FLOOD INUNDATION ANALYSIS BY USING RRI MODEL FOR KALAY CITY AREA IN 2015

ABSTRACT

Flood is one of the natural disasters, which generally occurs every year and the most destructive impacts in Myanmar.Severe flooding in Myanmar began in July 2015 and continued into September, affecting 12 of the country's 14 states and Regions, resulting in about 103 deaths and affecting up to 1,000,000 people.Most of the casualties were reported from the Ayeyarwady Delta. Torrential rains that began on 16 July destroyed farmland, roads, rail tracks, bridges and houses,leading the government to declare a state of emergency on 30 July in the four worst-hit regions in the westMagway Region, SagaingRegion, Chin State and Rakhine State.Kale city is one of the effected cities in this flood and the highest depth of inundation may affect the urban area of Kale.In this study, Rainfall Runoff Inundation (RRI) model was used to develop the estimate flood inundation area.

INTRODUCTION

The Republic of the Union of Myanmar is one of the South East Asia country and total land area of (676,578) sq km and a population of (57) million. Its agricultural based country which lies between 09° 32’ N -28° 31’ N latitude and between 92° 10’ E -101° 11’ E longitude.Its long coastline of about (2,000) km covers almost the entire east coast of the Bay of Bengal. Myanmar is prone to multiple natural hazards including cyclone, floods, drought, landslides and earthquakes. Previously, a cyclone would make landfall and cause flooding in Myanmar about once every three years. However, since the year 2000, cyclones have crossed the Myanmar coast every year, drastically increasing the exposure of the country to natural disaster. In Myanmar, majority of big cities and towns, economically strategic places in the country, usually situate along the major river. Figure 1 shows the location of Myanmar.

Figure l: Location of Myanmar

It’s highly vulnerable to weather, climate and hydrology related hazards. Tropical cyclone,

flood, heat waves and drought have a major impact on Myanmar. The “Dry Zone” is prone to

PDF Compressor Pro

droughts, the valley and delta experience extensive flooding, and the costal zones are vulnerable to sea level rise, tropical cyclones and storm surges. Due to Cyclone “Nargis” in 2008, the death tolls were 138,000 people and affected people were 2.4 million populations. The recent flood experienced at most part of the country in this year also is indicated how Myanmar is vulnerable to disaster.

During last mid-July of this year, continues heavy rain had been receiving in the large part of Myanmar because of vigorous monsoon strength. That severe weather was intensified by the depression formed over the North Bay of Bengal, which intensified up to cyclonic storm “Komen” when crossing the Bangladesh coast, had caused consecutive intense rains for a week and severe strong winds over west and northwestern part of the country. The accumulated rainfall amount observed during the last week of July exceeded the July monthly rainfall records and it is mostly in the state and regions located in the west and northwest part of the country(Figure 2).

Figure 2: Rainfall condition during July, 2015

So, many rivers and creeks became swollen and their water surfaces extremely exceeding

danger levels triggering severe flood in various parts of the country.There were floods at downstream of Chindwin River, middle and downstream of Ayeyarwady River, Thanlwin River,

PDF Compressor Pro

Sittoung River, Shwegyin River, Dokhtawady and Ngawun River. The big flood occurred at Mawlaik, Kalewa and Monywa of Chindwin River and the floods were the first highest record in Monywa and second highest records in Kalewa during last 50 years. Similarly, the floods occurred at Pakokku, NyaungOo, Chauk, Minbu, Magway, Aunglan, Pyay, Seiktha, Hinthada and Zalunof Ayeyarwady River and the flood were second and third records. Moreover, the floods occurred at Ngathainggyaungof Ngawun River, Hpaan of Thanlwin River, Madauk of Sittoung River, Shwegyin of Shwegyin River, Bago of Bago River, and MyitngeofDokhtawady. These floods exceeded by 3 ft to 11 ft above their respective danger levels and the flood duration stayed 2 days to 26 days above their respective danger levels Figure 3 and 4.

Figure 3: July and August Flood Condition above their respective danger levels (feet)

Figure 4: July and August Flood Condition above their respective danger levels (days)

Those flood affected roads, bridges,houses in various villages and towns, paddyfields and agricultural crops by inundation.Moreover, not onlybecause of severe floodingand erosion but also landslides were followedat someplaces. The official report describedthe death toll from flooding across the countryas 137 at least, withalmost 1.6 million peopleaffected and inundated nearly 1.4 million acresof farmlandwith damagedmore than 0.9 millionacres. Figure 5 shows Flood Effected People in Myanmar (2015 flood).

PDF Compressor Pro

Figure 5: Flood Effected People in Myanmar (2015 flood).

My study area is Kale city area. It’s situated in Sagaing Region and near the Myittha River. Kale city area is 294.12 km2and elevation is 140 m (450 ft). Study area islocated between Latitude 23°10′N and 58°61′N, Longitude 94°10′E and 94°14′E (Figure 6). Total population of Kale city is 400,000 people. Figure 7 shows the Average monthly rainfall of Kalewa and Kale city and Comparison of rainfall data. Figure 8 shows the Hydrograph for Kale (Myittha River) and Kalewa (Chindwin River).

Figure 6: Location of Study Area

PDF Compressor Pro

Figure 7: Average monthly rainfall of Kalewa and Kale city and Comparison of rainfall data

Figure 8: Hydrograph for Kale (Myittha River) and Kalewa (Chindwin River) Inundation analysis is one of the most effective non-structural measures for flood mitigation

system. This study was conducted by using Geographic Information System (GIS) interfaced with a Rainfall-Runoff-Inundation (RRI) model which can analyze rainfall, runoff and inundation simultaneously. Flood inundation analysis will help in estimation the loss that occurred to the paddy agriculture due to flood. In this study, possible damage percentage for various properties are assumed based on the peak inundation depth and duration results from RRI model simulation.

DATA AND METHODOLOGY

To analyze the flood inundation of Kale City area, we used the topography data such as digital elevation model (DEM), flow direction (DIR) and flow accumulation (ACC) and observed rainfall data is used as input data for the Rainfall Runoff Inundation (RRI) model. After parameterization, model run for simulation result and the output result from the model is flood inundation map and simulation discharge. The model can produce inundation map with depth and duration and calculated discharge. The model is calibrated with observed discharge.

In this study, we are using the ground rainfall data of 12 DMH observation stations and satellite rainfall data of GSMaP satellite rainfall data from 1 April, 2015 to 30 September, 2015. Table 1 shows the Location of the Ground Rainfall Observation Stations.We are apply default river width, depth, slope roughness and infiltration parameters. In this study, JAXA, ALOS-2 satellite

PDF Compressor Pro

image (for 2015 flood event) were used to validate the model inundation simulation in Kale City. Figure 9 shows the Methodology for Flood Hazard Mapping.

No. Station Latitude Longitude No. Station Latitude Longitude 1. Mawlaik 23.63 94.42 7. Vaar Camp 22.81 93.98 2. Kalewa 23.20 94.30 8. Falam 22.92 93.68 3. Mingin 22.87 94.50 9. Ramtholo 22.90 93.45 4. Tamu 24.20 94.30 10. Hakha 22.65 93.62 5. Gangaw 22.17 94.13 11. Pauk 21.45 94.47 6. Kale 23.20 94.07 12. Mindat 21.38 93.95

Table 1:Location of the Ground Rainfall Observation Stations

Figure 9: Methodology for Flood Hazard Mapping

RESULT AND DISCUSSION

Flood inundation simulation was conducted by using RRI Model with six month rainfall

data in 2015. At first, 12 rain gauge stations data were arranged in text file. Then Rain Thiessen Polygon in the RRI Model was used to create a rainfall file to use in the model. Figure 10 shows the flood inundation map of the Kale City in Sagaing Region and Table 2 shows the Flood affected area of Kale City areaby using RRI Model base on ground rainfall (12 stations) data.

PDF Compressor Pro

Figure 10: Flood inundation map of the Kale City in Sagaing Region

by using RRI Model base on ground rainfall (12 stations) data

Flood Depth(m) Flood affected area (km2)

0.5-1 71.48

1-2 95.58

2-3 59.13 3-4 38.07

4-5 34.83

5-6 38.68 Table 2: Flood affected area of Kale City areaby using RRI Model base on

ground rainfall (12 stations) data

According to the inundation analysis, Figure 11 shows the before flood (29 Jun, 2015), during flood (29 July, 2015) and after flood (29 August, 2015)maps by using RRI Model base on ground rainfall (12 stations) data. Figure 12 shows the flood water entered into the Kale City area and wards in 2015.

PDF Compressor Pro

Figure 11: Before Flood, During Flood and After Flood map by using RRI Model (GroundRainfall)

Figure 12: Flood water entered into the Kale City area and wards in 2015

29-Jun-2015 29-July-2015 29-Aug-2015

PDF Compressor Pro

Figure 13 shows the flood inundation map of the Kale City in Sagaing Region and Table 3 shows the Flood affected area of Kale City areaby using RRI Model base on satellite rainfall (GSMaP satellite) data.Figure 14 shows the before flood (29 Jun, 2015), during flood (29 July, 2015) and after flood (29 August, 2015) maps by using RRI Model base on satellite rainfall (GSMaP satellite) data.Figure 15 shows the comparison of RRI Model simulation result by using on satellite rainfall (GSMaP satellite) data and JAXA, ALOS-2 satellite image.

Figure 13: Flood inundation map of the Kale City in Sagaing Region

by using RRI Model base on satellite rainfall (GSMaP satellite) data

Flood Depth(m) Flood affected area (km2)

0.5-1 76.95

1-2 120.69

2-3 122.51 3-4 40.50

4-5 34.22

5-6 61.97 Table 3: Flood affected area of Kale City areaby using RRI Model base on

satellite rainfall (GSMaP satellite) data

PDF Compressor Pro

Figure 14: Before Flood, During Flood and After Flood map by using RRI Model (GSMaP Satellite Rainfall)

Figure 15 shows the comparison of RRI Model simulation result by using on

satellite rainfall (GSMaP satellite) data and JAXA, ALOS-2 satellite image

In this study, the result showed the flood depth is 0 to more than 5m. The flood inundated area at Kale City by RRI model was obtained to be 456.8Km2 for satellite rainfall (GSMaP) data. This value was more than the flood inundated area by ground rainfall (12 stations) data which was obtained to be 337.8 Km2.Figure 16 shows the flood inundation area of ground rainfall and satellite rainfall data at Kale Township area.

29-Jun-2015 29-July-2015 29-Aug-2015

PDF Compressor Pro

Figure 16:Flood inundation area of Kale Township area

(a) Ground Rainfall Data (12 Station) (b) Satellite Rainfall (GSMaP) Data

CONCLUSIONS

Rainfall-Runoff-Inundation (RRI) Model is useful for flood hazard analysis.To get more accurate result, upgrading of Meteorological and Hydrological observational networks is necessary.Flood hazard maps intend to apply the flood disaster management for reducing loss of the human life and properties in the flood affected area.If we can use the survey data of river width, river depth and cross sectional data, Digital elevation data, land use map etc…, result can be improved.

(a)

(b)

PDF Compressor Pro