UNITED NATIONS HIGH COMMISSIONER FOR REFUGEES (UNHCR)

Transcription

1 1 UNITED NATIONS HIGH COMMISSIONER FOR REFUGEES (UNHCR) PROGRESS REPORT ON CURRENT GROUNDWATER EXPLORATION AND BOREHOLE DRILLING PROJECTS AT REFUGEE CAMPS IN THE YUMBE (BIDIBIDI) AND RHINO CAMP AREAS OF NORTH- WEST UGANDA, NOVEMBER-DECEMBER 2016 Report compiled by Harmen van den Berg and David Soulsby Original photographs by authors unless otherwise stated DSS project reference nos. DSS16UG01/2 21 November 2016

2 2 Fig. 1. Geological Map of Uganda Area of Fig. 2

3 3 Zone 2 Zone 1 Zone 4 Zone 3 Zone 5 ALBERT NILE ARUA RHINO CAMP ~10km Fig. 2. Google Earth Image of Arua-Yumbe-Rhino Camp Region showing Bidibidi Refugee Camp Zones The recent renewal of political conflict in South Sudan has caused an exodus of refugees into north-western Uganda. A number of sites have been designated for South Sudanese refugee camps or settlements, including Bidibidi in Yumbe District and Rhino Camp. Since arrival in the field in early November, the principal field activities have been as follows: Locating, mapping, and recording the positions and details of boreholes and other water sources in and around Bidibidi, to the north-east, east, and south of Yumbe town. Meetings with other organizations carrying out field activities related to improvement of water supplies to the refugee camps, including the local District authority. Collection and incorporation of existing data relevant to the water supply problem to add to the project database. The project area is underlain by a Precambian basement complex consisting of a varying suite of gneisses, schists, and granitoids. Crystalline rocks such as there are generally unfavourable conditions in which to find groundwater, but secondary porosity can form as a result of weathering and fracturing. Fortunately this is the case in the project area, where deep weathering host aquifers above the basement complex, and networks of fractures form aquifers within the basement rocks. Consequently it has been possible to site boreholes within and around the refugee camp zones of Bidibidi.

4 4 The majority of boreholes so far constructed are relatively low-yield (<5m 3 /h) and fitted with hand-pumps. More importantly for the increasing refugee population sites are now being developed which are providing greater yields and can be fitted with motor (electric submersible) pumps. Attempts are being made to correlate high yield borehole sites with ground features, such as drainages, fractured outcrops, and natural lineaments in order to determine potential targets for future drilling. Fig. 3 for example, shows two known high-yield boreholes and their relation to a system of natural lineaments crossing Zone 2 in Bidibidi. To Baringo Oxfam borehole c.40m 3 /h MSF Borehole >8m 3 /h? ROADS km Fig. 3. Natural lineaments (yellow dotted lines) suggesting bedrock fracture lines north-east of Yumbe in Bidibidi Zone 2, plotted with the locations of high-yield boreholes. The Oxfam borehole drilling recorded fractured metamorphic bedrock from c.70mbgl. The Oxfam and MSF boreholes are alongside the same small drainage channel. The yellow circle indicates an interesting place where a strong natural lineament intersects the still-flowing Kochi River, just to the north of Zone 2. Unfortunately, this site turned out to inaccessible by foot, so would be extremely difficult for a geophysical survey crew and a drilling rig to reach (Image: Google Earth) Even high-yield boreholes are initially fitted with hand-pumps after testing, so that they can be used while awaiting installation of a motor pump. It has been agreed that the most cost effective intervention to improve water supplies to Bidibidi, and possibly Rhino Camp, would be to use or to rehabilitate and use existing boreholes, especially if they are known or found to be good producers (5m 3 /hr or more). However, most high-producing boreholes may turn out to be

5 5 newly-drilled, as shown in Fig. 4. Thus far about 10 high-yield borehole sites are known, plus one artesian well located outside of the Bidibidi zones (Fig. 5). Fig. 4. The new Oxfam borehole referred to previously being developed on 17 November, producing a blowing yield of 38 to 40m 3 /h. So far this is the strongest borehole known in Bidibidi. The principal aquifer appears to be in the weathered zone above the fresh basement formation. A driller s blowing yield gives a rough indication of future performance of the borehole prior to test pumping Fig. 5. A borehole with hand-pump in Bidibidi Zone 1. Note the queue of water containers

6 6 Our survey of the existing borehole inventory in Bidibidi indicates a general availability of groundwater, both in regolith zones and in bedrock fractures, but dry areas are known. It is likely that many boreholes now fitted with hand-pumps could have been better producers if they were originally drilled deeper (>100m) to intersect more water-bearing fractures in the bedrock. From now on drillers will be encouraged to drill to these depths if they can, but there could be contractual limitations. Fig. 6. An artesian well located to the east of Bidibidi Zone 2, being used to load water tankers Borehole surveys have been largely completed in Zones 1, 2, 3, and 4. A similar survey in Zone 5 will commence shortly. It is expected that hydrogeological work will continue in Bidibidi for several more days before a first assessment visit is made to Rhino Camp. Harmen van den Berg & David Soulsby, Yumbe, Uganda, November 2016.