Assessment of Hydro Morphology of lower Gumti River

Abstract

The present study has been conducted to investigate the hydro-morphological changes of Gumti River system lying within Bangladesh. The Gumti River is meandering one, carrying flashy flood from the hills and lakes. The Gumti River has been selected for the present study because the river is extremely unstable. The wide variation of river flow makes it difficult to choose a representative discharge in studying the river characteristics. The Gumti River here used to represent the lower river reach from Daudkandi bazar to Pastubi covering a reach length of about 125 km. To carry out the study cross sectional data, discharge and water level data were collected from BWDB for the last 30 years from 1977 to 2007. Analysis of cross sectional data revealed that cross sectional area and width varied very widely and randomly in different section. The average width of the Gumti was found to vary from 281 m to 1562 m for different years and different sections whereas maximum was found during the year 2004-2007. The average cross sectional area of the Gumti was found to be 1312m2 though it changes at different years and also at different sections. A relationship was established between cross-sectional area and width of the river and it shows that cross-sectional area increases with the increase of width. Relationship was also developed between width and hydraulic radius of the river and it was observed that hydraulic radius deceases with the increase of width. It is found from analysis that the results obtained from RSP (1996) approach is much better than the other approaches like Julien-Wargadalam (1995), Julien-Wargadalam-Lee (2006), Lee-Julien (2006), Singh et. al.(2003) and Lacey’s regime depth (1929) for prediction of channel width. The maximum water level for the Gumti at Comilla shows a rising trend. The average and minimum water level of the Gumti at Comilla has a slow trend of falling. It was found that the maximum discharge of the Gumti is at Comilla town. Non-dimensional relationship was established between shape factor, Froude number and discharge parameter of Gumti River and it was found that the width-depth ratio increased with the increase of discharge parameters and Froude number decreases with the increases of width depth ratio.