Crystalline Bedrock aquifers underlie about 40% of Sub-Saharan Africa and can generally sustain low-intensity abstraction. However, pumping rates and dependency is increasing in many areas, particularly for cities like Addis Ababa, Dakar, Nairobi and Dodoma. Projected growth in population and water demand for agriculture, plus the effects of climate change, mean that it is essential to develop a better understanding of the sustainable yields from these types of aquifers.
The study focuses on five groundwater abstraction boreholes, 3 in Uganda, 2 in Tanzania.
Long term groundwater records are only available for one of the boreholes and it shows that recharge happens more when the rainfall is more intense, which is often associated with periodic El Niño Southern Oscillation (ENSO) events.
Chemical analysis of the water was used to determine the residence times of the groundwater (how long the water has been in the aquifer since it fell as rain). Overall, that most pumped water comes from modern recharge (within the last 10-60 years), so while abstractions are not mining pre-modern groundwater, there may be a component of older water that is coming out.
Groundwater abstraction appears to be supported by recharge from across multiple years, rather than just the most recent wet season.
The investigation of the five sites shows that long term, high intensity groundwater abstraction is possible from East African weathered crystalline basement aquifers, but the sustainability is constrained, in part, by the high inter-annual variability in recharge. Therefore operation of such pumping stations needs to include sustained monitoring of groundwater levels, pumping rates and rainfall as a minimum.
Key Note Presentation by Prof. Alan MacDonald @ 1st SADC Groundwater Conference
Keywords: (Drought, Climate, Change, Infrastructure, Groundwater Resources, Resilience).
“Recent droughts have highlighted the need to understand and forecast the resilience of water supplies to climate variability. Resilience of groundwater supplies is determined by several factors: groundwater storage; long term recharge; permeability; and the infrastructure put in place to abstract groundwater.
“Drawing on recent research from across Africa, mainly funded through the UPGro programme, this talk examines the relative importance of each of these factors for rural drinking water supplies, and attempts to distinguish between the behaviour of the groundwater resource and the water infrastructure.
“A variety of data are presented and evaluated: detailed groundwater level monitoring of springs, wells and boreholes; national survey data of borehole functionality; groundwater residence time indicators; and also information from GRACE and global Land Surface Model.”
UPGro has a strong presence at the event as part of the build-up to Africa Water Week next month, in Gabon:
Opening Keynote: Karen G. Villholth (GroFutures) and Jude Cobbing.
“Adapting to Climate Change in the SADC Region – A Focus on Groundwater.”
Presentation: Theresa Mkandawire (Hidden Crisis) presented “An analysis of hand pump boreholes functionality in Malawi.”
Keynote speaker: Alan McDonald. (Hidden Crisis/GroFutures) “Resilience of rural
groundwater supplies to climate change”
Presentation: Thokozani Mtewa,Evance Mwathunga and Wapulumuka Mulwafu.
(Hidden Crisis) “They gave us breakfast and a good meal’: Roles, perceptions and
motivations of water point area mechanics in the maintenance of borehole handpumps in Balaka district, Malawi.”
Keynote speaker: Dr Callist Tindimugaya “Groundwater and African National Development Strategies”
You can follow the conference on Twitter: #gwconference2018
photo : Prof Theresa Makandawire presenting UPGro Hidden Crisis work in Malawi (credit BGS via Twitter)
Groundwater Recharge – the set of processes that govern how rainwater seeps through soils and rocks to replenish aquifers – is not well understood across much of Africa. It is important to understand because it is central to determine the sustainable use of groundwater resources;
The authors analyse three rare sets of long-term (19-25 years) groundwater-level observations from three different, but common, geological settings in Benin;
The year-to-year changes in groundwater storage correlate well with rainfall patterns, but there were big differences the relate to the type of geology:
In the shallow, sand aquifer as much as 40% of the rainfall becomes groundwater
In the deeper sandstone and weathered crystalline rocks, a much lower proportion of rainfall becomes groundwater recharge (13% and 4% respectively)
Recharge was found to occur on a seasonal basis; however on a daily basis the groundwater fluctuations are best explained with a threshold of 5-15 mm per day – meaning that only more intense rainfall events lead to recharge.
These results are consistent with the growing body of evidence that, in Sub-Saharan Africa, intensification of rainfall associated with climate change may increase groundwater recharge.
Because the groundwater recharge is so strongly influenced by geology, it is essential for water resource planning that good geological maps are available and used, and that investment is made into long-term groundwater monitoring of strategic aquifers.
GRACE (Gravity Recovery and Climate Experiment) satellite can be used to estimate changes in water storage on time resolution of 1 month and a spatial resolution of about 450 x 450 km.
GRACE can be used to estimate groundwater storage changes where it is the dominant water mass. It is therefore useful in many areas of Sub-Saharan Africa where there are relatively few direct groundwater level measurements.
The paper focuses on the major sedimentary aquifers basins, where the majority of Africa’s groundwater resources are to be found. Away from these basins, groundwater storage is 1-2 orders of magnitude less.
There is no evidence of continuous long-term declining trends of Total Water Storage (mostly groundwater) in any of the major sedimentary aquifers, which indicates that none are stressed by current abstraction rates – howeverit is important to stress that local scale depletion may be occurring but is beyond the resolution of GRACE to detect.
There are also some interesting findings in regard to the combination of GRACE and Land Surface Modelling and how well (or not) they represent groundwater recharge processes in the different basins.
Read the full paper here:
Bonsor, H.C.; Shamsudduha, M.; Marchant, B.P.; MacDonald, A.M.; Taylor, R.G. Seasonal and Decadal Groundwater Changes in African Sedimentary Aquifers Estimated Using GRACE Products and LSMs. Remote Sens.2018, 10, 904. http://www.mdpi.com/2072-4292/10/6/904
The GroFutures Team, working with the Tanzanian Ministry of Water and Irrigation, expanded monitoring infrastructure in the Upper Great Ruaha Observatory (UGRO) to include interactions between groundwater and surface water.
An outstanding question regarding the sustainability of groundwater withdrawals for irrigation and drinking-water supplies is whether groundwater in the agriculturally intensive lowlands is replenished by river flow, sustains river flow, or both depending upon the season.
On 25th October, the prestigious keynote Ineson Lecture 2017 at the Geological Society in London was given by Dr Callist Tindimugaya, head of Water Resource Planning and Regulation in Uganda’s Ministry of Water & Environment, and one of four UPGro Ambassadors. In his speech he highlighted the importance understanding and managing groundwater well, not for its own sake but because it is a natural resource that underpins most, if not all, African societies and economies.
However, he expressed his frustration that the economic contribution of this resource has not yet been properly quantified so that its invisible contribution is made plain to all, from ordinary citizens to political leaders. Nevertheless, he was encouraged by the many initiatives across the continent to address the knowledge gaps and to improve the visibility and use of groundwater – in particular the importance of the UPGro programme and GRIPP. He concluded: “You cannot milk a cow, if you do not feed it”, likewise if the potential benefits of Africa’s aquifers are to be realised, then investment is needed in research, monitoring, regulation and – most of all – in education and training.
The day-long event was well attended and as well as a lively debate and a presentation by Guy Howard, DFID WASH policy team leader, there were numerous inputs from across UPGro, including: presentations by Prof. Richard Taylor about GroFutures and the Chronicles Consortium; from Brighid Ó Dochartaigh about the Africa Groundwater Altas; from Prof. Alan MacDonald about the Hidden Crisis project; and an array of posters from UPGro Catalyst and Consortia research, including a poster on the AMGRAF project by David Walker (Newcastle University) supported by UPGro and REACH, which had won the award for best Early Career Researcher poster at the recent 44th IAH Congress in Dubrovnik.
A huge thank you to Brighid Ó Dochartaigh and all the organisers at IAHBGS, and Geol. Soc.