2 hydrology

STRAPEAT – Status Report Hydrology April 2002

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HYDROLOGY OF BORNEO’S PEAT SWAMPS

Henk Ritzema and Henk WöstenAlterra

The Netherlands


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HYDROLOGY OF BORNEO’S PEAT SWAMPS

1. Introduction ......................................................................................................................................12. Climate.............................................................................................................................................1

2.1.1 Evaporation.......................................................................................................................................12.1.2 Rainfall..............................................................................................................................................22.1.3 Dry spells ..........................................................................................................................................4

3 Topography......................................................................................................................................53.1 SURFACE TOPOGRAPHY ..............................................................................................................................53.2 MINERAL SUBSOIL ......................................................................................................................................63.3 CATCHMENTS .............................................................................................................................................6

3.2.3 Drainage Base...................................................................................................................................73.2.4 Drainability .......................................................................................................................................83.2.5 Water Management .........................................................................................................................10

4 The water balance in a peat swamp..............................................................................................124.1 WATER LEVELS.........................................................................................................................................124.2 DISCHARGES / RUN-OFF............................................................................................................................134.3 STORAGE CAPACITY .................................................................................................................................14

5 Gaps in knowledge ........................................................................................................................15References ............................................................................................................................................16


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1. Introduction

The lowland peat swamps of Borneo are purely rain-fed. They have their origins in thetopographic conditions that lead to semi-permanent waterlogging. Under natural conditions,they are formed by the accumulation of vegetation, which is deposited on the waterloggedsoils faster than it can decay. Hydrology is an important (if not the most important) factor inthe formation and functioning of peat swamp ecosystems. The hydrology of a peat swampdepends on the climate, topographic conditions, natural subsoil, and drainage base. Anychanges in the hydrology, especially those from the introduction of drainage, will have often-irreversible effects on the functioning of these fragile ecosystems. A better understanding ofthe hydrology of peat swamps will make it possible to develop and manage them in a moresustainable way.

2. Climate

The climate in Borneo is characterised by its uniform temperature, high humidity, and highrainfall intensity. The mean monthly temperature is stable and varies between 24°C and27°C. According to the Köppen classification system, which is based on precipitation andtemperature, the climate is a tropical rain climate without a dry season and a long-term meanprecipitation in the driest month higher than 60 mm (Class Af). The climate is influenced bytwo monsoon winds, namely the Northeast Monsoon from November to February and theSouthwest Monsoon from April to September.

2.1.1 EvaporationThe average evaporation is fairly constant, varying between 3.5 mm/d and 4.8 mm/d with atotal of around 1500mm per year (Table 1).

Table 1 Mean monthly evaporation and rainfall (mm) in Central Sarawak and SouthKalimantan

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec YearMukah, Central Sarawak:Evaporation 116 119 140 136 136 133 131 137 128 129 109 115 1529Rainfall 626 428 323 179 168 168 174 187 251 266 323 530 3623

Banjarmasin, South Kalimantan:Evaporation 109 111 125 133 125 117 126 136 143 139 115 114 1492Rainfall 436 298 323 269 206 156 156 98 70 141 273 397 2823


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2.1.2 RainfallFor the peat swamps, rainfall, in particular the rainfall that is in excess of evaporation, is themost important hydrology parameter. The annual rainfall is much higher than the annualevaporation (Table 1). The rainfall, however, is much more irregular, both in time and space.Along the coast of Sarawak, the annual rainfall varies from 2800 mm to 4700 mm (Table 2)with an overall average of around 3600 mm. In South Kalimantan, rainfall is significant lower,varying between 1900 and 3000 mm per year with an overall average of around 2800 mm.Differences is space (Figure 1) are linked closely to the average rainfall intensity and not somuch to the number of days of rainfall.

Table 2 Total annual rainfall at Mukah Airfield, Central Region of Sarawak

Year Rainfall(mm) Year Rainfall

(mm) Year Rainfall(mm)

1965 3429 1977 4159 1989 4099

1966 3291 1978 3387 1990 3272

1967 3892 1979 3066 1991 3283

1968 3401 1980 3486 1992 33191969 3717 1981 3739 1993 34541970 3877 1982 3796 1994 40311971 4516 1983 4631 1995 38091972 2878 1984 4453 1996 38131973 3823 1985 3560 1997 27481974 3478 1986 4116 1998 31981975 3742 1987 2783 1999 29851976 3147 1988 4698


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Figure 1 Map of the mean annual rainfall isohytes in the Central Region of Sarawak.

The rainfall is also not well distributed over the year (Figure 2). In the coastal region ofSarawak, during the Northeas t Monsoon, when rainfall may exceed 600 mm/month, thewettest months are December–February. During these months rainfall can exceed 300 mm/d(Table 3). During the dry season (March–November) the average rainfall is about 200–300mm/month, which still exceeds the rate of evaporation. This is not the case in SouthKalimantan, where during the driest months (August and September) evaporation exceedsrainfall.

Mukah, Sarawak

0100200300400500600700

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

(mm

) PEto


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Figure 2 Mean monthly rainfall and evaporation in a) Mukah, Central Sarawak andb) Banjarmasin, Central Kalimantan

Table 3 Rainfall duration frequency in for two rainfall stations in the Central Region ofSarawak (DID)

Rainfall (mm) for various return periods

Sibu Airport (1953–1990) Mukah JKR (1934–1990)Duration(days)

5 years 10 years 5 years 10 years

1 156 178 264 307

2 181 202 326 377

3 210 233 381 444

5 253 278 480 563

7 294 326 535 628

14 427 471 702 808

30 624 681 1056 1213

2.1.3 Dry spellsDespite the tropical rain climate, the peat swamps suffer from water shortage duringprolonged dry period. In Sarawak, these dry periods that last for two weeks and havenegligible rainfall (<10 mm/fortnight) occur at least once or twice every year. The averagefour-week minimum rainfall varies from 50 to 100 mm. This amount is often less than theevapotranspiration, which is around 3 mm/day (or 84 mm every four weeks). In SouthKalimantan, the average dry season (monthly rainfall < 100 mm) can last for 3 to 4 months(Figure 3). During this period the rainfall deficit is around 100 mm. In extreme dry years(probability of exceedance 10%) this period can be extended to seven months. Withoutwater conservation, evaporation can lead to slight but persistent moisture deficits and so toincreased oxidation. In very dry years, the water table can fall below 1 m below soil surface.

Banjarmasin, Kalimantan

0100200300400500600700

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

(mm

)

PETo


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3 Topography

The peat swamps are bordered by the sea and by rivers, and have a dome-shaped surface(Figure 3). On the seaward side of the swamps, the borders consist of mudflats or sandybeach deposits. On the landward side, there are sometimes very narrow levees or no leveesat all. Along the rivers, levees of mineral soils form the boundaries. These levees are proneto flooding.

Figure 3 Topography of a peat dome (Melling 2000).

3.1 Surface topographyThe youngest peat swamps are found close to the coast. The ground surface of the youngswamps rises gently from the edges to form a convex shape (dome) with slopes of 1–2m/km. The highest point may be only 3–4 m above mean sea level. In the older, moredeveloped swamps, the convexity at the edges is more pronounced. A rise of 6 m over thefirst 250 m has been recorded. The central bog planes are almost flat, with a rise of less than0.5 m/km (Tie, 1991).


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3.2 Mineral subsoilThe basal mineral substrata of the peat swamps consist of sand or clay. The topography ofthe subsoil usually drops gently from the riverbanks or the coast to the centre of theswamps. This is what gives the peat deposits their characteristic lens-shaped cross-section.Where old riverbeds or levees are buried under the peat, there are small rises and drops inthe mineral substrata. Levelling of transects across various peat domes has shown that themineral substrata usually lie within 1–2 m above or below mean sea level (Figure 4). Themineral substratum under peat soils is often sulphidic. When this is the case, the peat layeracts as a protective wet sponge that keeps the underlying mineral subsoil in a wet,anaerobic condition. Once the peat has disappeared, however, the mineral subsoil willsurface, available pyrite will oxidise, and acid sulphate soils with very low pH values willform. Acid sulphate soils are problem soils that can be farmed only under conditions of well-controlled water management. Box 2 presents the feasibility of farming on acid sulphate soilsat different locations in the landscape.

Figure 4. Cross-section through a peat dome (PS Konsultant 1998)

3.3 CatchmentsThe dome-shaped surface of the peat swamps causes rainwater to drain off to differentsides. This phenomenon divides a peat swamp into several catchments (Figure 5). Acatchment is the area from which a stream collects water. Water divides form the boundariesof a catchment. Contrary to upland catchments, peat swamps have minimal topographicgradients, which makes it difficult to distinguish the catchment boundaries. To establishcatchment boundaries, it is best to combine data from survey lines with information on landuse, vegetation, and drainage patterns. Aerial photographs, maps, and satellite images (e.g.LANDSAT images) can provide valuable information. Because catchments in lowlandswamps have a low relief and are often inter-linked, the catchment boundaries are not fixed.Under natural circumstances these boundaries can vary seasonally, due to extreme rainfall,drought, or tidal effects.

-2

-1

0

1

2

3

4

5

0 1000 2000 3000 4000 5000 6000 7000 8000

Chainage (m)

Leve

l (m

)

DrainStream

Streams

Batang BalingianPEAT PEAT

MINERAL SUBSOIL

South China Sea


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Jemoreng catchment

7 m

6m

5 m

5 m

4 m

0 5 K i l o m e t r e s

N

Matu

B a t a n g M atu

3 m2m

S e k aan c a t c h m e n t

K u a l a M a t u

Figure 5 The catchment of a peat swamp (adapted from SWRC,1997). The dotted linesare the catchment boundaries. Also visible are contour lines of the Jemorengcatchment.

Certain types of land use (e.g. intensive farming and logging of forests) influence thegroundwater table and the boundaries of the catchments. The groundwater table in adrained area influences the water table in an adjacent non-drained area. Activities that havelong-term impacts are:� Digging of transportation canals that connect streams or rivers� Construction of drains� Pumping of groundwater� Building of roads through swamp lands� Drainage for agriculture.

As drained areas influence water tables in contiguous undrained areas, so, too, docatchment areas influence each other. This influence can cause the hydrology of lowlandpeat swamps to behave in uncontrolled or unexpected manner. Activities or projects thattake place in one catchment can influence activities in another and lead to conflicts ofinterest. It is easy to imagine the conflicting interests that would occur if, for instance, anagricultural project were adjacent to a water-supply area. The drainage in the agriculturalproject would lower the water table in the water-supply area, reducing the volume of wateravailable for domestic and industrial use.

3.2.3 Drainage BaseTidal ranges along the Borneo coast may vary from about 2 m to almost 6 m. The influenceof the tide is not restricted to the coastal area. It can move up rivers, reaching as far as 200km inland. Most of the peat lands are located in areas under tidal influence.


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3.2.4 DrainabilityDrainability refers to drainage by gravity, thus drainage without the aid of mechanicaldevices such as pumps. Different classifications are used in Indonesia and Malaysia. InSarawak, the long-term drainability is assessed on the basis of the mineral subsoil level,rather than the present (peat) ground surface (Box 1). The drainage base is defined as thewater level in the adjacent river or stream, below which natural drainage by gravity cannot beachieved (conveyance losses add an additional hydraulic head of at least 20cm perkilometre). In Indonesia, four land categories are commonly distinguished in tidal swampareas. The classification is mainly based on the potential for irrigation, but they have beadjusted to incorporate the drainage potential (Box 2).

Gravity drainageGravity drainage of an agricultural scheme in peat lands is possible when the water levelinside the scheme is higher than the (outside) water level of the river. In the lower-lyingareas, drainage may be possible only during low tides. In such a case, control structures andbunds are needed to prevent water entering the scheme area during high tide. Adequatestorage should be available inside the scheme, so that it is possible to keep the excesswater until it can be discharged during low tide.

Box 1 Drainability classes (Agrosol, 1997)

Figure 6 The drainability concept.

Drainability refers to drainage by gravity, thus drainage without the aid of mechanicaldevices such as pumps. Long-term drainability is assessed on the basis of the mineralsubsoil level, rather than the present (peat) ground surface. The drainage base is definedas the water level in the adjacent river or stream, below which natural drainage by gravitycannot be achieved (conveyance losses add an additional hydraulic head of at least 20cmper kilometer). To assess drainability, the following classification is used:


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Very good: Mineral subsoil surface is above the drainage base established at High WaterLevel (HWL); therefore natural drainage can be achieved at all tide levels,including high tides.

Good: Mineral subsoil surface is between drainage base established at HWL andMean Water Level (MWL).

Moderate: Mineral subsoil surface is between drainage base established at MWL and LowWater Level (LWL).

Poor: Mineral subsoil surface is below drainage base established at LWL; thereforenatural drainage cannot be achieved at any tides, even low tides.

Note: This classification differs slightly between the various studies (see e.g. Alan Tan and Lim Hiok Hwa,1999).

Box 2 Tidal land Classification in Indonesia (AARD & LAWOO 1992)

class A class B class C class D

distance from river mouth

elevation of thewater level

average river water le

vel

mean sea level

high tide

low tide

rivermouth

land

Figure 7 Tidal land classification is based on the water levels in the main rivers.

Type A Areas between mean low tide and mean neap tide. Daily flooding and drainage. Theseareas appear close to the sea. The potential for irrigation and drainage is good becausethere is sufficient tidal fluctuation to allow a daily flooding and drainage of the soil surface

Type B Areas between mean neap tide and mean spring tide. Springtide flooding and dailydrainage. Irrigation is only possible during springtide. Absence of daily flooding requireswater conservation measures. Daily drainage is always possible.

TypeC Area above spring tide. No tidal flooding, permanent drainage. In these areas drainage ofexcess rainfall is always possible due to absence of high water levels in the canals.

TypeD Area outside the influence of daily tide. No tidal flooding, limited drainage. Due to theabsence of a drainage infrastructure, this area can not be drained. The water table dropsduring the dry season when evaporation exceeds rainfall.


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The assumption is that a peat swamp can be economically drained on a long-term basis onlyif the mineral subsoil level is above the mean water level in a nearby stream, river, or sea,into which the drainage water will be discharged. At present, also areas are being developedwhere the mineral subsoil is below mean sea level. Gravity drainage is possible in thesepeat swamps because of their dome-shaped morphology. Uncontrolled drainage – and thesubsequent excessive subsidence – could put an end to this quickly: it may take 50 to 750years before the overlaying peat soil has disappeared.

Pumped drainageCurrently, pumped drainage of peat swamps is not an option, and the drainability of areasthat lie below mean water level is classified as moderate or poor. In Mukah, a designrainstorm with a return period of five years may produce 480 mm of rain in 5 days. If weneglect the storage within the area, 11 l/sec/ha will have to be evacuated in this five-dayperiod. Pumped drainage might not be an option at present, but it might be one in future.Then, and on a limited scale, it might be more economical for crops with a very high rate ofreturn (e.g. horticultural crops). The alternative is to give the land back to nature.

3.2.5 Water ManagementPeat under natural conditions is waterlogged for most time of the year. Using peat land foragriculture requires a water management system that will lower the water table andguarantee a timely removal of excess rainfall. Peat, however, is a precious resource thatshould be handled with care to prolong its life. To avoid excessive subsidence, and toreduce water stress in dry periods, the level of the water table has to be controlled (Figure68.

Figure 8 Peat land requires a water management system that controls the water table.

The functions of the water management system are somewhat conflicting: on one hand thereis the removal of excess water, which requires unrestricted outflow conditions, and on theother hand is the control of the water table and water conservation, which can be achievedonly by restricting the outflow. To fulfil these requirements, two conditions have to beconsidered: the normal-water-level criterion for normal (= average) conditions and the high-water-level criterion for short periods of extreme rainfall:


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� The normal-water-level criterion refers to maintaining the water level at a level that isdeep enough to enhance the agricultural use of the land but, at the same time, shallowenough to sustain the peat;

� The high-water-level criterion refers to removing excess rainfall during extremeevents.

The design of the water management system should also be based on the specific soilhydraulic characteristics of peat (i.e. on the very high infiltration rate, storage capacity andpermeability). Because of these unique characteristics, excess rainfall will not be removedas surface runoff but mainly as groundwater runoff. For conditions in Borneo, with its humidclimate and prolonged periods of rather uniform rainfall, the steady-state approach (e.g. theHooghoudt Equation) can be used to calculate drain spacing. The simplicity and the limitedrequirement of input data make it very suitable. The spacing of the drains should be basedon the drainage requirements during normal-water-level conditions and the dimensions ofthe drains on the high-water-level conditions.

The design water level in the water management system will depend on the seasons. Duringthe monsoon season a lower level will have to be maintained to increase the dischargecapacity and during the dry season a higher level will have to be maintained to conservewater. Consequently, structures are needed to control the water levels in the system.Because peat is so highly permeable, we recommend a cascade of closely spacedstructures with small differences in head. The dynamic storage capacity in the drainagesystem is small compared to the recharge by excess rainfall and the correspondingdischarge. Therefore it is possible to use the steady-state approach for the design. Theabove considerations result in a water management system with narrowly spaced drains incombination with an intensive network of control structures. As a consequence ofmaintaining high water levels the percentage of the area occupied by the water managementsystem will be high: between 15 and 20% compared to less than 5% in mineral soil areas.

The layout of the water management system should make use of the dome-shapedtopography of the peat lands. Field drains should be located parallel to the contour lines andcollector drains perpendicular to these. Water storage is needed to replenish thegroundwater during prolonged dry periods. The best place to store water is in the centre ofthe peat dome.

To minimise the effects of rapid initial subsidence in the first few years after reclamation, werecommend a two-phase approach to implementing the water management system. In thefirst phase, the area is opened and the main drainage system is installed. In the secondphase, the field drainage system is installed. A time delay of at least 1 to 2 years isrecommended between the two phases. We must remember, however, that the continuoussubsidence of the peat will cause the land’s surface to fall and make it necessary to upgradethe system at regular intervals, probably every 5 to 10 years. Continuous subsidencerestricts the future drainability. In most peat swamps, the subsidence will ultimately lead to ashift from gravity drainage to pumped drainage or, if this is not feasible, to a return to nature.


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4 The water balance in a peat swamp

The lowland peat swamps of Borneo are completely rain-fed. No flow from upland areasenters these swamps. The rainfall either evaporates or is transported from the swamps asnear surface run-off, inter-flow, or groundwater flow. The general water balance of a peatswamp can be written as follows:

P = E + Q + ∆∆∆∆SWhere:

P total rainfall (m)E total evapotranspiration (m)Q total discharge (m)∆S change in storage (m)

Under natural conditions, the groundwater table will rise due to rainfall and fall due toevapotranspiration and the outflow of excess rainfall by surface flow, groundwater flow, orinterflow. The resulting change in storage can be considerable over short periods (i.e. daysor weeks). Over the years, however, this change in storage will be negligible compared tothe total in- and outflow.

4.1 Water levelsThe fluctuation of the water level in a peat swamp depends mainly on rainfall becauseevaporation and (groundwater) outflow are fairly constant. During the wet season(November–February), the rainfall always exceeds the combination of evaporation (Figure 2)and groundwater run-off. Thus, in this period, the water level is always above the soil’ssurface (Figure 9). These wet conditions are favourable for peat accumulation. During thedrier months of the year, when dry spells can last for weeks, the water level in the swampcan drop below the soil surface. Observations in different swamps have shown that the dropof the water table is not the same throughout the whole swamp. Between the dry and wetseasons, the water table in a peat swamp can fluctuate up to 0.58 m near the edge of a peatdome (Tie, 1991). In the centre, the seasonal fluctuation is slightly smaller (0.45 m). Therelatively steep periphery has a deeper water table than the flat centre. Under naturalconditions, fluctuation of the water table will be as follows (Ong and Yogeswaran, 1991):• On hot and non-rainy days, surface water may drop 10–15 mm daily.• When initial water levels are below soil surface, the drop is 5–10 mm.• Water levels drop fastest between 0900 hrs and 1700 hrs• The maximum drop of the water table depends on the length of the dry spell.• The maximum depth of the water table varies for different swamps from 0.3–1.0 m below

soil surface.


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Figure 9 Example of the fluctuation of the water level in a peat swamp in Penibong,Central Sarawak in 1991 (Ong and Yogeswaran, 1991).

4.2 Discharges / Run-offUnder natural, undrained conditions, there are three types of outflow from the peat body of aswamp:• Surface run-off or depression flow;• Sub-surface flow or interflow, and;• Deep groundwater flow.

Because of the predominantly high water levels in a peat swamp, surface flow will accountfor most of the natural outflow (Table 4). In the study, conducted in the Kut Catchment in


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Central Sarawak, groundwater flow formed only a small component of the water balance, butit was still about 170 mm/year. Interflow, which is defined as the flow that takes placethrough an upper soil layer of higher permeability, was about 340 mm/year. Because theresponses of the swamp were measured in an artificial drain, the results of the study maynot be fully representative of a natural situation.

Table 4 Water balance of Kpg. Kut catchment, Pulau Bruit (June 1988–June 1989)(SWRS, 1997)

P (mm/y) E (mm/y) Q (mm/y)

2789 1248 1541

Qsurface Qinter Qground

As a percentage of Q: 67% 22% 11%

As a percentage of P: 37% 12% 6%

4.3 Storage CapacityIn peat, rainfall can easily infiltrate into the soil. The storage capacity of peat works as abuffer during times of heavy rainfall; the deeper the water table, the larger the storagecapacity. Although tropical peat has a high drainage pore space (in Sarawak it variesbetween 0.3 and 0.85), the water storage capacity in the peat is relatively small, becauseunder natural, undrained, conditions, the water table fluctuates around the soil surfaces.Even in dry periods, when the water table can drop to 0.6 m below soil surface, the storagecapacity in the soil will only be in the same order of magnitude as rainstorm with a 1-yearreturn period.


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5 Gaps in knowledge

5.1 Climate changes:5.1.1 Rainfall: total rainfall and distribution5.1.2 Dry periods: frequency and duration

5.2 Hydrology5.2.1 Run-off under natural conditions: percentage Surface run-off or depression

flow, sub-surface flow or interflow, and deep groundwater flow.5.2.1 Water storage capacity of reclaimed peat soils5.2.2 Relation between water table and peat accumulation or oxidation5.2.3 Soil hydrologic characteristics of the deep peat: hydraulic conductivity,

saturated thickness, transmissivity, drainable pore space and storativity.5.2.4 Catchment changes after reclamation5.2.5 Effect of buffer zoning

5.3 Water Management5.3.1 Water level control: maintaining a high water table.5.3.2 Water storage in the canal system/ removal of excess rainfall5.3.3 Effect of subsidence on the canal system5.3.4 Operation and maintenance of the water management system


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References

Agrosol. 1997. Soil/Peat Drainability and Oil Palm Feasibility Studies of Balingian RuralGrowth Centre.

Alan Tan and Lim Hiok Hwa 1999. 1999. Peat hydrology and water management. In:Proceedings Workshop on Working Towards Integrated Peatland Management forSustainable Development, 17-18 August 99, Kuching, 11 pp.

Department of Irrigation and Drainage & LAWOO, 1996. Western Johore IntegratedAgricultural Development Project, peat soil management study. Kuala Lumpur,Malaysia and Wageningen, The Netherlands.

Department of Irrigation and Drainage. 1962/97. Hydrological Yearbooks: edition 1962-1997.Department of Irrigation and Drainage, Sarwak.

Department of Irrigation and Drainage. 2001. Water Management Guidelines for AgriculturalDevelopment in Lowland Peat Swamps of Sarawak. Department of Irrigation andDrainage, Sarawak.

Kselik, R.A.L., K.W. Smilde, H.P. Ritzema, Kasdi Subagyono, S. Saragih, Mauliana Damanikand H. Suwardjo. 1993. Integrated research on water management, soil fertility andcropping systems on acid sulphate soils in South Kalimantan, Indonesia. In: D.L. Dentand M.E.F. van Mensvoort (eds.), Selected papers of the Ho Chi Minh City Symposiumon acid sulphate soils. ILRI Publication 53: pp. 177-194.

Melling, L. 2000. Dalat and Mukah sago plantation peat soil study. Final Report. Soil Branch,Department of Agriculture Sarawak.

Ong,B.Y. and Yogeswaran,M., 1991. Peatland as a resource for water supply in Sarawak.Proceedings of the International Symposium on Tropical Peatland. Kuching, Sarawak.

PS Konsultant 1998. Detailed Design and Construction Supervision of Flood Protection andDrainage Facilities for Balingian RGC Agricultural Development Project, Sibu Division,Sarawak (Inception Report), Department of Irrigation and Drainage, Kuching. pp.24.

Ritzema, H.P., Mutalib Mat Hassan, A. and Moens, R.P. 1998. A New Approach to Watermanagement of Tropical Peatlands: A Case Study from Malaysia. Irrigation andDrainage Systems 12 (1998) 2, p.123-139.

Ritzema, H.P. and T.P. Tuong. 1994. Water-management strategies as a tool for thesustainable use of acid sulphate soils. Regional Workshop on the sustainable Use ofCoastal Land in South-east Asia, 18-22 April 1994, Asian Institute of Technology,Bangkok, 34 p.


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Sarawak Water Resources Council,1997. Sarawak Water Resources Study Projects - FinalReport submitted by PS Konsultant, Montgomery Watson, Australia, The Centre forWater Reseach (CWR).

Tie, Y.L. and Esterle, J.S., 1991. Formation of lowland peat domes in Sarawak, Malaysia.Proceedings of the International Symposium on Tropical Peatland. Kuching, Sarawak.

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