We recently ran across a special trench drain that was designed by a landscape architecture firm to assist in controlling the runoff while still having capacity for the storm surge. The trench drain utilized a small trench on the uphill side that collects most rainfall events and transitions them across the trench to a bio retention area. If heavy rainfall exists and the small trench fills up it will run over the internal wall of that small trench into a larger trench drain. This larger trench drain then caries the excessive water to an outfall structure to ensure the bio retention area is not overloaded.
We have manufactured the product and it will be installed in December 2017. An update of finished pictures will follow. What a novel concept and we can't wait to see the drain in action.