CHAPTER 1:
INTRODUCTION
1.1 Background
1.1.1 Background of research
The most severe natural disaster experiencing in Malaysia is flood. The damages caused by it, can be the most destructive of natural disaster. Malaysia receives over 4000 millimeters rainfalls average per years because of the influence of monsoons and located at the volcanic and seismological belts linger in Asia region. Flooding is defined as abnormal high stream flow that overtops the natural or out from level banks of a river. Technically speaking, these phenomenons can also be jargoned as a condition of re-excessive river flows. A flood plain can be defined as “the area of a river valley which is covered with water when the river overflows during floods” (Sabah Water Resources Enactment, 1998). These areas act as a natural reservoir and temporary channels for flood waters.
Two major type of flood occur in this country are monsoon flood and flash flood. The monsoon flood occur mainly from Northeast Monsoon which prevails during the months of November to March with heavy rains to the east coast states of the Peninsula, northern part of Sabah and southern part of Sarawak. Flood-prone areas in Malaysia are still under heavy development because there is no proper guideline for the development in flood plains area though several major floods had occurred in recent years (both as localized flesh floods and as basin-wide floods).
Hence the flood risk maps should depict the extent and the probability of a specific flood with a certain average recurrence interval (ARI). It is also clear that there is no holistic attempt to produce flood risk Maps that could determine the platform suitable for development. Hence, field measurement need to be done to verify the areas that are most vulnerable to flooding. The flood mitigation plans can be developed and managed efficiently of there are flood risk maps in digital form which could be updated to contain the flood depth information that are directly related to the spatial variation of the flood (sinnakaudan et,al, 2003)
History shown Sabah is included with the terrible affect of flood, figure 1.1 shows a flood scene in Sabah. There is estimated rm130 millions financial losses and 200 reported death,(see table 1.1)(Chan 1997). Prior to this situation, Sabah has played a part in the preparation of guidelines for developments, known as the ‘Sabah Water Resources Master Plan’ in the year 1995. In this master plan, the reserves of flood and flooding are considered as one of the current water issues in Sabah. In this plan too, a suggestion for implementing a flood and floodplain Management has been put forward In order to reduce negative impacts of flooding and flood liability on individual career and occupiers and to reduce private and public losses resulting from floods (SWRMP, 1995). A few years after the establishment of this plan, the ‘Sabah water resources enactment’ was enacted to provide for the sustainable management the water resources in Sabah to promote orderly , equitable and efficient use of water and to maximized economic, social and environmental benefits for the future (SWRE, 1998)
Figure 1.1: Floods in Sabah
Table 1.1: Official flood loss estimates for selected floods in Malaysia
In Sabah water resources master plan (SWRMP), these measures of managing floodplains are recommended. This can be used singly or combined, which is determined through the floodplain management. These three measures are the structural measures and planning measures and contingency measures (SWRMP, 1995). This research was conducted to aid hydraulic engineers in channel flow analysis, develop floodplain maps, determination and management at the Telipok River.
1.1.2 HEC-RAS
The Hydrologic Engineering Centers River Analysis System (HEC-RAS) (U.S. Army Corps of Engineers 2002a, b, c) is an integrated system of software designed to perform one-dimensional hydraulic calculations for a full network of natural and constructed channels and provide input and output information in tabular and graphical formats. The current version of this program will perform steady and unsteady flow analysis for subcritical, supercritical, and mixed flow regimes. Input and output data is provided in graphical as well as tabular formats. The HEC-RAS computer program uses a graphical user interface (GUI) for input and output data entry, and computational “engines” to perform the actual calculations. The program incorporates separate hydraulic analysis components, data storage and management capabilities, graphics and reporting facilities.
1.2 Background of the research area
Telipok river is located at the northern part of Borneo Island, on the west coast of Sabah. It is approximately 20 km from Kota Kinabalu. Since Telipok is located close to the seaside in the west coast of Sabah. It is subjected to severe flood occurrences. The west coast of Sabah experiences leaving downpours from November to December every year, due to the, the North-East monsoon. Several major flood occurrences in Telipok are described briefly in the next paragraphs.
A report writer by The Star Online in 2005 stated that the town of Telipok, located north of Kota Kinabalu was hit by the flood, its was the worst flood in 50 years on the 19th July 2005, affecting the entire town with the serious damages. The flood causes as many as 10 cars were submerged and 3 bodies were found death. Entire town was covered in a sea mud and also there were landslides at Jalan Lawa Mandau-Kiulu, Jalan Kokol and Jalan Ruminding-Tiko Pinahan, where roads and suspension bridges had collapsed.
In this research, flood simulation using computer modeling uses three different flood events, namely the year 1991, 92 and 1999 flood events. The primary flood event is the 1999 storm Hilda event and the other two are chosen for the purpose of hydrologic and the hydrodynamics modeling calibration and validation. These are the recent flood events that affected Telipok, and the information gathered from the events were made as impulse to the hydrodynamics and hydrologic modeling.
1.3 Research Objectives
Three objectives that become the backbone of this research had been determined; these objectives were made to complement previous studies done locally and globally. These objectives are:
a) The main purpose of this study is using Hec-Ras software to analyze topographic data and the effect of geometric data on the hydraulic models
b) To develop river map model include all a dendritic river system, or a full network (looped system) of stream channels
c) To develop flood risk maps depicting the current situation, the future development, and possible situations incorporating flood mitigation and floodplain management alternatives
1.5 Scope of study
This study was limited to Telipok district within state of sabah, specifically at the flood-prone areas of Telipok floodplains. The district was selected because of its closeness to the sea as well as its history of severe flood occurancies. In the model simulations, the 10 year, 50 year and 100-year storm return periods were chosen since they represent typical values for flood study. For the structural mitigation measures, detailed structural design such as the design materials were not elaborated. The flood risk maps generated were only made to investigate the impacts of the structural and non structural measures against the flood behavior in Telipok flood-prone areas.
1.6 Thesis Organization
This thesis is organized in 6 chapters. Chapter 2 presents a literature review comprised of a brief overview of the one-dimensional models used for this thesis, performed to analyze model geometry, and studies performed to analyze topography. Chapter 3 presents the methodology used to produce the results presented in this thesis, the methodology used for the one-dimensional floodplain mapping process (Hec-Ras) used for Telipok River. Chapter 4 presents the results. In the results section, the effects of topography and geometry are evaluated for the one-dimensional model (Hec-Ras) for Telipok River. Chapter 5 presents a hydraulic model for Telipok River will be introduced and the method/solution for the flood at the Telipok town will be discusses. Finally, Chapter 6 presents a summary of the results and the conclusions.
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