International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, Volume-8 Issue-6, March 2020 2531 Retrieval Number: F8511038620/2020©BEIESP DOI:10.35940/ijrte.F8511.038620 Published By: Blue Eyes Intelligence Engineering & Sciences Publication Abstract: Currently there has been a research gap in providing sufficient and reliable data for the estimation of surface runoff from ungauged catchment in Batang Kuranji watershed, City of Padang, West Sumatera, Indonesia. The need for such data arose from the fact that land cover changes occur rapidly in the past 20 years, and flash flood and river degradation have been experienced at an alarming scale. However, due to lack of discharge data from upstream catchment, modelling catchment response to the effect of land use changes is hampered. Field measurement is difficult due to accessibility to river tributaries in the upstream catchment. Therefore, the use of digital satellite images and digital elevation model is studied with various DEM (Digital Elevation Model) resolutions for the first time in this catchment. This catchment is situated from 95 to 1858 m above sea level with an annual rainfall of 3440 mm. This watershed is classified as steep with a watershed that has a slope of more than 40% reaching 37.01% of the entire Kuranji watershed area. This study used 30 m and 8 m DEM. Secondary data were gathered from satellite images such as MODIS (MODerate resolution Imaging Spectroradiometer) Land Use. Precipitation data were gathered from three rain gauging stations in or nearby the catchment. Stream geometry data were obtained from the Provincial Office for River Management. Annual discharge and 100-year discharge are calculated using rainfall data for the past 20 years. Runoff discharge was calculated using rational method and SCS (Soil Conservation Services) method. Overall, computed discharge decreases as DEM resolution decreases with percentage varies between 0.98% to 1.76%. The biggest difference between DEM of 30 m and 8 m was shown by the Rational method. However, the difference between years is inconsistent with methods used with no significant pattern. Using the rational method, the biggest difference was by 18.73 m3/s, making up 1.76%. With SCS-CN, however, the biggest difference was 14 m3/s or 1.32% and the smallest was 0.98%. Validation with field measurement suggests that the 8-m DEM varies only 0.16% with actual discharge. Therefore, in the Kuranji catchment, the SCS method coupled with 8-m DEM was found to be accurate for the estimation of surface runoff. Keywords: DEM, Land use, Runoff discharge. I. INTRODUCTION Padang City in West Sumatra, Indonesia has experienced a shift in urban development and rapid population growth over in last decade. The population of Padang City was 1.6 million in 2010. Population growth for 5 years increased by 8% to 1.8 million (www.padangkota.bps.go.id) in 2015. This has led to population growth and hence growing demands for public Revised Manuscript Received on March 10, 2020. * Correspondence Author Elvi Roza Syofyan*, Civil Engineering Department, Politeknik Negeri Padang, Padang, Indonesia. Email: syofyan_er@yahoo.co.id Bambang Istijono, Civil Engineering Department, Faculty of Engineering, University of Andalas, Padang, Indonesia. Amrizal Saidi, Soil Department, Faculty of Agriculture, University of Andalas, Padang, Indonesia. Revalin Herdianto, Civil Engineering Department, Politeknik Negeri Padang, Padang, Indonesia. transportation facilities, residential areas and other supporting facilities. In current global issues in climate change, Padang is facing serious problems in hydro-climatologic related disasters. In the past 20 years, Batang Kuranji watershed has experienced numerous problems related to hydrology. A massive flash flood in the Year 2012 and continuous river bed degradation has taken serious concerns on the health of the watershed. Yet, there has been a research gap in providing sufficient and reliable data for the estimation of surface runoff from ungauged catchment in Batang Kuranji watershed, City of Padang, West Sumatera, Indonesia. Due to lack of discharge data from upstream catchment, modelling catchment response to the effect of land use changes is hampered Numerical models can be used to predict runoff as an insight to catchment response to various environmental changes. HEC-HMS is one of the hydrological models in the past that has been able to estimate runoff with various accuracy between regions [1], [2], [3], [4]. Inputs required are Digital Elevation Model (DEM), precipitation, stream networks, land use, and other catchment conditions. DEM may be obtained in various resolutions. With adequate sub catchment arrangements, the results may give both quantitative and qualitative information on hydrologic response of catchments. Climate change in recent years has been intensively studied as a major cause of flood frequency [5], [6], [7]. Understanding global and regional climate conditions over a longer period is more important than local or catchment scale. Furthermore, [5], [6], [7] recommended that characteristics of flood must be understood by its causal mechanisms and dominant processes over statistical approaches alone [5]. Climate change would change flood peak discharges. Specifically, an increase in convective precipitation at a small catchment may growth maximum flood discharge [6]. Similarly, atmospheric conditions particularly rainfall will change magnitude of floods. Moreover, they highlighted that apart from the atmosphere, river systems and catchment land use changes are also attributed with the magnitude of flooding [7]. In line with the aforementioned studies, land use changes has an important roles because of its wide interactions with many hydrologic parameters. Land use alteration and management has been known to influence catchment hydrology due to changes in evapotranspiration, infiltration, antecedent soil moisture, and surface and subsurface storage that eventually change surface runoff and stream flow [8]. Nevertheless, the direct connection is difficult to disentangle because the processes are very complex on a long time scale. Interception and infiltration of rainfall which ultimately The Changes of Runoff with DEM Resolution Variations Elvi Roza Syofyan, Bambang Istijono, Amrizal Saidi, Revalin Herdianto