<blockquote><cite>Posted By: tony</cite>The river level and flow on the river near me has greatly increased but the turbine is producing less power!

The top level has risen by 600mm but the lower level by 1.6m meaning that the head is one meter less!

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Interestingly, when researching the flood history of the area around the plot we're buying (to help prove to the EA that their very crude hydrological model is deeply flawed at the local level) I found several historical references to the mill nearby having to stop whenever the brook water level rose for just the same reason. In that case there is a low bridge and water meadow just downstream from the mill, which similarly raised the outlet level to the point where the mill didn't generate enough power to operate (it was an undershot wheel).

Recent (expensive!) hydrological modelling has shown that the shape of the valley is such that the water level at the lower end (where the old water meadows are) rises quite dramatically in heavy rain, but the level of the brook upstream of the mill (and the area of interest for us) hardly changes at all.