ASSESSMENT OF CHANGING PATTERN OF THE RIVER COURSE AND ITS IMPACT ON ADJACENT RIPARIAN AREAS HIGHLIGHTING THE IMPORTANCE OF MULTI- TEMPORAL REMOTELY SENSED DATA

摘要

Change of river courses with time is attributed to natural and manmade factors such as bank erosion and developments along the river banks. These changes can create significant issues in the riparian zones due to loss of land, changes in biodiversity, impacts on the constructions located on the river banks, etc.. Also it could lead to the risk of river pollution. Assessment of the changes to the river course will also facilitate in identifying the exploitation of river bank over time and the possible future activities that can significantly affect the river water quality.Mahaweli is a multi purpose river which provides diverse benefits to different communities. The river segment which flows from downstream of Gampola to Kandy in the Central province is the major supplier of domestic and industrial water requirements to the surrounding including Kandy city. The river bank of this reach is occupied by private and publicly owned buildings and lands. The university of Peradeniya and Royal Botanical Gardens of Peradeniya are also located in the banks of Mahaweli. Hence, it is interesting to assess the changes in the river course of this segment over time to identify the changes that have occurred to the adjacent riparian zone. This study focused on assessment of the changes to the course of river Mahaweli from Gampola to Kandy using remotely sensed data of 1985 & 2003 and maps. River segment and the riparian land use of 100 m buffer along the river banks were identified using aerial photographs of 1985 and IKONOS satellite image of 2003. Comparisons were made to assess the changes during this period. It was found that no large scale shifting of river has occurred during the studied period except small changes that were observed in few locations. Islet formation is one of the identified features. This can be due to low flow conditions and accumulation of debries, sediments and sand as a result of low discharge and low flow velocity downstream the Kotmale impoundment. Land use in adjacent riparian areas has changed with time. Although the ecological impacts were not studied, conversion from home gardens to settlement areas can increase addition of waste material to the river thus causing river pollution. It is recommended to improve the analysis by incorporating assessment of riverine ecosystems and also by including data long before the construction of Kotmale reservoir.