It is interesting to read ...
Published by Achyut Man Singh
It is interesting to read the answers of the participants about the flood. Technically flood means excess water from the natural drainage channel over flow and breach its embankments engulfing the inhabitants with gust of water damaging huge properties and livings. The rain water comes from the sea to the land form due to some atmospheric phenomenon which brings flooding to the land if it exceeds its drainage boundary. The following factors are responsible to flooding or drainage through a watershed.
- Rainfall intensity,
- Vegetative coverage of the watershed.
- Size and shape of the Watershed and the land forms.
If the rainfall intensity is high like in the Houston flooding said to be more than 750 mm of rain within 12 to 24 hours, there is no way that such volume of water could be safely be drained out to sea. The eventual design of the drainage systems are designed for about 25 or 50 year return flood. with such magnitude of intensity the return period will cross 500 yrs return. we cannot avoid such fury of the nature, only early warning and evacuation to a safe high ground only will be possible. you can blame to Climate change or global warming but in a span of 1000 years time such events are possible and will be disaster any way.
The next factor is vegetative coverage of the watershed, which reduces the flow volume three times. A research at Minasota has found that vegetative coverage reduces the flow of the flooding to one third. Time of concentration as time taken by a drop of water from the farthest point of the catchment to the outlet level of the drainage considered, reduces drastically by vegetation. Therefore man made deforestation turning every piece of land in to cultivation exposing to direct rainfall also is a prime factor of flooding.
The size and shape of the water shed is obvious a flat lands will be inundated soon whereas hilly valleys will have less effect due to flooding.
If the people will realize the management of these three factors, the effect of flooding will be minimized. My paper on Hydro Nepal attached herewith would give some inside of the flooding problems in Nepal.