Article by the Technical University of Civil Engineering Bucharest (UTCB)
Urban growth transforms cities in ways that are immediately visible: new residential neighbourhoods, widened roads, bridges, public parks and modern transport links. However, some of the most significant changes happen quietly, out of sight, in the hidden environment beneath the urban surface. Water flows through soils, underground voids, pipes and utility networks, responding to every change/alteration in land use and infrastructure. When this fragile system is disrupted or reconfigured, the effects can be slow but decisive. Streets flood unexpectedly, foundations settle, groundwater levels fluctuate and lakes shrink or expand. Understanding these patterns is essential for resilient city planning, but urban water is often treated as a simple supply and drainage and issue rather than a complex, interconnected system.
This study is being developed as part of the three-year AWARD project (awardproject.eu), funded by the European Commission’s Horizon Europe program. Municipality of District 2, Bucharest is a key stakeholder in the AWARD project, actively contributing to and supporting the development and implementation of the proposed integrated water management measures.
Introducing Lacul Circului
The story of Lacul Circului, a small urban lake in Bucharest’s District 2 (Figure 1), illustrates how multiple invisible processes can accumulate until they become visible to everyone. The lake, located in a 138-hectare area that includes densely populated residential neighborhoods, two major parks, and the nearby chain of lakes connected to the Colentina River, is more than just a landscape element. It is a functional part of the district’s blue-green infrastructure, providing recreational value and ecological benefits. A crucial aspect is that it is hydraulically connected to the shallow aquifer. This means that the lake water level and the groundwater table rise and fall together, influencing each other in ways that are not immediately obvious to most observers.
Figure 1. Location of Lacul Circului in Bucharest city, Romania
Over the past decade, residents have begun to notice a steady decline in the lake’s water level (Figure 2), of approximately 1.4 meters. This decline was not caused by a single event, but rather by a combination of climatic, infrastructural, and hydrological factors. Changes in seasonal precipitation have reduced the inflow of natural water into the system. At the same time, improvements to the water distribution network have reduced leakage, which previously represented an unintended, but significant, source of groundwater recharge. Construction projects in the district introduced temporary or permanent dewatering systems that pumped groundwater to create dry excavation conditions for deep foundations and underground structures. Some of these systems operated only during construction, others continued to operate afterward, creating long-term changes in the groundwater regime. These combined pressures altered the hydrological balance of the area, and because of the lake’s hydraulic connection to the aquifer, the lake level responded by dropping/falling.
Figure 2 . Images from Lacul Circului
An NbS for Water Management
Recognising the severity of this trend, a multidisciplinary team from Technical University of Civil Engineering Bucharest (UTCB) began exploring sustainable solutions. The challenge was to stabilise or restore the lake’s water level in a way that did not rely on artificial pumping or the continuous input of external water sources. Instead of trying to compensate for the deficit mechanically, the team analyzed how to work with natural processes. The idea that emerged was to capture rainfall from the surrounding urban environment and direct it in a controlled manner to the lake and to recharge the aquifer. In that way, stormwater would not drain immediately into sewer pipes, where it could overload drainage capacity during intense rainfall events, but rather be retained, filtered and allowed to infiltrate the soil within the district.
This approach reflects a wider shift toward nature-based solutions in urban water management. Green infrastructure elements such as infiltration basins, permeable pavements, rain gardens and vegetated swales can transform rainwater into a resource. They reduce surface runoff, support natural infiltration processes and alleviate the burden on conventional sewer networks. In the context of the Tei district, these interventions offered the possibility of reconnecting the lake to its natural hydrological cycle and improving resilience to intense rainfall events. Rather than waste stormwater, the district could use it to replenish the aquifer and help stabilise lake levels.
The idea that emerged was to capture rainfall from the surrounding urban environment and direct it in a controlled manner to the lake and to recharge the aquifer.
As the team studied the issue more deeply, it became clear that the hydrological challenges extended far beyond the lake itself. The underground of the Tei district, and indeed the entire Bucharest District 2, is densely occupied by utilities, tunnels, large building basements and deep foundations. The subsurface is a three-dimensional environment in which every new structure alters the movement of groundwater. A tunnel can block flows, a deep foundation can divert them and an ageing sewer pipe can unintentionally act as a drain. Because of this complexity, the lake’s decline became a catalyst for a much broader initiative: developing a strategic framework for managing water across the entire neighbourhood, and eventually across the entire District 2, which covers 32 square kilometres and houses approximately 345,000 inhabitants.
Traditional water assessments, such as the truncated urban water balance (Figure 3), tend to focus primarily on what happens at the surface, often providing false results. This is why this strategic framework placed emphasis on creating a rigorous urban water balance. It brings together precipitation, evaporation, groundwater recharge, interactions between lakes and aquifers, the behaviour of sewerage networks, the contribution of drinking water leaks, losses from water distribution networks and the impact of underground construction, providing a much more complete picture of how water moves in a city. The framework also acknowledges the need to evaluate water quality, particularly in areas where natural waters may interact with potentially contaminated anthropogenic waters.
Figure 3. Truncated hydrological view (left) compared to the real image of the city’s underground (right).
A Modelling Scheme for Strategic Interventions
To support this integrated approach, the team designed a conceptual modelling system composed of three interconnected layers. The first layer focused on the urban land surface, simulating how rainfall interacts with different surfaces, from roofs and asphalt to parks and unpaved soils. This simulation analysed the balance between infiltration, runoff and stormwater capture. Understanding how much water reaches the ground and how much is immediately redirected into sewage systems became vital for estimating groundwater recharge.
The second layer examined the unsaturated zone and the complex urban fabric that surrounds it. Water passing through this layer is influenced by soil composition, the presence of paved or vegetated areas, the density of buildings and the configuration of underground utilities. Each of these elements affects how quickly water can percolate downward and how it travels before reaching the aquifer.
The third layer was the hydrogeological model of the urban aquifer itself. This model incorporated every significant element affecting groundwater, including lakes and rivers, green infrastructure components, sewer pipes, deep foundations, tunnels, dewatering operations, rainfall infiltration and leakage from water-supply systems. The hydrogeological model enabled the team to simulate different scenarios, assess the impact of proposed interventions and develop a clearer understanding of how groundwater levels might evolve under various urban and climatic conditions.
Figure 4. Conceptual modelling scheme
With these three layers working together, the modelling framework provides a detailed view of the water cycle in the Tei District. It allows researchers to explore how of green infrastructure location schemes could influence groundwater infiltration and recharge. It also enables the assessment of the effects of stormwater redistribution, adjusting construction dewatering practices and manage interactions between surface water and groundwater. Through this modelling effort, the team can identify solutions capable of stabilising groundwater levels, supporting lake restoration and reducing pressure on the sewage network during extreme precipitations.
The expected impact of this integrated approach is significant. By capturing and reusing stormwater, the district can efficiently use alternative water sources and strengthen its water security. Maintaining groundwater levels helps protect the lake and surrounding infrastructure, ensuring the stability of building foundations, green spaces, and public areas. Reducing runoff during severe storms minimizes the risk of sewer overflows and reduces the likelihood of local flooding. Perhaps most importantly, the project creates a replicable methodology that can be applied in other parts of Bucharest and in other cities facing similar challenges.
Epilogue
The case of Lacul Circului demonstrates how an apparently local environmental issue can reveal systemic weaknesses in urban water management. It also shows how a well-designed, analytical and nature-based approach can reconnect urban hydrology with natural processes. Using the careful modelling and strategic planning, the Tei district is moving toward a more balanced water cycle, one that supports ecosystems, protects infrastructure and enhances resilience in the face of climate variability. In the end, the project serves as a reminder that urban water is not just a technical utility but a dynamic system integrated into the city life, and restoring its balance requires understanding, foresight and the willingness to embrace solutions that work in harmony with nature.
