Journal on Geoinformatics, Nepal

Application of Geo-informatics for Soil Erosion Mapping

Susheel Dangol — 2023-05-28

Soil erosion is a most severe environmental problem in hilly area. The study is carried out on Upper Bagmati River basin, North of Kathmandu valley having an area of 61 Sq.km. (approx). Universal Soil Loss Equation (USLE) model, with Geographic Information System (GIS) has been used to quantify the soil loss. Erosion modelling requires huge amount of information and data, usually coming from different sources and available in different formats and scales and for management of these data, GIS was used, which helped considerably in organizing the spatial data representing the effects of each factor affecting soil erosion. Five essential parameters of USLE Rainfall erosivity factor (R), Soil erodibility Factor (K), Slope length and steepness (LS) factor, Cropping management factor (C) and Support practice factor (P) have been used to estimate soil loss amount in the study area. All of these layers have been prepared in Arc GIS using various data sources and data preparation methods. DEM was prepared from the contour data with the interval of 20m which was used to generate LS factor. The monthly rainfall data (2010) of 17 rain gauge stations within the catchment area have been used to predict the R factor. K, C and P factors in basin area are adopted from the literature. The spatial distribution map of soil loss of the basin has been generated and classified into six categories depending on the calculated soil erosion amount. The annual predicted soil loss ranges between 0 and 292.878 t/ha/y. Low soil loss (mean 9.7 t/ha/y) have been recorded under forested areas. The high rate (mean 40.4 t/ha/y) of soil erosion was found in the cultivation area.

Assessment of Landcover Change of Kathmandu District, Nepal

Bimala Lama — 2023-05-28

It is necessary to understand land cover changes for managing and monitoring natural resources and development, especially urban planning. Remote sensing and geographical information systems (GIS) are proven tools for assessing land use and land cover changes, which helps planners advance sustainability. Google Earth Engine is used in this study to detect land cover changes in one of the rapidly growing cities in Nepal. It was discovered that from 2013 to 2019, 0.26% of the total area was increased by forests, 3.28% by settlement, 0.015% by wetland, and 1.21% by otherland. The overall accuracy and kappa coefficient of the landcover change study for 2013 are 80% and 0.74, and the overall accuracy and kappa coefficient of the study of landcover change for 2019 are 83.33% and 0.78. The status of the landcover change in Kathmandu district before and after the earthquake showed that forest covers the highest area, followed by cropland, and then settlement in both years 2013 and 2019. Forest, settlement, wetland, and other land have increased by 0.26%, 4.54%, 0.015%, and 1.21%, respectively. However, cropland and grassland have been decreased by 3.28% and 0.22% respectively.

Can GNSS Derived Height Replace Levelling Height? - A Case of Low-Land of Nepal

Shanker KC — 2023-05-28

Orthometric height is the generally adopted type of height worldwide and in geomatics community. Precise levelling has been the method of obtaining orthometric height in past for most of the country, so as the Nepal. However, due to wide usage of Global Navigation Satellite System (GNSS), the alternative approach of combining GNSS derived ellipsoidal height with geoid undulation to get GNSS derived orthometric height, has been used extensively. In Nepal, this technique was officially adopted in 2020 for Everest height measurement and understood as the efficient way to comply with levelling height. In this study, GNSS surveying was conducted on 15 stations located at the lowland region of Nepal and orthometric heights were obtained from GNSS and geoid method. When compared GNSS derived orthometric height with precise levelling height, the difference remained within threshold of 5cm for majority of observation stations. However, these differences are not sufficient to support the standards set for the third order levelling by Survey Department (SD). The accuracy of GNSS derived orthometric height can be significantly affected by various environment and existing resources such as existing accuracy of geoid, nature of precise levelling height. Considering the revisit upon these conditions, we expect GNSS-levelling as a strong alternative to time consuming, tedious, and costly precise levelling which is most suitable method of obtaining orthometric height in lowland topography at a precision less than 4 cm.

Challenges of Current National Reference Frame (NRF) and Map Sheet Layout in Nepal Cadastral Mapping

Sushil Narsingh Rajbhandari — 2023-05-28

Systematic Cadastral mapping in Nepal used to be carried out using local coordinates. Later National Reference Frame (NRF) and a map sheet layout is being used to improve the situation. Current trend of use of GNSS in establishing control points demands a set of transformation parameters. The coordinates in NRF which are obtained by transforming the GNSS results, does not give expected accuracy to be used for large scale mapping. In addition, map sheet layout is being used not in line with the guidelines due to complications at the margins of projection zones. The conclusion is the current NRF and map sheet layout is not appropriate to use further for large scale mapping – which demands improvements in reference frame as well as projection system.

Estimation of Above Ground Biomass and Carbon Stock using UAV images

Sandesh Upadhyaya — 2023-05-28

Forests have a vital role in maintaining global climate stability by removing greenhouse gases like carbon dioxide from environment. Estimation of carbon stock is crucial in quantifying the amount of carbon that is present in the forest. The estimation of forest biomass and carbon stock through field measurements is a challenging and timeconsuming task. Here in this scenario, our study aims to estimate carbon stock in a forest area using the hybrid technique i.e., aerial survey and ground survey. We used low-altitude remote sensing data acquired by UAV to estimate biomass and carbon stock in an efficient way compared to the traditional techniques. We developed an orthomosaic from the collected aerial imageries and manually delineated tree crowns to obtain crown projection area (CPA) for the entire study area using GIS tools. Our study area contained a mixed species with Pinus Wallichiana to be the dominant species while other species are negligible. Using field-measured tree height and diameter at breast height (DBH) as input, we estimated above-ground biomass (AGB) with an allometric equation and then used a factor value to estimate carbon stock or aboveground carbon (AGC) for six sample plots. Next, we developed a relationship between CPA and carbon stock and validated it by comparing the carbon stock values obtained from the allometric equation for the remaining four sample plots. Among the various developed model, 4th order Polynomial model was chosen due to its highest coefficient of correlation. After the model validation was done the AGC of whole study area was obtained by using the CPA delineated manually from the orthomosaic image. The total AGC and AGB obtained for our study area which was about 7 hectare was 210.7480 tons and 448.4 tons respectively.

Restoration of Land Parcels using Land Consolidation & Readjustment: A Case of Resilience after Flood Disaster

Tanka Prasad Dahal — 2023-05-28

Millions of people are affected from natural disaster leading to loss of land tenure around the world. People affected from the disaster leading to loss of land tenure are often excluded from post disaster assistance. The parcel boundary may change or obliterated because of disaster or also from some infrastructure development. Re-establishing of the cadastral boundary is very crucial and challenging task to re-establish the tenure rights and other cadastral details. This paper focuses on the restoration of land parcels after flood. Paper highlights the impact of flood in parcel boundary and proposes a concept for restoration of those obliterated parcels of Melamchi bazar, Sindupalchok, Nepal which was affected from the flash flood on 15th June 2021. The model for restoration of land parcel using the concept of land consolidation and re-adjustment has been recommended focusing on land pooling, creating a regular shape of the parcel. This paper also evaluates the current legal provisions for restoration of land parcels after land use change due to flood.

Susceptibility Modeling for Potential Fire Risk Zone in Semi-Urban Area

Bikash Kumar Karna — 2023-05-28

Fires inflict major losses in global forest resources as well as human lives and property. Forest fires and their tendencies have increased in recent years in Nepal that, necessity for adequate management actions. The fire risk zone is identified with the origin of the ignitions and the pattern of their occurrence, as well as by shared environmental variables that translate into the same risk potential. To reduce the detrimental impacts of fire, several strategies for preventing and combating fires have been implemented based on identified potential fire risk zone. The work is carried out in Shambhunath Municipality, Saptari. In this study, spatial modeling with integration of MCE, fuzzy and AHP is applied for susceptibility assessment for identifying the potential fire risk zone. In fire risk assessment index map shows that 21.14 percent of municipality extent land occurred in the fire risk in which the distribution of the high risk occupied 0.01 percent, medium risk, 0.49 percent, low risk 20.64 percent and remaining 79 percent land free from fire risk. The high risk of potential fire zone were identified along the east west highway surrounding to the high voltage transmission route and petrol pump location. Likewise, potential high risk of forest fire also found in the dense forest area in elevation greater than 400m.

Topographic Base Map Update in Nepal: Overview, Accomplishments and Way Forward

Tina Baidar — 2023-05-28

The latest series of topographic base map of Nepal were prepared by Survey Department of Nepal during 1992-2001 A.D and preparation of their digital database namely National Topographic Database started in 1999 A.D. Understanding the utmost need of updating these maps and database, the department started update process in a rapid pace from fiscal year 2075/76 B.S based on ZiYuan-3 Survey and Mapping (ZY-3) satellite images with 2.1 m panchromatic and 5.8 m multispectral spatial resolution. The overall update procedure includes satellite image processing, feature update, field verification, field data compilation, finalization, map and database approval from Mapping Technical Subcommittee and finally map reproduction. The technical aspects of this whole process is based on standard specification document namely “Specifications for 1:25000 and 1:50000 Topographic Base Maps”. First level of update and field verification of all grid sheets covering Nepal was completed by fiscal year 2078/79 and is now in the phase of approval by Mapping Technical Subcommittee and reproduction. At the end of 2079 B.S, around 250 number of sheets have been approved and are made available by the department. With the completion of this update series, there are further opportunities to produce thematic data/maps as well as administrative maps of smaller scales. Furthermore, with the availability of higher resolution images through LiDAR, UAV and other resources, the department has opportunities to work on large scale mapping in coming days.

UAV Images for Agriculture Land Parcel Delineation through Edge Detection Algorithm: A Case Study of Hilly and Terai Regions

Arun Kumar Bhomi — 2023-05-28

The use of unmanned aerial vehicles (UAVs) for remote sensing applications has gained significant attention in recent years. One important aspect of UAV-based remote sensingis the accurate delineation of parcels, which is essential for a wide range of applications, including land use planning, agricultural monitoring, and cadastral map preparation among several others. The on-screen manual digitization method can delineate parcelswith great precision. However, the method is labor-intensive, time-consuming, and expensive. Alternatively, it can be achieved by utilizing automated algorithms. In this study, an edge detection algorithm is employed to delineate agriculture parcels using UAV images in the ENVI platform. The algorithm uses a pre-programmed algorithm to automatically detect and delineate field boundaries. The delineated boundaries were cleaned and refined by smoothing the polygon and the line vectors. The obtained parcel boundaries and their geometric parameters were assessed against manually digitized parcel boundaries using the same UAV ortho-mosaic. The method was tested on two scenarios: i) Terai farms having flat topography and small dikes and ii) Hill farms having undulated terrain in a terraced farming structure and crowded parcels. The mean of the percentage change in area for the land parcel was found to be 2.43% and 4.69% respectively for Terai and Hilly regions. Similarly, the mean of the percentage change in the perimeter of the land parcels were 8.82% and 2.43% respectively for Terai and Hilly regions. The study demonstrated the feasibility of using UAV images for agriculture land parcel delineation and highlighted the potential of an in-built edge detection algorithm as a time-efficient and reliable alternative to manual digitization if refinement and proper selection of algorithm and parameters are done. Thus, automated algorithms can be utilized to reasonably delineate agriculture parcels from UAV images.

Editorial Vol.22

Karuna KC — 2023-05-28