Narayani River Management Project has been working out for the protection of the flood affected areas by East Rapti River. Study area for this assignment was from Lothar Bridge at East – West Highway to the Golaghat (confluence of Narayani and East Rapti River). The assignment intends to prepare detailed project report for the Lothar and East Rapti River flood protection works.
This study conducted a detailed cross-section and profile survey for the entire river length for the purpose of flood modeling and protection structures design. Differential Global Positioning System (DGPS) technology was utilized to establish 20 permanent benchmarks along the river within the study area. Bank cross-section and full cross-section (i.e., bank to bank covering beyond the observed high flood level at both the banks) were taken at an interval of 250 m and 500m, respectively. Information on historical floods and their consequences were collected from a structured social survey such as Focus Group Discussion (FGD) and Key Informant Interviews (KII) with aid of carefully derived questionnaire and checklists. Randomly sampled household surveys were also conducted in each ward lying in the flood risk area along the river to further validate information collected from the FGD and KII.
Data collected from primary and secondary sources were fed with HEC-RAS model for flood modeling. Geometry data required for the model was prepared based on the field survey data. Flood discharge of various return periods were estimated using established methods of flood forecasting. Long term flow data measured at Rajaiya (Station no. 460), Manahari (Station no. 465) and Lothar (Station no. 470) by Department of Hydrology and Meteorology were utilized for frequency analysis.
Proposed structural measures after appropriate evaluation of various options are - Embankment with pitching and launching studs at regular interval; Gabion walls with slope pitching and studs at regular interval; strengthening of existing structures and vegetative measures along the delta formed at the confluence of major rivers. The proposed protection alignment runs for the entire length along the right bank of the river.
Total cost of the project is 4.32 millions NRs.