FullPaper Title in upperCase Gowmaran SUniversity Of Moratuwa,Jaffna,[email protected]/s name/sInstitute/Company, Address Abstract: The rainfall event is the mainreason for very heavy flooding. This occurs because of the urbanization in thecities. the urbanization causes the natural unbalance between effectivedrainage capacity and generated urban runoff. To stop this unbalance, we musthave a proper drainage system.

the drainage system is disturbed due to solidwaste deposited in the channels.so we must maintain proper drainage channel tomove the runoff very effectively. We mustconsider hydrologic impact assessment to design the storage and urban drainagesystem. When we model the drainage, a system using SWMM (Storm Water Management Modelling) software inputthe pre-and post-hydrological model to analyzethe existing drainage system. Then we must consider flooding issues and sewagewater mixed with rainwater and other water-related issues to come up with the newdesign.  The drainage system I design should considerthe groundwater protection because there are a lot ofspecies inside the ground. Keywords: Heavy flooding; urbanization; solidwaste; runoff; ground water 1.

   IntroductionFlooding is thenatural disaster. These disasters we can’t control by our hands. We can controlonly by protecting the nature. This flooding disaster causes severe damages topeople as well as properties. This disproportionate impact in densely populatedcities may affect flooding heavily. This occurs normally in the down streamareas where people are living in informal settlements. For them it isfrequently occurred. When we consider the affected people are mostly the low-incomepeople in Colombo city.

The victim of these natural hazards is mainly affectedby without pre-warning is given by the officials.The main goalof this research·        Give a good drainage system to the critical area inColombo city.·        Modify the land profile for efficiency of thesurface run off.In Colombo cityis becoming very sensitive areas because of high level organizations areestablished in this area. So, the urbanization is the most commonly occurred inthis area. These also leads to flooding. We can call this as increases ofimpervious areas causing these issues. When we analyse the real scenario of theColombo city higher peak flow and shorter time to peak is the main factor affectsthe flooding.

The intensity of precipitation also increases due to variousreasons like climatic changes. That also causes high run off in the downstreamareas.To overcomethis issued we have to have a proper drainage infrastructure should bedeveloped. We must model a drainage system in SWMM for the pre-and post-conditions.Then only we can come up with every difficulty in the existing drainage system.As all know this is fully computerized model we can model different types ofmodel find the final effective drainage model.

Not onlymodelling drainage system leads to stop the flooding. We must maintain theproperly otherwise it will not continue functioning. People also put theirsolid waste in near the open space this also leads to block the drainage.itreduces drainage capacity. So, people also think about this as well. That’s fortheir own benefits.When weconsider the drainage is one of the least concentration factor in urbandevelopment cycle.

This tends to decrease the efficiency and workability. Mainproblem in srilanka is very low finance allocation for the drainage infrastructure.Consider allthese effects we have to design a effective drainage to consider all the safetyissues of the people.Study area We have consideredthe critical area which is sensitive area in Colombo.

Here the area we consideris Kelaniya. Which is consisting of 450 hec area. This consist of mixture ofresidential areas, roads, marshy areas. The Kalani area is 1.50 m above themean sea level.

this existing drainage system is constructed in 1910.                                                                                                                                                                                                                                                                    Figure1 GeneralOutline of the study areaWe must continue our further study of flood managementbased on the topographical map in Kelaniya area. then only we can clearlyidentify the land profile. After that we can identify which land area should becut or fill depend on their present condition to make the runoff efficiently.The main reason is unplanned urbanization in thedownstream area which is heavily affected the flooding.

the solid wastemanagement should well organize otherwise it will also block the drainagechannels. We have to give the solution for the drainage system in the sensitivearea.Urban drainagecycle Natural hydrological cycle should be well organizedotherwise it will also leads to flooding. normally hydrological cycle startswith precipitation. It is fully developed by rainfalls. It also createsoverland flow. As well as ground recharge  done by infiltration.

there is an initial loss governed by evaporation.This cycle can be implement very clearly by the below diagram.Imperviousness of the ground also affect the flooding inthe considerable amount.so we can see the relationship between imperviousness  Introduction about computer modelling in storm watermanagement Model(SWMM)SWMM software is commonly used hydraulic software fordesigning planning analyzing used in srilanka.

SWMM software can design a pre-modelusing the data of existing drainage system get from CMC and run in thissoftware and find out the problem in this current system. Then we can get theidea of the land profile and existing runoff patterns and design a post modelin SWMM software this leads to help us to find a effective and economical way.From this software we can analyze for differentscenario. This software basically models with quantity and quality of runoffmade within each catchment before modeling in SWMM software we must identifythe sub catchment area which can causes the heavy runoff in our segment.We can analyze and come up with differentimplementation depend on our anylysis·        Timechanging rainfall due to the climatic changes and man-made effects to theenvironment.·        Evaporationin the surface arun off ·        Infiltrationof the rainfall in to unsaturated soils.·