Conducting Kosi River Cross- Section Survey, Hazard Map Preparation, Embankment Breach Analysis, soil Sampling and Analysis (Package 1), (Emergency flood Damage Rehabilitation Project (EFDRP), Part E Institutional Strengthening of DWIDP for Disaster Risk Reduction)

Project Description

Every Year, the monsoon floods in almost all regions of Nepal take several lives and cause widespread damage and destruction. Primary vicitims form these water induced hazards are always the marginal poor of the country living densely along the flood plains of the river bank in the Terai region and along the steep slopes of the rugged fragile terrain within the mountain area. These major floods have directly resulted in the loss of livelihoods, particularly for the poor people who inhabit in the vulnerable flood plain areas, and caused significant economic damage. The country frequently suffers from different kinds of water induced disasters like soil erosion, river bank erosion, embankment breach, landslide, debris flow, flooding and sedimentation. These phenomenon cause loss of lives and property and pose severe hazards to the physical infrastructures resulting interruption of the social and economic development of the country.
Hence the restore economic activities quickly, mainly in the three districts; Sunsari, Kailali and Kanchanpur and to improve the livelihoods of about 300000 people affected seriously by the 2008 floods, the ADB and the Government of Nepal signed an agreement to carryout the Emergency Flood Damage Rehabilitation Project. The project aims at contributing to sustainable economic growth by minimizing the devastating impact of the flood and reduce future risks from similar disasters.
Water induced / flood hazard mapping and embankment breach analysis provided information on inundation, bank erosion together with evacuation and other information. The purpose of the hazard maps is to minimize damage and to promote non-structural measures in mitigating flood disaster. The main aim of project was to enhance cost – effective construction specifications of rehabilitated infrastructure, and supporting capacity building and the Government’s disaster preparedness.

Assignment Description

The main activities carried out by consultant are as follows: Pre-Field Study : i) Review of available reports and relevant literature; ii) Collect and study all the available digital maps, topographic maps, satellite imageries, aerial photographic maps, geological maps, land utilization maps, land classification maps, soil maps and other available relevant maps for the river basin delineated map; iii) Collected historical data on water-induced disasters from the relevant institutions and reports; iv) Study and analyze the collected maps and imageries to generate preliminary hazard map; v) Prepare the criteria for the hazard classification for each return year flood; vi) Identify the areas to be studied in detail in terms of the severity of water-induced hazards; vii) Prepare the field study format, for the following hazard types, respectively; a) Erosion and bank-cutting; b) Flood and Inundation c) Develop questionnaire for field survey and vii) Prepare the preliminary hazard maps and identify the most hazardous area River X-section Survey: i) Carry out cross section survey of the river from river cross-section survey from chatara (DHM Hydrometric Station) to barrage and behind the embankment covering flood inundation area; ii) Establishment of Bench Mark at every km for 50 km of river stretch with maximum 13 km river width, carried river cross and longitude section at every km at straight, and at bend every 250 m or more; iii) Carryout river cross and longitudinal section at every km interval at straight reach, and at bends every 250m; iv) Tiedthe traverse survey into existing national grid triangulation points (UTM coordinates) established by the Department of Survey; v) Conducted Bench mark leveling Field and Other Activities : i) Prepare preliminary hazard maps and validate the data in the field; ii) Collect additional information on geology, soil structure, soil depth, trend of bank cutting and other locally available hydrological data; iii) Cross-check in the field the areas of settlement, infrastructure, historic important places, and different land uses etc. considering the threats from water induced disaster; iv) Disseminate the preliminary findings of study to concern district water induced disaster office; v) Extract X-sections from DEM/Field survey at every km and bridge section; vi) Extract X-sections from DEM/Field survey at u/s and d/s of bridge also Post Field Activities: i) Compile the information obtained during the pre-field study and field study; ii) Analyze all the data and prepare the validation table; iii) Compute catchment flow for different (25,50 and 100 years return period); iv) Run GIS based suitable hydrologic & Hydrodynamic Model (HECRAS Model); v) Preparation of Flood / water –induced hazard map (scale 1:10000); vi) Preparation and submission of Water Induced Hazard Maps with and study reports; vii) Preparation of evacuation map with evacuation route for the most hazardous area Embankment Breach Analysis : i) Carryout embankment breach analysis at Rajabas and Prakashpur at different flood return period (25, 50 and 100 years) using suitable software HECRAS and Arc GIS; ii) Use of available contour plan map/ digital map (provided by the client) of river and behind the embankment and iii) Preparation of separate reports on embankment breach analysis Soil Sampling and Grain Size Distribution Analysis : i) Collection of river bed materials (under water and adjacent dry bed), flood plain and embankment material from different reaches at every 2 kms form Chatara to Barrage and at every 5 km at banks; ii) Collection of samples from the armor layer that extends from the surface down to a depth; iii) Collection of available historical sediment data from DHM, Sunsari – Morang Irrigation Project and other sources; iv) Carryout grain size distribution analysis; v) Determine d90 and d50 particle size material and vi) Preparation of grain size distribution analysis report. Preparation of Flood / Water Induced Hazard Map : i) Preparation of Flood Hazard Maps for 25yr, 50yr and 100 return periods; ii) Identification of flood management & flood mitigation strategies