Title: The deltas of Peninsular India.
Author: George F. Hart. Year: 1999
THE DELTAS OF PENINSULAR INDIA
FINAL REPORT TO THE SMITHSONIAN INSTITUTION
PART ONE: Field studies and data collection
Peninsular India is drained by five major river systems: Mahanadi, Godavari, Krishna, Penner and Cauvery.
The geology and climate of Peninsular India are two overriding physical controls effecting the rivers of the region. By effecting the soils and vegetation the geology and climate determine the sedimentological characteristics and the whole process of erosion, transportation and deposition within each drainage basin.
The sparse vegetation of the highlands contrasts with the moderately luxuriant vegetation of the river valleys.
The climate is dominated by the monsoonal rains. The northeast monsoon provides the greater portion of the annual precipitation. The far northwestern part of the drainage basin has a Perhumid climate which passes eastwards into humid, moist subhumid, dry subhumid and semiarid zones.
The geology of the drainage basin is predominantly formed from Precambrian rocks, principally the Dharwars, Peninsular granitic Gneiss, Charnockites and the Closepet Granite [Krishnan, 1968]. The Dhawar metamorphics comprising phyllites, slates, schists with chlorite, biotite, garnet, staurolite, kyanite, silllimanite and hornblende. Accompanying these are greenstones and quartzite [Rama Rao, 1940; Srinivasan & Sreenivas, 1977; Krishnan, 1968; Naqvi et al., 1974]. The Closepet Granite of the upper reaches of the drainage basin is a pink granite consisting mainly of quartz, plagioclase, microcline, perthite, and subordinate hornblende, biotite, rutile, apatite, zircon and occasional fluorite [Radhakrishna, 1956; Chatterji, 1974].Over the main part of the basin the Peninsular granites and gneisses comprise biotite granitic gneiss, hornblende granitic gneiss adamellite, granodiorite, diorite, and pegmatite [Chatterji, 1974; Pichamuthu, 1978]. The Charnockites are confined to the Nilgiri Range in the central part of the drainage basin. The are represented by gabbros, olivine norites, pyroxene - hypersthene granulites [Pichamuthu, 1953; Viswanathiah & Tareon, 1970; Chatterji, 1974]. Cretaceous sediments crop out in the coastal region and consists of conglomeratic sandstone, coralline limestone and shale [Rao & Sundaraw, 1978].
To the south, in the region of the Penner River the climate is predominantly semi-arid with summer temperatures of 25 - 46oC and winter temperatures of 18 - 28oC. In the head region of the basin the climate is arid. The northeast monsoon [October through January] provides a little precipitation but the predominant rain falls when the southwest monsoon [June through September] occur. Post monsoonal cyclonic activity in the Bay of Bengal during September and October produces an increased rainfall in the coastal region. The mean annual rainfall within the drainage basin various from about 550 mm around Anantapur area to 900 mm around Nellore.
The geology of the drainage basin is predominantly formed from Archean rocks, principally granitic intrustives into metamorphic schists. Pichamuthu, 1978 notes that the Archeans in this region comprise biotite and hornblende granite-gneisses, granodiorite, diorite, and pegmatite. Of secondary importance are the Dhawar metamorphics comprising phyllites, slates, schists with chlorite, biotite, garnet, staurolite, kyanite, silllimanite and hornblende. Accompanying these are greenstones and quartzite [Srinivasan & Sreenivas, 1977; Krishnan, 1982]. In the central part of the basin the dominant rocks belong to the Cuddapah and Kurnool Groups consisting of conglomerates, sandstones, shales, dolomites, limestones and cherts. These are intruded by doloritic and basaltic igneous materials in many places. In the coastal regions the major sediments are laterites and recent alluvium.
The climate of the drainage basin is dominated by the southwest monsoon which provides most of the precipitation for the whole region. High water in the river is August - November and low water is April - May [at Vijayawada]. Climatic types range from per-humid through dry sub-humid in the west through semi-arid in the central and eastern parts of the basin [Subramaniam et al 1882a, b]. Only in the very south central part of the basin truly arid.
The geology of the drainage basin is dominated in the northwest by the Deccan Traps, in the central part by unclassified crystallines and in the east by the Cuddapah Group. The Dharwars [southwest central] and the Vindhian east central] form a significant part of the outcrops within the unclassified crystallines. The deltaic region itself is formed predominantly of Pleistocene to Recent material.
NASA image NRSA. India
The climate of the Godavari drainage basin has high humidity throughout the year effected by the northeast and southwest monsoons. The delta region is semi-arid with an average annual rainfall of 1042 mm and a maximum temperature in May of 37.3oC. The coldest month is January with a mean daily maximum temperature of 26.9oC and a mean daily minimum temperature of 19.2oC.
The upper reaches of the Godavari drainage basin is occupied by the Deccan Traps containing the minerals hypersthene, augite, diopside, enstatite, magnetite, epidote, biotite, zircon, rutile, apatite and chlorite [K. Srinivasa Rao, 1993]. The middle part of the basin is principally Archean granites and Dharwars composed of phyllites, quartzites, amphiboles and granites. The downstream part of the middle basin is occupied mainly by the Cuddapah and Vindhyan metasediments and and rocks of the Gondwana Group. The Cuddapahs and Vindhyan are quartzites, sandstones, shales, limestones and conglomerates. The Gondwanas are principally detritals with some thick coal seams. The eastern Ghats dominate the lower part of the drainage basin and are formed mainly from the Khondalites which include quartz- feldspar- garnet- silllimanite gneisses, quartzite, calc-granulites and charnockites [Dutt, 1986]. In the coastal region the Tertiary Rajahmundry sandstones crop out.
NASA image NRSA, India
To the north, in the region of the Mahanadi River the climate is predominantly sub-tropical with summer temperatures of around 29oC and winter temperatures of 21oC. The bulk of the precipitation is in the July to September period [800 to over 1200 mm] with January to February precipitation of less than 50 mm.
THE PRINCIPLE PARTICIPANTS