Environmental Engineering Reference
In-Depth Information
Water quality, flow and seasonality of flow are not normally disrupted in the
upstream area above the reservoir so impacts are generally less than for the reservoir
and downstream areas. Nevertheless, the dam and the reservoir affect migratory
movements of species into and out of this upstream area. The genetic exchange with
downstream segments is reduced or prevented. A study was made of molluscs
upstream in a braided river that enters a reservoir on the River Inn in Austria (Foeckler
et al.
1991
). Data shows that there was a decline of species upstream of the reservoir.
In the construction of reservoirs, the clearing of vegetation, movement of earth and
rock, the presence of humans and machinery, bringing in construction materials, use of
explosives, noise, and reducing or cutting off river flow and increasing turbidity, will
affect biodiversity. Removal of forests or other vegetation over a wide area, excavation,
earth and rock movement and reduction in river flow are the most significant. Some of
the on-site activities are mirrored in off-site disturbances such as the mass displacement
of earth and rocks and road building. During reservoir filling the river and any associated
wetland areas become inundated. Riffles, runs and pools of the river are lost beneath the
rising waters, leading to the extirpation (or extinction) of habitat sensitive riverine spe-
cies with tightly defined niche requirements. Fishes in rivers are generally well adapted
to flowing water. Similarly molluscs are often restricted to specific habitats within the
river system, e.g. some species are bottom-dwelling filter feeders, and others live in
weeds at the edge of the channel. The construction of reservoirs converts lotic (running)
into lentic (still water) habitats. Species dependent on running water will diminish or
disappear. In almost all cases, the diversity of fish species will drop (McCully
1996
).
The changed or fluctuating conditions in the reservoir may lead to opportunities
for weed or exotic species e.g. the water hyacinth,
Eichhornia crassipe
. Increases in
the number of mollusc-borne diseases following dam construction in various coun-
tries. For example at least four genera of mollusc-borne human diseases have
increased as a result of impoundments in Thailand (Woodruff and Upatham
1992
).
Our results show that the minimum and maximum temperatures of water have shown
a significant variation. This change might be attributed mostly due to reduced water
level. As water levels are low, the heating and cooling of river bed might be having an
effect on water temperature. Due to this change in water temperature, the habitat and
tolerance of aquatic species might be showing variations. During the study, it was noted
that the characteristics of water after the dam wall is more “stream like” rather than
“river”. Change in DO level might also be another reason for difference of species rich-
ness in case of phytoplankton and micro invertebrate fauna. As per the review of litera-
ture done by our lab, very few to almost none of the long studies have ever been
conducted in Garhwal Himalaya on impact of hydro-electric power project/plant's dam
wall on aquatic fauna. Our study has thrown light on this aspect and came up with data
that should be a cause of concern and clearly highlight the need of long-term data sets
on various aspects of river ecology especially in areas of hydro-electric power projects.
Our study clearly shows that the fauna and flora is clearly being affected due to
construction of power projects. The main cause is drastic changes in water level.
The situation is alarming and immediate steps will have to be taken to counter the
situation. Either the hydro-electric power companies need to follow the recommended
guidelines or policy makers will have to think about new policies on this issue.
Search WWH ::
Custom Search