Transparent dam concept for everlasting reservoirs

Water needs are increasing worldwide while the stored volumes are decreasing because of siltation. Global warming will worsen this situation in a lot of countries. Even more closely than before, reservoirs must pass as much sediment as possible to maintain their capacities, i.e. being transparent regarding solid transportation. Construction of new dams today don’t compensate the loss of water storage due to sedimentation. ‘Drawdown’ or ‘pressure’ flushing are generally organized. Nevertheless a proper flushing must respect the biodiversity of the river downstream of the dam. Therefore ‘friendly flushing must be applied. It consists in sending downstream of the dam only the concentration of solid materials that the environment can withstand. The example of 40+ years of friendly flushing on the Genissiat dam on Rhone River is given, Ref: 1, 2. Appropriate gates are necessary to provide this proper concentration downstream. Said gates should be included in the original design of the dam. Total transparency may finally remain an inaccessible goal, nevertheless to get high rates of transparency must be a practical objective, when refurbishing existing dams or designing new ones, Ref: 3. Transparency concept for dams can also be extended for fish transit boat transit. If a lock exists for boats, it can be used to improve fish transparency, allowing the fish to cross the dam upstream and downstream, call ‘fish lockage’. Another system also using the lock for fish transit but differently can be used: the ‘fish shuttle’ system. Reservoir siltation is not a fatality. Friendly flushing must be seen as an investment not as a cost. Time life of a reservoir, dead storage are old fashioned words. Now we have to think “transparent dam”. Dams are built for ever. Desiltation of existing dams, appropriate design for new ones using friendly flushing, are the major issues for the next decades.