Human influence on increasing flood hazard in Nilwala River in Akuressa area

Abstract

Flood is a major natural hazard in Sri Lanka. Even though flooding is a natural phenomenon, anthropogenic factors have intensified the hazard in recent time. Objective of this study is to identify and analyze anthropogenic factors that give rise to flood hazard. Akuressa area is some times vulnerable to over flow due to over bank flow of Niiwala river during rainy seasons was selected for this study. Over flow usually drains back within two or three days and the process could not be considered as major flood. The area consists of major tributaries and six sub catchments. For the study, 46 Grama Niladari divisions that covers 149 km2 were selected. The population of the area is 49752 consisting of 12170 families. A questionnaire was submitted to cover 35% of the families. In addition to the primary data, information from secondary sources such as reports of the RSO, Grama Niladari Office, was gathered. The results show that the flood preventive program which carried out since 1986 has adversely affected to intensify the flood hazard in the area. The other adverse affects are the changing land use pattern and less attention on agriculture by farmers of the area, the indirect effects are the crocodile intrusion in to villages and salinity intrusion in to wells. Forest clearing and construction activities and improper land use pattern, in the upper catchment, sand mining, structures constructed along the river banks have affected to intensify flood hazard. The removal of sand from river at the Akuressa area amounts to 2000m2 and it leads to bank erosion and widening of the river channel. Enforcement of the existing laws against sand mining, and organizing people’s awareness programmes will help to manage the situation. In addition, proper utilization of land under suitable methods and protection of forest reserves may help to control the flood hazard of the area.