MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
VIETNAM NATIONAL UNIVERSITY OF FORESTRY

STUDENT THESIS
Title
APPLICATION OF GEOGRAPHIC INFORMATION SYSTEM
& REMOTE SENSING ON ASSESSING SOIL EROSION IN SOME
PROTECTION PLANTATION MODELS AT HONG LINH TOWN,
HA TINH PROVINCE

Major: Natural Resources Management
Code: D850101
Faculty: Forest Resource and Environmental Management

Student: Phan Thi Thuy Linh

Student ID: 1453090571

Class: K59A Natural Resources Management Course: 2014 – 2018

Advanced Education Program
Developed in collaboration with Colorado State University, USA
Supervisors: Dr. Bui Manh Hung
Assoc. Prof. Bui Xuan Dung

Ha Noi, 2018


ACKNOWLEDGEMENT
The research has been supported by many individuals as well as organizations. First
of all, I would like to thank to Dr. Bui Manh Hung and Assoc. Prof. Bui Xuan Dung who

are my advisers for supporting me during conducting my thesis for their motivation,
enthusiasm and immense knowledge.
Second of all, I also thank Board of Hong Linh protection forest management,
People‘s Committee of Hong Linh town.` Especially, I would like to thank to Mr. Nguyen
Hai Van and Mr. Ho Phuc Trung in Board of Hong Linh protection forest management for
their useful, enthusiasm and providing helpful data on this study.
I am so thankful for the supporting of Nguyen Thuy Duong, Nguyen Dieu Huyen,
Le Sy Hoa in conducting map and sample plot establishment. To complete my thesis, I
also received a lots of helps from Mr. Le, Mr. Thanh, Ms. Phuc who work in the
Laboratory of Vietnam National University of Forestry, therefore I would like to say
thank you to all of them for lending some equipments to measure the parameters.
Lastly, my family and my friends are a large motivation for me to complete my
thesis. I really thankful for all of you.
I sincerely thank you!


CONTENTS
LIST OF ABBREVIATIONS ................................................................................................. i
LIST OF TABLES ................................................................................................................. ii
LIST OF FIGURES .............................................................................................................. iii
ABSTRACT........................................................................................................................... 1
INTRODUCTION ................................................................................................................. 2
CHAPTER I ........................................................................................................................... 4
LITERATURE REVIEW ...................................................................................................... 4
1.1.

Geographic information system and remote sensing .................................................. 4

1.2.


Studies on soil erosion................................................................................................. 6

1.2.1. General of soil erosion ............................................................................................... 6
1.2.2. Impact factors to soil erosion ..................................................................................... 7
1.2.3. Effect of soil erosion .................................................................................................. 9
1.2.4. Research on erosion ................................................................................................... 9
CHAPTER II........................................................................................................................ 12
GOALS, OBJECTIVES AND STUDY SITE ..................................................................... 12
2.1. Goals ............................................................................................................................. 12
2.2. Objectives ..................................................................................................................... 12
2.3.

Study site ................................................................................................................... 12

2.3.1. Natural conditions. ................................................................................................... 12
2.3.2. Economics ............................................................................................................. 15
CHAPTER III ...................................................................................................................... 17
METHODS .......................................................................................................................... 17
3.1. Assessing the status of some protection plantation in Hong Linh town. ...................... 17
3.1.1. Factor investigation.................................................................................................... 17
3.1.2. Plot investigation and collection data ........................................................................ 17


3.1.3. Strip transect ............................................................................................................ 22
3.1.4. Data analysis ............................................................................................................ 24
DBH .................................................................................................................................. 25
3.2.

Creating potential erosion map and erosion map of protected plantation forest in HL


town. .................................................................................................................................. 29
3.2.1. Method approach...................................................................................................... 29
3.2.2. Data investigation .................................................................................................... 32
3.2.3. Creating maps .......................................................................................................... 34
3.3.

Assessing the ability of soil protection against soil erosion of protection plantation

in HL town. .......................................................................................................................... 38
3.3.1. Standard TCVN5299:2009 about ―Soil quality‖ ..................................................... 39
3.3.2. Two standard soil to protect forest based on Hundson 1971 ................................... 40
3.4.

Proposing some solutions to raise the effective of erosion control of some protection

plantation forest in Hong Linh town. ................................................................................... 41
CHAPTER IV ...................................................................................................................... 42
RESULTS AND DISCUSSIONS ........................................................................................ 42
4.1. The characteristics of protection plantation in Hong Linh town .................................. 42
4.1.1. Information about protection plantation in Hong Linh town ..................................... 42
4.1.2. Stand information ..................................................................................................... 44
4.1.3. Descriptive statistics results ....................................................................................... 46
4.1.4. Quality of tree statistics ............................................................................................. 48
4.1.5. Frequency distributions.............................................................................................. 49
4.2. Creating potential erosion map and vegetation cover map ........................................... 50
4.2.1. Potential erosion map (C2) ....................................................................................... 50
4.2.2. Vegetation Cover Map (C1) ..................................................................................... 54
4.3.

Assessing the ability of soil protection against soil erosion of protected plantation


forest in Hong Linh Town ................................................................................................... 55


4.4.

Proposing some solutions to raise the effective of erosion control of some protected

plantation forest in Hong Linh commune. ........................................................................... 60
4.4.1. Silviculture approach ............................................................................................... 60
4.4.2. For within threshold erosion .................................................................................... 60
4.4.3. For over threshold erosion ....................................................................................... 61
CHAPTER V ....................................................................................................................... 62
CONCLUSION AND RECOMMENDATION................................................................... 62
5.1. Conclusion .................................................................................................................... 62
5.2. Limitation...................................................................................................................... 63
5.3. Recommendation .......................................................................................................... 63
REFERENCES .................................................................................................................... 64
APPENDIX .......................................................................................................................... 66
1.1. Stand information for plots ........................................................................................... 66
1.2.

Value of frequency distribution of DBH and Height in all forest types.................... 67

1.3. Descriptive information ................................................................................................ 67
1.4. Frequency distribution in five representative plots for each forest type ....................... 68
1.5. Information about DEM 30*30..................................................................................... 72
1.6. Non-spatial data uses to create map .............................................................................. 73



LIST OF ABBREVIATIONS
C

Circumference

CC

Canopy cover

C1

Vegetation cover

C2

Potential erosion

DBH

Diameter breast height

DEM

Digital elevation model

GIS

Geographic information system

H


Height

Hc

Commercial height

LC

Litter cover

GC

Ground cover

K

Rainfall erosion index

RS

Remote sensing

S
USLE
P

Slope
Universal soil loss equation
Porosity


i


LIST OF TABLES
Table 3.1. Assessing the quality of the tree ......................................................................... 21
Table 3.2. Tree position inventory ....................................................................................... 22
Table 3.3. Survey of Canopy closure (CC), ground cover (GC), liter cover (LC) ............. 24
Table 3.4. Calculation for stand information ....................................................................... 25
Table 3.5. Methods of descriptive statistics ......................................................................... 26
Table 3.6. A measure of dispersion and variability [20] ..................................................... 26
Table 3.7. The ways to statistic frequency distribution ....................................................... 29
Table 3.8. Data collection of porosity.................................................................................. 33
Table 3.9. Classifying current erosion ................................................................................. 40
Table 4.1. Descriptive statistics for diameter variable......................................................... 47
Table 4.2. Statistics of tree quality in each status ................................................................ 49
Table 4.3. Slope analysis in Protection plantation at Hong Linh ....................................... 51
Table 4.4. Value of vegetation structure in each forest type in protection plantation. ........ 55
Table 4.5. Classification of current erosion in protection plantation at HL ........................ 56

ii


LIST OF FIGURES
Figure 2.1. Location of protection plantation in Hong Linh town, Ha Tinh. ...................... 13
Figure 2.2. Land use and distribution area in Hong Linh town ........................................... 14
Figure 3.1. Shape, location of investigation plots and measuring distance in plot. ............. 18
Figure 3.2. Definition of breast height [18] ........................................................................ 19
Figure 3.3. Using Fiberglass tape to measure DBH (a) and Blume-leiss to measure H (b ) ... 20
Figure 3.4. Measuring tree height ........................................................................................ 21

Figure 3.5. The processing of using gap light analysis ........................................................ 23
Figure 3.6. Types of Skewness [18] .................................................................................... 27
Figure 3.7. Interpolation method [11] .................................................................................. 31
Figure 3.8. Processing of creating map C1 and C2 ............................................................. 32
Figure 3.9. Flowchart of building C1 and C2 map ............................................................... 34
Figure 3.10. Flowchart of S factor in ArcGIS 10.3 ............................................................. 36
Figure 3.11. Flowchart of P factor in Arc-gis 10.3 .............................................................. 36
Figure3.12. Flowchart of C2 map......................................................................................... 37
Figure 3.13. Flowchart of C1 map ........................................................................................ 38
Figure 3.14. Processing of creating current erosion map ................................................... 39
Figure 4.1. Types of forest in Hong Linh town ................................................................... 42
Figure 4.2. Classification of forest status in protection plantation at Hong Linh town ....... 43
Figure 4.3. Distribution of stand density in protection plantation area at Hong Linh ........ 45
Figure 4.4. Distribution of DBH, height, commercial height of the tree in each plot. ....... 45
Figure 4.5. Total BA for stand and stand volume per hectare ............................................ 46
Figure 4.6. Frequency distribution of DBH and height in all forest types .......................... 50
Figure 4.7. Slope distribution in protection plantation at Hong Linh town ......................... 51
Figure 4.8. Soil porosity distribution of protection plantation in Hong Linh (P factor) ..... 52
iii


Figure 4.9. Map of potential erosion in protection plantation area at Hong Linh .............. 53
Figure 4.10. Vegetation cover of protection plantation area at Hong Linh ......................... 54
Figure 4.11. Distribution of current erosion in protection plantation at Hong Linh............ 56
Figure 4.12. Distribution of erosion area ............................................................................. 57
Figure 4.13. Amount of over soil erosion in protection plantation in Hong Linh .............. 58
Figure 4.14. Current erosion in each forest types at protection plantation Hong Linh ....... 59

iv



ABSTRACT
Soil erosion is one of serious environment problem in the world so protecting forest
plays an important role in reducing erosion in which each forest type has the different
ability of protecting soil. With aim of improving the effect of erosion, in this study we
conducted field observation in 20 plots & 80 random areas and assessed soil erosion in
some protection plantation models at Hong Linh town, Ha Tinh province by using soil loss
prediction equation of Quynh et al (1996) and applying of GIS & RS. Soil loss is predicted
from rainfall erosivity index (564 mm/year), slope, porosity and vegetation structures. A
map of potential erosion was generated from slope map, and soil porosity map by using
spatial interpolation and calculate to rainfall index by map algebra techniques in ArcGIS.
Vegetation index, a function of CC, H, GC and LC are classified into five groups. After we
conduct slope factor, porosity factor and vegetation factor map, we built current erosion
map by using equation of Quynh et al (1996). The results show that (1) There are five
main forest types (Pinus merkusii, mixed Pinus merkusii & Acacia auriculiformis, Acacia
auriculiormis, Eucalyptus, mixed Eucalyptus & Acacia) in which pinus merkusii is a
native species and dominant in protection plantation with 47.65% (665.96 ha); (2) Potential
erosion in this study is not high, from 0- 3.75 and the erosion rate is highest in other forest
and somewhere of pinus merkusii from 1.57 to 3.75, vegetation cover is from 0.9 to 1.53
that means C1 coefficient map of each forest type isn‘t much different; (3) Current erosion
based on TCVN 2009 are classified into 5 levels in which almost area is eroded slightly
and be medium; Assessing amount of

current erosion based on standard of Hundson

(1971), there are 364.74 hectares in protection plantation are exceed eroded threshold
(>0.8mm/year) occupied 26.22% in which erosion area of other forest is highest. Almost
area of each forest type belongs within eroded threshold and Pinus merkusii dominant with
51.9 %; (4) Keep ground cover and planting replaced species is one of solution to reduce
erosion in protection plantation at Hong Linh.


1


INTRODUCTION
Soil is the movement of soil particles from one place to another under the influence
of water or wind. Soil erosion by water is one of the most serious environmental problems
in the world [1]. Worldwide, soil erosion rate are highest in Asia, Africa, and South
America, averaging 30 to 40 tons ha-1yr-1, and lowest in Europe and the United States,
averaging about 17 tons ha-1yr-1[1]. However, erosion rates are low on land with natural
vegetation cover, about 2 tons ha-1yr-1 in relatively flat land and about 5 ha-1yr-1 in
mountainous areas [2]. In tropical regions where mean annual sediment yield estimated is
greater than 250 tons km-2 [1, 3], upland areas are usually protected from erosion by a
dense vegetation cover. The Food and Agriculture Organization estimates that the global
loss of productive land through erosion is 5-7 million ha/year. Zeuro et al (2011) estimated
global soil loss to erosion to be 26 million Mg/year. According to land use analyzed,
Vietnam has about 25 million of steep land, with huge potential of erosion, about 10
tons/ha/year [4, 5]. According to systematic monitoring from 1960 until now, there is 10 20% of area affected by erosion from moderate to strong [5, 6].
There are many different approaches and methods in researching soil erosion, the
one is field observation such as small slope, erosion transect, hillslope and catchment. This
way measure soil erosion in long-term with small scale so it is not efficiency. The other is
using soil loss prediction such as: MUSLE (William, 1975), ANSWERS (Beasley et al,
1980), SLEMSA (Elwell, 1981), SOILOSS model (Rosewell, 1993), RUSLE model
(Renard, 1997)[5]. Using modeling to predict soil erosion will save time and money,
moreover it also measure erosion faster in big scale. In practice, the Revised Universal
Soil Loss Equation (RUSLE) model initially developed by Wishchmeier and Smith (1965)
has been most widely used. However, this equation has some disadvantage in Vietnam,
amount of erosion is predicted in long-term average annual rate of erosion (more than 30
years) and suitable in slope topography less than 20 %; applying on sheet erosion and small
rill erosion; the experimental plots were designed in a small range of the factors. Due to the


2


complexity of defining factors of RUSLE for a given region, the application of the RUSLE
in Vietnam has been challenging in term of prediction accuracy and its validation [1, 7].
Soil loss prediction equation of Quynh et.al resolved these disadvantage of RUSLE that are
applying this equation is suitable in slope topography of Vietnam (5-360) and predict soil
erosion in short-term average annual rate. The most important of this equation is that
shows the relationship between soil loss prediction and rainfall, slope, vegetation cover and
soil porosity factors. Traditionally, soil loss was predicted at the local scale based on the
factors usually calculated from field measurement. Soil erosion prediction at large scale is
often difficult due to spatial and temporal variability of model‘s factors.[1] In recent
decades, the development of GIS techniques has facilitated the estimation of soil erosion
and its spatial distribution over large areas. Spatial analyses and interpolation techniques in
GIS are used for this study. The input data layers for mapping include DEM, rainfall and
vegetative cover.
Soil erosion is a significant problem in the uplands of the Central Coast, Vietnam
so that it is important to pinpoint estimated locations where soil erosion occurs in order to
prevent substantial soil loss. By 2017, Ha Tinh province has 360,700 ha of forest and
forest land, with forest cover reached 51.3% [8]. In which Hong Linh protection forest
plays an important role in protecting the environment, regulating the climate in the north of
Ha Tinh province[9]. At Hong Linh town, area of protection plantation is about 1390.89 ha
occupied 77.6% of plantation[10]. Moreover, there are not report about erosion control
though the equation of erosion prediction in Hong Linh. Stemming from such perceptions,
topic is chosen: “Application of Geography Information System and Remote Sensing on
assessing soil erosion in some protection plantation models at Hong Linh town, Ha Tinh
province”. Hopefully, it will make some contributions and bring some solutions to
improve the management for protection forests in Hong Linh town in particular and
Vietnam in general.


3


CHAPTER I
LITERATURE REVIEW
1.1. Geographic information system and remote sensing
A geographic information system (GIS) is a framework for gathering, managing,
and analyzing data. Rooted in the science of geography, GIS integrates many types of data.
It analyzes spatial location and organizes layers of information into visualizations using
maps and 3D scenes. With this unique capability, GIS reveals deeper insights into data,
such as patterns, relationships, and situations helping users make smarter decisions. GIS is
a computer-based tool for mapping and analyzing feature events on earth [11]. GIS
technology integrates common database operations, such as query and statistical analysis,
with maps. GIS manages location-based information and provides tools for display and
analysis of various statistics, including population characteristics, economic development
opportunities, and vegetation types. GIS allows you to link databases and maps to create
dynamic displays. Additionally, it provides tools to visualize, query, and overlay those
databases in ways not possible with traditional spreadsheets. These abilities distinguish
GIS from other information systems, and make it valuable to a wide range of public and
private enterprises for explaining events, predicting outcomes, and planning strategies. GIS
integrates many different kinds of data layers using spatial location. Most data has a
geographic component. GIS data includes imagery, features, and base maps linked to
spreadsheets and tables.
The field of GIS started in the 1960s as computers and early concepts of
quantitative and computational geography emerged. Early GIS work included important
research by the academic community. Later, the National Center for Geographic
Information and Analysis, led by Michael Goodchild, formalized research on key
4



geographic information science topics such as spatial analysis and visualization. These
efforts fueled a quantitative revolution in the world of geographic science and laid the
groundwork for GIS. GIS gives people the ability to create their own digital map layers to
help solve real-world problems. GIS has also evolved into a means for data sharing and
collaboration, inspiring a vision that is now rapidly becoming a reality—a continuous,
overlapping, and interoperable GIS database of the world, about virtually all subjects.
Today, hundreds of thousands of organizations are sharing their work and creating billions
of maps every day to tell stories and reveal patterns, trends, and relationships about
everything. Jack Dangermond (CEO, Esri) said that: ―GIS is about uncovering meaning
and insights from within data. It is rapidly evolving and providing a whole new framework
and process for understanding.‖
Remote Sensing (RS) is the art and science of acquiring information about the earth
surface without having any physical contact with it. This is done by sensing and recording
of reflected and emitted energy. Remote sensing is used in numerous fields, including
geography, land surveying and most Earth Science disciplines (for example, hydrology,
ecology, oceanography, glaciology, geology); it also has military, intelligence,
commercial, economic, planning, and humanitarian applications. Remote sensing makes it
possible to collect data of dangerous or inaccessible areas. Remote sensing provides fast,
high-resolution digital imaging. The quality of remote sensing data consists of its spatial,
spectral, radiometric and temporal resolutions. They are spatial resolution, spectral
resolution, radiometric resolution, temporal resolution, radiometric correction, topographic
correction. Some remote sensing applications are land cover and land use, agriculture,
forestry, geology, geomorphology, hydrology, mapping, ocean & coastal monitoring and
monitoring of atmospheric constituents.

5


Remote sensing technology combined with geographical information system has

been applied to perform scientific research and projects related to survey natural conditions
and natural resources, expertise environment monitoring, reduce to minimum the number
of natural disaster in some regions.
1.2. Studies on soil erosion
1.2.1. General of soil erosion
Erosion is a natural process where energy provided by water, wind and gravity
drives the detachment, transport and deposition of soil particles [12]. Detachment occurs
when the forces hold a soil particle in place is overcome by the forces of raindrop impact,
moving water or [5]. There is two type of erosion water erosion and wind erosion. Soil
erosion by water is one of the most serious environmental problems in the world [1].
The soil water erosion process is detachment and deposition. Rainfall, and the
surface runoff which may result from rainfall produces four main types of soil erosion by
water: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is
generally seen as the first and least severe stage in the soil erosion process, which is
followed by sheet erosion, then rill erosion and finally gully erosion (the most severe of the
four) [12]. In splash erosion, the impact of a falling raindrop creates a small crater in the
soil, ejecting soil particles. The distance these soil particles travel can be as much as 0.6 m
(two feet) vertically and 1.5 m (five feet) horizontally on the level ground. If the soil is
saturated, or if the rainfall rate is greater than the rate at which water can infiltrate into the
soil, surface runoff occurs. If the runoff has sufficient flow energy, it will transport
loosened soil particles (sediment) down the slope.
The second type is sheet erosion is defined as the uniform removal of soil in thin
layers from sloping land. It happens when rainwater flows into lower elevations, carrying
6


sediments with it. Sheet erosion is the transport of loosened soil particles by overland
flow. Detachment and movement of soil particles due to a relatively smooth, thin sheet of
water flowing across the ground surface [12].
The third erosion type is rill erosion refers to the development of small, ephemeral

concentrated flow paths which function as both sediment source and sediment delivery
systems for erosion on hill slopes. Generally, where water erosion rates on disturbed
upland areas are greatest, rills are active. Flow depths in rills are typical of the order of a
few centimeters (about an inch) or less and along-channel slopes may be quite steep. This
means that rills exhibit hydraulic physics very different from water flowing through the
deeper, wider channels of streams and rivers.
Gully erosion occurs when runoff water accumulates and rapidly flows in narrow
channels during or immediately after heavy rains or melting snow, removing soil to a
considerable depth.
1.2.2. Impact factors to soil erosion
a. Rainfall erosion index
Elision (1940) is the first person pointed out that raindrop caused erosion. In 1985,
Hudson N.W concluded that raindrop has a dynamic of 256 times more than it surface flow
[5]. So mainly the impact of the raindrop is the structural break topsoil by its own kinetic
energy, this very activity made the grain detected from the ground. In addition, rain also
made the flow to transfer grain to sediment.
b. Slope factor
The length and steepness of slope are two essential features of topography relating
to soil erosion and surface runoff. Topography steepness is a significant factor affecting
sediment yield. Soil erosion increase with slope length and steepness as a result of
7


respective increase in volume and velocities of surface runoff. The determination of slope
factor is necessary for measuring soil erosion.
Slope is an important topography unit of hills and broken plateau, and the drag
force of the shallow overland flow and the splash of the raindrop are the main forces of soil
erosion. Because the sediment transport mechanism of shallow overland flow under rain
splash is very complex, it is a difficult issue in the field of soil erosion [13].
c. Porosity

Soil texture also influences surface runoff and soil erosion. Soil erodability is a
factor to estimate the ability of soil to resist erosion based on the physical characteristic of
each soil. Soil has a mixture of sand silt and clay and in many soil the ratio is very similar.
However, even with soils with similar ratios of sand, silt and clay may have drastically
different soil erodability. Soil with good soil structure will allow more water infiltration,
thereby reducing surface runoff water and erosion.
d. Vegetation structure
Vegetation cover is the most significant factor to determine the severity of erosion
process, is a function of canopy closure, height, ground cover, and litter cover. Plant and
litter cover play an important role in soil surface protection or soil erosion prevention.
―Plant slow down water as it flows over the land (surface runoff) and this allows much of
the rain to soak into the ground. Plant roots hold the soil in position and prevent it from
washed away. Plants break the impact of a raindrop before it hits the soil, thus reducing its
ability to erode. Plant in wetlands and on the banks of rivers are particular importance as
they slow down the flow of the water and their roots bind the soil, thus preventing
erosion‖(NDA) [14].

8


In general, vegetation layer has two main functions. Firstly, ground cover absorbs
the energy impact of raindrops, disintegrate the impact of rain, water move along the stem
of the tree will be reduced the impact on soil. Secondly, leaves and branches when fall
down will deposit and form a slime layer which limits the surface runoff.
1.2.3. Effect of soil erosion
Soil loss and nutrient loss make the amount of soil loss by erosion is very big it
reduces the soil source for agriculture production. Nutrient in soil surface is eroded so that
trees do not have nutrient to growth. Besides nutrient loss also changed the
physicochemical characteristic of soil.[5]
Harmful for environment and ecosystem: Nutrient is washed away by flow with soil

particle which was abort by plant (usually algae). When algae die, the decomposition of
organic matter by microorganism reduce oxygen in water and threat to the living of fish
and other animals. Finally, it will destroy the balance of water ecosystem. Soil erosion also
causes water pollution because soil particle contain phosphorus, nitrate or it absorbs
pesticide which harms people‘s health. [5]
1.2.4. Research on erosion
a. In the world
According to Baver (1939), studies about the issue of soil erosion carried out by
German scientists in 1877 [5]. In 1907, researcher on soil erosion has been carried out
when America‘s Ministry of Agriculture announced the policy of protecting soil sources.
The first detailed researches performed by Law (1941) analyzed the mechanical of
raindrops on soil and then gave out the erosion process. Zingg (1940) introduced a
mathematical equation to access the effect of the slope and the length of downhill slope on
erosion.
9


In 1947, Musgrave et al developed an empirical equation called Musgrave
equation, this equation had been applied until it was replaced by the universal soil loss
erosion (USLE) in 1958 [5]. Science the mid-1980s to the early 1990 different erosion
models had been developed based on USLE in many places in the world such as Soil Loss
Equation Model for South America-SLEMSA (Elwell, 1981). SOILOSS model (Rosewell,
1993) was developed in Australia and ANSWERS model was expanded in the late 1970s
to assess the level of aggradation at river basin (Beasley et al, 1980).
The rates of surface erosion depend on the extent dynamic management practices
disturb and compact soil, alter ground cover, and modify soil properties. Therefore,
accurate estimation of soil loss or evaluation of erosion risk has become an urgent task.
Erosion studies in the world has solved that problem.
b. In Vietnam
In Vietnam, forests have long been recognized to provide an important role in

environmental protection [1, 7, 15]. Erosion in Vietnam occurs gradually because the
country has mountainous topography so researcher about this problem has been carried out
early. Soil erosion studies have started in Vietnam in the 1960s. Tung and Moorman
(1958) had some basic researcher about researcher about soil erosion. After completing the
study, they concluded that terraced farming method help to reduce soil erosion. Up to 1960
erosion researcher raised the influences of slope to soil erosion, which contribute to
making the soil protection criteria, using and exploiting steep soil, Chu Dinh Hoang (1962,
1963) had researcher about the effect of rain of on soil erosion and how to prevent erosion
by farming methods [5].
From the 1980s, researcher works have begun to use USLE of Wischmenier and
Smith (1978) such as Dung (1991) researched about ―Application of university soil loss

10


equation on predicting soil erosion potential and raising possible solutions to prevent
erosion in Tay Nguyen‖, Xiem and Phien (1996) also researched about mountainous land
in Vietnam. Karine VezinaEmail, Ferdinand Bonn, Cu Pham Van researched ―Agricultural
land-use patterns and soil erosion vulnerability of watershed units in Vietnam‘s northern
highlands‖[1, 5]. Soil erosion at regional scale has been studied in northern Vietnam by
Bac (1984) and in central Vietnam by Vi (1983), in small-scale studies, in which rough
estimates of soil erosion were made, on the basis of changes in flow regimes in river
systems, and crop damage in provincial domains. Ha (1996) analyzed ten years‘ rainfall
data, in combination with three years‘ observed soil erosion data, to identify the factors
influencing soil erosion in six regions of northern Vietnam [16]. In general, erosion studies
in Vietnam are not widespread by using model approach. Therefore, it is necessary to
promote further to bring about the efficiency studies of erosion.

11



CHAPTER II
GOALS, OBJECTIVES AND STUDY SITE
2.1. Goals
The research will contribute a number of scientific bases to improve the effect of
erosion control of some protection plantations in Hong Linh town, Ha Tinh province.
2.2. Objectives
- To assess the status of protection plantations in Hong Linh.
- To create potential erosion map and vegetation cover map in Hong Linh.
- To determine the ability of soil protection against soil erosion of protection
plantations in Hong Linh.
- To propose some solutions to raise the erosion control efficiency of some
protection plantations in Hong Linh.
2.3. Study site
The study site is located in some plantation types in Hong Linh town, Ha Tinh
province.
2.3.1. Natural conditions.
Hong Linh town is located in the North of Ha Tinh province in North Central Coast
region of Vietnam at 1050 45‘ latitude – 180 32‘ north, are the crossroads of National
Highway 1A & 8A. Hong Linh is located 20 km north of Vinh City and 30 km south of Ha
Tinh town (provincial capital) and 92 km West of Cau Treo international border crossing
and is a very important North and South international traffic of the area. Hong Linh is
considered to be the economic, cultural and social center of northern Ha Tinh province.

12


Figure 2.1. Location of protection plantation in Hong Linh town, Ha Tinh.
- On the border:
+ In the North with Nghi Xuan district and Nghe An province.

+ In the South with Can Loc district.
+ In the East with Hong Linh mountain (mainly in Nghi Xuan district)
+ In the West with Duc Tho district.
Hong Linh has 6 administrative units including 5 wards (Nam Hong, Bac Hong,
Dau Lieu, Trung Luong, and Duc Thuan) and 01 commune (Thuan Loc), with a natural
area of 6031.895 hectares and a population of approximately 40000 people. The figure 2.2
shows the status of Hong Linh town‘s area.

13


Figure 2.2. Land use and distribution area in Hong Linh town
a. Topographic characteristics
Hong Linh town is a mountainous town with a slope from east to west consisting of
three main types: high mountainous terrain, narrow valley terrain and a plain part. There is
a Le River running around the town. Mountainous terrain with peaks> 390m, slope > 20%,
are adjacent to Nghi Xuan and Can Loc districts. Narrow valley terrain: Run along
National Highway 8B (old road 18) in Dau Lieu commune, with an average elevation of
12-15m.
Plain is located in the western part of the town, stretches from north to south, with
an average elevation of 3-5 meters.
b. Climate
Hong Linh is characterized by tropical and monsoon climate of Vietnam that is
affected by the transition climate between North and South, divided into two distinct
seasons: Cold winter with north-easterly winds and hot and dry summers with strong
south-west winds.
Observation data at the North Central Meteorological Station show:
- Average annual rainfall is from 2,200mm to 2,300mm. The highest monthly
rainfall is 639 mm (September) and Maximum daily rainfall is 550 mm. The rainy season
14



usually lasts from August to December, is affected by many storms, tropical low pressure,
causing great flood concentration from September to October every year. September has
the highest rainfall, accounting for 45% of the annual rainfall, fluctuation amplitude
approximately 1,000mm / year. The dry season is from May to August (driest month is
July).
- The average annual temperature fluctuation 23-240 C, the average temperature of
the hottest month is 410 C (July) and the coldest month is 6.80 C (January). Average
temperature fluctuation day and night: 6.2 ° C and average annual sunshine hours is 1,800h
/ yr.
- Relative humidity is relatively high, from 84 to 86%. The wettest season in the
winter months (January to March), the driest month is July.
- Annual humidity in Hong Linh is 86%. The highest monthly humidity is 90% and
the lowest monthly humidity is 72%.
- Prevailing wind direction in summer is west and southwest, northeast winter
winds. Average wind speed is 1, 5¸ 2,5m / s. and Maximum wind speed when the storm
can be from 30-40m / s.
c. Hydrological
Hong Linh town is affected by the hydrographical regime of Song La, Song Lam
(belonging to the Ca river system), along with the dike along the Lam river in the north.
2.3.2. Economics
The situation of industrial production, small industry, and handicraft of
establishments and enterprises in the locality continue to produce stable. Some companies
in the field of building materials, especially unbaked bricks are continuing to invest in
machinery to expand production, increase capacity, meet the needs of the market. Total

15



value of industry, small industry in the first 4 months of 2017 is estimated at VND 336.07
billion, reaching 30.8% of the plan. In the area, there are about 2,286 individual business
households operating in the field of trade and service providing more than 3,285 laborers
and stable incomes; Total retail sales reached 164.83 billion VND, up 1.27% over the same
period in 2016 and up 1.82% compared to March 2017.

16