Effect of Rainfall on Groundwater Level Fluctuation in Terengganu, Malaysia

Groundwater refers to the water that occurs below the surface of the earth. It starts with rain and snow melt that seeps or infiltrates into the ground. The amount of water that seeps into the ground differs widely from place to place due to different types of land surface present. Groundwater is the purest form of water on the earth and found to be unlimited natural resources to mankind at the cheapest cost. It always flows through the fractures of rock and pore spaces over a long distance in the aquifers and to be available to the vast number of people at their firm [1].


Introduction
Malaysia is a country with many rivers and ocean crossed over it but, with all of this surface water cannot be relied upon for irrigation industrial and domestic uses. Some state uses groundwater as their source of irrigation, industry and domestic application among these states were the study area.
Groundwater refers to the water that occurs below the surface of the earth. It starts with rain and snow melt that seeps or infiltrates into the ground. The amount of water that seeps into the ground differs widely from place to place due to different types of land surface present. Groundwater is the purest form of water on the earth and found to be unlimited natural resources to mankind at the cheapest cost. It always flows through the fractures of rock and pore spaces over a long distance in the aquifers and to be available to the vast number of people at their firm [1].
Groundwater is free from air pollution and other pollutants that can easily pollute water from its pure form and wisely manage and protected against undue exploitation and contamination by the users Reddi 1986. Groundwater is dynamic natural resources that can be recharge most during the rainy season by the rainwater for the rest of the year. Over withdrawal of groundwater causes decline in the water table due to the stress and distorting the aquifer and may also leadadverse surface and subsurface environmental effect [2].
Groundwater recharge is usually influenced by climate variability and human intervention such as groundwater abstraction excessive or unsustainable withdrawal and the rest.
Siebert et al. [3] assessed groundwater use for irrigation in a global inventory via a range of pumping technologies. Recent studies in India and Bangladesh reported that a groundwater level (0.1-0.5 m/yr) was declining indicating reduction in aquifer storage for unsustainable groundwater abstraction for both irrigation and urban water supplies, this cases was also similar to Malaysia and other Asian countries.
Sayeed et al. [4] also assess groundwater recharge using Empirical method in the tropical zone (Selangor Malaysia) in which the groundwater recharge coefficient and effective rainfall were determined. The results showed that groundwater recharge was 326.39 mm per year, and recharge coefficient was found to be 18% for the study area. They further illustrated that unsustainable withdrawal can cause a decline in groundwater level.
The primary aim of this research is to evaluate the rainfall effect on groundwater level fluctuation in Terengganu Malaysia because of water demand is increasing rapidly due to increases in population growth and socioeconomic development. This encourage the current research in groundwater level so as the finding will provide some information to the government for water management and for predicting the future climatic event as well as groundwater level in order to avoid decline or shortage of it.

Physiography, climate, and hydrogeology of the study area
The study area is a state of the east coast of Peninsular Malaysia; it is situated in the coordinate 4°45'N latitude and 103°0'E longitude that is located in the north-eastern part of Peninsula Malaysia. Terengganu is bordered on the northwest by Kelantan, the southwest by Pahang and the east by South China Sea, the main river of the state is called River Terengganu. The state has a total area of 13,035 km 2 (5,033 sq. mi) and the total population of 1,015,776 as for the 2010 census with a density of 78 km 2 (200/sq. mi) [5,6].
Terengganu Malaysia for the period of 2001 to 2013 were sorted and arranged in an Excel for different homogeneity test. So also, the Evapotranspiration and rainfall data for the same years were collected from Department of Irrigation and Drainage (DID) and were sorted in the same format as above. And the map of the study area obtained from the Land and Survey Department Terengganu was used to locate the districts/stations were the data was obtained by the listed department above using GIS ( Figure 1).

Data quality
The homogeneity of data (Rainfall, Runoff and Groundwater level) in this study was checked using the standard approaches such as Wijngaard et al. [8], Von Neumann ratio test and the Standard normal homogeneity test. All the data from these seven stations were found to be homogenous. The missing value were found to be less than 5% for the period 2000 to 2012, these missing values in the data series were estimated using various types of weighting methods such as inverse distance, correlation, and normal ratio.

Runoff
The portion of precipitation on land that ultimately reaches streams with dissolved or suspended materials is known as runoff. Water from rain and snow usually flows over the surface of the ground into the streams; this is the current collected from the drainage basin and appearing at an outlet of the basin. There is some contrast between precipitation and runoff; the runoff is more uniform compared to precipitation while the precipitation is sporadic and irregular in nature.
Climatically, like the other states of the country, Terengganu has tropical monsoon climate that is generally moderately hot and humid all year around. The temperature is relatively uniform within the range of 21°C to 32°C throughout the year. During the months of January to April, the weather is generally dry and warm. Humidity is consistently high which approximately 80%. Terengganu has characterized by two main types of monsoon, usually the southwest monsoon season established in the latter half of May or early June and end in September. The northeast monsoon that usually starts in November and end in March. Terengganu receives heavy rainfall of approximately between 2034 mm to 2504 mm per year which can easily break the bank of the rivers and cause overbank discharge [7].
The aquifer in the study area is mostly covered with Indogangetic alluvium and is somehow deep. They are tapped primarily by private devices such as tube wells; pump sets rahats and the rest which are found mainly in the rural areas for their domestics used as well as for irrigation purposes. Some places have shallow aquifer ranges from 20 to 30 meters easy to dig for private purposes but for the state were dogs up to 100 to 130 meters. The groundwater fluctuation varies from place to place usually 0.2 to 0.8 meter between the pre-monsoon to postmonsoon season.

Data collection
The daily groundwater level data from seven hydrological stations collected from the Department of Minerals and Geosciences Runoff can be calculated using the following relation: Where, Kb and P are the rainfall and runoff coefficient, respectively.

Infiltration
The process by which water on the ground surface enters the soil that is governing by two forces: gravity and capillary action are known as infiltration. The water enters the surface starter of the earth. The infiltrated water first meets the soil moisture deficiency if any, and further the excess water moves vertically downwards to reach the groundwater table as recharge water. It is a measure of the rate at which soil is able to absorb rainfall or irrigation. During the infiltration, the rate decreases as the soil becomes fully saturated. Therefore, if the precipitation rate exceeds the infiltration rate runoff will usually occur unless there is some physical barrier. Infiltration can be calculated from equation (2): Where, I, P, ET, and R indicate the infiltration, rainfall, evaporation, and runoff, respectively.

Rainfall variation
The monthly rainfall variations of seven Districts of the study area during 2001 to 2013 are shown in the (Figures 2-8). The maximum rainfall was found throughout September to January during the rainy season of the area. The minimum rainfall was observed from February to August and sometimes very little or none in some month between

Estimated runoff
The results show that, the maximum estimated runoff was found in 2010 during the study period as the rainfall received was excessive. But throughout the study area, the estimated runoff was average and from 2010 to 2013 was gradually increasing as expected due to higher rainfall received during the years. The highest runoff estimated was 523 mm in 2010 in Menerong District, and the lowest runoff was 221 mm in 2001 at Nerus during the study period.

Estimated infiltration
The infiltration data of Trengganu, Malaysia illustrate that, the highest infiltration was estimated in 2010 during the study period as the maximum rainfall received during the year. Before the year 2010 the infiltration due some fluctuation and was average. The amount of infiltration was increased from 2010 to 2013 but did not reach the highest values obtained in 2010. The estimated highest infiltration was 3645 mm in 2010 at Menerong, and the lowest was 980 mm in 2001 at Nerus.

Relationship between rainfall and water level fluctuation
The result of the analysis entailed that, annual rainfall of the state is increases but not linear and decreases in 2013 for the study period as recorded in Table 1. Similarly for runoff and infiltration data in Tables 2 and 3 above, this result shows a good relationship among the parameters which indicate that, the higher the value was the rainfall, the higher amount where the estimated runoff and infiltration ( Table 4).
The above (Figure 9) illustrates the trends in the water table of the study area during 2001 to 2012. The result showed that, the minimum water table was in 2005, and the maximum was in 2011 due to different in rainfall, infiltration, and runoff. The result indicated the good relationship between these parameters as the fluctuation curve indicated which was abiding by the nature of the rainwater of the area. The highest deflection occurred from April to August, and the water table slowly increased until it reached the minimum during September to November it maintained an average level until February.  2002  2189  2878  2298  3011  2655  2321  1033   2003  2190  3024  3200  2746  2345  3220  1243   2004  3100  3001  2179  3256  2376  2198  2716   2005  2877  3122  3112  2398  3121  3111  2189   2006  2299  3010  2780  3312  2323  2299  2718   2007  2829  2728  2263  2306  2423  3020  2010   2008  2749  2829  2727  2416  2221  3018  1011   2009  2468  2298  2827  3002  2242  3120  2121   2010  3100  3100  2990  3645  3247  3122  2123   2011  3205  3102  3080  3444  3290  3124  2143   2012  3311  3108  3090  3536  3201  3124  2140   2013  3212  3110  3019  3240  3021  3031 2144 The water table starts to decreases till the heavy rain will start again in September. However, the overall yearly water table result indicating decline in groundwater level trend is due to unsustainable withdrawal of groundwater for domestic and irrigation purposes as the state used groundwater for water supply, this were played a vital role in water level fluctuation in Terengganu, Malaysia.

Conclusion
The study results illustrate that, the maximum rainfall occurred during October to December, and little rainfall was recorded during January to September. However, the maximum runoff and infiltration were also estimated during October to December. The water table fluctuation was recorded monthly, and analysis showed that, rainfall, runoff, and infiltration have an influence in recharge of the water table in Terengganu, Malaysia. The water table elevated during January to February due to the recharge by the listed parameters and usually declined from June to August. The lowest level of groundwater level fluctuation was found to be from August to September. The result of this study entails that the groundwater level fluctuations in Terengganu is depended solidly on rainfall pattern. The findings of this research can provide some information to the government for water management and for predicting future climatic events.