LANDSLIDE INVENTORY, CHARACTERIZATION AND ENGINEERING DESIGN FOR MITIGATION WORKS OF CHURE AREA IN TEN DISTRICTS Submitted to: Submitted by: Government of Nepal Central Department of Environmental President Chure-Tarai Madhesh Science Conservation Development Board Tribhuvan University, Kirtipur Kathmandu September, 2016 © September 2016 President Chure-Tarai Madhesh Conservation Development Board and Central Department of Environmental Science, Tribhuvan University Citation: TU-CDES (2016). Landslide Inventory Characterization and Engineering Design for Mitigation Works of Chure Area in Ten Districts. Central Department of Environmental Science, Tribhuvan University and Government of Nepal, President Chure-Tarai Madhesh Conservation Development Board, Kathmandu. Project Steering Committee Chair Dr. Annapurna Das, Secretary , PCTMCDB/GoN Prof. Dr. Madan Koirala, Professor, TU-CDES Member Prof. Dr. Kedar Rijal, Head of Department, TU-CDES Member Prof. Dr. Rejina Maskey, Project Team Leader, TU-CDES Member Dr. Prem Paudel, Under Secretary, PCTMCDB/GoN Member Dr. Subodh Dhakal, Project Coordinator, TU-CDES Member Mr. Gehendra Keshari Upadhya, Joint Secretary , PCTMCDB/GoN Member Mr. Pashupati Koirala, Under- Secretary, PCTMCDB/GoN Project Team Team Leader Prof. Dr. Rejina Maskey Project Co-ordinator Dr. Subodh Dhakal Geo-Technical Engineer Dr. Ram Chandra Tiwari GIS Expert Mr. Ajay Bhakta Mathema Geologist Mr. Suman Panday Assistant Geologist Mr. Niraj Bal Tamang Assistant GIS Analyst Mr. Padam Bahadur Budha Assistant GIS Analyst Ms. Shanta Banstola Social Surveyor Mr. Kumod Lekhak Field Assistant Mr. Nabin Nepali Review Technical Reviewer: Dr. Ranjan Kumar Dahal English Reviewer: Dr. Dinesh Raj Bhuju ii ACKNOWLEDGEMENTS Hazards like earthquake, landslide, soil erosion and sedimentation all shape the landscape and relief of the Himalaya. Land degradation of the Chure area of Nepal is primarily contributed by different types of landslides and mass wasting phenomena. Landslides and other mass wasting processes are collectively controlled by the lithospheric plate dynamics, geology, topography, intense precipitation and human interference. The upstream and downstream of the major river basins in these areas are highly interlinked and therefore such land degradation in the Chure area pose serious threat of flooding and inundation to the southern Tarai. Landslides cause a huge loss of human life and property as well as environmental degradation in Nepal requiring extra resources for relief and recovery. With all these facts in background, conservation of Chure area has been considered as the issue of national challenge in Nepal. President Chure Tarai Madesh Conservation Development Board (PCTMCDB/GoN) has initiated some steps for the conservation of Chure area realizing the lack of adequate and appropriate research findings which is essential for the conservation of Chure itself and sustainable development in this area. To bridge this research gap, Tribhuvan University Central Department of Environmental Science (TU-CDES) and PCTMCDB/GoN signed a Letter of Agreement on August, 2015. This report is the outcome of this collaboration between PCTMCDB/GoN and TU- CDES. The ultimate goal of the agreement is to provide technical and financial plan for the mitigation of existing high risk landslides in ten districts of Chure area and to delineate the landslide susceptibility zonation for future planning. The ten working districts belong to the Chure area of central and eastern Nepal namely Bara, Dhanusha, Makawanpur, Mahottari, Rautahat, Sarlahi, Saptari, Siraha, Sindhuli, and Udayapur. We express our heartfelt gratitude to PCTMCDB/GoN for identifying TU-CDES as the qualified collaborator to protect the Chure area through detail mapping, characterization and mitigation of landslides on priority basis. The project team completed the task performing desk study, field study and laboratory analysis at different time during the project period. We express our deep gratitude to chairman of PCTMCDB/GoN, Mr. Birendra Yadav and immediate past chairman Mr. Rameshwor Khanal for encouraging us time and again during the project period. We are highly thankful to Dr. Annapurna Nanda iii Das, member secretary of PCTMCDB/GoN for trusting our effort and helping in all the administrative issues with the board. We are thankful to Dr. Prem Prasad Poudel, under secretary in PCTMCDB/GoN for giving suggestions time and again regarding technical issues. We are equally thankful to the district level officials of District Soil Conservation Office (DSCO), District Forest Office (DFO) and Regional Office of PCTMCDB/GoN in the working districts and regions. TU-CDES extends its sincere thanks to all the board members of PCTMCDB/GoN and its immediate past board members. Our special thanks are to all the local residents of the working districts and communities. Prof. Dr. Kedar Rijal Head of Department iv EXECUTIVE SUMMARY The Chure area is one of the distinctive physiographic belts in Nepal that occupies the area lying in the southern part and running from east to west throughout the length of the country. It touches some or major area of thirty six districts of Nepal and is situated in the form of small hills. Chure area lies between the Lesser Himalaya in the north and Tarai in the south and is located within two major geological structures namely Main Frontal Thrust (MFT) in the south and the Main Boundary Thrust (MBT) in the north. These hills are formed of very fragile, weak and young sedimentary rocks called the Siwaliks that range in age from 1 to 14 million years belonging to Middle Miocene to Upper Pleistocene times. The area is typically comprised of high percent of forest cover offering habitat for charismatic wild fauna. For millennia, the Chure hills remained almost pristine because of lack of human settlements, agriculture practices and other interferences. As a consequence of lithospheric plate dynamics between the Indian Plate and Tibetan Plate, the young and fragile sedimentary rocks of Chure area are highly weathered and deformed. Interbedding of soft mudstone and hard sandstone beds provide differential weathering, providing plenty of options for slope instabilities and occurrence of different types of landslides in these hills. The last few decades have witnessed deforestation, over exploitation of forest products, development of road networks, forest encroachment, open grazing and unscientific use of land in the Chure area. Such activities on fragile ecosystem have exacerbated landslides in the hills and mountains and consequent flood hazards in the river valleys and lowland Tarai in the south. Due to its fragility and vulnerablity, conservation of Chure area has been considered as the issue of national challenge in Nepal. This research is intended to overcome the conservation issue of Chure area. The ultimate goal of the research is to provide technical and financial plan for the mitigation of existing high risk landslides in ten districts of Chure area and to delineate the landslide susceptibility zonation. The ten working districts belong to the chure area of central and eastern Nepal namely Bara, Dhanusha, Makawanpur, Mahottari, Rautahat, Sarlahi, Saptari, Siraha, Sindhuli, and Udayapur. Landslides inventory, landslide characterization, laboratory analysis and vulnerability and risk assessment were performed by the combination of desk study, field study and laboratory analysis to meet the objectives. v The results of the study are presented in five thematic chapters: Landslide Inventory, Landslide Characterization, Landslide Susceptibility Mapping, Landslide Risk and Vulnerability Assessments, Landslide Mitigation Measure and Financial Plans. The following section provides highlights of different chapters. Landslide Inventory Landslide inventory is a spatial dataset of mapped landsides usually derived from aerial photograph interpretation, satellite imagery or direct field observation. Google Pro Earth Imagery 2015/16 was used to identify and document the landslides. Similarly, GIS tool was applied to determine the location and distribution under different attributes such as Elevation, Slope, Aspects, Geo-form distribution, Soil types, Landuse/landcover etc. In total, 3456 landslides were identified and inventoried for the ten districts, which hold an area of 12.7234 square kilometer (Km2). According to the inventory, Makawanpur district consisted of highest number of landslides (792) and Mahottari district consisted of lowest number of landslides (98). Other districts with higher number of landslides were: Siraha (717), Udayapur (684) and Sindhuli (469). In terms of the density of landslides per unit area, Bara, Rautahat, Siraha and Saptari districts were found to have higher occurrence of landslides per square kilometer. Siraha was identified to be the district with highest landslide density (3.424). In terms of the size of landslides, three classes were distinguished namely small scale landslides (<1000 square meter (m2)), medium scale landslides (1000-10,000 m2) and large scale landslides (>10,000 m2). The inventory data was presented up to the ward level with distinct Landslide Identity (LID) number for each landslide. The LID was developed by using the codes of districts, Village Development Committees (VDCs), ward number and landslide numbering. The code was of 10 digits where first two digits refer to district, second three digits are for VDC, then it is followed by ward number, finally ending with three digits of landslide numbering