STUDY OF EFFECTS OF RIVER TRAINING WORKS ON RIVERINE GEOMORPHOLOGY AT SOME SELECTED PLACES ON RIVER BRAHMAPUTRA

Abstract

Rivers in its flood plains carry on its natural activities in the form of changing the4riverine geomorphological features by way of erosional as well as aggradational activities, which, though generally useful to man sometimes pose many problems like floods etc. Man has been adopting various river training works not only to find solution to these problems but alsoio utilise the river waters according to his requirements. As such, the river training measures adopted for any river are experimental in nature, which necessitate evaluation of the performance of these structures. Since they influence the behaviour of the river which results in changes in riverine geomorphology, their performance can be evaluated by considering their effects on the riveribe geomorphology. In the present study, four such sites along the river Brahmaputra have been adopted where some specific and major river training measures have been taken up. These. are Palasbari near Guwahati. le.liabhomora bridge near To2pur, Kokilamukh near JorhAt and at Dibrugarh. LANDSAT MSS and TM data products of various bands as well as false colour composites, in combination with toposheets of the area have been used as source of information ff)r-the part of the study involving use of remote sensing techniques. Base maps are prepared from the toposheets which were used as reference for informations of later dates. To correlate the findings obtained from remote sensing data with variation of bard levels during floods, ground hydrological data of flood discharger, sediment load etc. have been used to run a mathematitcal rivotr model. The study has yielded information about Ci) changes in banklines at the sites, Cii) migration of deep flow channels in the river width and Ciii) changes in the riverine morphology. The changes in the morphological features have also been correlated by evaluating the parameters "Braiding Index" and "Arc-Chord ratio". It has been concluded that the adopted measures have been generally successful at the three sites of Palasbari, Koliabhomora bridge and Kokilamukh in fulfilling the objectives of their construction though the spur spacing at a particular reach at Palasbari seem to be inadequate. But at Dibrugarh, the erosional activity of the river seem to have been shifted to the upstream of the dibrugarh town. An indepth study of this site on the upstream was not possible due to lack of further data for that region. Finally, it has emerged from the study that satellite imageries can be advantageously used not only to monitor morphological changes of a river in general but also for an appraisal of the efficacy of costly river training works. Further, the use of a mathematical model simulating bed level changes in combination with the satellite data appears to be promising for better understanding of the river behaviour.