Scenario analysis to identify a sustainable pond rehabilitation approach for flood mitigation: A case study in Jaffna, Sri Lanka.

Abstract

Jaffna peninsula which includes a land mass of 1026 km2 with 9.3% of inland water bodies suffers from severe flooding during the second inter-monsoon (October ~ December) where it receives about 68% of its total annual rainfall. Its ancient pond system used to drain the accumulated runoff to the lagoon without much inundation. However, due to the dilapidating condition of the pond system, now the flood spreads out into the highly populated areas causing inconvenience to the public. This study seeks to identify the most sustainable pond rehabilitation approach for flood mitigation considering HECm ResSim model results of the Paalkulam pond cascade in Jaffna Municipal Council. The analysis results show that in upstream ponds, bund level raising and pond bed dredging reduce the total inundation area by 27.5% and 19.7%, respectively. However, in downstream ponds, the results do not tally with the upstream ponds, where bund level raising reduces the total inundation area by only 21.4% while the pond bed dredging reduces the total inundation area by 34.3%. Therefore, results conclude that when the pond system is rehabilitated, the actual intervention at an individual pond should be based on its relative location in the cascade system in order to achieve sustainable results with positive impact on flood risk mitigation.