UPGro Ambassador, Dr Callist Tindimugaya, attended last month’s COP meeting in Madrid – the United Nations global negotiation meeting to try an agree ways forward to tackle climate change.
He was attending as part of the Government of Uganda delegation to bring forward opportunities and challenges – in particular the key role of groundwater as a resource that can help buffer against some of the effects of shifting rainfall patterns across Eastern Africa.
Substantial increases in groundwater withdrawals are expected
across Sub-Saharan Africa to help nations increase access to safe water and to
amplify agricultural production in pursuit of UN SDG 2 and SDG 6.
Long-term groundwater-level records or chronicles play an important role
in developing an improved understanding of the hydrogeological and climatic
conditions that control access and sustain well yields, informing where, when
and how groundwater withdrawals can sustainably contribute to building
resilience and alleviating poverty.
Evidence from chronicles in seasonally humid Benin and Uganda
show annual cycles of replenishment from direct, diffuse recharge generated
preferentially by heavy rainfalls. Kotchoni et al. show how chronicles
from different geological environments in Benin can be modelled very
effectively on a daily timestep with an improved watertable fluctuation model.
In semi-arid southwestern Niger, chronicles show that
recharge to weathered crystalline rock aquifer systems occurs directly from
rainfall but is restricted by a thick clayey aquitard developed from
schist. However, greater recharge is shown to occur indirectly via riverbeds of
ephemeral streams which provide preferential pathways through the saprolite.
Evidence from the Makutapora Wellfield of semi-arid central Tanzania
that groundwater, abstracted at rates exceeding 30,000 m3/day, is
sustained by episodic recharge associated with El Niño Southern Oscillation
(ENSO). Further, abstracted groundwater is partially modern, derived from
rainfall within the last 10–60 years.
Studies from Benin and Niger highlight the low
storage of weathered crystalline rock aquifers and the importance of modern
recharge in sustaining groundwater use. The low storage and low but highly
variable hydraulic conductivity of weathered and fractured crystalline rock
aquifers found over more than 40% of Sub-Saharan Africa may, however, have a
potential advantage. Such aquifer systems restrict opportunities for intensive
and competitive abstraction and are thus potentially self-regulating.
Low-intensity groundwater abstraction distributed across the landscape also
complements existing land-tenure systems in many areas of Sub-Saharan Africa
dominated by smallholder agriculturalists.
The chronicles provide invaluable datasets to help direct
assessments of past impacts of climate variability—e.g. ENSO, Atlantic
Multi-decadal Oscillation (AMO)— and abstraction on groundwater storage. Such
records, when continuously updated, can also provide key input to water
resources management by tracking emerging risks to water security from
groundwater storage decline or groundwater flooding (e.g. Murray et al. 2018).
Regional-scale (>50,000 km2) networks of long-term
piezometric records can also be used to test the reliability of largescale,
satellite observations from the Gravity Anomaly and Climate Experiment (GRACE).
Indeed, the emergence of GRACE measurements of changes in total terrestrial
water storage adds a potential tool, albeit at a much larger scale (>200,000
km2), to estimate changes in groundwater storage where records do
not exist. However, there are substantial uncertainties from such estimates.
Millions of people in towns and cities across Sub-Saharan Africa depend on groundwater day-to-day – but is it safe to drink? How can we measure the safety quickly, cheaply and accurately? In this RWSN-UPGro webinar, Dr Jenny Grönwall (SIWI/T-GroUP) and Dr Dan Lapworth (BGS) present the latest updates on their research into urban groundwater monitoring and use, and how it can be improved.
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.
The GroFutures team at Sokoine University of Agriculture (SUA, Tanzania), led by Japhet Kashaigili (SUA) with support from PhD students, Hezron Philipo (SUA) and David Seddon (UCL), established in July (2017) a groundwater-level monitoring network in the Upper Great Ruaha Basin Observatory in southern highlands of Tanzania. This area is part of the Southern Agricultural Growth Corridor of Tanzania (SAGCOT) where increased use of groundwater and surface water is anticipated to support agricultural production. Constructed monitoring wells at depths ranging from 18 to 32 m below ground were drilled using a PAT-DRILL 421 rig. The team also instrumented monitoring wells recently constructed by project partners at the Rufiji Basin Water Board (RBWB) in the Tanzanian Ministry of Water and Irrigation.
The new monitoring network comprises an upstream location at Chimala at the base of an escarpment and a downstream location at Mbarali within the alluvial plain. A monitoring well at Chimala Secondary School was installed into coarse unconsolidated sands and gravels to a depth of 26 m. This monitoring well is linked to both an additional monitoring well at Usangu Secondary School and a river gauge. Both monitoring wells are equipped with automated dataloggers providing hourly groundwater-level measurements. A third borehole was constructed at Chimala Primary School though no groundwater was encountered up to a depth of 30 m. At Mbarali, two monitoring wells were constructed on the St. Ann’s Secondary School and now form a transect of 4 monitoring wells as the team also instrumented two monitoring wells recently constructed by the RBWB at Rujewa at Mbarali Secondary School and Jangurutu Primary School.
The new infrastructure is expected to reveal for the first time the dynamics between groundwater and surface water in the Upper Great Ruaha sub-catchment of the Rufiji Basin and answer key questions around the nature of groundwater recharge and whether seasonal river flow recharges groundwater or groundwater sustains river flow. Further work will also seek to ensure that this observatory is equipped with both tipping-bucket rain gauges to record sub-daily (hourly) rainfall intensities and soil-moisture probe arrays to better understand how intense rainfalls are transmitted through alluvial soils.
Shallow groundwater wells, are the main source of drinking water in many rural and peri-urban communities.
The quantity and variety of shallow wells located in such communities make them more readily accessible than private or government operated deep boreholes, but shallow wells are more susceptible to faecal contamination, which is often due to leaching pit latrines.
For this reason, online monitoring of water quality in shallow wells, in terms of faecal pollution, could dramatically improve understanding of acute health risks in unplanned peri-urban settlements.
More broadly, inexpensive online faecal pollution risk monitoring is also highly relevant in the context of managed aquifer recharge via the infiltration of either stormwater or treated wastewater into the subsurface for aquifer storage and recovery.
To tackle this challenge, IN-GROUND – an UPGro Catalyst Project – trialled four different types of Microbial Fuel Cell (MFC) water quality biosensor in the lab (Newcastle University, UK) and in the field (Dar Es Salaam, Tanzania).
While further work is needed, the results provided proof-of-concept that these biosensors can provide continuous groundwater quality monitoring at low cost and without need for additional chemicals or external power input.
The UPGro programme, supported by AfriWatSan & ESPRC, conducted a pan-African capacity-strengthening and knowledge co-production workshop at Sokoine University of Agriculture in Morogoro, Tanzania from the 10th to 12th of February, 2017.
40 participants from 12 countries in Africa took part and analysed multi-decadal, groundwater-level data (“chronicles”) from 9 countries including Benin, Burkina Faso, Ghana, Niger, Sénégal, South Africa, Tanzania, Uganda and Zimbabwe.