Heavy rainfall during monsoon season: Point and spatial distribution

The daily rainfall records of about 5000 stations in India, during the monsoon periods of several decades, have been examined for occurrence of heavy rainfall. The point values of (i) the highest annual rainfalls, (ii) the highest rainfalls of one, two, and three day durations, and (iii) the highest hourly values, are presented in the form of tables and charts. The highest depth-area-duration values for twelve storm-centres are also given

Generalised technique for the estimation of probable maximum precipitation in India

In this paper a version of a generalised method of estimating probable maximum precipitation (PMP) is applied to the catchments of four large dams in India. The value of a secure dam is high both in terms of human life and in economic terms. Reliable estimates of PMP are required in estimating the design flood for spillways of large earth and rockfill dams. Estimates of PMP obtained using the traditional method of moisture maximisation and storm transposition can be unreliable as highly efficient rain storms may not be represented in the rainfall records of an are

The rainstorm ( Machhu valley)which caused the Morvi dam disaster in August 1979.

On 11 August 1979, the Machhu-2 earth dam, situated about 6 km upstream of the town of Morvi in the Saurashtra region of India, collapsed under the onrush of an unprecedented volume of water. An 8–10 m high flood wave rolled down Machhu valley, entirely submerging Morvi and nearby villages. This flash flood caused the deaths of thousands of people and totally destroyed urban and rural property downstream of the dam. The heavy rainfall of August 1979 over and around the Machhu basin has been analysed by both depth-area-duration and depth-duration methods. Important aspects of heavy rainfall distribution such as: analysis of past severe rainstorms, maximum point rainfall of different return periods, and probable maximum precipitation, were also studied. This study has shown that this event was not the most severe rainstorm in this region. Possibly, the antecedent conditions of the Machhu basin played a significant role in generating the flood volume which caused the earth flanks of the dam to give way

Highest floods in India

This paper provides information on the highest recorded floods at some sites in India's major river basins. The data available for the last 100 years or so indicate that the highest floods recorded on rivers in India had peak discharges ranging from 1170 m3 s-1 for a 133 km2 area to 72 900 m3 s-1 for a 935 000 km2 area. The flood comparison studies showed that the highest recorded floods in India are remarkably comparable with the highest floods reported from other parts of the world for drainage areas larger than 1000 km2. Two powerful floods recorded in India-the flood of 6 September 1970 on the Narmada River and the flood of 11 August 1979 on the Machhu River were found to be record-breaking events in the world

Counting on perfect storms

Throughout the world, severe rainstorms are responsible for causing destructive floods, landslides, levee breaches, dams overtopping, sedimentation, erosion and other such occurances. Some of the most severe rainstorms have even destroyed dams, causing enormous loss of life and property damage. For example, an extreme flood resulted from the severe rainstorm of August 1979 over the Machhu river catchment in India totally destroying the Machhu-2 dam on 11 August. The disaster killed between 1500 and 2000 people and totally devastated urban and rural property downstream of the dam. Another instance is the catastrophic flood generated from an extreme rainstorm of August 1975 in the Huai river basin in China, which destroyed the Banqiao and Shimantan dams. Lemperiere (1993) goes on to describe many dam failures by flooding in various parts of the world. At present it is only possible to consider controlling floods from the heavy rainfalls because we are not in a position to control rainfall