Study on flood risk analysis of a river basin in Sri Lanka
Dr. Kasun De Silva
Department of Civil Engineering
Faculty of Engineering
UNIVERSITY OF MORATUWA-SRI LANKA
TOC o “1-3” h z u Introduction PAGEREF _Toc513178938 h 1Problem Statement PAGEREF _Toc513178939 h 1Significance of the research PAGEREF _Toc513178940 h 2Scope of the study PAGEREF _Toc513178941 h 3Aims and Objectives PAGEREF _Toc513178942 h 3Methodology PAGEREF _Toc513178943 h 4Time schedule & work plan PAGEREF _Toc513178944 h 6Estimated cost PAGEREF _Toc513178945 h 6References PAGEREF _Toc513178946 h 6
Flooding is a natural disaster whose damage to human beings is higher than other natural disasters, such as drought and famine, and is a major concern in many regions of the world. Therefore, we must select appropriate and effective methods for flood management and control by understanding the hydraulic flow in the flood plains. The change in land use can cause changes in hydrological conditions, such as the frequency of floods, the base flow and the average annual discharge. As it is not possible to fully protect against the risk of flooding, it is necessary to live in floods and apply new policies on land use management and residential development on the river bank to reduce the impact of their destruction.
The knowledge of floods and the study of their behavior require sufficient data on the hydrological condition of the basin and the discharge of the river, and it is not possible to reach this objective in seasonal rivers and regions where there is no constant flow, so the implementation of hydrological models is useful for rainfall simulation. Runoff process and hydraulic models for the analysis of runoff flow in the river and its distribution. Traditional rain gauges provide a fine enough resolution for accurate runoff calculations and flood warnings. Therefore, flood modelling requires predictions of distributed models related to planning and insurance.
Recently, interest in flood analysis has been increased using powerful HEC-HMS and HEC-RAS tools to manage spatially distributed data and the distributed basin model. The use of these hydrological and hydrological parameters of the watershed can analyze the risk of flooding in my selected watershed in Sri Lanka.
In Sri Lanka flood is the one of major disaster which harms human beings, wild lives, public and private properties, environment etc. Due to many reasons there would be occurred flood in river basins. So, in this case, analyze of risk of flood in river basin is very important to mitigate the lot of problems.
Significance of the researchFloods are natural processes that are difficult to prevent but can be managed in ways that minimize their social and economic impacts. Floods are a threat to life and damage property. Therefore, it is very important to consider flood risks during any planning process. There are areas more vulnerable to flooding than others.
Good planning and management can help to reduce flood risks. In simple terms, flood risk analysis is an assessment of the various risks associated with residential, industrial and commercial land use. This is required in any planning application for large development sites, especially in flood-prone areas. Analysis can be used by insurance companies to reduce premiums.
The flood risk analysis examines the impacts of floods and how the proposed development project can affect the area. In addition, the analysis includes a recommendation on how to improve flood risk after development. These strategies help to reduce the region’s exposure to floods.
Information about the development of the flood risk analysis area, proposed and current development information is required to determine whether the proposal can continue or not.
The analysis ensures that future flood risks can be avoided or managed and can be addressed in a timely and inexpensive manner. The analysis is similar to an assessment that not only provides recommendations, but also includes management of flood risks.
Clearly, there are many significances of flood risk analysis. Whether the application is for a major commercial purpose, individual development purposes, industrial or even small extension of our residential land, analysis is inevitable.
Scope of the studyThe one type of floods occurs in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. While river basin flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry. In my study area is limited around analysis of river basin flooding.
Aims and Objectives
The aim of the research is to identify formal flood risk areas and other areas of significant flood risk of selected river basin.
Also there are objectives in my research.
Monitoring past and current flood levels and flooded areas.
Mapping of flooded areas and height of floods for future flood scenarios.
Long term planning and organization of land use.
Technical design and construction of structures for flood control or resistance.
Short-term monitoring, alert and response.
Study area: Kelani river basin around Kaduwela area was selected as the study area for this research. Kaduwela is the one of most populated and industrial area in Gampaha district.
Data collection: In HEC HMS modelling, it needs to find the number of catchments and area of each catchments in my study area. So Arc GIS software can use to find those parameters by using DEM (Digital Elevation Modelling) file which can collect from Survey Department of Sri Lanka. Also rainfall data can be collected from rain gauge stations which are situated in catchments of my study area and cross-section details of Kelani river can be collected from Irrigation Department of Sri Lanka.
Model calibration: Using the two different rainfall runoff models based on the physical basis to generate simulated discharges, it is compared the proposed hydrological model in this work.
The HEC-HMS model uses a graphical interface to build the semi-distributed basin model for flood simulation. For each sub-basin of the selected river basin, the hydrological model is forced by the use of a single hyetograph. Using the kriging method, the spatial distributions of precipitation are produced from hourly metrology values for the upper part of the Kelani river. Then, for each sub-basin, the series of precipitation per hour are calculated. The Soil Conservation Service (SCS-CN) curve number method is used for calculation of runoff volumes in the rainfall-runoff model.
The HEC-RAS model, when presented with the appropriate hydraulic and geometric data, calculates the profiles of the water surface. The original reference for the method of determining roughness coefficient in sections is Cowan’s method because it includes several factors that control the roughness coefficient. Next, the HEC-Geo RAS extension is used to prepare and enter geometric information about the scope of these data: flow path, left and right bank, and cross sections that, in the form of new data layers, are entered in the HEC-RAS. Then, during the import of HEC-HMS output hydrographs and the introducing roughness, convergence and divergence coefficients, the HEC-RAS model is executed and the results of the hydraulic analysis and extracting of flood zones and flood depths are performed. Finally, floodplains are determined for return periods of 10, 20 and 50 years.
This can be summarised as follows.
Time schedule & work plan
Task Cost (Rs.)
Metrological data and survey data 10000
Estimated total cost = Rs.12000
ReferencesADDIN Mendeley Bibliography CSL_BIBLIOGRAPHY Hashemyan, F., Khaleghi, M. R., & Kamyar, M. (2015). Combination of HEC-HMS and HEC-RAS models in GIS in order to Simulate Flood ( Case study?: Khoshke Rudan river in Fars province , Iran ), 4(8), 122–127.
Heimhuber, V., Hannemann, J., & Rieger, W. (2015). Flood Risk Management in Remote and Impoverished Areas—A Case Study of Onaville, Haiti, 3832–3860. https://doi.org/10.3390/w7073832
Horritt, M. S., & Bates, P. D. (2002). Evaluation of 1D and 2D numerical models for predicting river flood inundation, 268, 87–99.
Oleyiblo, J. O., & Li, Z. (2010). Application of HEC-HMS for flood forecasting in Misai and Wan ‘ an catchments in China. Water Science and Engineering, 3(1), 14–22. https://doi.org/10.3882/j.issn.1674-2370.2010.01.002
Plate, E. J. (2002). Flood risk and flood management, 267, 2–11.