DEGREE THESIS SUBMITTED TO THE DEPARTMENT OF WATER ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DIPL. Anika Yunus, Professor and Head of Department of Water Resources Engineering (WRE), BUET; dr.
INTRODUCTION
- Major River systems and their Characteristics
- Overall Study Objectives and Expected Outcomes
- Rationale and Significance of this Study
- Study Area/Model Domain
- Structure of the Study Report
The combined flows of the Jamuna and Ganges constitute the course of the Padma River. The study area is selected 48 km from Padma river including Harirampur total of Manikganj district.
FLOOD AND WATER RESOURCES MANAGEMENT PRACTICES
- Natural Hazard
- What is Flood?
- Historical Evaluation of Flood Investigations
- Flood Classifications and its types
- Flood Classifications Based on Goods and Services
- Flood Classification Based on Different Sources
- Causes of Floods
- Flood and its Impacts
- Statistics of Flood in Bangladesh
- Flood in Study Area
- Past Flood and Water Resources Management Initiatives/ Studies
- Flood Mitigation Measures
- Flood and Water Resources Management Measures of BWDB
- BWDB
- LGED
- BIWTA
- Non-Structural Measures
- Flood Forecasting and Warning Centre (FFWC)
- CFIS Projects of CEGIS
- Flood Inundation Maps
- Embankment Overtopping and Breaching
- Flood Hazards Map
- Use of Flood Hazard Map
The cause-and-effect relationship of floods in Bangladesh is presented in the following matrix developed in Table 2-1:. The left sides of the study areas along with charlandas in the middle of river falls in Harirampur.
LITERATURE REVIEW
Studies on Hazard Mapping
- National Studies
- International Studies
Flood frequency and flood water depth were the main components for flood risk assessment in the study area. Flood hazard maps were developed considering the interactive effect of flood frequency and flood water depth simultaneously.
Uses of HEC-RAS in Flood Inundation Modelling
- National Studies
- International Studies
The output of the calibrated and validated HEC-RAS hydrodynamic model was exported to Arc-Map 10.1, where it was visualized as a flood inundation map using the HEC-GeoRAS extension. The HEC-RAS and HEC-GeoRAS hydrological models were used to delineate flood-vulnerable areas at different flow rates.
Benefits of Reviewing the above Mentioned Studies
To model the physical process of the Padma River with flood plains, the dynamics of the flow regimes of the three integrated large river systems together (Ganges, Brahmaputra and Padma) must be understood. The average water levels and flows of the Brahmaputra-Jamuna river system at Bahadurabad, the Ganges-Padma river system at Hardinge Bridge and the Padma river at Baruia Transit are shown in Figure 4-5. This component of the modeling system is intended to simulate one-dimensional sediment transport/moving boundary calculations resulting from scouring and deposition over moderate time periods (typically years, although individual flood applications are possible). Sediment transport potential is calculated by grain size fraction, thus enabling the simulation of hydraulic sorting and reinforcement. This scenario took into account the full protection provided by the 17 km flood embankment on the left bank of the Padma River.
BASELINE SETTING OF STUDY AREA
Geographical Location and Socio-Economic Aspects
Harirampur, Manikganj's largest upazilla in terms of area, came into existence as a thana in 1845 and was upgraded to an upazila in 1983. It is bounded on the north by Shibalaya upazilla, Manikganj Sadar upazilla and Ghior upazilla, on the east by Nawabganj upazlla and Dohar upazilla of Dhaka district and Manikganj Sadar upazila, south by river Padma, Char Bhadrasan upazilla and Faridpur Sadar upazilla of Faridpur district and west by Faridpur Sadar upazilla and Goalanda upazilla of Rajbari district and Shibalaya upazilla (Population and Housing Census.2011). According to Population and Housing Census (2011) all unions in the upazilla have brought under electricity connection by Rural Electrification Board (REB) Program.
Environmental Aspects and Issues
Regarding communication and transportation, Palanquin, house cart, bullock cart and Gaina boats are the traditional water transports found in the rural areas of Manikganj district. The main fishes available in Padma river are Carp (Rui, Catla, Mrigal, Ghania, Kalbasu, Kalia) Hilsa, Shrimp, Catfish (Rita, Boal, Pangas, Silon, Aor, Bacha) and Snake head (Shol, Gazar) , Taki) fish. Hils in the sea move at the surface, while in the river and other aquatic environments, they move at a depth of 14 to 18 meters, but on a cool or rainy day they can rise up to 2 meters from the surface.
Meteorology, Water Resources System, Riverine Floods and Erosion
Error indices quantify the deviation in the units of the data of interest (Legates and McCabe, 1999). A polygon boundary for the 2D flow area along Harirampur was drawn on the right and left sides of the Padma River. This was the best case scenario and full protection provided by the 17 km flood control dam on the left bank of the Padma River.
Erosion Control Interventions (Implemented)
Field Visit for information collection and ground trothing
SALIENT FEATURES OF THE MODEL
- HEC-RAS
- Theoretical Basis for ID & 2D Hydrodynamic Calculation
- Geographic Information System (GIS)
- HEC-GeoRAS
- HEC-Geo RAS Tools
The following articles are the description of the main possibilities and application rationales of HEC-RAS. Data can be transferred between HEC-RAS and other programs using HEC-DSS. This is the functional form of the momentum equation used in HEC-RAS.
METHODOLOGY, DATA COLLECTION AND MODEL SETUP
Steps of Methodology in Flow Chart
- Preparation Phase
- Execution Phase
- Exporting GIS Data to HEC-RAS
Model Calibration Results
The calibration was first performed for the n value of 0.018 and then for the second time for 0.015, and a comparison was made between the observed and simulated hydrographs of the water level. A comparison of the observed and simulated hydrographs at the Baruria Transit station shown in Figure 7-1 and the calibration results are shown in Table 7.1. Simulated volume larger than observed, but relatively smaller than observed volume for n value 0.018.
Model Validation Results
The best roughness value of n is 0.015 as it met the statistical criteria and fit of shape of the hydrographs, volumetric fits, R2 value 0.9974 which is almost 1 and NSE value is 0.68 greater than 0.5 and close to the maximum value of NSE and this value is accepted during calibration. However, the optimum roughness value of n for flood plain is 0.030 established from literature review and expert judgement. Now the model is ready to apply for predicting expected results of four different scenarios such as without embankment, with embankment, embankment breach and embankment skip respectively.
Model Application
Interventions or Lateral Infrastructures for model application
Model generates the flood inundation (depth and extent) maps of both parts of Harirampur, falls left side of the Padma river and within the transport and charland of the river. A proposed full flood control embankment of 17 km length from Kanchanpur Union to Dhulshura Union on the left bank of Padma River. Assume that floodwater entered the mainland section on the left side of the Padma River by crossing the embankment due to rise of water level that crossed danger level.
Rational for preparation of Flood Inundation Maps
Scenarios of Model Applications
The calibrated and validated model was then applied to the flood that occurred on August 3, 2007, selected through frequency analysis and the highest flood level. In the study, two scenarios viz. i) inundation due to embankment breach and ii) inundation due to overtopping of flood control embankment were considered for the application of the model according to the purpose of the study, but to understand the overall physical process of flood inundation due to embankment breach and overtopping and its response to hazards, two other scenarios were developed as i) flood inundation without any intervention and ii) flood inundation with the implementation of the full 17 km flood control embankment on the left bank of the Padma river. In this case, 10 unions cannot be flooded, except for the unions that are exposed and closest to the flood control embankment based on the existing ground level.
Model Application for Flood year 2007
In this scenario, it was assumed that the flood would uniformly cross the embankment crest of 17 kilometers in length and the flood water would enter the left bank of Harirampur. Almost all the hazards mentioned above occurred under this scenario in HR4, unions of the Harirampur located near the mighty Padma River. It was found that more flooding occurred in the flood scenarios with a return period of 100 years than in the peak flood of the year 2007 (which was a flood with a return period of more than 50 years).
Flood inundation results analysis inclusive and exclusive river area
Flood Hazards in the study area
The listed flood hazards are i) river erosion; ii) crop damage; iii) damage to fish mouths; iv) damage to fruit trees; v) communication interruptions; vi) damage to the communication infrastructure; vii) drowning of the drinking water pipe well and its platform; viii) the sewage problem; ix) damage to grazing land for cattle; x) flooding in the place of the house; xi) water-borne diseases; xii) outbreak of poultry and livestock disease; xiii) damage to property and resources; xiv) labor crises for day laborers, laborers and farmers; xv) crises of wood fuels; .. xvi) increase in poverty; xvii) damage to educational systems; xviii) remote rural schools and the education system remain closed; xix) deterioration of the living conditions of the local poor; xx) food hunger and xxi) damage to rural ecosystems.
Development of Hazard Map of Harirampur
Administrative Unit for Hazard Mapping
There were 13 (thirteen) unions in the study area in the Harirampur administrative unit map shown in Figure 7-7. Very little change was found in the flood hazard maps for scenario 3 (overtopping) and scenario 4 (breach). Harirampur is in the most flood-prone place along the mighty Padma River.
Development of Hazard Map of Harirampur upazilla for year 2007
Model Application for flood of 100 year return period
In this scenario, the model generated the flood extent and flood map of Harirampur upazilla, which consists of thirteen unions. And the remaining lands in other unions, including the unions mentioned above, had a mixed distribution, such as 9.52% land in F1 and 11.87%. The model generated the flood extent and flood map of Harirampur upazilla for all thirteen unions.
Comparison of Flood Inundation including and excluding the Padma river…. 101
Among the 13 unions, the stakeholders confirmed that 10 unions were located on the left bank of the Padma river and the other three unions (Lesarganj, Sutalari and Azimnagar) were admitted that these three unions are located in charland on the Padma river. The local administration should be involved in the monitoring of flood control and dredging activities considering it as an urgent requirement. The combined HEC-RAS 1D/2D model was successfully applied to determine the depth and extent of flooding in Harirampur for four different scenarios described earlier considering no flood control embankment, full flood control embankment (17 km), crossing and breaching the flood control embankment at two specific locations (Andharmanik and Gopinathpur).
Comparison for 100 years return period flood and Peak flood flow of 2007
Field findings on Flood Impacts and Hazards
In the hill ranges, Sutalari, Lesarganj and Azimnagar have been more or less affected by floods during the last decades. According to people's perception in both the situation either overstepping and breaking, Kanchanpur, Ramkrisnapur, Gopinathpur are in Very High Hazard Ranking (HR4), Boyra, Dulsura, Lesarganj were in High Hazard Rank (HR3), Chala, Gala, Balla, Balara, Harukandi, Sutalari and Azimnagar were between the medium hazard ranking (HR2) to low hazard ranking (HR1) under both dam overflow and dam breach scenarios. Finally, the people of these areas recommended that necessary initiatives should be taken as the highest priority is to initiate the dredging program in Ichamati river along with other rivers and Moshakhali khal along with other khals to increase the carrying capacity of the river and wetlands to drain out the flood water.
CONCLUSIONS AND RECOMMENDATIONS
Recommendations
Flood hazard maps were successfully generated from a GIS database using the output of a coupled HEC-RAS 1D/2D model. Therefore, this model has the potential to be replicated in other river floodplains with the improvised knowledge and experience gained from this study. In addition, WRM planners can use the results of this study to identify water management interventions such as river re-excavation, construction of marginal levees; construction of elevated platforms; improving the capacity of water bodies; insurance against potential flood damage and establishment of flow connectivity to generally improve drainage capacity in each water system.
Limitations of the Study
Assessment of the flood mapping of the city of Surat by coupled 1D/2D hydrodynamic modeling: a case application of the new HEC-RAS 5. Application of 2D numerical simulation for the analysis of the February 2014 flood of the Bolivian Amazon: Application of the new HEC -RAS version 5. Prediction of flash floods using estimated rainfall from global satellite maps in the northeastern region of Bangladesh.
