Urbanization is one of the key factors that contribute to urban flooding, which has caused majorrndestruction to the environment, public and private buildings and disrupts public life. Inrnparticular, the increase in population and building density influence the change in hydrologicalrncharacteristics in urban areas. Conversion of pervious areas into impervious areas increases thernstormwater runoff quantity dramatically. rnrnOne way of minimizing urban flooding is to convey stormwater to receiving waters throughrnstormwater drainage systems, which has been practiced in some parts of Assosa town. In Assosarntown, drainage problem become an issue during rainy season. This study deals with evaluate thernexisting stormwater drainage system of Assosa town considering hydraulic and hydrologicrnparameters in stormwater model. Despite there are many places in the city facing storm drainagernproblem; Stadium-Mazoria, Stadium-Hibret Bank, Sarbetoch-Anuar, Police commissionEthiopiarnHotelrnandrnGebriel-Muluwongelrnchurchrnarernareasrnselectedrnforrnthisrnstudy.rnrnrnrnThisrnstormwaterrndrainagernproblemrnhasrnnecessitatedrnusernofrnsimulationrnstudiesrnforrnunderstandingrnrncomplexitiesrnrelatedrntornthernurbanrnfloodrnmanagement;rnso,rnthernsimulationrnhasrndonernbyrnStormwaterrnrnManagementrnModelrn(SWMM).rnDailyrnrainfallrndatarnisrnobtainedrnfromrnnearbyrnAssosarnmeteorologyrnrnstation.rnThernselectedrnextremerndailyrneventrnwasrndisaggregatedrnintornhourlyrnrnevents using reductionrnformula. Thereafter, the EPA SWMM is used to simulate the response of catchment to rainfallrnevents in which runoff, water depth profile, and outflow hydrograph are obtained. Runoff is alsornobtained from rational formula for comparison purpose, and for obtaining design intensity arnfrequency analysis is carried out. LID measures (vegetative swales) also performed to evaluaternhow LID measures (vegetative swales) influenced urban runoff reduction.rnrnThe result of this study shows that the problem in the study area caused by insufficient drainagernoperation, minimum drainage pipe size, improper maintenance and clogging of drainage line byrnwaste material. In addition the results showed that the LID measures are effective in controllingrnthe surface runoff.