assessment of impacts of level rise on coastal lagoons -{ase in...

Assessment of Impacts of Sea Level Rise on Coastal Lagoons-{ase Studies in Japan and Thailand-

Yukihiro HIRAI*I, Tetsuo SATOH*2, Charlchai tANAVUnx3

Abstract

Global warming is one of the most serious environmental issues of the present day. Theaverage temperature is predicted to rise 1.7'C to 3.8t by the end of the next centu4f. Sea levelis also projected to rise 15 cm to 90 cm during the same period.

In this paper the authors first present an example of the assessment of impacts of sea level riseof the lagoons in Japan. We also present the common methodology of vulnerability assessment

and an original procedure to assess the impact of sea level rise on the Songkhla Lake in southernThailand. Following this procedure we describe the natural and socioeconomic characteristicsof the Songkhla Lake, and we identify major factors that control the development of eachnatural region. It is most important to clarify the natural and socioeconomic systems and alsoto identify the development factors at each natural region for the proper assessment of theimpact of sea level rise.

I. Introduction

The study on Land-Ocean Interaction in theCoastal Zone (LOICZ) started in 1993 as one ofthe Core Projects of IGBP (International Geo-sphere Biosphere Programme). The objective ofLOICZ project is to predict the change of coastalenvironment by global warming in the nearfuture, and also to develop further sustainableways of utilization of coastal areas. Four majorfields of LOICZ research are proposed as follows(Yonekura et al., 1998):

( 1) Effects of changes in external forcing orboundary conditions on coastal fluxes.

(2) Coastal biogeomorphology and globalchange.

(3) Carbon fluxes and trace gas emissions.(4) Economic and social impacts of global

change on coastal systems.This study focuses on the fourth domain, i.e. to

forecast how the responses of coastal systems toglobal change affect the habitation and usage ofcoastal environments. Hirai (1998), one of theauthors, has discussed the impacts of sea level riseon the coastal lagoons in Japan and presentedstrategies against their responses. In that discus-sion, he emphasized that the impact would have

various aspects depending on the natural andsocioeconomic conditions at coastal area of eachlagoon. Major thirty-four coastal lagoons inJapan were grouped into five types (namely fromType-A to Type-E) in terms of "artificial littoralshoreline" and "intensive land use in littoral low-land" (Figure I ).

The littoral lowland of type-A lagoon remainsalmost natural without any artificial structure orland use. This type of lagoon is very valuable inJapan and important especially for the protectionof wild waterfowl. The Lake Kucharo, for in-stance, has been registered since 1989 as one ofthe designated lakes of Ramsar Convention. Inthe littoral lowlands of type-8, the rate of arti-ficial littoral shoreline is very low, but aboat 40Vo

of the area is used for grassland. In the case

of type-A and -B lagoons, few environmentalchanges will be observed when sea level risesseveral tens of centimeters to 1 m.

Littoral shorelines of type-C and -D lagoonsare partly artificial and urban or industrial landuse is found in the littoral lowlands. Urbaniza-tion has been taking place rapidly for the last twoor three decades. In the process of developmentplanning around these types of lagoons, it is nec-essary to consider carefully the influences of lakelevel rise caused by sea level rise.

*r Department of Geography, Faculty of Education, Ehime University, Matsuyama, Japan.*2 Department of Geography, Kom azawa University, Tokyo, Japan.*3 Faculty of National Resources, Prince of Songkhla University, Hat Yai, Thailand

33

Regional Views No. 12 1999

0 l0 m 30 .{o 50 60 70 8[) 90 100

Rate of Artificial Shoreline(%)

Figure 1. Relationship between "artificial 511on1 ghslshine" md "intensive land use in littoral lowland" oflagoons in Japan

Source: Hirai (1998)

Type-E lagoons are transformed artificially tothe greatest extent, and the littoral lowlands areintensively utilized,. Almost all the littoral shore-line is artificially embanked with shore protec-tions, and urban land use is predominant. In thecase of this type of lagoons, the impact of sea levelrise on the littoral lowland will be immense, caus-ing serious damage to these areas.

For the sake of appropriate assessment of theimpacts of sea level rise on coastal lagoons, it is

most important to clarify the natural and socio-economic characteristics of each lagoon and itslittoral lowland. In this paper, the authors firstshow the common methodology of vulnerabilityassessment developed by the IPCC Coastal ZoneManagement Subgroup. And an original proce-dure is presented to assess the impacts of sea levelrise on the coastal lagoons in developing coun-tries. In this process, emphasis is laid on theidentification of development factors at each litto-ral zone. Natural systems and socioeconomicsystems in lacustrine lowlands are delineated toidentify the relevant development factors, 2s

shown in the case of the Songkhla Lake in south-ern Thailand.

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II. Methodology of vulnerability assess-

ment of the impacts of sea level rise

1. Common methodology of the vulnerabilityassessment by IPCC

The IPCC common methodology was devel-oped by Coastal Management Subgroup of IPCCin order to promote vulnerability assessment inevery country. Aiming at making assessment ofvulnerability on both physical and human aspects,

the common methodology consists of seven steps

as shown in Figure 2 (Center for Global Environ-mental Research, 1996). According to this meth-odology, a case study area is selected and thescenario for sea level rise and climatic change ispresumed at the first step. Based on the data ofnatural and socioeconomic systems (step-2), rele-vant development factors should be identified(step-3). And the assessment of physical changesand natural system responses will be conducted as

the forth step.

Such physical changes may be recognized as

inundation or displacement of lowlands, coastalerosion, intensification of coastal flooding, in-

34

Assessment of Impacts of Sea Level Rise (Hirai et al.)

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Figure 2. Common methodology of vulnerability assessment by IPCC

Source: IPCC (1992)

crease in salinity at estuary, salt water intrusion,change of tide, change of sedimentation patterns,decrease in the amount of light reaching sea

bottom, and so on. On the other hand, theresponses of natural system are supposed to besome impact on local ecosystems such as wet-lands, tidal flats, mangroves, and coral reefs in thecoastal zones. Such physical changes and re-sponses of the natural system heavily depend onthe natural or socioeconomic conditions of eachlagoon or each coastal zone. That is to s&y, it isvery important to identify the relevant develop-ment factors at each lagoon or coastal zone.

2. Original procedure of assessment of the im-pacts of sea level rise on coastal lagoons

Considering the importance of identifying rele-vant development factors, the authors show anoriginal procedure to assess the impacts of sea

level rise on coastal lagoon (Figure 3). Thisprocedure consists of seven steps that start withcollecting both general and detailed data on phys-ical and human conditions at a study area (step- 1

and step-2). The data on natural system is ar-ranged from geomorphological and hydrologicalviewpoints. In the same w&y, the data on socio-economic system is analyzed in relation to theland use pattern and water use conditions of the

area (step-3).Then the study area is divided into some homo-

geneous zones through integration of the data onnatural and socioeconomic systems (step-4).After that, development factors in each zone willbe identified and the impacts of sea level rise willbe estimated (step-5). Then the assessment of theimpact on the whole lagoon area will be made bythe synthesis of assessment at each zone (step-6).Finally this procedure is supposed to be applied toother coastal lagoon areas (step-7). In this study,we discuss mainly step-3 and -4 of the procedure.

IfI. Natural systems in the lacustrine low-lands of the Songkhla Lake

1. Geomorphological conditionsIt is very effective to know local geomorpholog-

ical conditions not only for estimation of the areasubject to inundation or erosion caused by sea

level rise, but also for discussion about the rela-tionship between natural and socioeconomic sys-tems. In this study we classified our study areawith such geomorphological units as follows;beach, erosional cliff, swamp, dune, beach ridge,littoral lowland, delta, Holocene lacustrine ter-race, Pleistocene marine terrace, tower karst andhill or mountain. Two kinds of remote sensing

―- 35 -一

Step-1

Collectingof basic data on the case study area

(Remote Sensing Images such as LANDSAT, SPOT, JERS, Geomorphological Map,

NavigationChart, Land Use Map, General Statistics)


I *analysis of the data,Field Survey

I -consrcieratrcn

t *Pormulation

Figure 3. Original procedure of assessment of the impacts of sea level rise on coastal lagoon.

data, namely LANDSAT 5-TM images and JERSI-VNIR images, were used to classify the topog-raphy in general. In addition, we measured actualtopography in the field to prepare some crosssections of typical geomorphological units.

The Songkhla Lake, located on the eastern

coast of the Malay Peninsula, is the biggestcoastal lagoon in Thailand. Total area of the lakebasin is about I 182 km2 and six or seven times as

large as Lake Kasumigaura in Japan. The lake is,

however, very shallow and about only 1.1 to 1.8

m deep in the mean depth. It consists of threemajor basins; Thale Noi, Thale Luang and ThaleSap Songkhla. Thale Noi is a small lake north ofThale Luang. Thale Luang is the main lake,being separated from the Gulf of Thailand by awide and long beach ridge plain. Thale Sap

Songkhla is the southern part of the Songkhla

Lake, which is linked to the sea through a narrowchannel (Figure 4).

Littoral lowlands of the Songkhla Lake can bedivided into five zones; ( 1) Beach ridge plain, (2)Thale Noi and its vicinity, (3) Western part ofThale Luang, (a) Deltaic lowlands of Thale Sap

Songkhla, and (5) Holocene terraces and Pleisto-cene terraces.

( 1) Beach ridge plainA wide and long beach ridge plain is developed

between the basin of the Songkhla Lake and theGulf of Thailand. The width of the plain is 3 to8 km, and its height is less than a few meters. Thebeach ridges are separated 2W to 300 m fromeach other in the northern part, but they becomecloser in the south, about 50 to 100 m or in a

complex form (Pitmatr, 1985). Number of ridges

Step-2

Coliectingof cietaiiedciata on the case stuciy area

ndMap, Detailed Statistic,s )

Natural Systems

a,Geomorphological Conditions ( t-

Classification of lacustrine lowland)

b.Hy drological Conditions (Rainfa

Groundwater, Lake Water

Socioeconomic Systems

a. Land Use Patterns

b. Water Use Conditions

! *mregration

Classification of Lacustrine Lowland Based on both Natural Systerns and Socioeconomi

Identification of Development Factors of Each Unit and Assesst'nent of impact ofLevel Rise

I -svnthesis

of Sealevel Rise on Whole

ion of the Assessment to other coastal I

36

Assessment of Impacts of Sea Level Rise (Hirai et aI.)

②Thale

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be grouped into 3 or 4 types by difference of theirshapes. The height of the top of these ridges isabout 2 to 3 m above sea level, being 1 to 2 m

Gヽ“J/。/Tttlib″

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Figure 4. Geomorphological map of the Songkhla Lake Area

Source: Hirai ( 1995 )

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一- 37 -一

higher than the lowlands between the ridges.

(2) Thale Noi and its vicinityThe area of Thale Noi itself is only 26 kmz, but

a swampy area called Phru Khuan Khreng ex-tends around the lake over l26km2. This hugeswamp includes wetland covered with variouskinds of aquatic plants, grassland, peat swampforest, and tropical evergreen forest.

(3) Western part of Thale LuangMarine or lacustrine lowlands lower than 10 m

above mean sea level are developed along thewestern coast of Thale Luang. These lowlandsare flooded every year because the lake level risesup to about 1 to 2 m at the maximum in the rainyseason.

(4) Deltaic lowland of Thale Sap SongkhlaPresent and former river deltas of the U-taphao

River and the Phu Mi River are developed at thesouthern and western coast of Thale Sap Songk-hla. The littoral shoreline of this zone is indenteddue to the development of natural levee along thediverged river courses. The height of this deltaiczone is so low, almost the same as the mean lakelevel, that the littoral lowland is often inundatedby flooding every rainy season.

(5) Holocene and Pleistocene terracesA Holocene marine or lacustrine terrace is seen

at the height of below 4 m above mean sea level inthe southern coast of Thale Sap Songkhla (Hirai,1995; Haruyama, 1995). On the other hand, fourkinds of Pleistocene marine terraces are devel-oped at the height of 10 to 50m to the west of theSongkhla Lake. Among these marine terraces,the second lowest terrace (T2) covers this areamost extensively at about z0m above mean sea

level.

2. Hydrological conditionsHydological data of the Songkhla Lake, both

on the drainage basin and the lake systems, werecollected to estimate the impacts of sea level rise,especially that of the physical changes such as

intensification of flooding and increase in salinity.

( 1) Hydrological conditions of the drainagebasin

The study area is under tropical monsoon cli-mate and the annual mean temperature of Songk-hla City is 27.7"C with little seasonal changes.The average annual precipitation of the basin is


2l0O mm. Heavy rains are observed during thenortheast monsoon season from October to De-cember, because the dividing mountain ranges ofthe Malay Peninsula lie in the north-south direc-tion to the west of the Songkhla Lake.

The groundwater of this area is found mainlyin the following three types of aquifer (NESDB,1985). Shallow but limited amount of ground-water is contained in the beach sand of the beachridge plain east of the Songkhla Lake and also inthe alluvial deposits of the western coast of ThaleLuang. On the other hand, a large quantity ofgroundwater is contained in the deep gravellayers, which have been deposited in the bottomof ancient river channels formed at an earlv stageof basin development. The third type of aquifer isthe fractures or solution cavities in the basal rocksor limestone in the west of the study area.

(2) The lake systemsThe Songkhla Lake consists of three main lake

basins; Thale Noi, Thale Luang and Thale Sap

Songkhla, and it is connected to the Gulf ofThailand through a deep narrow channel to theeast of Thale Sap Songkhla. The total lake area is1082 km2(Lake Biwa Institute and InternationalLake Environment Committee, 1988) to 1182km2lNESDB, 1985), with about 90 km lengthfrom north to south, and 25 km width from eastto west. Total area of the drainage basin is 6999km2(Lake Biwa Institute and International LakeEnvironment Committee, 1988) to 8020 km2(NESDB, 1985).

Lake water level fluctuates usually from -0.3m to +0.3 m above mean sea level. The annualflood peak level is commonly above * I m, butthe level rises up to about *2 m in the upper lakewhen extreme flooding occurs. There are almostno littoral banks or shore protections along theshoreline of the Songkhla Lake. The littoralshoreline is not defined so clearly as those ofJapanese lagoons, and it generally retreats land-ward in the rainy season while it advances off-shore in the dry season.

The lake systems of Thale Noi, Thale Luangand Thale Sap Songkhla are described in thereport by NESDB (1985) as follows.

a. Thale NoiThale Noi has an area of 26km2 and mean

depth of the lake is 1. I m. This is the deepest partof the huge swamp of Phru Khuan Kreng. Thereis a low ridge between Thale Noi and ThaleLuang at about 0.5 m above mean sea level, and a

38


connecting river flows across it. But at the timeof flooding, two lakes connect with each otheralong this boundary for about 13 km.

b. Thale LuangThale Luang can be divided into northern and

southern parts of the lake basin by the peninsulaof Ko Yai, which is not a true island (Ko) but a

land-tied island connected by tombolos.The northern part of Thale Luang has an area

of 491 km2 and its mean depth is 1.8 m. Thesalinity of lake water is predominantly fresh, orlower than L%0, but it increases above this level inAugust, September and November. In the years

of low rainfall with long dry season or with fewfloods in the rainy season, its salinity is raised andmay exceed lO%0. The waters of Thale Luang are

usually very muddy because of fine suspended

loads carried from catchment area or derivedfrom bottom sediments by wave action.

The southern part of Thale Luang has an areaof 267 km2 and its mean depth is 1.2 m. The lakewater is predominantly brackish, forming the tra-nsition zone between salty and fresh systems.

Although the salinity level varies from year toyear and from season to season, it usually stays at5 to l1%oo and exceeds 200/oo in the dry season. Incontrast, it becomes fully fresh in the rainyseason. There are some rock islands in the south-ern part of Thale Luang, which suppress waveaction and resuspension of bottom sediments.

c. Thale Sap SongkhlaThale Sap Songkhla has an area of 190 km2 and

its mean depth is 1.4 m. The water quality isusually brackish or salty because this lake is con-nected to the Gulf of Thailand through a deepchannel. The usual salinity level is 20-3OToo, but itbecomes fresh in the flood season, or in Novem-ber, December and January.

At the southern and western coasts, the U-taphao River, which is the largest tributarystream, and the Phu Mi River flow into this lake.Therefore severe flood sometimes occurs in thelittoral lowlands of this area. For example, lakelevel rose up to I to 1.2 m, inundating houses andfarm gardens for two weeks in a severe flood in198 8.

2. Relationship between geomorphological andhydrological conditions

The features of natural systems in the SongkhlaLake are arranged in Table 1 from both geomor-phological and hydrological viewpoints. The

littoral lowlands around the Songkhla Lake areaare divided into three geomorphological zones;

swampy lowland, littoral lowland and deltaic low-land. They are deeply connected with the lake

systems of Thale Noi, Thale Luang and Thale Sap

Songkhla respectively. We can find some devel-

opment factors of the study area to assess theimpacts of sea level rise. The factors to be notedare as follows;

( 1) Intensification of flooding at the southerncoast of Thale Luang and the deltaic zoneof Thale Sap Songkhla.

(2) Increase in salinity of both northern andsouthern parts of Thale Luang.

(3) Salt water intrusion to the groundwaterat beach ridge plain, the western coast ofThale Luang and deltaic lowland of ThaleSap Songkhla.

Further investigation will be necessary on these

matters.

III. Socioeconomic systems in the lacus-trine lowlands of the Songkhla Lake

1. Land use

Land use is one of the most comprehensiveindicators to understand local socioeconomicconditions, and is closely related with geomorp-

hological and hydrological conditions. Land use

patterns around the Songkhla Lake are classified

as shown in Table 2 according to the "Land Use

Map of Songkhla Lake Basin; 1996 prepared

with GIS by the Laboratory of Land Reclamationat the Faculty of Natural Resources, Prince ofSongkhla University.

According to the land use data on the catch-ment area of the Songkhla Lake (Lake BiwaInstitution and International Lake EnvironmentCommittee, 1988), forest area occupied 24.7Vo,

while agricultural land covered 73.OVo, and settle-ment area reached only 2.3Vo in 1982. Agricul-tural land includes paddy field (35.3Vo) andrubber plantation (37 .7 Vo). Paddy fields are dis-tributed mainly in the beach ridge plain and lacus-trine lowland of the western coast of ThaleLuang, while rubber plantations are found pri-marily on the Pleistocene terraces or hills in thewest of the Songkhla Lake. But recently, rubberplantations are rapidly spreading by clearing nat-ural tropical forest. Typical land use pattern ineach geomorphological zone is described as fol-lows.

( 1) Beach ridge plain

39

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Table 2. Classification of land use in the Songkhla Lake Basin

Water Surface

Swamp

NaturalForest

Agricultural Land

Urban Area

Mangrove ForestMelaleuca ForestPeat Swamp ForestTropical Evergreen Forest

Windbreak Forest

Plantation

Cultivated FieldOrchard

Paddy Field

Stock FarmFish/Shrimp Farming Pond

Residential Zone

ColmIIlercial Zone

lndustrial Zone

Public Zone

Open Space

In this beach ridge plain, settlements and or-chards, especially of sugar palms, are situated onthe ridges, and the lowlands between the ridgesare utilized for paddy fields. But many shrimpponds have been developed recently mainly in thenorthern coastal zone of this plain about 2.5 kmwidth from the seacoast. These shrimp pondswere converted from paddy fields or fruit gar-dens. On the other hand, in the southern coastalzone of the plain near Songkhla City, a consider-able area of lowlands between ridges has turnedinto wasteland without cultivation for the last 5 to6 years. In addition to that, severe coastal erosionis taking place in this region. According to ourinterview with a resident in Ranot, he had tomove his house twice in the last l0 years becausethe coast line has retreated about 35 to 40 m byerosion.

(2) Thale Noi and its vicinityThale Noi (28 km2) and its vicinity (22km2)

have been designated as a no-hunting area int975, and are famous for "Thale Noi WaterfowlPark" today. Although this zone is globally im-portant for the protection of wild birds, some partof the forest in this zone has been cleared by localpeople for timber and fuel wood.

(3) W'estern part of Thale LuangIn this zone, lacustrine lowland is utilized

mainly for paddy fields, but the farmers also growmany kinds of fruit trees and raise chickens andpigs. Some farmers began fish or shrimp cultiva-tion in recent years. They made small pondsconverted from paddy fields. This zone is charac-teristic of diversified farming, or so-called mixedfarming.

The Khuan Rae River flows into the northernpart of Thale Luang from the west, forming asmall delta about 500 m in width, on which LamPam Resort was opened in 1992. There is an

amusement complex with some restaurants, acampsite, a small park and so on. But its physicalconditions are disadvantageous, as those facilitieswere almost submerged in December of 1997

when we visited. People say that lake level in theflooding season rises about 50 to 60 cm higherthan usual.

On the other hand, along the western coast ofthe southern part,lacustrine lowlands are utilizedfor rubber plantations as well as paddy fields andfruit gardens. Although soil condition of suchlowland is not suitable for rubber cultivation, thefarmers try to grow rubber trees to earn moremoney by receiving government subsidies.

(4) Deltaic lowland of Thale Sap SongkhlaNew settlements with detached urban type

houses, or housing estates, have appeared alongthe former river course of the U-taphao River.

-41-

And it is remarkable that a great number ofshrimp ponds have been built on a large scale one

after another along the littoral lowland of thesouthern coast. On the other hand, a complex ofgovernment facilities, such as municipal hospitaland college, was constructed recently in the low-land near the new bridge across the lake throughKo Yo. The built-up area with large factories andcommercial buildings is rapidly expanding aroundthis complex. These lowlands were formerly cov-ered with mangrove and melaleucc forests.

(5) Holocene and Pleistocene terracesRubber plantation is the most predominant

land use on the Holocene and Pleistocene ter-races, but many "open lands" are recognized inthe "Land Use Map of Songkhla Lake Basin;1996. In this ffi&p, the land where old rubbertrees, aged about 25 to 30 years, have been cle-ared and left without vegetation is assigned to"open land". In such "open land", the red soilcovering terrace surface will be eroded by heavyrains, and this makes more fine materials flow intothe Songkhla Lake in the rainy season.

2. lVater use

It is necessary to make a comprehensive surveyabout actual water use conditions in the studyarea for assessment of impacts of sea level rise.

But systematic data on water use in this area has

not been collected yet. Accordingly only a briefnote is presented here as inductive informationobtained from interviews at each location during1997 /98 surveys.

( I ) In the northern part of beach ridge plain,they can crop rice twice a year owing to thegovernment irrigation syst€fr, which utilizes thewater from Thale Luang. The pumping station islocated on the northeastern coast of the lake. Butthey cannot use water when its salinity level rises

over 1.5%0, as in the dry season of 1990. They say

that such a problem arises about every ten years.

In the coastal area, shrimp farmers use a largeamount of seawater for shrimp cultivation, andpolluted waste water is said to flow into irrigationcanals or directly into the Gulf of Thailand.

(2) In the middle to southern part of beachridge plain, local people use more rainwater be-

cause groundwater from shallow well is saltyexcept in October. The communal irrigationsystem, which utilizes the lake water, is also suff-ering from salinity problem more seriously thanthe government system because of its lower loca-tion of water intake.


(3) In the delta of Phu Mi River on thewestern coast of Thale Sap Songkhla, they use

two kinds of groundwater; from shallow aquiferand also from deeper one about 50m in depth.The former contains high salinity and is used onlyfor general purposes, while the latter can be utili-zed for drinking and irrigation.

3. Socioeconomic characteristics of the Songk-hla Lake area

Typical land use patterns and water use condi-tions in the study area are examined for eachgeomorphological zone (Table 3). Their socio-economic characteristics and potential environ-mental problems are described as follows;

( 1) Beach ridge plainThe area of shrimp ponds has been expanding

rapidly for the last two decades from north tosouth along the coast of this beach ridge plain. Inthis area, many palm trees on ridges are dyingbecause of the increase in salinity of groundwater.On the other hand, in the double-cropping area inthe northern part of this plain, the increase insalinity of the lake water will be a serious problemwhen the sea level rises in future because theirrigation system of this area depends on the freshlake water.

(2) Western part of Thale LuangIn this zone, rice cultivation is the most exten-

sive and predominant land use for the moment,and normal flooding does not damage it severely.

It is, however, necessary to pay more attention tothe vulnerability of new types of land use againstinundation. Some new types of land use, such as

a resort area, fish farming ponds, grassland fordairy cattle and rubber plantations, have been

introduced to the littoral lowland along the lakecoast.

(3) Deltaic lowland of Thale Sap SongkhlaRapid development of shrimp ponds on a large

scale as well as urbanization in the suburbs of HatYai and Songkhla City are in progress with defor-estation of mangrove and melaleuca forests. It isimportant to prevent water pollution caused bythe waste water from shrimp farming and urbanactivities. At the same time, new urban areas

should be protected from severe floods or long-term inundation.

(4) Holocene and Pleistocene terracesRubber plantations have spread from the top of

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一- 44 -一

the terrace to both hilly areas and lacustrinelowlands. Soil erosion may become more severeon the slopes and greater amounts of fine materi-als will flow into the lake and deposit there in therainy season.

fV. Concluding Remarks

The final goal of this study is to make anassessment of the impacts of sea level rise on thecoastal lagoons in developing countries. For thefirst step of this study, the authors presented anoriginal procedure of assessment. And as a case

study following that procedure, the data on bothnatural and socioeconomic systems in the lacus-trine lowlands of the Songkhla Lake are collectedand analyzed. According to our study, the lacus-trine lowlands can be divided into eleven distinc-tive geographical units, and the development fac-tors of each unit are identified tentatively as

shown in Table 4.

Lacustrine lowlands of the Songkhla Lake areclassified into four zones from geomorphologicaland hydrological viewpoints; Beach ridge plain,Thale Noi and its vicinity, Western part of ThaleLuang, and Deltaic lowland of Thale Sap Songk-hla. Each zone except Thale Noi and its vicinityconsists of some distinctive sub-units with differ-ent land use patters and water use conditions.And development factors were reasoned fromnatural and socioeconomic features of each unit.

In order to carry forward this study for moreprecise assessment, it is necessary to identify thedevelopment factors more precisely with the helpof more systematic data on both natural andsocioeconomic systems. More detailed compari-son with the case of lagoons in Japan as well as

more intensive use of GIS data with discussions inthe field survey would be helpful to elaborate theprocedure of the assessment.

Acknowledgements

The authors wish to thank the staff of theLaboratory of Land Reclamation, Faculty ofNatural Resources, Prince of Songkhla Universi-ty, for their helpful advice and kind cooperationto our field survey around the Songkhla Lake.This study was financially supported by GlobalEnvironment Research Fund from Environment

Agency of Japan (Grant No. B-12, Project Man-ager; Hiroyuki Kawaguchi of GeographicalSurvey Institute of Japan).

References

Center for Global Environmental Research. 1996.Data Book of SEA-LEVEL R/,SE. 88p. Envi-ronment Agency of Japan.

Haruyama, S. 1995. Geomorphological featuresof the littoral zone of the Songkhla Lake. Scr.

& Tech. (Journal of JIMSTE\, 8(3), 2l-29.(in Japanese).

Hirai, Y. 1995. Geomorphological Features andEnvironmental Problems Around SongkhlaLake in South Thailand. Mem. Fac. Ed. EhimeUniv., Natural Science, 15(2), 1-16. (in Japa-nese with English summary).

Hirai, Y. 1998. Koshyo no kaihatu-riyou to kan-kyou-hozen (Development and environmentalpreservation of coastal lagoons). In Mizube-kankyou no hozenn to tikeigaku (Preservationof environment of waterside and geomorphol-ogy), €d. Geomorphological Union of Japan,86-111. Tokyo: Kokon-shoin Ltd. (itr Japa-nese).

Lake Biwa Institute and International Lake Envi-ronment Committee. 1988. Lake Songkhla. InSur-vey of the State of World Lakes InterimReport I ASI-2, l-I4.

NESDB (National Economic and Social Devel-opment Board), and National EnvironmentBoard in Thailand. 1985. Physical Natural andHuman Resource of the Basin. In SongkhlaLake basin planning study, Final Report, vol.2, Annex A.

Ohkura H., S. Haruyama, S. Vibulsresth, andT. Simking. 1996. Geomorphological LandClasstfication Map of the Songkhla Lake andIts Vicinity. Natural Research Laboratoryfor Earth Science and Disaster Prevention(Japan).

Pitman, J. I. 1985. Thailand. In The World'sCoastline.ed. E. C. Bird and M. L. Schwartz,771-787. Van Nostrand Reinhold CompanyInc.

Yonekura N., H. Kayane, N. Mimura, and T.Yanagi. 1998. Recent Japanese Activities Re-lated to the IGBP-LOICZ Project. Global En-vironment Research, vol. 1, no. I &2, I-9.


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