ANNUAL FLOOD REPORT 2007

Transcription

1 ANNUAL FLOOD REPORT 2007 Water Level Station at Bahadurabad 21 Water Level (PWDmeter) Water Level (PWDmeter) Water Level (PWDmeter) Jul Water Level Station at Goalundo 22-Jul 24-Jul 26-Jul 28-Jul 30-Jul 1-Aug 3-Aug 5-Aug 7-Aug 9-Aug 11-Aug 13-Aug 15-Aug 17-Aug 19-Aug 21-Aug 23-Aug 25-Aug 27-Aug 29-Aug 31-Aug 2-Sep 4-Sep 6-Sep 8Water Level Station at Bhairab Bazar 20-Jul Time (year 2007) 22-Jul 24-Jul 26-Jul 28-Jul 30-Jul 1-Aug 3-Aug 5-Aug 7-Aug 9-Aug 11-Aug 13-Aug 15-Aug 17-Aug 19-Aug 21-Aug 23-Aug 25-Aug 27-Aug 29-Aug 31-Aug 2-Sep 4-Sep 6-Sep Time (year 2007) 20-Jul 22-Jul 24-Jul 26-Jul 28-Jul 30-Jul 1-Aug 3-Aug 5-Aug 7-Aug 9-Aug 11-Aug 13-Aug 15-Aug 17-Aug 19-Aug 21-Aug 23-Aug 25-Aug 27-Aug 29-Aug 31-Aug 2-Sep 4-Sep 6-Sep Time (year 2007) Observed Data 24 hr Forecast 48 hr Forecast 8-Sep 10-Sep 12-Sep 14-Sep 16-Sep 18-Sep 20-Sep Observed Data 24 hr Forecast 48 hr Forecast 8-Sep 10-Sep 12-Sep 14-Sep 16-Sep 18-Sep 20-Sep Observed Data 24 hr Forecast 48 hr Forecast 8-Sep 10-Sep 12-Sep 14-Sep 16-Sep 18-Sep 20-Sep FLOOD FORECASTING & WARNING CENTRE PROCESSING & FLOOD FORECASTING CIRCLE BANGLADESH WATER DEVELOPMENT BOARD

2 CONTENTS PREFACE...i EXECUTIVE SUMMARY, FLOOD iii CHAPTER 1: INTRODUCTION THE PHYSICAL SETTING THE RIVER SYSTEM ACTIVITIES OF FFWC OPERATIONAL STAGES BEFORE FORECAST CALCULATION NATURE AND CAUSES OF FLOODING...6 CHAPTER 2: RAINFALL SITUATION MONTH OF MAY MONTH OF JUNE MONTH OF JULY MONTH OF AUGUST MONTH OF SEPTEMBER...21 CHAPTER 3: RIVER SITUATION BRAHMAPUTRA BASIN GANGES BASIN MEGHNA BASIN THE SOUTH EASTERN HILL BASIN RECORDED HIGHEST WATER LEVEL...40 CHAPTER 4: FORECAST EVALUATION, GENERAL EVALUATION CRITERIA OF FORECAST PERFORMANCE Mean Absolute Error, MAE Co-efficient of Determination, r PRE-DEFINED SCALES TO EVALUATE FORECAST PERFORMANCE FORECAST STATISTICS AND MODEL PERFORMANCE, CHAPTER 5: INUNDATION STATUS GENERAL...79 CHAPTER 6: CONCLUSIONS...85

3 LIST OF TABLES Table 1.1: Year-wise Flood Affected Area in Bangladesh...9 Table 2.0: Rainfall statistics for the monsoon 07 over the four Basins:...10 Table 2.1: Brahmaputra Basin Rainfall in May (mm)...11 Table 2.2: Ganges Basin Rainfall in May (mm)...12 Table 2.3: Meghna Basin Rainfall in May (mm)...12 Table 2.4: South Eastern Hill Basin Rainfall in May (mm)...12 Table 2.5: Brahmaputra Basin Rainfall in June (mm)...14 Table 2.6: Ganges Basin Rainfall in June (mm)...15 Table 2.7: Meghna Basin Rainfall in June (mm)...15 Table 2.8: South Eastern Hill Basin Rainfall in June (mm)...15 Table 2.9: Brahmaputra Basin Rainfall in July (mm)...17 Table 2.10: Ganges Basin Rainfall in July (mm)...17 Table 2.11: Meghna Basin Rainfall in July (mm)...18 Table 2.12: South Eastern Hill Basin Rainfall in July (mm)...18 Table 2.13: Brahmaputra Basin Rainfall in August (mm)...20 Table 2.14: Ganges Basin Rainfall in August (mm)...20 Table 2.15: Meghna Basin Rainfall in August (mm)...20 Table 2.16: South Eastern Hill Basin Rainfall in August (mm)...21 Table 2.17 Brahmaputra Basin Rainfall in September (mm)...22 Table 2.18Ganges Basin Rainfall in September (mm)...23 Table 2.19: Meghna Basin Rainfall in September (mm)...23 Table 2.20: South Eastern Hill Basin Rainfall in September (mm)...23 Table 3.1: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Brahmaputra Basin Table 3.2: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Ganges Basin Table 3.3: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Meghna Basin...37

4 Table 3.4: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 and 1998 of Some Important Station in South Eastern Hill Basin Table 3.5: Recorded Highest Water Level with Date...40 Table 4.1: Scales used for performance evaluation...60 Table 4.2: Statistics for 24- hour forecast performance...61 Table 4.3: Statistics for 48- hour forecast performance...62 Table 4.4: Statistics for 72- hour forecast performance...63 Table 5.1 Zone-Wise Damage Assessment of BWDB Infrastructures...80

5 LIST OF FIGURES Figure 2.1: Isohyets of Actual Rainfall (May 2007)...25 Figure: 2.2: Isohyets of Actual Rainfall (June 2007)...26 Figure: 2.3: Isohyets of Actual Rainfall (July 2007)...27 Figure: 2.4: Isohyets of Actual Rainfall (August 2007)...28 Figure: 2.5: Isohyets of Actual Rainfall (September 2007)...29 Figure 3.1: Comparison of Hydrographs (Darla at Kurigram)...42 Figure 3.2: Comparison of Hydrographs (Brahmaputra at Bahadurabad)...43 Figure 3.3: Comparison of Hydrographs (Brahmaputra at Serajganj)...44 Figure 3.4: Comparison of Hydrographs (Brahmaputra at Aricha)...45 Figure 3.5: Comparison of Hydrographs (Buriganga at Dhaka)...46 Figure 3.6: Comparison of Hydrographs (Punarbhaba at Dinajpur)...47 Figure 3.7: Comparison of Hydrographs (Ganges at Rajshahi)...48 Figure 3.8: Comparison of Hydrographs (Ganges at Hardinge Bridge)...49 Figure 3.9: Comparison of Hydrographs (Ganges at Goalondo)...50 Figure 3.10: Comparison of Hydrographs (Ganges at Bhagyakul)...51 Figure 3.11: Comparison of Hydrographs (Surma at Sylhet)...52 Figure 3.12: Comparison of Hydrographs (Surma at Sunamganj)...53 Figure 3.13: Comparison of Hydrographs (Kushiyara at Sheola)\...54 Figure 3.14: Comparison of Hydrographs (Manu at Moulvi Bazar)...55 Figure 3.15: Comparison of Hydrographs (Khowai at Habiganj)...56 Figure 3.16: Comparison of Hydrographs (Halda at Narayan Hat)...57 Figure 3.17: Comparison of Hydrographs (Matamuhuri at Chiringa)...58 Figure 4.1: 24 hr Forecast Evaluation (Year, 2007)...64 Figure 4.2: 48 hr Forecast Evaluation (Year, 2007)...65 Figure 4.3: 72 hr Forecast Evaluation (Year, 2007)...66 Figure 4.4: Observed Vs. Forecasted (24 hr) WL (Jamuna at Sirajganj)...67 Figure 4.5: Observed Vs. Forecasted (48 hr) WL (Jamuna at Sirajganj)...68 Figure 4.6: Observed Vs. Forecasted (72 hr) WL (Jamuna at Sirajganj)...69 Figure 4.7: Comparison of Forecasted (24 hr) Hydrograph WL (Jamuna at Sirajganj)..70 Figure 4.8: Comparison of Forecasted (48 hr) Hydrograph WL (Jamuna at Sirajganj)..71

6 Figure 4.9: Comparison of Forecasted (72 hr) Hydrograph WL (Jamuna at Sirajganj)..72 Figure 4.10: Observed Vs. Forecasted (24 hr) WL (Padma at Goalundo)...73 Figure 4.11: Observed Vs. Forecasted (48 hr) WL (Padma at Goalundo)...74 Figure 4.12: Observed Vs. Forecasted (72 hr) WL (Padma at Goalundo)...75 Figure 4.13: Comparison of Forecasted (24 hr) Hydrograph WL (Padma at Goalundo) 76 Figure 4.14: Comparison of Forecasted (48 hr) Hydrograph WL (Padma at Goalundo) 77 Figure 4.15: Comparison of Forecasted (72 hr) Hydrograph WL (Padma at Goalundo) 78 Figure 5.1: Flood Inundation Map of Bangladesh (August 5, 2007)...81 Figure 5.1: Flood Inundation Map of Bangladesh (24 hr Forecast Based on August 5, 2007)...82 Figure 5.1: Flood Inundation Map of Bangladesh (48 hr Forecast Based on August 05, 2007)...83 Figure 5.3: Flood Inundation Map of Dhaka (August 05, 2007)...84 Figure 5.4: River Situation Map (48 hr Forecast based on August05, 2007)...84

7 PREFACE Bangladesh is the lowest riparian of world s three great river basins: the Ganges, the Brahmaputra and the Meghna (GBM Basins) covering a combined total catchment area of about 1.7 million sq. km. extending over Bhutan, China, India and Nepal, flow through Bangladesh. Only 7%of this huge catchment area lies in Bangladesh and 93% outside the country. The annual flow volume of the rivers is to the tune of 1200 billion m 3, and 80% of the flow passes during June to September to the sea which if impounded on our Flood Plain would have about 9 metres deep standing water. Over the years, due to the sediment that it carries the rivers valley conveyance capacity has reduced. Moreover, at some river stretches we have localised congestions due to river aggradations and man made interventions over time that impeding drainage adding woos to the flood recession like that occurred in 1998, 2004 and also to a limited scale in The country has an average rainfall of about 2300 mm; the range can be 1500 mm to 5000 mm. Bangladesh has also a unique coast line, conical in shape, which causes a higher sea level during monsoon period. Due to the unique topography, river system and rainfall pattern, flood occurs in Bangladesh almost every year and devastating ones in every 5 to 10 years interval. In flood management, Bangladesh has taken many structural and non- structural measures. One of the main non-structural measures is the flood forecasting and warning system. Flood Forecasting and Warning System of the country are in the process of continuous advancement since 1970 s. Starting with a very simple way of forecasting (Gauge to Gauge correlation), it has now developed a most advanced flood forecasting system using the MIKE11 software. Flood Watch a data management system combining with the MIKE 11 hydrodynamic model and real-time forecasting system, MIKE 11 FF, together with the Geographical Information System (GIS) are being used for flood forecasting and warning services. To mitigate flood hazard, dissemination and communication of flood warnings and response systems are very important. Flood warning will be useless if it is not delivered to the people at risk with a sufficient lead time in such a manner so that people can easily understand the message for taking appropriate measure. In Bangladesh, dissemination of flood warning is extremely difficult because a majority of the vulnerable people have no access to mass communication media. Nevertheless, local government agencies have limited resources and facilities to pass the flood warning to the communities at grassroots level. Flood Forecasting and Warning Centre (FFWC) under the Bangladesh Water Development Board (BWDB) is working as the national focal point with respect to forecasting, monitoring and disseminating information of disasters and calamities to its field offices and related organizations from the very beginning. As mandated, FFWC issued flood forecasting & warning messages during the flood 2007 and earned immense appreciation from different government agencies, national and international organizations. This Centre really feels proud of its officials and staffs who work with encouraging sprits and interests. This Centre does not claim that it has reached to high levels of technical development but acknowledges that it has started the beginning of the i

8 development and needs to go a long way to satisfy the real need of the people and country. The officials of the Centre were highly encouraged with the valuable advice and guidance of Mr. Syed Mohammad Zobaer, Secretary, and Ministry of water Resources, Govt. of Bangladesh during flood 07. This Centre gratefully acknowledges the guidance and valuable advice of Mr. H.S. Mozaddad Faruque, DG, BWDB to enrich the overall performance of this Centre to face the crisis during the whole flood period. His personal interest, continuous impetus and suggestion made the centre distinctly elevated. The direct involvement and participation of ADG, Planning, Chief Engineer, Hydrology and Director, Processing & Flood Forecasting Circle, BWDB, are respectfully remembered in implementing and monitoring the whole activities in this centre. They implied their personal interest and maintained the guidance to the undersigned to face the national and international news media including honorable Chief Advisor s office and the other Government offices. The Centre is also grateful to the News Media, Journalists of different Dailies, Radio & Television authority and those who helped in disseminating the flood information during flood 07. The undersigned also acknowledges the relentless support of the officers and staffs of FFWC and related field officials to make the centre effective and reliable. The efforts of FFWC, IWM and CEGIS experts in developing high-tech technology in regards of flood forecasting in the Centre are noteworthy remarkable. The undersigned hopes that this report would be a point of interest to the planners and designers who are working in water sector. And thus the report could be a measure for formulating various flood mitigation activities in Bangladesh. The Centre always warmly welcomes valued comments and suggestions from any quarter. Finally, I sincerely thank my colleagues in the center whose earnest and sincere cooperation made it possible to publish this annual flood report. (Md. Saiful Hossain) Executive Engineer Flood Forecasting & Warning Centre BWDB, Dhaka. ii

9 EXECUTIVE SUMMARY, FLOOD 2007 The 2007 flood although not has been as disastrous as the 1998 and 1988 mega floods, however has been about as big as that occurred in 2004 causing possibly similar damages to economy as well as miseries on livelihoods and immense human sufferings. During the last 50 years, at least 7 big floods have occurred, affecting about 35-70% of the land area. A historical overview of floods since 1954 indicates that there is no significant change in the trend of normal floods in Bangladesh. However, it is quite visible that severe floods have become more frequent. Due to the geographical position and obscured natural phenomenon, Bangladesh experiences flood more or less every year in different magnitudes. Therefore, publication of Annual Flood Report by the Flood Forecasting & Warning Centre (FFWC) of BWDB is a regular activity. Like previous years this year also, as per government Standing Orders for Disaster (SOD) Flood Information Cell (FIC) under the Flood Forecasting & Warning Center (FFWC) was opened in April 1 and continued upto 21st October. The year 2007 is one of the worst scenarios in the context of flood. During this monsoon, the country experienced various types of flood sporadically in different places. The magnitude and duration of flood can even be compared to the big flood events like 1988 and Before the big events of 2007 river Flood, a typical flash flood hit the northeast region in the month of June with not very significant contribution from the inland rainfall of about 28.1% more than normal. This flash flood took place in the 2 nd fortnight of June with almost all the main rivers in this region flowing above danger level at several locations ranging from 5 to 11 days. That time, the Khowai at Habiganj delivered a flow level greater than previously recorded highest flood level. Henceforth, everything seemed normal until the month of July. iii

10 The monsoon flood this year occurred in two distinct spells of peaking followed by a relatively dry spell in early July; rainfall intensity rapidly increased from 19 th July as monsoon became vigorously active over the GBM basins simultaneously. Floods started in Nepal, Assam, Bihar and Uttar Pradesh from 3 rd week of July. This triggered flash flood in the north-eastern part of the country from July 20 and onrush of floodwater from Assam, Bihar & Nepal started coming through the Brahmaputra and the Ganges simultaneously from July 22. The rate of rise of both the major river system were very rapid and northern districts started flooding from July 28 and the flood water spread to central & south-central part of the country. Fortunately, the Ganges was flowing much below danger level and also July was not the usual time for Ganges basin flooding. In the 1 st week of August, dry spell prevailed over the GMB basins and water level started decreasing in the Brahmaputra from August 1 and in the Ganges from August 7. All the five small rivers in and around Dhaka and Narayanganj crossed danger levels and caused flooding especially in the eastern part and the south-western part (outside BWDB flood embankment) of the Dhaka city. During this spell of flooding, main Dhaka city was well protected by BWDB flood protection embankment and well-managed drainage pumps in the north-western Dhaka.. Monsoon flood 2 nd spell: While all the rivers were in receding trend till Sept. 05 and 1 st spell flood water receded from almost all areas, from Sept. 06 the mighty Brahmaputra again started rising alarmingly and crossed danger level again. In the Teesta basin the rapid increase in flooding inundated the international road links and land port and required the Teesta barrage flood bye-pass to be opened with consequential easing of flooding in the upstream areas of Teesta barrage. The river started falling from Sept. 13 and gone below danger level at Bahadurabad on Sept. 17, at Serajganj on Sept. 22 and at Aricha on Sept nd spell peak of Brahmaputra-Jamuna was lower than 1 st spell peak and duration was also shorter than 1 st spell. The Ganges also continued rising from 1 st week of September and crossed danger level at Pankha for a short duration. The river didn t cross danger level at Rajshahi and Hardinge bridge during the flood season 2007 thus the country was saved from prolonged severe flooding. But the Ganges-Padma caused flooding in the south-central part of the country which continued till Sept. 23. The 2 nd spell flooding in the south- central part of the country was not more severe than the 1 st spell monsoon flooding. The flood receded quickly and the country became flood free by the end of September. iv

11 On the other hand in the 2 nd spell of monsoon flooding (3 rd spell for north-eastern part of the country), Kushiyara at Sheola crossed highest ever recorded level and the flood situation in the districts of Sylhet and Sunamganj was worse than the pre-monsoon flash flood and 2 nd spell monsoon flood. Consecutive heavy rainfall experienced over the South-eastern hilly regions on Sept. 7, 8 & 9 and Feni, Noakhali, Chittagong, Bandarban, Rangamati & Khagrachari experienced flash flood in 2 nd spell and the situation has improved quickly. The 2007 flood damages could however be minimised quite significantly by timely structural and non-structural interventions particularly in the Haor areas and FCD projects from the learning since. In some astray cases like in Kurigram, Sirajganj and Dhaka districts however the damages became inevitable due to the failure of protection measures due to reasons beyond WDB control. With the increase in population and increase in non-farm activities, such as culture fisheries, poultry farming, livestock husbandry, establishment of small and medium-size industries in the floodplains more and more people are settling in the flood- prone areas, making them more vulnerable to floods. Flood 2007 although not severe as 1998 or 1988 did a mammoth damage to the country s economy due to its unusual two peaks. v

12 CHAPTER 1: INTRODUCTION 1.1 THE PHYSICAL SETTING Bangladesh lies approximately between 20 o 30 and 26 o 40 north latitude and 88 o 03 and 92 o 40 east longitude. Bangladesh occupies one of the biggest deltas in the world and has an area of about 1,47,570 Sq. km. It enjoys sub-tropical monsoon climate and experiences annual average 2,300 mm precipitation, varying from as little as 1,200 mm in the west to over 5,000 mm in the east. India borders the country in north, east and west. The southern part of the country lies on coastal belt of the Bay of Bengal while Myanmar borders part of the southeastern area. It has 230 rivers including 57 international rivers. Among them 54 rivers originated from India including three major rivers such as the Ganges, the Brahmaputra and the Meghna. Three minor rivers originated from Myanmar. The rivers both big and small gradually became incapable of draining the huge quantity of silt-laden run-off passing through them during the monsoon period and cause floods. Inundation to the extent of 20% area of the country is beneficial for crops and ecological balance. But the flood more than 20% cause direct and indirect damages and considerable inconveniences to the people. The country is extremely flat with low land relief with only a few hills in the southeast and the northeast part of the country. Generally ground slopes of the country extend from the north to the south and the elevation ranging from 60 meters to 1 meter above Mean Sea Level (MSL) at the boundary at Tentulia and at the coastal areas in the south. The land to the west of Brahmaputra is generally higher than that in the eastern part of the country. Several large depressions have been formed during the process of delta building, particularly in greater Mymensingh and Sylhet districts. The country consists of the flood plains of the Ganges, the Brahmaputra and the Meghna rivers and their numerous tributaries and distributaries. The Ganges and the Brahmaputra join together in Bangladesh near Goalundo and is known as the Padma River. The river Meghna joining the Padma near Chandpur flows to the Bay of Bengal as the Meghna River. 1

13 These river systems together, drain the huge runoff generated from one of the heaviest rainfall areas in the world. Their total catchment area is approximately 1.6 million sq. km of which only about 7.5 % lies in Bangladesh and the rest, 92.5% lies outside the territory. It is assumed that an average flow of 1,009,000 Million cubic meters passes through these river systems during the monsoon season. Most of the rivers are characterized by having fine sandy bottoms, flat slopes, substantial meandering, banks susceptible to erosion and channel shifting. 1.2 THE RIVER SYSTEM The river system that focuses on Bangladesh is one of the most extensive in the world, and the Ganges and the Brahmaputra are amongst the largest rivers on earth in terms of catchment size, river length and discharge. The Brahmaputra (Jamuna) above Bahadurabad has a length of approximately 2,900 km and a catchment area about 5,83,000 sq. km. It rises in glaciers in the northernmost range of the Himalayas and flows east far above half its length across the Tibetan plateau. In the complex mountain terrain bordering north-east India and China it bends through a series of gorges and is joined by a number of major tributaries, e.g., the Dihang and the Luhit before entering its broad valley section in Assam. This stretch is about 720 km long to the border of Bangladesh and throughout most of this, the course is braided. This braided channel is continued to the confluence with the Ganges. Within Bangladesh, the Brahmaputra receives four major Right Bank tributaries - the Dudkumar, the Dharla, the Teesta and the Hurasagar. The first three are flashy rivers, rising in steep catchments on the southern side of the Himalayan between Darjeeling and Bhutan. The Hurasagar River is the outlet to the complex Karatoa-Atrai system, which comprises much of the internal drainage of northwest of Bangladesh. The Old Brahmaputra is the main left-bank distributary of the Brahmaputra presently known as the Jamuna. The shift of courses appears to have been taken place after a major earthquake and catastrophic floods in It is now essentially a high flow spill channel, as in the Dhaleswari, and their behavior is highly dependent on the variations of siltation at their entries. 2

14 The Ganges has a total length of about 2,600-km to its confluence with the Brahmaputra and a catchment area of approximately 9,07,000 sq. km. Also rising in glaciers in the high western Himalayans, the Ganges has a short mountain course of about 160-km. From there it flows south easterly in a vast plain being joined by major tributaries from the southern Himalayans in Nepal and by smaller rivers from the central Indian Plateau to the south. About having a sinuous deep-water channel with numerous bar formations (chars), the Ganges is not braided. After its confluence with the Brahmaputra at Goalundo, the river, now known as the Padma, flows in a wide, straight, trench like channel. At Chandpur, the Padma is joined by the Meghna from whence it flows to the sea and is fully under the influence of tides. The Meghna system originates in the hills of Shillong and Meghalaya of India. The main source is the Barak River, which has a considerable catchment in the ridge and valley terrain of eastern Assam bordering Burma. On reaching the border with Bangladesh at Amalshid in Sylhet district, it bifurcates to form the Surma and the Kushiyara rivers. The Surma, flowing on the north of the Sylhet basin receives Right Bank tributaries from Khasia and Jaintia Hills of Shillong. These are steep, highly flashy rivers, originating in one of the wettest area of the world, the average annual rainfall at Cherrapunji at Assam being about 10,000 mm. The Kushiyara receives left bank tributaries from the Tripura Hills, the principal ones being the Manu. Although also prone to producing flash floods the lesser elevations and rainfall of Tripura makes these rivers less violent than the northern streams. Between the Surma and Kushiyara, there are a complex of internal draining depressions (haors), meandering flood channels and abandoned river courses, which are widely flooded every monsoon season. The two rivers rejoined at Markuli and flow via Bhairab as the Meghna to join the Padma at Chandpur. The major tributaries of any size outside the Sylhet basin are the Gumti and the Khowai River, which rises in Tripura and other hilly streams from Meghalaya and Assam to join the Meghna. 3

15 The streams of the southeast region are all short and of a flashy nature, rising in the Chittagong Hill Tracts or adjacent parts of eastern India. The main streams are the Muhuri, Halda, Sangu, Matamuhuri, etc. 1.3 ACTIVITIES OF FFWC The importance of the flood forecasting and warning is widely recognized as a vital nonstructural measures to aid the mitigating the loss of lives, crops and properties caused by the annual flood occurrence. The Flood Forecasting and Warning Centre, under the Directorate of Processing and Flood Forecasting Circle, Hydrology, BWDB carries out monitoring of 86 representative water level stations and 56 rainfall stations throughout the country. The principal outputs are the daily statistical bulletin of floods, river situation, a descriptive flood bulletin, forecast for 24, 48 & 72 hours about 52 monitoring points, production of Thana Status Map, Satellite Imageries, special flood report along with different graphical and statistical presentation during the monsoon season. The Centre is also involved in preparation of flood status report on National level, a weekly bulletin during dry season and monthly and annual flood reports. The Centre is responsible to act as a focal point in respect of flood from the month of April to November as per Government order for formulating the flood forecasts that are issued with the river situation bulletin and also provide support services to DMB, BMD and SPARRSO during cyclonic disaster. Earlier before 1990, forecast for six locations viz. Bahadurabad, Serajganj, Aricha, Goalondo, Bhagyakul and Hardinge Bridge on the Padma Brahmaputra Jamuna system were issued by Co-axial correlation, Gauge to Gauge relation and Muskingum- Cunge Routing Model. After the devastating flood of 1987 and catastrophic flood of 1988, it was deeply realized that the forecast formulation should be introduced in the process of river modelling. In view of the above, the simulation model MIKE11 developed by Danish Hydraulic Institute (DHI) was installed at FFWC and a special version of MIKE11 FF conceptual Hydrodynamic model is in operation for forecast formulation. 4

16 The general Model (GM) developed under MIKE11 was adapted to real time operation in which boundary extended near to the Indian border on all main rivers. A supermodel now is in operational at FFWC covering entire northern flood affected area of Bangladesh. The Supermodel covers about 82,000 km 2 of entire northern areas of the country. The areas are sub-divided into 107 sub-catchments. It includes 195 river branches, 207 link channels, 40 Broad Crested Weirs. The total river length modeled is about 7270 km. Model operation and data base management, a well-managed server based (Widows 2000) LAN Operating System has been installed with 15 PCs at the FFWC. 1.4 OPERATIONAL STAGES BEFORE FORECAST CALCULATION Data Collection: The real time hydrological data is collected by SSB wireless, fixed & mobile telephone from the BWDB hydrological network. Water level data from 86 stations and rainfall from 56 stations are collected. Water levels for non-tidal stations are collected five times daily 3 hours interval in the day time 6 AM to 6 PM but for tidal stations collected every hours. Rainfall is collected daily basis period beginning at 9 AM. The data collections at FFWC are generally completed by 10:30 A.M. everyday. Very limited water level and rainfall and forecasts from Indian stations are also collected through BMD by Tele-printer link and also from Internet. Essential Information s: Estimation of water level at the boundaries and rainfall for the catchments are required to be input to the model upto the time of Forecast (24h, 48h & 72h). For the rainfall estimation satellite picture from NOAA satellite collected at SPARRSO is used. In addition a dedicated land line radar link with BMD (Bangladesh Meteorological Department), which provided very frequent (five minutes interval) at four stations at Dhaka, Rangpur, Cox's Bazar and Khepupara. Forecast Calculation: Collected water level and rainfall data are given input to the computer database and checked. The water level and rainfall estimation has to be prepared. The basis for water level estimation is considering trend Hydrograph extrapolated upto the period of forecast from previous few days levels, response characteristics of rivers, effect of rainfall on water level and Indian available water level 5

17 & forecasts data. Rainfall estimation based on previous 2-day s rainfall and analysis of information collected for. After input required data and boundary-estimated data to the model, submit model run. It takes 30 t0 40 minutes time to complete the calculations. Forecasts are using in the daily forecast bulletin upto 72 hours for important locations and region-wise flood warning messages. The forecast bulletins are disseminated to more than 100 different offices/officials, individuals, news media, Radio & TV, foreign missions, donor agencies, NGO s etc. including President & PM s Secretariat. Whenever, the forecast river stage cross the danger level, the concern field offices are informed. So that appropriate measure can be taken before the occurrence of hazards. The flood forecast is intended to alert the people in a given locality about the predicted water level of floodwater well ahead of its occurrence. An accurate forecast would be one where the forecast level and corresponding observed level at the stipulated time are within a small range of variation. 1.5 NATURE AND CAUSES OF FLOODING Causative Factors Climatologically, the country has two distinct seasons, a dry season from November to May and the wet (flood) season from June to September (or October). Over 80% of the rainfall occurs during the monsoon or rainy season when flooding normally occurs. The normal annual rainfall of the country varies approximately from 1,200 mm in the west to over 5,000 mm in the east. Long periods of steady rainfall persisting over several days are common during the monsoon, but sometimes - local high intensity rainfall of short duration also occurs. The basic causative meteorological condition for monsoon rainfall is the extensive, deep incursion of warm, saturated air from the Bay of Bengal over the whole northern Indian sub-continent. Within this system, the detailed synoptic conditions vary to give periods of greater or lesser rainfall activity. The occurrence of monsoon lows passing over Bangladesh and West Bengal produces period of heavy rain, as do fluctuations in the position of the monsoon axis, which at its fullest northward extent lies along the southern margin of the Himalayan. This in turn is controlled by complex upper air pressure and 6

18 wind pattern in relations to the Tibetan plateau. The squally, thundershower outbreaks level convergence of warm air from the Bay of Bengal below cold continental air at upper levels. Water levels of the rivers begin to rise steadily at the onset of the monsoon and reach their peak level in July, August or September and the inundation normally may cover about 20% area of the country. Flash floods occur in the northeastern, southeastern and extreme northern areas of the country at any time during the monsoon. Wide spread overland flooding become severe and devastating when the peak of the Ganges, the Brahmaputra and the Meghna synchronize along with spring tide and remain at high stage for long periods. The following factors have been identified as being responsible for flood in Bangladesh: Heavy and incessant rainfall in the upper catchment of the cross-boundary rivers as well as inside the country. Topographically about half of the country is situated below about 7.60 meter (about 25 ft) above mean sea level (MSL). Floodwater spills from the rivers and accumulates on these low-lying areas. Bangladesh and surrounding catchment areas lie in the heavy monsoon rainfall area that leads to a concentrated large discharge in the rivers. As a result, this channel is frequently overloaded and spills over the banks and cause flood in the plain. There have been significant changes in the behavior of off-takes of the main rivers distributaries of the Ganges Padma and the Brahmaputra after the Assam earthquake of 1950, which caused the Brahmaputra River to become heavily silted. Due to blockage at confluence and off-take of distributaries, there has been a concentration of water in the main river system. Simultaneous high discharge of the upland streams and high tides in the estuaries, low topography of the country and river bed siltation all contribute to the over bank spilling of the rivers. More than 80% of the annual precipitation occurs during the monsoon. This localized heavy rainfall and runoff coincide with the high discharge in external rivers resulting in drainage congestion. Locally concentrated rainfall of more than 300 mm in 2 6 hours leads to severe flash / local flood. The Springtides of the Bay of Bengal retards the drainage of floodwater into the sea and locally increases monsoon flooding. A rise of MSL at times during the monsoon period 7

19 due to effect of monsoon winds also adversely affect the drainage and rises the flood level along the coastal belt. High water level of the main rivers slows down the flow from the tributaries. In particular, the flow of the Dharla and the Teesta being backed up by the Brahmaputra and mutual backing up by the Ganges and the Jamuna affect the drainage of the Hurasagar. This increases the flood intensity in the adjoining areas. The backing up the drainage of the Sylhet Mymensingh haors through the Meghna due to high water prevailing in the lower Meghna at Chandpur is a well-known phenomenon. A series of geographical faults have created depression in Rajshahi, Pabna, Bogra and the Sylhet- Mymensingh haor area. These areas become inundated with the advent of monsoon and remain waterlogged until November. Generally, the Brahmaputra records its peak flood during the month of June-July and the Ganges in the August-September, while the Meghna remains high from May to September. Some years it may happen that these rivers reach peak-flood level simultaneously and aggravate the flood situation in the country Statistics of Flooding Many parts of the Asia during monsoon frequently suffer from severe floods. Some parts of India and Bangladesh experience floods almost every year with considerable damage. The floods of 1954, 1955, 1974, 1987, 1988, 1998, 2004 including the 2007 all caused enormous damages to properties and considerable loss of life. The floods of 1987, , 2004 and the present 2007 flood caused heavy damage. The magnitude and duration of flood 2007 was one of the worst in history. Flood statistics for Bangladesh are available since 1954 and are summarized in Table

20 Table 1.1: Year-wise Flood Affected Area in Bangladesh Year Flood Affected area Year Flood affected area Year Flood affected area Sq. Km % Sq. Km % Sq. Km % , , , , , , , , , , , , , , , , , , ,00, , , , , , , , , , , , , , , , , , , , , , , , , , , ,

21 CHAPTER 2: RAINFALL SITUATION In monsoon 07, the country was severely affected by floods in comparison with other flooding year (viz and 1998). During this monsoon, the country experienced as a whole 3.46% less rainfall than normal year. Considering monthly rainfall, the Ganges, the Meghna and the South-Eastern Hill Basin experienced more rainfall than normal in July But, the country experienced above rainfall concentrically in the last week of July and in the mid of September. As a result, the country was severely flooded two times during the year Comparison of Normal and Actual rainfall for the monsoon is shown in following pie chart Normal Rainfall (mm) among the four Basins for the monsoon Actual Rainfall (mm) among the four Basins for the monsoon Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Table 2.0: Rainfall statistics for the monsoon 07 over the four Basins: Month Brahmaputra Basin Ganges Basin Meghna Basin South Eastern Hill Basin Normal Monsoon average (mm) Monsoon average (mm) Normal Actual Normal Actual Normal Actual Normal Actual May June July August September Total % More/Less 4.72% Less 3.15% less 2.64% less 3.57% Less 3.46 % Less 10

22 2.1 MONTH OF MAY The country experienced less rainfall than the normal rainfall in the Brahmaputra, the Ganges basin, the Meghna & the South Eastern Hill Basin during the month of May The Brahmaputra, the Ganges basin, the Meghna and the South Eastern Hill Basin were experienced rainfall below than that of normal by 68.30%, 60.00%, 26.57% and 59.5% respectively during May Important Rainfall Information for May 2007 Maximum, at Sylhet : 772 mm One day maximum, at Kanighat: 117 mm Exceeded Highest Record (May): Rainfall at none of the stations exceeded its Highest Record. Comparison of normal and Actual rainfall for the month of May are shown in following Pie chart: Actual Rainfall (mm) among the four Basins for the month of May Normal Rainfall (mm) among the four Basins for the month of May Brahmaputra Basin Ganges Basin Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Meghna Basin South-Eastern Hill Basin Basin-wise rainfall statistics for month of May 2007 are shown in the Table below: Table 2.1: Brahmaputra Basin Rainfall in May (mm) Station Max. Nor Act Dev 1dymax 10dmax % More/ Less Kurigram Dalia Kaunia Rangpur Chilmari Dewanganj Gaibandha Bogra Jamalpur Mymensingh Dhaka Tangail Average % less 11

23 Table 2.2: Ganges Basin Rainfall in May (mm) Station Max. Nor Act Dev 1dymax 10dmax % More/ Less Panchagarh Dinajpur Naogaon Rajshahi Kushtia Jessore Khulna Satkhira Faridpur Barisal Patuakhali Average % less Table 2.3: Meghna Basin Rainfall in May (mm) Station Max. Nor Act Dev 1dymax 10dmax Kanaighat Sylhet Sunamganj Sheola Moulvi Bazar Manu Rly Br Habiganj Durgapur Bhairab Bazar Comilla Chandpur Average % More/ Less 26.57% less Table 2.4: South Eastern Hill Basin Rainfall in May (mm) Station Max. Nor Act Dev 1dymax 10dmax Parshuram Noakhali Narayanhat Panchpukuria Bandarban Rangamati Lama Chittagong Ramgarh Sandwip Cox' Bazar Average % More/ Less 20.49% less 12

24 The above table shows that 12 out of 12 stations in the Brahmaputra basin, 11 out of 11 stations in the Ganges basin, 8 out of 11 stations in the Meghna and 8 out of 11 stations South Eastern Hill basin received less rainfall than their monthly normal rainfall. Among all monitoring stations Sylhet, Sheola, Chandpur in the Meghna basin and Bandarban, lama & Cox s Bazar in the South Eastern Hill basin received more rainfall than their monthly normal rainfall. The table shows that 3 out of 11 stations in the Meghna basin and 1 out of 11 stations in the South-Eastern Hill Basin received more than 300 mm rainfall in 10-day period. 300 mm or more rainfall in 10-day period may cause rain fed flood. During third week in this month, excessive rainfall in the Meghna basin caused flash flood in the north-eastern region of the country. Rainfall Isohyets of the actual rainfall of the month May is shown in the Figure

25 2.2 MONTH OF JUNE The country, as a whole, experienced rainfall more than normal during the month, June In the third week of the month, the country received an excessive rainfall especially in the northeastern region. For this, the country experienced flash flood in the northeastern region during the same period. Among the four hydrological basins, the Brahmaputra, the Ganges and the Meghna received 49.08%, 14.85% and 28.10% more rainfall than their respective monthly normal rainfall. And the South Eastern Hill basins received 10.05% less rainfall than its monthly normal rainfall which has shown in the following tables. Important Rainfall Information for June 2007 Maximum, at Sunamganj : mm One day maximum, at Sunamganj : mm Exceeded Highest Record (June): Rainfall at None of the stations exceeded its Highest Record. Comparison of normal and Actual rainfall for the month of June is shown in following pie chart: Normal Rainfall (mm) among the four Basins for the month of June Brahmaputra Basin Ganges Basin Actual Rainfall (mm) among the four Basins for the month of June Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Meghna Basin South-Eastern Hill Basin Basin-wise rainfall statistics for the month of June 2007 are shown in the Table below: Table 2.5: Brahmaputra Basin Rainfall in June (mm) Station Max. Nor Act Dev 1dymax 10dmax %less /more Kurigram Dalia Kaunia Rangpur Chilmari Dewanganj Gaibandha % more Bogra Jamalpur Mymensingh Dhaka Tangail Average

26 Table 2.6: Ganges Basin Rainfall in June (mm) Station Max. Nor Act Dev 1dymax 10dmax %less /more Panchagarh Dinajpur Pabna Naogaon Rajshahi Kushtia Jessore % more Khulna Satkhira Faridpur Barisal Patuakhali Average Table 2.7: Meghna Basin Rainfall in June (mm) Station Max. Nor Act Dev 1dymax 10dmax %less /more Kanaighat Sylhet Sunamganj Sheola Moulvi Bazar Manu Rly Br Habiganj % more Durgapur Bhairab Bazar Comilla Chandpur Average Table 2.8: South Eastern Hill Basin Rainfall in June (mm) Station Max. Nor Act Dev 1dymax 10dmax %less /more Parshuram Noakhali Narayanhat Panchpukuria Bandarban Rangamati Lama % less Chittagong Ramgarh Sandwip Cox' Bazar Average The above table shows that 10 out of 12 stations in the Brahmaputra basin, 7 out of 12 stations in the Ganges basin and 9 out of 11 stations in the Meghna basin received more 15

27 rainfall than their monthly normal rainfall. In the South Eastern Hill basin, 8 out of 11 stations received less rainfall than its monthly normal rainfall. Among all monitoring stations, Sunamganj in the Meghna basin is the daily highest rainfall recipient station. The table shows that 10 out of 12 stations in the Brahmaputra basin, 5 out of 12 stations in the Ganges basin, 10 out of 11 stations in the Meghna basin and 8 out of 11 stations in the South-Eastern Hill Basin received more than 300 mm rainfall in 10-day period. 300 mm or more rainfall in 10-day period may cause rain fed flood. During third week in this month, excessive rainfall in the Meghna basin caused flash flood in the north-eastern region of the country. Rainfall Isohyets of the actual rainfall of the month of June is shown in the Figure MONTH OF JULY The intensity of rainfall in the Brahmaputra and the Ganges basins was very heavy at most of places in the last ten days during the month of July. On Important Rainfall Information for July 2007 Maximum, at Sunamganj : mm One day maximum, at Bandarban : mm Exceeded Highest Record (July): Rainfall at None of the stations exceeded its Highest Record. the other hand, the Meghna and the South Eastern Hill basins experienced relatively higher rainfall at most of the places during the last fifteen days of this month. Among the four hydrological basins, the Brahmaputra basin received rainfall 1.13% less than their respective monthly normal rainfall and the Ganges, the Meghna and the South Eastern Hill basins received rainfall 34.30%, 2.51% and 10.20% more than their monthly normal rainfall respectively. 16

28 Comparison of normal and Actual rainfall for the month of July is shown in following Pie chart: Normal Rainfall (mm) among the four Basins for the month of July Actual Rainfall (mm) among the four Basins for the month of July Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Basin-wise rainfall statistics for the month of July 2007 are shown in the Table below: Table 2.9: Brahmaputra Basin Rainfall in July (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Kurigram Dalia Kaunia Rangpur Chilmari Dewanganj Gaibandha % less Bogra Jamalpur Mymensingh Dhaka Tangail Average Table 2.10: Ganges Basin Rainfall in July (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Panchagarh Dinajpur Pabna Naogaon Rajshahi Kushtia Jessore % more Khulna Satkhira Faridpur Barisal Patuakhali Average

29 Table 2.11: Meghna Basin Rainfall in July (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Kanaighat Sylhet Sunamganj Sheola Moulvi Bazar Manu Rly Br Habiganj % more Durgapur Bhairab Bazar Comilla Chandpur Average Table 2.12: South Eastern Hill Basin Rainfall in July (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Parshuram Noakhali Narayanhat Panchpukuria Bandarban Rangamati % more Lama Chittagong Ramgarh Cox' Bazar Average From the above table it shows that monthly rainfall in the Ganges, the Meghna and the South Eastern Hill basins exceeded their monthly normal rainfall. Out of 12 stations, 10 stations received higher rainfall than their respective normal rainfall in the Ganges basin. And in the Meghna basin, out of 11 stations, 5 stations received higher rainfall than their respective normal rainfall and in the South Eastern Hill basin, out of 10 stations, 7 stations experienced higher rainfall than their respective normal rainfall. On the contrary monthly rainfall in the Brahmaputra and the South Easter Hill basins showed lower than the normal rainfall. 7 out of 12 stations in the Brahmaputra basin observed lower than the normal rainfall respectively. All the monitoring stations, Sunamganj in the Meghna basin is the highest rainfall recipient station. The table shows that 4 out of 12 stations in the Brahmaputra basin, 7 out of 12 stations in the Ganges basin, 8 out of 11 stations in the Meghna basin and 9 out of 12 stations in the 18

30 South Eastern Hill basin received more than 300 mm rainfall in 10-day period. 300 mm or more rainfall in 10-Day period may cause rain fed flood in this area. During the fourth week in this month, excessive rainfall in the Brahmaputra, the Ganges and the Meghna basins and inflow from upstream caused river flooding in the districts of Manikganj, Munshiganj, Faridpur, Rajbari, Madaripur, Shariatpur, Chandpur and the part of Dhaka. Rainfall Isohyets of the actual rainfall of the month of June is shown in the Figure MONTH OF AUGUST The country as a whole experienced less rainfall than the normal of the month. The intensity of rainfall in the Brahmaputra basin and Ganges basin was light to moderate at most of the places with heavy rainfall at a Important Rainfall Information for August 07 Maximum, at Kanaighat : mm One day maximum, at Kanaighat : mm Exceeded Highest Record (May): Rainfall at None of the stations exceeded its Highest Record. few places during the month of August. On the other hand the Meghna and the South Eastern Hill basin experienced moderate with heavy rainfall at several places during this month. In the month of August, all the four hydrological basins such as the Brahmaputra, the Ganges, the Meghna and the South Eastern Hill basin received rainfall 11.67%, 32.44%, 24.51% and 32.42% less than their respective monthly normal rainfall. Comparison of normal and Actual rainfall for the month of August is shown in following pie chart: Normal Rainfall (mm) among the four Basins for the month of August Actual Rainfall (mm) among the four Basins for the month of August Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin 19

31 Basin-wise rainfall statistics for the month of August 2007 is shown in the Table below: Table 2.13: Brahmaputra Basin Rainfall in August (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Kurigram Dalia Kaunia Rangpur Chilmari Dewanganj Gaibandha % Less Bogra Jamalpur Mymensingh Dhaka Tangail Average Table 2.14: Ganges Basin Rainfall in August (mm) Station Max. Nor Act Dev 1dymax 10dmax % less or more Panchagarh Dinajpur Pabna Naogaon Rajshahi % less Kushtia Jessore Khulna Satkhira Faridpur Barisal Patuakhali Average Table 2.15: Meghna Basin Rainfall in August (mm) Station Max. Nor Act Dev 1dymax 10dmax Kanaighat Sylhet Sunamganj Sheola Moulvi Bazar Manu Rly Br Habiganj Durgapur Bhairab Bazar Comilla Chandpur Average % less or more % less 20

32 Table 2.16: South Eastern Hill Basin Rainfall in August (mm) Station Max. Nor Act Dev 1dymax 10dmax Parshuram Noakhali Narayanhat Panchpukuria Bandarban Rangamati Lama Chittagong Ramgarh Sandwip Cox' Bazar Average % less or more % less From the above table it shows that monthly rainfall in the Brahmaputra, the Ganges, the Meghna and the South Easter Hill basins is less than their monthly normal rainfall. All the stations in the Brahmaputra basin, the Ganges basin, the Meghna basin and the South- Eastern hill basin received lower rainfall than their respective monthly normal rainfall. Out of 12 monitoring station in the Brahmaputra basin, Rangpur received lowest rainfall and Dhaka received highest rainfall, in Ganges basin Khulna received lowest rainfall and Panchagarh received highest rainfall, in Meghna basin Comilla received lowest rainfall and Kanaighat received highest rainfall, in the South Eastern Hill basin Sandwip received lowest rainfall and Chittagong received highest rainfall. All the stations in the Brahmaputra basin, the Ganges basin, South Eastern Hill and 10 stations in the Meghna basin received less than 300 mm rainfall in 10- day period. Rainfall Isohyets of the actual rainfall of the month of August is shown in the Figure MONTH OF SEPTEMBER The intensity of rainfall over the country was very heavy during the first fifteen days of the month of September. On the other hand, the South Eastern Hill basins also experienced relatively higher rainfall at most of the places during the last fifteen days of this month. Important Rainfall Information for September 2007 Maximum, at Sylhet : mm One day maximum, at Narayanhat : mm Exceeded Highest Record (May): Rainfall at None of the stations exceeded its Highest 21

33 Among the four hydrological basins, the Brahmaputra, the Ganges and the South Eastern Hill basins received rainfall 12.09%, 3.33% and 0.24% less than their respective monthly normal rainfall respectively and the South Eastern Hill basins received rainfall 46.65% more than their monthly normal rainfall respectively. Comparison of normal and Actual rainfall for the month of August is shown in following pie chart Normal Rainfall (mm) among the four Basins for the month of September Actual Rainfall (mm) among the four Basins for the month of September Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Brahmaputra Basin Ganges Basin Meghna Basin South-Eastern Hill Basin Basin-wise rainfall statistics for the month of September 2007 are shown in the Table below: Table 2.17 Brahmaputra Basin Rainfall in September (mm) Station Max. Nor Act Dev 1dymax 10dmax Kurigram Dalia Kaunia Rangpur Chilmari Dewanganj Gaibandha Bogra Jamalpur Mymensingh Dhaka Tangail Average % less/more 12.09% less 22

34 Table 2.18Ganges Basin Rainfall in September (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Panchagarh Dinajpur Pabna Naogaon Rajshahi Kushtia Jessore % less Khulna Satkhira Faridpur Barisal Patuakhali Average Table 2.19: Meghna Basin Rainfall in September (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Kanaighat Sylhet Sunamganj Sheola Moulvi Bazar Manu Rly Br Habiganj % less Durgapur Bhairab Bazar Comilla Chandpur Average Table 2.20: South Eastern Hill Basin Rainfall in September (mm) Station Max. Nor Act Dev 1dymax 10dmax % less/more Parshuram Narayanhat Panchpukuria Bandarban Rangamati Lama % more Chittagong Ramgarh Sandwip Cox' Bazar Average The above table shows that in the Brahmaputra basin 10 out of 12 stations, 6 out of 12 stations in the Ganges basin and in the Meghna basin 4 out of 11 stations received less rainfall than their monthly normal rainfall. And in the South Eastern Hill basin 8 out of 10 23

35 stations received more rainfall than their monthly normal rainfall. Among all monitoring stations, Sylhet in the Meghna basin is the daily highest rainfall recipient station. The table shows that 1 out of 12 stations in the Brahmaputra basin, 3 out of 12 stations in the Ganges basin, 7 out of 11 stations in the Meghna basin and 8 out of 10 stations in the South-Eastern Hill Basin received more than 300 mm rainfall in 10-day period. 300 mm or more rainfall in 10-Day period may cause rain fed flood. During the first half of this month, excessive rainfall in the Brahmaputra and the Ganges basins and inflow from upstream caused river flooding in the districts of Kurigram, Gaibandha, Bogra, Jamalpur, Serajganj, Tangail, Rajbari, Faridpur, Manikganj, Munshiganj, Nawabganj, Dhaka, Madaripur, Shariatpur, Gopalganj and Chandpur. Rainfall Isohyets of the actual rainfall of the month of September is shown in the Figure

36 Figure 2.1: Isohyets of Actual Rainfall (May 2007) 25

37 Figure: 2.2: Isohyets of Actual Rainfall (June 2007) 26

38 Figure: 2.3: Isohyets of Actual Rainfall (July 2007) 27

39 Figure: 2.4: Isohyets of Actual Rainfall (August 2007) 28

40 Figure: 2.5: Isohyets of Actual Rainfall (September 2007) 29

41 CHAPTER 3: RIVER SITUATION 3.1 BRAHMAPUTRA BASIN In this basin, almost all the rivers flowed above its respective danger level for one to six weeks during the monsoon The flood phenomenon was not very less in this basin in comparison with other flooding year (viz.2004 and 1998). A comparative statement of water level for current year 2007 and historical events of 2004 and 1998 for the Brahmaputra Basin is shown in Table 3.1. The details of the river situation in this basin are described below: The Dharla at Kurigram The Dharla at Kurigram registered several peaks during the monsoon It crossed the danger level on 27 th July for 9 consecutive days and on 8 th September for 6 consecutive days. It attained its highest peak on 8 th September and the level was of m, which was 116 cm above its danger level (26.50 m). The Teesta at Dalia and Kaunia The river Teesta is flashy in nature. The river showed several peaks during the monsoon both at Dalia and Kaunia. At Dalia it crossed its danger marks for eight times. First it crossed it danger mark at 12 th July, then at 18 th July, 25 th July, 1 st August, 15 th August, 30 th August, 3 rd September, 5 th September. As a whole, the Teesta at Dalia was under danger mark for 16 days. But at Kaunia, it followed below danger level. The river attained its highest peak at Dalia was m on 8 th September, which was 70 cm above its danger level (52.25) and at Kaunia was m on 8 th September, which was 34 cm below its danger level (30.0). The Brahmaputra at Noonkhawa and Chilmari The river Brahmaputra at Noonkhawa and Chilmari observed steady rise and fall at several times throughout the year. But, it showed relatively sharp rise at the last week of 30

42 July and at the beginning of September. It crossed the danger level on 27 th July, 9 th September, 12 th September at Noonkhawa and on 27 th July, 8 th September at Chilmari. The river attained its highest peak of m at Chilmari on 30 th July and m at Noonkhawa on the same day which were 81 cm and 66 cm above the danger marks of these two points. The Jamuna at Bahadurabad and Serajganj The Jamuna at Bahadurabad and Serajganj showed similar trend as of Brahmaputra at Chilmari. During this monsoon it crossed the danger level on 27 th July, 8 th September at Bahadurabad and on 25 th July, 7 th September at Serajganj. The highest peak attained Bahadurabad was m on 30 th July which was 90 cm above its danger mark (19.50 m). At Serajganj, its highest peak was m attained on 1 st August, which was 120 cm above its danger mark (13.75) The Jamuna at Aricha In 2007, the Jamuna at Aricha showed rising slope from the beginning of the monsoon which is continued upto the last week of June. After short recession at the mid of July it continued to rise upto the first week of August. At the middle of September it again went up to its danger mark (9.40). The maximum peak attained during this monsoon was m on 3 rd September, which was 127 cm above its danger mark (9.40 m). The Old Brahmaputra at Jamalpur and Mymensingh The river Old Brahmaputra at Jamalpur and Mymensingh showed several rise and fall during the monsoon but it rose sharply at the last week of July and at the first week of the September. The river flowed above danger level on 1 st August, 14 th September at Jamalpur and on 4 th August at Mymensingh. The maximum peak attained at Jamalpur was m on 2 nd August, which was 24 cm above the danger level (17.00 m). At Mymensingh, it was m on 5 th August, which was 5 cm above the danger level (12.5 m) The Buriganga at Dhaka The Buriganga at Dhaka observed rise and fall with tidal influence and crossed danger level during the monsoon 2007 on 6 th August. It recorded its yearly maximum peak 6.02 m on 7 th August, which was 2 cm above the danger level (6.00m PWD datum). 31

43 The Lakhya at Narayanganj The Lakhya at Narayanganj showed the similar trend as of the Buriganga at Dhaka and crossed the danger level on 1 st August and 15 September during the monsoon The maximum peak attained during this period was 6.05 m on 6 th August, which was 65 cm above its danger mark (5.50 m). The Turag at Mirpur The Turag at Mirpur showed steady rise from the middle of July up to the 2 nd week of August and then after a small recession it again started steady rise from the 1 st week of September. It crossed danger level on 2 nd August and 16 th September. The maximum peak attained during this period was 6.62 m on 8 th August, which was 68 cm above its danger mark (5.94 m) at this point. The Tongi Khal at Tongi The Tongi Khal at Tongi also showed same trend as of the Turag at Mirpur and crossed danger mark on 1 st August and on 18 th September. The highest peak attained during the monsoon was 6.87 m on 8 th August, which was only 79 cm above its danger mark (6.08 m). The Kaliganga at Taraghat The Kaliganga at Taraghat showed sharp rise during the middle of July till end of first week of August. It again showed sharp rise during the 2 nd week of September. It crossed it danger mark on 29 th July and 10 th September during this monsoon. The highest peak attained during this period was 9.79 m on 4 th August, which was 141 cm above its danger mark (8.38 m). Comparative hydrographs for the year of 2007, 1998 & 1988 of Dharla at Kurigram, Brahmaputra at Bahadurabad, Serajganj & Aricha, Buriganga at Dhaka are shown in figures 3.1, 3.2, 3.3, 3.4, and

44 Table 3.1: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Brahmaputra Basin. Sl. No River Station Recorded Maximum (m) Danger Level Peak of the year (m) Days above Danger level (m) Dharla Kurigram Teesta Dalia Teesta Kaunia Brahmaputra Noonkhawa NA 12 - NA 5 Brahmaputra Chilmari Jamuna Bahadurabad Jamuna Serajganj Jamuna Aricha Old Br.putra Jamalpur Old Br.putra Mymensingh Buriganga Dhaka Lakhya Narayanganj Turag Mirpur NA NA 14 Tongi Khal Tongi NA NA 15 Kaliganga Taraghat GANGES BASIN In this basin, almost all the rivers down the confluence flowed above its respective danger level during the monsoon The flood phenomenon was also severe in this basin in comparison with other flooding years (viz.1998 & 1988). A comparative statement of water level for current year 2007 and historical events of 1998 & 1988 for the Ganges Basin is shown in Table 3.2. The details of the river situation in this basin are described below: The Padma at Pankha The river at Pankha showed sharp rise from the mid of July. In the month of August and September, it crossed danger level on 21 st August for 7 days and on 11 th September for 6 days. The river at this point attained its highest peak of the year m on 14 th September, which was 21 cm above the danger level (21.5-m PWD datum). The Padma at Rajshahi The river at this point observed nearly similar trend as Pankha and recorded several peaks in the month of August & September but did not cross danger level throughout the 33

45 monsoon. The River attained its highest peak of the year m on 15 th September, which was 70 cm below the danger level (18.5-m PWD datum). The Padma at Hardinge Bridge The river at this point showed nearly similar trend of Rajshahi and did not cross danger level throughout the monsoon. It attained its yearly highest peak 14.0 m on 6 th August, which was 25 cm below the danger level (14.25-m PWD datum). The Padma at Goalundo The river started to rise significantly after the 2 nd week of July. It crossed the danger level on 23 rd July for consecutive 37 days and 7 th September for consecutive 17 days during this monsoon. It attained its yearly highest peak m on 3 rd August, which was 151 cm above the danger level (8.5-m PWD datum). And it also crossed the previous recorded highest water level (9.83 m) The Padma at Bhagyakul The river has tidal influence at this point. At this point it observed several peaks during the monsoon in the month of July, August & September and it crossed danger level on 24 th July for consecutive 37 days and 7 th September for consecutive 18 days during this monsoon. The river attained its highest yearly peak 7.15 m on 4 th August, which was 115 cm above the danger level (6.00-m PWD datum). The Gorai at Gorai Rly Bridge The river Gorai at Gorai Rly Bridge observed sharp rise from mid of July and continued till 1 st week of August and after then it showed gradual rise & fall but did not cross danger level throughout the monsoon. The river attained its yearly peak m on 7 th August, which was 30 cm below the danger level (12.75-m PWD datum). The Punarbhaba at Dinajpur At Dinajpur the river Punarbhaba showed several peaks during the monsoon but did not cross danger level throughout the monsoon. It attained its highest peak m on 7 th September, which was 94 cm below the danger level (33.50-m PWD datum). 34

46 Comparative hydrographs for the year of 2007, 1998 & 1988 of Punarbhaba at Dinajpur and Padma Rajshahi, Hardinge Bridge, Goalundo and Bhagyakul are shown in figures 3.6, 3.7, 3.8, 3.9 and Table 3.2: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Ganges Basin. Sl. No River Station Recorded Maximum (m) Danger Level (m) Peak of the year (m) Days above Danger level (m) Punarbhaba Dinajpur Padma Pankha NA NA 3 Padma Rajshahi Padma Hardinge Bridge Padma Goalundo Padma Bhagyakul Gorai Gorai Rly Bridge MEGHNA BASIN This basin experienced concentrated heavy rainfall during the monsoon The river Surma, Kushiyara, Manu, Khowai, Someswari, Meghna, Gumti crossed their respective danger levels at different points mostly in the month of June, July and September. As a result, flash floods of high magnitude were experienced in the districts of Sylhet, Sunamganj, Moulvi Bazar, Habiganj, Comilla during the same period. A comparative statement of water level for current year 2007 and historical events of 1998 and 1988 for this basin is shown in Table 3.3. The Surma at Kanaighat As a flashy river, the Surma at Kanaighat showed several peaks during this monsoon. It flowed above the danger level on 24 th May (1 day), 16 th June (7 days), 19 th July (20 days) and 26 th July (31 days). It attained its highest yearly peak m on 9 th September, which was 202 cm above the danger level (13.20-m PWD datum). 35

47 The Surma at Sylhet Like Kanaighat, the river at this point registered several peaks during the monsoon However, the Surma at Kanaighat distinctly crossed its danger level on 17 th June (7 days), 26 th July (10 days) and 8 th September (14 days). It attained its highest yearly peak m on 11 th of September, which was 58 cm above the danger level (11.25-m PWD datum). The Surma at Sunamganj The river at this point also followed the same pattern as in Sylhet. The Surma at Sunamganj crossed the danger level on 10 th June (3 days), 16 th June (8 days), 25 th July (13 days) and 8 th September (8 days). It attained its highest peak 9.10 m on 26 th July, which was 85 cm above the danger level (8.25-m PWD datum). The Kushiyara at Amalshid The river at this point observed several medium & high peaks during the monsoon It crossed danger level on 17 th June (10 days), 28 th July (9 days) and 27 th August (29 days). It attained its yearly highest peak m on 11 th September, which was 210 cm above the danger level (15.85-m PWD datum). The Kushiyara at Sheola The Kushiyara at Sheola observed similar rise and fall as of Amalshid. It crossed its danger level on 17 th June (10 days), 28 th July (10 days) and 27 th August (30 days). It attained its yearly highest peak m on 9 th September, which was 110 cm above the danger level (13.50-m PWD datum). And it also crossed the previous recorded highest water level (14.46 m) The Manu at Manu Rly Bridge As a flashy river, the river at this point observed several peaks during this monsoon but it showed significant sharp rise during the month of June and September. It crossed its danger level on 11 th June (3 days), 17 th June (2 days) and 8 th September (3 days). It attained its highest peak of the year m on 18 th June, which was 158 cm above the danger level (18.00-m PWD datum). 36

48 The Khowai at Habiganj As the flashiest river in Bangladesh, the Khowai at Habiganj crossed its danger level for six times during the monsoon It crossed its danger level on 11 th June (3 days), 16 th June (3 days), 22 nd July (1 day), 27 July (1 day), 7 th September (1 day) and 9 th September (2 day). It attained its yearly highest peak m on 18 th June, which was 2.50 m above the danger level (9.50-m PWD datum). And it also crossed the previous recorded highest water level (11.82 m) Comparative hydrographs for the year of 2007, 1998 & 1988 of Surma at Sylhet & Sunamganj, Kushiyara at Sheola, Manu at Moulvi Bazar, Khowai at Habiganj are shown in figures 3.11, 3.12, 3.13, 3.14, and Table 3.3: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 & 1998 of Some Important Stations in Meghna Basin. Sl. No River Station Recorded Maximum (m) Danger Level (m) Peak of the year (m) Days above Danger level m) Surma Kanaighat Surma Sylhet Surma Sunamganj Kushiyara Amalshid Kushiyara Sheola Manu Manu Rly Br Manu Moulvi Bazar Khowai Habiganj Someswari Durgapur Upper Meghna Bhairab Bazar Gumti Comilla

49 3.4 THE SOUTH EASTERN HILL BASIN The South Eastern Hill basin is constituted with the basin areas of the hilly rivers like the Muhuri, the Halda, the Sangu, the Matamuhuri and the Feni in the South Eastern Part of the country. This basin also received heavy concentrated rainfall during the monsoon Thus, the Halda at Narayanhat, the Muhuri at parshuram, Sangu at Bandarban, Mathamuhuri at Lama & Chiringa, Feni at Ramgarh crossed danger level during the same period. As a result, a short duration but extreme flash flood occurred at some places during monsoon The details of different river situations are given below. A comparative statement of water level for current year 2007 and historical events of 1998 and 1988 for this basin is shown in Table 3.4. The Muhuri at Parshuram The river at this point observed several significant peaks in June, July and September and it had exceeded its danger level at 10 th June (3 days), 16 th June (2 days), 19 th July (4 days), 7 th September (3 days) and 9 th October (1 day). It attained its highest peak m on 10 th June, which was 2.00 m above the danger level (13.00 m). The Halda at Narayanhat The river Halda at Narayanhat also showed several peaks during this monsoon. It crossed danger mark for five times during the same period. It exceeded its danger level on 2 nd July (1 day), 18 th July (3 days), 15 th August (3 days), 7 th September (4 days) and 9 th October (1 day). The highest peak attained by the river was m on 8 th September, which was 175 cm above the danger mark (15.25 m). The Halda at Panchpukuria The river attained several peaks at Panchpukuria but did not cross danger mark during the monsoon At Panchpukuria it attained its highest peak of the month 6.38 m on 11 th September, which was 62 cm below the danger level (7.00 m). 38

50 The Sangu at Bandarban The river at this point showed several medium and high peaks during this monsoon and flowed above danger level on 20 th July for 1 day. The highest peak of the year attained by the river was m on 20 th July, which 1.25 m below its danger mark (15.25m). The Sangu at Dohazari The river at this point also showed several peaks as of Bandarban and flowed above danger level on 20 th July for 3 days during this monsoon. The highest peak attained by the river at this point was 7.10 m on 20 th July, which was 135 cm above its danger mark (5.75 m). The Matamuhuri at Lama The river Matamuhuri at Lama observed several peaks and crossed the danger level on 12 th June for 1 day. The highest peak attained by the river was m on 12 th June, which was 140 cm above its danger mark (12.25-m). The Matamuhuri at Chiringa Matamuhuri at Chiringa crossed its danger marks several times during this monsoon. On 12 th June, it crossed it danger level for the first time for 2 days. It also crossed its danger level on 4 th July for 3 days, 19 th July for 3 days, 6 th and 10 th September for 1 day each. The highest peak of the year attained by the river was 6.41 m on 12 th June, which was 66 cm above the danger mark (5.75m). The Feni at Ramgarh The river at this point observed several sharp rises and crossed the danger level on 8 th September for 3 days during the monsoon The highest peak attained by the river was m on 8 th September, which was 106 cm above the danger level (17.37-m). Comparative hydrographs for the year of 2007, 1998 and 1988 of Halda at Narayanhat and Matamuhuri at Chiringa are shown in Figures 3.16,

51 Table 3.4: Comparison of Water Level of the Current Year 2007 and Historical Events of 1988 and 1998 of Some Important Station in South Eastern Hill Basin. Sl. No River Station Recorded Maximum (m) Danger Peak of the year Days above Level (m) Danger level (m) (m) Muhuri Parshuram Halda Narayanhat NA NA 3 Halda Panchpukuria Sangu Bandarban Sangu Dohazari NA - 2 NA 6 Matamuhuri Lama Matamuhuri Chiringa NA 10 5 NA 8 Feni Ramgarh NA 3 1 NA 3.5 RECORDED HIGHEST WATER LEVEL Table 3.5: Recorded Highest Water Level with Date Sl. No. River Station Danger level (m) Recorded highest Water level (m) before 2007 flood with date Water level and date Exceeding previous Highest water level (m) 1 Dharla Kurigram ( ) - 2 Teesta Dalia ( ) - 3 Teesta Kaunia ( ) - 4 Brahmaputra Noonkhawa Brahmaputra Chilmari ( ) - 6 Jamuna Bahadurabad ( ) - 7 Jamuna Serajganj ( ) - 8 Jamuna Aricha ( ) - 9 Old Br.putra Jamalpur ( ) - 10 Old Br.putra Mymensingh Buriganga Dhaka ( ) - 12 Lakhya Narayanganj ( ) - 13 Turag Mirpur ( ) - 14 Tongi Khal Tongi ( ) - 15 Kaliganga Taraghat Punarbhaba Dinajpur Padma Pankha ( ) - 18 Padma Rajshahi ( ) - 19 Padma H- Bridge ( ) - 20 Padma Goalundo Padma Bhagyakul Gorai Gorai Rly Br ( ) - 23 Surma Kanaighat

52 Sl. No. River Station Danger level (m) Recorded highest Water level (m) before 2007 flood with date Water level and date Exceeding previous Highest water level(m) 24 Surma Sylhet ( ) - 25 Surma Sunamganj ( ) - 26 Kushiyara Amalshid ( ) - 27 Kushiyara Sheola ( ) ( ) 28 Manu Manu Rly Br ( ) - 29 Manu Moulvi Bazar Khowai Habiganj ( ) ( ) 31 Someswari Durgapur ( ) ( ) 32 Upper Meghna Bhairab Bazar ( ) - 33 Gumti Comilla ( ) - 34 Muhuri Parshuram Halda Narayanhat Halda Panchpukuria Sangu Bandarban ( ) - 38 Sangu Dohazari Matamuhuri Lama Matamuhuri Chiringa ( ) - 41 Feni Ramgarh ( ) - 41

53 Figure 3.1: Comparison of Hydrographs (Darla at Kurigram) 42

54 Figure 3.2: Comparison of Hydrographs (Brahmaputra at Bahadurabad) 43

55 Figure 3.3: Comparison of Hydrographs (Brahmaputra at Serajganj) 44

56 Figure 3.4: Comparison of Hydrographs (Brahmaputra at Aricha) 45

57 Figure 3.5: Comparison of Hydrographs (Buriganga at Dhaka) 46

58 Figure 3.6: Comparison of Hydrographs (Punarbhaba at Dinajpur) 47

59 Figure 3.7: Comparison of Hydrographs (Ganges at Rajshahi) 48

60 Figure 3.8: Comparison of Hydrographs (Ganges at Hardinge Bridge) 49

61 Figure 3.9: Comparison of Hydrographs (Ganges at Goalondo) 50

62 Figure 3.10: Comparison of Hydrographs (Ganges at Bhagyakul) 51

63 Figure 3.11: Comparison of Hydrographs (Surma at Sylhet) 52

64 Figure 3.12: Comparison of Hydrographs (Surma at Sunamganj) 53

65 Figure 3.13: Comparison of Hydrographs (Kushiyara at Sheola)\ 54

66 Figure 3.14: Comparison of Hydrographs (Manu at Moulvi Bazar) 55

67 Figure 3.15: Comparison of Hydrographs (Khowai at Habiganj) 56

68 Figure 3.16: Comparison of Hydrographs (Halda at Narayan Hat) 57

69 Figure 3.17: Comparison of Hydrographs (Matamuhuri at Chiringa) 58

70 CHAPTER 4: FORECAST EVALUATION, GENERAL This chapter describes the performance of FFWC Super model for forecasting water levels during 2007 monsoon (April to October). Model simulations were carried out in each and every day for forecast period of maximum 72 hours. Forecasts were made for 24-hour, 48-hour and 72-hour intervals during the flood season. And it has been evaluated in this chapter using statistical analysis. Forecasts for 24 and 48 hours in most of the stations in 2007 are found quite satisfactory. Besides, forecasts for 72 hours did not reach that much satisfactory level and even some are found very poor. 4.2 EVALUATION CRITERIA OF FORECAST PERFORMANCE Two statistical criteria considered for the performance evaluation of the model are as follows: Mean Absolute Error, MAE Co-efficient of Determination, r Mean Absolute Error, MAE MAE is the mean of the absolute difference between Observed and Forecast levels as shown in the following equation: MAE = n i= 1 x i n y i Where, x 1, x 2. x n are Observed water levels y 1, y 2. y n are Forecast water levels n is the number of Observed/Forecast levels 59

71 4.2.2 Co-efficient of Determination, r2 r 2 is the Co-efficient of Determination for the correlation of Observed and Forecast water levels and is given by the relation as show in the equation below: r n 2 i= 1 = n Where, ( x x )( y y) i n 2 ( x x) ( y y) i i= 1 i= 1 i i x 1, x 2. x n are Observed water levels 2 2 x is the average of Observed water levels y 1, y 2. y n are Forecast water levels y is the average of Forecast water levels n is the number of Observed/Forecast levels 4.3 PRE-DEFINED SCALES TO EVALUATE FORECAST PERFORMANCE The forecast performances have been evaluated from the statistical components r 2 (Coefficient of Determination) and MAE (Mean Absolute Error). Values of the above two components in their ideal case are generally assumed to be in the order of MAE = 0 r 2 = 1 Utilizing above two indicators, 5 category scales have been used to describe forecast performances. Stations having a minimum value of 0.9 for r 2 and a maximum value of 15 centimeter for MAE have been considered as Good performance. Table 4.1 presents the definition of scales used in the evaluation: Table 4.1: Scales used for performance evaluation Sl. No. Scale Value 1 Good MAE <= 0.15 meter & r 2 >= Average MAE <= 0.2 meter & r 2 >= Not satisfactory MAE <= 0.3 meter & r 2 >= Poor MAE <= 0.4 meter & r 2 >= Very Poor MAE > 0.4 meter or r 2 <

72 Simulations were made for maximum 72 hours in the forecast period and forecasts were saved in the database at 24-hour and 48-hour and 72-hour intervals. At most of the locations, the forecast quality gradually deteriorated where forecast intervals were moved further away from the time of forecast. It is not surprising as the increases of lead time decreases the accuracy. This means that forecasts were the best at 24-hour interval followed by 48-hour interval and then 72-hour interval. Figure shows the comparison of observed and forecasted water level for 24, 48 and 72 hours. Result of the statistical analysis and performance on the basis of the aforesaid scale are presented in table 4.2, 4.3 and FORECAST STATISTICS AND MODEL PERFORMANCE, 2007 The following 38 stations which are located within the model area (including some boundary stations) are taken for evaluation. The forecast statistics along with their performance are provided in table 4.2 to 4.4 and in figure 4.1 to 4.3. Table 4.2: Statistics for 24- hour forecast performance Sl. No. Station MAE (meter) r 2 Performance 1 Aricha Good 2 Bahadurabad Good 3 Bhagyakul Good 4 Bhairabbazar Good 5 Bhusirbandar Not Satisfactory 6 Bogra Good 7 Chakrahimpur Good 8 Chilmari Good 9 Demra Good 10 Dhaka Good 11 Goalondo Good 12 Gorai-RB Good 13 Hardinge-BR Good 14 Jagir Good 15 Jamalpur Good 16 Kamarkhali Good 17 Kaunia Average 18 Mirpur Good 19 Moulvibazar Not Satisfactory 20 Mymensingh Good 21 Mohadevpur Not Satisfactory 61

73 Sl. No. Station MAE (meter) r 2 Performance 22 Naogaon Good 23 Narayanganj Good 24 Nayarhat Good 25 Rajshahi Good 26 Serajganj Good 27 Sheola Good 28 Sunamganj Good 29 Sylhet Good 30 Taraghat Good 31 Tongi Good Table 4.3: Statistics for 48- hour forecast performance Sl. No. Station MAE (meter) r 2 Performance 1 Aricha Good 2 Bahadurabad Good 3 Bhagyakul Good 4 Bhairabbazar Good 5 Bhusirbandar Good 6 Bogra Not Satisfactory 7 Chakrahimpur Not Satisfactory 8 Chilmari Average 9 Demra Good 10 Dhaka Good 11 Goalondo Good 12 Gorai-RB Good 13 Hardinge-BR Good 14 Jagir Good 15 Jamalpur Good 16 Kamarkhali Not Satisfactory 17 Kaunia Not Satisfactory 18 Mirpur Very poor 19 Moulvibazar Very poor 20 Mymensingh Good 21 Mohadevpur Average 22 Naogaon Good 23 Narayanganj Good 24 Nayarhat Good 25 Rajshahi Good 2 Serajganj Good 26 Sheola Average 27 Sunamganj Good 28 Sylhet Average 29 Taraghat Average 30 Tongi Good 62

74 Table 4.4: Statistics for 72- hour forecast performance Sl. No. Station MAE (meter) r 2 Performance 1 Aricha Good 2 Bahadurabad Average 3 Bhagyakul Good 4 Bhairabbazar Good 5 Bhusirbandar Very Good 6 Bogra Poor 7 Chakrahimpur Poor 8 Chilmari Not Satisfactory 9 Demra Good 10 Dhaka Good 11 Goalondo Good 12 Gorai-RB Average 13 Hardinge-BR Average 14 Jagir Good 15 Jamalpur Good 16 Kaunia Not Satisfactory 17 Kamarkhali Not Satisfactory 18 Mirpur Good 19 Moulvibazar Very Poor 20 Mymensingh Poor 21 Mohadevpur Very Poor 22 Naogaon Not Satisfactory 23 Narayanganj Good 24 Nayarhat Not Satisfactory 25 Rajshahi Not Satisfactory 26 Serajganj Average 27 Sheola Poor 28 Sunamganj Not Satisfactory 29 Sylhet Not Satisfactory 30 Taraghat Average 31 Tongi Good 63

75 Figure 4.1: 24 hr Forecast Evaluation (Year, 2007) 64

76 Figure 4.2: 48 hr Forecast Evaluation (Year, 2007) 65

77 Figure 4.3: 72 hr Forecast Evaluation (Year, 2007) 66

78 15 24 hrforecasted WL (mpwd) y = x R 2 = Obsered WL (mpwd) Figure 4.4: Observed Vs. Forecasted (24 hr) WL (Jamuna at Sirajganj) 67

79 y = x R 2 = hr Forecasted WL (mpwd) Observed WL (mpwd) Figure 4.5: Observed Vs. Forecasted (48 hr) WL (Jamuna at Sirajganj) 68

80 y = x R 2 = hr Forecasted WL (mpwd) Obsrved WL (mpwd) Figure 4.6: Observed Vs. Forecasted (72 hr) WL (Jamuna at Sirajganj) 69

81 Comparison of Observed and Forecast Water levels Water level (mpwd) Serajganj 24hr-forecast Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.7: Comparison of Forecasted (24 hr) Hydrograph WL (Jamuna at Sirajganj) 70

82 Water level (mpwd) Observed WL hr-forecast Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.8: Comparison of Forecasted (48 hr) Hydrograph WL (Jamuna at Sirajganj) 71

83 Water level (mpwd) Observed WL 12 72hr-forecast Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.9: Comparison of Forecasted (72 hr) Hydrograph WL (Jamuna at Sirajganj) 72

84 24 hr Forecasted WL (mpwd) y = x R 2 = Observed WL (mpwd) Figure 4.10: Observed Vs. Forecasted (24 hr) WL (Padma at Goalundo) 73

85 y = x R 2 = hr Forecasted WL (mpwd) Observed WL (mpwd) Figure 4.11: Observed Vs. Forecasted (48 hr) WL (Padma at Goalundo) 74

86 y = x R 2 = hr Forecast WL (mpwd) Observed WL (mpwd) Figure 4.12: Observed Vs. Forecasted (72 hr) WL (Padma at Goalundo) 75

87 Water level (mpwd) Observed WL 24hr-forecast 6 07-Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.13: Comparison of Forecasted (24 hr) Hydrograph WL (Padma at Goalundo) 76

88 Water level (mpwd) Observed WL 48hr-forecast Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.14: Comparison of Forecasted (48 hr) Hydrograph WL (Padma at Goalundo) 77

89 Water level (mpwd) Goalondo 7 72hr-forecast Jun Jun Jul Aug Aug Sep Oct Oct-07 Date Figure 4.15: Comparison of Forecasted (72 hr) Hydrograph WL (Padma at Goalundo) 78

90 CHAPTER 5: INUNDATION STATUS 5.1 GENERAL The country experienced severe flooding in the Brahmaputra Basin during the flood season of The flooded area in the peak period of August was 62,300 Sq. km (Source: SPARSO) during the flood season of And the total damages of different infrastructures of different projects of Bangladesh water Development Board were assessed and estimated as Taka Lac in the same period. In flood period, Flood Inundation Map for the whole country as well as Dhaka city was developed at FFWC as a part of daily routine. This was done by using MIKE 11 GIS, where the results were found from MIKE 11 rainfall-runoff and Hydrodynamic modeling. In addition, River Situation Map was also developed in the centre. A sample of Flood Inundation Map and River Situation Map has been placed in this chapter end. 79

91 Table 5.1 Zone-Wise Damage Assessment of BWDB Infrastructures Name of Zone Protective Works(m) WCS(nos) Embankment(km) Irrigation Canal/ Drainage Canal(km) Bank Revetment(m) Groyne( Nos.) Spur/Hard Points.(Nos) Total Full Part TK. Total Full Part TK. Total Full Part Part Part TK. Total Full Part Central Zone,Dhaka North-Eastern Zone,Comilla South-Eastern Zone, Chittagong South-Western Zone,Faridpur North-Western Zone, Rajshahi spar-25 Groyne Southern zone, Barisal Northern zone, Rangpur , 54 km project Road 6 97 CERP.Dhaka Total= spar-25 Groyne , 54 km project Road

92 Figure 5.1: Flood Inundation Map of Bangladesh (August 5, 2007) 81

93 Figure 5.1: Flood Inundation Map of Bangladesh (24 hr Forecast Based on August 5, 2007) 82

94 Figure 5.1: Flood Inundation Map of Bangladesh (48 hr Forecast Based on August 05, 2007) 83

95 Figure 5.3: Flood Inundation Map of Dhaka (August 05, 2007) Figure 5.4: Flood Inundation Map of Dhaka (48 hr Forecast based on August05, 2007) 84