CHANGES IN THE MAGNITUDE AND FREQUENCY OF LATE HOLOCENE MONSOON FLOODS ON THE NARMADA RIVER, CENTRAL INDIA

Citation
Ll. Ely et al., CHANGES IN THE MAGNITUDE AND FREQUENCY OF LATE HOLOCENE MONSOON FLOODS ON THE NARMADA RIVER, CENTRAL INDIA, Geological Society of America bulletin, 108(9), 1996, pp. 1134-1148
Citations number
63
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
9
Year of publication
1996
Pages
1134 - 1148
Database
ISI
SICI code
0016-7606(1996)108:9<1134:CITMAF>2.0.ZU;2-0
Abstract
During the past three decades, the Narmada River of monsoon-dominated central India has undergone extraordinarily large floods that rank amo ng the highest recorded rainfall-runoff discharges per drainage area i n the world, The floods on this river are a direct result of intense t ropical cyclones embedded within the summer monsoon circulation, The c luster of extreme floods in the past few decades represents an anomalo us increase in both the magnitude and frequency of large floods when c ompared with the >1700 yr record of paleoflood deposits on this river Sand deposits from recent floods consistently blanket older flood depo sits at numerous slack-water paleoflood sites along a 15 km reach of t he Narmada River, At the site of the highest flood deposits, 4-5 sandy flood deposits yielding post-A.D. 1950 C-14 dates cap an underlying s equence of 7-10 silty flood deposits with a minimum C-14 age of 650 +/ - 70 B.P. and a maximum age older than 1720 +/- 185 B.P. The post-A.D. 1950 floods are thus the largest in at least the past several hundred years. An undisturbed surface archaeological site of microlithic arti facts <0.5 m above the post-1950 flood sands provides further evidence that no significantly larger floods have occurred in at least the pas t 3000 yr. Incipient soil development on the buried surfaces of some o f the higher paleoflood deposits indicates long intervals in the past when no floods reached the highest slack-water site. The largest flood in the 1951-1991 gaged record of the Narmada River at Mortakka (55 32 3 m(3)s(-1) in 1961) is equivalent to a 1000 yr flood in a probability distribution based on the 1700 yr paleoflood record, but is less than a 50 yr flood based on the 1951-1991 gaged record alone, demonstratin g the enormous recent increase in the frequency of severe floods, This cluster of severe floods could reflect changes in either climate or l and use, A number of paleoflood studies in tropical-storm regions show a similar increase in high-magnitude floods within the past four deca des, suggesting a widespread climatic cause for this pattern.