earliest stages of this project, and it was with his encouragement in May 2005 that this article has been produced. The authors join many others in expressing deep gratitude to NASA and the USGS for facilitating collection, processing, and distribution of the SRTM mission data, which provided topographic intelligence that was crucial to this project. Similar appreciation is extended to the governments of Chad, Europe, France, Japan and the United States for providing the aforementioned data used in the project. Finally, RTF wishes to recognize the vision and courageous support of Craig Sanders & Marc Andre Bunzli of the UNHCR, Alain Retiere of UNOPS, and Olivier Senegas of UNOSAT. References
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