Assessment of river encroachment and land-use patterns in Dhaka city and its peripheral rivers using GIS techniques

After 70’s decade Dhaka city started as a densely populated mega city with high land scarcity for its ever growing population. Some opportunistic people take this advantage and make illegal constructions over the bank of river. These illegal constructions are increasing day by day and now turn into a sore called river encroachment. As a result, Dhaka city has been suffering from many socio-environmental problems including flooding, water logging and other related problems. The present study was conducted to assess the areas of illegal intrusion of navigable rivers and its canals over the period of 2001 to 2014, and unsupervised image classification was performed over the area of 200 meters by using the Arc GIS 10.1 and Google earth software, which is focused on different criteria. Rapid river encroachment has been observed in many places of Dhaka city and its peripheral river's corridor. The order of encroached rivers was: Turag (Abdullahpur > Gabtoli), 120.7943 acres > Buriganga (Kamrangirchar > Bosila), 97.1697 acres > Sitallakhya (Katchpur > Narayangang), 23.8315 acres > Balu (Demra > Nandipara), 8.8424 acres within an area of 5.7581 miles, 7.4120 miles, 3.5679 miles and 4.2032 miles respectively. By ISO unsupervised image classification it was observed that the area was mostly encroached by human settlement and infrastructure. It was alarming that the infrastructure level in the study area of 2014 was several times higher when it is compared to the infrastructure level of 2001. The greatest percentages of infrastructures were built on the bank of Buriganga River in Bosila (56.10%) and the lowest percentages of infrastructures were built on the Balu River in Nandipara (1.77%). Not only these rivers, but also the Turag, and Sitallakhya River are also narrowing day by day. Due to the rising of illegal infrastructures and human settlement, the water bodies, barren lands, croplands and vegetation decreased significantly in the encroached areas.