THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY LE THI THU THAO REMOTE SENSING DATA AND GIS APPLICATION STUDY ON LANDSLIDE RISK MANAGEMENT IN CHO DON DISTRICT, BACKAN PROVI
INTRODUCTION
Research rationale
Bac Kan is a mountainous province in the Northeast region of Vietnam, with complicated topography, primarily hills and high mountains, a deep interior and upstream of the Cau River, Nang River system, and other rivers Due to its rugged terrain characterized by steep hills and mountains, Bac Kan Province is consistently vulnerable to the dangers of land and rockslides, which have a significant impact on the local living conditions In the province, there are approximately 300 locations where over 2,000 households reside in areas highly prone to landslides, especially during the prolonged rainy season The majority of families residing in these areas face safety hazards due to inadequate infrastructure investment and the presence of high slope, which increases the potential risk of landslides
Cho Don District is located in the western part of Bac Kan province, characterized by a rugged terrain with more than 90% of the area comprising hills and mountains The mountains have heights ranging from 400 to 1000 meters The average slope is approximately 25 to 30 degrees, while some mountain slopes reach as high as 45 to 50 degrees This is the major factor influencing the susceptibility to landslides in the area The vegetation cover is quite good Many areas still have natural forests with large trees, wide canopies, and minimal disturbance The geological characteristics of this area mainly consist of shale, clay, limestone, quartzite, and cemented sandstone belonging to the Phu Ngu, Mia
Le, Pia Phuong, and Khao Loc stratigraphic formations There are also scattered granite blocks of the Phia Bioc complex and small magma blocks of the Cho Don complex along the Northeast-Southwest fault line The degree of weathering here is quite strong, with thickness exceeding 10 meters in many places The primary weathering products are clay and loose silt, which tend to become muddy when exposed to water
The main rivers in Cho Don district are Nam Cuong in the north, Cau River, Pho Day River, and Binh Trung River in the south and the district has a dense network of rivers and streams, with their flow varying with the seasons The steep and rugged terrain creates waterfalls, deep gorges, and during the rainy season, there is a high velocity of water flow, making it prone to flash floods and landslides along the riverbanks During the dry season, many streams have turned into deep gorges The reduced water coverage has negatively impacted agricultural productivity The main flow of the streams is from north to south When the flood season comes, it frequently causes erosion along the riverbanks The majority of the terrain in the district has steep slopes, causing surface water to accumulate quickly Therefore, during the rainy season, there are often flash floods in the hilly areas and along the riverbanks, leading to overflow onto cultivated land and temporary flooding in the area near the streams Recently, there has been a decrease in forest area due to land use conversion, resulting in water scarcity, soil nutrient depletion, and erosion along the riverbanks (particularly in areas where rice is grown)
Under the influence of climate change and rapid urbanization in recent times, natural phenomena such as landslides, flash floods have been occurring more frequently and with increasing severity Therefore, it is necessary to have the appropriate tools and timely solutions to minimize the damages caused by these natural disasters and landslides Building a map of landslide hazard zones to identify areas with a high risk of landslides is a necessary task and it is a useful tool to enhance the effectiveness of natural disaster management, landslide prevention and mitigation efforts With the support of remote sensing and Geographic Information Systems (GIS), the use of GIS will provide an effective solution for mapping and organizing data on the current status of landslides in a scientific and comprehensive manner
Derived from the reality and the aforementioned reasons, the study researched on the subject: “Remote sensing data and GIS application study on landslide risk management in Cho Don district, Backan Province, Vietnam ”.
Research objectives
Mapping and Zoning areas of landslide risk in Cho Don district using remote sensing data and GIS application
Identifying the main factor causing landslides in Cho Don district
Providing strategies to reduce the probability of landslides.
Research questions and hypothesis
What elements significantly contribute to landslides in Cho Don district?
What is the level of landslide risk in Cho Don district?
What is the technique to assess the risk of landslides?
What are the measurements to lessen the landslides in Cho Don district? 1.3.2 Hypothesis
Due to the heavy rainfall and human activities, it can be high risk on landslide in Cho Don district.
Limitations
Limited resources and logistical constraints make extensive field surveys challenging, hindering the validation of remote sensing findings The rugged and mountainous terrain adds complexity, making it difficult to accurately identify and characterize landslide features and their spatial patterns.
LITERATURE REVIEW
Theoretical basis about Landslide
The surface of earth is shaped by a variety of natural processes, one of which is land sliding Landslides are a subset of mass movement, a considerably larger category of slope dynamics "Landslide" denotes downward and outward movement of slope-forming materials composed of natural rock, soils, artificial fills, -or combinations of these materials (Varnes, 1978)
The kind of materials used and the method of movement can be used to distinguish between the many types of landslides Figure 2.1 displays a graphic representation of a landslide along with the terms used to describe its characteristics (Varnes, 1978)
Figure 2.1: Components of a landslide (David J Varnes, 1978)
Based on the type of movement and the type of material involved, distinct types of landslides can be identified In a nutshell, the components of a landslide mass can be either rock or soil (or both); the latter is referred to as debris if it is mostly made up of coarser fragments and is defined as earth if it is mostly made up of sand-sized or smaller particles The type of movement refers to the internal mechanisms that really cause the displacement of the landslide mass: falls, slide, topples, or flow Table 2.1 illustrates clearly a classification scheme based on these factors and Figure 2.2 depict the main categories of landslide movement
Table 2.1: Landslide types and a condensed taxonomy of slope motions according to Varnes (USGS, 2004)
Falls Rock fall Debris fall Earth fall
Topples Rock topple Debris topple Earth topple
Translational Lateral Spreads Rock spread Debris spread Earth spread
Complex Combination of two or more principal types
Figure 2.2 Diagrams showing the main categories of landslide movement
Slides: Although the general term "landslide" encompasses a wide range of mass movements, the more specific use of the term only refers to mass movements where there is a clear zone of weakness that divides the slide material from more stable underlying material Rotational slides (fig 2.2A) and translational slides (fig 2.2B) are the two primary categories of slides A block slide is a translational slide in which the mass that is traveling downslope is made up of just one unit or a small group of closely linked units (fig 2.2C)
Falls: Falls are sudden movements of geologic material masses, such as rocks and boulders, that separate from cliffs or steep slopes (fig 2.2D) Separation takes place along discontinuities like joints, fractures, and bedding planes, and movement happens through free-fall, bouncing, and rolling
Topples: The forward rotation of a unit or units about a pivot point that is below or low in the unit, under the influence of gravity, forces from neighboring units, or fluids in fissures, distinguishes toppling failures (fig 2.2E)
Flows: There are five primary types of flows, and each one differs significantly from the others a Debris flow: A debris flow is a type of swift mass movement in which a slurry made of loose soil, rock, organic matter, air, and water moves downhill (fig 2.2F) About