Humanity has lived with floods for centuries but the impact of floods was not felt to the same extent in the in the past as is experienced now. Rapid increase in population and urbanization coupled with increased economic and developmental activities together with the nonregularisable river bed colonization have resulted in the hazardous occupation of the floods plains to an ever increasing extent. India is subject to monsoon, which accounts for the rainfall. In our region the monsoon period is between July and September and three-fourth of the monsoon rain in any year is concentrated within rain in any year is concentrated within about 100 hours of intense downpour. Floods are common occurrences, particularly in the Brahmaputra and Ganga (including the Yamuna) basins. However, the actual intensity and the extent of flooding as also the flood damages vary from year to year.
Delhi lies within the Yamuna sub basin of the Ganga sytem, which itself is a part of the greater Ganga Brahmaputra Mega basin. River Yamuna rises in the Himalaya at Yamunotri in UP. The uamuna receives many tributaries before it debouches into the plains near Tajewala. It then travels Generally along the UP - Haryana border before it reaches Delhi state. It traverses some 40km. in Delhi and has an average bed width varying from two to three km. thereafter the river runs again through UP and joins the Ganga near Allahabad.
Delhi state has flat land, however there is a big depression in the southwest known as the Najafgarh jheel area, which receives the drainage from the adjoining states of Haryana and Rajasthan. The only outlet for these waters is the Yamuna.
The Sahib river that flows through Rajasthan and Haryana used to be absorbed in the sandy areas of Haryana and has no definite course downstream of Masani in Haryana. The waters of the Sahibi flow into Delhi through the Dhansa bund. The waters find a final outlet in to the Yamuna (throught eh Najafgarh nala) below wazirabad. There are barrages across the Yamuna in Delhi at Wazirabad, Indraprastha and Okhla. There are also some 18 drains that join the Yamuna in Delhi. Delhi's flooding is due to
- Spills from the Yamuna
- Drainage congestion due to intense rainfall
- Flooding from various drains of Haryana and the Sahibi nadi.
Delhi state covers an area of 1483 sq. km. its population, which was less than half a million in 1911 now cross 14 million. Delhi has experienced many high floods in the past, but the effects were not so significant as the population was small and rural. With increased population, particularly after the partition in 1947, the damages have been high. It will be a convenient starting point to review the flood scene in the last five decades, after India attained its independence. In fact statistical compilations relating to flood incidences are available since 1953 only.
Between 1953 and 1990, the period for which published damages data are available, there were high floods in Delhi 1in 1956, 1958, 1962, 1964, 1966, 1967, 1971, 1975, 1976, 1977, 1978 and 1988. Prior to 1953 there were such floods in 1924 and 1947. Since 1990 the floods of 1995 were high. The highest flood level on record so far was in 1978, through the Yamuna. The 1924 floods, which comprised successive peaks of lesser order, had generated the largest volume of flood flows so far. The 1977 flood was the highest through the Sahibi nadi.
Flood damage figures are reported by the Delhi state administration and these have been compiled by Central Water Commission. Taking these as reflecting the true position some inferences could be drain. The maximum area that was affected in Delhi was 70,000 ha of which 40,000 ha were stated to be under crops and this was in 1978. A million people were reportedly affected. Some 400 heads of cattle and 18 human lives were lost. The total damage to crops, houses and public utilities was put at around 18 crores rupees. Int eh 1977 floods, which was next in order of magnitude, the total damage was put at over Rupees five crores. A damage of comparable order earlier was in 1967.