Flood is a natural disaster which is able to damage humanbeings, animals and other properties than other natural disasters such aslandslides, droughts, wind storms etc. So, the analysis of risk of flood isvery important to get many decisions as to mitigate above problems. Suitablemodelling approach can use as a solution of this risks(Heimhuber, Hannemann, & Rieger, 2015). Changes in climaticvariables, especially temperature and humidity, are probably the main driversof the change in precipitation and extreme hydrological risk.
Climate changecan affect the intensity, frequency, duration and scope of risks and thevulnerability of communities to disasters.(Ntajal, Lamptey, Mahamadou, & Nyarko, 2017).There is the flood which canoccur in river and surrounding of the river basins when the flowrate exceedsthe capacity of the river, particularly at bends or meanders on the path of theriver. Occurrence of flood in Sri Lanka is mainly due to excessive of rainfallduring monsoon period(Central & Consultancy, 2014) Therefore, this study is based on theavailable data of the study area.Recently, usage of HEC-HMS and HEC-RAS software has beenincreased for flood analysis. Those can use to manage spatially distributeddata and the distributed basin model (Hashemyan, Khaleghi, & Kamyar, 2015). The use of thesehydrological and hydrological parameters of the river and river basin cananalyse the risk of flooding in selected river basin in Sri Lanka.
The HEC model is used to simulate the surface runoff ofthe catchment due to precipitation by interconnecting hydrologic and hydrauliccomponents. It is primarily appropriate to flood simulations. In HEC-HMS, theriver basin model includes different functions of the precipitation-runoffprocess of the basin. An element of this application is depicted a surfacerunoff.
Each of the elements is assigned a variable in HEC-HMS which defines theattribute of the element and mathematical relationship of the actual processesand also the result of the modelling process is the computation of stream flowhydrographs at the catchment outlet(Oleyiblo & Li, 2010). 1. Paper Format According to past studies, the simulation of runoff events withhigh hydraulic risk has posed many challenges for policymakers, environmentalistsand engineers around the world. Using 1-D modelling to predict flood risk fromdifferent return period events or multiple land use and climate changescenarios are common(Horritt & Bates, 2002).It is noticeable that the use of the Digital Elevation Model (DEM) inthe creation of flood models have reached an important role of the topographicand hydrological analysis of basin data, since it represents a series ofelevations in the basin at regularly spaced intervals. This removes theassumption that the basin or area is a flat surface without contours(Heimhuber et al., 2015).
In case study on flood risk andflood prediction using GIS and the model of hydrodynamic presented thepossibility of using DEM controlled in a GIS and translated into MIKE21. In thestudy, different scenarios were checked out, and results were translated intothe GIS environment for flood visualization and analysis during a 100-yearflood return period(Ntajal et al., 2017). However, Jagadish Prasad Patraa, Rakesh Kumaraand Pankaj Manib pointed out that there was no real way to calibrate thesimulations from the modelling output, as flood and stage data for the floodswere rarely recorded and compared between the MIKE21 and MIKE1 results, thefirst being an improvement of the last one(Prasad, Kumar, & Mani, 2016).In a researchconducted by Sarawut Jamrussri and Yuji Toda on the hydraulic models and GISfor the study of the Mae Klong River in Thailand. Flow frequency analysis wasused in the creation of a flood risk map. The study also showed that thesimulation results were correctly presented in GIS and DTM format, usingcontour and height data from the river point. Sarawut Jamrussri and Yuji Toda concludetheir study by suggesting that more studies be done in large basins, dividingthem into sub-basins and introducing the network link to integrate them to havea general view of the basin.
Runoff from floodplains, fluvial canals andartificial structures are important factors in the study of the prediction ofrunoff flow patterns, the researchers added. rainwater in upstream areas andnot stable(Jamrussri& Toda, 2017).HMS uses a project name as the identifier for a hydrological model. AHMS project must have the following components before it can be executed: abasin model, a climate model and control specifications.
The characteristics ofthe basin model and basin were created as a lower map file imported into theHMS from the data derived from HEC-HMS for model simulation. The observedrainfall and discharge data were used to create the climate model using theUser Indicator Weight Method (UIWM), and then the control specificationtemplate was created. The control specifications determine the time model forthe simulation; its characteristics are: a start date and time, a date and timeof completion, and a calculation time step. To operate the system, the basinmodel, the climate model and the control specifications were combined. Thehistorical data observed from six precipitation stations representing eachsub-basin and one measuring station in the Misai basin and four precipitationstations representing each sub-basin and one measuring station in the Wan’anbasin were used to calibrate the model. check.
One-time step per hour was usedfor the simulation according to the time interval of the observed data.