Department of Sanitary and Ecological Engineering Thakurova 7, Praha 6, Czech Republic

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1 NOVATECH 2013 Drainage Area Study of the city of Hradec Kralove, Czech Republic, and its utilization for urban planning L étude des taux d écoulement sur le territoire de la Ville de Hradec Kralove et son utilisation pour la planification urbaine Suchanek M. 1, Vitek, J. 2, Finfrlova P. 3, Stransky D. 4 and Kabelkova I. 4 1 DHI a.s., Na Vrších 1490/5, Praha 10, Czech Republic m.suchanek@dhi.cz 2 JV PROJEKT VH s.r.o., Kosmákova 1050/49, Brno, Czech Republic vitek@jvprojektvh.cz 3 Magistrat mesta Hradce Kralove, Ceskoslovenske armady 408, Hradec Králové, Czech Republic. finpav1@tiscali.cz 4 Czech Technical University, Faculty of Civil Engineering Department of Sanitary and Ecological Engineering Thakurova 7, Praha 6, Czech Republic stransky@fsv.cvut.cz; kabelkova@fsv.cvut.cz RÉSUMÉ L étude des taux d écoulement sur le territoire de la Ville statutaire de Hradec Kralove et des zones tributaires connexes est un vaste projet d économie des eaux définissant la conception de traitement des eaux de pluie dans le bassin en question en conformité avec les principes du développement durable. L étude a pour but d entrelacer les principes et les critères de l économie de l eau pluviale sur le plan territorial de la ville. L étude comprenait l évaluation complexe de l état actuel du traitement des eaux pluviales incluant les risques d inondations, l évaluation du potentiel des constructions existantes du point de vue de rapprochement des taux de précipitation et d écoulement aux conditions naturelles et la délimitation des conditions d assèchement des nouvelles constructions. ABSTRACT Drainage Area Study of the city of Hradec Kralove, Czech Republic, and its utilization for urban planning of Hradec Kralove and adjacent regions is a large water management project defining concept of stormwater management in the region in accordance with the sustainability principles. The goal of the study was to link rules and criteria of sustainable stormwater management with urban planning. In the framework of the study a complex assessment of the current status of water management including the risk of flooding was performed, potential of the existing development to approach pre-urbanization runoff behavior was evaluated and conditions of stormwater management in the planned development were specified. KEYWORDS Stormwater management; Sustainable development; Urban drainage; Urban planning 1

2 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY 1 INTRODUCTION The process of sustainable stormwater management implementation in the Czech Republic was delayed compared to the most developed countries. Till 2009, virtually no sustainable urban drainage systems were applied with exception of individual projects of environmental enthusiasts and EU financed projects (e.g. INTERREG IIIB CADSES project RainDROP, code: 5C052). Since 2009, after the revision of Water Act and regulations to the Building Act, the attitude towards stormwater management has started to change towards sustainability. Priorities of stormwater management were given (Table 1): Table 1. Priorities of stormwater management (if no other utilization of stormwater is planned) in the regulation to the Building Act (2009) Priority 1 Infiltration, in the case of polluted runoff, pre-treatment is needed. If not possible, then: Priority 2 Priority 3 Retention and regulated discharge to the receiving waters (directly or by a separate sewer system), pre-treatment if needed. If not possible, then: Retention and regulated discharge to the combined sewer system In this paper, a pioneer Drainage Area Study of the city of Hradec Kralove (DAS HK) (DHI and JVPROJEKTVH, 2011) focusing on sustainable stormwater management in relation to urban planning is presented, where these priorities were respected and rules and criteria were defined for planned as well as existing development. 2 METHODS 2.1 Pilot catchment The city of Hradec Kralove is situated at the confluence of rivers the Elbe and Orlice having 7 smaller tributaries. Hradec Kralove (96,000 inhabitants in 2010) was planned as a green city before the Second World War by architect Josef Gocar (Figure 1). Today, it is still an excellent example of clever urban planning. Stormwater drainage was solved as a first priority before starting planning the urbanization itself. Gocar designed a system combining natural water bodies and open vegetated channels. Moreover, infiltration systems were created in some areas. However, in the past few decades, Hradec Kralove has suffered from massive urbanization resulting in overloading of the system of natural and artificial water bodies as well as of the sewer system. Figure 1. Regulation plan of Hradec Kralove created by Josef Gocar in

3 NOVATECH 2013 The area of interest of the Drainage Area Study comprised the region of 243 km 2 with about 332 km of rivers, streams and channels (Figure 2). Figure 2. The area of interest 2.2 Goals of the project The Drainage Area Study was a large project comprising many goals. The most important goals in the area of water management were to set a long-term conception of the city stormwater drainage respecting sustainability principles, to link stormwater management within the region with the new City Development Plan and to provide decision support for city authorities. It comprised following tasks: Assessment of current status of the stormwater management in the area and identification of regions of high flood risk both at open channels and in the sewer system, Analysis of the potential of the existing development to approach pre-urbanization runoff behavior, Definition of rules and criteria of sustainable stormwater management in the planned development, Design of measures in the in the catchment, sewer system and open channels. 2.3 Assessment of current status of stormwater management The DAS HK incorporated extensive monitoring and surveys (rainfall, water levels, discharges, water quality parameters, ecological status of streams, catchment hydrogeology and infiltration potential etc.) Hydrodynamic modeling of the sewer system, water bodies, artificial open channels, underground waters and elements of stormwater management was performed (MIKE Urban, MIKE11) and hydraulic capacity of the individual parts of the system as well as flooding frequency was assessed based on a 10-years rainfall data series. CSOs impacts were assessed with REBEKAII. Paralelly, a groundwater flow model was created by Jacobs Consultancy. 3

4 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY 2.4 Analysis of the BMPs potential of the existing development The analysis of the BMPs potential of the existing development focused on the determination of the impervious areas, which can be potentially disconnected from the combined sewer system by applying best management practices (BMPs) of stormwater drainage. The analysis contained four steps: 1. Analysis of the City Plan from the point of view of BMPs application, 2. Field survey of the potential of the area to infiltrate or to delay stormwater runoff (e.g. sufficient green areas), 3. Evaluation of the technical and available BMPs potential in different areas (based on the enhancement of the field survey for hydrogeology, slopes, ecological burdens, character of the development, ownership of the buildings and grounds), 4. Determination of the total BMPs potential of the existing development. 2.5 Water management rules and criteria for the planned development For the purposes of the future city planning, rules a criteria for the areas to be urbanized had to be specified: 1. Analysis of the water regime had to be performed and water management criteria distinguishing areas suitable and unsuitable for the future urbanization had to be set, 2. Possibilities of stormwater management (the selection of the stormwater recipient) in areas suitable for urbanization had to be evaluated respecting priorities set in Table 1, 3. Requirements regarding maximum specific regulated discharge from individual building plots and supplementary assessments had to be specified. 3 RESULTS AND DISCUSSION 3.1 Current status of the stormwater management For the sewer network evaluation a model from the Drainage Masterplan from 2005 was available, however, updating was necessary. The complex network of open channels and streams was mapped and documented for the first time. Hydraulic capacity of streams, open channels and sewers was evaluated using both 10 years rainfall series and design storms. Streams and open channels were ranked according to the reaching of a certain relative water depth during rain events (the categories were set as <60%, 60-80%, % and > 100% of filling). The limiting filling for flooding was considered to be 80% (due to model uncertainties). Sewers were classified based on their overloading defined as the pressure line level above the top of the pipe and a level below the surface. Water levels higher than 10 cm above the top of the pipe for 10 minutes were considered to cause flooding. The capacity of the whole system was presented in thematic maps showing the frequencies of overloading (Figure 3). Areas of flood risk were identified The overloading of the system in urbanized areas begins with the frequency between 2 and 5 years (the sewer system was designed for a 2-years storm originally). Thus, it is apparent that the hydraulic capacity limits the further development of the city as the reserves are small. 3.2 BMPs potential of the existing development In total 92 evaluation sheets were elaborated for existing development giving an overview on the possibilities and restrictions of the introduction of BMPs instead of the conventional drainage system (Table 2). Grounds with areas suitable for stormwater infiltration and prevailing surface slope less than 3% were marked as having technical BMPs potential. Only grounds under city ownership were considered to have an available BMPs potential. Similar evaluation sheets were elaborated for streets and roads within the urban area. The BMPs potential was ranked as available, conditionally available, not available or none (Figure 4). 4

5 NOVATECH 2013 The evaluation of the total BMPs potential showed that the city can disconnect 43 ha of impervious surfaces connected to the combined sewer system, and thus reduce the connected impervious area by 15%. In this way, free hydraulic capacity in the sewer system can be gradually created. Figure 3. Example of evaluation of open channels - frequency of overloading (Map presents number of events per year exceeding the limit on particular branch of the open channel. Ranges are specified: 0-5, 2-10, 10-20, >20 events and they are presented by graduated colors from light to dark blue.) Figure 4. Potential of introduction of BMPs in the existing development (available dark green, conditionally available light green, not available - orange, none red) 5

6 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY Table 2. Example of the BMPs evaluation sheet for existing development Streets POD ZAMECKEM, MILADY HORAKOVE, PROSTEJOVSKA, FRICOVA, URXOVA Local part Trebes Acreage 35 ha Hydrological catchment Trunk sewer C Borders of area Information on the development Technical potential of infiltration Available potential of infiltration Criteria Prevailing development Ecological burdens Stormwater infiltration Presence of areas suitable for stormwater infiltration Prevailing slope of surface Owner of buildings Owner of adjacent areas suitable for stormwater infiltration Classification city centre 5 % multi-storey dwellings 95 % low-storey dwellings industrial area traffic infrastructure Yes no limitations 10% conditionally suitable difficult 90 % impossible Yes < 3% 3% City other City other 6

7 3.3 Incorporation of water management criteria in urban planning NOVATECH 2013 Due to water management restrictions, urbanization is limited in following areas: areas of natural water retention (due to a high underground water level; less than 1 m bellow surface), areas of flood risk, areas that can be used for the accumulation of surface waters in case of flooding. These areas were determined in the catchment and incorporated into the new City Development Plan processing. (Figure 5). Figure 5. Detail of the map with water management limitations to the city development (flooding risk area blue, area for surface water accumulation green, area natural water retention - grey) In addition, decision support and rules for the city authorities and the building politics in terms of sustainable stormwater management were provided: 1. Local possibilities of stormwater management for individual planned development areas were evaluated. In total 24 development areas of ha were assessed in 80 sheets (Table 3). 2. Design criteria and rules for the planned development were specified as following: For individual (scattered) developments, the maximum specific regulated discharge from the ground plot was set as 3 l/(s.ha), the return period for the design of a retention volume as 5 years, Extensive individual developments or large development projects are in addition under the obligation to recalculate the effects on the water regime in terms of the hydraulic capacity of the sewer system, water bodies and artificial channels, and of groundwater level changes. 7

8 A2 - STRATÉGIE D'AGGLO. / CITY SCALE STRATEGY Table 3. Example of the stormwater management evaluation sheet for planned development Development area. 3 ZA METELKOU, DRTINOVA STREET Borders of area Identification of areas Acreage of areas Functional type 6-9/6, 7-9/14, 7-9/30, 6-9/ m 2 suburban low-storey development 6-9/ m 2 multi-storey dwellings Studies and regulation plans Areas of special water regime Natural water retention area Flood risk area Inundation area Adjacent recipients Groundwater groundwater level hydraulic conductivity ecological burden Available surface receiving waters / storm sewers Available combined sewers / foul sewers Drainage concept for stormwaters Groundwater Surface receiving water / storm sewer Combined sewer - Drainage concept for foul waters combined sewer system, sewers B, B18 or B19 Comments - 2 to 5 m below surface 1 x 10 6 m/s no limitations for infiltration Melounka Brook (Identification , Hydrological catchment ) combined sewer B (DN 500) Petra Jilemnického Street combined sewer B 18 (DN 300) U Drevony Street combined sewer B 19 (DN 300) Predmericka Street Decentralized infiltration devices recommended (detailed hydrogeological survey necessary) Melounka Brook recommended for overflows from infiltration devices 8

9 NOVATECH Measures Measures designed to achieve sustainable stormwater management in the city in the long-term comprised not only the above mentioned non-structural measures for both existing and planned development (3.2 and 3.3), but also a range of technical measures such as measures aiming at the reduction of the impervious area of the existing development by 15% within the next 30 years: Removal or sinking of existing curbs, Lowering or adjustment of the surface, Transfer of stormwater from the area of street inlets to decentralized devices, Taking apart gutters and street inlets within green areas, Technical measures in the planned development aim at approaching pre-urbanization runoff conditions (similar hydrograph volume and shape). Four functional types of stormwater management structures were recommended in dependence on the bedrock and ground water level. However, it is beyond the scope of this paper to discuss all measures in detail. 4 CONCLUSIONS The study demonstrates the necessity of integrating storm water management into urban planning. On contrary to past times when Urban Drainage Masterplans were elaborated independently of City Plans, the approach applied shows the important role of water management engineers already during the first phases of urban planning. The water management engineers impose limits on urbanization for urban planning as well as specify technical rules for constructions. Water management criteria incorporated in the City Development Plans guarantee sustainable development of the city. Urban planning is a complicated process going from general tools such as the City Development Plan down to the approval of individual buildings in terms of their technical functionality. Moreover, a large number of actors is involved in this process that must be coordinated (in the case of Hradec Kralove it was the city council, four city commissions and departments, two departments of the state administration, six different surface waters administrators and a sewer system administrator). Thus, it is necessary to prepare transparent step-by-step guidelines specifying activities and responsibilities at each level of urban planning from the stormwater management point of view and provide actors with a decision support system containing consistent data about water issues in the city. The project presented went beyond the current Czech legislation and serves as a good example for similar studies. For the city of Hradec Kralove, the project represents a reconnection to its modern origins and timeless urban planning by Josef Gocar. ACKNOWLEDGEMENTS This work was supported by the project of Czech Ministry of Education, Youth and Sport. MSM LIST OF REFERENCES Act 183/2009 Coll., on town and country planning and building code (the Building Act). DHI and JVPROJEKTVH (2011). Stormwater Runoff Study of City of Hradec Kralove. Technical Report for City of Hradec Kralove (in Czech). 9