According to Lin et al. [1] flood can be defined as a high water flow naturally or artificially from the river bank that dominates the surrounding area to cause overflow. The high flow of the water may extend over the floodplain and generally become a hazard to the society. Flood is one of the devastating hazard or disasters that Malaysia had been experiencing over the decades, this includes the Sabah and Sarawak. There is a problem of flash flood in the Terengganu watershed particularly during monsoon period ( November to January) every year, but more severe in 2014, 2015 and 2017 (Table 1).

Table 1: Total area of the watershed.

According to Zhang et al. [2] SWAT is increasingly being used in the watershed hydrological processes widely accepted and understood for evaluation of modeling application Javier et al. [3] has explored the degree of complexity on spatial variables in the watershed on examination of parameters. This is because input data are not only affected by parameters but also modifies the inbuilt model structure. The Department of Irrigation and Drainage Malaysia (DID) is responsible for providing flood forecast and warning services to the public Mah et al. [4] land use affects land cover and vice-versa, but changes in land cover by land use do not explain the reason for degradation of land (Table 2). However, it denotes shifting land use pattern by various factors of social changes also result in land cover changes that affect ecosystem and biodiversity. Radiation budget and water trace gas emission and other processes which directly affect climate and biosphere Riebsame et al. [5] The application of SWAT and the 3D environment has contributed greatly in identifying areas or zones affected by flood in each subbasin parameter within the Terengganu watershed. The 3D modeling and simulation using the 5 m resolution from the ASTER DEM were converted into Arc Scene using ArcGIS-3D software. During the ancient times, people developed ways of monitoring flood level and this enables them to predict the water flow and the risk or hazard involved. The 3D visualization techniques include the remote sensing, such as satellite imageries, aerial photogrammetric, Geographic Information System (GIS) and LiDAR modeling. The recent application of 3D GIS had provided clear presentation and visualization of flood hazard event than the previously used of 2D maps [6].

Table 2: Land use result.

Geographic modeling and simulation are now considered to be fundamental in process and mining as well as dam-break flood. The dam is of benefit to people but there is a tendency to be broken due to flood hazard event [7,8].

The 3D model display information uses in Google Earth. The KML files will be read in ArcGIS. Google Earth Pro is more advanced than the standard version which allows high image resolution to be overlaid with other information included in GIS data. It is necessary to analyze water flow direction within 2 meters that can allow flood monitoring and change it from 2D to 3D [9]. The DEM was used to develop mesh in the system and the water mask was generated for simulation of flood and produce flood models. This can be successfully visualized in the realistic 3D environment [10].

Flood has been affecting human habitat and create the unsustainable environment. The current study about event in many cities, towns or villages can never be overemphasized due to the fact that climatic conditions are not static. The land covers as well as the geographical settings. The Geographic Information System (GIS) will be applied in acquiring spatial and non-spatial data. The river flows are quite high during the monsoon, and the water level becomes high, therefore we create the DEM to simulate the flow direction at regular interval to avoid the flood. We need to get informed or be informed about the aftermath of flood event that is the hazard and damages as quickly as possible, so as to assess the magnitude of losses and plan for the relief operation. Flood is most severe in hazard in Malaysia [11]. The issue of flood disaster is a global phenomenon that requires attention in other to control life and properties. There is need to monitor the activities of the flood by applying the modern technology of Geographic Information System [12].

Study area

The study focuses on the flood mitigation in one of the floodprone regions in the Eastern part of Peninsula Malaysia called Kuala Terengganu Catchment area. The Kuala Terengganu catchment has a total area of 286507.3500 hectare or 707973.9872 acres and the catchment lies within the wet tropical climate that exhibits vital roles in manipulating weather, soil, organic matter sediment yield that drained into the South China Sea. It is located at upper left corner 50305.407N, 10202315.536E and the lower right corner is 403924.251N, 103011 6.211E respectively. The bottom has gentle slope gradually deepening toward the open sea as cited in (Figure 1) [13].

Figure 1: Study area map.

Methods

The SWAT Data Sources are obtained

• Department of Irrigation and Drainage (DID)

• Data of flood event in the study area (previously)

• Digital Elevation Model data (DEM)

• Stream flows data

• Land cover/land uses data

• Soil types

These are obtainable base on a different location of the stations

1. Climate data from Malaysian Meteorological Department (METMalaysia) from 2000-2015.

2. Land covers images from Malaysian Remote Sensing Agency (MRSA).

3. Malaysian soil map was obtainable from online source European Digital Archives of soil maps (EuDASM) named Reconnaissance soil map Peninsular Malaysia 1968.

Required spatial datasets and Optional spatial datasets

Required spatial datasets and Optional spatial datasets

1. DEM

2. Land Cover

3. Soil map/data

The optional spatial datasets include:

1. Weather parameters

2. Daily rainfall data

3. Daily stream flow

4. Daily suspended-sediment

The result from the SWAT was obtained on 13th May 2017 at 05:29 pm with the total area of the watershed having 286507.3500 hectare or 707973.9872 acres. The total numbers of sub-basins are 25 characterized by 305 numbers of Hydrologic Response Units (HRUs). The threshold of 10/10/10 percent was chosen and selected. The flood risk event has been overcome by developing real-time simulation in the 3D scenario. This becomes apparent when the use of Geographic information system was employed to solve the problems of flood risk. This is done through visualization of selected zones affected by flood in Terengganu Malaysia (Figure 2).

Figure 2: flow chart.

The results from the SWAT watershed delineation was presented in Figures 3-5. Watershed is also known as a basin or catchment, or simply an area delineated with a specified outlet point that emptied in a large body of water. The Figure 6 represents the delineated watershed of Kuala Terengganu Catchment.

Figure 3: Watershed delineation in Terengganu catchment.

Figure 4: Stream network and reservoirs in Terengganu catchment.

Figure 5: The main divisions of Terengganu catchment sub-basins.

Figure 6: Land use classification of Kuala Terengganu catchment.

The stream links and reservoirs are developed through the stream network. 10 stream links are obtained from the Terengganu catchment. Each stream link had been connected with the defined sub-basins.

There are about 25 different sub-basins in the study area selected. Each of the sub-basins was characterized by a distinct parameter for classification and hydrologic analyses. Figure 6 shows the classified subbasins in Kuala Terengganu catchment.

In the hydrologic response unit (HRU) analysis obtained from the SWAT, four major sub-basins were fully discussed. The subbasins number 16 and 23 are selected as the smallest sub-basins in the Terengganu River catchment with 468.990 hectares SWAT area of 0.16%. The land covers characteristics include water and forestevergreen. The soils found within the sub-basins are the local soils called Marang and Steepland then the lowest slope has 8.36% and the highest slope is 52.88% respectively. Furthermore, the sub-basins number 23 has 221.49 hectares with total SWAT area of 0.08% with a land cover of forest-evergreen and water and the local soil type called Marang. The lowest slope of 0-10 meters has 14.3% and the highest slope area have 27.46%. The largest sub-basins found in the catchment area of Terengganu are the sub-basins number 2 and 4. The total area in sub basin 2 is 27,019.53 hectares with SWAT area of 9.43%; the land covers include the water, oil palm, and the forest-evergreen. The local soils are Marang and Steepland and the lowest slope from 0-10 with 8.69& and the highest slope with 30.39% (Table 3).

Table 3: Soil types result.

The below explains the different pattern of the land cover which includes forest, water, urban land use, rubber paddy orchard oil palm, and grassland. The soils classification was based on the USGS with default SWAT soil database. The local soils in the study area are edited base on the SWAT update from the existing soils of the world. Table 4 shows the result of the soil classification with total areas in hectares, acres as well as the total percent obtained during the analysis (Figures 7 and 8).

Table 4: Slope result.

Figure 7: Soil map of Kuala Terengganu catchment area.

Figure 8: Slope map of Kuala Terengganu river catchment.

The Soils has the ability to absorb moisture and get cooler and hotter quickly. Depending on the temperature, the water retention capacity varies from equatorial wet climate to monsoon as well as arid and semi-arid environment. The steep land has the highest percentage 69.85%. However, most likely to have less water retention capacity.

The slope data derived from the SWAT database was an inbuilt developed from the threshold of 10/10/10 percent from the HRU. Table 4 shows the result of total area from each category of slope in hectares and acres while taking cognizance of slope percent from 0-10 up to 40 meters above.

The elevation or slope map of the Kuala Terengganu catchment shows dark grey color depicts the lowest elevation that is 0-10 meters. The green color pattern is 10-20 meter slope, the blue color is between 20-30 and lastly, the light grey color in the map represents the highest slope.

Flood risk and mitigation model was developed as shown in Figures 9 and 10. The yardstick is to measure the magnitude of the flood risk in the catchment area of Kuala Terengganu. Here we arrived at the categories of flood risk from the highest risk to moderate and no risk zones within the watershed. The flood risk map represents the risk zones which can be used for mitigation, planning, and a warning to the public.

Figure 9: High and low flood risk map of river Terengganu.

Figure 10: Removal of forest develop more flood risk in Terengganu river catchment.

The removal of major land cover such as forest land cover in Kuala Terengganu will significantly affect the zones which are predominantly occupied by evergreen forest. While both zones are at flood risk, the presence or absence of more land covers will ultimately change the water flow. The aftermath of flood event usually is associated with pollution. Dirty water with refuse and garbages, as well as blocked drainages, might cause an outbreak of epidermal disease, the risk of lives through broken cables can easily electrocute humans and live animals.

The 3D flood models were produced from the digital elevation model (DEM) of the study area was overlaid with the mask and the Terengganu river flow was considered as a base height. Figure 11 describes the 3D model developed from the ArcScene. At this point, the Z values are calculated in other to create the simulation. The real-time simulation is presented in Figure 11 while the simulation was displayed, the purpose is to create a quick alert or warning through animation video perhaps all the areas prone to flooding will be easily identified and mitigation action can be applied.

Figure 11: 3D flood simulation model of Terengganu river catchment.

Flood simulation model of Terengganu catchment in Figure 11 presents the real-time 3D simulation with the blue color representing the flood event that ranges from 1 to 205 meters of elevation while other zones from 205 to 314 meter will be a flood if the water level increases. The model is also available in animated form.

The study of flood simulation become paramount in other to evaluate and provide information for decision making and flood control planning. At present, the two-dimensional (2D) visualizations are not sufficient in presenting real scene and therefore cannot make a full representation of data available. Today geographical 3D simulation and modeling are regarded as a fundamental approach to solving complex geographic problems. The SWAT has developed the scenario from the individual sub-basins for the Terengganu catchment where about 25 sub-basins parameter are obtained in the catchment. The watershed has been delineated creates sub-basins parameters where each sub-basin are having distinct characteristics of hydrologic response unit (HRU). The recent trend in flood monitoring was applied to 3D for the quick response, alert and warning, mitigation, planning, and management. Each time there is a flood in Terengganu we can visualize it base on the predicted simulation in 3D. The research is vital to urban planners, surveyors, environmentalist as well as engineers and geologist.

This research was fully supported by my able supervisor Dr. Razak Bin Zakariya from the faculty of Marine and Environmental Sciences Department of Remote Sensing and GIS, University Malaysia Terengganu.