PERFORMANCE ASSESSMENT OF STORM WATER DRAINAGE SYSTEM OF HOSANNA TOWN THE CASE OF GOFER-MEDA SUB-CITY USING STORM WATER MANAGEMENT MODEL 5.1

Abstract

Urban storm water drainage systems are an increasingly important part of urban infrastructure that conveys storm water away from urban areas. Since such infrastructure play a key role in preventing urban floods, their performance should be monitored and quantified. In the study area, there is improper interconnection between road and urban storm water drainage system, lack of periodic maintenance, waste damping and absence of adequate size drain which result flooding during rainy season and damages properties and road users. The objective of this study was performance assessment of storm drainage system of Hosanna town for the case of Gofer meda sub-city. The various Meteorological data and spatial data were collected to assess performance of drainage system. Rainfall data for period of (1988- 2017) was used to identify probability distribution and to develop the intensity duration frequency (IDF) curve for Hosanna town. Log-Pearson type III have better R2 value in range( 0.6-0.88) and best fit of goodness of easy fit professional software and also used for this study to analysis of design RF for required return period 10 year for design and 25 year to check. The IDF Curve developed for various return periods to analyze RF and determine adequacy of existing drainage system and Compute peak runoff using rational method and SWMM 5.1. Observation and field visit method were used to explore and describe existing condition of drainage system. Digital elevation model (DEM) used as input data for ArcGIS software which used to delineate the runoff contributing areas and to prepare the SWMM input parameter. Storm water management model (SWMM5.1) was used to simulate 1-D view of the flood depth in the drainage system. Manning’s equation used for compute storm water drainage system capacity. Based on primary and secondary data collected, Storm water drainage system were designed with inadequate hydrological data and hydraulic analysis, the existing drainage system problems associated with in study area categorized as construction, community awareness and design. Total estimated peak discharge by rational method was 43.89m3/s and calculated existing drainage system capacity by manning’s formula was 33 m3/s. So, approximately 25% additional drainage system provision needed to handle coming flood. Therefore; this study recommends improvement of existing storm water drainage system, integration of solid waste management system in order to prevent the over flowing of floods as a result of blockage of drains, the drainage structures should be carefully cleansed, and suitable measures should be taken in order to make and drainage structures serve for intended purposes