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Interfan area >> Geomorphology >> Regional Geomorphology
Relief/ Landforms
The interfan area between the Gandak and Kosi megafans is monotonously flat but with a south easterly slope, as inferred from the general direction of the majority of the rivers. The channels of the major interfan rivers namely, the Burhi Gandak, Baghmati, and the Kamla-Balan, and their old courses define, in a general way, the location of their floodplains. In case of smaller channels the floodplains are less extensive and restricted to narrow patches alongside the channel, generally limited by the adjoining river bank or by the natural levees. Further, the floodplains of the major rivers are dissected by numerous minor channels which are often interconnected. These minor channels play an important role in shaping the interfan area as they rework and redistribute the sediments deposited by the major rivers. In the monsoon period, all the major and minor channels are filled with water and overbank flooding occurs frequently.
Here you find general aspects about Fluvial Landforms Baghmati River
A Digital Elevation Model (DEM) for parts of the interfann area constituting the Baghmati basin shows the general topography of the area and depicts the changes in basin slope from upstream to downstream. In general, the upstream basin area shows a regional slope in SW direction with relatively steep gradient, whereas downstream basin area is characterized by SE slope. The overlaying of the Baghmati stream on the DEM indicates the relationship between slope and the river flow direction. Barring a few exceptions, the channel follows the basin topography.
Satellite image of parts of the interfan area show the anabranching Baghmati river. Anabranching is initiated downstream of the confluence of Lalbakeya and Baghmati rivers. The right anabranch flows southward and the left anabranch initially flows southeastward for 15 km before turning south to close the anabranching reach. Sequential reconstruction of channel configuration since 1924, based on maps and satellite images, shows that the right anabranch has been unstable with several avulsions recorded. At present, the right anabranch joins the Burhi Gandak River to the west instead of rejoining the anabranching system. In addition to the major anabranches, there are numerous smaller anabranches that are connected to the major drainage network for short periods. Major changes in river course have been documented (Sinha, 1996; Jain, 2000), resulting in temporarily abandoned channel reaches, some many kilometers long. Most abandoned channels are partially filled from rainfall during the monsoon season. Crevasse splays, levees, large point bars, and floodplain lakes (tals) can be identified in the field and are visible on satellite images.
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