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Abstract

IESL

Development of flood damage estimation functions based on

flood simulation scenarios and a GIS platform- A case study at Thawalama, Galle

Kulathunga S.P.S.P.a, Rajapaksha R.M.K.C .b, Ransara N.D.P.c, Silva G.H.A.C.d

a Undergraduate Student, Department of Civil and Environmental Engineering, Faculty ofEngineering.

Kulathunga.eng@gmail.com

b Undergraduate Student, Department of Civil and Environmental Engineering, Faculty ofEngineering.

chinthana138@gmail.com

cHydraulic Modeller, Sri Lanka Land Reclamation & Development Corporationndpransara@yahoo.com

dSenior Lecturer, Department of Civil and Environmental Engineering, Faculty of Engineering.amila@cee.ruh.ac.lk

Flood damage estimation and provide compensation for victims are utmost important post

flood procedures. Generally the flood damage is estimated through conducting post-flood

field surveys. This consumes more time and the collected information may not be reliable and

fair as often questioned by many flood-victims. Eventhough Sri Lanka is experiencing

frequent flood catastrophies, very limited reseach has been done in relation to flood damage

estimation. Hence the flood damage compensation is mostly made through adhoc methods. A

GIS-based flood damage estimation model is proposedas a solution to these ever expandingproblems which has been widely used in many flood affected regions across the globe. Such a

system would generate swift damage estimation and well organized outputs. Main objective

of this study is to prepare GIS and Hydrological/Hydrodynamic based flood damage

estimation model for Thawalama area that often confronts with flash floods due to overspill

of the Gin River. Developed methodology would be a good resource for the relevant

authorities to estimate actual flood damage for future flood scenarios. Catastrophic floodwhich in May 2003 has been recognized as the most desperate event during the last century

and which has been considered for the development of the flood-damage estimation model.

Preparation of flood-damage estimation demands, many parameters such as property

distribution, inundated area and depth, flow velocity, stage-damage functions etc. In thisstudy, an attempt has been made to estimate some of these parameters. Available 2003 flood

mailto:Kulathunga.eng@gmail.commailto:Kulathunga.eng@gmail.commailto:chinthana138@gmail.commailto:chinthana138@gmail.commailto:ndpransara@yahoo.commailto:ndpransara@yahoo.commailto:ndpransara@yahoo.commailto:chinthana138@gmail.commailto:Kulathunga.eng@gmail.com

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extent which was generated using Hydrological Engineering Centre (HEC), a public domain

hydrological/hydrodynamic model has been used and the flood depths were extracted by

overlaying the topographic layer with the flood extent. Subsequently, an onsite questionnaire

survey was conducted to gather damage related information. Flood-compensation data those

are issued from Thawalama Divisional Secretariat office were compared with the flood

damage parameters. Finally depth-damage functions for the flood affected Thawalama area

were developed. Validated model can generate reliable flood damage estimation includingpercentage property damage at particular house location for particular inundation height.

Keywords:Flood damage estimation, GIS, HEC, Thawalama, depth-damage functions