Category:02. Sediment flow quantity improvement

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Sediment flow quantity improvement

General description

Like water and organisms also solid components are essential ingredients of every river. This solid fraction mostly is of natural origin and finds its way via erosion processes into the water body. Starting at the rivers source solid components usually begin as eroded massive rock. Transport processes changes rock size first to gravel size bedload and furthermore to fine-grained sediment. This sediment settles at the river floor. Depending on the local current this sediment does also come loose again by erosion effects. In middle and lower parts of natural rivers sedimentation and erosion usually balance each other.

A natural river changes it morphology fundamentally when installing a dam or other barrage across a river section. Permeability is still given for water and mostly for aquatic life by discharge elements and if applicable fish ladders. The extended cross-section upstream of a barrage leads to low current velocities and therefore to profoundly more sedimentation while erosion is minimized. Therefore a barrage often is a barrier for sediment transport. Many reservoirs are affected by massive sedimentation and consequently a loss of storage volume.

Extracting large sediment quantities from the river upstream of the dam also leads to massive changes downstream. For example, by trapping sediment in its tributary reservoirs, the German river Rhine alone - which certainly does not represent a major sediment carrier concerning worldwide average - is facing an annual sediment deficit of 2.5 million tons. To heal only major riverbed erosion damages an annual mass of more than 600.000 million tons of soil is dropped into the Rhine at its middle and lower reaches, causing significant expense.

Therefore, besides all desired ecologic benefits, sediment flow quantity improvement also saves large scale financial expenses for both erosion damage repair and questionable sedimentation removal.