52
Fig. 5.1 : Effect of ground water flow on river discharge
(Source : S.K.Garg, 1988)
Application of unit hydrograph for estimating the flood discharge, however, are
based on certain assumption, namely,
1)
Distribution of effective rainfall throughout the drainage area over a
specific time is uniform.
2)
The effective rainfall is uniformly distributed throughout the whole area
of the drainage basin.
3)
The base or time duration of the hydrograph of direct run-off due to an
effective rainfall of unit duration is constant.
4)
For a given drainage basin the hydrograph of run-off due to a given
period of rainfall reflects all the physical characteristics of the basin.
5)
The ordinates of direct run-off and common base time are directly
proportional to the total amount of direct run-off represented by each
hydrograph.
Flood Protection Work
As has already been mentioned, when the river water overtops the banks and
the adjacent areas which may be cities, industrial areas or agricultural lands
are submerged, causing enormous damage to the country. On the other hand
there are some beneficial effects of flood - it carries enormous amount of silt
and nutrients covering the adjacent flood affected areas.
