 |
|
II. FLOOD LOSS REDUCTION AND REVIEW OF PAST EXPERIENCES
[ II-A | II-B
| II-C | II-D | II-E
| II-F ]
E. Environmental impacts of flood control projects
[ E-1 | E-2
| E-3 ]
2. Impact on ecological environment
The most notable positive ecological impacts include the changes in the
bio-mass through increased rice production and reduced flood damage to
field crops, cultured fisheries and non-agricultural flood damage. Other
areas where biological changes may have led to additional benefits include
increased fruit and timber tree cropping and increased production induced
in other crops and animal products such as vegetables and eggs.
The most significant negative ecological impact is associated with the
reduction and delinking of the areas of standing perennial and seasonal
water bodies by FCD projects. Consequently breeding grounds of fisheries
have been lost and migration routes have been disrupted (Figure 11). These
have directly led to considerable loss to capture fisheries (see Table
9). In the Brahmaputra Right
Embankment Project, loss of capture fisheries stands at 81 per cent (ODA,
1995). Partial flood control
projects have however had very little impact on capture fisheries (Shawinigan
Lavalin, 1994). In order to mitigate the impact on this important floodplain
resource, fish friendly structures are now being constructed under pilot
programs. FCD projects have also brought about reductions in the population
of frogs, snakes and some birds, all of which play an important role in
controlling pests. Rodent populations have benefited, which, because their
habitats are often found in embankments, has led to greater risk of breaches.
Figure 11. Impact of prevention of flooding of floodplain:
a schematic
As the size and status of wetlands changes, the connections to the drainage
and floodplain network are broken and the recharge of water and nutrients
is considerably hampered. Submerged aquatic vegetation is less prevalent
as a source of organic matter as the wetlands decline. The contributions
of biological organisms and organic matter which arrive in the flood water
do have vital linkages to the fertility and vitality of the floodplain
eco-system. Therefore prevention of annual flooding can rapidly change
the physical quality of the soils in protected areas.
|
|
|
