Sustainable Water Retention Strategy for Urban Resilience: A Valorization and Action Model for Cities

Abstract

The objective of this article is to propose a novel model for evaluating retention solutions in urban areas. This model is designed to serve as a tool to support integrated urban planning in the context of reurbanization and climate change adaptation processes. The model is both diagnostic and decision-support in nature, integrating spatial, environmental, and functional data. It analyzes these data based on a spatial dependency matrix. A comprehensive consideration of both physiographic factors (e.g., geomorphological typology and land ownership) and social and institutional factors (e.g., institutional readiness and stakeholder engagement) was undertaken. The modelling employs methodologies that are characteristic of urban and landscape design, including multi-criteria analysis, case studies, expert assessment, and Geographic Information System (GIS) tools. The assessment of the retention potential was conducted with consideration for the typology of buildings, infiltration capacity, soil permeability, and existing infrastructure. The findings of the present study demonstrate that local spatial and social conditions exert a substantial influence on the efficacy of retention implementation. The model enables the prioritization of actions and the selection of suitable solutions (context-sensitive retention strategies), thus making it a valuable instrument for designers, urban planners, and decision-makers. The proposed approach can be used in urban planning as a practical tool to support decisions on resilient city development and urban water management.

1. Introduction

Reurbanization, defined as the renewal and intensification of the use of already urbanized areas, is currently one of the key tools for shaping urban space in Europe. This paradigm shift encompasses not only the repopulation of city centers but, more significantly, a profound functional, environmental, and infrastructural metamorphosis of urbanized regions. This term, first introduced by Elisabeth Pfeil, was a response to problems related to urban sprawl and chaotic spatial growth of cities [1,2]. The process of reurbanization has been defined as the optimization of existing spatial and technical resources, counteraction of the degradation of urban centers, and rebuilding of their social and environmental potential. Leo Klaassen’s approach to reurbanization posits that the process is not confined to the number of inhabitants; rather, it entails a transformation of the urban structure that fosters local community development, enhances access to services and public spaces, and augments the functionality and appeal of the city [3]. For countries such as Poland and the Czech Republic, where approximately 60% and 73% of the population live in cities, respectively, it is imperative to enhance the resilience of urbanized areas to the challenges posed by climate change, water scarcity, environmental degradation, and deteriorating health conditions [4].

In recent years, Central European cities have been encountering an escalating degree of severity in the impacts of climate change. Extreme weather phenomena, including but not limited to prolonged droughts, heavy rainfall, urban floods, and rising urban surface temperatures, have been shown to have a direct impact on the quality of life of residents and the stability of technical infrastructure. Such pressures serve to highlight the structural urban weaknesses of cities, whose urban fabric has frequently been developed in a manner that is not adapted to contemporary environmental challenges. In response to the aforementioned threats, concepts related to blue–green infrastructure are gaining increasing importance in European strategic documents. This term is understood to denote a system of spatial and technological solutions that support water circulation and retention, as well as city adaptation to climate change. The European Green Deal, the EU’s overarching environmental strategy, signifies the imperative to incorporate climate, biodiversity, water resources, and soil actions within spatial planning and infrastructure investments [5,6,7,8,9,10]. Projects that are focused on decreasing surface sealing, restoring land retention, and establishing novel forms of rainwater management in urban environments are endorsed.

At the EU level, current spatial strategies are centered on the models of a compact city, a functionally diverse, regenerated, and ecological city. This approach promotes urban areas with high building density, limited dispersion (no land take), adaptive capacity, and a high share of greenery and water in the landscape [6,7,8,9,10,11,12]. The aforementioned activities are complemented by the concept of a sponge city (Sponge City), a strategy that has been successfully implemented in numerous European countries. The concept is predicated on the utilization of natural mechanisms of infiltration and retention in order to regulate water circulation within the urban environment. As demonstrated in [13], solutions based on this model have been shown to reduce costs related to water and sewage investments by up to 20–30%, whilst simultaneously increasing hydrological safety and the quality of public space.

The development of new housing estates and commercial investments often leads to radical changes in the water relations of the area, increased surface runoff, increased risk of flooding, and deterioration of surface water quality. The absence of suitable retention solutions exacerbates the impact of sealing the area, and the sewage infrastructure frequently proves ineffective in the face of increasingly frequent heavy rainfall [14,15]. Disturbances to the local hydrological cycle have been shown to have significant consequences for the environment, including the impairment of ecosystem self-purification capacity, the obstruction of groundwater infiltration, and the disruption of natural habitats [16,17]. In response to the aforementioned challenges, EU Member States, including Poland and the Czech Republic, have introduced a series of legal regulations with the objective of supporting the implementation of blue infrastructure and the sustainable management of stormwater. In this context, national legal acts, including the Polish Water Law of 2017 and the Czech Water Act No. 254/2001 Coll., assume particular significance. These legislative instruments delineate the institutional, technical, and planning framework for the implementation of retention systems within the context of the urbanized environment [8,10].

The integration of spatial planning activities with adaptation solutions, including but not limited to local retention, permeable surfaces, rain gardens, and infiltration tanks, has been demonstrated to be an effective strategy for mitigating flood risk. In addition, this approach has been shown to enhance the ecosystem resilience of the city, improve microclimatic conditions, and quality of life for residents. In this context, reurbanization can be conceptualized as a multi-level process, in which resilience is defined not only as physical resistance to the effects of climate change, but also as the capacity to maintain the functionality, identity, and social integrity of the city in conditions of uncertainty.

The contemporary approach to urban planning is predicated on the assumption that resilience is not confined to the physical durability of infrastructure, but rather extends to the capacity of urban systems to sustain functionality, social cohesion, and environmental value in the face of climate and hydrological disruptions. This concept has gained a strong foothold in research on urban water management, especially following the introduction of the resilience index by Todini. In a 2000 article, Todini proposed an operational definition based on the analysis of the reliability and regenerative capacity of water systems [18]. This model was subsequently developed and adapted in various contexts, including urban planning. In the contemporary context, water resilience indicators have been incorporated into integrated blue–green infrastructure planning models. These models encompass a range of factors, including the retention capacity of space, infiltration, the operational flexibility of systems, and their impact on the quality of life of residents and ecosystem services [19,20]. Analyses of this kind facilitate the evaluation of not only the technical effectiveness of selected solutions, but also their long-term impact on the resilience of urban spatial and environmental systems. Recent publications also emphasize the importance of multi-level modelling, which combines spatial, social, and hydrological data in assessing urban resilience to extreme events such as urban flooding, droughts, and urban heat islands [21,22]. These approaches form the basis of contemporary planning strategies that regard water as a resource, integrating environmental, interpersonal, and functional aspects.

As posited by numerous scholars, models such as the Compact Smart City are currently the foundation of urban policies in many European cities. These models promote the integration of urban functions, the development of public transport, the reduction of the ecological footprint, and the inclusion of nature-based solutions [23,24]. Within this theoretical framework, blue–green infrastructure is posited not only as a tool for adaptation but also as the foundational principle for contemporary urban space design. Nevertheless, the utilization of water as a natural resource remains underutilized. It is predominantly regarded as an infrastructural issue rather than as a component that fosters development and enhances quality of life. The introduction of innovative solutions is hindered by a number of factors, including inefficient sewage systems, a lack of local retention solutions, and inadequacies in planning regulations. Concomitantly, the value of water, in both its utility and environmental dimensions, must be recognized as a pivotal element of urban policy, particularly in the context of the global Sustainable Development Goals (SDGs) [6]. As stated in Goal 6 of the 2030 Agenda, entitled “Clean water and sanitation”, access to potable and sustainable water is recognized as a fundamental human right. However, the implementation of such a model demands not only the assurance of access to resources, but also a paradigm shift in the approach to urban design, transitioning from a technocratic to a systemic and ecosytemic framework [25,26,27].

Despite the proliferation of publications concerning blue–green infrastructure, there persists a paucity of integrated models for assessing urban resilience that encompass both technical retention parameters and the local socio-spatial context. A pressing issue that has yet to be addressed is the lack of a systemic approach that integrates environmental indicators with functional and institutional adaptability. The extant literature suggests that the efficacy of retention infrastructure in crisis situations is contingent not solely on its capacity or throughput, but also on the flexibility of its management and its alignment with local planning strategies [20,22].

The objective of this study is to develop and evaluate an analytical model that will facilitate the valuation and assessment of the efficacy of retention solutions implemented in urban areas, with a focus on their impact on the resilience of the urban structure and adaptation to climate change. This research is predicated on an analysis of local spatial, planning, and environmental conditions, as well as on guidelines resulting from European and national spatial development strategies.

The research conducted herein constitutes an attempt to answer the question of how to effectively integrate reurbanization and blue infrastructure activities with urban landscape design, so that water retention is not only a technical means of managing rainwater, but also a coherent element of public space, the functional structure of the city, and its adaptation policy. A key challenge remains in determining the criteria that should inform the selection of the type and location of retention solutions, with these decisions being dependent on the specific urban context. Different logics apply in dense downtown development and in areas that have been transformed from industrial or post-industrial functions. This study posits the hypothesis that effective retention planning is contingent upon the consideration of numerous factors, including but not limited to building typology, hydrological conditions, the adaptability of existing infrastructure, the directions of local spatial policy, and social expectations.

Despite the extensive scientific literature on blue–green infrastructure and adaptation strategies implemented in cities [23,28,29,30,31,32], the majority of studies focus on the analysis of individual technical solutions or case studies, neglecting to consider the complexity of urban systems in their entirety. It is evident that no approach has yet been developed that would combine the assessment of retention efficiency with the conditions of urban morphology, land use structure, and functional transformation processes within reurbanization. The tools that are available for selecting solutions in a hierarchical manner, based on a multi-criteria analysis of local needs and constraints, are also insufficiently developed. Existing design and decision-making models rarely consider the relationship between urban structure and the potential of space for implementing retention measures, often limiting themselves to hydrotechnical or aesthetic aspects. Conversely, effective adaptation necessitates a systemic approach that integrates knowledge from the domains of hydrology, urban planning, landscape planning, and spatial management.

This publication constitutes an endeavor to address this lacuna by means of the development of an integrated assessment model that has been designed to be utilized by urban designers and landscape architects, as well as decision-makers responsible for the creation of urban policies and the management of public investments. This model is distinguished by its comprehensive approach to spatial data, incorporating not only basic spatial information but also a consideration of the socio-ecological specificity of the area, its historical utilization, the prevailing planning context, and its adaptation potential. The combination of these variables allows not only for the selection of the most appropriate retention solutions but also for their staging and scaling, depending on the available resources and the objectives of local development strategies. The model is predicated on a multi-level analysis. This analysis begins with the identification of technical and spatial possibilities and continues with the assessment of ecological and social effects. Ultimately, it concludes with an evaluation of the potential impact on the resilience of the city as a system. The model is constructed on the basis of spatial data, field inventories, and case studies, which demonstrate the functionality of different types of retention in specific urban systems. The objective of this study is twofold: firstly, to provide a comprehensive overview of existing solutions, and secondly, and most importantly, to develop a novel diagnostic and decision-making tool. The tool will facilitate enhanced integration of water planning with reurbanization and adaptation processes in urban areas.

2. Materials and Methods

The subject of this study is an original model for assessing retention solutions, created for the purposes of planning water resources management strategies in the process of urban reurbanization. It is predicated on the consideration of the context of implementing blue infrastructure in urban spatial structures, and various forms of retention, which are adapted to the specificity of local environmental, urban, and social conditions. Its fundamental component pertains to the evaluation of implementation potential, the identification of implementation barriers, and the analysis of the potential environmental, social, and functional benefits that may arise from the introduction of retention systems. The model is predicated on the assumption that the integration of blue infrastructure with reurbanization processes necessitates the utilization of an interdisciplinary analytical approach, combining knowledge from the fields of urban planning, landscape planning, urban hydrology, and spatial and environmental policy with the objective of providing a framework to facilitate decision-making processes in prioritizing retention measures at the local level. It was asserted that water retention should be recognized as a pivotal mechanism for enhancing urban resilience in the context of climate change and the European Green Deal strategy.

In the course of designing and developing the model, a wide range of research sources was utilized, incorporating the following: (1) A review of current scientific publications and specialist studies on blue–green infrastructure, adaptation strategies, and retention practices used in urban planning and landscape architecture will be conducted. (2) Queries of legal acts and strategic documents will be made, including national and EU guidelines on water policy, spatial planning, environmental protection, and standards related to stormwater management. (3) Examples of technologies and design solutions will be analyzed. This paper presents a comprehensive review of reorganization implementations in European cities, encompassing a wide range of spatial interventions. (4) The analysis encompasses case studies of selected reurbanization projects, with a focus on those incorporating a retention component in diverse spatial and functional contexts.

The detailed analysis of publications also encompassed issues related to technical standards, the history of spatial transformations, ecophysiographic documents, and the results of local climate studies. A comparison was made between all the aforementioned elements and the requirements resulting from the implementation of the objectives of the European Green Deal and the pursuit of climate neutrality.

The research model adopted a diagnostic and decision-support framework, serving to facilitate spatial planning and analysis of spatial flow within the context of urban water retention planning. The design of the model is predicated on the integration of spatial and environmental data with the relationships between urban, infrastructural, and natural components. These relationships are analysed using a spatial dependency matrix. This approach is reflected in research on sustainable water resource management in cities globally [30,33].

A comprehensive consideration of environmental factors is imperative for a nuanced understanding of urban retention systems. These factors encompass topography, hydrological networks, geomorphological classifications, and functional and spatial data. The type of land development, land ownership, and the availability of biologically active areas are crucial components of this multifaceted analysis. The recommended analytical framework for urban retention systems [34] provides a structured approach to evaluate these elements, ensuring a comprehensive and systematic examination of the environmental factors that influence urban retention systems. Analogous criteria are employed in analyses of small-scale retention in urban areas in Poland [35], as well as in assessments of landscape susceptibility to rainwater absorption in Central Europe [36].

The model facilitates the evaluation of the retention potential of urbanized areas, incorporating a range of factors including the degree of surface sealing (impervious surface ratio), soil permeability, infiltration coefficients, stormwater storage capacity, and the potential for restoring natural hydrological processes [37]. Local retention conditions are analysed in a similar manner in projects related to green infrastructure planning and distributed retention [38].

The modelling process incorporated a comprehensive consideration of factors that impede the implementation of retention solutions. These factors encompass technical, organizational, and social dimensions. The analysis encompassed a range of factors, including resource availability, stakeholder engagement levels, institutional readiness, and constraints imposed by existing infrastructure [39]. The examination of social and institutional barriers underscores the significance of stakeholder integration, a fundamental aspect of European water resource management models [38].

Furthermore, an estimated assessment of environmental and social effects was conducted, incorporating the valuation of ecosystem services, microclimatic benefits, biodiversity enhancement potential, impact on the quality of life of residents, and landscape value, consistent with methodologies employed in contemporary urban planning [40,41]. A similar approach was used in studies on green infrastructure in European conditions, with an emphasis on urban ecosystem services [33], and in analyses of Polish riverside areas, where the impact on quality of life and city resilience was assessed [30].

In the calculation part, a simplified quantitative model was used, based on applicable national standards, including the Polish Standard PN-EN 752-2 [42], enabling the estimation of the surface runoff volume ($Q_r$), in accordance with the following formula: $Q_r = r \times \psi m \times \mathsf{\Sigma }A$, where $r$—precipitation intensity [mm/h], $\psi m$—runoff coefficient (depending on the type of surface), and $\mathsf{\Sigma }A$—total catchment area [m²] [43,44,45,46].

The empirical element of the research concentrated on ascertaining the implementation conditions for retention in specific urban areas. Field inventories were conducted in order to ascertain the following: the presence of fauna and flora that are characteristic of a given area; the structure of land use, including the share of biologically active and sealed surfaces; the functions of buildings and public spaces; communication systems; infrastructure availability and connections with the urban transport system; and soil quality, water and ground conditions, and existing water resources. Spatial and environmental analyses were conducted in the context of the broader landscape structure of the city. This approach enabled the consideration of the functional, compositional, and ecological relations of a given area. The findings from these studies were utilized to ascertain the viability of implementing retention systems within the context of local specificity.

The applied approach combines multi-criteria analysis methods, GIS elements, and expert assessment. Spatial analyses were conducted using QGIS (version 3.x), based on proprietary vector and raster layers prepared on the basis of field surveys and spatial data obtained from public sources. A rudimentary expert classification scheme (semi-quantitative) was utilized to evaluate the retention potential, employing a comparative analysis of local environmental and urban indicators. The model is not founded upon sophisticated statistical or hydrodynamic modeling techniques, but rather upon spatial decision support tools within the domain of urban planning. The methodology employed in this study is consistent with the approach commonly used in architectural and urban planning practice. This methodology involves the analysis of space based on its functional and spatial relationships, the urban landscape structure, building typologies, and the adaptability of existing infrastructure. This approach facilitates the development of scenarios for the implementation of retention solutions that consider the urban, compositional, and social context, as well as technical parameters. For each case, a set of key spatial and environmental parameters was determined, from which valuation categories were then derived. This enabled the comparison of retention solution variants in terms of their adaptive efficiency, implementation costs, and added value for the urban landscape. The analysis of functional and environmental parameters was conducted in alignment with the principles of sustainable development, climate neutrality, and the Smart City concept [47,48,49,50,51]. The model presented here functions as a tool to support integrated urban design, thereby facilitating the incorporation of environmental, functional, and social dimensions into planning decisions. This approach aligns with the principles of modern resilient urbanism. The methodology has been meticulously designed to facilitate the adaptability of the model to diverse spatial scales and local conditions.

3. Results

The resilience and adaptive capacity of cities have so far been determined based on the identification of factors influencing the transformation of urban infrastructure and urban systems, such as the natural system, which includes biologically active areas, public spaces, and mobility in relation to the urban landscape. The analyses conducted during the development of the discussed model included the identified additional categories and factors important for shaping the water retention index and water footprint of cities, the necessary scope of the database, and the structure of connections for regenerative spatial planning in situations of crisis and climatic stress. It was considered advisable to link the analysis of solutions in the field of water retention and the ability to adapt to climate change with studies of city morphology, riverbed development, because a fully urbanized recreational zone with a natural character and small water reservoirs significantly contributes to improving the quality of urban space.

The model adopts the following criteria, which, according to the authors, are necessary for the assessment of the following:

➢

Typology of water retention in reurbanized areas: a collection of examples and case study analysis;

➢

Characteristics and indicators important for shaping the resilience of urban areas and sustainable development;

➢

Characteristics and urban indicators in shaping the functional and spatial structure and landscape of the city and its infrastructure;

➢

Characteristics and indicators important for water retention capacity and for social and ecosystem services.

In the adopted model, the developed databases should be compared with water retention categories and representative examples of implementation. It was considered reasonable to assess the impact of water retention on the resilience and sustainable development of cities in relation to the following areas, divided into the following groups requiring assessment:

➢

Outdoor retention tanks, water garden, and riverbank;

➢

Temporary outdoor retention: rain gardens, retention basins, channels, absorbent blinds, basins, channels, and absorbent silting;

➢

Temporary outdoor retention: retention roofs and wet roofs;

➢

Underground retention tanks;

➢

Temporary underground retention seepage tanks and absorption wells;

➢

Temporary underground retention of water, absorbing geocomposite and hydrobox.

As part of the assessments of the impact and importance of water retention for the resilience and sustainable development of cities, it was considered appropriate to determine the following:

➢

The role of water retention in urban resilience and adaptive capacity in the face of climate change;

➢

The role of water retention in urban planning: application in the urban landscape and urban factors directly related to water retention in urban planning;

➢

Data and indicators are used to determine the retention capacity and demand for water for social and ecosystem services.

The above-mentioned research criteria, in connection with the collected retention types and source materials, became the basis for formulating recommendations for the use of retention solutions and blue infrastructure in order to shape the city’s resilience in the reurbanization process. The research model is illustrated in the diagram below (Figure 1):

The validity of the adopted assumptions regarding the significance of the impact of the research assumptions adopted in the model was confirmed by the study research, the results of which are presented in

Table 1. Roles of water retention for urban resilience and sustainability.

Role for Urban Resilience and Adaptability in View of Climatic Changes	Typology of Water Retention in Re-Urbanized Areas
	1	2	3	4	5	6
The ability to absorb disturbances	+	+	+	+	+	+
Adaptability to stress	+	+/−	+/−	+	+/−	+/−
Absorption and neutralization of pollutants	+	+	+/−	+/−	−	−
Temperature regulation—reduce temperature	+	+/−	+	−	+/−	+/−
Improve environmental parameters	+	+	+	−	+/−	−
Self-sufficient solution	+	+/−	+/−	−	−	−
Social services—conditions for social activities	+	+/−	−	−	−	−
Ecosystem services regulation	+	+/−	+/−	−	+/−	+/−
Improve safety for ecosystem services	+	+	+	+/−	+	+
Regulation for sustainable use of resources	+	+/−	+/−	+	+/−	+/−
Preventing water runoff and flooding during flash floods	+/−	+	+	+	+	+/−
Air flow regulation	+	+/−	+/−	−	+/−	−

Notes: Designations of assessment areas: 1. Open-air retention tanks, water garden, river waterfront; 2. Temporary open-air retention: rain gardens, retention basins, channels, absorptive muddles, basins, channels, absorptive muddles; 3. Temporary open-air retention: retention roofs and wetland roofs; 4. Underground retention tanks; 5. Temporary underground retention infiltration boxes and absorption wells, 6. Temporary underground retention water sorbing geocomposite and hydrobox.

,

Table 2. Roles of water retention for urban planning: application in the urban landscape and urban factors directly related to water retention in urban planning.

Role for Urban Planning: Application in the City Land- Scape and Urban Factors Directly Related to Water Retention in Urban Planning for Green Deal Strategy Implementation	Typology of Water Retention in Re-Urbanized Areas
	1	2	3	4	5	6
Important city landscape element	+	+	+	−	−	−
Functional local attractor	+	+	+/−	−	−	−
Important waterfront solutions	+	+	−	−	+/−	−
Temporary waterfront	+/−	+	−	+/−	+/−	−
Landform and slope parameters for the surface water runoff zone	+	+	−	+/−	+	+/−
Special zone for blue infrastructure	+	+	+/−	+	+	+/−
Special zone for green infrastructure	+	+	+	+/−	+/−	+/−
Index biologically active area	+	+	+	−	+/−	−
Watershed area site area	+	+	+	+	+	+/−
Functional greenery system index	+	+	+	−	+/−	+/−
Functional public space index	+	+	+/−	−	−	−
Intensity index	+	+	+/−	+	+	+/−
Underground intensity index and development area	+/−	−	−	+	+/−	−
Distance required between the retention facility and buildings, and the project site boundary	+	+	−	+/−	+	+/−
Parameters of the impact of development on water resources (depression funnels and the effect of lowering groundwater levels as a result of development)	+/−	+/−	−	+	+/−	−
Field water absorption and infiltration capacity index	+/−	+	−	−	+	+/−
Flood or waterlogging risk index	+	+	+/−	+	+	+/−
Permeable surface index	+/−	+	−	−	+	+/−
Green roof and green wall area index	+/−	+	+	−	+/−	−
Drought-tolerant plant area index	+/−	+	+/−	+/−	+/−	+/−
Area index of hydrophilic plants	+	+	+	+/−	+/−	−
Greenery leaf area index (LAI) evapotranspiration plot index	+	+	+	−	+/−	+/−
Index of shading areas: tree crowns, screens, and canopies	+/−	+	+/−	−	−	−
Index of cooling surfaces or water areas	+	+	+	−	+/−	+/−
Storage Tank Capacity Index	+	+/−	−	+	+/−	−
Site function and purpose of the retention basin	+	+	−	+	+/−	−
Ecological Footprint	+	+	+	+	+	+

Notes: Designations of assessment areas: 1. Open-air retention tanks, water garden, river waterfront; 2. Temporary open-air retention: rain gardens, retention basins, channels, absorptive muddles, basins, channels, absorptive muddles; 3. Temporary open-air retention: retention roofs and wetland roofs; 4. Underground retention tanks; 5. Temporary underground retention infiltration boxes and absorption wells; 6. Temporary underground retention water sorbing geocomposite and hydrobox.

and

Table 3. Data and indicators for determining the retention capacity and water demand for social and ecosystem services.

Data and Indicators for Determining the Retention Capacity and Water Demand for Social and Ecosystem Services for Adaptability	Typology of Water Retention in Re-Urbanized Areas
	1	2	3	4	5	6
Soil type (cohesiveness and permeability)	+	+	−	+/−	+	+/−
Groundwater level	+	+	−	+	+	+
Rainwater and stored water quality index	+	+	+	+	+	+
Destination indicator for stored water	+	+/−	−	+	+/−	−
Water consumption rate for production and distribution purposes	+	−	−	+	−	−
Indicator of rainwater and snowmelt demand for ecosystem purposes and microclimate improvement	+	+	+	+	+	+
Rainfall index (means and extremes)	+	+	+	+	+	+
Index of daily temperature amplitudes	+	+	+	−	+/−	+/−
Air quality index (averages and extremes)	+	+	+	−	−	−
Index of areas absorbing or accumulating solar energy	+	+	+	−	−	−
Surface runoff design rain value, the runoff coefficient, and the total surface	+	+	+	+	+	+

Notes: Designations of assessment areas: 1. Open-air retention tanks, water garden, river waterfront, 2. Temporary open-air retention: rain gardens, retention basins, channels, absorptive muddles, basins, channels, absorptive muddles, 3. Temporary open-air retention: retention roofs and wetland roofs, 4. Underground retention tanks, 5. Temporary underground retention infiltration boxes and absorption wells, 6. Temporary underground retention water sorbing geocomposite and hydrobox.

as a summary of the analysis conducted: queries and publications, reports and legal guidelines, selected examples of solutions, implementations, and technologies.

The “+” sign indicates a significant impact of a given indicator on the assessment result, the “+/−” sign indicates that the factor should be taken into account, but does not have to be, and the “−” sign indicates that the factor is insignificant.

The presented analysis results constituted the basis for determining the typology and elements of the retention system in the city and the selection criteria for the analysis of sample investments and building a database for the theoretical model in order to verify and form guidelines to facilitate decision-making processes.

Models for Selecting Retention Types in Relation to Local Conditions

Although the catalogue of possible solutions for shaping the city’s resistance to threats resulting from climate change, such as torrential rains, floods, or other threats, is wide, their selection is always limited to a specific case, the nature of which is usually very diverse. These may be planning decisions, spatial, landscape, soil conditions, etc.

Based on the analysis of case studies in the context of local conditions, a detailed retention type selection model was built (Figure 2), in which selected parameters were assessed:

The following part of the paper presents examples of residential buildings diversified in terms of the scale of development (basic size parameters), location, and planning conditions (

Table 4. Case study no. 1—multi-family housing estate at Berensona Street in Warsaw (2010–2015).

1.	Plot area	17,427 m2
	Building area	4150 m2 (24%)
	Hardened surface	4303 m2 (24%)
	Biologically active surface on native soil	8974 m2 (52%)
	Green area over the garage	No underground garage
2A.	Favorable ratio of building area to plot area. Large area of undeveloped and unpaved land
2B.	High level of groundwater, very low soil absorption. Threat of local flooding if an appropriate rainwater retention system is not used. Planning guidelines specifying the need to cover the designed buildings with pitched roofs with an angle of inclination of the roof surface from 30 to 45 °, and cover with a tight material (sheet metal or ceramic roof tiles)
3.	Qr = 98.12 l·s−1, Capacity of designed tanks = 120 m3
4.	Open evaporative tank with a capacity of 120 m3, reinforced concrete, partially recessed, fenced. Storm sewerage with inspection wells (it is necessary to filter rainwater collected from the surface of paved sidewalks and roads)
5.	0–100%

,

Table 5. Case study no. 2—multi-family housing development with underground garages at Lipowa Street in Pruszków.

1.	Plot area	4470.00 m2
	Building area	1765.28 m2 (39%)
	Hardened surface	696.50 m2 (16%)
	Biologically active surface on native soil	1112.58 m2 (25%)
	Green area over the garage	895.64 m2 (20%)
2A.	Absorbent soil, existing storm sewer system at the plot, enabling partial collection of storm water, the Surface of flat roofs of underground garages enables the use of green roofs
2B.	A relatively large development area, partly occupied by underground garages.
3.	Qr = 37.56 l·s−1, Capacity of designed tanks = 28 m3
4.	Sealed retention tanks with a total capacity = 28 m3
5.	47–53%

,

Table 6. Case study no. 3—multi-family residential building at Ogińskiego Street in Warsaw, 2018–2021.

1.	Plot area	708.00 m2
	Building area	256.38 m2 (37%)
	Hardened surface	40.96 m2 (6%)
	Biologically active surface on native soil	66.10 m2 (9%)
	Green area over the garage	344.56 m2 (48%)
2A.	The relatively large surface area of the slab above the garage and the need to ensure an appropriate biologically active surface coefficient favor the use of a green roof as an auxiliary solution for water retention.
2B.	The garage area is over 80% of the plot area. Limited area of land for development
3.	Qr = 4.06 l·s−1, Capacity of designed tanks = 16.85 m3
4.	Green roof on the slab above the garage, Sealed rainwater tank located in the building under the access ramp to the garage, with a capacity of 16.85 m3. Water collection from the tank to the rainwater sewerage system in portions specified by the conditions of connection to the network.
5.	47–53%

and

Table 7. Case study no. 4—complex of residential buildings with commercial premises and an underground garage at Ostródzka Street in Warsaw, 2020–2023.

1.	Plot area	6627.7 m2
	Building area	2523.4 m2 (38%)
	Hardened surface	1124.8 m2 (17%)
	Biologically active surface on native soil	2578.11 m2 (39%)
	Green area over the garage	401.39 m2 (6%)
2A.	The characteristics of the subsoil allow for the use of underground devices that temporarily collect and drain rainwater. The large surface area of the slab above the garage (despite the impossibility of including a green roof in the balance of biologically active area, a limitation resulting from local planning guidelines) allows the use of a green roof as an auxiliary solution for water retention.
2B.	Local planning guidelines prevent the inclusion of the surface area occupied by surface water in the balance of biologically active surface area, which, given the relatively large surface area of the open reservoir in relation to the plot area, ruled out the use of such a retention method. The requirement to cover buildings with pitched roofs and cover them with sheet metal prevents local water retention and requires its drainage through the sewage system to reservoirs located below the ground surface (drainage boxes).
3.	Qr = 47.0 l·s−1, Capacity of designed tanks = 98 m3
4.	Green roof on a slab above the garage, retention and drainage tank embedded in the ground
5.	20–80%

). Using individual catalog cards, an analysis of the facilities was presented based on the detailed retention selection model.

In order to systematize the dependencies, a graph was prepared (Figure 3) presenting the percentage share of the development area, hardened and biologically active, in relation to the amount of rainwater to be managed per m² of biologically active area.

In the diagram below (Figure 4), a curve showing the level of rainwater load on the biologically active surface has been superimposed on the bar graphs illustrating the basic numerical values characterizing the analyzed cases, separately for the gross biologically active surface (on the native soil and on the garage slab) and the net, only on the native soil. This distinction is important because in the context of the retention problem, green areas are considered its natural solution (under certain conditions, which will be discussed later). Of course, this refers to natural retention at the place where precipitation occurs. Nevertheless, it should be noted that local planning guidelines (local spatial development plans) define the biologically active surface in a different way; therefore, the data used in the analysis refer to the actual sizes of these surfaces, and not their interpretation based on planning guidelines.

A summary table was created with the assigned retention type that was used (

Table 8. Types of retention in each multi-family complex/building, marked with “+” sign.

1. open-air retention tanks, water garden, river waterfront, 2. temporary open-air retention: retention roofs and wetland roofs, 3 underground retention tanks, 4. temporary underground retention infiltration boxes and absorption wells	1	2	3	4
Multi-family housing complex, Berenson Str., Warsaw	+
Multi-family housing complex, Lipowa Str., Pruszków			+
Multi-family residential building, Ogińskiego Str., Warsaw		+	+
Multi-family housing complex, Ostródzka Str., Warsaw		+		+

).

Based on the analysed cases, a very complex list of dependencies can be built, in which specific conditions influence each other, determining the choice of retention method. However, based on the analysed cases, three basic categories of problems that designers face when deciding on the retention method can be distinguished. If we expand each category with a list of basic data resulting from the conditions of a specific location, we can try to create a basic model for selecting the retention type presented in the diagram below (Figure 5).

4. Discussion

The development of city resilience in the process of reurbanization is the ability to absorb disturbances while maintaining the same basic structure and ways of functioning, the ability to self-organize, and the ability to adapt to stress [52,53]. Currently, various mathematical models are used for hydrological research; some of them are based on local indicators, others are based on global and comprehensive studies for a given country [54,55]. The ability to adapt to changing factors is described by the model presented in this article, which is necessary to determine the structure of connections and interactions of systems and dependencies in connection with the functional and spatial structure, building development parameters, and the analysis of ecosystem needs and social needs [56,57]. The implementation of a water retention system is an important issue for the resilience of cities and urban landscapes [58,59]. Effective strategies combine nature-based solutions, hybrid infrastructure, and participatory management to mitigate floods, stabilize groundwater, and increase biodiversity [60,61]. The role of water reservoirs can only be ensured in the case of careful and responsible design and sensitive integration into the landscape in order to increase water retention and water quality [62]. In urban environments, they can significantly contribute to the retention and infiltration of rainwater. Therefore, it is necessary to comply with regulations on stream regulation, rainwater drainage, and reservoir designs. This is the only way to ensure safe water flow in urban environments, which is well illustrated by the example of Zagreb (Croatia) [63,64]. Attention should also be paid to solutions based on the natural capabilities of the terrain regarding the city’s resistance to water management problems, indirectly related to water reservoirs. The use of dams in combination with ponds is one of the strategies for dealing with flash floods, an example of which is the Püspökszilágy system (Hungary), which has allowed for the reduction of infrastructure losses by 250,000 euros per year. Savings were brought by actions based on the monitoring of the retention structure by involving 9 million farmers and residents of the areas covered by the program in coordination and participatory management [65,66]. Another action is the use of rain gardens and permeable surfaces on a large scale, as illustrated by the example of Wuhan (China) as an urban structure based on the Sponge City system, where infiltration rates were increased by 32 mm·day⁻¹ [67,68]. This example clearly shows how important a holistic approach to water management issues is in city planning policy [69]. Appropriate management of green (ecosystems), grey (engineering), and blue (water) elements with the use of appropriate technical infrastructure allows for savings of around EUR 600 million per year [70,71]. The multi-level nature of the adopted water management strategies is also important, from the macro scale at the level of managing urban development policy to the micro scale related to specific buildings [72,73]. Studies have shown that rainwater collection and dry wells used in households have reduced the demand for urban water by 15–20% [74]. Action based on various types of hybrid structures combining retention with specific social functions in cities is also important, an example of which is Oslo (Norway) on the scale of urban development policy [75]. An example of such a procedure is the “delay-store-drain” (DSD) systems in Dong Hoi (Vietnam), where the management of the water system in the city was combined with recreational functions [76]. The research presented in the article and the above examples indicate a very important role played by water management in the contemporary development of cities [77]. Appropriate actions at the level of design, financing, and implementation of the adopted solutions are responsible for the water safety of urban structures [78,79].

5. Conclusions

Summarizing the above results, it seems reasonable to shape urban indicators, development parameters, and the functional and spatial structure of the city, taking into account the functions that blue and green infrastructure can perform. Solutions such as a water retention system should be elements of a spatial policy strategy and critical infrastructure in relation to the need for rational and sustainable water management. The conscious shaping of regenerative and adaptive solutions with ecosystem services provides the basis for the introduction of spatial and infrastructural solutions that influence the parameters of the built environment. The identification and designation of crisis areas at risk of drought, water scarcity, and overheating is the basis for selecting mitigation solutions to climate change and adaptability in regenerative design. The importance of green space in the city and the city’s water retention and use system provides the basis for shaping new functions in the city, including food and energy production.

Urban agriculture and agroforestry in the city can be a response to further emergencies related to the effects of climate change. The move towards self-sufficiency and the use of renewable energy sources, together with the drive to reduce the ecological footprint, including carbon and water footprints, is a very important element of the reurbanization process. Thus, the design of sustainable development and regeneration in the re-urbanisation of urban crisis areas is linked to the urban infrastructure management system and the introduction of development elements to reduce the negative effects of climate change. This demonstrates the relevance of interdisciplinary research in this area and the discussion and presentation of infrastructural solutions that can be applied and are recommended for consideration in urban and architectural design and city landscaping.

The studies presented in this article were an attempt to unify the guidelines and create a package of indicators necessary to be determined when planning the structure and sustainable development of a compact city, referring also to city landscape design and urban resilience.

The presented analyses and results allowed the following:

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Development of the typology of blue infrastructure elements in the structure of the city landscape is important for urban resilience and the mitigation of climate change;

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Development of the multicriteria analysis and making the conclusions about the most important urban indicators and parametric data that should be determined for an effective water retention system and waterfront management in the re-urbanization process have been selected;

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Draw attention to resilience related to adaptability to climate change and crisis situations, and the social and ecosystem needs of the modern city.

However, the authors would like to point out that the use of the above recommendations always requires detailed calculation data, which should be determined for the indicated location. Such calculations will be presented for a specific object in the next article.