Journal Paper Format

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2759 - 2774

Evolution of River Characteristics Impact on Post-Flood and Normal Season in Pinang River Basin, Malaysia

Muhammad Hafiz Md Saad1, Mohd Khairul Amri Kamarudin1,2*, Ahmad Shakir Mohd Saudi3, Firdaus Mohamad Hamzah4, Marlia Mohd Hanafiah5, Noorjima Abd Wahab1 and Siti Nur Aisyah Md Bati1 1East Coast Environmental Research Institute (ESERI), Universiti Sultan Zainal Abidin, Gong Badak Campus, 21300 Kuala Nerus, Terengganu, Malaysia 2Faculty of Applied Social Sciences (FSSG), Universiti Sultan Zainal Abidin, Gong Badak Campus, 21300 Kuala Nerus, Terengganu, Malaysia 3Department of Environmental Health, Institute of Medical Science Technology, Universiti Kuala Lumpur, Kajang, Selangor, Malaysia 4Department of Engineering Education, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia 5Department of Earth Sciences and Environment, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia *[email protected]

Abstract Characterization of river outflow characteristics in the post-flood and normal seasons was carried out in the Pinang River Basin, Penang. Field sampling was performed twice in November 2017 (post-flood) and in March 2019 (normal season). Cross-sectional measurements involving the measurement of river width, river depth and velocity were performed at both sampling times. The objective of this study was to identify the pattern of river discharge in the Pinang River Basin and to assess the relationship between the occurrence of water discharge and other factors for both seasons. The results showed that the average discharge rate for each river after the rainy season was 0.85 m3/s for the Dondang River, 1.11 m3/s for the Ayer Itam River and 3.23 m3/s for the Sungai Pinang. For the normal season, the mean readings were 0.13 m3/s for the Dondang River, 0.38 m3/s for the Ayer Itam River and 0.69 m3/s for the Pinang River. Subsequent estimates of flood rates during floods were also estimated by estimating an increase in water depth by five meters. As a result of this estimate, the average drainage rate for the Dondang river is 8.58 m3/s, the Ayer Itam River at 8.12 m3/s while the Pinang River is 20.68 m3/s. The results from the correlation statistics analysis showed a very significant reading between river depths and outflow with R2 = 0.85. The relationship between velocity and water discharge shows a reading of R2 = 0.089 which is not significant. Whereas, the relationship between width and discharge shows a R2 = 0.495 which is significant. It is hoped that this study will provide as much information as possible before the proper steps are taken to prevent future flood events.

Keywords: River characteristics, post-flood impact, normal season impact, river discharge, Pinang River Basin.

1. Introduction Water resources are one of the most important elements in all aspects of life in the world. Malaysia is one of a country who rich in natural water resources. Southwestern and northeasters monsoon that caused the country to average an average rainfall annually which is more than 2500 mm (Amran et al., 2018; Kamarudin et al., 2015a; Abdullah et al., 2013). The river is one of the primary sources of water and also provides fertility for lands. Due to favourable conditions, it also supports the development of highly populated

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2759 - 2774 residential areas (Kamarudin et al., 2019a; Armas et al., 2013; Barasa et al., 2017). Water catchment areas such as dams will supply water to rivers. Several rivers in Malaysia have a Class 2 in Water Quality Index (WQI) such as Terengganu River. Lack of pollution and environmental awareness can be applied; many people will benefit from it. There are important to improve the knowledge and the practice of environmental management ability among communities about environmental issues. There are also important to achieve environmental awareness and ethics, values and attitudes, skills and behaviours (Syazni Jusoh et al., 2019; Amri Kamarudin et al., 2013). The river, which is also a reservoir and waterway, should always be prepared to accept the presence of water from various angles such as surface runoff, rainwater and high tide. Control in the event of extreme flows such as floods or drought. Therefore, river discharge characteristics are important depending on the water source, be it geomorphology, hydraulics, flood control, sailing, stabilization or development of water resources for municipal and industrial purposes (Jaafar et al., 2010a; Toriman et al., 2012; Simons, 1969). In many places, hilly areas that were supposed to be water catchment areas have begun to recharge to become populated areas due to the sudden increase in population. These conditions can have adverse effects in the future due to the lack of a water catchment area. Natural rivers will also find it difficult to sustain water capacity in the event of a sudden increase in water levels due to the loss of this catchment area. Little attention has been given to river-wide catchment dynamics on the spatial variance of river flow and human being interferences (Zhijun Dai et al., 2015; Jaafar et al., 2010b) Wahab et al. (2019) states that aspects of water quality are also being neglected while many reservoirs and rivers are being polluted due to human settlements and activities in the catchment area. Therefore, river discharge rates should be studied to facilitate the authorities to detect and evaluate the best measures to minimize the negative impacts such as floods, cliffs and so on. Due to human activities, river morphology is changing from its natural channel, such as agricultural activity, sand excavation from the bed, disposal of municipal waste and construction on the river. Human activities should not extremely disturb the environment of the river because they should be maintained (Kamarudin et al., 2015b; Samanta & Pal, 2012). In ongoing decades, the quantities of extreme climatic events like storms, flood, dry spells and heatwaves have expanded around the world (Kamarudin et al., 2019b; Sungip et al., 2018; Field et al., 2012; Toriman et al., 2009). Flood control and drought are also important ecologically as they affect populations and distribution of aquatic organisms. Hydrologists are more concerned with estimating the probability and magnitude of flood events. Floods affect the ecology of a river by destroying the habitat at the base of the river, eliminating aquatic and riparian vegetation, increasing the rate of evaporation of aquatic insects in the river (Kamarudin et al., 2015c; Gordon et al., 2004). The monitoring of river discharge is a fundamental frequency for the body of water resources direction, water residue rating at the basin scale and flood purpose as well as for the calibration and validation of hydrological models. Data on river flow usually consist of recorded water levels and river discharge rates over a given period of time. Most rivers also have a unique relationship between river water level and river flow at a given location. Despite the major impact of discharge data on many environmental management takings, their evolutional most always relies on the use of the so-called rating curves (Kamarudin et al., 2017a; Spada et al., 2017). There are three basic steps for obtaining data on river flow – water level measurement; river discharge calculations; defines the relationship between water level and river discharge (Bruce & Clark, 1966). Hydrologists focus on the flow rate or outflow characteristics of a river in cubic meters per second (m3s-1). In the study of open channel flow, complex cross-sectional sections are ready to be determined, the velocity of water in

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2759 - 2774 meters per second (ms-1) is also an important feature. Generally, the river is composed of three parts, the upper, middle and lower. A river is a lotus ecosystem, a volatile ecosystem with varying depths (Kamarudin et al., 2017b; Chiras, 2001). In order to obtain the depth value of the river, the average value must be taken by measuring the vertical depth according to the cross-section. Ismail (1994) state that the river has a one-way movement and has a seasonal variation of water volume. One-way movement causes the riverbank and riverbank to be unstable and prone to erosion. This phenomenon is closely related to the frequency and intensity of rainfall at certain times in the area. The main objective of this study was to identify the pattern of river discharge in the Sungai Pinang Basin and to assess the relationship between the occurrence of water discharge and other factors. This is to see whether or not there is a correlation between these factors and seasonal discharge rates.

2. Methodology Penang has a relatively large drainage basin (Table 1). This drainage system that could be used to cater for the future water supply needs of the population is seen to be less isolated as the island has been a focus of industry development year after year after being recognized as Penang Cybercity by the Multimedia Super Corridor Malaysia (MSC Malaysia). As a result, there has been rapid development especially in the manufacturing industry which has had little impact on the rivers in Penang. In addition, many areas of the city have expanded and the hills have been cultivated for agriculture, settlements, administrative centres, industrial, tourism and so on. As a result, there is a shortage of wetlands in Penang and this has led developers to develop hilly land. This may slightly affect the condition of rainfall areas (Misnan & Rindam, 2012). In addition, it will also cause disasters such as floods.

Table 1: Information of Pinang River Basin catchment area Catchment Area (Acre) Capacity (Million Gallons) Air Hitam 2,294 10.0 Guillemard 1,609 10.0 Sungai Pinang 1,676 7.5 Air Terjun 1,285 4.0 Teluk Bahang 3,073 3.6 Batu Feringgi 2,668 0.3 Total 12,605 29.4 Source: Penang Water Authority, 1996 The sudden flooding of September 2017 in Penang especially in Georgetown City has opened the eyes of local authorities to take further precautions. Although this is due to factors beyond the control such as heavy rainfall which is constantly falling and also the phenomenon of high tide in the sea, it is undeniable that physical and human factors also play a role in addressing this problem from time to time. Due to the probable cause of this problem, sampling of this study was carried out at the Pinang Basin which includes the Dondang River, Ayer Itam and Pinang Sungai located in Georgetown Penang (Figure 1 and Table 2). These rivers are located on the east side of the island at 5 ° 23'33.2 "N 100 ° 16'39.5" E for Dondang River, 5 ° 24'06.2 "N 100 ° 17'09.5" E for Ayer Itam River and 5 ° 24'40.4 "N 100 ° 18'35.1" E for Pinang River. The position of the sampling station has been identified using the Digital Global Positioning System (DGPS) tool which has been conducted in the post-flood season in November 2017 and the normal season in March 2019. According to the Malaysian Meteorological Department, the weather in Malaysia is characterized by the monsoon of the Southwest Monsoon from late May to September, and the Northeast Monsoon from November to March. The Southwest monsoon brings

International Journal of Advanced Science and Technology Vol. 29, No. 4s, (2020), pp. 2759 - 2774 heavy rainfall mainly to the states off the west coast of Peninsular Malaysia while the Northeast monsoon is relatively low in this area. The transition period between the two monsoons is known as the monsoon intermediate season.

(a)

(b) Figure 1: The study location in Pinang River Basin. (a) Map of Pinang River Basin from Malaysia; (b) Map of sampling location and Pinang River Basin areas

Table 2: Coordinate of sampling stations Code Station Latitude Longitude S1 Sg Dondang (Upstream) 5°22'58.6"N 100°16'32.5"E S2 Sg Dondang (Middle) 5°23'33.2"N 100°16'39.5"E S3 Sg Dondang (Downstream) 5°23'48.2"N 100°17'20.3"E S4 Sg Ayer Itam (Upstream) 5°24'07.7"N 100°16'44.4"E S5 Sg Ayer Itam (Middle) 5°24'06.2"N 100°17'09.5"E S6 Sg Ayer Itam (Downstream 1) 5°24'25.3"N 100°18'01.1"E

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S7 Sg Ayer Itam (Downstream 2) 5°24'50.8"N 100°18'33.5"E S8 Sg Pinang (Upstream) 5°24'40.4"N 100°18'35.1"E S9 Sg Pinang (Middle) 5°24'39.0"N 100°18'47.3"E S10 Sg Pinang (Downstream) 5°24'15.5"N 100°19'33.1"E

2.1. In-Field Analysis Field sampling is based on cross-sectional measurement which involves river width measurement (b), river vertical depth (d) and water velocity measurement (v). All of these readings were recorded for analysis and calculated to obtain river discharge values (Q). The measuring instruments used are measuring tape for width (Figure 2a), Staff Gauge for depth (Figure 2b) and Flow Meter to measure current velocity (Figure 2c). The velocity of the current was measured at 0.2 meters deep at the water level and was taken three times to read.

a) Tape Meter b) Staff gauge c) Current Meter Figure 2: The equipment used for field sampling in this study. (a) Tape Meter; (b) Staff gauge; (c) Current Meter

2.2. Hydrographic Calculation Calculation Area (A): The area of each section is obtained by taking into account the depth absorbed by the vertical boundary and multiplied by the distance between the vertical boundaries.

A = b x d ...... [1] A = cross sectional area (m2) b = distance between vertical boundaries (m) d = water depth (m)

2.3. Calculation of River Discharge (Q) If the cross-sectional area (A) and average velocity (v) are known, the slope (Q) can be calculated from Q = vA. Because the water depth and flow velocity are not uniform for the entire cross section. Accurate discharge measurements are obtained by dividing the cross section into several sub-sections called sections. Each section is limited by surface water, river bottom and 2 vertical lines, called vertical. Each vertical is a common dimension of 2 continuous sections and the depth of water and the velocity of the stream are set for observation. Adequate velocity observations were made to obtain the average velocity at each vertical boundary (Figure 3). So, the average velocity of the section is:

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V = (v0.2d x v0.8d)/2 or v0.6d ...... [2] The result of the average and wide velocity of each section gives the cut off.

Q = (bd)(v0.2d x v0.8d)/2 ...... [3] or Q = (bd) (v0.6d) And the sum of all the cutoffs gives the sum of the sums.

Q = (Q0,1) +(Q1,2) +(Q2,3) ...+(Qn,n +1) ...... [4] where n is a perpendicular number (Toriman et al., 2015; Jamil et al., 2012).

Figure 3: Theory of Measurement of Discharge

2.4. Data Analysis The data obtained from field analysis were analyzed using Microsoft Excel 2016. The data analysis is to facilitate the work of interpreting the data and looking at the relevance of the parameters studied.

3. Results and Discussion During field sampling, several geometric elements were absorbed and measured in situ. Average values of river depth, river width and stream velocity are used to obtain the discharge. The value obtained is variable at each sampling time. This is due to climate factors, river vegetation, soil and rock structure as well as basin morphology and river hydraulic geometry as well as soil erosion and sedimentation (Zachar, 1982).

3.1. Hydrographic Measurement Results Post-Flood In this study, there are three sampling stations in the Dondang River covering upstream, middle and downstream, four sampling stations in the Ayer Itam River, upstream, middle, downstream as well as three sampling stations in Sungai Dondang covering upstream, central and downstream areas. The cross-section of the Dondang River, Ayer Itam River and Pinang River after the flood are as shown in Figure 4 (a) (b) (c) (d) (e) (f) (g) (h) (i) (j).

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(a) Station 1 (b) Station 2

(e) Station 5 (f) Station 6

(g) Station 7 (h) Station 8

(i) Station 9 (j) Station 10 Figure 4: The characteristics of river cross-section on post-flood in the study areas

The depth and width of the Pinang River is higher compared to the Ayer Itam River and the Dondang River. This is because the Pinang River is located downstream of the basin towards the sea compared to the Dondang River and the Ayer Itam River located at the upstream and middle of the basin. Based on Figure 4(a), station 1 is the Dondang

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River (upstream) located in the upstream basin. Water flow from hilly areas and residential areas begins in this area. River width is 11.5 meters and average water depth is 1.2 ± 0.8 meters. The average current velocity recorded was 0.354 ± 0.384 ms-1. Although the station was not very wide, the elevation from the bank to the river bottom recorded a relatively high reading of 4.7 meters. This is because the area is upland and hilly with a mean height of Mean Sea Level (MSL) reaching 33.5 meters. Figure 4(b) shows Station 2, the Dondang River (middle). The width of the river is 7.2 meters and the average depth of the river is 0.2 ± 0.3 meters. The average current velocity recorded was 0.428 ± 0.295 ms-1. The station is located near the residents' housing. So the river has been put in concrete to mitigate the effects of soil erosion that may occur especially when heavy rains can cause damage to property. Whereas Figure 4(c) is Station 3, the River Dondang (Downstream). The width of the river is 14 meters and the average depth of the river is 0.4 ± 0.2 meters. The average current velocity recorded was 0.357 ms- 1. Next to the second river in this basin is the Ayer Itam River. Figure 4(d) shows Station 4, the Ayer Itam River (Upstream). The river is not too wide, with a width of only 10 meters. The average depth of river water recorded 1.1 ± 0.3 meters. The average current velocity recorded was 0.199 ± 0.221 ms-1. The height of MSL in this area is 20.6 meters. Figure 4(e) shows Station 5, the Ayer Itam (Middle) River. The recorded width is 13 meters. While the average depth of river water is reading 0.3 meters. The average of current velocity recorded was 0.119 ms-1. This area is also a residential area. Station 6, the Ayer Itam River (Downstream 1) which refers to Figure 4(f), shows a river width of 14 meters with an average depth of 1 ± 0.4 meters. The average current velocity was 0.322 ± 0.298 ms-1. This station is located after the Dondang River stream. The Ayer Itam River (Downstream 2), Station 7 as shown in Figure 4(g), has an average reading depth of 1.3 ± 0.5 meters with a width of 11 meters. The average of current velocity recorded was 0.353 ± 0.316 ms-1. The station is located just before the water outlet goes to Sungai Pinang and near the residential area. Next is the third river for the Pinang River Basin, the Sungai Pinang. The river is located at the head of the basin leading out to the sea. Compared to the Dondang River and the narrower Ayer Hitam River, the Pinang River has read more and more. This is because all the water from the catchment area passes through this river to the sea. Figure 4(h) shows Station 8 which is the Pinang River (Upstream). The width of the station is 16 meters with an average river depth of 0.88 ± 0.4 meters. The average current velocity recorded was 0.362 ± 0.224 ms-1. The height of this MSL station is 9.5 meters. Figure 4(i) refers to Station 9, the Pinang (Middle) River. The width of the river recorded at this station is 19 meters. While the average depth of river water is reading 1 ± 0.1 meters. The average current velocity recorded was 0.387 ± 0.182 ms-1. Next to Station 10 is the Sg Pinang (Downstream) in Figure 4(j) located just 30 meters from the road to the sea. The station recorded a width of 28 meters with an average river depth of 3.6 ± 1.2 meters. The average current velocity recorded was 0.144 ± 0.118 ms-1. The depth of the station is quite high as it is near the face of the sea at Georgetown.

Table 3: Average value of flow velocity, depth and river width in the post-flood season Station Average Depth (m) Average Velocity (m/s) River Width (m) 1 1.2 ± 0.8 0.354 ± 0.384 11.5 2 0.2 ± 0.3 0.428 ± 0.295 7.2 3 0.4 ± 0.2 0.357 14 4 1.1 ± 0.3 0.199 ± 0.221 10

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5 0.3 0.119 13 6 1 ± 0.4 0.322 ± 0.298 14 7 1.3 ± 0.5 0.353 ± 0.316 11 8 0.88 ± 0.4 0.362 ± 0.224 16 9 1 ± 0.1 0.387 ± 0.182 19 10 3.6 ± 1.2 0.144 ± 0.118 28

3.2. Hydrographic Measurement Results in Normal Season For comparison purposes, sampling in the normal season was also performed. The average river flow velocity in the regular season is lower than the post-flood season. The average depth of water for both seasons is also different because of the fact that the amount of rainfall is much lower during the flood than in the regular season. The cross section of the Dondang River, Ayer Itam River and Sungai Pinang during the regular season are as shown in Figure 5(a)-(j).

(a) Station 1 (b) Station 2

(e) Station 5 (f) Station 6

(g) Station 7 (h) Station 8

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(i) Station 9 (j) Station 10 Figure 5: The characteristics of river cross-section on normal season in the study areas

Based on Figure 5(a), during the season, station 1, the Dondang River (upstream), recorded a river width of 11.5 meters and an average river depth of 1.2 ± 0.8 meters. The average current velocity recorded was 0.411 ± 0.324 ms-1. The height from the cliff to the river bottom recorded a height of 5.1 meters. Figure 5(b) shows Station 2, the Dondang River (middle). The river is 7.2 meters wide and the average river water depth is 0.35 ± 0.15 meters. The average current velocity recorded was 0.443 ± 0.144 ms-1. This stream of river at this station shows a very high current velocity. Whereas Figure 5(c) is Station 3, the River Dondang (Downstream). The width of the river is 14 meters and the average depth of the river is 0.1 meters. The average current velocity recorded was 0.369 ms-1. Next is the Ayer Itam River. Figure 5(d) shows Station 4, the Ayer Itam River (Upstream). The width of the river is only 10 meters. The average depth of river water recorded 0.9 ± 0.2 meters. The average current velocity recorded was 0.184 ± 0.165 ms-1. Figure 5(e) shows Station 5, the Ayer Itam River (Middle) during the regular season. The recorded width is 13 meters. While the average depth of river water is reading 0.3 meters. The average current velocity recorded was 0.075 ms-1. Station 6, which is the Ayer Itam River (Downstream 1) which refers to Figure 5(f), shows a river width of 14 meters with an average depth of 0.7 ± 0.1 meters. The average current velocity was 0.093 ± 0.065 ms-1. The Ayer Itam River (Downstream 2), Station 7 as shown in Figure 5 (g), recorded an average depth of 1 ± 0.4 meters with a width of 11 meters. The average current velocity recorded was 0.205 ± 0.122 ms-1. The station is located just before the water outlet goes to Sungai Pinang and near the residential area. Next is the third river for the Pinang River Basin, the Sungai Pinang. Figure 5(h) shows Station 8 which is the Pinang River (Upstream). The width of this station is 16 meters with an average river depth of 1 ± 0.2 meters. The average current velocity recorded was 0.065 ± 0.039 ms-1. The height of this MSL station is 9.5 meters. Figure 5(i) refers to Station 9, the Pinang River (Middle). The width of the river recorded at this station is 19 meters. While the average depth of river water is reading 0.45 ± 0.1 meters. The average current velocity recorded was 0.27 ± 0.143 ms-1. Next to Station 10, the Sg Pinang (Downstream) in Figure 5(j) is located only 28 meters wide with an average river depth of 3 ± 0.7 meters. The average current velocity recorded was 0.028 ± 0.02 ms-1.

Table 4: Average values of current, depth and width of river during normal season Station Average Depth (m) Average Velocity (m/s) River Width (m) 1 1.2 ± 0.8 0.411 ± 0.324 11.5 2 0.35 ± 0.15 0.443 ± 0.144 7.2 3 0.1 0.369 14 4 0.9 ± 0.2 0.184 ± 0.165 10 5 0.3 0.075 13

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6 0.7 ± 0.1 0.093 ± 0.065 14 7 1 ± 0.4 0.205 ± 0.122 11 8 1 ± 0.2 0.065 ± 0.039 16 9 0.45 ± 0.1 0.27 ± 0.143 19 10 3 ± 0.7 0.028 ± 0.02 28 From the gross differences in river shape and cross section, it can be said that the river is deeper and has a higher flow velocity in the post-flood season than in the normal season. This is because during the aftermath of the flood, it is still raining and this is causing the river to flow faster.

3.3. Hydrological Data Results 3.3.1. River discharge Calculations were performed using flow velocity data, width and depth of the river to derive the outflow rates and water capacity of the two rivers. Outflow rate is the amount of water that exceeds one cross section at a time (Gordon et al. 2004). The mean drainage rates in the Dondang River, Ayer Itam River and Sungai Pinang in the post-flood season were 1.58 ± 0.43 m3s-1, 2.15 ± 0.07 m3s-1 and 5.08 ± 0.29 m3s-1 while after floods were 0.21 ± 0.06 m3s-1, 0.94 ± 0.05 m3s-1 and 0.70 ± 0.17 m3s-1. The differences in mean and average rates for all rivers by season are shown in Table 5 and Figure 6.

Table 5: Water discharges occurring by place and season Station Location Discharge (m3/s) Post-Flood Normal S1 Sg Dondang (Upstream) 1.58 0.06 S2 Sg Dondang (Middle) 0.54 0.21 S3 Sg Dondang (Downstream) 0.43 0.11 S4 Sg Ayer Itam (Upstream) 0.31 0.19 S5 Sg Ayer Itam (Middle) 0.07 0.05 S6 Sg Ayer Itam (Downstream 1) 2.15 0.32 S7 Sg Ayer Itam (Downstream 2) 1.90 0.94 S8 Sg Pinang (Upstream) 1.08 0.17 S9 Sg Pinang (Middle) 0.29 0.50 S10 Sg Pinang (Downstream) 5.08 0.70

Figure 6: Water discharge values by station and season.

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Based on Figure 6, it is found that the outflow value after the flood is higher for almost all stations except station 9 which is slightly lower than the regular season. This may be due to obstruction of waste material or waste dumped into the river. Station 9 is located behind the morning market and business premises. This condition slightly affects the flow velocity and also affects the value of the water discharge.

3.3.2. Estimation of flood Sampling in the Dondang River, Ayer Hitam and Pinang rivers could not be made during the severe floods that hit Penang especially Georgetown in September 2017 due to security reasons. Therefore, the Manning equation was used to estimate the outflow of these three rivers for the season with an estimated water level increase of 5 meters per river. The average outflow rates for all three rivers are shown in Table 6 and Figure 7. From the estimates made, it is found that the river discharge rates have reached a level higher than the regular season. The average drainage rate of the Dondang River is 8.58 m3s-1, the Ayer Hitam average is 8.12 m3s-1 and the Pinang River is 13.80 m3s-1.

Table 6: Estimated water discharge during floods Station Location Discharge (m3/s) Post-Flood Normal Flood S1 Sg Dondang (Upstream) 1.58 0.06 10.46 S2 Sg Dondang (Middle) 0.54 0.21 9.51 S3 Sg Dondang (Downstream) 0.43 0.11 5.78 S4 Sg Ayer Itam (Upstream) 0.31 0.19 2.46 S5 Sg Ayer Itam (Middle) 0.07 0.05 1.26 S6 Sg Ayer Itam (Downstream 1) 2.15 0.32 14.91 S7 Sg Ayer Itam (Downstream 2) 1.90 0.94 13.86 S8 Sg Pinang (Upstream) 1.08 0.17 10.67 S9 Sg Pinang (Middle) 0.29 0.50 14.92 S10 Sg Pinang (Downstream) 5.08 0.70 15.77

Figure 7: Estimating discharge value in flood

Based on Figure 7, all stations have been increased by the probability of flooding, with an increase in river depth of 5 meters per station. From this figure it is found that the value of the discharge during floods is high for all stations during floods. This situation indicates that increased water capacity due to heavy rainfall or upstream discharge will cause flooding. Authorities need to take immediate action to ensure that in the event of a flood, the impact on the property and lives of the residents is minimal.

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3.3.3. Statistical analysis (correlation) Correlation tests were performed to determine whether changes in river discharge rates were influenced by the river depth values for each station. The results are as shown in Figure 12 Based on Figure 8(a), there is a significant correlation (R2 = 0.85) and this shows that the change in the value of the discharge rate is influenced by the depth value of each station. The high depth of the river led to the increase in river discharge rate.

(a) Graph of depth and water discharge

(b) Graph of velocity and water discharge

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Figure 8: Result of the relationship correlation analysis. (a) Relationship of the depth and water discharge; (b) Relationship of the velocity and water discharge; (c) Relationship of the width and water discharge

Correlation tests were also performed to determine whether the outflow rate changes were influenced by the velocity values. Referring to Figure 8(b), the current velocity value does not show a significant correlation (R2 = 0.089) with flow rate. This indicates that the flow velocity did not significantly affect the outflow rate compared to river depth. Correlation tests between river width and water runoff rate (R2 = 0.495) showed that changes in river runoff values were also slightly influenced by river width. Referring to Figure 8(c), a significant correlation exists between the discharge rate and river width. Therefore, a wider river may cause an increase in the value of the water discharge rate.

4. Conclusion This study shows that the rate of discharge is directly proportional to the depth of the river. Depth of the river can also be caused by uncontrollable variables such as rainfall. In addition, the occurrence of cliff erosion, sedimentation and transport of sediment in the water can also cause the river to become shallow and further influence the rate of erosion which may occur in the event of sudden increase in water. The process of sedimentation also causes rivers to become shallow resulting in the flood in the estuary of a drainage. Loads of sediment load policy are between 0.2 mm to 2 mm in diameter, depending on the basic structure of the rocks and soil around the area (Razak et al., 2019; Hashim et al., 2001). The sudden increase in river water level beyond the maximum capacity of the river can result in floods, thereby increasing the risk and impact of floods in areas near the river. The area most affected by this situation is the Georgetown area because of the location of the Pinang River located there. The Pinang River is located at the downstream of the basin. In the event of high tide and heavy rainfall at the same time, the City of Georgetown will experience unforeseen flood events like September 2017.

Acknowledgments The authors would like to acknowledge UniSZA and MOHE for scholarship under research grants: (FRGS/1/2017/WAB05/UNISZA/01/1) - RR222. The authors would like to specially thank the Department of Irrigation and Drainage (DID) for the secondary data and East Coast Environmental Research Institute (ESERI), Universiti Sultan Zainal Abidin (UNISZA) who gives permission to use research facilities and support in this research.

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