Topographic Map Production using GIS and Remote Sensing

Project Description

Tamaksohi -3 (TA-3) and Tamakoshi- 2 (TA-2) Hydroelectric Project is located on the Tamaksohi River in Dolakha district of central Nepal and is conducting the Feasibility Study and Environmental-Social Impact Assessment Study (ESIA) after receiving survey license from Government of Nepal. The Project intends to develop these two projects as combined TA-23. The objective of the assignment is to produce detailed topographic maps of TA23 project based on the existing maps and satellite imageries using GIS and remote sensing technique.

Assignment Description

Digitization of existing topographic maps in 1:25,000 scale produced by Department of Survey, Topographic Branch. The topo-maps of the area, Charikot, Jiri, Melun, Hatdanda, Lambagar, Manthali, and Dhobi were digitized in the GIS environment. • Interpolation of the digitized contours and production of topo-maps in 1:10,000 scale with contour interval (CI) of 5 m in GIS and AutoCAD formats • Collection of 2nd and 3rd order Geodetic points (coordinates) in the TA23 Project area from Department of Survey, geodetic Branch and locate them in the existing topographic maps (1:25,000) after site verification • Updating of digitized topographic maps (350 sq. km) with remote sensed data from high resolution satellite images with spatial resolution of 2.5 m as per Spatial Data Accuracy standards. • Generation of ortho-images on the Digital Terrain Model (DTM) at a contour interval of 5m • Correlation of image points with reference to the ground conditions and on-screen digitations work of different layers for changed are and subsequent editing of vector data, • Updated topographic features including man-made structures in the digitized maps based on the recent satellite images (not older than 6 months) • Prepared database of different features in different layers with designation of appropriate symbols/legend • Establishment of vertical control on site at a density of 4 points in a hectare that was spread equally over the Project area using high-precision GPS survey instrument. In addition high precision survey was conducted using Total Station as required. • Preparation of D-cards including color photographs of the BM’s with sufficient ground details in the captured photographs • The horizontal accuracy achieved was within +/- 1mm, and vertical accuracy of +/- m in the map. The output topographical map was produced in 1:10,000 scale with CI of 5 m