Regimes of human and climate impacts on

Regimes of human and climate impacts on coastal changes in Vietnam Tran Duc ThanhÆ Yoshiki Saito Æ Dinh Van Huy Æ Van Lap Nguyen Thi Kim Oanh TaÆ Masaaki Tateishi Abstract Vietnam is a t

Regimes of human and climate impacts on coastal changes

in Vietnam

Tran Duc ThanhÆ Yoshiki Saito Æ Dinh Van Huy Æ Van Lap Nguyen Thi Kim Oanh TaÆ Masaaki Tateishi

Abstract Vietnam is a tropical to subtropical

country located on the eastern Asian coast where the

Red (Song Hong) and Mekong rivers discharge into

the sea The catchments of these two transboundary

rivers cover parts of six countries, and their water

and sediment discharges greatly influence the

coastal seas of Vietnam The impact of human

activities include changes in the supply and

distribution of water, sediments, and nutrients;

changes in the relationships and balance among

dynamically interacting factors and processes; and

changes in the quality of the coastal and marine

environments due to the increased use and

accumulation of pollutants and the loss of habitats

These impacts have resulted in increasing

unpredictability and severity of coastal problems

such as floods, erosion, sedimentation, and saltwater

intrusion; environmental pollution; and the

degradation of ecosystems, with accompanying

decrease in biodiversity and fishery productivity

Keywords River catchment-based drivers Æ

Climate change Æ Land-use change Æ

Coastal impact Æ Vietnam

Introduction The Vietnamese shoreline stretches across more than 3,200 km The area of coastal waters 50 m deep or less is about 206·103 km2, including 1,600 km2 occupied by more than 3,000 islands (Fig 1) The Vietnamese coastal zone can be divided into four natural parts: the Gulf of Tonkin, the central coast, the southeast coast, and the Gulf

of Thailand Along the coastline where 114 small and large rivers flow in, the largest is the Mekong River and the second largest is the Red River (Song Hong) Water and suspended sediments from these two rivers greatly influ-ence the coastal waters of many countries in Southeast Asia In addition to estuaries associated with these rivers, there are also many bays and lagoons that have resulted from the natural interaction between the sea and the land Because of the high productivity of ecosystems such as estuaries, lagoons, mangrove forests, coral reefs, and sea-grass beds, the Vietnamese coastal zone is high in biodi-versity About 11·103aquatic and more than 1,300 island species inhabit the coastal zone, including many rare and precious endemic species

Because of the presence of rich natural resources and other favorable natural conditions, the coast is a zone of active development Recently, there have been dramatic changes

in the terrestrial ecosystems of the coastal environment because the natural interactions between the land and the sea have been modified by human activities taking place both in the coastal zone and in the catchments of the rivers In this paper, we review the present environmental status of the Vietnamese rivers and coast and related problems, and discuss the protection of the Vietnamese coastal environment

Materials and methods This paper mainly integrates data from existing publica-tions Almost all of them are synthetic works on river hydrology and water resources (Pho 1984; World Bank 1996; Hau et al 2002), marine hydrology (Ninh et al 1992; Thuy and Khuoc 1994), upstream forest and land use (World Bank 1996; Cuong 1997), mangrove forests (Hong and San 1993), coastal living resources (Ministry of Fish-ery 1996; Thuoc 2001), and the state of riverine and coastal environments (Ninh et al 1995; Thanh 1995; Hoi et al

Received: 18 July 2001 / Accepted: 2 September 2002

Published online: 19 November 2003

ª Springer-Verlag 2003

T.D Thanh ( &) Æ D.V Huy

Haiphong Institute of Oceanology,

246 Danang Street, Haiphong City, Vietnam

E-mail: tdthanh@hio.ac.vn

Fax: +84-31-761521

Y Saito

MRE, Geological Survey of Japan, AIST,

Tsukuba 305-8567, Japan

V.L Nguyen Æ T.K.O Ta

Sub-Institute of Geography,

01 Mac Dinh Chi St., District 1, Ho Chi Minh City, Vietnam

M Tateishi

Department of Geology,

Niigata University, Niigata, 950-2181, Japan

1997; Nguyen et al 1999; Dieu and Hoi 1999; Thanh and

Huy 2000; Dieu et al 2000) Some data used in this paper

were collected and analyzed by us The data are not as yet

synchronized with respect to time and location, and they

are still limited in those many coastal areas affected by the

catchments of small rivers This circumstance, that data

are not systematic and detailed, reflects the current

situ-ation of Vietnamese coastal environment research; there

are many gaps in coastal environmental information, and

publication and exchange of data is still suffering from limitations

Nevertheless, we have attempted to estimate Vietnamese coastal changes reflecting the impact of human activities taking place in both the coastal zone and the river catch-ments in relation to the ‘‘Land–Ocean Interactions in the Coastal Zone’’ (LOICZ) program Some important coastal changes, for example, coastal erosion and saltwater intrusion, appear to be the consequence of both climate

Fig 1 Sketch map of some natural factors and resources in Viet-namese coastal zone

changes and human activities For this reason, the

fol-lowing ‘‘setting’’ section is included focusing primarily on

the climatic forces so that ultimately the combined impact

of these two main forces on the coastal environment can

be evaluated

Results

Physical setting and indication of changing

climatic forces

The Vietnamese coast is located in a tropical monsoon

zone that experiences two seasons The season from

October to April is characterized by a prevailing northeast

(NE) wind (the NE monsoon), and the season from May to

September by a southwest (SW) wind (the SW monsoon)

The mean wind velocity is 2.5–5 m/s, and the maximum

velocity is 30 m/s during the NE monsoon and 50 m/s

during the SW monsoon The mean temperature ranges

from 22.6–27.2
C, increasing southward The mean

an-nual rainfall ranges between 1,000 and 2,400 mm, with the

least precipitation occurring along the central coast

During the period from 1975 to 1995, the coastal zone was

struck directly by an annual average of 2.52 typhoons and

2.2 tropical lows The number of typhoons increased

during the latter part of that period; for example, an

average of 2.8 typhoons/year was recorded from 1991 to

1995 The irregularity of the typhoons also increased

re-cently A mean wave height ranging between 0.5 and 2.0 m

was measured at different sites Maximum wave heights of

4.5 m during the NE monsoon and 7.5 m during the SW

monsoon were recorded

The coastal tides include diurnal, semidiurnal, and mixed

types, with a range of 0.5 to 4.0 m The tidal range is high

(meso-tide) in the Mekong and Red river deltas facing the

South China Sea The coastal current varies in velocity and

direction according to season and location Three areas of

upwelling exist in the Vietnamese coastal zone The largest

is along the central coast, and the second largest is offshore

of the Mekong deltas In the Gulf of Tonkin, the site of the

upwelling changes according to the season; it lies near the

SW gulf coast during the SW monsoon season and in the

center of the gulf during the NE monsoon (Ministry of

Fishery 1996) Storm surges, which pose a danger to the

coastal inhabitants, have amplitudes ranging from 0.5 m to

a maximum of 3 m along the coast to the west of the Gulf of

Tonkin The average amplitude is 1.4 m along the central

and south coasts (Ninh et al 1992) Sea-level rise has been

recorded at some coastal sites For example, at Hon Dau

station (Red River Delta), a rise averaging 2.24 mm/year

was recorded from 1957 to 1989 (Thuy and Khuoc 1994)

Catchment influence

Every year, rivers discharge about 880·109 m3 of water

and between 200 and 250·106 t of suspended sediments

into the Vietnamese coastal zone, which are concentrated

in the Mekong and Red river deltas (Fig 2; Tables 1, 2, 3

and 4) The Mekong River catchment includes parts of six

countries (China, Myanmar, Laos, Thailand, Cambodia,

and Vietnam) and has an area of 795,000 km2, 9% of which is in Vietnam Its annual discharge is 520.6·109m3

of water and 98·106t of suspended sediments The Red River catchment includes parts of two countries (China and Vietnam) and has an area of 169,000 km2, 51% of which is in Vietnam Its annual discharge is 137·106 m3of water and 116·106 t of suspended sediments (Pho 1984; World Bank 1996) Monthly water discharge shows clear seasonality, with the period of high discharge being from June to September (Table 5)

Pressure from human forces

In both the coastal zone and the catchments, human activities have influenced land–sea interactions and have had great impact on the environment and ecosystems of the coastal zone and adjacent areas (Key economic drivers are mapped in Fig 3)

The coastal lands have a high population density; of Vietnam
s 77 million people, 24% live in coastal districts Along the coast, there are 12 cities with a population of over 100·103and 37 smaller ports and harbors Seventeen million people live on only 17·103 km2 in the Red River Delta (RRD), an area which also accounts for 20% of the rice production of Vietnam Fifteen million people live on 39·103km2in the Mekong River Delta (MRD), where 50%

of the nation
s rice crop is grown Annually, 0.8·106 t of fish are caught in the coastal waters and oil production is about 10·106t/year

In 1943, there was 400·103 ha of mangrove forests, including 250·103ha in the MRD alone, but by 1993 only about 170·103 ha of mangrove forests remained in the whole country (Hong and San 1993) Almost 200·103 ha of brackish aquaculture ponds have replaced the mangroves

A large part of the tidal floodplain, including the mangrove marshes, has been reclaimed for agriculture as well From

1958 to 1995, 24·103ha of the tidal flood plain in the RRD was reclaimed During this period, 985 ha/year of tidal flood plain, mainly mangrove marshes, was reclaimed for agriculture or converted to brackish aquaculture ponds During the same period, the land area expanded at a rate

of only 361 ha/year by seaward accretion

During the last 1,000 years, a great system of dikes has been built to protect the plain and its inhabitants from river and ocean floods In all of Vietnam, there are 5,700 km of river dikes and 2,100 km of sea dikes There are 3,000 km of the river dikes and 1,500 km of sea dikes

in the RRD, dividing it into compartments that are lower than the rising sea level

Pressures also originate in coastal mining The exploita-tion of coal deposits, sand and gravel use for construcexploita-tion, and exploitation of heavy minerals, are important activi-ties that deform the landscape, produce solid and liquid wastes, and increase coastal erosion Furthermore, coastal mining operations in Quang Ninh Province annually dump 10·106 t of solid waste and 7·106 m3of liquid waste into the coastal zone

Upstream, forests have been destroyed by war, cultivation, logging, and fire Forest coverage decreased from 67% to 29% during the period between 1943 and 1993 (see Table 6; World Bank 1996; Cuong 1997)

Vietnam has a cultivated land area of more than 7·106ha,

60% of which is paddy lands (Table 7) A great volume of

river water is needed for irrigation every year (Table 8)

For example, in 1990, 47·109m3of water was used for

irrigation: 7.4·109 m3 in the RRD and 18.4·109 m3in the

MRD (World Bank 1996) The demand for irrigation water

is most pressing in the dry season In the RRD during the

dry season, the demand ranges from 25 to 50% of the

river
s water discharge, leading to a large decrease in water

discharge to the coastal zone In 1993, 2.1·106t of

chemical fertilizers were used in the cultivated lands, including 1.2·106 t urea, 793·103t phosphate, and 22·103t potash In 1988, 20·103 t of pesticides was used, including DDT, lindane, methamidophos, and methyl parathion; by 1994 pesticide use had increased to 30·103t Pesticide residues have been transported by rivers to the coastal zone, where they may accumulate in the bottom sediments to high concentrations such as has occurred in the RRD Average water quality in selected small rivers of the RRD is shown in Table 9

Fig 2 River system in Vietnam

The rivers have been dammed to create many reservoirs in

the catchments and coastal plains for irrigation and

hydroelectric power Nine large reservoirs for

hydroelec-tric power cover an area of 1,267 km2 The largest, Hoa

Binh, was built in 1987 on the Da River, which is the

largest tributary of the Red River The Hoa Binh reservoir

occupies an area of 208 km2 and holds 9.5·109 m3 of

water Annually, 48·106t of sediments, equal to 83% of the

suspended-sediment load, is transported into the reservoir

and deposited Consequently the building of Hoa Binh

Dam has made a substantial change to the sediment and

water discharge of the Red River (Tables 10 and 11) An

even larger reservoir to be named Son La (Lake Son La),

which will have an area of 440 km2, is planned for the

upper Da River above the Hoa Binh reservoir

Annual domestic and industrial water demand is over

4·109m3 A great volume of wastewater, most of which is

left untreated, is dumped into the rivers and discharged

into the coastal zone From 657·103to 820·103 m3/day of

wastewater is produced by the industrial area of Hanoi–

Viet Tri–Haiphong in the north and 550·103m3/day by

the industries of Ho Chi Minh City in the south The

34·106 m3 wastewater/year dumped into the Red River

from the Viet Tri industrial site includes 100 t H2SO4, 40 t

HCl, 300 t benzene, and 25 t pesticide (Hoi et al 1997) An

initial estimate shows that every year 24,747 t PO4 )and

35,068 t NO3 )are transported into the coastal zone by the currents of the Red River (Ninh et al 1995)

Impact of coastal changes Recently, changes in the Vietnamese coastal environment and ecosystems have become obvious However, quanti-tative analyses of these changes are few The changes have been caused by both natural processes and human activ-ities Changes due to human activities can be global, as in the case of sea-level rise, unusual typhoons, and meteo-rological disturbances related to human-induced global warming; or regional such as from upstream deforestation and the construction of dams, or they can be localized to the coastal zone In terms of land–sea interactions, human activities have had the following impacts on the Viet-namese coastal zone:

– Changed supply and distribution of water, sediments, nutrients, and other materials The present status of nutrient concentrations in the RRD and MRD are shown

in Tables 12 and 13

– Changed quality of coastal and marine environments by pollution, eutrophication, and reduction of biodiversity resulting from the increased loading and accumulation

of pollutants The change of some pollutants such as oil,

Cu and Zn in the Vietnamese coastal zone are shown in

Table 1

Characteristics of Vietnamese river catchments (after Pho 1984, World Bank 1996) River basins in Vietnam (from north to south)

River basin Catchment area (km 2 ) within Vietnam Mean annual discharge in Vietnam (10 9 m 3 ) Bang-Ky Cung 10,500 8.9

Red River delta 17,000

Gianh-Tri-Huong 20,084 17.0

Mekong River delta 39,000

Table 2

Catchment areas (km 2 ) of major Vietnamese river basins

River basin Outside Vietnam In Vietnam Percentage in Vietnam Total

All basins 832,614 323,920 28 1,156,534

Red River 82,340 86,660 51 169,000

Mekong River 723,000 72,000 9 795,000

Table 3

Mean annual water discharge in Vietnam (109m3)

River basins Total Generated in Vietnam

Mekong River 520.6 50.5

Tables 14 and 15 The changes of some nutrient

con-centrations and water quality parameters in the coastal

zone of North Vietnam are shown in Table 16

– Loss of coastal habitat, e.g., mangroves

These impacts have led to various negative consequences

as explained below

Increase in coastal risks Floods

Coastal floods have increased in intensity and in fre-quency of occurrence They are a consequence of the combined impact of upstream deforestation, heavy rains, sea-level rise, and the blocking of lagoonal inlets or river mouths by sedimentation Coastal floods are especially severe and very dangerous when heavy rains and storm surges coincide with spring tides Annual flooding in the MRD, which lasts from 2 to 6 months mainly between August and October, inundates an area of more than 1.7·106 ha affecting 9 million people directly From 1926

to 1997, there were 23 heavy floods, of which those in

1991, 1994, and 1996 were particularly noteworthy Floods along the central coast involving the many small rivers are particularly heavy because of their sudden onset after heavy rains, a consequence of destroyed up-stream forests, steep coastal landforms with longshore sand dunes, and rapid blocking of lagoonal inlets and the

Table 4

Characteristics of the Mekong and Red River basins (after Pho 1984, World Bank 1996)

Mekong River basin

Number of river mouths Has nine great river mouths on the 320-km-long deltaic coastline Measurements of river details

Catchment area 795 ·103km2

Delta area in general and in Vietnam 50·10 3

km2, 36·103km2 Maximum elevation 5,000 m

Length 4,500 km of which 200 km is in Vietnam

Gradient within Indochina 16 cm/km

Sediment discharge in Laos 132 ·106t/year

Sediment discharge in Vietnam 98·106t/year

Flood season discharge 60·109m3held by Tonle Sap Lake in Cambodia, which is part of the

Mekong River system Date of flood season June to November

Date of date season December to May

Water discharge measured at Crache, Cambodia

Average annual discharge 13.56·103m3/s

Average discharge during wet season and dry season 23.87·103m3/s, 3.27·103m3/s

Maximum in September, minimum in April 38.81·10 3 m 3 /s, 1.91·10 3 m 3 /s

Sediment concentration in dry season and flood season 50–100 g/m 3 , 250–300 g/m 3

Salt intrusion landward 60–70 km

Dates of wet period 1937–1953

Date of dry period 1954–1977

Red River Basin

Measurements of river details

Catchment area 169 ·103km2(including 14 ·103km2 in the catchment area of the

Thai Binh River, entirely in Vietnam) Delta area 17 ·103km2entirely in Vietnam

Coastline 150 km length

Length 1,126 km of which 556 km is in Vietnam

Mean basin elevation 1,090 m

Maximum elevation 3,000 m

River gradient 230 cm/km

Details of flood season June to October with 74.4% of total annual discharge and a maximum

of 21.2% in August Details of dry season November to May with 25.6% of total annual discharge and a

mini-mum of 2.05% in March Sediment concentration Very high, annual mean value 1,000 g/m3at Son Tay near Hanoi Salt intrusion landward 30–50 km

Wet period 1932–1951

Dry period 1952–1967

Table 5

Monthly water discharge of the Red River (m3/s) at Son Tay Station

near upper Hanoi (1961–1980; after Pho (1984)

Month m3/s %

Jan 1,328 3.0

Feb 1,100 2.5

Apr 1,071 2.4

May 1,893 4.3

Jun 1,692 10.8

Jul 7,986 18.4

Aug 9,246 21.3

Sep 6,690 15.3

Oct 4,122 9.5

Nov 2,813 6.4

Dec 1,746 4.0

Mean annual discharge 3,633 100

Flood season % 75.3

Dry season % 24.7

Fig 3 Sketch map of economical zones and activ-ities in Vietnamese coastal zone

Table 6

Deforested and barren lands in Vietnam After World Bank (1996), Cuong (1997)

Region Land area (1,000 ha) Percentage forest

cover in 1943

Percentage forest cover in 1991

Percentage barren land area in 1993 Northern mountains 7,645 95 17 60–65

Northern midlands 3,982 55 29 27–33

Red River delta 1,030 3 3 5–14

North central coast 4,002 66 35 40–44

South central coast 4,582 62 32 42–49

Central highlands 5,557 93 60 25–32

NE of Mekong R 2,348 54 24 23–34

Table 7

Land use in 1993 (ha; after World Bank (1996)

Land use Entire Vietnam Red River delta Mekong River delta

(lowlands only) Total area 33,099,093 1,251,167 3,956,918

Total crop land 6,771,060 668,851 2,444,060

Total annual crop land 5,523,899 643,021 2,104,593

Area with rice paddies 4,079,483 585,284 1,933,280

Table 8

Agricultural water use (10 6 m 3 ; after World Bank 1996)

Entire country 40,660 46,996 60,479

Red River delta 6,601 7,377 8,902

Mekong River delta 15,617 18,398 23,775

Table 10

Suspended sediment in transport in the Red River at Son Tay Station (mg/m 3 ) between period 19592–1985 (before completing Hoa Binh Dam) and period 1986–1997 (after completing Hoa Binh Dam; after Hau et al (2002)

Month 1 2 3 4 5 6 7 8 9 10 11 12 Yearly 1959–1985 200 172 170 220 556 1,070 1360 1,530 1050 797 581 299 1,010 1986–1997 128 123 137 203 458 719 855 936 847 776 303 143 677

Table 9

Average water quality in selected small rivers in Hanoi–upper RRD (1992–1994) From the Interim Report of the Institute of Water Resources Planning and Management Please note that these values are high (after World Bank 1996)

River BOD5(mg/L) COD (mg/L) NH4(mg/L) PO4(mg/L)

Set River at Cau Set 31.6 95.4 1.1 2.2

To Lich River at Thanh

Liet

Kim Nguu River at Yen So 38.4 106.3 1.1 2.2

BOD 5 biochemical oxygen demand; COD chemical oxygen demand

Table 11

Change of water discharge distribution patterns at Son Tay, Ha Noi and Thuong Cat Stations in the Red River (m3/s) every month between periods 1976–1985 (before completing Hoa Binh Dam) and 1986–1995 (after completing Hoa Binh Dam) Son Tay Station lies above on the main branch of the Red River Ha Noi and Thuong Cat Stations lie below on two sub-branches of the Red River (After Hau et al 2002)

Month Son Tay Station Ha Noi Station Thuong Cat Station

1976–1985 1986–1995 1976–1985 1986–1995 1976–1985 1986–1995

1 1,309 1,222 1,098 963 293 272

2 1,133 1,124 955 895 244 244

4 1,053 1,294 926 989 231 289

5 2,045 2,519 1,632 1,521 491 496

6 4,061 5,092 3,175 3,402 1,111 1,304

7 6,570 8,768 5,105 5,884 1,808 2,608

8 8,345 7,347 6,463 5,209 2,377 2,098

9 6,871 4,779 5,633 3,501 2,025 1,252

10 4,099 3,910 3,362 2,857 1,192 975

11 2,868 2,208 2,417 1,681 812 529

12 1,640 1,474 1,405 1,163 427 340

mouths of small rivers by sedimentation due to longshore

sand drift in the dry season In November 1999, terrible

floods along the central coast caused a great loss of life

and destroyed considerable parts of the infrastructure

Protected by the dike system, the coastal lowlands of the

RRD are flooded only by local heavy rainfall Floods in

the RRD are especially dangerous when waves linked with

storm surges break the sea dikes, as happened in 1955

and 1996

Erosion/accretion

In both the MRD and the RRD, which are known to have

usually accreting coastlines, erosion has nevertheless

oc-curred along one-fourth of the coastline of each delta

Nowadays coastal erosion is a key concern, increasing in

scale and amount with the resulting damage Overall, 243

coastal sites covering 469 km of coastline have eroded at a

rate of 5–10 m/year Ninety-six of these sites have lost

even more than 1 km of coastline to erosion The longest

eroded coastal stretch extends 60 km at Ganh Hao in the

MRD and along the Bo De coast; some 36 km of coastline

have been eroding at a rate of 30–50 m/year On average,

112 ha of coastal land has been lost each year for the last century

Following is a discussion of the second longest eroding coastal stretch at Vanly in the RRD, which extends over a length of 30 km (Thanh 1995; Thanh and Huy 2000; Dien

et al 2003) In the RRD, the Vanly coast has been eroding

at a rate of 10–15 m/year during the last half century, even though dikes and embankments protect this coast Cor-responding to the completion of the big Hoa Binh Dam in the Red River catchment at the end of 1989, the mean rate

of coastal erosion increased from 8.6 m/year during 1965–

1990 to 14.5 m/year during 1991–2000 along the Vanly coast (Thanh and Chien 2002; Dien et al 2003) An effective means of protecting the area has not yet been found At present, two sea-dike systems are used When-ever the seaward dike system is damaged by erosion, a new dike system is built landward, and a great number of the inhabitants are forced to move Figure 4 gives some detail

on how accretion processes have been replaced by con-siderable erosion

Coastal erosion has also long been a serious problem in the Bach Dang estuary in the north and in the Dong Nai

Table 12

PO4and NO3in the coastal zone of the RRD (mg/L) The Vietnam standards in 1995 for aquaculture were: PO4, 0.01 mg/L; NO3, 0.05 mg/L The standards for swimming beaches in 1995 were: PO 4 , 0.065 mg/L; NO 3 , 0.05 mg/L (after Ninh et al 1995)

Season River River mouth Coastal sea

PO 4 Dry season 0.12 0.07 0.03

Flood season 0.448 0.224 0.077

NO 3 Dry season 0.307 0.144 0.090

Flood season 0.728 0.121 0.085

Table 14

Change in average content of oil in Vietnamese coastal waters (mg/L) from 1995–1998 The Vietnam standards in 1995 for aquaculture were 0.05 mg/L, and 0.3 mg/L for swimming beaches These average values were calculated from data of 16 national stations of environment observation (four stations for each area) measured every three months (after Dieu et al 2000)

Near shore of the northern part 0.24 0.61 0.45 0.56

Near shore of the central part – 0.18 0.13 0.16

Near shore of the southern part – – 0.18 0.44

Offshore area of oil exploitation and international shipping way – 0.55 0.54 0.53

Table 13

Total N and P in surface water at selected locations in the Mekong River delta These values are averages of monthly samples collected over a 24-month period ending in October 1994 Critical concentrations of total N and phosphate-P are generally considered to be 0.5 mg/L and 0.05 mg/L, respectively In these data, total N might reflect analysis problems From the Interim Report of the Sub-Institute of Water Resources Planning and Management World Bank (1996)

Region\area Site Total N (mg/L) Total P (mg/L)

Mekong River Tan Chau 0.42 0.14

Chau Doc 0.42 0.10 Plain of Reeds Hong Ngu 0.27 0.12

Kien Binh 0.27 0.05 Camau Peninsula Ho Phong 1.05 0.17

Thoi Binh 0.99 0.07 Longxuyen Quadrangle Thoai Son 0.71 0.14

Tam Ngan 0.80 0.10

estuary in the south, regions where population density is

high Along the central sandy coast, erosion localized in

both time and place happens suddenly In general, the

erosion rate ranges from 1–5 m/year, but sometimes it is

as much as 10–15 m/year Typical eroded coasts are found

at Canh Duong, Thuan An, and Phan Ri

In the MRD, coastal accretion has occurred on the Camau

Peninsula at a rate of 50–80 m/year, with a maximum rate

of 150 m/year, while the peninsula expanded seaward at a

rate of 122 ha/year between 1885 and 1985 (Nguyen et al

1999) The RRD has expanded seaward 27 m/year at a

maximum rate of 120 m/year, and 360 ha/year have been

added to this delta In the deltas, deposition provides us

with the precious resource of land However,

sedimenta-tion is a major risk, which has become more extensive

recently (Thanh 1995), having a particularly negative

im-pact on marine ports and harbors Haiphong is a typical

example: for more than a century, it was the biggest port in

Vietnam, but recently big ships have not been able to reach

the port owing to the heavy sedimentation in its channel

caused by the building of the Dinh Vu coastal dam This

dam has closed the Bach Dang estuary, blocked the

dis-charge of sediments from a natural tributary, and

con-centrated sediments into the shipping channel Along the

central coast, longshore sand drifts generated by wave

action have closed lagoonal inlets and the mouths of small

rivers, leading to coastal floods, the freshening of saltwater

lagoons, and the loss of water on its way to the sea; for

example, the closure of the Tu Hien inlet in Tam Giang

lagoon

Shifts in the saltwater–freshwater boundary

Flood-related water freshening has caused losses in the

coastal fishery, including both the fishery catch and

mar-ine and brackish water aquaculture Because of tidal

pressures, saltwater now penetrates 30–50 km up the Red River and 60–70 km up the Mekong River More than 1.7·106 ha of land has been affected by saltwater intrusion

in the MRD; this area is predicted to increase to 2.2·106 ha

in the near future if suitable management practices are not implemented In recent decades, the 1& salinity contour (isohaline) has moved landward by 4–10 km in the northeast part of the RRD Owing to gradual saltwater intrusion landward, salinity has also increased everywhere

in the MRD during the dry season, reaching its maximum

in March and April every year A comparison of the 4& salinity contours during the 20 years between 1978 and

1998 revealed movement of approximately 20 km land-ward (Nguyen et al 1999) Most of the Mekong water during the dry season comes from the upper reaches of the river in China A combination of factors such as the de-crease in river-water discharge caused by dams, irrigation and the sea-level rise may have led to more saltwater intrusion, which is a serious problem not only for coastal agriculture, but for other economic sectors as well Along the central coast, the Thua Thien Hue Province with a population of nearly one million, also suffers from fresh water shortage for agricultural, domestic, and industrial uses because of saltwater intrusion in the valley of the Huong River, a small river, during the dry season

Environmental pollution For the most part, coastal and marine environmental quality with respect to contaminants is still rather good, although varying levels of pollution have been recorded at some sites resulting from contaminants produced by hu-man activities in catchments or in coastal or marine areas (Ninh et al 1995; Hoi et al 1997) Among those, oil pol-lution is locally a comparably serious problem (see Fig 3) This pollution is generated mainly by activities off shore

Table 15

Change in average content of Zn and Cu in Vietnamese coastal waters (mg/L) from 1996–1998 The Vietnam standards in 1995 for aquaculture were 0.01 and 0.01 mg/L for Zn and Cu, respectively; and for swimming beaches, 0.1 and 0.02 mg/L for Zn and Cu, respectively These average values were calculated from data of 12 national stations of environment observation (four stations for each area) measured every three months (after Dieu et al 2000)

1996 1997 1998 1996 1997 1998 Near shore of the north part 0.0053 0.0465 0.0538 0.0078 0.0066 0.0086 Near shore of the center part 0.0233 0.0287 0.0185 0.0055 0.0051 0.0042 Near shore of the south part 0.0219 0.0219 0.0473 0.0168 0.0093 0.0064

Table 16

Changes in some key parameters of water quality in the coastal area of North Vietnam from 1995–1998 The Vietnam standards in 1995 for aquaculture were: DO, 5 mg/L; NO 2 , 0.002 mg/L; PO 4 , 0.1 mg/L; SiO 3, 3 mg/L; Coliform, 1,000 MNP/100 ml The standards for swimming beaches were: DO, 4 mg/L; NO 2 , 0.001 mg/L; PO 4 , 0.65 mg/L; SiO 3, 3 mg/L; 1,000 MNP/100 ml; After Dieu and Hoi (1999)

Parameter Unit 1995 1996 1997 1998

NO 2 mg/L 0.0049 0.0050 0.0088 0.0115

PO4 mg/L 0.0098 0.0065 0.0177 0.0224

SiO 3 mg/L 0.3140 0.5990 0.9570 1.1875

Coliform MNP/100 ml – 773 804 866