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Research Journal of Applied Sciences, Engineering and Technology 6(3): 387-392, 2013ISSN: 2040-7459; e-ISSN: 2040-7467 Maxwell Scientific Organization, 2013Submitted: July 17, 2012Accepted: August 28, 2012Published: June 15, 2013Analysis and Simulation of Drainage Capacity of Urban Pipe Network1Wenting Zhang, 1Xingnan Zhang and 2, 3Yongzhi LiuNational Engineering Research Center of Resources Efficient Utilization and Engineering Safety, HohaiUniversity, Nanjing 210098, China2The State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, NHRI,3Hydrology and Water Resources Department, Nanjing Hydraulic Research Institute,Nanjing 210029, China1Abstract: With the rapid development of urbanization, impervious areas spread quickly, which have greatlyinfluenced regional hydrology and water resources. The water quality is getting worse and worse. The flood anddrought disasters have aggravated. Human living environment has changed and consequently sustainabledevelopment of economy is restricted. The drainage pipe network plays a very important role in urban drainage andflood control. In the study, using of computer technology, the drainage capacity of study area in different designrainstorm return periods (P 0.25, 0.5, 1, 2, 5, 10 a, respectively) is analyzed and simulated by Storm WaterManagement Model (SWMM). Part of the pipe network that are filled slowly and change great are found out fewerthan 6 design rainstorms, which provide the basis for reconstruction of urban conduits. The simulation results canprovide strong technical support for the city drainage system planning and management.Keywords: Drainage capacity, modeling, numerical simulation, pipe network, SWMMuse changes and city construction. Face this issue, thedrainage network in many cities start to redesign andtransformation, in order to meet the needs of the city'sdrainage capability.In this background, the storm water managementmodel (referred to as the SWMM model) has beenapplied in this study; the drainage capability in designstorm conditions of Yuhua District in Nanjing city wassimulated. Through simulation, provide the basis for thedesign and reconstruction of the actual pipe network, toavoid the city water logging disaster.INTRODUCTIONDue to the urbanization, the city population and theimpervious areas are increasing. These two parts willalso lead to other aspects of problems. First, theprecipitation that falls on impervious surfaces becomessurface runoff which is connected directly to the sewernetwork. This will increase peak flows and decreasespeak flow lag times. The drainage system must be ableto cope with the increased peak flows to reduce potentialdamage and inconvenience. But the initial sewernetwork's capacity has been not enough to contain allthe runoff from surface; the exceeding surface runoffwill cause urban flooding. Second, because of the largecity and its population, the demand of water resourceswill also increase sharply.The drainage network as an important andindispensable infrastructure for city, which is using forcity Underground Drainage, drainage, flood controlworks. With the accelerating progress of urbanization,drainage task assumed by the drainage network becomeheavier. In many cities, the existing drainage networkdue to the construction of age-old design, the drainagecapacity is lack (Parka et al., 2008); drainage capabilitycan no longer meet the increasing demand of urban landBASIC THEORY OF SWMMThe EPA Storm Water Management Model(SWMM) is a dynamic rainfall-runoff simulation modelused for single event or long-term (continuous)simulation of runoff quantity and quality from primarilyurban areas. It was used in Tianjin and Shanghai city(Liu and Xu, 2001). This model is mainly used in smallcities’ runoff and water quality forecasting, riverdrainage simulation and compute and drainage pipenetwork system verification and management. It consistsof runoff yield model, infiltration model, surface runoffconcentration model and pipe hydraulic dynamic model(Wang and Xu, 2008).Corresponding Author: Wenting Zhang, National Engineering Research Center of Resources Efficient Utilization andEngineering Safety, Hohai University, Nanjing 210098, China387

Res. J. Appl. Sci. Eng. Technol., 6(3): 387-392, 2013RUNOFF YIELD MODELThe process of rainfall turning into net rain is calledrunoff yield. Based on the land use status and surfacedrainage directions, study area is discredited into severalsub catchments. According to the hydrology differences,each Sub catchment can be divided into pervious andimpervious sub areas. Surface runoff can infiltrate intothe upper soil zone of the pervious subarea, but notthrough the impervious subarea. Impervious areas arethemselves divided into two subareas - one that containsdepression storage and another that does not. Thosethree subareas’ runoff yield is computed separately andthe sub catchments’ runoff is the sum of subareas.Surface runoff concentration model: The task ofsurface runoff concentration is to convert the subareas’net rainfall process into sub catchments’ dischargeprocess. In SWMM, this task is realized by making threesubareas approximated as nonlinear reservoir. Namely,solving continuity equation and Manning Formulasimultaneously. It is a lumped model.𝑄𝑄𝑔𝑔𝑔𝑔 𝑄𝑄 𝐴𝐴(1)1𝑔𝑔𝑔𝑔 ℎ 𝑆𝑆𝑓𝑓 𝑆𝑆0 0 Steady flow: Steady Flow routing represents thesimplest type of routing possible (actually norouting) by assuming that within eachcomputational time step flow is uniform and steady.Thus it simply translates inflow hydrographs at theupstream end of the conduit to the downstream end,with no delay or change in shape. The normal flowequation is used to relate flow rate to flow area (ordepth).Kinematic wave: This routing method solves thecontinuity equation along with a simplified form ofthe momentum equation in each conduit. The latterrequires that the slope of the water surface equal theslope of the conduit. The maximum flow that can beconveyed through a conduit is the full normal flowvalue. Any flow in excess of this entering the inletnode is either lost from the system or can pond atopthe inlet node and be re-introduced into the conduitas capacity becomes available. Kinematic waverouting allows flow and area to vary both spatiallyand temporally within a conduit. This can result inattenuated and delayed outflow hydrographs asinflow is routed through the channel. However thisform of routing cannot account for backwatereffects, entrance/exit losses, flow reversal, orpressurized flow and is also restricted to dendriticnetwork layouts. It can usually maintain numericalstability with moderately large time steps, on theorder of 1 to 5 min. If the aforementioned effectsare not expected to be significant then thisalternative can be an accurate and efficient routingmethod, especially for long-term simulations.Dynamic wave: Dynamic Wave routing solves thecomplete one-dimensional Saint Venant flowequations and therefore produces the mosttheoretically accurate results. These equationsconsist of the continuity and momentum equationsfor conduits and a volume continuity equation atnodes. With this form of routing it is possible torepresent pressurized flow when a closed conduitbecomes full, such that flows can exceed the fullnormal flow value. Flooding occurs when the waterdepth at a node exceeds the maximum availabledepth and the excess flow is either lost from thesystem or can pond atop the node and re-enter thedrainage system. Dynamic wave routing canaccount for channel storage, backwater,entrance/exit losses, flow reversal and pressurizedflow. Because it couples together the solution forboth water levels at nodes and flow in conduits it Pipe hydraulic dynamic model: The pipe flow routingin SWMM is calculated by conservation of mass andconservation of energy formula. And three solvingmethods are supplied: Steady Flow, Kinematic Waveand Dynamic Wave (Rui, 2004): Infiltration model: Infiltration is the process of rainfallpenetrating the ground surface into the unsaturated soilzone of pervious sub catchments areas. SWMM offersthree choices for modeling infiltration: Horton'sEquation, Green-Ampt Method and SCS Curve NumberMethod. Horton's Equation mainly describes therelationship that infiltration intensity changes withrainfall duration and does not reflect the underlyingsurface status of saturated and unsaturated zone. GreenAmpt Method assumes that a sharp wetting front existsin the soil column, separating soil with some initialmoisture content below from saturated soil above. Asufficient rainfall and infiltration process can make thesoil saturated. SCS Curve Number Method assumes thatthe total infiltration capacity of a soil can be found fromthe soil's tabulated Curve Number. During a rain eventthis capacity is depleted as a function of cumulativerainfall and remaining capacity. txSfSo(2)where,Q Discharge, m3/sA Area of the wetted cross section, m2h Pipe water depth, m388Time, sPipe length along the water directionResistance slopePipeline slope

Res. J. Appl. Sci. Eng. Technol., 6(3): 387-392, 2013can be applied to any general network layout, eventhose containing multiple downstream diversionsand loops. It is the method of choice for systemssubjected to significant backwater effects due todownstream flow restrictions and with flowregulation via weirs and orifices. This generalitycomes at a price of having to use much smaller timesteps, on the order of a minute or less (SWMM canautomatically reduce the user-defined maximumtime step as needed to maintain numerical stability).is located in the Yuhua District, Nanjing, JiangsuProvince, which an area of 950.28 ha, an averagegradient of 4.67%, including residential area accountedfor 28%, road area accounted for 9.98%, other land andgreen area accounted for 62.02%.The drainage capacityof the study area as Fig. 1.Subcatchment division: Need to division the study areawhen use the swmm model to simulation, which processincluding division the whole catchment into several subcatchments and generalization each sub-catchmentshydrological characteristics. In the cities, existence ofreal sub-catchment areas, but due to the development ofthe city's own characteristics and urbanization change ofsurface condition, so leading to determine its true subcatchment areas become difficult. If reasonablydetermine the sub-catchment areas, makes the modelsimulation results to better fit the actual situation. Inorder to better divide sub-catchment areas and try tosimplify the model input data in the condition of ensureits simulation accuracy, this study use an approachescombination the road and DEM of the study area.Through the method using the Hydrological Analysisdivision the study area and then using the land use mapwith artificial merger and adjustment, which finalcompletion the division of the sub-catchmentEach of these routing methods employs theManning equation to relate flow rate to flow depth andbed (or friction) slope. The one exception is for circularForce Main shapes under pressurized flow, where eitherthe Hazen-Williams or Darcy-Weisbach equation isused instead.THE APPLICATION OF SWMM INSTUDY AREAThe surface area, catchment area width, slopegradient, the Manning roughness coefficient, infiltrationrate, the length of the pipeline, pipeline diameter andother data is necessary input of the model. In order toevaluation the drainage capacity of the study area, firstneed to build model of the research area. The study areaFig. 1: Drainage system of study area389