SADC-GMI embarked on a project to investigate and provide management strategies for Groundwater Dependency and Vulnerability in the Coastal Cities of Dar es Salaam and Cape Town. The dependency and vulnerability of coastal cities stem from multiple factors. Rapid urban growth and population increases drive higher water demand, often met by groundwater due to insufficient surface water sources. Many urban authorities struggle to supply water through reticulated systems, leaving informal settlements reliant on shallow wells and boreholes. Coastal cities are particularly susceptible to saltwater intrusion into aquifers, especially during dry seasons or due to excessive groundwater abstraction. Pollution from urban runoff, industrial activities, agricultural activities, and improper sanitation can degrade groundwater quality, making it unfit for consumption. Additionally, Climate change has given rise to changed precipitation patterns, increasing temperatures and affecting groundwater recharge rates. These changes may increase water demand due to higher temperatures and evaporation, or reduced surface water availability, potentially leading to over-exploitation. The urban sprawl in coastal cities, inadequate enforcement of regulations and improper management of groundwater resources can exacerbate these vulnerabilities. Given these challenges, this project aims to assess groundwater dependency and vulnerabilities of groundwater in the selected coastal cities of Cape Town and Dar es Salaam in the SADC region.

The overall objective of this project is to determine the dependency and vulnerability of groundwater in coastal cities using Cape Town and Dar es Salaam as case studies. This will involve engaging with stakeholders, conducting high-level hydrogeological and environmental assessments, identifying gaps in the current monitoring networks, assessing vulnerability factors, evaluating the impacts of pollution and climate change, and incorporating socio-economic and gender dynamics. As part of this, a conjunctive management strategic action plan will be developed to build resilience in each city. These strategic action plans will provide frameworks to guide sustainable groundwater use, mitigating risks and enhancing resilience to climate change and environmental stresses in coastal cities.

The first main technical task is the analysis of the groundwater dependency of various sectors and the environment within the two cities. The combined effect of growing water demand and a drying climate has led Cape Town to make groundwater a key part of its resilience strategy. In response, the City’s “New Water Programme” and Water Strategy call for diversified sources (reuse, desalination, and aquifer development) and explicit monitoring of groundwater use. The groundwater resources of Dar es Salaam are a vital component of the city’s water supply network, particularly in areas where surface water infrastructure is limited or absent. In the northern regions of the city, the main water supply comes from the Mtoni River, Lower Ruvu River and Upper Ruvu River. However, within these areas, there is private groundwater use targeting the shallow Quaternary aquifer. Groundwater dependency is particularly high in the south of Dar es Salaam (Temeke and Kigamboni municipal districts), where municipal surface water supply infrastructure is unable to reach. Within these regions, the Neogene Aquifers are the main source of water supply, supporting municipal, agricultural, industrial and communal water supply needs. In addition to this, groundwater also sustains groundwater-dependent ecosystems (GDEs) such as rivers, wetlands, springs and terrestrial vegetation across the region, playing a crucial role in maintaining baseflow during the dry months.

A groundwater vulnerability assessment was undertaken to identify risks to the aquifers, such as saltwater intrusion, contamination, over-abstraction, and impacts of climate change. Factors like sea-level rise, groundwater abstraction, land use practices, and development scenarios were evaluated.

Groundwater contamination poses a significant risk to both aquifer integrity and the users who rely on this resource in Cape Town. The risk arises from the combined influence of the identified hazard (land use-related contamination sources), the aquifers’ physical vulnerability, the exposure and sensitivity of user groups, and the varying coping capacities across sectors. Over abstraction presents a significant risk to both the physical sustainability of Cape Town’s aquifers and the users who depend on them. Sea-level rise presents a gradual but significant risk to Cape Town’s coastal aquifers, primarily through the hazard of saline intrusion. The physical risk to the aquifers is not uniform across the City. The CFA is most vulnerable due to its shallow, unconfined nature, proximity to the coast, and low elevation relative to sea level. Reduced recharge due to climate change is a risk to groundwater availability in the City of Cape Town.

Aquifer contamination risk in Dar es Salaam is highest in the Quaternary Aquifer system, particularly the upper portion, due to its shallow unconfined nature that results in high infiltration rates and a limited natural protection. In Dar es Salaam, the Quaternary Aquifer faces the highest risk of over-abstraction due to its shallow nature, easy access and heavy utilisation, particularly in the central parts of the region, which forms the city’s economic hub. Districts such as Temeke and Ilala are especially vulnerable because they have the highest registered groundwater use and extensive impervious surfaces that reduce natural recharge. The Quaternary Aquifer is the most vulnerable to climate change-induced sea-level rise because of its shallow, unconfined nature, proximity to the coast, and elevation relative to sea level. The low-lying coastal plains and areas such as those found in Kigamboni and the Msimbazi Basin are the most susceptible to groundwater inundation, while saline intrusion in coastal boreholes has been observed in several locations along Dar es Salaam’s coast. It is likely that climate change-induced reductions in recharge, should they occur, will disproportionately affect the Quaternary Aquifer, especially in urbanised areas with limited infiltration. While prolonged dry seasons and erratic rainfall patterns will exacerbate water scarcity, straining the groundwater resource. The Kimbiji Aquifer, in contrast, is at less risk of reduced recharge as its main recharge zones are thought to be in the hinterlands of the region, where higher rainfall occurs and the area of impermeable surfaces is minimised.

Project Manager: Eng. James Sauramba, jamess@sadc-gmi.org

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