Abstract— The objective of this paper is to explain the potential of dam flooding caused a prolonged flooding. Dam flooding is a rapid and uncontrolled release of reservoir volume which, leads to severe flood at the downstream, specifically towards the people and environment of the affected region. Apart from causing severe flood, dam flooding also can accumulate stagnant water within a second or worsen the stagnant water if it already exists due to heavy rainfall. In other words, it caused prolonged flooding. Due to significant impact at the downstream, it is important to evaluate the potential of dam flooding. This will enable the authorities to analyze the downstream human safety, especially where no dam flooding and prolonged flooding histories are documented. Furthermore, there is no warning were issued for dam flooding.
Index Term— dam flooding, prolonged flooding, stagnant water; flood
I. INT RODUCT ION
DURING the monsoon or flood season, dam operation facing conflict objectives like flood control, irrigation, power generation and conversation at the end of the period [1]. At the same time, dam water levels are often lowered in order to avoid dam flooding or overtopping and maintain the dams’ safety [2]. Both [3] and [4] acknowledged that the key difference between dams and all other flood protection measures lies in the fact that dams introduce a new risk of dam flooding which usually results in dam flooding is one of major factors of dam failure. A group of researchers; [5-6], [2] and [7] stated that the chance of a dam break from the world record due to flooding is about one-third or 35% (International Commission on Large Dams ,ICOLD, 1973).
Though [8], opinionated that dam flooding is relatively slow process compare to failure of a dam, he also agreed with [9] and [10] that the risk of dam flooding during extreme floods has become a primary concern for hydraulic engineers, emergency planners and responders. In recent years, the design floods of
T his work was supported in part by the Ministry of Higher Education (MOHE)and Universiti T eknologi MARA (UiT M), Malaysia under
Grant Exploratory Research Grant Scheme (ERGS). P. D. Caroline is the PhD. Candidate, Faculty of Civil Engineering, Univerisiti T eknologi MARA 40450 Shah Alam, Selangor, Malaysia
(e-mail: [email protected]).
T . Wardah (Dr.) is the Assoc. Prof, Faculty of Civil Engineering, Univerisiti T eknologi MARA 40450 Shah Alam, Selangor, Malaysia
(e-mail: [email protected]).
a number of dams were re-examined and discovered that the revised flows were often exceeded than the allowable designs flows, which would resulted in dam flooding due to insufficient existing storage and spillway capacity [8].
During intense rainfall also, it is known to cause massive flooding, a damaging natural hazard faced by society [11], as water entering the residences and commercial buildings. Even worse, where large parts of areas are facing prolonged flooding that lasted for several days or months [12].
Due to the reason above, dams should be closely monitored during periods of heavy rainfall, especially dams with large numbers of people immediately downstream [13] because dam flooding poses a public health threat in terms of the prolonged flooding at the downstream.
This paper presents the preliminary study of potential dam flooding caused a prolonged flooding. Although warnings are issued for heavy rains and flash flooding, no warnings were issued for potential dam flooding [13]. Evaluation the impact of dam flooding enables the regulatory authorities to analyse the downstream human safety, especially where no dam flooding and prolonged flooding histories are documented [14], [15] and [16].
II. DAM FLOODING AND PROLONGED FLOODING A. Dam Flooding
The Northeast Monsoon starts from November to March, is the major rainy season (600 mm) for Malaysia, particularly to the east coast states (Kelantan, Terengganu, Pahang and East Johor) of Peninsular Malaysia and western Sarawak. The operation of dams is a major issue[17] especially during a period of high rainfall, dam flooding or a spill [18] may occur when the reservoir elevation reaches its maximum. It also worsens the flood conditions on the river system which lead to increasingly destructive floods downstream of the dam. As what happened to Ahning Dam [19] Kedah, at the Pedu-Muda area and Timah Tasoh Dam, Perlis, Malaysia (Fig. 1).
Kenyir Dam in Kuala Terengganu, Terengganu experienced flooding during the major rainy season (Fig. 2), stated that, the water level was categorized as emergency as it reaches 149 meters and this level can be achieved if the water level continuously increases at this rate and heavy rainfall within a week.
Dam Flooding Caused A Prolonged Flooding
Fig. 1. T imah T asoh Dam, Perlis experienced dam flooding in the year 2010 that caused a destructive flood in Perlis.
Fig. 2. Kenyir Dam, Kuala T erengganu, T erengganu experienced dam flooding (article dated 13 February 2006 from Berita Harian)
B. Prolonged Flooding
A new type of flood problem is prolonged flooding. It is also known as stagnant water or water standing or submergence [20]. In fluid mechanics, the term of stagnant is to describe the velocity of water of zero or no motion [21]. Prolonged flooding is associated with public health threat or major environmental hazard due to accumulation of municipal sewage, foul odours, mosquitoes, and growth of water hyacinth [22]. The economic impact of the floods was also widespread [23] and one of the most serious impacts to the agricultural productions of the country [20].
III. THE CHRONOLOGY OF DAM FLOODING CAUSE PROLONGED
FLOODING
In the end of year 2006 until early 2007, during the
Northeast Monsoon, all eight districts in Johor were stricken with two flood waves, first on 19 - 31 December 2006 followed by 12 - 17 January 2007. The most affected area is Batu Pahat, Johor, as it was facing a dam flooding of Sembrong Dam (Fig. 3, 3a and 3b) and prolonged flooding.
Fig. 3. T he Sembrong Dam experienced dam flooding (Source : Holistik, 1 February 2007, www.pmbj.gov.my).
Fig. 3a. T he water level of Sembrong Dam.
SEMBRONG DAM
2
3
1
a.
e.
4
d.
c.
b.
a. Normal Level Level = 8.50 m Capacity = 18 mil m3 Surface Area = 8.5 km2
e. Overflows at the ungated spillway indicate, dam experience flooding. d. Danger level = 12 meter (the maximum water level). Exceed this level dam flooding will occurred.
Fig. 3b. Chronology of dam flooding caused a prolonged flooding
Fig. 4. Hydrograph starting 14 December 2006 until 28 January 2007 for Sembrong Dam and Sembrong River at Batu 2.
Fig. 4a. Hydrograph for station Sembrong Dam and Sembrong River at Batu 2 during the first flood wave occurred from 17 until 31 December
2006.
Fig. 4b. Hydrograph for Sembrong Dam and Sembrong River at Batu 2 during the second flood wave occurred from 9 until 26 January 2007 .
The hydrograph in Fig. 4, 4a. and 4b., shows that the Sembrong Dam experienced flooding which, cause Sembrong River reached the danger level. Eventually leads to the river overflow and flooding the downstream area.
In Fig. 4a and 4b, the dam water levels reach its maximum and had it first released on 20 December 2006, which was a day after the first flood waves start. The water was continuously released which cause until it reached the maximum on 13 January 2007 with water levels was 13.60 m and the capacity almost 75 million m3. The recorded overflow was 300 m3/s.
According to the several public reports, including in Holistik bulletin dated 1 February 2007 stated that, due to dam flooding from Sembrong Dam, only Batu Pahat district was inundated by prolonged flooding (Fig. 5) that lasted for one and a half months from the first flood wave until it drained out fully.
Fig. 5. T he occurrence of prolonged flooding in Johor.
A group of doctors conducted a survey during the prolonged flooding occurrence found that:
• Prolonged flooding provided favourable conditions for mosquito vectors to breed [24].
• The highest rate for the majority of the water borne communicable diseases such as acute respiratory infections (ARI), skin infections, fever, acute gastroenteritis (AGE) and acute conjunctivitis [25]. 4. 13 Jan 2007
Peak overflow 300 m3/s 3. 13 Jan 2007 Peak inflow 700 m3/s
1. 20 Dec 2006 Level = 12.65 m Capacity = exceed 52 mil m3 Surface Area = exceed 12.1 km2
2. 13 Jan 2007 Level = 13.60 m
Dam failure studies have always been emphasizing on the effect of flood at the downstream either due to dam break or flooding. A sudden, rapid and uncontrolled release of reservoir volume [26] leads to severe flood [27] in which there will be significant impact at the downstream specifically towards the people and environment of the affected region [16, 28]. Dam floodingcan worsen the stagnant water if it already exists due to heavy rainfall, which leads to prolonged flooding. Dam flooding and prolonged flooding has directly relo cated thousands of people and poses a public health threat [23, 29-30].
IV. CONCLUSION
Number of the dam in Malaysia has been rising along with social progress and economic growth indicating that dams highly demanded for sufficient power generations and vital source of water supply for municipal, industrial and agriculture. Apart from fulfilling the demand, dam also plays an important
role as a defence mechanism for flood disaster [31]. During the period of
benefits, the presence of a dam induces an additional risk [32-33] because it is known that main criteria in building dam is, it must be constructed in mountainous area [34]. Therefore, here is a huge destructive potential of the water stored in the dam, especially densely populated area downstream[5].
Dam flood routing map can show the largest area [35-36] that might be prolonged flooding at the downstream. Though the probability of flooding from dams is relatively low, by providing the dam flood routing map involving prolonged flooding can protect the lives and property of downstream residents.
Though the dam is safe hydrological assessment [37] and chance of flooding from dams is very small, understanding where water could go or dam flood routing map can protect the lives and property of downstream residents.
ACKNOWLEDGEMENT
This first author is a PhD candidate of Faculty of Civil Engineering, Universiti Teknologi MARA Malaysia and this paper is partially of her research.
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C aroline Pe te r Diman was born in
Asajaya, Sarawak, Malaysia, on 9 September 1977. She completed her Bachelor of Science (Civil Engineering) (Hons.), in year 2000, from Universiti T eknologi MARA Shah Alam, and started her carrier as a lecturer at Universiti T eknologi MARA Sarawak. Year 2004, she
