They have expressed the view that the river sediments are mainly derived from
the rocks of the Western Ghats through the west flowing rivers in Kerala. Though there
are 41 west flowing rivers in Kerala, no detailed study has been carried out to decipher
the origin of the sediments. In this paper, we attempt to assess the influence of
river Pamba on the distribution of sediments and the mode of transport along the course
of the river. This information will be useful to understand the hydrological
and sedimentological behavioral characteristics of the river basin and in turn help
in reservoir sedimentation studies.
Along the central Kerala coast Pamba Ar (Figure 1) is one of the major rivers
flowing towards the west, joining the Lakshadweep Sea at Alleppey through Vembanad
Lake. Pamba river basin covers an area of 2,235 sq km with a length of 176 km. It
debauches its vast sediment load into Vembanad
Lake, a comparatively long distance through lowland terrain. The Pamba river is
formed by the confluence of several streams having their origin in the Pollachi malai,
Naga malai and Sundara malai, in the Peermade plateau at an altitude of about 1,650 m
above the Mean Sea Level (MSL). The larger of these streams has two reservoirs, one
at Kakki and the other at Pamba.
Geologically, Kerala coast comprises tertiary Cenozoic sediments which
are underlain by Archaean crystalline rocks consisting of khondalities,
leptynites, charnockites and mica-hornblende gneisses, as there are no rocks of
other geological formations along the west coast.
Sediment samples were collected from the middle of the river channel from
the selected locations (Figure 1) with varying intervals. The bottom sediment
was collected by using Van-Veen grab.
The river sand samples were washed, dried and subjected to both sieve
and pipette analysis (Krumbein and Pettijohn, 1938). For pipette analysis
known quantities of dried sediments were dispersed overnight in a solution
of sodium hexametaphosphate. |
