IHA Congress 2011 - Session 8b - Domingo Fernandez

1. Downflow regimes impacts and perspectives Domingo Rodriguez Fernandez June 16th 2011

2. Rivers possess quite diverse features that are morphological (composition of the river bed and banks that influences sediment transport), hydrological (flow velocity, water depth), chemical (temperature, pH, dissolved oxygen, alkalinity) and ecological (aquatic biota). Dynamic characteristics are influenced by seasonal climate and geography of the region. Introduction In natural systems, the communities are present as a result of a long period of evolution: the life cycles of the species are strongly associated with the dynamics of the hydrological regime (Junk, Bayley and Sparks, 1989 Neif 1990).

3. Main environmental impacts of concern to downstream flow regimes - Regulation of natural flood regime; - The impoundments affect the natural hydrological regime by attenuating and retarding flood peaks ; - Interruption of fish migration routes - Difficulties for fish eggs andlarvae to downstream passage - Trapped fish in cofferdams and in stretches with reduced flow ; - Changes in water quality by spillway and turbines - Reduction in nutrient input down steams

4. Mitigation Measures - Closure of cofferdams and formation of reservoirs outside the fish migration period - Location of outlets and intake pipes closer to the water surface - Maintenance of hydraulic systems near their natural regime, especially with relation to the natural flooding period - Monitoring and studies of fish fauna in the environments of the area under the influence of impoundments - Transposition systems where there are fish spawning, nurseries and feeding areas above the dam must conform to the local fish fauna specifications

5. Bela Vista River

6. Bela Vista River – Cutting by damming downflow

7. Longitudinal icthyoplancton gradients Fish egg density – Lajeado reservoir Fonte: Neamb-UFTO

8. Longitudinal icthyoplancton gradients Fish larvae density – Lajeado reservoir Fonte: Neamb-UFTO