(Gis) Approach for Analyzing Channel Planform Change with Examples of Langat River, Malaysia

ID:327 USE OF GEOGRAPHICAL INFORMATION SYSTEM (GIS) APPROACH FOR ANALYZING CHANNEL PLANFORM CHANGE WITH EXAMPLES OF LANGAT RIVER, MALAYSIA M.E. Toriman1; M.Mokhtar2; M.B.Gasim3; R. Elfithri2 & Nor Azlina A.B1 1School of Social, Development & Environmental Studies, FSSK, Universiti Kebangsaan Malaysia. 43600 Bangi, Selangor 2Institute of Environmental & Development (LESTARI), Universiti Kebangsaan Malaysia.43600. Bangi Selangor, Malaysia. 3School of Environmental Sciences and Natural Resources, Faculty of Sciences and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi Selangor Malaysia 4Fakulti Kejuruteraan Awam, Universiti Teknologi Malaysia, 81310 Universiti Teknologi Malaysia, Skudai Johor, Malaysia This article focuses on the Langat River Channel Planform changes in medium (25 to 100 years) and short time (over last few months to 25 years) scales using Geographical Information System analysis (GIS) involving the cross section and sinuosity analyses. Three sets of topographical maps for three different years (1969, 1976 and 1993) were digitized and rectified and type of changes for the non-stable reaches were defined by superimposing the digital maps of all dates. The results indicate that, middle stream is the most unstable reach followed by upstream which has a few unstable sub-reaches while the downstream shows no changes during the study period. Type of most of the lateral changes for upland reach was meander progression and for middle stream meander progression and avulsion construct most of changes. The middle stream of the channel was identified as the most unstable reach with an average 11.81% change in its sinuosity index. Meanwhile, the upland and downstream of the channel were behaving as more stable reaches with an average 6.92% and 8.47% changes in their sinuosity, respectively. In conclusion, this study proved that, during the short and intermediate timescales, Langat River experienced continuous river planform with active modification in the middle and down sections of the river. Keywords: River planform change; GIS; Meandering; Langat River; River channel Introduction Rivers display a dynamic pattern of meandering over time. Channel stability is the ability of the stream to transport the flows and sediment of its watershed in such a manner that the dimension, pattern and profile of the rivers are maintained without aggrading or degrading (Elfithri 2011; Mohd Ekhwan 2009, 2010). The stability status of a river channel can be determined by assessment of the channel planform over time. In this study the Langat River channel assessment has been studied in different time scales. The topographical maps of the river in different dates are manipulated in Geographical Information System (GIS) software to measure the planform changes of the channel over an intermediate time scale. Technical advances in more recent years, most notably, the development of GIS, have enhanced the ease with which data on channel planform from a variety of sources can be combined to assess and analyses river channel change (Sear & Milne 2000; Gilvear 2000). GIS is one of the tools widely used for assessment of river channels recently. This powerful tool is able to scale correct and superimpose different maps or aerial photographs with great precision. It is also possible to add any other ID:327 spatial documents as an attribute to the related location and use them whenever required (Winterbottom 2000). The effects of climate change are probably the most important natural factors controlling fluvial hydrosystem equilibrium and, therefore, river channel change (Mohd Ekhwan 2009). Leopold, Wolman and Miller (1964) used two simple and general parameters namely, mean annual temperature and mean annual precipitation to characterize the climate. They also emphasized that both magnitude and frequency of the climatic factors strongly control the significance of different geomorphic processes. In this work the rainfall information are studied to find out their effect on Langat River channel changes. Various catchment developments and project features such as deforestation, urbanization, channelization and flow diversion are examples of anthropogenic factors that may increase inflow discharges. Increased discharges tend to cause cross section enlargement, accelerated meander migration and eventual lengthening of meanders and longitudinal profile change. Study Area and Methodology The Langat River has a total catchment area of approximately 1815 km2 with its uppermost stretch originates from the Titiwangsa main range of the State of Selangor and Negeri Sembilan. It lies within latitudes 2O 40’ 152” N to 3O 16’ 15”N and longitudes 101O 19’ 20” E to 102O 1’ 10” E. The main river course length is 141 km mostly situated about 40 km east of Kuala Lumpur and ends its journey into the Strait of Malacca (Mohd Ekhwan et.al. 2010; Mazlin et. al. 2010). The Langat River basin is shared between Federal Territory, State of Selangor and State of Negeri Sembilan, serve as the core natural river within premier development activities like Putrajaya, Cyberjaya, Kuala Lumpur International Airport (KLIA), Nilai, Ulu Langat and Puchong industrial estates, commercial and housing estates and at least four higher learning institutions. Topographically, Langat River catchment can be arbitrarily divided into the plains of the west and mountain and valleys of the east and north. Generally, the physical features of the Hulu Langat are distinctive with undulating lowland, hills and mountains. About 55 percent of the catchment is steep mountainous country rising to heights of 900 m (Bukit Pening), and the reminder is hilly land with some swamps along the river’s reaches. Geologically, Bedrock in the mountain area is granite that forms the mountain bone of the Peninsular and extends around the hilly areas near Kg. Cheras. Layers of the hilly areas are called Kenny Hill Formation and Kajang Formation, consisting of metamorphosed sandstone, shale, mudstone, and schist. The upper part of the bedrock including those of granite is weathered. In the low flatlands, thick quaternary layers are deposited on the bedrock. At the study area, the soil is formed by granite and sandstone. It has been designated as a steepland ‘Serdang’ and lowland ‘Selangor-Kangkung’ soil series. The soil profiles in steep area at high elevation are always more than one meter. In the Langat River catchment, soil depth extends to more than two meters depth, a feature described by Gasim, et.al (2009). GIS technique was employed with the main objective to extrapolate channel planform changes from various scale topographical maps at a uniform scale. The database used in GIS analysis comprises of four incomplete sets of topographical maps dated 1993, 1984, 1976 and 1969 with a scale of 1:50,000, 1:10,000, 1:63,360 and 1:63,360, respectively. All maps were digitally scanned and joint in Microsoft Visio 2003 and Microsoft Paint software to establish a digital geographical database. The maps then were ID:327 rescaled in Microsoft Visio 2003 to a uniform scale. Then the digital maps were converted into 24-bit Bitmap format and exported into GIS ArcView software run on a personal computer with Microsoft Windows XP platform. The rectification process was carried out in ArcView software for map of each year by adding a new theme to the view and using the polylines tool. Having a uniform scale, the rectified maps of different dates were superimposed to identify stable and unstable areas within the study reaches (Downward & Brookes 1994; Mohd Ekhwan 2008; Wellmeyer 2005) Quantitative analyses then were undertaken in order to examine river channel planform changes along the study reaches of Langat River. It involves determining and measuring the channel sinuosity which is channel length over valley length. In this respect, channel sinuosity index is one of a major indicator of channel response (Hooke & Redmond 1992). The process of sinuosity measurement involves measuring the valley length as a straight line drawn from the starting point to the end point of each sub-reach and the channel length which is a meandering line along the channel axis. The calculation of sinuosity index was carried out in Excel file. By superimposing the digitized maps of Langat River from different years, the channel planform changes were highlighted and the stable, unstable and highly unstable reaches were extracted (John et al 1992; Mohd Ekhwan 2005). Results and Discussion Upland Reach For the upland area, topographical maps over three years were used, namely 1969, 1976 and 1993 where the map of year 1976 was available only for half of the reach. Figure 1 shows the superimposed maps of Langat River for the upstream reach. Figure 1: Superimposed maps of Langat River at upland Reach ID:327 The lateral change statistics of sub-reaches in upland area are presented in Table 1. According to the statistics, the upland reach has two unstable sub-reaches, namely sub- reach 5 and 7 with two changes each between the years 1969 and 1993, but the rest of the reach performs a good stability. Table 1: Type and frequency of lateral changes of upland reach: (1969-1993) Sub-reach No. Frequency and type of change(s) Stability status 1 No change Stable 2 No change Stable 3 No change Stable 4 Meander progression: 1 Stable 5 Meander progression: 2 Unstable 6 Meander progression: 1 Stable 7 Increasing amplitude: 2 Unstable The sinuosity index of sub-reaches of Langat River upstream over the period of 1969-1993 is shown in Table 2. Among the sub-reaches, the sub-reach 4 with a total sinuosity change of 0.2 over the period 24 years registered the biggest change in sinuosity and the sub-reach 7 with a total sinuosity change of 0.03 registered the smallest change (Figure 2). Table 2: Sinuosity of the parts of the upland reach Reach No. 1969 1976 1993 1 1.14 1.16 1.13 2 1.15 1.12 1.23 3 1.06 1.04 1.13 4 1.37 NA 1.58 5 1.48 NA 1.37 6 1.48 NA 1.34 7 1.46 NA 1.43 ID:327 Up stream 50 40 69-93 Percentage 30 change of 76-93 sinuosity 20 69-76 10 0 1234567 Sub-reach No.

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