OR/15/019 Case study area – Amuria and Katakwi districts, Uganda

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Bonsor H C1, Oates N2, Chilton P J1, Carter R C3, Casey V3, MacDonald A M1, Calow R2, Alowo R4, Wilson P1, Tumutungire M5, Bennie M5. 2015. A Hidden Crisis: strengthening the evidence base on the sustainability of rural groundwater supplies – results from a pilot study in Uganda. British Geological Survey Internal Report, OR/15/019.

1BGS Edinburgh, 2ODI London, 3Wateraid UK, 4Wateraid Uganda, 5Makerere University

The Amuria and Katakwi Districts of Uganda were considered an appropriate location for the pilot study, based on: existing failure rates of groundwater based supplies in the region (typically around 30%); existing strong working relationships between the UK project team members and the WaterAid Uganda programme team in the region; and the existing strong links and collaboration between the research team and national‐level decision makers in the Government of Uganda (GoU) — in the Directorate of Water Resource Management (DWRM) and the Directorate of Water Development under the Ugandan Ministry of Water and Environment.

Location and population

Amuria and Katakwi Districts are situated in north‐eastern Uganda — Figure 2. The rural population of these districts is approximately half a million, of which it is estimated 65% have access to safe water (MWE 2010[1]). In both districts the main water supply technology is deep boreholes (15–100 m deep) fitted with handpumps. These water points are largely community managed (90%), and funded by either NGOs such as WaterAid (70%), or by government programmes (25%) — the remaining 5% being privately funded (MWE, 2010[1]).

Figure 2 The location of the neighbouring Amuria (left) and Katakwi (right) Districts of Uganda (MWE, 2010).

Climate

Uganda has a tropical climate, with average annual rainfall ranging from 1500 to 2500 mm/year across the country. Dry northeasterly and northerly air masses cause the northern regions of Uganda to be drier than southern Uganda, where Lake Victoria provides a continuous supply of moisture. Rainfall is seasonal in Amuria and Katakwi Districts, with two dry seasons (December to February, June to August) in which rainfall is generally 20–40 mm per month, and a wet season in which monthly rainfall ranges from 100 to 150 mm (DWRM, 2010). Mean annual rainfall in the two districts in the last ten years has been 1343 mm, with an inter‐annual range of 1055 to 1765 mm (Cuthbert and Tindimugaya, 2010[2]).

Hydrogeology

The geology of both districts is predominantly ancient Precambrian crystalline Basement Complex, covered by weathered regolith or overburden. These rocks occupy 36% of the land surface in Africa in some of the areas of highest rural population (MacDonald et al. 2012[3]). They can provide a complex and sometimes discontinuous aquifer with low groundwater potential relative to some of the major sedimentary aquifers in Africa, but which generally supports borehole yields of 0.5–1.0 litres/second if the boreholes target the most productive parts of the aquifer and are properly constructed — Figure 3. Aquifer systems in the Crystalline Basement Complex of sub‐Saharan Africa consist of a weathered regolith/overburden of variable thickness and the underlying fractured bedrock, both of which can contain and transmit water — Figure 4. Elsewhere in Uganda these two units are found to form an integrated aquifer system, in which the more transmissive (5–20 m2/d) and porous weathered overburden provides storage to the underlying fractured bedrock (transmissivity typically 1 m2/d) (Taylor and Howard, 2000[4]). The thickness of the weathered overburden, and permeability of the deeper weathered zone, is therefore fundamental in controlling the sustainable yield of borehole supplies.

Figure 3 Map showing location of Uganda within Africa, in the context of both aquifer productivity (main panel), and population density (upper panel).

The hydrogeology of the basement aquifer system in Amuria and Katakwi Districts has not been investigated in detail. If the weathered overburden is of sufficient thickness it could provide or supplement the potential sustainable yield of a borehole, and the design of the borehole should enable this by including screening within the deeper regolith horizon. However, without detailed hydrogeological investigations it is not possible to develop a good understanding of the aquifer processes, and what is the most appropriate borehole target and design.

Groundwater recharge to the system as a whole has been estimated to be 120–150 mm/year by Cuthbert and Tindimugaya (2010)[2] at Soroti, 25 km to the south of the field area.

Figure 4 A schematic representation of crystalline basement aquifer systems, with a weathered overburden and regolith on top of the underlying, lower yielding fractured bedrock aquifer (source: MacDonald et al. 2005[5]).
Figure 5 Schematic diagram of a traditional open hole in rock design (source: MacDonald et al. 2005[5]).

Water point design and construction Nearly all groundwater based supplies in Amuria and Katakwi Districts are deep boreholes fitted with a handpump — the India Mark II, India Mark II Extra Deep Well, or U2 handpumps being the most common — Appendix 2. ‘Deep’ boreholes span a wide range of depths from 15 to 100 m, but are typically in the range 40‐60 m. Groundwater piezometric levels are generally 1 to 5 m below ground. The standard construction of boreholes in the region is an open hole in rock design – Figure 5. Casing material used in the region is typically uPVC (125 mm diameter).

Siting and drilling of new borehole supplies are procured at district level in Amuria and Katawi. The general practice is for one contractor to undertake both the hydrogeological mapping/survey investigations as well as the drilling. The procurement process is such that a flat fee is paid per successful borehole, rather than by a bill of quantities in most cases. Where the survey and investigations are undertaken by a separate contractor, the liability for a dry borehole point is transferred to the surveyor, rather than the driller.

Supervision of the siting and construction of new water points is the responsibility of the District water office, and to a lesser extent, staff from technical support units. However, due to the limited‐capacity at district‐level, there is in reality often very limited supervision.

Existing estimates of functionality

Functionality of groundwater based supplies in rural areas within the Amuria and Katakwi Districts is approximately 85%, based on Ministry of Water and Environment (MWE) surveys (MWE, 2010[1]). Failed water points are found throughout the districts, with no obvious spatial clustering or bias (MWE, 2010). Reasons for non‐functionality are put forward by the MWE to be largely technical failure (40–60%), or low yields (17–35%) in the two districts — Figure 6.

Figure 6 Immediate reasons observable for non‐functionality in the Amuria and Katakwi districts (source: MWE, 2010[1]).

References

  1. 1.0 1.1 1.2 1.3 MWE. 2010. The Water Supply Atlas, Ministry of Water and Environment, Uganda.
  2. 2.0 2.1 Cuthbert, M O & Tindimugaya, C. 2010. The importance of preferential flow in controlling groundwater recharge in tropical Africa and implications for modelling the impact of climate change on groundwater resources, Journal of Water and Climate Change, 1(4), 234–245.
  3. MacDonald AM, Bonsor HC, Ó Dochartaigh BÉ and Taylor RG. 2012. Quantitative maps of groundwater resources in Africa. Environmental Research Letters, 7; 024009.
  4. Taylor et al. 2013. Groundwater and climate change, Nature Climate Change 3: 322–329, 10.1016/j.wrr.2014.04.001
  5. 5.0 5.1 MacDonald AM, Davies J, Calow RC, Chilton PJ. 2005. Developing groundwater: a guide for rural water supply. Rugby, UK: ITDG Publishing.