Climate change is making the management of urban groundwater more critical than ever before. Radu Gogu, Susie Mielby, Jane Dottridge and Stephen Foster highlight some of the knowledge shared at IWA’s groundwater management workshop held at IWA’s World Water Congress in Copenhagen last year.
Climate change has made it a necessity for groundwater to be used efficiently and sustainably to protect the resilience of cities. Experiences from Zambia, Brazil, Romania, Denmark and the UK were debated at a workshop held at the IWA World Water Congress in Copenhagen, Denmark, in September 2022. Organised by IWA’s Groundwater Management Group, the results of the workshop are summarised here to highlight the critical role of groundwater in relation to urban resilience.
The challenges
Groundwater is essential for sustainable urban development, but requires improved management and monitoring as growing subsurface infrastructure and climate change continue to impact on this resource.
Improved understanding of the urban subsurface is required to identify effective methods of groundwater management. These will differ significantly between developing and developed cities, with some generic points of convergence, such as the delineation of wellfield protection zones, the use of groundwater vulnerability assessment techniques to establish risk from inadequate in situ sanitation, and the legacy of historical land contamination from past industrial activity.
In cities with limited infrastructure, groundwater abstraction from private self-supply wells requires private investment to maintain urban water security. In addition, it is necessary to harmonise the actions of local government and water utilities with public water supplies to monitor water quality and advise on any restrictions that may be required. In cities with developed infrastructure, more accurate urban groundwater and surface water balances are essential for the improvement of urban water management. From the outset, a clear understanding of urban growth (Figure 1) is essential.
Water balance analysis
Urban water balance analysis investigates the flow of surface water and groundwater, considering natural and anthropogenic processes, and how these are impacted by climate change. Unfortunately, such studies are often overlooked and leakage from water supply distribution systems is not factored in as a major source of recharge for shallow urban aquifers.
The sewer network can recharge or receive groundwater depending on the hydraulic gradient between groundwater and the wastewater conduit. Seepage into the sewer network can produce excessive sewer flowrates (Gogu et al 2017), in some cases dramatically increasing the cost of wastewater treatment.
Major works on urban subsurface infrastructure can sometimes produce a significant impact on groundwater flow, and thus have the effect of causing ground stability and drainage problems. Urban growth and past industrialisation can also result in widespread contamination of shallow aquifers.
Bucharest, Romania
Subsurface engineering works designed with insufficient data or based on geotechnical studies of a narrow zone around a construction site can result in costly errors, including dewatering procedures leading to unstable conditions off site. Gheorghe et al (2020) reported a subsidence of 40 mm in the centre of Bucharest in December 2015, because of construction of a subway tunnel. When the boring machine perforated the last tunnel wall into a central station, it mobilised approximately 500 cubic metres of sediment-loaded water. The station is located close to the river Dâmbovița and is subject to major water infiltration.
London, UK
Historical legacies must be understood if climate change adaptation strategies are to be reliable. Dottridge (2022) has highlighted significant improvement in the sustainable management of London aquifers over the past 30 years. From the late 19th century, over-abstraction of groundwater from the deep chalk aquifer caused an extensive cone of depression, with the lowest water levels occurring in the 1960s. When abstraction decreased, groundwater levels rose rapidly, leading to concern about the foundations of buildings and basement flooding.
However, urban regeneration in east London (such as at the site of the 2012 Olympic Games) has improved groundwater quality through large-scale remediation. A multi-stakeholder scheme (named the General Aquifer Research Development & Investigation Programme) manages the rising groundwater levels and provides additional water supplies through controlled groundwater abstraction of 70 Ml/d, including some dewatering from railway construction.
Since 1990, deep subsurface construction has been carried out for railways, water services, road tunnels and sewerage systems. Although these infrastructure projects reach deep into the ground, with potential risks of groundwater contamination, they have also provided opportunities for extensive investigation and monitoring to improve understanding of the groundwater system.
Observations
The sustainable development of cities, including climate change adaptation, requires careful urban groundwater management and protection. This must encompass both historical legacies and dense infrastructure by:
- Improving the understanding of groundwater flow and quality through enhanced monitoring
- Understanding the historical contamination legacies of industrial activity in developed nations and inadequate in situ sanitation in developing nations
- Applying existing concepts of mapping groundwater resource vulnerability and delineating protection zones for wells, in cooperation with local stakeholders
- Recognising the groundwater challenge provided by growing subsurface infrastructure.
These tasks will require partnerships with key stakeholders, such as water utilities, local communities, local authorities, civil engineering companies, geological surveyors, and academic centres. Support from water service utilities and city environment departments is particularly critical. •
The authors
Radu Gogu is head of the Groundwater Engineering Research Centre at the Technical University of Civil Engineering of Bucharest in Romania, Susie Mielby is senior advisor at the Geological Survey of Denmark and Greenland in Denmark, Jane Dottridge is secretary general at the International Association of Hydrogeologists in the UK, and Stephen Foster is professor of Groundwater Science at University College London in the UK and Chair of IWA’s Groundwater Management Group.
