Advances in Environmental , Development and Chemistry

The analysis of stormwater runoff and overflow from the catchment

Srdjan R. Kolakovic1, Matija B. Stipic2, Goran B. Jeftenic3, Borislav T. Masic4, Filip M. Stipic5, Slobodan S. Kolakovic6, Svetlana R.Vujovic7

outfall at the north city subcatchment pump station GC II. The Abstract— The subject of the work is the analysis of combined equipment installed by the Faculty of Technical Sciences sewer system in the city of Novi Sad in order to provide a better Department of the Environmental Protection is used to understanding of the wastewater and stormwater management. The measure the flow. This is followed by the precipitation data simulation is run for 3- and 5-year storms using the existing sewer collection (ITP rainfall curve for different return periods) from system mathematical modelling with two options that is, with the weather station Rimski Šančevi, which curve is used as an constant stormwater runoff coefficient throughout the entire input for the flow calculation in the sewer system hydraulic catchment and the variable runoff coefficient as by individual areas of the city. The widely used software package EPA SWMM 5.0 is modelling. used in the hydraulic calculation for the entire sewer system of the Hydraulic model of the upgraded sewer system is formed city of Novi Sad. using the existing hydraulic model, data from the geographic information system and KAT-KOM base, the existing projects Keywords—hydraulic calculation, combined sewer system, and the data from imediate measurements on site. The data on stormwater runoff coefficient the ratio of the pervious and impervious surfaces in individual areas of the city are taken based on the Novi Sad GIS system, I. INTRODUCTION Google map and urban plans. he flow analysis in the sewer system includes the flow Hydraulic calculations in the three analyzed cases are made Twith no overloading (free water level) and with for free flowing (gravity flow) where the receiving overloading (sewer mahnole overflowing and flooding). water level is lower than the outlet invert level that is, where The existing sewer system model includes the force mains of the Danube water level is lower than +240 cm i.e. the Danube diameters larger than 600 mm and designed 35% impervious level is lower than 71.73 m.a.s.l. + 2.4 m = 74.13 m.a.s.l. surface with constant flow coefficient. Pipelines of diameters The sewer system is modelled according to the existing smaller than 600 mm but larger than 250 mm are added to the regulations in the country and the EU regulations for the urban upgraded Novi Sad sewer system model which is the subject of drainage system dimensioning (with return periods of 3 and 5 the work. years) as well as the standards and recommendations used in In the upgraded model the starting uniform impervious the country. surface of 35% throughout the entire city area is replaced with the variable based on the actual construction on impervious II. METHODOLOGY surfaces in individual areas of the city. To provide real-time A. Location data a flow meter is installed in a part of the city catchment, which flow meter shows the flow distribution at the catchment Novi Sad is the administrative center of the Autonomous Province of . It is located on the border between the regions of Bačka and Srem in the Pannonian Basin and the This work is supported by Ministry of and , Republic of northern hillsides of Fruška Gora. The city location is shown (Grant No. TR 37003, TR 37018). in Figure 1. 1 PhD Srdjan R. Kolakovic, grad.civ.eng, Faculty of Technical Sciences, , Serbia, (e-mail: [email protected]). 2 PhD Matija B. Stipic, grad.civ.eng., ,,Vojvodinaprojekt", Novi Sad, Serbia, [email protected]. 3 MsC Goran B. Jeftenic, grad.civ.eng, Faculty of Technical Sciences, University of Novi Sad, Serbia, (e-mail: [email protected]). 4 MsC Borislav T.Masic, grad.civ.eng, Faculty of Technical Sciences, University of Novi Sad, Serbia, (e-mail: [email protected]). 5 MsC Filip M. Stipic, grad.civ.eng., ,,Vojvodinaprojekt", Novi Sad, Serbia, (e-mail: [email protected]). 6MsC Slobodan S. Kolakovic, grad.civ.eng, Faculty of Technical Sciences, University of Novi Sad, Serbia, (e-mail: [email protected]). 6MsC Svetlana R. Vujovic, grad.civ.eng, Faculty of Technical Sciences, Figure 1. The location of Novi Sad University of Novi Sad, Serbia, (e-mail: [email protected]).

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The altitude of the Pannonian Basin flat bottom where the quality of the wastewater from each drainage area as well as city of Novi Sad is situated ranges from 76 m.a.s.l. to 82 the flow, level and velocity of the wastewater and the water m.a.s.l. The right Danube banks are at the altitude ranging quality in each pipeline and conduit are monitored in SWMM from 77 m.a.s.l. to 180 m.a.s.l. during the simulation comprised of many time steps. Hydrological features of the subcatchments studied are B. Climate defined by the following set of input parameters in SWMM: Novi Sad is located in the middle moderate climate zone. 1) Area – the area enclosed within the subcatchment boundary; The average annual precipitation is cca 609 mm as measured 2) Width – the surface flow which depends on the gutter inlets č at state weather station Rimski Šan evi. distribution. The mean spacing between the inlets represents C. The existing sewer system of Novi Sad the width and should not exceed 30 m; 3) Slope – the inclination of the drainage area and it is the The sewer system within the area of Novi Sad is a general same for pervious and impervious surfaces; (combined) sewer system with the common wastewater 4) Imperviousness – the ratio of impervious surfaces on the (sanitary, industry) and stormwater drainage. The system has catchment such as rooftops, roads with no infiltration; been designed to receive the rainfall runoff with the return 5) Roughness coefficient – this represents the resistance or the periods of two and three years depending on the city area it friction applied to the surface flow. Since Manning’s equation serves. The system is divided in two subcatchments: the south is used in SWMM this coefficient is the same as Manning’s city subcatchment and the north city subcatchment ending in roughness coefficient n; main pump stations GC II and GC I, respectively. 6) Detention ponds – correspond to the capacity which has to The north city subcatchment encompasses the area of about be reached prior to the runoff occurance. 930 ha. The receiving water of the total flow rate is the Three different methods for the calculation of losses due to Danube immediately downstream of the GC II. The south city the infiltration on the catchment pervious areas are available in subcatchment covers the area of about 1060 ha. The receiving SWMM. They include the Horton, Green-Ampt and Curve water of the total flow rate is the Danube immediately Number models. The Horton model has long been applied in downstream of the pump station GC I. dynamic simulations. The Green-Ampt model is rather a Stormwater and wastewater at the main pump stations GC I physical model whereas the curve number (CN) model is used and GC II are discharged into the river by gravity at the in simplified discharge models. The Horton model is used in Danube water level lower than +240 cm whereas the water is the work. pumped into the Danube at the higher river levels. Figure 2 The software enables the use of the hydraulic calculation illustrates the existing sewer system in the city of Novi Sad under different flow conditions, unsteady flow in open where the force mains are shown in bold. channels and overloading in pipelines. It enables the

application of different flow coefficients across the subcatchments and rainfall hyetographs for the subcatchment under consideration. Unsteady flow in open channels represents the flow where the water level and flow rate change in time, Q = Q (x, t), z = z (x, t). The flow in open channels is spatial, 3D, but one-dimensional analysis is used for practical reasons. The intersection mean velocity is used as a referential value instead of the valocity at each intersection point, the distribution of streamlines is quasi-parallel and the head distribution is hydrostatic. The Saint Venant equations describe the flow. E. Setting of the impervious surfaces per the city areas Imperviousness represents the ratio of the subcatchment Figure 2. The sewer system in the city of Novi Sad (force mains in covered with surfaces such as rooftops, roads, pavements or bold) car parks from which stormwater is discharged into the sewer D. Application of EPA SWMM 5.0 in the hydraulic system. This is usually the most sensitive parameter in the calculation hydrological description of a catchment. The ratio of EPA stormwater management modelling (SWMM) is a impervious surface ranges from 5% with undeveloped land up dynamic model of the rainfall-runoff simulation for a single to 95% with high density developement. The ratio of storm event or a long (continuous) wastewater quantity-quality impervious surfaces in Novi Sad has been calculated for each simulation from urban areas in particular. The SWMM works individual area of the city. The impervious surfaces have been based on the sum of drainage areas receiving rainfall and calculated for the following areas of the city: Liman, , ć generating runoff carrying pollutants. In the part of SWMM Novo Naselje, , Banati , , , Centar regarding the hydraulic calculation the runoff is transported and . The percentage of impervious surfaces per the through a system of pipelines, conduits, retention/treatment city areas is specified in Table 1. Rooftops, roads, pavements facilities, pumps and control structures. The quantity and are defined as impervious surfaces whereas the remaining surfaces are green pervious surfaces from which no runoff

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flows into the sewer system. The ratio of the impervious surface and the total area of a subcatchment is the runoff coefficient. In addition, the parks and cemeteries from which there is no runoff have been separated. This results in a more real model of impervious surfaces in the city.

Table 1. Percentage of impervious surfaces per the city areas[3] Percentage of impervious City area surfaces (%) Banatic 30 Novo Naselje 35 Telep 30 Liman 30 Detelinara 31 Salajka 26 Figure 4. Storm intensity – storm duration – return period [1]

Podbara 39 According to Serbian standard SRPS EN 752-4 regarding Centar 60 sewer systems outside buildings hydraulic calculation of the Grbavica 50 sewer system in the central urban areas is made such that the system overloading and pressurized flow in the pipelines are Georeferential layouts – KAT-KOM layouts used to calculate not allowed where the system is designed for the 5-year storm the total impervious surfaces per the city areas were first put for the central urban area and the 3-year storm for residential into AutoCAD which then generated the impervious and green areas. The sewer system is designed to receive runoff from surfaces. Figure 3 illustrates pervious and impervious surfaces storms with the return period of three and five years (Figure in the Centre of Novi Sad with roofed surfaces in red, 5). The central city area is dimensioned for the 5-year storm pavements in gray and green surfaces in green. whereas the residential areas (Telep, Novo Naselje, Detelinara) are dimensioned for the 3-year storm. This is the first hydraulic requirement [1].

Figure 3. Impervious surfaces in the Centre of Novi Sad (the impervious surface of 60%)

The calculated mean (average) ratio of impervious surfaces for the entire Novi Sad catchment is 35%.

F. Determination of design storms Stormwater drainage system is dimensioned according to the Figure 5. Three- and five-year storms design design storm. The statistic analysis of storms was made at the G. Determination of the design stormwater runoff from nearest weather station Rimski Šančevi (Figure 4) to determine non-public areas design storms. The storm intensity on ITP curves represents Stormwater management from non-public areas is analyzed average storm intensities in their duration. in this section and the design stormwater runoff recommended

as a function of the subcatchment size. Non-public areas include the areas outside streets or boulevards that is, city block interior courtyards, single lots, trade and industrial facilities, public buildings (hospitals, military barracks, schools, universities, ...). The average designed ratio of impervious surfaces for the entire city catchment is 35%. The sewer system has been

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designed for the stormwater drainage from these surfaces. The non-commercial usage. It can be taken based on the construction of some large buildings such as shopping malls in consumption structure that 90% of the total used water is certain city areas will significantly increase impervious discharged into the sewer system. surfaces. It is assumed that impervious surfaces will increase Thus the total daily mean wastewater discharge from homes to 90% after the construction [2]. Maximum allowed runoff and businesses to the city outfalls is 290 000 people x 250 rates from these surfaces into the public sewer system of Novi L/per capita x 0.9 = 65250 m3/day. Sad depend on the subcatchment size. Maximum runoff rates The total daily mean discharge of wastewater from the north from the subcatchment of 1 ha into the sewer system are shown city subcatchment is 140 000 people x 250 L/per capita x 0.9 = in Figure 6. 31500 m3/day. The total length of the north city subcatchment drainage system is about 200 km. Provided the infiltration of 0.25 L/s/km’ per sewer the total daily inflitration is 200 km x 0.25 L/s/km’ = 50 L/s that is, 4320 m3/day. The total calculated mean daily flow from the north city subcatchment is 31500 m3/day (households and industry + 4320 m3/day (infiltration) = 35820 m3/day i.e. 414 L/s. The results of the wastewater discharge rate measurement in a single day at the GC II pump station outfall are shown in Figure 7. It can be concluded based on the measurements that the mean daily discharge rate from the north city subcatchmen is 407 L/s.

Figure 6. Runoff rates depending on the ratio of imperviousness for the area of 1 ha

It can be seen in Figure 6 that the maximum runoff rate with the imperviousness of 35% is 65 L/s. Maximum runoff rates with the imperviousness of 35% calculated for the subcatchments of 2 ha, 5 ha and 10 ha are 132 L/s, 256 L/s and 358 L/s, respectively. The analysis of runoff from impervious areas of various Figure 7. Pump station GC II daily discharge rate. sizes indicates that the runoff rates range from 36 L/s for the subcatchment of 10 ha to 65 L/s for the subcatchment of 1 ha. III. RESULTS AND DISCUSSION It is recommended for the allowed runoff rate – flow Qdir discharged directly into the sewer system to range between 30 A. Hydraulic calculation analysis by the existing model and 65 L/s/ha depending on the subcatchment size. The existing model includes the model of force mains of diametres larger than 600 mm. The area of Novi Sad under H. Analysis of the relevant water consumption consideration encompasses the area of 1985 ha [6]. This area It is determined based on the document ’Demographic includes parks and cemeteries. The design ratio of impervious Development of the City of Novi Sad, Vojvodina Spatial surface is 35%. The total length of the sewer system is 71.3 Information Centre, Novi Sad, 2009’ that 230 000 people live km. The model consists of 414 nodes and 418 sections (Figure in the city area oriented to the GCI and GCII subcatchments 8). Manning’s roughness coefficient of 0.014 m-1/3/s is used in [5]. In the city there are 20 000 students who live here but are the calculation [2]. The hydraulic calculation with the software not registered. Wastewater from the local communities of package EPA SWMM 5.0 for 3- and 5-year storms has shown and with the population of 42 000 is neither manhole overflowing nor pressurized flow in the sewer discharged into the sewer system of Novi Sad [5]. The total system. population on the city catchment is 290 000 [5]. It is estimated that 140 000 people live in the north city subcatchment based on the housing study made for the Novi Sad General Development Plan where the information on the population in the city areas is provided. The average specific water consumption per capita of 250 L/per capita a day is determined based on the analysis of the public water supply consumption. This specific consumption also includes the average consumption in public buildings, sport facilities, restaurants, hotels, schools and commercial and

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Figure 11. Inflow hydrograph for the pump station GC II outfall for 3- and 5-year storms

Figure 8. The existing Novi Sad sewer system model

Longitudinal profiles of the force mains in the north and south city subcatchments with maximum water elevation are shown in Figures 9 and 10, and it can be concluded that there is neither manhole overflowing nor pressurized flow in these mains. The force mains are filled up to 70% at maximum.

Figure 12. Inflow hydrograph for the pump station GC I outfall for 3- and 5-year storms B. Analysis of the hydraulic calculation in the upgraded model of the sewer system for 3- and 5-year storms and the constant impervious ratio of 35% The study catchment of Novi Sad including green surfaces (parks and cemeteries) encompasses the area of 1985 ha. The green areas cover 73 ha. The sewer system with added pipelines of diameters larger than 300 mm is simulated in the upgraded model. The model is more complex and it consists of 1323 nodes and 1325 sections. (Figure 13). There are 382 Figure 9. Longitudinal profile of the north city subcatchment force main with maximum water elevation and 941 nodes in the north and south city subcatchments, respectively. The total length of the input sewer system is 155 km. Manning’s roughness coefficient is set at 0.014 m-1/3/s.

Figure 10. Longitudinal profile of the south city subcatchment force main with maximum water elevation

Inflow hydrographs at the main pump station GC II and GC I outfalls for 3- and 5-year storms are shown in Figures 11 and Figure 13. The upgraded model of Novi Sad sewer system 12. The hydrographs indicate maximum discharge rate at the pump stations GC II and GC I of 7215 L/s and 6620 l/s, Longitudinal profiles of the force mains in the north and respectively. south city subcatchments with maximum water elevation are shown in Figures 14 and 15. It can be concluded that there is

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neither manhole overflowing nor pressurized flow in these mains. The force mains are filled up to 80% at maximum.

Figure 17. Inflow hydrograph for the pump station GC I outfall for 3- and 5-year storms

Figure 14. Longitudinal profile of the north city subcatchment force C. Analysis of the hydraulic calculation in the upgraded main with maximum water elevation model for the imperviousness calculated per areas for 3-and 5-year storms Longitudinal profiles of the force mains in the north and south city subcatchments with maximum water elevation are shown in Figures 18 and 19. It can be concluded that there is neither manhole overflowing nor pressurized flow in these mains. The force mains are filled up to 80% at maximum.

Figure 15. Longitudinal profile of the south city subcatchment force main with maximum water elevation

Inflow hydrographs at the main pump station GC II and GC I outfalls for 3- and 5-year storms are shown in Figures 16 and 17. The hydrographs indicate maximum discharge rates at the pump stations GC II and GC I of 8380 L/s and 7155 l/s, respectively.

Figure 18. Longitudinal profile of the north city subcatchment force main with maximum water elevation

Figure 16. Inflow hydrograph for the pump station GC II outfall for 3- and 5-year storms Figure 19. Longitudinal profile of the south city subcatchment force main with maximum water elevation

Inflow hydrographs at the main pump station GC II and GC I outfalls for 3- and 5-year storms are shown in Figures 20 and 21. Maximum discharge rates at the pump stations GC II and GC I are 9417 L/s and 7190 l/s, respectively.

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section connections to large drainage areas. Drainage areas in the upgraded model are smaller due to more sections and the water flows into the sewers faster than in the existing model. Maximum discharge rates at the outfalls are larger in the upgraded system. The total stormwater volume discharged in the upgraded model approximates that in the existing model. 3) The hydraulic simulation has been run for the case with the impervious ratio calculated for each city area instead of the impervious ratio of 35%. The average calculated imperviousness for the entire city is 35% but it varies across the city areas ranging from 23% in Salajka to 60% in the city centre. The hydraulic calculation has shown neither manhole Figure 20. Inflow hydrograph for the pump station GC II outfall for overflowing nor pressurized flowing in the system. The mains 3- and 5-year storms are filled up to 80%. The system has been well designed. Maximum inflow rate at the pump station GC II is by cca 1000 L/s larger in the case with the calculated imperviousness than in the model with the imperviousness of 35% for the entire city area whereas it is approximately the same as that at the pump station GC I. The larger maximum inflow rate in the case with the calculated imperviousness is due to the fact that the part of the north city subcatchment is the city centre located downstream and 60% impervious, which is significantly more than the existing 35%. The south city subcatchment is about 35% impervious and the inflow rate at the pump station GC I is approximately the same.

Figure 21. Inflow hydrograph for the pump station GC I outfall for 3- ACKNOWLEDGMENT and 5-year storms This work is supported by Ministry of Education and Science, Republic of Serbia (Grant No. TR 37003, TR 37018). IV. CONCLUSION The following can be concluded based on the analysis REFERENCES results and calculations: [1] M.Stipic at all., 2011, Novi Sad sewerage system development 1) The existing model has been hydraulically analyzed. There programme revision, Novi Sad, Serbia are 414 nodes (manholes) and 418 sections (sewers). The total [2] M. Stipic at all., 2012, Redesign of the Existing Combined Sewer System (CSS) od Novi Sad, 9th International Conference on Urban Drainage length of the sewer system is about 71 km. The combined Modelling, Belgrade, Serbia sewer system has been designed for 5- (the central city area) [3] F.Stipic, The analysis of stormwater runoff and overflow from the Novi and 3-year (the residential area) storms. The impervious rate of Sad catchment-Master’s Thesis, Faculty of Technical Sciences, 35% has been taken into account. The hydraulic calculation University of Novi Sad, Serbia,2014. [4] Serbian standards SRPS EN 752-4:2007. Sewer systems beyond the has indicated that there is no pressurized flow in the sewer objects-part 4: Hydraulic calculation and aspects of the environmental system. The force mains are filled up to 70% at maximum. The protection. sewer system can be considered well designed based on the [5] Demografic development of Novi Sad, Center for spatial planning of results since the requirement for no manhole overflowing and Vojvodina, Novi Sad, Serbia, 2009. [6] JP Zavod za urbanizam Novi Sad, Study of hydrotechnical systems, pressurized flowing during 3- and 5-year storms has been met. Novi Sad, Serbia, 2009. 2) The upgraded sewer system model has been hydraulically calculated. The upgraded sewer system model provides a more real and complete understanding of the city sewer system. There are 1323 nodes and 1325 sections in the upgraded sewer system model. The total length of the sewer system is about 155 km. The system is designed for 3- and 5-year storms. The impervious ratio of 35% is taken into account. The upgraded model hydraulic analysis has shown neither manhole overflowing nor pressurized flowing. The force mains are filled up to 80% at maximum. It can be concluded that the system has been well designed. Runoff inflow hydrographs at the outfalls in the existing model and the upgraded model show different maximum discharge rates. In the existing model discharge rates at the outfalls are smaller but the discharge time is longer. This is due to the sparse existing network and

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