THE KRISHNA RIVER SYSTEM

The drainage basin

The Krishna drainage basin originates near Mahabaleswar [1438 m.] in the Western Ghats.  Geologically this is the Dharwar [Karnataka] Craton, which is a Granite-Gneiss-Greenbelt massif. The provenance consists of Deccan Traps and the Dharwar Archean rocks. From its source the river flows west northeast to east southeast across Peninsular India for about 1280 km. Before it enters the Bay of Bengal. The total drainage length is 25,344 km. [Rao, 1964] with a total annual mean runoff of 55764 million cusecs and a maximum - minimum discharge of 33810 - 3 cusecs [Rao, 1975].

About 75% of the basin is under a semi-arid [Dd] climate, receiving monsoonal rainfall. The rainfall of the delta is 910 mm with precipitation mainly in June through October.  The temperature is 22 - 27.5 - 34^oC [Hema Malini, 1979].

The alluvial valley

Common features of the Krishna River are channel bars and river islands giving it a braided appearance. 

The deltaic plain

The Krishna delta is situated between ~15^o 42’ to 16^o 30’N and 80^o 30’ to 81^o 15’E. After cutting the Eastern Ghats the river forms a deltaic plain some 95-km. wide before its four distributaries debauch into the Bay of Bengal. The first channel of the river starts near Avanigodda but the three main distributaries of the modern river splits into the Golumuttapaya, Nadimieru and Main channels.  Vast amounts of material have been added during the past 50 years at the mouths of the distributaries with the formation of river mouth bars and barrier islands with associated back island lagoons.  As the delta prograded these lagoons were infilled with finer grained sediments. From Vijayawada to the Bay the average slope is 20 cm./km.  The delta itself has an area of ~4736 sq. Km.

The Krishna Delta has large tracts of Mangrove Swamps along the coast with maximum concentration surrounding the three main distributaries.  The common species are:

Rhizophora mucronata

Avicennia marina

Exoecaria agallocha

Cherodendron inerme.

Tidal flats occupy a considerable area of the lower deltaic plain especially between the Golumuttapaya and Avanigodda distributaries [Div island], although the tidal flats may be the product of a degraded inter-distributary bay between two, now abandoned, former channels.

The marginal coastline

Bhanu Murthy  [199?] discussed the shelfal deposits off the Krishna Delta. There is a very narrow continental shelf  [~15 km.] off the present Krishna delta when compared to adjoining portions of the coastal margin.  This is presumably a result of rapid progradation.  The hypsometric integral for the Krishna Delta is 0.36 which means the offshore slope is slightly concave suggesting a slight dominance of wave power over the discharge effectiveness of the river.  This value is similar to the Nile Delta which has a hypsometric integral of 0.37. The volume of the Krishna bulge is 9.93 cubic km. [using the Wright and Coleman formulae] and there is a Skewness ratio of 1.37 which indicates a pronounced littoral drift from the northeast towards Nizampatnam Bay [Vr=5.5 cu. Km. And Vl=4.18 cu. Km: Data from Coastal Studies Institute, LSU files].

Based on the Beach Ridge studies of K. N. Rao [1980] five [5] strandlines are recognized for the modern delta and at least seven [7] distributary lobes.

TABLE  [after Rao 1980]

The receiving basin

Two canyons are recognized off the mouth of the Krishna Delta: Nagarajuna Canyon and Machili Canyon.