Tree Selection for the Enrichment of Lower Areas of Kalu Ganga River Basin

Presentation Abstract

Chathuri Liyanage

Department of Forestry and Environmental Science

University of Sri Jayewardenepura, Sri Lanka

Kalu Ganga which is also known as the “Black River” is the second largest river in Sri Lanka. It originates from the central hills of mountain Sri Pada and falls to the sea in Kalutara after travelling for 129 km. Kalu Ganga river basin in Sri Lanka has an extent of 2,766 km². Its river basin is situated entirely in the wet zone of Sri Lanka. The average annual rainfall in this area is 4,000 mm and it varies from 2,800 mm which is for the lower reaches to about 5,300 mm for the upper reaches of the basin. The average slope of the basin is steep in the upper catchment from about 30-70 degrees and it becomes gentle to very gentle from the middle catchment(0-30 degrees) to the lower catchment(0-10 degrees). As a result, runoff abruptly changes from very fast in the upper catchment to very slow in the lower catchment corresponding to the slope angle. Due to the change of slope angle, bottleneck at Ellagawa and due to illegal sand mining activities, the lower basin area suffers from floods. It also causes for the erosion at river banks. Therefore the river basin should be enriched with suitable native trees like Hora (Dipterocarpus zeylanicus), Walla-Patta (Gyrinops walla), Gon-kanduru (Cerbera odollam), Asoka (Saraca asoca) and Goda-Midella (Barringtonia racemosa (L.) Spreng) which are the native trees growing in wet-lowland forests. Dry zone trees such as Kumbuk (Terminalia arjuna) and Mee (Madhuca longifolia) can also be used as they grow successfully near waterways. Tree selection for the enrichment should be done considering many factors such as tree characteristics (height, growth rate etc.), use (medicinal and aesthetic value etc.). Developing a system for the regular monitoring of the river basin and to take remedial actions to correct negative trends are recommended to ensure the conservation of riverine areas. Further, illegal sand mining activities should be controlled by imposing laws and higher penalties.