Detailed Study for the Preparation of River Training Master Plan of Narayani River

Project Description

The Narayani River basin extends from 27°15’N to 29°15’N and from 83°00’E to 85°45’E. The river originates in the higher Himalayan zone and is classified as a class I, snow-fed river and is one of the main rivers of the Gandaki basin. The river lies in one of the four major basins of river systems that drain into India. The present scope of the study is Narayani River from Narayanghat (i.e. from the bridge of East-West Highway) to about 65 km d/s, i.e. about the junction with Binai Khola. The river is located in Dun area and surrounded by the Siwalik Hills. The East Rapti (including other small rivers like Lothar, Manhari, Kayar, Reu) which originates from Makwanpur district joins the Narayani River in the Dun area on its eastern (left) bank. Similarly, rivers like Binai, Arun, Deusat, Girwari, etc. originate from the Mahabharat ranges and join Narayani river on the western (right) bank. The Narayani River receives a lot of sediment such as gravel, sand and clay through these rivers and other small tributaries from the Siwalik Hills. The Narayani River also acts as the regional boundary between Central and Western regions, zonal boundary between Narayani and Lumbini zones and district boundary between Chitwan (on the east) and Nawalparasi (on the west).
The Narayani Master Plan shows it is an attractive investment with EIRR of 11.56% at discount rate of 10% with B/C ratio comfortably at 1.99 and NPV of 3,211,504. But as the discount rate increase and reaches 14% the EIRR is not attractive for investment though the B/C ratio is 1.55 with NPV nearly half of that of first case. Hence, the project can be justified from social point of view rather than economic aspect. The sensitivity analysis shows the project is benefits are low in all the three parameters (B/C ration, IRR, and NPV) but the B/C ratio still remains more than 1 with low EIRR and NPVs. Hence, it can be summed that the project needs to be cautiously looked upon and in the event of price fluctuation and benefits being downsized it can only be justified from the social aspect and not from the economic aspect

Assignment Description

Review of relevant data, maps, literature on river training, past studies conducted in the Narayani River • Conducted a engineering survey (BM survey, X-section, L-section, Flood mark survey etc.) of Narayani River from Narayanghat (Narayani Bridge Axis) up to about 65 Km. downstream of the river along the both banks • Carried out thorough walkthrough survey in order to assess the filed condition and existing river training measures and problem identification; used GPS for spatial locations of the visits and inventories • Photographic documentation of river bank lines showing existing condition • Conduct socio-economic, hydrologic and sediment studies based on primary and secondary data as appropriate • Identification of environmental parameters of the river system and influence area of the river system for IEE and EIA purpose • Hydrological analysis for obtaining flood discharges of various return periods to be used in HEC-RAS hydrologic model • Extensive use of GIS for data analysis, review and map preparation • Preparation of DEM/TIN using various past survey data, data from topographic maps, and field survey • Hydrologic modeling using HEC-RAS and HEC-GeoRAS software for obtaining high flood level, inundation area, inundation depth • Estimation of rate of erosion of bank line with the interpretation of past and recent satellite images • Design of river training and associated works including recommendations of non-structural measures • Preparation of GIS and AutoCAD based maps and drawings • Preparation of project cost estimates of the proposed river raining works and associated other costs • Economic and financial analysis obtaining B/C ratio, IRR, and NPV including sensitivity analysis • Formulation of overall River Training Master Plan of Narayani River