Abstract
Cities worldwide are undergoing sustainable transformations driven by environmental, societal, and economic concerns. This includes improving living standards and addressing global challenges such as climate change and pollution. Urban planning strategies are being re-evaluated, emphasizing the expansion of green spaces. Pécs, Hungary, exemplify this trend through projects like the “Green Gate,” focusing on new pedestrian walkways and increased green areas. To optimize the project's impact, emphasis is placed on integrated water management and considering elements inspired by the “sponge city” concept for flood mitigation. The goal is to assess potential outcomes and feasibility in a real-world setting.
1 Introduction
Urbanization has significantly impacted urban hydrological conditions, leading to an escalating severity of urban waterlogging and flooding disasters [1].
Recognizing the potential for diverse damages, the management of urban storm-water has become a pervasive concern [2]. Climate change adds complexity to future urban storm-water management, amplifying water-related challenges like flooding.
The swift expansion of impermeable surfaces due to extensive urbanization has disturbed the natural hydrologic cycle [3], resulting in severe repercussions including flooding and water environment degradation [3]. Traditional storm-water management methods fall short of achieving the objectives of sustainable urban development [3]. In contrast, sponge cities offer an innovative approach to urban storm-water management, presenting a solution to tackle these challenges.
Sponge cities employ innovative methods in urban storm-water management by enhancing infiltration, storage, treatment, delay the runoff, and drainage. This effectively tackles problems that includes urban flooding, pollution reduction and promotes rainwater resource utilization through Low Impact Development (LID) techniques [4] also offer storage, recycling, and purifying rainwater, improving storm-water management's effectiveness. Additionally, it integrates natural water bodies like wetlands into drainage design for multifunctional benefits.
As it is emphasized by Chan et al. [5] and colleagues in their research article “Sponge City” in China - the sponge city concept boosts climate resilience through benefits like increased urban greenery and diminished heat-island effects.
Berlin, a European example of the sponge city concept, is experiencing increasing heat-waves and rainstorms due to climate change. To combat this, the city has launched a plan to enhance green infrastructure, including rooftop greenery and improved pavement permeability [6]. The Rummelsberg neighborhood, developed 20 years ago, exemplifies this strategy with deep green roofs, substantial soil layers, and a swale network for rainwater. Now, city-wide initiatives aim to replicate these benefits across Berlin [7].
2 The sponge city principle concept
The sponge city concept revolves around three primary objectives:
- i)Embracing LID concepts to improve the efficient control of urban peak runoff, including the temporary storage, recycling, and purification of storm-water;
- ii)Improving conventional drainage systems by integrating flood-resistant infrastructure, including underground water storage tanks and elevating drainage standards with LID systems to reduce storm-water overflow;
- iii)Incorporating natural water bodies like wetlands and lakes into urban areas for diverse drainage design goals and create additional artificial water bodies and green spaces to enhance overall amenity value.
The sponge city concept brings about positive transformations in urban environments by offering advantages over traditional drainage systems [8].
2.1 The sponge city concept element
Sponge city approaches incorporate elements designed to align with the functionality of infiltration [2]. These landscaped facilities showcase advanced retention capabilities and are interconnected with drainage systems.
2.1.1 Green roofs
Improve water management by absorbing and retaining rainwater. They play a vital role in minimizing storm-water runoff and fostering sustainable water usage in urban settings. These create attractive green spaces and typically consist of vegetation, along with layers for filtration and waterproofing over a roof [8].
2.1.2 Permeable pavements
An essential cost-efficient approach [9] it enables water to infiltrate to the subsoil for groundwater recharge. This pavement is a practical substitute for traditional surfaces in parking lots, pedestrian access.
2.1.3 Rain gardens
It functions as a bio-retention system [9] and possess the capacity to reduce flood risk [8] because it minimizes rainwater flow also it prevents pollution from sediment in waterways and encourages groundwater recharge, collects excess rainwater from building roofs, guiding it through layers of vegetated sand for filtration. The purified water is directed into storage for reuse.
2.1.4 Wetlands
Wetlands are valuable open natural assets that offer recreational benefits and help promote more sustainable urban water management. These play a role in encompassing rainwater retention and resilience against floods, assists groundwater recharge and the enhancement of water quality [9].
2.1.5 Storage tanks
Storage tanks serve as reservoirs for collecting and retaining rainwater to be used in the future. These tanks aim to combat water scarcity, minimize the risk of flooding, and encourage sustainable water management practices [10].
2.2 The scales of implementing sponge city elements
Micro system: This entails applying sponge city principles on a smaller scale, focusing on capturing rainwater at a micro scale to improve water quality. This includes the use of strategies like green roofs and rain gardens [11];
Medium system: Involves storing rainwater through wetlands or retention pods, with the goal of mitigating flooding and improving water quality [11];
Macro system: It encompasses the establishment of green infrastructure to the city-wide drainage system, aimed at diminishing flooding and fortifying water resilience across the urban landscape. The objective is to capture, store, and proficiently manage rainwater on a citywide scale and replenish groundwater.
The impact of implementation varies with the scale, yielding diverse benefits across bio-ecology, water quality and hydrology.
3 Green gate project
3.1 Project details
The study area located at the intersection of Petőfi Street and Hungária Street in Pécs city (46.07125°N 18.23311°E), which is in the center of the southern Hungarian county of Baranya. The square is designated to be named after Captain Steinmetz (Fig. 1).
Project location, existing plan (Source: [12])
Citation: Pollack Periodica 2025; 10.1556/606.2024.01056
The square presently lacks an inviting atmosphere and primarily functions as a thoroughfare. The suggested design involves creating an economic function within a pavilion available for rent to serve multiple purposes. This area could accommodate various intelligent solutions, including Wi-Fi, solar panels and other innovations.
The process of renovating encompassing various tasks from improving the space by renewing the pedestrian walk paths and replacing the old seating area, to enhance the parking area by remodeling it and adding more space also installing new public lighting and build a new food cubicle and a restroom.
In the current layout, it is evident that the green space lacks organization and a cohesive presentation. The arrangement of trees appears random, and the parking area is insufficient and poorly organized. The utilization of the green space seems suboptimal, and the pedestrian path is not clearly defined (Fig. 1).
3.2 The original design
The design strategy involves repositioning trees more thoughtfully, expanding green spaces to improve sustainability and enhance the site's landscape character, and fostering cohesive green connections with the rest of the city [13] and reconfiguring the parking area to provide additional spots. Furthermore, there is a focus on expanding seating options to create a welcoming space for the local community to enjoy beverages (Fig. 2). Thus, the full designed area total is 8,660 m2 that includes 2521.64 m2 green areas [14].
Considering this as a small-scale initiative aimed at improving storm-water management and promoting water reuse, the project can be enhanced by incorporating elements of the sponge city concept. The focus will be on implementing and applying these elements to effectively capture and control storm-water. The study will specifically concentrate on the application of green roofs on individual blocks and the utilization of permeable pavements as key components in managing storm-water from these structures.
3.3 Roof planned calculation
The hospitality unit would consist of a restroom and a catering facility, forming a building block. Between them, a terrace would be situated, serving as a guest area. Those roofs will be calculated and then can be converted to be green roofs.
As climate change is expected to result in less frequent but more intense and short-duration precipitation, near the location, measurements on the green roof established at the Faculty of Engineering and Information Technology, University of Pecs (FEIT, UP) Boszorkány Street Campus showed that runoff from the green roof only occurs after high-intensity precipitation [15, 16]. Therefore, in the calculations for extensive green roofs, the precipitation considered has a 1% frequency and duration of 10 min. The 1% frequency indicates that it occurs once every 100 years [17]. Location: Pécs-Árpádtető, 1% rainfall (occurs once every 100 years).
Taking into account the roof's runoff coefficient the 0.9, approximately 16.60 m³ of water flows annually without being used.
3.4 Asphalt pavements calculation
The current state of the project without changing the pavement material: Sandy gravel soil type C and the project total area 8,660 m2; green area 1958.41 m2; pavement area 2,885 m2 [13].
With a runoff coefficient of 0.5 for the pavement, an average of 970.8 m³ of water flows annually without being utilized.
4 The application of the “Sponge City” model at the green gate project
4.1 Version I
4.1.1 Implementing green roofs on both block roofs only
In general, green roofs can be categorized by their purpose, characteristics [18], into three types: intensive green roofs, semi-intensive green roofs, and extensive green roofs. Each type of green roof demands distinct vegetation and different depths [19].
Intensive green roofs necessitate a substantial soil 80–150 mm depth and call for skilled labor, consistent irrigation, and ongoing maintenance [20].
Seven types of vegetation are suitable including lawns for intensive ones, low-lying shrubs, coppices and others [21].
Extensive green roofs (the least expensive one) are a relatively thin soil layer 50–100 mm, cultivate sedums and moss, roots are shallow between 6 and 8 mm and are specifically designed to be nearly self-sustaining, demanding minimal maintenance [20]. Sedum species are preferred due to their distinctive traits, like shallow root growth, which minimizes water loss [19], an extensive green roof structure consists of a root-resistant waterproof membrane, a drainage layer. A filter layer (The geotextile layer is added to prevent the planting medium from migrating into the drainage layer. It is recommended to use a free-draining textile to avoid waterlogging), a layer of planting medium, and plants [22].
Last the semi-intensive, which combines features of both extensive and intensive types [20].
Considering the average annual rainfall volume on the roof is 18.44 m3 and considering the green roof's runoff coefficient an average of 9.22 m3 flows further annually without being utilized, but retaining 9.2 m3 improves the microclimate of the environment and reduces the magnitude of runoff.
4.1.2 Implementing permeable pavements
The challenge with existing permeable concrete lies in its high tortuosity, resulting in clogging. Traditional permeable concretes lack the strength for heavy loads [23] therefore; the considered material for pavement is clogging-resistant permeable pavement with high strength, which is created by incorporating straight pore channels into a self-compacting mortar, leading to a consistent pore structure characterized by low tortuosity to enhance efficiency, durability, and cost-effectiveness [24]. Moreover, initiating the calculation of pavement slab thickness (Hp) involves determining California Bearing Ratio (CBR) test to provide values based on soil type. Next, establish subgrade and foundation layer thicknesses while considering the design traffic load. Calculate design rainfall intensity and runoff volume. Compare and select the larger thickness between subgrade and foundation. Determine the necessary pavement porosity for infiltration, enabling the calculation of compressive strength for permeable pavement. Utilize all data to determine the pavement slab thickness [24].
The design of permeable pavements is influenced by factors like the scale of the pavement, the specific application (whether it is for walkways or parking areas), and the types of loads they will bear.
The pavement profile illustrates the current layers, with the topmost finishing layer (dense surface) measuring 6 cm, followed by a 3 cm aggregate layer, and finally, a 20 cm sub-base. For the implementation of permeable pavement, the pavements are designed without reinforcement because the applied loads on them are comparatively low also there will be no requirement for foundations [25].
In the project, it is categorized as a micro-scale pavement designed to accommodate only foot or light traffic [26].
Considering the average annual rainfall volume is 1941.61 m3 and considering the runoff coefficient an average of 1359.13 m3 flows further annually without being utilized, but retaining 582.48 m3.
4.2 Version II
4.2.1 Implementing green roofs on both block roofs and surrounding buildings
The catchment area will change and include building A, B, C and D roof but the rest of the data will remain the same and the area will be A = 1,900 m2 (Fig. 3) [14].
Surrounding buildings roofs to be converted into green roofs (Source: [14])
Citation: Pollack Periodica 2025; 10.1556/606.2024.01056
Considering the average annual rainfall volume on the roof is 1278.7 m3 and considering the green roof's runoff coefficient an average of 639.35 m3 flows further annually without being utilized, but retaining 639.35 m3.
4.2.2 Implementing clogging-resistant permeable pavements and permeable parking area
With a runoff coefficient of 0.5 for the pavement, an average of 1542.85 m³ of water flows annually without being utilized.
Considering the average annual rainfall volume is 3085.71 m3 and considering the runoff coefficient an average of 2,160 m3 flows further annually without being utilized, but retaining 925.71 m3.
5 Results
Based on the data presented in Table 1, it is evident that the absence of green roofs and the use of impermeable pavement materials lead to significant runoff.
Comparison between version I and II
| Category | Q (m3 h−1) | V (m3) | Vret (m3) | |||||
| Green roof | Permeable pavements | Green roof | Permeable pavements | Green roof | Permeable pavements | Green roof | Permeable pavements | |
| Design | 2.77 | 162.48 | 18.44 | 1941.61 | 18.44 | 1941.61 | None | None |
| Version I | 18.44 | 1941.61 | 18.44 | 1941.61 | 9.22 | 1359.13 | 9.22 | 582.48 |
| Version II | 1278.71 | 3085.71 | 1278.71 | 3085.71 | 639.35 | 2160.00 | 639.35 | 925.71 |
where, Q is the runoff, V in the annual rainfall volume, Vret is the water retention volume after implementation.
Source: Author'.
Increased runoff, worsened by unpredictable weather patterns, may lead to future flood risks. However, implementing clogging-resistant permeable surfaces and green roofs boosts water retention capacity to about 600 m3. This translates to enough water for approximately 80 irrigation cycles since 3 L are needed per 1 m2, which can adequately cover multiple summer irrigation needs. Expanding these elements across larger surfaces yields superior outcomes in rainfall collection and runoff mitigation. This not only helps control flooding but also eases strain on the primary system.
6 Conclusion
The observation of the positive impact of implementing new measures in urban water management, specifically in controlling rainwater and enhancing livability, motivates to focus on the city of Pécs. Aiming to explore more the effects of implementing new strategies in Pécs to enhance urban water management practices and ultimately contribute to the overall livability of the city of Pécs.
The implementation of green roofs significantly enhances water capture and retention. Extensive green roofs on two blocks can catch and retain 50% approximately 9 m³ of runoff. Expanding the area by adding surrounding roofs increases captured water by about 70%. In comparison, permeable pavements retain around 30% of runoff (582 m³), when limited to pedestrian pathways. When extended to include parking spaces, permeable pavements capture nearly 1.5 times more. However, the results suggest that the reduction in runoff and alleviation of sewer system pressure from green roofs are substantially greater than those from using permeable materials. However, the results suggest that the reduction in runoff and alleviation of pressure on the sewer system due to green roofs are substantially greater than the impact of using permeable materials.
Ultimately, incorporating sponge city elements can foster a more favorable environment. This enhances livability and contributes to a more sustainable design.
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