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Study of some characteristics of the cau river basin in bac kan province

THAI NGUYEN UNIVERSITY
UNIVERSITY OF AGRICULTURE AND FORESTRY

NGUYEN THI LAN
TOPIC TITTLE:

STUDY OF SOME CHARACTERISTICS OF THE CAU
RIVER BASIN IN BAC KAN PROVINCE

BACHELOR THESIS

Study Mode

: Full-time

Major

: Environmental Science and Management

Faculty


: International Training and Development Center

Batch

: 2011-2015

Instructor : Dr. Pham Van Dien

Thai Nguyen, September 2015


DOCUMENTATION PAGE WITH ABSTRACT

Thai Nguyen University of Agriculture and Forestry
Degree Program

Bachelor of environmental Science and Management

Student name

Nguyen Thi Lan

Student ID

DTN1153150048
STUDY OF SOME CHARACTERISTICS OF THE CAU

Thesis Tittle
Supervisor(s)

RIVER BASIN IN BAC KAN PROVINCE
Prof. Dr. Pham Van Dien, Viet Nam Forestry University
(VFU), Viet Nam.

Abstract:
The development of the country towards industrialization - modernization,
environmental problems have risen including the water environment problems in
the river basin. Therefore, the exploitation of the river, beyond the knowledge of
the network of hydrological and geographical characteristics of its forms. This
study conducted in the stretch of the Cau river running through Bac Kan province.


Cau river basin in Bac Kan province includes Bac Kan town, Cho Don district (Ra
Ban, Dong Vien and Phuong Vien commune), Bach Thong district and Cho Moi
district. Studying some characteristics such as topography, landforms, climate
features, and hydrological and vegetation characteristics. The Cau river basin in
Bac Kan province in the high mountain regions, the terrain is quite complex and
special; steep slope and altitude, and the upstream of many rivers, so the
concentrating flow in the rainy season is very fast. The climate there is a clear
seasonal difference. Winter is low temperatures, little rain and under the influence
of the northeast monsoon. Summer has high temperatures with lots of rain so
rainfall generated floods in highly concentrated areas, frequency of rain that created
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flooding during the months of fairly uniform, concentrated mainly in the June, July
and December. Study of some characteristics of the Cau river basin will be
addressed to assess the advantages and difficulty of watershed from which
resources most effectively, as well as the protection and development of Cau river
basin in a sustainable manner. So study of some characteristics of the Cau river
basin such as topographical land use, vegetation cover, hydrological and climate
characteristics will be addressed to assess the advantages and difficulty of
watershed from which resources most effectively, as well as the protection and
development of Cau river basin in a sustainable manner.
Keywords

Cau river basin, topographical land use, vegetation cover,
hydrological and climate characteristics

Number of
papers

66 pages

Date of
submission:

9/30/2015

Signature of
supervisor

Pham Van Dien

ii


ACKNOWLEDGMENT
On the occasion of the thesis completion, I would like to express my appreciation
to the Department of Natural Resources and Environment, Department of flood
protection, Department of Agriculture and Rural Development in Bac Kan Province
for support and kind provision of necessary information concerning this study.
In particular, I would like to express my gratitude to Dr. Pham Van Dien who
guided, instructed, coached me in the course as well as in implementation of this thesis.
Due to the time frame and my ability and experiences are limited, some
shortcomings of the thesis should not be avoided. I look forward to the comments by
the teachers for improving my graduation thesis.
I would like to sincerely thank you!

Thai Nguyen, Wednesday, 31 August, 2015
Student
Lan
Nguyen Thi Lan

iii


TABLE OF CONTENTS
LIST OF TABLES ..................................................................................................... 1
LIST OF FIGURES ................................................................................................... 2
INTRODUCTION ..................................................................................................... 3
CHAPTER 1: LITERATURE REVIEW ................................................................. 4
1.1. Concept of river basin ........................................................................................... 4
1.2. The characteristics of a river basin ........................................................................ 5
1.2.1 The geometrical characteristics of the river basin ................................................ 5
1.2.2. Characteristics denote the flow .......................................................................... 7
1.2.3. Climate factors ................................................................................................... 9
1.2.3. Buffer factor ...................................................................................................... 9
1.3. The characteristic elements of river basin in Vietnam ......................................... 10
1.3.1. The climate factors ........................................................................................... 10
1.3.2. Soils and lava ................................................................................................... 11
1.3.3. Topographic ..................................................................................................... 11
1.3.4. Forest ............................................................................................................... 12
CHAPTER 2: OBJECTIVES, OBJECTS AND LIMITATION, THE CONTENT
AND RESEARCH METHODS ............................................................................... 13
2.1. Objective ............................................................................................................ 13
2.2. Scope of research ............................................................................................... 13
2.3. Research Content ................................................................................................ 13
2.4. Research Methods ............................................................................................... 13
CHAPTER 3: RESULTS AND DISCUSSION....................................................... 15
3.1. Overview of the Cau river basin in Bac Kan Province......................................... 15
3.1.1. Natural characteristics ..................................................................................... 15
3.1.2. Characteristics of economy and society ............................................................ 18
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3.2. Topographical, geomorphology features of the basin .......................................... 20
3.2.1. The topographical zones .................................................................................. 21
3.2.2. The slope of the terrain .................................................................................... 22
3.2.3. The type of terrain ............................................................................................ 25
3.3. Geological characteristic ..................................................................................... 26
3.3.1. Geological structure. ........................................................................................ 27
3.3.2. Features of stratigraphy .................................................................................... 28
3.3.3. The intrusive magma rock ................................................................................ 30
3.3.4. Overview of fault system ................................................................................. 31
3.4. haracteristics of vegetation layer and coating plant ............................................. 32
3.4.1. Vegetation Features ......................................................................................... 32
3.4.2. The major forest types...................................................................................... 34
3.4.3. The percentage of forest cover ......................................................................... 35
3.4.4. Assess the advantages and difficulties .............................................................. 37
3.5. Climate Characteristics ....................................................................................... 38
3.5.2. Climatic feature................................................................................................ 39
3.6. Hydrological characteristics ................................................................................ 48
3.6.1. The main characteristic of the rivers and streams of Cau the river basin. .......... 48
3.6.2. Hydrological station network ........................................................................... 49
3.6.3. The characteristics of hydrological flow ........................................................... 49
3.6.4. Assess the advantages and disadvantages of water resources............................ 54
CONCLUSIONS, RECOMMENDATIONSU........................................................ 55
1. Conclusion ............................................................................................................. 56
2. Recommendation ................................................................................................... 57
REFERENCES ........................................................................................................ 58

v


LIST OF TABLES

Table 3.1. Decentralization of the slope of the Cau river basin in Bac Kan province........... 22
Table 3.2. Forest status in district of the Cau river basin in Bac Kan province in 2014 ..... 32
Table 3.3. The percentage of forest cover through the years from 2009 to 2014 ........ 35
Table 3.4. The percentage of forest cover in the districts and towns of Cau river basin..... 36
Table 3.5. A meteorological station and rainfall measuring station in Bac Kan
province. ................................................................................................... 38
Table 3.6. Air temperature characteristics ................................................................. 40
Table 3.7. Relative humidity of the air ...................................................................... 41
Table 3.8. Total average sunshine hours in a month and year .................................... 41
Table 3.9. The average evaporation in the month and year piche tube ....................... 42
Table 3.10. Average wind speed of month and year .................................................. 43
Table 3.11. The average total rainfall in the month and year ..................................... 44
Table 3:12. Distributor average rainfall for the month and year ................................ 45
Table 3.13. yearly rainfall frequency ........................................................................ 45
Table 3:14. The ratio of year rainfall is seasonal distribution .................................... 45
Table 3:15. statistically the highest rainfall of periods 1,3,5,7 days. .......................... 46
Table 3:16. m coefficient calculated on the average for positions rainfall stations..... 47
Table 3:17. Percentage (%) of rainfall that generated floods appear during the
rainy season in some regional stations ...................................................... 47
Table 3.18. hydrological station network, time factors and monitoring ..................... 49
Table 3:19. The annual average flow is measured on the stations.............................. 50
Table 3:20. Flow in the dry season in Cau river basin in Bac Kan province .............. 51
Table 3.21. the frequency of runoff courses in some river basins of Cau stations
in Bac Kan province ................................................................................. 51
Table 3.22. The frequency of flood flow at several stations in Cau river basin .......... 52
Table 3.23. Average turbidity in monitoring period .................................................. 53

1


LIST OF FIGURES

Figure 3.1. Map of Cau river basin in Bac Kan province........................................... 16
Figure 3.2. The percentage of forest cover in the districts and towns of Cau river
basin in Bac Kan province. .......................................................................... 35

2


INTRODUCTION

Research rationale
Currently, along with the development of the country towards industrialization modernization, environmental problems have risen including the water environment
problems in the river basin. Therefore, the exploitation of the river, beyond the
knowledge of the network of hydrological and geographical characteristics of its
forms, must also have the full understanding of the geographical factors affecting the
flow, formation and evolution of river basin flow. On that basis, we understand in
detail the nature of the physical and hydrological characteristics.
Cau river basin is one of the largest river basins in the country. This is the most
important watershed in the Thai Binh river system that the area is 6,030 km2 with main
flow is Cau river of 288.5 km long which originates from the Van On mountains at an
altitude of 1.175m and flowing into the Thai Binh river at Pha Lai district. Cau river
basin has 26 tributaries at levels I and 41 tributaries at levels II with a total length of
671km and 643 km, respectively, and hundreds of kilometers of branches at levels III,
IV and shorter ones, which its length is under 10km.
Topic "Study of some characteristics of the Cau river basin", such as
topographical land use, vegetation cover, hydrological and climate characteristics will
be addressed to assess the advantages and difficulty of watershed from which
resources most effectively, as well as the protection and development of Cau river
basin in a sustainable manner.

3


CHAPTER 1
LITERATURE REVIEW
1.1. Concept of river basin
River basin is the water area that water (including surface water and
groundwater) will flow into the river. The river is limited by watershed (watershed
line) of the basin. There are two kinds of watershed: the watershed line of surface and
groundwater.
- The source of the river is where the beginning of the river. The big rivers are
often rooted in the high mountains, and dense forest. In which having many ravines,
crisscrossing small streams, and water flows all the year. Sometimes the river
originates from groundwater or a large lake.
- The upper course of a river is often high areas with steep terrain, and is
complicated separation. This is where the beginning of rivers, and surface often
covered by forests which is like the "green water storage " that have a role in flow
condition, reducing flows of flood peak and increase dry season flow for downstream.
- The middle course of a river is often mountainous or highland areas where
terrain is low, and is the intermediate zone which transfer water into a downstream
area. In the middle course, the rivers often have smaller slopes, riverbeds begin to
expand out, and riverbed has many fine sandy. The riverside often at risk of being
inundated that forming dumps containing flood.
- Lower course of a river is the lowest zone of the river basin that mostly
perennial alluvial can create the broad plains. Generally, when the river flows to the
river downstream, river section is expanded, and often divided into several branches to
flow into the sea. River in the lower course area usually has a small slope, and mud
4


flow at the bottom of the river is mostly fine sand and mud. Since the river section is
expanded so speed of water is small rate that leading to sedimentation process is
primary, and erosion only occurs during floods in a certain number of points. At the
downstream near the sea, rivers are prone to be branched, riverbeds is deformed and
meandering in sine form and often morphological change under the impact of process
of accretion and erosion constantly.
- River mouth: river mouth is the place adjacent to the sea, lake, or another river.
Determining watershed must be based on topographic maps with elevation contour
drawing.
1.2. The characteristics of a river basin
1.2.1 The geometrical characteristics of the river basin
a. River basin area
The river basin area (F km2) is the area that is controlled by a regional distributor.
The basin area is determined from a map with scaling in approximately from 1/10,000
to 1/100,000. We can use the method of apportionment squares or the gauge for
determining the area of the basin area.
b. The main river length (L) and the river basin length (L1)
The main river length of L (km) is the length that following the flow direction is
measured from the river source to the river mouth basin. Length of L1 (km) is
calculated according to the center lines of the basin from the farthest point of the basin
of the river mouth. In fact, it often takes river length as river basin length: L1≈L.
c. The average width of the basin B (km):
The average width of the basin B (km) is the ratio between the river basin area
and length

5


(1)
d. Basin shape coefficient
Basin shape coefficient (Kd) is the ratio between the width and length of the river
basin. Kd denotes the shape of the basin, usually with Kd ≤ 1. Basin shaped the more
square, the Kd -> 1.0, whereas the more narrow and longer river basin is; the smaller
Kd is and the greater floodwaters get.

(2)
e. Average height of river basin:
The average height of the river basin is determined from the elevation
contour map

(3)
In which: hi - Average elevation between two contours
Fi - The area between the contour elevations adjacent (km2)
N - Number of plots have area
f.Average slope of river basin

:

Average slope is the average slope of the basin

(4)
Where: ∆H - The difference in height between the two contour lines
Fi

- An area between two adjacent contour lines (km2)

li

- The average distance between two adjacent contour lines

6


In case there are no elevation contour lines, we can use the following
approximation formulas:

(5)
In which

Hmax - The highest elevation point of the region.

Hmin - The lowest elevation point of the basin
F

- the basin area

This formula is only true when the basin slope changes little.
g. River mesh density D:
River mesh density (km/km2) is the total length of all rivers and streams in the
basin dividing the river basin area.

The thicker the streams are, the greater density grids of river are. The region has
abundant water resources, the D is often high value. (Tuan, L.A, 2008).
1.2.2. Characteristics denote the flow
a. The water flow
The water flow (water discharge) is the amount of water flowing through
sections of the mouths of rivers that poured outside in a time unit is 1 second (m3 / s).
The water flow at any one time is called the instantaneous flow.
The process of change of water flow over time as an exit route called the water
flow process, denoted by Q (t) or Q ~ t. A graph of the change between the water flow
and time is the water flow line.
The average water flow over a period of time (t) randomly is the average value of the
water flow in that period. Average water flow is calculated by the following formula:

7


(6)
where

is the average value of the water flow, n is the number of computing

time, Qi is the average flow at each initial interval.
b. The total amount of the flow W
The total amount of the flow W (m3 or km3) is the amount of water flowing
through the section in river mouths over a period of time from t1 unit to t2,

(7)
where

is the average flow during the period t2-t1.

c. Flow depth (Y)
As the thickness of the average water layer is produced on the surface of river
basin over a certain time period (mm).

(8)
Where W - The total water volume (m3)
d. Flow Module (M)
Modular flow is the flow value of 1 unit of river basin area is 1 km2
)
e. Flow coefficient

(9)

)

Flow coefficient ( ) denotes the ability to create the flow in a certain river basin.

(10)
where X is the rainfall that generates the flow of Y. The greater alpha coefficient
is, the greater flow losses and vice versa. (Tuan, L.A, 2008).
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1.2.3. Climate factors
Climate factors effect directly to runoff, which is rainfall and evaporation.
Rainfall is causing runoff and evaporation that reduces the flow, but rainfall and
evaporation are also related to many other climate factors as temperature of buffer
factors (the land surface, water suface), air temperature, humidity, and air pressure,
wind, and storm, so before considering rainfall and evaporation, we need to research
basic concepts of the above factors.
1.2.3. Buffer factor
The characteristics of the location, soil, geology, vegetation cover, ponds in the
river basin have a direct influence in the formation of the flow, and calling is generally
buffering factor.
Geological sites of river basin reflect the climatic conditions in the area. Terrain,
topography of the river basin are not only influence to evaporation and rainfall, but
also affect directly to the flow concentration. If the higher and the more sloped terrain
have; the faster the flow is and vice versa.
The terrain and pedological characteristics of the basin. It decides the water
amount that penetrates into the soil and the amount of water stored in the river basin
that are two factors which influence obviously to the flow. In addition, because of the
geological structure properties of the river basin generally lead to the watershed line in
the surface and groundwater in river basin which aren’t overlap, making the
hydrological analysis become more complicated.
Vegetation cover increases the absorbed level on the surface, making the soil
porous layers discrete, increasing water infiltration, greater groundwater flow and flow

9


distribution in the year were more harmonious. Vegetation cover increases roughness
on the surface that leading to disturbances of air flow increases, resulting in increasing
rainfall in part. Vegetation cover prevents quickly erosion on the ground, which
reduces the small amount of sand in rivers.
1.3. The characteristic elements of river basin in Vietnam
1.3.1. The climate factors
1.3.1.1. Rainfall
Features of humid tropical climate in our country, monsoon have shown very
markedly the average rainfall in many years and the relationship between annual
rainfall and evaporation. Considering the whole territory of our country, the average
rainfall of about 1960mm in some years. In comparison with average rainfall the same
latitude (100-200 in the north) in our country, there is abundant rainfall, about 2.4
times. Only areas are hidden wind, annual average rainfall fall below 1000 mm.
The distribution rule of average rainfall amount in many years is irregular in
space, and depending on the terrain elevation and direction of the slopes which get
wind. Rain factor affects surface runoff distributing in space and time.
The amount of the flow and its distribution on the territory of our country
depends primarily on the distribution of rainfall. Features have nature of rule which is
reflected very clearly in practice and on contour line maps and the average flow in
many years.
1.3.1.2. Water evaporation
Besides the rainfall factor, the evaporation factor from surface of river basin also
participated directly in the water balance of rivers, significantly influence the flow
formation. In our country, there are high temperatures that made the process of
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evaporation on river basin from north to south are quite large. Average annual
evaporation is 953 mm in the entire territory, compared with average annual rainfall,
the evaporation coefficient is 0.48, less than about 35% compared to the same latitude.
In conclusion, rain and evaporation are the two most important factors affecting
the flow, it determines the potential flow of rivers in our country. Climatic factors have
a decisive influence on the flow distribution in space and time.
1.3.2. Soils and lava
The river basin is composed of soil and lava. Soils and lava are important factors
influencing the flow. The fact shows that the river basin has a large rainfall that don't
still creates enough produce a rich surface flow, because the flow depends on the water
permeability of the soil and geological architecture of the river basin.
Impact of soil and lava on flow in two directions river: it may increase or
reducing the amount of flow, conditioning or erratic flow regime. In whole territory of
the country, there are two kinds of soil and lava clearly influence and the most
important for the river flow and its regime is limestone and basalt soils.
1.3.3. Topographic
The whole territory of our country, increasing the absolute height of the terrain is
often manifested in the increase of rainfall, and basin slope, decreasing the
temperature, increasing river density. In such conditions, the amount of flow increases
with altitude quite well.
The amount of flow and rainfall increases with elevation. The largest increase
occurs in the range from 300-600 m elevation and elevation limit that rainfall rule
increases with defunct elevation which often estimated from the height of 2000 meters
or more.
In addition, the elevation increase rule of precipitation and the amount of annual
flow, we also see that the influence of the terrain is quite apparent to the quantity and
flow distribution due to the direction and slope characteristics of the terrain. Under this
rule, the slopes get wind, which has precipitation greater flow in comparing to the lee.
This difference is quite obvious, especially in the south of northeast and southwest of

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Dong Trieu mountain; between two stations in Cam Binh Lieu and Cam Dan where
the amount of flow differ to 35%. Thus, elevation and direction of getting winded.
1.3.4. Forest
In fact, in our country the influence of the forest on the streams depend on many
factors, including forest coverage rate and type of forest are the most important factors.
According Winliam and Nikhitsin, the woods transformed soil very strong, so
when forest cover change that is often accompanied by changes in forest type and flow
regime of the river. In our country, the changing process often changes from the
primitive forest to regrow forest, bamboo forest, reeds, bushes and finally the barren
hills. The change direction is the contrary, even though, there is very little and very slowly.
Particularly, the surface flow on slopes of forest have the effect greatly reduced.
Experiment document of flow proved that the amount of flow close to surface slopes
which occupy a significant proportion of the formation of flood flow.
Effects of forest on runoff courses through the results of experimental studies in
foreign countries and in our country have confirmed that forest increase runoff courses
with a considerable amount. In many areas, forest are still large that runoff courses can
be increased by 30-100%. Module value of the average minimum flow in many years
in having forest area is much greater significantly forest than no forest areas.
(Forest Protection Department of Bac Kan Province, 2014)

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CHAPTER 2
OBJECTIVES, OBJECTS AND LIMITATION, THE CONTENT AND
RESEARCH METHODS
2.1. Objective
- Identifying some characteristics of the Cau river basin.
- Proposing some recommendations for the conservation of the Cau river basin.
2.2. Scope of research
- The scope of space: Studying conducted in the stretch of the Cau river running
through Bac Kan province. Cau river basin in Bac Kan province includes Bac Kan
town, Cho Don district (Ra Ban, Dong Vien and Phuong Vien commune), Bach Thong
district and Cho Moi district.
- Scope of time: Implementation of 6 months (from January to June 2015).
- The scope of content: Studying some characteristics such as topography,
landforms, climate features, and hydrological and vegetation characteristics.
2.3. Research Content
- Overview of the Cau river basin in Bac Kan province.
- The characteristics of topography, geomorphology of the river basin
- Geological characteristic.
- Characteristics of vegetation and plant cover.
- Climate characteristic.
- Hydrological characteristics.
2.4. Research Methods
Methods of gathering documents and secondary data
- Collecting data on natural and economic - social conditions in Bac Kan
province. The secondary data collected from the Department of Natural Resources and
13


Environment of Bac Kan province, the Department of Agriculture and Rural
Development, Department of flood prevention in Bac Kan province, Department of
Forestry in 2014.
- In addition, the report also uses secondary materials such as reports, results of
the ministerial level, the legal documents related and other documents in order to
obtain specialized information, particularly differences in soils, geology, and minerals.
- Finally, the electronic website of the province, district, and also used as a
reference material otherwise.
- Based on the nature of the data, the report uses both qualitative information (the
description, quotations, and comments) and quantitative information (statistics) in the
analysis process.

14


CHAPTER 3
RESULTS AND DISCUSSION

3.1. Overview of the Cau river basin in Bac Kan Province
3.1.1. Natural characteristics
a. Geographic location
Cau river basin belongs to the Thai Binh river system in the range 105027 106018 east longitude; 21007 - 22020 north latitude, the basin is mostly located in Bac
Kan and Thai Nguyen province. Cau river basin in Bac Kan province begins Cau river
basin upstream that originates from Tam Tao mountain with 1600 meters altitude and
across Cho Don, Bach Thong districts, and Bac Kan town.
The terrain is mainly mountainous with an average altitude of 500-600 meters,
the northwest is the Gam river bow that begins from Chu Cho district,
The northwest is Gam River bow running from Bac Me Cho Chu. In the east, the
Bac Son mountain range runs west, which extend from the Ngan Son district to Yen
Lac district. The basin topography is rugged with steep mountain ranges. The main
direction of the basin is north - south, then turning to the East - West. The area is
approximately 1100 km2, forest covers area accounts for approximately 56%, the
average slope of the basin is about 24%0.
Cau river basin runs through in Bac Kan province that is the upstream area of the
Cau River basin. In Bac Kan province, the Cau river basin is located in 4 districts and
towns like Cho Don district, Bach Thong district, Bac Kan town, Cho Moi district, and
having location as follows
- The East adjacent to Na Ri district, Bac Kan province.
15


- West adjacent to Cho Don district, Bac Kan province.
- Southern adjacent to Dinh Hoa district, Phu Luong district, Vo Nhai district,
Thai Nguyen province.
- North and northwest adjacent to Ba Be District, Ngan Son district, Bac Kan
province

Figure 3.1.Map of Cau river basin in Bac Kan province
b. Climate Characteristics
Cau river basin has the common characteristic of Vietnam northeastern climate,
is influenced by the northeast monsoon and the physical activity of the weather:
tropical convergence zone, the low trench, and typhoon fall in the basin due climate
divides into many small regions with different climates. The cause of the difference is
due to the terrain which was divided sharply, and forming narrow valleys.
16


Thac Rieng basin is located in the opposite side that facilitate to get wind as a
Cho Don valley of Bac Kan province, so it has centers of heavy rain as a Cho Don
district and Bac Kan town, with average annual water volume from 1500mm to
2000mm
The rainfall regime in the basin is divided into two distinct seasons, the rainy
season usually starts from May to October, which accounts for about 80% of the total
annual rainfall, rainy months are usually in July or August with the month rain amount
may account for 40% of total annual rainfall. The dry season usually lasts from
November to April of the next year, rainfall amount of this season is only about 20% of
the total annual rainfall, the driest month of the year usually falls in January or February,
rainfall in this month usually negligible. Prevailing wind direction is the southeast, but
due to the terrain should be deflected into the southwest, in the winter, the prevailing
wind direction is the northeast. The annual average temperature is 21,50C, and tends to
increase from upstream to downstream, typically the hottest month in June, usually the
coldest month is January. The evaporation in the basin ranges from 650-800mm, and
transformation increases from upstream to downstream.
c. Hydrological situation in the Cau river basin
Small river network Cau river basin is relatively thick, the main river is twist, and
there are many local flowing directions, but main direction is the east-west to Bac Kan
town and then this flow transfer to the north-south. The mainstream is combined by two
tributaries flow, which is the hot river (the main branch) is derived from Tam Tao mount
of Cho Don district, cold tributaries are rooted in the Bach Thong district. The river bed
is in deep steep and many waterfalls. Fan shaped basin with river length is L = 64 km.

17


The average width of the basin is B = 9.25 km. Allocation of basin on both sides is
asymmetric and skewed to the left of the river.
The main direction of the river runs north-south direction and come to Phuong
Vien district, the river is east-west navigation. When coming to Bac Kan town, the river
moved to the north-south direction with river mesh density is 1.30km / km2. The flow in
the river is mainly caused by rainwater, partly formed surface flow, the rest provides
groundwater system. The flow in the year also divides two distinct seasons, the rainy
season with flooding often occurs from May to October, which is usually around 80% of
total annual flow, and usually the driest months are March and April.
Flood flow carries many characteristics of the flow of mountainous areas.
Floodwaters is often up and down very quickly and often causing widespread flash
floods. Usually high flood time is from 9 to 12 hours, and low flood time is from 20 to
30 hours. (Department of Flood Protection in Bac Kan province, 2014)
3.1.2. Characteristics of economy and society
a.

Economic development

In 2011, GDP increased by 13% in comparison with 2010 (plan is 13.5%)
including: the agriculture, forestry, and fisheries increased by 11.36% (planning is
7.5%). Industrial sector, capital construction rose to 2.64% (planned 23%): industry and
construction decreased to 14.7% and 21.4%, respectively. The service sector increased
to 20.29% (planned 14%). Per capita income reached 14.6 million, and an increase of
2.7 million compared to 2010.
Economic growth already has a huge impact on the social life and the
environment in the province. On the one hand, helping the material and moral life is
improved and increasingly advance. The cultural, society, science - technology sectors
18


continue to develop, on the basis having conditions invested back to protect the
environment.
b. Social characteristics
- Population and Labor
According to the Statistical Yearbook of Bac Kan province in 2011, the Cau river
basin in Bac Kan province has an area is 1372.78 km2, including 44 communes, wards,
and towns. The population in the area is 153 096 people. The proportion of relatively high
population growth is 0.63%, the population of urban areas tends to increase every year.
The inhabitants of the province are not distributed evenly among regions. The
majority of people live in rural areas. Labor structure is primarily in the fields of
agriculture, forestry, fisheries and services; in the industrial sector in which
construction accounted 6.3%. Labor in rural areas is mainly associated with livestock
farming, horticulture and services in households.
The increase in population will lead to an increase in the exploitation of
environmental resources and this means that depleting resources, making
environmental issues become increasingly pressing and intractable. The migration
from rural areas to urban areas and the disparities in population growth between the
regions leads to poverty in rural areas and the excess spending in urban areas that
generate source waste that focus beyond environmental biodegradable lead to
environmental pollution.
- Infrastructure
+ Transportation: The road network in the system, including highways,
provincial roads, district roads, urban roads, communal roads and village roads. To
ensure the road network convenient to serve the economy and national security
effectively. Many roads have been renovated and upgraded as 257 roads from Bac Kan
19


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