Mid–late Holocene hydrological changes in the Mahi River, arid western India

Abstract

This paper attempts to quantify contemporary and palaeo-discharges and changes in the hydrologic regime through the mid–late Holocene in the alluvial reach of the arid Mahi River basin in western India. The occurrence of terraces and pointbars high above active river levels and change in the width/depth ratio can be regarded as geomorphic responses to changes in discharge. Discharge estimates are made based on the channel dimensions and established empirical relations for the three types of channels: mid–late Holocene, historic (the channel that deposited extensive pointbars above the present-day average flow level) and the present ones. The bankfull discharge of the mid–late Holocene channel was ∼ 55 000 m 3 s − 1 and that of the historic channel was ∼ 9500 m 3 s − 1 , some ∼ 25 times and ∼ 5 times greater than that of the present river (2000 m 3 s − 1 ), respectively. Since the mid–late Holocene, the channel form has changed from wide, large-amplitude meanders to smaller meanders, and decreases in the width/depth ratio, unit stream power and the bed shear stresses have occurred. It can be inferred that there has been a trend of decreasing precipitation since the mid–late Holocene.