International Journal of Scientific & Engineering Research Volume 11, Issue 4, April-2020 452 ISSN 2229-5518 IJSER © 2020 http://www.ijser.org PERFORMANCE ASSESSMENT OF URBAN DRAINAGE SYSTEMS OF HOLETA TOWN USING STORMWATER MANAGEMENT MODEL (SWMM). WAGARI EJIGU CHALI , MOLTOT ZEWDIE b a* Water Resources Engineering (Thesis: Performance Assessment of Urban Drainage Systems of Holeta Town Using Stormwater Management Model (SWMM)),Bule Hora University, College of Engineering, Water Resources and Irrigation Engineering Department, Ethiopia. b Water Resources and Hydraulic Engineering (Thesis: Performance Assessment of Urban Drainage Systems of Holeta Town Using Stormwater Management Model (SWMM)), Hawassa University, Institute Of Technology, Water Resources and Irrigation Engineering Department, Ethiopia. Keywords: Holeta Town, Stormwater drainage systems, SWMM, Runoff, junctions, ABSTRACT The general objective of the study was the Performance Assessment of Urban Drainage Systems of Holeta Town using the Stormwater Management Model (SWMM). The catchment that contributes runoff areas, weighted runoff coefficient was delineated using Arc GIS 10.3 tool. The Stormwater Management Model (SWMM 5.1) was applied to simulate the water level in the links and junctions by considering the current land use condition. The intensity duration frequency (IDF) curve was developed by using log-Pearson Type III to analyze rainfall and the consequent peak runoff for different return periods using a rational method. The existing storm drainage systems of Holeta Town were: lack of well-connected drainage lines, solid and liquid wastes were directly disposed into the storm drainage system, which results in decreasing the efficiency of the system, unavailability of drainage systems at the proper place. Additionally the awareness of the community towards such an issue was less, the major percentage of drainage system performs severely degraded, e.g out of 100%, at Birbisa Siba 50.75%,at Sadamo area 41.384%,at Burka Harbu 63.225% and at Tulu Harbu 42.42% were severely degraded. This result shows the majority of the drainage systems are not adequate to carry the design flood based on intensity with a return period of 10 years. The SWMM output indicates that in most of the junctions, the flood level was greater than the designed water level. IJSER