Hydrodynamic modelling for stormwater management for river basing planning : a case study Welipenna river

Abstract

Storm induced flood are considered as one of the major natural hazards in Sri Lanka, with high precipitation in the monsoon and inter-monsoon seasons. Therefore, it is essential to maintain a proper stormwater management plan for vulnerable river basins. Especially when the development works carried out within the river basins in the form of changing land cover and locking of drainage paths with highway embankments have further aggravate the problem. Therefore it is essential to have a stormwater management plan within a river basin. The present study describes the work carried out in the Welipenna river basin regarding how to efectively use hydrodynamic modeling tools in stormwater management. Required data were illected through systematic field surveys, agency visits and through literature surveys. A comprehensive hydraulic analysis was carried out to estimate the design discharge for both existing nd expected future conditions with the construction of Southern expressway through the Welipenna ver basin. For the assessment of stormwater management options, a hydrodynamic model was developed with calibration error of 33% and verification error of 36% for watershed, and it was used evaluate the existing stormwater management options and to predict the effects of future development scenarios. It has been found that incorporating a highway embankment with the proposed bridge will result in 12mm water level rise at the proposed bridge location.