University (UERJ), Rua São Francisco Xavier, 524, , Rio de Janeiro, RJ, Brazil.

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1 Unconventional Measures and Hydrodynamic Simulation with Mathematical Model in Sacarrão River Basin, Jacarepaguá, West Area of the City of Rio de Janeiro, Brazil P.L. da Fonseca 1 *, L. Pimentel da Silva and D.P.Batista 3 1 Subsecretary of Watershed Management RIOÁGUAS, Campo de São Cristóvão 68, , Rio de Janeiro, RJ and Civil Engineering Department of the Fluminense Federal University(UFF), Rua Passo da Pátria, 156, , Niterói, RJ, Brazil. Post- Graduation in Environmental Engineering Program (PEAMB), Rio de Janeiro State University (UERJ), Rua São Francisco Xavier, 54, , Rio de Janeiro, RJ, Brazil. 3 Rio de Janeiro State University (UERJ) ), Rua São Francisco Xavier, 54, , Rio de Janeiro, RJ, Brazil. *Corresponding author, paulofonseca@vm.uff.br ABSTRACT In the last decades, the model used in the urbanization process involved deforestation and the increase of impervious areas in association to traditional measures within a hygienist perspective for urban drainage projects. Unconventional measures have been characterized as a paradigm shift in the design of urban drainage systems, such as flood control at source, flood detention basins, whose ultimate aim is runoff control. This paper has as its focus, the use of SOBEK 1D hydrodynamic model in order to analyze the flow of the Sacarrão River in Jacarepaguá, Rio de Janeiro. It will be developed simulations of the flows, considering the transitory nature of them. It utilizes exploratory research methodology, involving applicable updated technology in the control of floods, as well as mathematical model. Moreover, a diagnostic for the macro drainage basin of the Sacarrão river in Rio de Janeiro, Brazil, based on river flow simulations for return period of 5 years, as well as the routing of a dumping reservoir flood. For developing of this paper, it will be made research of the bibliographic collection and data of the Fluminense Federal University, of the Rio de Janeiro State University and of the Subsecretary of Watershed Management RIOÁGUAS. KEYWORDS Urban Storm Management, Flood Control, Reservoirs, Hydrodynamic Simulation. INTRODUCTION The accelerated urbanization process that took place in the last decades in the major urban centers of Brazil resulted in a number of environmental impacts, mainly due to the increase of impervious areas and resulting soil sealing. The direct impacts are related to diminishing groundwater recharge rates and increasing of surface runoff. Moreover, water quality is also impacted. The increase of surface runoff accelarate soil erosiion, aggravate urban floods,and entrainment of pollutants into water courses. The increase of floods due to urbanization has brought about the adoption of corrective measures to control runoff increasing. In the traditional measures, the focus is on increasing the capacity of the drainage network, causing, in general, the transfer of floods downstreams. Unconventional measures and control at Fonseca et al. 1

2 source have been adopted in order to promote the infiltration and temporary storage of stormwater in order to mitigate the impacts of urbanization on the hydrological responses. The project HIDROCIDADES (Pimentel da Silva et al., 008) aims the conservation of water in the urban and peri-urban environment. As object of study it is taken the Morto river catchment and its main tributary, the Sacarrão River, in Jacarepaguá, west area of the city of Rio de Janeiro, Brazil (Figure 1). This project is developed in a participatory way and has attempted to provide solutions to local problems, as in the Low Impact Urban Design and Development (LIUDD), van Roon (005), Figure 1. Location of Morto River Catchment and its main tributary, the Sacarrão River, Jacarepaguá, Rio de Janeiro, Rosa (003). OBJECTIVES This article presents a diagnostic for the macro drainage basin of the Sacarrão River, based on simulations produced for the current river channel for return period of 5 years, as well as the routing of a dumping reservoir flood, localized in the middle part of the basin, which has favorable topographical conditions for the detention of stormwater. The simulations took into account the transitory nature of flows to allow a more realistic representation of physical phenomena, enabling to achieve more reliable solutions to the problem. For hydrologic analysis, it was used the Triangular Unit Hydrograph method, U.S. Soil Conservation Service, and the equation intensity-duration-frequency (IDF) for Via Onze gaging station, used by the Secretariat for Watershed Management of the Municipality of Rio de Janeiro. METHODS Model is a physical or mathematical representation of the reality, which seeks to reproduce the behavior of a system, in order to predict the system response given an input and its initial state. Models, allow to analyze scenarios and explore alternatives for managing processes. The mathematical models seek to represent the system by means of equations which reproduce their processes. The simulation of mathematical models may require solving complex equation systems which require the use of computational tools. Softwares are developed for hydrological and hydrodynamic modeling simulations. Unconventional Measures and Hydrodynamic Simulation with Mathematical Model in Sacarrão River Basin, Jacarepaguá, West Area of the City of Rio de Janeiro

3 A hydrological model commonly used in urban hydrology is the SCS, developed by the Natural Resources Conservation Service, and widely accepted because of its simplicity and ease of application parameters. In this model, rainwater retention in ground depressions and infiltration are the main factors affecting the rainfall-runoff relationship, determining the amount of rainfall that becomes runoff, called effective rainfall. To calculate the flow rates of each sub basin, it was used the Triangular Unit Hydrograph method. It seeks to synthesize the SCS unit hydrograph for a given duration of rainfall unit D. The peak time is based on the following empirical relationship: D = tp / tc, where tc is the time of concentration of the basin. For the determination of CN, curve number runoff of the basin, due to adopt the value obtained by the weighted average number of CNs corresponding to homogeneous areas, in which case the basin presents different soil types and occupancy, taking also consider the future occupation of the soil. The values adopted varied from 60 (point C) to 64 (point E). The Intensity Duration Frequency (IDF) equation for the area is referred to Via Onze gaging station, used by the Subsecretary of Watershed Management RIOÁGUAS (equation 1). I a T b x R d t c I = rainfall intensity (mm/h); Tr = return period (years); t = rainfall duration (min); a, b, c e d = constants determined from the analysis of rainfall historical data set. For Via Onze gaging station, a=143,0, b=0,196, c=14,58 and d=0,796. It is extremely important the fact that, due to the hydrodynamic characteristics of drainage networks, calculations based on concepts of simplified and approximated results does not hit the goals of a particular study. To overcome this limitation, it will be used mathematical models that take into account the transitory nature of stormwater runoff, where the magnitudes vary over space and time on the same cross section - not permanent flow. The model will use Saint-Venant equations, which is the result of combining the continuity equation with the equation of moments, described respectively as follows (equations and 3). Q Af x t q Q t Q x Af g Af h gq Q x C RAf wi Wf w 0 Q = discharge (m³/s); t = time (s); x = distance along the axis of flow (m); Af= wet area of the cross section (m²); q lat = lateral discharge (m³/s /m); Fonseca et al. 3

4 g= acceleration of gravity (m/s²); h= water level (m); C= Chézy coefficient (m½/s); R= hydraulic radius(m); Wf= width of flow (m); wi = wind pressure (N/m²); w = specific mass of water (Kg/m³). Regarding the terms of the equation of moments, the first term is the inertia, the second is convection, the third is the gravitational potential, the fourth is the friction between the fluid and the channel bed and the fifth term is due by the wind. SOBEK 1D modeling suite 1 was applied for processing integral simulation. It is a powerful suite for flood forecasting, optimisation of drainage systems, control of irrigation systems, sewer overflow design, ground-water level control, river morphology etc. It has been further developed by WL/Delft Hydraulics part of Deltares jointly with Dutch public institutes and private consultants. The model SOBEK URBAN was used considering riverflow transitory nature. Related to another line of action in the control of urban drainage, compensatory measures are used to promote infiltration and temporary stormwater storage in order to minimize the effects of urbanization (increasing impervious surface) on the hydrological responses. The use of flood detention basins is a measure of runoff control that reduces hydrograph peak-flow through the temporary storage of part of the runoff. Release of stored water is under conditions according to downstream channel capacity. The areas for rainwater reservation may have a secondary use during rainless periods, such as recreation ground, soccer fields and for sports in general. Besides that, unconventional practices are proposed with the aim of improving the current conditions of the river. These measures are being adopted all over the world, as a way of the maintenance of the initial urbanization flow. RESULTS AND DISCUSSION The Sacarrão river has its sources in the State Park of Pedra Branca, at an altitude of 60m, and receives the contribution of the Café River, plus some other smaller tributaries. Joins with the Branco River, giving rise to the Morto River, at an elevation of 10.9 m. It has an approximate length of 5.3 km and the total catchment area of 6.18 km. Figure. Sacarrão River Basin, Jacarepaguá, Rio de Janeiro. 1 Deft Hydraulics Software. 4 Unconventional Measures and Hydrodynamic Simulation with Mathematical Model in Sacarrão River Basin, Jacarepaguá, West Area of the City of Rio de Janeiro

5 The hydrological model used was developed by the Natural Resources Conservation Service (1976). To calculate the flow rates of each sub basin, it was applied the Triangular Unit Hydrograph method, for return period of 5 years. Figures 3 to 8 show the flood hydrographs on river sections C, D and E. Flood Hydrograph - Point C Recurrence Time = 5 years 16,000 14,000 Discharge (m 3 /s) 1,000 10,000 8,000 6,000 4,000,000 0,000 0,000 0,500 1,000 1,500,000,500 3,000 Time (h) Figures 3 and 4. Flood Hydrograph, Cross Section C, Return Period = 5 years. 5,000 Flood Hydrograph - Point D Recurrence Time = 5 years 0,000 Discharge (m 3 /s) 15,000 10,000 5,000 0,000 0,000 0,500 1,000 1,500,000,500 3,000 3,500 Time (h) Figures 5 and 6. Flood Hydrograph, Cross Section D, Return Period = 5 years. Flood Hydrograph - Point E Recurrence Time = 5 years 30,000 5,000 Discharge (m 3 /s) 0,000 15,000 10,000 5,000 0,000 0,000 0,500 1,000 1,500,000,500 3,000 3,500 Time (h) Figures 7 and 8. Flood Hydrograph, Cross Section E, Return Period = 5 years. Fonseca et al. 5

6 SOBEK 1D modeling suite was used for the integral process simulation. The model SOBEK URBAN was applied considering the transitory flow nature. Figures 9 to 13 show the results of the simulation, considering rectangular project sections (width of 3.90m and height of.0m) and trapezoidal ones (bottom width of 8.0m and slope H/V of.5). Figure 9. Longitudinal profile of the flow through hydrodynamic simulation, Return Period= 5 years. TeeChart TeeChart 14 37, Discharge max.(m³/s) 5 37, Velocity max. (m/s) :00 00:30 01:00 01:30 0:00 0:30 03:00 03:30 04:00 00:00 00:30 01:00 01:30 0:00 0:30 03:00 03:30 04:00 Figures 10 and 11. Graphics of discharge and velocity, Cross Section, Return Period = 5 years. TeeChart TeeChart 0 49, Discharge max.(m³/s) 49, Velocity max. (m/s) :00 00:30 01:00 01:30 0:00 0:30 03:00 03:30 04:00 00:00 00:30 01:00 01:30 0:00 0:30 03:00 03:30 04:00 Figures 1 and 13. Graphics of discharge and velocity, Cross Section D, Return Period = 5 years. 6 Unconventional Measures and Hydrodynamic Simulation with Mathematical Model in Sacarrão River Basin, Jacarepaguá, West Area of the City of Rio de Janeiro

7 In order to minimize impacts downstream, it was considered in this study the alternative of deploying a detention basin near control section D (Figure ), which has favorable topographical conditions for stormwater detention. It was proposed the adoption of a reservoir that will serve to multiple purposes, being used for stormwater detention during rainy periods and serve as recreation ground during rainless periods. The idea is to run a depression in the local terrain, in order to maintain the natural characteristics of the area using a minimum of reinforced concrete, allowing the reservation. The approximate area of the proposed reservoir is,500 m, possessing an average height of 1.40 m with a total volume of 31,500 m³, with a spillway sill with a length of 10 m and height 0.40 m, 1.10 m located to the background. It was also considered a discharge aperture of 0.40 m in diameter, and auxiliary spillway with rectangular dimensions of m (base) by 0.30 m (height). Figures 14 and 15 show the results of the reservoirs routing, considering the modified Pulz method (Tomaz, 00). Figures 14 and 15. Routing of the reservoir, Cross Section D, Return Period = 5 years. Fonseca et al. 7

8 Analyzing the influence of reservoir flood damping, it was observed for the return period of 5 years, a hydrograph peak-flow reduction of 3,1%, which was considered satisfactory in terms of runoff peak reduction However, it is essential the implementation of monitoring and maintenance programs of these devices. CONCLUSIONS The use of mathematical modeling considering flows transitory nature where the magnitudes vary over space and time at the same river section reproduced a more realistic result, closer to the physical phenomena. Sacarrão River flows were analyzed for return period of 5 years. In order to reduce downstream projected sections, as well as hydrograph peak-flow delay, it was considered alternative to deploying a detention basin near D control section. The results showed a hydrograph peak flow reduction of 3,1% for a return period of 5 years, considering the modified Pulz method. REFERENCES Pimentel da Silva, L., Reinert F., Marques, M., Cerqueira, L.F.F., Rosa, E.U., Moraes, M. F. (008). HIDROCIDADES - Cities, Quality of Life and Water Resources: Integrated Water Resources Management and Urban Planning for Low-Land Region of Jacarepaguá, Rio de Janeiro, Brazil. 11 th International Conference on Urban Drainage. Edinburgh, Scotland. Rosa, E. U., Kauffmann, M. O. Pimentel da Silva, L. (003). Installment Management and Land Use in the City of Rio de Janeiro. VII Brazilian Congress of Environmental Defence, Proceedings, Engineering Club. Rio de Janeiro, Brazil. Tomaz, P. (00). Hydrologic and Hydraulic Calculations for Municipal Works (in Portuguese). São Paulo, Brazil. Van Roon, M. (005). Emerging Approaches to Urban Ecosystems Management: The Potential of Low Impact Urban Design and Development Principles. J. Environ. Assess. Policy Manage. 7(1), WL/Delft Hydraulics Part of Deltares et al. (008). SOBEK URBAN. Technical Reference Manual. 8 Unconventional Measures and Hydrodynamic Simulation with Mathematical Model in Sacarrão River Basin, Jacarepaguá, West Area of the City of Rio de Janeiro