freshwater discharges into malaysian coastal seas

(c) 2008 Zelina Zaiton IbrahimMelaka, 19-20 May 2008

JSPS MCRP Coastal Marine ScienceNational Coordinators Meeting 1

Freshwater Freshwater Discharges Into Discharges Into

Malaysian Coastal Malaysian Coastal SeasSeasS. M. OyopS. M. Oyop(1)(1), Z.Z. Ibrahim, Z.Z. Ibrahim(1)(1) and T. and T. YanagiYanagi(2)(2)

(1) Faculty of Environmental Studies, Universiti (1) Faculty of Environmental Studies, Universiti Putra MalaysiaPutra Malaysia

(2) Research Institute for Applied Mechanics, Kyushu (2) Research Institute for Applied Mechanics, Kyushu UniversityUniversity

email: (1) [email protected], email: (1) [email protected],

(2) tyanagi@(2) [email protected]

(c) 2008 Zelina Zaiton IbrahimMelaka, 19-20 May 2008 2

JSPS MCRP Coastal Marine ScienceNational Coordinators Meeting

RationaleRationale

The Southeast Asian The Southeast Asian regional seas have regional seas have reduced salinity reduced salinity valuesvalues

Freshwater Freshwater discharges from discharges from surrounding surrounding landmasseslandmasses

Freshwater Freshwater discharges bring discharges bring land-based materialsland-based materials

Indian Ocean

Pacific OceanSouth

China Sea

Andaman Sea

Java Sea



Some QuestionsSome Questions

How quickly do these materials How quickly do these materials move out into the deep ocean?move out into the deep ocean?

Or do they stay in the area?Or do they stay in the area? Are rivers important nutrient Are rivers important nutrient

sources? sources? Or is upwelling more important?Or is upwelling more important?



Some Flushing Estimates Some Flushing Estimates for for

South China Sea and South China Sea and Malacca StraitsMalacca Straits South China SeaSouth China Sea

Flushing time about 40 years Flushing time about 40 years Chen and Huang, 1995 Chen and Huang, 1995

Top 350 m layer about 2.6 (dry season) to Top 350 m layer about 2.6 (dry season) to 6.8 (wet season) years 6.8 (wet season) years Chen et al (2001)Chen et al (2001)

Malacca StraitMalacca Strait Low velocities; low salinities; ... low Low velocities; low salinities; ... low

flushing? flushing? Hii et al 2006Hii et al 2006



FlushingFlushingDefinitions and MethodDefinitions and Method

a.a. Turnover TimeTurnover Time

= Sea Volume/Flux= Sea Volume/Flux

b.b. Tidal Prism MethodTidal Prism Method

= Sea Volume/Tidal = Sea Volume/Tidal Volume per DayVolume per Day

c.c. Residence Time Residence Time

= (Concentration x = (Concentration x Volume)/FluxVolume)/Flux



Data SourcesData SourcesData Data ValuesValues

SourceSource

11 Bathymetry Bathymetry forfor

area, area, volumevolume

ETOPO2 provide 2 min by 2 ETOPO2 provide 2 min by 2 min grid depth valuesmin grid depth values

22 Annual Annual surface surface runoff, runoff, rainfall, rainfall, evaporationevaporation

Malaysian Drainage and Malaysian Drainage and Irrigation Department Irrigation Department Hydrological Network Hydrological Network databasedatabase

33 Mean Mean salinitysalinity

World Ocean Database World Ocean Database 20012001



1. Volume of the Malacca 1. Volume of the Malacca StraitStrait

0

500

1000

1500

2000

2500

ETOPO2 Grid Depth Class

Co

un

ts

Surface Area=202,422.4 km2

Total Volume=45525.1 km3



2. Annual Rainfall, 2. Annual Rainfall, Runoff, EvaporationRunoff, Evaporation

Rainfall Rainfall

= land rainfall x 0.7 x = land rainfall x 0.7 x areaarea= 334.5 km3

RunoffRunoff

= Peninsular Malaysia x 2= Peninsular Malaysia x 2

= = 93.17 km3

Evaporation Evaporation

= 3 mm/day x area= 3 mm/day x area

= 216.2 km= 216.2 km33

0

20

40

60

80

100

120

140

160

180

1 2 3 4 5 6 7 8 9 10 11 12

MonthMe

an M

onth

ly Di

scha

rge,

m3/s



a. Freshwater Turnover a. Freshwater Turnover TimeTime

Turnover Time = Volume/fluxTurnover Time = Volume/flux

Total MS volume 45525.14 km3

Potential Runoff Input 93.17 km3/a

Rainfall input over the sea Rainfall input over the sea (0.7 of land)(0.7 of land) 334.5435334.5435 km3/a

Evaporation output (3 Evaporation output (3 mm/day)mm/day)

216.1871216.187122 km3/a

Flux = River + Rain - Flux = River + Rain - EvaporationEvaporation 211.53211.53 km3/a

Turnover time of freshwater 215.22 a



b. Tidal Prism Volumeb. Tidal Prism Volume

Tidal prism per tide (semi-diurnal)Tidal prism per tide (semi-diurnal)

= surface area x tide height = surface area x tide height differencedifference

= surface area x 2 m= surface area x 2 m

= = 404.84 km3

How much of the water returns on the tide? % of return flow



Tidal FlushingTidal Flushing

Tidal prismTidal prism

= volume/(1-return flow)(tidal = volume/(1-return flow)(tidal volume per day) volume per day)

Assumming % return flowTidal volume per semidiurnal tide 404.84 km3

Total MS volume45525.1

4 km3

Tidal prism flushing 56.23 days



But there is return But there is return flow ...flow ...

0

100

200

300

400

500

600

0 0.2 0.4 0.6 0.8 1

Proportion of Flow Returned

Flu

sh

in

g T

im

e, d

ays

280 days



c. Residence Time of c. Residence Time of FreshwaterFreshwater

Residence TimeResidence Time

= Mean Concentration in Strait = Mean Concentration in Strait

× Strait Volume / Input per × Strait Volume / Input per yearyear



3. Salinity Distribution3. Salinity Distribution0

200

400

600

800

1000

1200

31 31.5 32 32.5 33 33.5 34 34.5 35 35.5

Salinity, psuD

ep

th,

m 3. Salinity 3. Salinity Variation with Variation with

DepthDepth



Volume of the Upper Volume of the Upper Layer Layer

(0 - 200 m)(0 - 200 m)

Surface Area=202,422.4 km2

Total Volume=45525.1 km3

Volume of 0-200 m = 8298.5 km3

Shallow water volume is 18% of total volume



Residence Time Residence Time in the Upper 200 m Layerin the Upper 200 m Layer• We ignore water volume deeper than

200 m

Volume of upper 200 m layer 8298.

48 km3

Volume of freshwater (Andaman Sea end member

is 36 psu)496.7

5 km3

Flux=River+Rain-Evaporation

211.53

km3/a

Residence Time of freshwater 2.35 a



SummarySummary

MethodMethod TimeTime

aa Turnover time of freshwater flux

215.22 years

Turnover time in upper 200 m Turnover time in upper 200 m fluxflux

39.23 39.23 yearsyears

bb Tidal prism flushing of total Tidal prism flushing of total volumevolume

56.23 56.23 daysdays

Tidal prism flushing of upper Tidal prism flushing of upper 200 m200 m

20.5 20.5 daysdays

cc Residence time of freshwater in upper 200 m (based on salinity values)

2.35 years



Some Other Some Other Considerations ...Considerations ...

Seasonal variationsSeasonal variations Spatial variationsSpatial variations

0

20

40

60

80

100

120

140

160

180

1 2 3 4 5 6 7 8 9 10 11 12

Month

Mean

Mon

thly

Disc

harg

e, m

3/s

0200400600800

10001200140016001800

1 2 3 4 5 6 7 8 9 10 11 12

Month

Month

ly Evap

oratio

n, mm

Langat

Perlis Ke

dah

Pulau

Pina

ng

Perak

Selan

gor

Nege

ri Sem

bilan

Melak

a

Joho

r

0

5

10

15

20

25

StateAn

nual

Poten

tial R

unof

f, km3

North South

freshwater discharges into malaysian coastal seas

Documents

mmday x area

land rainfall x

sea volumetidal volume

return flowtidal volume

peninsular malaysia

tidal prism volumetidal

dayresidence time

methodturnover time