Impact of large dams river
Bypass systems are designed to connect adjoining impoundments within alluvial floodplains and represent innovative solutions for enhancing longitudinal and lateral connectivity of the fragmented environment as well as for substituting lost fluvial habitat.
Since the head sections of reservoirs still offer relatively high hydromorphological dynamics, river-type-specific rehabilitation can most likely be achieved here. Leitbild-specific measures for the rehabilitation of the heavily modified Austrian Danube River.
The images or other third party material in this book are included in the book's Creative Commons license, unless indicated otherwise in a credit line to the material. Hence, any attempt to improve the ecological condition can be regarded as a mitigation effort to reduce but not to remove the impacts.
Impact of dams on environment ppt
The flow of the bypass system should mimic pre-damming flow hydrographs to enable dynamic hydromorphological processes Fig. Migratory and rheophilic species experience declines in the reservoir due to the lentic environment, spatial fragmentation imposed by the dam, and the loss of critical habitats e. After damming, annual maximum peak discharges have decreased, minimum discharges increased, but average discharges remained similar to pre-damming conditions Fig. Consequently, hydrological connectivity among environments is considerably modified in space and time. Density current venting can be practiced at these reservoirs as well as dredging to recover lost storage capacity Basson Long distant migrants such as Tor sp. They impact on the migratory patterns of fish, and flood riparian habitats, such as waterfalls, rapids, riverbanks and wetlands. They create novel and artificial types of aquatic environment for the life span of the dam. However, healthy ecosystems are usually able to compensate these effects in the long run. When these conditions exist, individuals move to poor-quality habitats, fitness is reduced, and populations are threatened. For example, the release and decay of organic matter and resulting oxygen depletion may lead to suffocation of fish and benthic invertebrates. As an example, the dam cascade at the Lancang River upper Mekong has the potential to trap most of the sediments Kummu and Varis , Fig. Nevertheless, the construction of artificial, stabilized silt or sand islands at hydraulically appropriate zones along the embankments can provide valuable habitats for various species Fig.
Most reservoirs have a capacity mean annual flow ratio of between 0. In the absence of floods, even if adults successfully reproduce in tributaries, eggs, larvae, and young fish drifting downstream have limited access to lateral habitats, and population recruitment is negatively affected Agostinho et al.
This affects aquatic communities of the hyporheic interstitial Ward et al. Shoreline erosion and rapid and intensive drawdown are other problems faced by fish as they affect spawning and egg incubation.
based on 19 review