Environmental impact due to changes in geometric characteristics of the Kapataksha river

Abstract

The Kapataksha river is one of the main arteries of the water resource system located in the southwest region of Bangladesh. Tnthe past, continued flow of fresh water from the Ganges tluough Mathabhanga river kept the saline water away from the upstream of the river and pushed it to the downstream and flU5hedthe incoming sediments into the Bay of Bengal. But, after being disconnected from the Ganges, the Kapataksha river has been subjected (0 tidal domination, associated with increasing sedimentation by tidal pwnping process. Gradual sedimentation causes the reduction of the cross-section of the river and loss of the COIWeyaOCe capacity of the river. Change of these geometric characteristics of the river results in water logging at the adjacent area of the river and thereby other adverse impact on environmental components. Various types of direct and indirect environmental impacts are shown through network. The main activities that were performed in this study are simplification, building up a conceptual model to show how the impacts are taking place, impact analysis and impact classification. During the period of 1994 and 2001, the cross-sectional area of the river decreased about 86% to 95% and the convoyance decreased 96% to 99% over the study area. The width and average depth decreascd about 15% to 58% and 84% to 88%, respectively over the study arca from 1994 to 2001. Deterioration of drainage capacity of the river has rcsultcd in wide spread drainage congestion, which further causes water logging to its adjoining area About 55% to 77% of the total areas of the villages over the study area were waterlogged in 2000. Due to prolonged water logging, various types of environmental degradation are taking place over the study area. Due to water logging problem, diversity offish specics over the study area has been reduced. In addition with the reduction of fish species, after water logging, availability of some fish species (mostly floodplain & beel fisheries) are increasing whereas, availability of some fish species (reverine fish species) are dccreasing over the study area. Due to stagnancy of water, a good portion of the river stretch over the study area is covered by watcr hyacinth. about 60% to 80% ponds of the study area wero affected by various means after waterlogging condition has set in and they could not be used this water for household purposes. The wetlands and waler bodies of the study area are also becoming degraded due to the drainagc congestion and waterlogging problem. In addition with these environmental impacts, changes of the geometry