Study Area Description:

The West Seti Transmission Line project area spans across four districts in the Far Western region of Nepal: Kanchanpur, Doti, Dadeldhura, and Bajhang. These districts present a highly diverse geographical terrain, ranging from flatlands in the Terai region to rugged, mountainous landscapes in the mid-hills and high hills. The transmission line runs approximately 130 kilometers, requiring a detailed topographic survey to aid in the planning and design of the 400 KVA transmission line that will help distribute electricity generated from the West Seti Hydropower Project.

1. Kanchanpur District:

   Kanchanpur is located in the southwestern part of Nepal, bordering India to the south. The district lies primarily in the Terai region, characterized by flatlands with fertile soil, dense forests, and scattered settlements. The district also hosts parts of the Shuklaphanta National Park, a key ecological area. In terms of infrastructure development, Kanchanpur is an important hub due to its proximity to the Indian border and access to major highways. For the transmission line project, the area posed fewer logistical challenges compared to the hill districts but still required precise mapping for the alignment and construction of transmission towers.

2. Doti District:

   Moving northward from Kanchanpur, Doti is situated in the mid-hill region of the Far West. The district features steep valleys, ridges, and river systems, including the Seti River. These geographical characteristics made the survey particularly challenging, as the transmission line has to navigate through rugged, mountainous terrain. Doti’s elevation varies significantly, ranging from 400 meters to 3,200 meters, which required precise topographical mapping to address the elevation changes. The area is largely rural, with terraced agricultural fields, small settlements, and dense forests, demanding a combination of LiDAR data and ground control points to achieve accurate results.

3. Dadeldhura District:

   Further northeast from Doti lies Dadeldhura, a district characterized by more rugged and elevated terrain. With elevations that go beyond 2,000 meters, the region has a mix of steep slopes, river valleys, and densely forested areas. The Seti and Mahakali rivers flow through this region, and the landscape features numerous streams, tributaries, and river basins. These natural features posed significant challenges for establishing control points and planning the transmission line route. The area is sparsely populated, and its inaccessibility made it necessary to rely on airborne LiDAR to capture accurate data over large, difficult-to-reach regions. The LiDAR flights helped to map out the undulating terrain and potential hazards that could affect the transmission line’s design and stability.

4. Bajhang District:

   Bajhang, located in the far north, is the most remote and least developed district within the survey area. The district consists of mountainous terrain, with elevations that exceed 3,000 meters, as well as several peaks and high passes. Bajhang is home to numerous rivers and streams, including the Seti River, which cuts through the region. The area experiences harsh climatic conditions, especially in the winter months, which adds complexity to infrastructure projects. The transmission line’s alignment in Bajhang had to take into account the steep slopes, landslide-prone areas, and potential seismic risks. The district’s remoteness made it necessary to conduct helicopter-based LiDAR flights to cover vast expanses in a short amount of time.

 Survey Planning and Execution:

Given the diverse and challenging terrain across the four districts, planning for the airborne LiDAR survey was crucial. The survey was carefully designed to capture the intricate details of the landscape, ensuring that all necessary data was collected for the transmission line’s alignment and construction.

1. Establishing Benchmarks and Control Points:

   A key part of the survey was establishing benchmarks and control points throughout the project area. This involved selecting strategic locations for placing Differential Global Positioning System (DGPS) receivers and using Total Station (TS) methods to ensure that the LiDAR data was aligned with ground-based measurements. The steep and rugged terrain in districts like Doti, Dadeldhura, and Bajhang required significant effort to identify and access suitable locations for these control points. In many instances, the team had to trek to remote areas or use helicopters to place equipment at high elevations.

2. Airborne LiDAR Flights:

   The core component of the survey was the execution of airborne LiDAR flights via helicopter. This method allowed for the rapid collection of high-density point clouds across the entire 130-kilometer transmission line route. Helicopter-based LiDAR was particularly useful in the remote and inaccessible parts of the project area, such as the high mountains of Bajhang and the steep valleys in Doti and Dadeldhura. The flights were conducted in multiple passes, ensuring complete coverage of the terrain and capturing data with high accuracy. In addition to the point cloud data, high-resolution aerial imagery was captured to complement the LiDAR data and produce ortho-rectified images of the study area.

3. Pre-Processing of LiDAR Data:

   Once the LiDAR data was collected, the next step involved pre-processing to create georeferenced point clouds. This process was essential for converting the raw LiDAR data into a usable format for generating topographical maps, Digital Surface Models (DSM), and Digital Terrain Models (DTM). The data was classified into various categories, including ground, vegetation, and structures, allowing for the generation of accurate terrain models that could be used for the transmission line’s design and planning.

By overcoming the geographical challenges of the study area, the airborne LiDAR survey provided invaluable data for the development of the West Seti Transmission Line project, ensuring that the 400 KVA transmission infrastructure could be efficiently designed and implemented across the diverse landscapes of Kanchanpur, Doti, Dadeldhura, and Bajhang.