WEENTECH Proceedings in Energy 7 (1) (2021) 269-277 International conference on Innovative Development and Engineering Applications, 8-10 February 2021, Gaya College of Engineering, Gaya, India Flood estimation of Gangabal lake in Indus river basin using MIKE 11 Shailesh Kumar*a,N.K. Goelb and Sunidhi Supriyac aAssistant professor,Nalanda college of engineering,Chandi, bDepartment of Hydrology, Indian Institute of Technology Roorkee,Roorkee-247667, India, Email:[email protected], cFormer B,Tech student, National Institute of Technology, Srinagar,Email:[email protected] * Corresponding author’s mail: [email protected] Abstract The on-going retreat of glaciers in the Hindu Kush- Himalaya has been reported to be attributed to global warming in the recent years. While deglaciation may cause a suite of impact, one of the most visible and tangible impact is the formation of glacial lake. Large flash floods resulting from these types of lakes can be responsible for significant loss of lives and property. In this study a methodological approach for the GLOF risk analysis is presented. A glacial lake outburst hydrograph was simulated in case of worst case scenario using a dam break model in MIKE 11 for Gangabal lake. The peak discharge were found to be of the order of 8791, 9991, 11089 cumecs for breach width 80,100,120 meters respectively at failure time of 60 minutes. Keywords: GLOF; MIKE 11; Climate change Copyright © 2021 Published by WEENTECH Ltd. All Peer-review process under responsibility of the scientific committee of the International Conference on Innovative Development in Engineering Applications, Gaya College of Engineering, Gaya, India, IDEA2021 https://doi.org/10.32438/WPE.242021 Manuscript History Receipt of completed manuscript: 20 December 2020 Receipt of Revised Manuscript: 05 January 2021 Date of Acceptance: 10 January 2021 Online available from: 10 February 2021 1. Introduction Global warming is the dominant factor for the accelerated glacial melt and retreat, giving birth to hazardous glacial lakes in the Hindu-Kush Himalayas. In coming decades, it is possible that global warming will intensify the Glacial lake outburst flood (GLOF) events and formation of many potentially dangerous glacial lakes. GLOF events are usually tragic on life and property of the mountainous people Page | 270 living downstream. So it becomes necessary to monitor glaciers and glacial lakes in order to understand the status of the lake and to prioritize the installation of early warning systems and mitigation measures before planning the mountain infrastructure for sustainable development. National Remote Sensing Centre (NRSC) identified 2028 lakes having area more than 10 ha in 2009. Since 2013, Planning and Development Directorate of Central Water Commission (CWC) has been monitoring the glacial lakes and water bodies in Hindu-Kush Himalayan Region using satellite data in collaboration with NRSC. The pinpointed objective of this study is to carry out glacial Lake Outburst study to assess the impact of outburst flood in identified vulnerable location in downstream of Gangabal Lake using MIKE 11 Software. 2. Earlier GLOF studies in HKH region Recently Glacial Lake Outburst Floods (GLOF) has become one of the most sought after research area. The GLOF phenomenon is common in mountainous regions such as Andes, European Alps, as well as Himalayas. In these areas several incidents of loss of human lives due to settlement in flood plains due to GLOF have been reported. Many researchers have studied GLOF phenomena in HKH region. Jain et al. (2012) studied the glacial lakes and glacial lake outburst floods in a Himalayan basin using remote sensing and GIS. They used IRS LISSIII data for Monitoring of the glacial lakes in the Alaknanda valley in Uttarakhand (India). They found a total of 91 lakes in the year 2008, and out of these, 45 lakes were having area more than 0.01 km2. However, no lake was found to be vulnerable from GLOF point of view. They also observed increasing trend in the lake area as 0.193, 0.199 and 0.203 km2 in the years 2004, 2006 and 2008 respectively. Using MIKE 11 the flood peak at catchment outlet was found to be 994, 1,184 and 1,296 cumecs for breach width of 40, 60 and 80 m due to GLOF and 100-year return flood as 3,275, 3,465 and 3,577 cumecs respectively. They estimated time of travel of flood peak from the lake site to outlet as 1 hr and 10 min and discharge at the worst case scenario of GLOF was estimated as 1,296 cumecs. 3. Study area and data used 3.1 Study area The Gangabal Lake is main study area for glacial lake outburst flood study in Indus basin. The Gangabal Lake (34°25'55.56" N, 74°55'27.12" E), also known as Haramukh Ganga is a lake situated at the foothills of Haramukh mountain in Ganderbal district of Kashmir valley. It is a high altitude lake on the north- east slopes of Harmukh mountains at an elevation of 3570 meters above mean sea level. It is about 3 Kms long and about 500 meters wide. Maximum width of Gangabal lake is 950 meter. It is about 45 Kms north of Srinagar on way of Wangat village (34°19'29.07" N, 74°56'45.51" E. According to “Inventory of Glacial Lakes Water Bodies in Himalayan Region of Indian River Basin” prepared by NRSC (2009), Gangabal Lake is abbreviated as 01_43J_017. The digital elevation model from the Shuttle Radar Topography Mission (SRTM) is used for delineating the catchment boundaries in this study. Mosaic of SRTM 51_05 and SRTM 52_06 data was used to develop the catchment map with the help of ArcGIS software. The study area generated using SRTM DEM is shown in the Fig. 1. Figure 3.2 shows vulnerable locations at downstream of Gangabal Lake. Page | 271 Fig. 1: Gangabal lake catchment map 3.2 Assumptions and Limitations of GLOF or Dam break modeling study Dam break modelling has implicit estimation through following assumptions. 1) The River is assumed to be as a Virgin River (i.e.) no Water Resources project is present in the river. 2) The cross sections considered are not actual and they are derived from SRTM Digital Elevation model. 3) The water is homogeneous and incompressible i.e. without relevant variation in bottom slope and density is small. 4. Methodology 4.1 GLOF Modeling Glacial lakе outburst flood or Dam break analysis include thrее distinct parts. Firstly, it dеals with generation of thе outflow hydrograph at dam-break site. Thеn thе dam-break hydrograph is routed and lastly, to estimate thе inundation levels and damages to downstrеam structurеs arе еstimatеd. For dam brеak a numbеr of softwarе’s havе bееn dеvеlopеd in thе past such as iDAMBRK, HiЕC-RAS and MiIKЕ 11 еtc. For Sеlеction of an suitablе modеl to undеrtakе dam brеak studies for GLOF, is important to еnsurе thе right balancе bеtwееn Modеling accuracy and cost (both in tеrms of softwarе cost and timе spеnt in dеvеloping and running thе modеl). GLOF еvеnts is a typе of unsteady flow. MIKЕ 11 modеl is sеlеctеd for thе present study duе to its robustnеss and easily availability. Also this model has been adopted by CWC as a uniform model to study a number of GLOF studies. MIKЕ 11 is a six point distributеd 1D modеl usеd for unstеady flow analysis. For GLOF studiеs, MIKЕ 11 has bееn еxtеnsivеly usеd by various Page | 272 dеscribе unstеady flow simulation. 4.2 Dam brеak modеl sеtup in MIKЕ 11 For GLOF analysis, a hypothеtical dam brеak structurе is crеatеd along thе lakе in downstrеam. Thеrе will be two typеs of arrangеmеnts of dam-structurе. Onе of thеm is dam and another is rivеr nеtwork crеatеd aftеr thе downstrеam of lake. Simulation filе is rеquirеd for sеtting up and running MIKЕ 11 dam brеak modеl. MIKE 11 simulation file consists of network, cross-sеction, boundary and hydrodynamic filеs. So first create a nеtwork filе and thеn crеatе branch for lake or rеsеrvoir. Dam break structure create in network file. Figure 4.1 shows thе arrangеmеnt of Dam Structurе in Mikе-11 modеl. Fig. 2: Arrangеmеnt of Dam Structurе in Mikе-11 Now, crеatе a cross-sеction filе using SRTM data aftеr completion of nеtwork part. Cross-sеction data is created for lakе branch and rivеr branch of Gangabal lakе. Lake or reservoir is storagе but it is required of arеa-еlеvation data for i dеfining thе lake. Lake or reservoir branch is first Chainagе and Gangabal river is second chainage. Details of all input file used in MIKE 11 for GLOF study as described in next section: 4.3 Model setup River Network has been created along with Glacial Lakes. Glacial lake is represented as separate branch using a dummy cross-sections and storage volume of cross-section is assigned with the volume of the glacial lakes. This branch is hydraulically connected to the main river at the appropriate location. 5. Results and discussion MIKE 11 HD model is used for GLOF modeling as dam break analysis. For Gangabal lake outburst analysis, MIKE 11 HD model is simulated for the period of 14-10-2014 to 15-11-2014. For this river network, cross-sections, boundary conditions, hydrodynamic parameter input files are used. The aim of this study is to calculate stage and discharge at different downstream sections. MIKE 11 HD simulation results give water level and discharge time series at different cross section and longitudinal profiles of water level and discharge along the river. 5.1. Dam Break Analysis for different Breach Parameters The analysis has been carried out for following set of parameters with breach depth of 20 m for following cases: Case I: Breach Time 60 minute and Breach Width 80 m Page | 273 Case II: Breach Time 60 minute and Breach Width 100 m Case III: Breach Time 60 minute and Breach Width 120 m 5.1.1.