Cyclone and Storm Surge - Iczmpwb.org

6.2
From a hydrological point of view the islands of the Sundarban, presently under cultivation, should be
looked at as "polders" because the water levels of the surrounding river sections are periodically
higher than the field levels.
Polders require man-made embankments to prevent flooding. The river water in the Sundarban is
saline throughout the year and consequently the damage to the crops of the inundated areas is
severe.
The embankments to be constructed, rehabilitated and maintained should meet two criteria: they
need to be high enough to prevent overflow and they need to be strong enough to prevent bursts and
other forms of damage.
These criteria have their effects on the following issues which are related to the construction and the
maintenance of the embankment:
1. The typical cross-section,
2. The alignment of the embankment and the importance of the “berm” situated between the
river and the embankment,
3. The quality of the construction material,
4. The method of construction,
5. Measures to protect the slope of the embankment
6.2.1. Typical Cross-Section
The cross-section of an embankment is determined by: the field level of the strip of land where the
embankment is built or needs to be built, the required level of the crest of the embankment, the width
of this crest and the gradients of the inner and the outer slopes.
In their proposal to improve and repair the flood protection works in the North-Eastern part of the
Sundarban, the Irrigation Department stated that the islands in this area are flat and that the field
level is +1.80 GTS.
Although at macro level the cultivated areas of the islands are relatively flat, observations reveal that
at micro level there are significant differences in level. These observations are confirmed by farmers,
who moreover reported that according to their experience some islands are lower than others. This
topography is characteristic for land reclaimed in tidal area.