2nd International Conference on Managing Rivers in the 21st Century: Solutions Towards Sustainable River Basins

Deforestation Effect to the Runoff Hydrograph at Sungai Padas Catchment

JOSEPH DINOR, Master Student (M.Sc.), River Engineering and Urban Drainage Research Centre (REDAC), Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia.

NOR AZAZI ZAKARIA, Professor & Director of REDAC, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang Malaysia.Email: [email protected]

ROZI ABDULLAH, Assoc. Prof. & Lecturer, School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia. Email: [email protected]

AMINUDDIN AB GHANI, Assoc. Prof. & Deputy Director, REDAC Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang Malaysia. Email: [email protected]

Keywords: Deforestation, HEC-HMS, SCS-CN, Hydrograph estimation, Design rainfall

ABSTRACT Deforestation activities have been widely known as one of the devastating factors to the river system and ecological system in a catchment. Severe destructions of forest always brings about a number of interferences to the natural catchment such as increase the surface runoff in the stream and rivers, soil erosions, sedimentation in the rivers or streams, degradation of water quality, elimination of the flora and fauna, and destruction of the wild life habitat in the jungle. The present study is intending to develop a hydrologic model for the Sungai Padas catchment and to investigate the effect of land cover changes to the runoff hydrograph from the catchment using HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System), which has been established by USACE (United State of America Corps of Engineers). Sungai Padas catchment experienced several deforestation activities particularly of commercial loggings and agriculture at some areas such as at the upstream of Tambunan catchment, Sook catchment, and Sipitang catchment. The analyses cover from the determination of the land cover from the topographic maps, and hydrologic analysis such as rainfall and discharge data. The design rainfall data from the HP-26 manual (Hydrologic Procedure no.26 for Sabah dan Sarawak) was applied to predict the runoff hydrograph for 2 year ARI (Average Recurrence Interval) within 72 hours rainfall duration. The average rainfall distribution of this catchment was estimated using the Thiessen Polygon Method, whereas, the loss model, transform model (catchment routing), baseflow model, and channel routing were analyzed by applying the SCS curve number, Clark Unit Hydrograph, recession method, and Muskingum method, respectively. The evaluation of the future runoff hydrograph due to the conversion of the disturbed area into large scale agriculture such as rubber and oil palm plantation was also carried out The results of the study that employed 2 year ARI for 72 hours duration indicated that the simulated runoff hydrograph at JPS Beaufort discharge station increased by 5% due to the increased of deforested area (none-cultivated) by 11%. In the case that the deforested areas (11%) are assumed to be cultivated with large scale agriculture such as rubber and oil palm plantation, the runoff hydrograph would increase by 25%. The results imply that the higher surface runoff resulted from the conversion of deforested area into large scale agriculture compared to the none-cultivated deforested area.

Keywords: Deforestation, HEC-HMS, SCS-CN, Hydrograph peak estimation, Design rainfall

1 Introduction catchment which has less altered landuses. Deforestation activities will also lead to the decrease of catchment average In general, land cover or land use changes usually result in the rainfall intensity and increase temperature due to the decrease of changes of the catchment hydrologic responses to the rainfall. evapotranpiration and the radiative effect of CO2 (Costa and Also, land use disruption such as deforestation activities causes Foley, 1998). The effect of deforestation to the runoff peak is many adverse impacts to the water quality and quantity as many also depending on the catchment profile. A study carried out by bared areas at the upstream are exposed to the rainfall. The Stednick (1996) in the United States indicated that the runoff cleared areas will no longer capable to absorb and retain some peak was effected by smaller percentage of land use changes at amount of moisture from the rainfall, which play as an the steeper or mountainous area compared to the plain area. important role to reduce the surface runoff and to maximize the This implies that the deforestation activities have greater impact soil retention capacity within the subsoil surface. This factor on the runoff and water yield when practiced at the steeper will result to the shorter time of concentration of the catchment. upstream area. Deforestation effect on the annual water yield is A study conducted by Costa et.al (2002) at the Tocantins River, also influenced by several factors such as the type of vegetation Porto National with the area of study around 175, 360 sq.km., cover, climate and catchment sizes (Sun and Li, 2005). The indicates that in large river basin, the two most likely drivers of study carried out by Sun and Li in China implies that the long-term discharge modification are precipitation variability differences of impact on catchment annual water yield among and changes in landuse in the upstream catchment. It has also different forest types were somewhat different with those from indicated that the hydrograph peak from the catchment which other countries; there is a higher water yield changes in humid has more altered landuses occurs earlier than that from the regions compared to that of drier regions; and the water yield is

351 Rivers‘07 June 6-8, 2007, Riverside Kuching, Sarawak, Malaysia consistent in both small and large catchment due to the the hydrologic modeling in Sungai Padas catchment using the deforestation effect, but there is a large fluctuation in HEC-HMS 2.2.2. Several model most sensitive parameters have streamflow responses to forest cover changes in smaller been analyzed by performing some sensitivity analyses such as catchments. Bruijnzeel (1990) pointed out that the changes initial loss, Soil Conservation Service Curve Number (SCS CN) in infiltration associated with the land use changes overrides the value, the catchment storage coefficient (R), recession constant effect of reduced evaporation, then a shift in the streamflow of the baseflow, and Muskingum-K for the channel routing. The regime may be expected with increased peaks during the rainy time of concentration (tc) values of the catchment were selected season and lowered flows during the dry season. Deforestation based on the comparison results from five (5) methods such as increases surface runoff and catchment response to rainfall is Izzard, Kerby, Kirpich, Kinematic wave, and Bransby William highly variable and unpredictable (Hibbert, 1965). The removal formulas. The model was calibrated using the rainfall and of forest almost invariably leads to higher streamflow and streamflow data of May 1991 and validated using the rainfall- reforestation of open land generally reduces the overall runoff event of June 1992. Both data used in the calibration and streamflow (Bosch and Hewlett, 1982). Studies about validation process were consisted of multiple rainfall events, deforestation effects to the runoff were leading to one general which have produced the annual highest runoff hydrograph conclusion that it causes the increase of runoff hydrograph. peak within the range of events. The rainfall temporal distribution calculation was performed based on the DID Hydrological Procedure No.1 (HP-1). The DID Hydrological 2 Methodology Procedure No.26 (HP-26) which has been designed for Sabah and Sarawak state was adopted as the design rainfall guideline The study process (Figure 1) started with the collection of within 72-hours duration. The deforestation analysis was then rainfall data, discharge data, topography maps, land-cover, and performed using the calibrated model, rainfall temporal soil map. The rainfall data, discharge data, catchment distribution and the design rainfall informations. The delineations, and land-cover map are derived from Sabah deforestation analysis has been carried out by applying at 2 year Department of Irrigation and Drainage (Sabah DID), whereas within the 72-hours duration period. the soil map was acquired from Sabah Department of Agriculture (Sabah DOA). These informations are applied for

DATA COLLECTION

DETERMINATION OF THE CATCHMENT PARAMETERS

USING HEC-HMS MODEL SENSITIVITY ANALYSIS OF THE HEC-HMS MODEL PARAMETERS

MODEL CALIBRATION

MODEL VALIDATION

ANALYZING THE CATCHMENT RAINFALL DETERMINE THE CATCHMENT DESIGN DETERMINE THE APPROPRIATE HISTORICAL DATA TO DETERMINE THE RAINFALL TEMPORAL DISTRIBUTIONS RAINFALL DURATION (e.g. 24 and 72-hours) CATCHMENT RAINFALL TEMPORAL DISTRIBUTIONS USING THE HP.26 FOR ACCORDING TO THE ACCORDING TO THE HP-1 PROCEDURE TIME OF CONCENTRATION VALUE 2, 5, 10, AND 20 YEARS ARI

CATCHMENT RESPONSE ANALYSIS

ANALYSIS RESULTS

CONCLUSIONS AND RECOMMENDATIONS

END

Figure 1 Research Methodology

352 2nd International Conference on Managing Rivers in the 21st Century: Solutions Towards Sustainable River Basins

3 The Study Area

Padas 3.1 Geographical Features U Catchment

The research has been carried out for Sungai Padas catchment, located at the south-western part of Sabah, lies between latitude 030 30’(N) and 060 10’(N) and longitude 1150 10’(E) and 1160 50’(E). The catchment is the second largest catchment in Sabah, which comprises of five (5) districts include Tambunan, Keningau, Tenom, Sipitang, and Beaufort district. The fraction of the catchments has been divided into Padas Downstream Catchment 152 smaller subcatchments according to the geographical (Sub-E) (519 sq.km) Pegalan Upstream topography features. The total area of the catchment is Catchment Pegalan Downstream (Sub-A) 2 Catchment approximately 8,668 km . There are three (3) major river (Sub-D2) (2,238 sq.km) (664 sq.km) Sook Catchment tributaries which lead to the catchment division into three river (Sub-B) Padas Mid-Catchment (1,733 sq.km) Catchment (Sub-D1) systems, they are Sungai Pegalan catchment, Sungai Sook Padas Upstream (267 sq.km) Catchment (Sub-C) catchment, and Sungai Padas catchment (upstream). The (3,248 sq.km) cathmnent area has been divided into six (6) subcatchments for the study purposes as shown in Figure 2, this includes Sub-A, LEGEND B, C, D1, D2, and E. Primary and secondary forests are the Pegalan Upstream Catchment main vegetation cover of the catchment area (Figure 3). The Sook Catchment Padas Upstream Catchment primary forest is the undisturbed natural forest which is mostly Mid-Padas Catchment covering the hilly and mountainous area at the upstream, Pegalan Downstream Catchment Padas Downstream Catchment whereas secondary forest is the disturbed forest due to some deforestation activities such as loggings and agriculture which are mainly dominating the downstream at the lower elevation 01020304050KM area. The Sungai Padas catchment valley is mainly subjected to some agriculture activities such as paddy plantations, mix types of crops and some large scale agricultures such as oil palm and rubber. Urbanization areas are very small within the catchment Figure 2 Sungai Padas ca tchment subcatchments and they particularly located at the plain area near to the downstream. Small towns within the catchment are located at Tambunan, Keningau, Tenom, and Beaufort town. Smaller Tambunan towns are located Ansip, Biah, and Kemabong town. N Town In general, the catchment is mostly dominated by W E mountainous and hilly region with steep geographical surface S conditions particularly at the upstream areas. Most hilly region Keningau Town catchment rises up to 1230 m (4050 ft) above sea level. At the western part of the catchment the Crocker Range rises up to Ansip 1548 m (5080 ft) a.s.l. (above sea level). Witti Range and Town Maitland Range are lying as the catchment border at the eastern and south-eastern part of the catchment (Figure 4).

Sungai Pegalan and Sungai Padas proper is the major tributary of the Sungai Padas. Sungai Sook is the main tributary of the Beaufort Town Biah Sungai Pegalan where they joined near Biah town. Sungai Town Pegalan confluenced with the Sungai Padas at Tenom and continues flowing northwest, between the Crocker Range Tenom valley and the Tenom gorge to Beaufort. The river meanders Town across the Klias Peninsula and finally discharged at the river Kemabong mouth to the Brunei Bay. Town

LAND COVER (1984-1995) 3.2 Rainfall and Discharge Gauging Stations Farmstead Large scale agriculture Logged forest NOT INCLUDED Primary forest Secondary forest Five (5) rainfall stations were selected based on the availability Ur ban and the goodness of recorded data, as shown in Table 1. The Wetland agriculture weighted rainfall average for the catchment was estimated using 0 1020304050Kilometers the Thiessen polygon method, denoted as dash line in Figure 5.

There are four (4) discharge stations located at the outlet of each subcatchment of A, B and C. The final discharge station is located at the catchment most downstream at Beaufort (Figure Figure 3 Sungai Padas geographical features

5). The discharge stations are summarized as shown in Table 2.

353 Rivers‘07 June 6-8, 2007, Riverside Kuching, Sarawak, Malaysia

Padas Sg. Pegalan Catchment

RG(5663001)

n la ga e .P g S RG(5357003) DG(5357403) RG(5361002) DG(5261401) S g .P a DG(5261402) d a s

S

g

. S

o o k RG(5163002) Sg. Padas

Sg. Sook

RG(4959001) DG(4959401)

TELUK Sg. Padas BRUNEI

s a d

a

P .

g S

LEGEND

Rainfall Gage Station Discharge Gage Station Thiessen Line Main River Subcatchment boundary Sub-Subcatchment boundary TOTAL CATCHMENT AREA = 8,668 sq.km

01020304050KM Figure 4 Topographical features

Table 1 Rainfall Stations

Station Elevation Rainfall Station Figure 5 Rainfall and discharge gages Number (m) Tambunan Agriculture 5663001 680 Keningau Meteorologic 5361002 290 N

Sook 5163002 350 W E S Kemabong 4959001 228 JPS Beaufort 5357003 9.4

Table 2 Discharge Stations Discharge Station Elevation Catchment Station Number (m)

Sub – A Ansip 5261401 262

Sub – B Biah 5261402 258 Sub – C Kemabong 4959401 228

Padas JPS Beaufort 5357403 9.4 catchment

3.3 Land Cover LAND COVER (Before 1984) Farmstead Figure 6 and 7 show the landcover pattern before and after the Large scale agriculture NOT INCLUDED Primary forest year 1984. It is obviously seen that the deforestation area at the Secondary forest Urban catchment has been increased. The primary forest areas are Wetland agriculture reduced after the year 1984 due to the deforestation activities especially from logging works. The percentage of conversion of primary forest area into disturbed forest area at Sungai Padas 0 1020304050Kilometers catchment was approximately 11%. Disturbed forest includes Figure 6 Sungai Padas catchment land cover (Before 1984) all deforested areas such as secondary forest, logged forest and bared areas as displayed on the topographic maps.

354 2nd International Conference on Managing Rivers in the 21st Century: Solutions Towards Sustainable River Basins

3.4 Soil Types types (Figure 9). The soil type information indicated that the most dominant parental soil types within the Sungai Padas Soil types as provided by the Department of Agriculture (DOA) catchment is consisted of sandstone and mudstone that is of Sabah are classified according to the Food and Agriculture classified into soil Type-B. The area of Subcatchment-C and Organization-United Nations Educations, Scientific and Subcatchment-D1 and D2, are consisted of parent material soil Cultural Organization (FAO-UNESCO). Some countries are from sandstone, mudstone, and alluvium, which are classified using the Textonomy soil classification system in which soil into Type-C soil. Soil classes imply the soil infiltration rate, types are classified into four major soil classes, that is A, B, C, according to the SCS soil classification standard. Soil Type-B and D. The most abundant soil types in Sungai Padas catchment and C has the moderate infiltration rates, which potentially to are soil class B, C and D (Figure 8) based on the parental soil produce moderate runoff (USDA).

N N

W E W E

S S

Sub_a-e(simple).shp Soilmap_combined.shp Acic igneous rocks Al luvi um Alluvium & alluvium derived fr. basic or ultrabasi Al luvi um & pe at Alluvium derived from ultrabasic rocks Alluvium, sandstone & mudstone Basic igneous rodks & alluvium Basic intermediate igneous rocks Padas_soil.shp Calcareous alluvium Collovium, sandstone & mudstone B Limestone Mudstone & alluvium C Mudstone & sandstone Mudstone, sandstone & miscellaneous rocks D Sandstone Sandstone & mudstone Sandstone, mudstone & alluvium Sulphidic alluvium, sulphidic peat & alluvium Ultrabasic igneous rocks

Figure 8 Soil classification at Sungai Padas catchment Figure 9 Parental soil types at Sungai Padas catchment (Source: Department of Agriculture, Sabah, Malaysia)

4 ANALYSIS RESULTS

4.1 Calibration and Validation The calibration and validation results are evaluated using R2 The HEC-HMS model has been calibrated and validated by values as shown in Figure 12 and 13, respectively. Table 3 applying the rainfall and runoff data of May 1991 (Figure 10) summarizes the model parameters that have been used in the and June 1992 (Figure 11), respectively. analysis.

355 Rivers‘07 June 6-8, 2007, Riverside Kuching, Sarawak, Malaysia

RUNOFF HYDROGRAPH AT ANSIP DISCHARGE STATION RUNOFF HYDROGRAPH AT BIAH DISCHARGE STATION (May 1991 - Calibration) (May 1991 - Calibration) 140 140 Observed Observed 120 120 Simulated Simulated 100 100

80 80

60 60 Discharge (cms) (cms) Discharge 40 40

20 20

0 0 0 50 100 150 200 250 300 350 400 450 0 50 100 150 200 250 300 350 400 450 Time (h) Time (h)

RUNOFF HYDROGRAPH AT KEM ABONG DISCHARGE STATION RUNOFF HYDROGRAPH AT JPS BEAUFORT DISCHARGE STATION (May 1991 - Calibration) (May 1991 - Calibration) 800 1200 Observed Observed 700 1000 Simulated Simulated 600 800 500 400 600 300 400 Discharge (cms)

Discharge (cms) Discharge 200 200 100 0 0 0 50 100 150 200 250 300 350 400 450 0 50 100 150 200 250 300 350 400 450 Time (h) Time (h)

Figure 10 Calibration results for the Sungai Padas HEC-HMS model

RUNOFF HYDROGRAPH AT ANSIP DISCHARGE STATION RUNOFF HYDROGRAPH AT BIAH DISCHARGE STATION (June 1992 - Validation) (June 1992 - Validation) 300 140 Observed Observed 250 120 Simulated Simulated 100 200

80 150 60 100 Discharge (cms) Discharge (cms) 40 50 20

0 0 0 50 100 150 200 250 300 350 400 450 500 550 600 0 50 100 150 200 250 300 350 400 450 500 550 600 Time (h) Time (h)

RUNOFF HYDROGRAPH AT KEM ABONG DISCHARGE STATION RUNOFF HYDROGRAPH AT BEAUFORT DISCHARGE STATION (June 1992 - Validation) (June 1992 - Validation) 1200 800 Observed 700 Observed 1000 Simulated 600 Simulated 800 500 400 600

300 400 Discharge (cms) Discharge (cms) Discharge 200 200 100 0 0 0 50 100 150 200 250 300 350 400 450 500 550 600 0 50 100 150 200 250 300 350 400 450 500 550 600 Time (h) Time (h)

Figure 11 Validation results for the Sungai Padas HEC-HMS model

Hydrograph Peak Comparison at JPS Beaufort Discharge Station Hydrograph Volume Comparison at Beaufort Discharge Station (May 1991 - Calibration) (May 1991 - Calibration) 1200 450 400 R2 = 0.9832 1000 R2 = 0.9435 350 ) 3 m

800 6 300 250 600 200 400 150 Simulated (cms) Simulated (1 x Simulated 10 200 100 50 0 0 0 200 400 600 800 1000 0 100 200 300 400 500 600 Observed (cms) Observed (1 x 106 m3)

(a) (b)

Figure 12 The R2 Values for hydrograph peak (a) and volume (b) at JPS Beaufort discharge station from the HEC-HMS model calibration for Sungai Padas catchment 356 2nd International Conference on Managing Rivers in the 21st Century: Solutions Towards Sustainable River Basins

Hydrograph Peak Comparison at JPS Beaufort Discharge Station Hydrograph Volume Comparison at JPS Beaufort Discharge Station (June 1992 - Validation) (June 1992 - Validation) 700 900 800 R2 = 0.8129 600 R2 = 0.9876 )

3 700

m 500 6 600 400 500 400 300 300 200 Simulated (cms) 200 (1 x 10 Simulated 100 100 0 0 0 100 200 300 400 500 600 0 200 400 600 800 1000 1200 Observed (1 x 106 m3) Observed (cms)

(a) (b)

Figure 13 The R2 values for hydrograph peak (a) and volume (b) at JPS Beaufort discharge station from the HEC-HMS model validation for Sungai Padas catchment

Table 3 Model Parameters of the HEC-HMS Model for Sungai Padas Catchment Subcatchment A B C D1 D2 E Area (km2) 2238 1733 3248 267 664 519 SCS-CN 49 57 46 52 50 47

Ia (mm) 7.6 4.2 12 1.8 3.2 2.2 Imp. (%) 6.2 1 1 0.5 0.5 5

tc (h) 19.56 23.98 26.23 13.88 13.92 10.48 Storage Coeff. (h) 60 90 30 50 50 50 Muskingum-K 0.5 0.3 0.3 1 1 1 Muskingum-X 0.2 0.2 0.2 0.2 0.2 0.2 Reccesion Ratio 0.2 0.2 0.2 0.2 0.2 0.2 Channel length (km) 98.6 94.8 105.87 32.71 46.41 26.97 Channel slope (m/m) 0.05 0.01 0.01 0.001 0.001 0.005 SCS-CN = Soil Conservation Service Curve Number Ia = Initial abstraction tc = Time of concentration

The SCS-CN values in Table 3 are adjusted at certain 4. 2 Deforestation Effect Analysis percentage to fulfill the local condition according to Equation 1 (Hassan, 2006). The HEC-HMS model hydrograph simulation analysis results at JPS Beaufort discharge station are shown in Figure 14, for CN'= CN(I) + []()CN(III) CN(I) * x% (1) ARI ranging from 2 to 20 years ARI within 72 hours duration. The results shown in Figure 14 are the comparisons of whereby, hydrograph resulted from different land cover pattern before CN’ = Adjusted Curve Number and after 1984 (based on Figure 6 and 7), in which CN(I) = Curve Number value for AMC(I) deforestation activities have been carried out within the CN(III) = Curve Number value for AMC(III) catchment. Figure 15 also shows the runoff hydrograph x% = Percentage of adjustment analysis results, but due the conversion of deforested area into agriculture. The results shown in Figure 15 are the comparison between deforested area with none-cultivated and cultivated The time of concentration value (tc) was estimated using the Kirpich method (Equation 2). with large scale agriculture.

0.77 L 1 tc = 0.0078 * ( ) * (2) 0.385 16 S whereby, tc = time of concentration (h) L = length of overland flow (m) S = slope (m/m)

357 Rivers‘07 June 6-8, 2007, Riverside Kuching, Sarawak, Malaysia

Hydrograph at JPS Beaufort (72h, 2yrs) Hydrograph at JPS Beaufort (72h, 5yrs) 1600 0 3000 0 1400 5 Design Rainf all (72h, 5y rs) 10 Des ign Rainf all (72h, 2y rs ) 2500 10 <1984 (Qpeak = 2457.30 cms) 20 1200 <1984 (Qpeak = 1303.10 cms) >1984 (Qpeak = 2558.10 cms) >1984 (Qpeak = 1370.80 cms) 15 2000 30 1000 20 40 800 25 1500 50

Q (cms) 600 30 Q (cms) 60

35 Rainfall (mm) 1000 70 Rainfall (mm) 400 40 500 80 200 45 90 0 50 0 100 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Time (h) Time (h)

Hydrograph at JPS Beaufort (72h, 10yrs) Hydrograph at JPS Beaufort (72h, 20yrs) 3500 0 4500 0 Design Rainfall (72h, 10yrs) 10 4000 Design Rainfall (20y, 24h) 10 3000 <1984 (Qpeak = 2893.70 cms) 20 3500 <1984 (Qpeak = 3773.50 cms) 20 >1984 (Qpeak = 3911.30 cms) 30 2500 >1984 (Qpeak = 3011.30 cms) 30 3000 40 40 2000 2500 50 50 1500 2000 Q (cms) Q (cms) 60 60 Rainfall (mm)

Rainfall (mm) 1500 1000 70 70 80 1000 80 500 90 500 90 0 100 0 100 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Time (h) Time (h)

Figure 14 Hydrograph changes due to deforestation

Hydrograph at JPS Beaufort (72h, 2yrs) Hydrograph at JPS Beaufort (72h, 5yrs) 0 1800 3500 0 5 1600 3000 10 20 1400 15 2500 )

1200 20 ) 2000 40 1000 25 800 Q (cms) 30 1500 60 Q (cms 600 (mm) Rainfall 35 1000 (mm Rainfall 400 40 80 200 45 500 0 50 0 100 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Time (h) Des ign Rainf all (72h, 2yrs ) Design Rainfall (72h, 5yrs) Time (h) (1984-1995) Discharge (Qmax = 1370.80) (1984-1995) Discharge (Qmax = 2558.10) Future Discharge (Qmax = 1703.70) Future Discharge (Qmax = 3036.70)

Hydrograph at JPS Beaufort (72h, 10yrs) Hydrograph at JPS Beaufort (72h, 20yrs) 5000 0 4000 0 4500 10 3500 4000 20 20 3000 3500 30 3000 40 2500 40 2500 50 2000 2000 60 Q (cms)

Q (cms) 1500 60 1500 70 (mm) Rainfall (mm) Rainfall 1000 1000 80 80 500 500 90 0 100 0 100 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Time (h) Design Rainfall (72h, 10yrs) Time (h) Design Rainfall (20y, 24h) (1984-1995) Discharge (Qmax = 3011.30) (1984-1995) Discharge (Qmax = 3911.30) Future Discharge (Qmax = 3531.60) Future Discharge (Qmax = 4498.90)

Figure 15 Hydrograph changes due to agriculture

Table 4 Maximum runoff simulation results from different landuses (72-hours, 2-years ARI) RUNOFF HYDROGRAPH RUNOFF HYDROGRAPH DEFORESTED PEAK INCREASE VOLUME INCREASE AREA (%) (%) DISCHARGE (or LARGE CATCHMENT Due to Due to STATION SCALE Due to Due to Large Large AGRICULTURE) Deforestation Deforestation Scale Scale (%) Activities Activities Agriculture Agriculture Ansip A 13.88 3.45 1.67 3.46 1.69 Biah B 32.09 6.32 2.21 6.54 2.30 Kemabong C 23.03 5.75 41.88 6.09 47.08 JPS Beaufort A,B,C,D1,D2 & E 10.92 4.94 24.29 5.02 22.35

358 2nd International Conference on Managing Rivers in the 21st Century: Solutions Towards Sustainable River Basins

The highest runoff hydrograph peak resulted from the design 4. Yip, H.W. (2002), Storm Runoff Estimation of Ungauged rainfall within the duration of 72-hours for 2-years ARI are River Catchments Using Soil Conservation Service summarized in Table 4. The deforestations activities which Method. Universiti Sains Malaysia, Kampus Cawangan have been carried out during 1984 to 1995 lead to the decrease Kejuruteraan, Sri Ampangan, Nibong Tebal, Pulau Pinang. of primary forest area by 11% within the Sungai Padas 5. Hassan, J. (2006). Permodelan Sungai dan Dataran Banjir catchment. The decrease of 11% of the primary forest area Untuk Penjanaan Peta Risiko Banjir: Kajian Kes Sungai causes the runoff peak and volume was increased by 5%, in the Selangor. Universiti Sains Malaysia, Kampus Cawangan condition which none-cultivated disturbed forest area. The Kejuruteraan, Sri Ampangan, Nibong Tebal, Pulau Pinang. runoff peak and volume are increased by 25% and 22% 6. Chow, V.T. (1988), Applied Hydrology. McGraw-Hill, respectively when the deforested areas are converted into Inc., USA. agriculture (e.g. rubber and oil palm). The values of runoff 7. Sabah Department of Agriculture (2004). hydrograph as estimated at the JPS Beaufort discharge station 8. Department of Irrigation and Drainage (1983), indicate that the increase of hydrograph peak is higher due to Hydrological Procedure No.26 (HP26), Estimation of the conversion of land use from deforested area into large scale Design Rainstorm in Sabah and Sarawak. Ministry of agriculture than the non-cultivated deforested area does. Agriculture, Kuala Lumpur: p.10-18. 9. Department of Irrigation and Drainage (1982), Hydrological Procedure No.1 (HP1), Estimation of Design 5 Conclusion Rainstorm in Peninsular Malaysia. Ministry of Agriculture, Kuala Lumpur: p. 62-69. The deforestation effect on the runoff hydrograph value is 10. Mohamed, M., L.Y. Heng, and Gopir, G. (2002). The rather significant. In spite of the small percentage of primary Surface Water Resource of Crocker Range Park, Sabah. forest are disturbed, but it has been shown that the hydrograph In: ASEAN Review of Biodiversity and Environment peak and volume at the catchment outlet (Beaufort discharge Conservation (ARBEC), July/September 2002. p.1-14. station) has increased by 5%. The deforestation by logging 11. Environment Protection Department (EPD) (2003). activities particularly at the upstream near the Sook catchment Environment Indicator Report, Sabah, Malaysia. Kota and Sipitang catchment would always contribute to the Kinabalu, Sabah, Malaysia. increase of the flood peak at the downstream particularly at the 12. Ning SUN, Xiubin LI (2005). A Summary of the Effects of area of Beaufort. Runoff hydrograph increase was greater when Afforestation and Deforestation on Annual Water Yields. the areas are cultivated with large scale area of commercial Institute of Geographic Sciences and Natural Resources crops such as rubber and oil palm. The effect of runoff Research, Chinese Academy of Sciences, Beijing, P.R. hydrograph peak and volume are approximately five times China, 100101. higher when the deforested areas are replanted with rubber and 13. Randazzo, C. and Mach, M. (2004). Effects of oil palm compared to the none-cultivated deforested area. In Deforestation on River Dynamics in a Costa Rican order to control the deforestation activities (especially illegal Watershed. University of Washington. loggings) in the catchment the state government has been 14. Stednick, J.D. (1994). Monitoring the Effects of Timber allocated some areas within this catchment as reserved and Harvest on Annual Water Yield. Watershed Science protected areas (Environment Protection Department, 2003 Program, Department of Earth Resources, College of (EPD)). Natural Resources, Colorado State University, Fort Collins. Colorado, USA. 15. Costa, M.H., Foley, J.A. (1998). Combined Effects of 6 References Deforestation and Doubled Atmospheric CO2 Concentration on the Climate of Amazonia. Institute for 1. United States Army Corps of Engineer or USACE (2001). Environment Studies, and Department of Atmospheric and HEC-HMS 2.2.2: Hydrologic Modeling System User’s Oceanic Sciences, University of Wisconsin-Madison. Manual, Version 2.1. California: Hydrologic Engineering Madison, Wisconsin. USA.. Center. 16. Costa, M.H., Botta, A., Cardille, J.A. (2002). Effects of 2. United States Army Corps of Engineer or USACE (2000). Large-Scale Changes in Land Cover on the Discharge of HEC-HMS: Technical Reference Manual. California: the Tocantins River, Southeastern Amazonia. Department Hydrologic Engineering Center. of Agriculture and Environment Engineering, Federal 3. Cunderlik, J.M. and Simonovic, S.P. (2004). Calibration, University of Vicosa (UFV), Centre for Sustainability and Verification, and Sensitivity Analysis of the HEC-HMS the Global Environment (SAGE), Gaylord Nelson Institute Hydrological Model. CFCAS Project: Assessment of for Environment Studies, University of Wisconsin. Water Resources Risk and Vulnerability to Changing Madison, USA. Climatic Conditions. Project Report IV.

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