Flood hazard assessment and management of Left Bank Outfall Drain (LBOD) for flood prevention in Badin district, Sindh, Pakistan | |
| Author | Memon, Shakir Habib |
| Call Number | AIT Thesis no.WM-19-44 |
| Subject(s) | Flood prediction--Pakistan--Badin district Flood control--Pakistan--Badin district |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Flood disasters consistently have negative and multi-faceted effects on the country's overall development affecting significant aspects such as agriculture, infrastructure, environment and health. Since 1947, fifteen major floods have caused significant human and economic damages in Pakistan. The big floods in Sindh have been in 2003, 2006, 2007, 2010, 2011 and 2012 over the past decade during which the most affected area was the catchment of Left Bank Outfall Badin (LBOD). The LBOD, was originally designed to carry 130.24 m3/sec saline effluent and storm water from four districts namely, Shaheed Benazir Abad, Sanghar, Mirpurkhas and Badin to dispose of it into the sea. However, during the historical rainfalls of 2003, 2006 and particularly 2011, surface runoff generated about two times more than the design discharge of LBOD. As a single source for runoff drainage of the area to the sea, the LBOD due to its insufficient ability to carry water, could not sustain the magnitude of rainfall-runoff, resulting in breaching and overtopping at several places in the system. This condition causes serious flooding, particularly of the areas in lower district Badin and coastal zone. In this study, the flood hazards to the lower district Badin caused by the inadequate and inefficient performance of LBOD, is being assessed. This study mainly focusses on the quantification of the floodwater carrying capability of Spinal Drain, the key constituent of LBOD, using the integration of Hydrologic Engineering Center’s-Hydrologic Modeling System (HEC-HMS) and River Analysis System (HEC-RAS) with Geographic Information Systems (GIS). Furthermore, the development of suitable mitigation measures by assessing the different scenarios and selection of the optimal flood mitigation measures along the reach of LBOD is also carried out. The Left Bank Outfall Drain River reach from 261.98 Km to 50.88 Km was selected for the hydrological and hydraulic study. The hydrological study was carried out for assessment of rainfall-runoff generation of the extreme rainfall period 2011 by applying the Hydrological Model System (HEC-HMS). Frequency Period Frequency Curve was generated with a frequency of two, four and seven days for a return period of 2, 5, 10, 30, 50 and 100 years based on a normal rainfall cycle from 1988 to 2017 in four weather stations, namely Shaheed Benazirabad, Hyderabad, Chhor and Badin. Flood Hydrograph was generated for the 50 years return period which generated a runoff of 313 m3/sec. Accuracy of HEC-HMS model was determined by performing model calibration and validation at chainage km 50.88 (Outlet) by using two sets of daily precipitation and observed discharges data for the year 2011-12 and 2015 respectively. The results of the HEC-HMS model were then compared to the data observed. Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) with 30meter resolution Digital Elevation Model (DEM) was used and Triangulated Irregular Network (TIN) was created using ArcGIS, HEC-GeoRAS tool along with field survey. HECGeoRAS also arranged necessary data sets such as stream centerline, banks, flow paths, and cross-sections, thus generating import files and importing them into HEC-RAS. The downstream boundary situation has been defined in HEC-RAS. However, for a return cycle of fifty years flood discharge was also submitted and the tests were tested for steady flow. Calibration of HEC-RAS model was done at gauging station Km 50.88 (Outlet) by using the simulated peak discharges of HEC-HMS model for the period August-October 2011 and using September to October 2012 for Validation. Multiple maximum discharge scenarios and flood mitigation steps were then simulated with the HEC-RAS system. Flood extent maps were prepared for peak discharges to compare the flood impacts before and after mitigation measures. The results show that both the mitigation measures namely rehabilitation and redesign of LBOD and diversion of excess flood water during the rainy season are suitable. |
| Year | 2019 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Shrestha, Sangam |
| Examination Committee(s) | Shanmugam, Mohana Sundaram;Roa, Arturo Gementiza |
| Scholarship Donor(s) | Irrigation Department, Government of Sindh, Pakistan |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 2019 |