deforestation effect to the runoff hydrograph at sungai...

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

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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 In general, land cover or land use changes usually result in the changes of the catchment hydrologic responses to the rainfall. Also, land use disruption such as deforestation activities causes many adverse impacts to the water quality and quantity as many bared areas at the upstream are exposed to the rainfall. The cleared areas will no longer capable to absorb and retain some amount of moisture from the rainfall, which play as an important role to reduce the surface runoff and to maximize the soil retention capacity within the subsoil surface. This factor will result to the shorter time of concentration of the catchment. A study conducted by Costa et.al (2002) at the Tocantins River, Porto National with the area of study around 175, 360 sq.km., indicates that in large river basin, the two most likely drivers of long-term discharge modification are precipitation variability and changes in landuse in the upstream catchment. It has also indicated that the hydrograph peak from the catchment which has more altered landuses occurs earlier than that from the

catchment which has less altered landuses. Deforestation activities will also lead to the decrease of catchment average rainfall intensity and increase temperature due to the decrease of evapotranpiration and the radiative effect of CO2 (Costa and Foley, 1998). The effect of deforestation to the runoff peak is also depending on the catchment profile. A study carried out by Stednick (1996) in the United States indicated that the runoff peak was effected by smaller percentage of land use changes at the steeper or mountainous area compared to the plain area. This implies that the deforestation activities have greater impact on the runoff and water yield when practiced at the steeper upstream area. Deforestation effect on the annual water yield is also influenced by several factors such as the type of vegetation cover, climate and catchment sizes (Sun and Li, 2005). The study carried out by Sun and Li in China implies that the differences of impact on catchment annual water yield among different forest types were somewhat different with those from other countries; there is a higher water yield changes in humid regions compared to that of drier regions; and the water yield is

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

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CONCLUSIONS AND RECOMMENDATIONS

DETERMINE THE CATCHMENT DESIGN

END

CATCHMENT RESPONSE ANALYSIS

MODEL VALIDATION

MODEL CALIBRATION

USING HEC-HMS MODEL

DETERMINATION OF THE CATCHMENT PARAMETERS

DATA COLLECTION

RAINFALL TEMPORAL DISTRIBUTIONSUSING THE HP.26 FOR

ANALYSIS RESULTS

SENSITIVITY ANALYSIS OF THEHEC-HMS MODEL PARAMETERS

DETERMINE THE APPROPRIATERAINFALL DURATION (e.g. 24 and 72-hours)

ACCORDING TO THETIME OF CONCENTRATION VALUE

ANALYZING THE CATCHMENT RAINFALLHISTORICAL DATA TO DETERMINE THE

CATCHMENT RAINFALL TEMPORAL DISTRIBUTIONSACCORDING TO THE HP-1 PROCEDURE 2, 5, 10, AND 20 YEARS ARI

Figure 1 Research Methodology

consistent in both small and large catchment due to the deforestation effect, but there is a large fluctuation in streamflow responses to forest cover changes in smaller catchments. Bruijnzeel (1990) pointed out that the changes in infiltration associated with the land use changes overrides the effect of reduced evaporation, then a shift in the streamflow regime may be expected with increased peaks during the rainy season and lowered flows during the dry season. Deforestation increases surface runoff and catchment response to rainfall is highly variable and unpredictable (Hibbert, 1965). The removal of forest almost invariably leads to higher streamflow and reforestation of open land generally reduces the overall streamflow (Bosch and Hewlett, 1982). Studies about deforestation effects to the runoff were leading to one general conclusion that it causes the increase of runoff hydrograph. 2 Methodology The study process (Figure 1) started with the collection of rainfall data, discharge data, topography maps, land-cover, and soil map. The rainfall data, discharge data, catchment delineations, and land-cover map are derived from Sabah Department of Irrigation and Drainage (Sabah DID), whereas the soil map was acquired from Sabah Department of Agriculture (Sabah DOA). These informations are applied for

the hydrologic modeling in Sungai Padas catchment using the HEC-HMS 2.2.2. Several model most sensitive parameters have been analyzed by performing some sensitivity analyses such as initial loss, Soil Conservation Service Curve Number (SCS CN) value, the catchment storage coefficient (R), recession constant of the baseflow, and Muskingum-K for the channel routing. The time of concentration (tc) values of the catchment were selected based on the comparison results from five (5) methods such as Izzard, Kerby, Kirpich, Kinematic wave, and Bransby William formulas. The model was calibrated using the rainfall and streamflow data of May 1991 and validated using the rainfall-runoff event of June 1992. Both data used in the calibration and validation process were consisted of multiple rainfall events, which have produced the annual highest 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 Procedure No.26 (HP-26) which has been designed for Sabah and Sarawak state was adopted as the design rainfall guideline within 72-hours duration. The deforestation analysis was then performed using the calibrated model, rainfall temporal distribution and the design rainfall informations. The deforestation analysis has been carried out by applying at 2 year within the 72-hours duration period.


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Figure 3 Sungai Padas geographical features

Tambunan Town

Keningau Town

Tenom Town

Beaufort Town

Kemabong Town

Biah Town

Ansip Town

3 The Study Area 3.1 Geographical Features 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 152 smaller subcatchments according to the geographical topography features. The total area of the catchment is approximately 8,668 km2. There are three (3) major river tributaries which lead to the catchment division into three river systems, they are Sungai Pegalan catchment, Sungai Sook catchment, and Sungai Padas catchment (upstream). The cathmnent area has been divided into six (6) subcatchments for the study purposes as shown in Figure 2, this includes Sub-A, B, C, D1, D2, and E. Primary and secondary forests are the main vegetation cover of the catchment area (Figure 3). The primary forest is the undisturbed natural forest which is mostly covering the hilly and mountainous area at the upstream, 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 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 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 towns are located Ansip, Biah, and Kemabong town.

In general, the catchment is mostly dominated by mountainous and hilly region with steep geographical surface conditions particularly at the upstream areas. Most hilly region catchment rises up to 1230 m (4050 ft) above sea level. At the western part of the catchment the Crocker Range rises up to 1548 m (5080 ft) a.s.l. (above sea level). Witti Range and 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 Sungai Pegalan where they joined near Biah town. Sungai Pegalan confluenced with the Sungai Padas at Tenom and continues flowing northwest, between the Crocker Range valley and the Tenom gorge to Beaufort. The river meanders across the Klias Peninsula and finally discharged at the river mouth to the Brunei Bay.

3.2 Rainfall and Discharge Gauging Stations Five (5) rainfall stations were selected based on the availability and the goodness of recorded data, as shown in Table 1. The weighted rainfall average for the catchment was estimated using 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 5). The discharge stations are summarized as shown in Table 2.

Catchment

Pegalan Downstream

(519 sq.km)

(664 sq.km)

Catchment

(267 sq.km)

(3,248 sq.km)

Sook Catchment

(1,733 sq.km)

(2,238 sq.km)

PadasCatchment

Pegalan Upstream Catchment

Sook Catchment

Padas Upstream Catchment

Mid-Padas Catchment

Pegalan Downstream Catchment

Padas Downstream Catchment

U

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Catchment

Padas Mid-Catchment

Padas Downstream

(Sub-A)

(Sub-B)

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(Sub-D2)

(Sub-E)

Figure 2 Sungai Padas catchment subcatchments


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Table 1 Rainfall Stations

Rainfall Station Station Number

Elevation (m)

Tambunan Agriculture 5663001 680 Keningau Meteorologic 5361002 290 Sook 5163002 350 Kemabong 4959001 228 JPS Beaufort 5357003 9.4

Table 2 Discharge Stations

Catchment Discharge Station

Station Number

Elevation (m)

Sub – A Ansip 5261401 262

Sub – B Biah 5261402 258

Sub – C Kemabong 4959401 228

Padas catchment JPS Beaufort 5357403 9.4

3.3 Land Cover Figure 6 and 7 show the landcover pattern before and after the year 1984. It is obviously seen that the deforestation area at the catchment has been increased. The primary forest areas are 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 catchment was approximately 11%. Disturbed forest includes all deforested areas such as secondary forest, logged forest and bared areas as displayed on the topographic maps.

Figure 4 Topographical features

Sg. Pegalan

Sg. Sook

Sg. Padas

Sg. Padas

Figure 6 Sungai Padas catchment land cover (Before 1984)

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PadasCatchment

Main River

Subcatchment boundarySub-Subcatchment boundary

DG(5261402)

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Discharge Gage Station

Figure 5 Rainfall and discharge gages


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Soilmap_combined.shpAcic igneous rocksAlluviumAlluvium & alluvium derived fr. basic or ultrabasiAlluvium & peatAlluvium derived from ultrabasic rocksAlluvium, sandstone & mudstoneBasic igneous rodks & alluviumBasic intermediate igneous rocksCalcareous alluviumCollovium, sandstone & mudstoneLimestoneMudstone & alluviumMudstone & sandstoneMudstone, sandstone & miscellaneous rocksSandstoneSandstone & mudstoneSandstone, mudstone & alluviumSulphidic alluvium, sulphidic peat & alluviumUltrabasic igneous rocks

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

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Figure 8 Soil classification at Sungai Padas catchment

3.4 Soil Types Soil types as provided by the Department of Agriculture (DOA) of Sabah are classified according to the Food and Agriculture Organization-United Nations Educations, Scientific and Cultural Organization (FAO-UNESCO). Some countries are using the Textonomy soil classification system in which soil types are classified into four major soil classes, that is A, B, C, and D. The most abundant soil types in Sungai Padas catchment are soil class B, C and D (Figure 8) based on the parental soil

types (Figure 9). The soil type information indicated that the most dominant parental soil types within the Sungai Padas catchment is consisted of sandstone and mudstone that is classified into soil Type-B. The area of Subcatchment-C and Subcatchment-D1 and D2, are consisted of parent material soil from sandstone, mudstone, and alluvium, which are classified into Type-C soil. Soil classes imply the soil infiltration rate, according to the SCS soil classification standard. Soil Type-B and C has the moderate infiltration rates, which potentially to produce moderate runoff (USDA).

4 ANALYSIS RESULTS 4.1 Calibration and Validation The HEC-HMS model has been calibrated and validated by applying the rainfall and runoff data of May 1991 (Figure 10) and June 1992 (Figure 11), respectively.

The calibration and validation results are evaluated using R2 values as shown in Figure 12 and 13, respectively. Table 3 summarizes the model parameters that have been used in the analysis.


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RUNOFF HYDROGRAPH AT ANSIP DISCHARGE STATION(June 1992 - Validation)

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RUNOFF HYDROGRAPH AT KEMABONG DISCHARGE STATION(June 1992 - Validation)

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

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

RUNOFF HYDROGRAPH AT ANSIP DISCHARGE STATION(May 1991 - Calibration)

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RUNOFF HYDROGRAPH AT JPS BEAUFORT DISCHARGE STATION(May 1991 - Calibration)

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Hydrograph Peak Comparison at JPS Beaufort Discharge Station(May 1991 - Calibration)

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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 percentage to fulfill the local condition according to Equation 1 (Hassan, 2006).

( )[ ]%x*)I(CN)III(CN)I(CN'CN += (1) whereby, CN’ = Adjusted Curve Number CN(I) = Curve Number value for AMC(I) CN(III) = Curve Number value for AMC(III) x% = Percentage of adjustment The time of concentration value (tc) was estimated using the Kirpich method (Equation 2).

( )16

1*385.0S

77.0L*0078.0ct = (2)

whereby, tc = time of concentration (h) L = length of overland flow (m) S = slope (m/m)

4. 2 Deforestation Effect Analysis The HEC-HMS model hydrograph simulation analysis results at JPS Beaufort discharge station are shown in Figure 14, for ARI ranging from 2 to 20 years ARI within 72 hours duration. The results shown in Figure 14 are the comparisons of hydrograph resulted from different land cover pattern before and after 1984 (based on Figure 6 and 7), in which deforestation activities have been carried out within the catchment. Figure 15 also shows the runoff hydrograph 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 with large scale agriculture.

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Hydrograph Peak Comparison at JPS Beaufort Discharge Station(June 1992 - Validation)

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Figure 14 Hydrograph changes due to deforestation

Figure 15 Hydrograph changes due to agriculture

Table 4 Maximum runoff simulation results from different landuses (72-hours, 2-years ARI) RUNOFF HYDROGRAPH

PEAK INCREASE (%)

RUNOFF HYDROGRAPH

VOLUME INCREASE (%)

DISCHARGE STATION CATCHMENT

DEFORESTED AREA

(or LARGE SCALE

AGRICULTURE)(%)

Due to Deforestation

Activities

Due to Large Scale

Agriculture

Due to Deforestation

Activities

Due to Large Scale

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


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The highest runoff hydrograph peak resulted from the design rainfall within the duration of 72-hours for 2-years ARI are summarized in Table 4. The deforestations activities which have been carried out during 1984 to 1995 lead to the decrease of primary forest area by 11% within the Sungai Padas catchment. The decrease of 11% of the primary forest area causes the runoff peak and volume was increased by 5%, in the condition which none-cultivated disturbed forest area. The runoff peak and volume are increased by 25% and 22% respectively when the deforested areas are converted into agriculture (e.g. rubber and oil palm). The values of runoff hydrograph as estimated at the JPS Beaufort discharge station indicate that the increase of hydrograph peak is higher due to the conversion of land use from deforested area into large scale agriculture than the non-cultivated deforested area does. 5 Conclusion The deforestation effect on the runoff hydrograph value is rather significant. In spite of the small percentage of primary forest are disturbed, but it has been shown that the hydrograph peak and volume at the catchment outlet (Beaufort discharge station) has increased by 5%. The deforestation by logging activities particularly at the upstream near the Sook catchment and Sipitang catchment would always contribute to the increase of the flood peak at the downstream particularly at the area of Beaufort. Runoff hydrograph increase was greater when the areas are cultivated with large scale area of commercial crops such as rubber and oil palm. The effect of runoff hydrograph peak and volume are approximately five times higher when the deforested areas are replanted with rubber and oil palm compared to the none-cultivated deforested area. In order to control the deforestation activities (especially illegal loggings) in the catchment the state government has been allocated some areas within this catchment as reserved and protected areas (Environment Protection Department, 2003 (EPD)). 6 References 1. United States Army Corps of Engineer or USACE (2001).

HEC-HMS 2.2.2: Hydrologic Modeling System User’s Manual, Version 2.1. California: Hydrologic Engineering Center.

2. United States Army Corps of Engineer or USACE (2000). HEC-HMS: Technical Reference Manual. California: Hydrologic Engineering Center.

3. Cunderlik, J.M. and Simonovic, S.P. (2004). Calibration, Verification, and Sensitivity Analysis of the HEC-HMS Hydrological Model. CFCAS Project: Assessment of Water Resources Risk and Vulnerability to Changing Climatic Conditions. Project Report IV.

4. Yip, H.W. (2002), Storm Runoff Estimation of Ungauged River Catchments Using Soil Conservation Service Method. Universiti Sains Malaysia, Kampus Cawangan Kejuruteraan, Sri Ampangan, Nibong Tebal, Pulau Pinang.

5. Hassan, J. (2006). Permodelan Sungai dan Dataran Banjir Untuk Penjanaan Peta Risiko Banjir: Kajian Kes Sungai Selangor. Universiti Sains Malaysia, Kampus Cawangan Kejuruteraan, Sri Ampangan, Nibong Tebal, Pulau Pinang.

6. Chow, V.T. (1988), Applied Hydrology. McGraw-Hill, Inc., USA.

7. Sabah Department of Agriculture (2004). 8. Department of Irrigation and Drainage (1983),

Hydrological Procedure No.26 (HP26), Estimation of Design Rainstorm in Sabah and Sarawak. Ministry of Agriculture, Kuala Lumpur: p.10-18.

9. Department of Irrigation and Drainage (1982), Hydrological Procedure No.1 (HP1), Estimation of Design Rainstorm in Peninsular Malaysia. Ministry of Agriculture, Kuala Lumpur: p. 62-69.

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deforestation effect to the runoff hydrograph at sungai...

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