Use of a hydrodynamic model to forecast floods of Kalu River in Sri Lanka


  • This paper was presented at the 4th International Symposium on Flood Defence, Toronto, Canada (6–8 May 2008), and will be published in a special issue of Journal of Flood Risk Management entitled ‘Integrated Flood (Risk) Management’ edited by Professor Slobodan P. Simonovic, University of Western Ontario.

K.D.W. Nandalal, Department of Civil Engineering, University of Peradeniya, Peradeniya KY 20400, Sri Lanka


Kalu River, the third longest river in Sri Lanka, discharges the largest amount of water into the ocean while causing floods along its route from the most upstream major town, Ratnapura, to the most downstream town, Kalutara. It has become necessary to either totally control these floods or instruct people to adjust their activities to the rhythm of the river and prepared them to live with floods with minimum damages. This paper presents a model developed to determine water levels along the river from Ratnapura to 79 km downstream Kalutara using the HEC-RAS hydrodynamic model. The model was calibrated and verified for both steady and unsteady flow conditions. It provides water levels and inundation areas along the river for different discharges. A set of tables, which could be used by people with less technical knowledge, were prepared to predict flood levels at downstream locations based on observed water levels at upstream locations.