The Stillwater and Its Retarding Basin
The Stillwater River as a tributary of the Great Miami and the Englewood Dam on the Stillwater as one of the five Miami Conservancy District structures — its specific location, its basin geometry, and what it contributes to the system's total capacity.
A tributary with its own dam
The Stillwater River runs roughly parallel to the Great Miami before joining it at Dayton, draining a valley that rises into west-central Ohio's glaciated uplands. Because it reaches Dayton from the northwest — directly from uncontrolled watershed — it was treated by the Miami Conservancy District's engineers as a separate hydraulic problem requiring its own retarding basin, not a secondary concern managed through the main-stem structures.
The answer was the Englewood Dam, built across the Stillwater near the village of Englewood in Montgomery County, completed in 1922 along with the other four district structures. Its placement is characteristic of the system's logic: the dam sits well upstream of the confluence, giving the basin room to absorb a Stillwater flood event before that water can add to whatever the Great Miami is simultaneously carrying through Dayton.
The structure itself is an embankment dam — compacted earth fill across the valley floor, broad-shouldered and unspectacular from a distance. Like every Miami Conservancy District dam, it holds no permanent reservoir: the valley behind it stays dry, farmed and inhabited between flood events. Water enters through the ungated conduit in the embankment and passes through continuously; only when inflow exceeds the conduit's capacity does the pool begin to rise toward the design water surface. When the storm passes, the basin drains itself.
The Englewood basin's contribution to total system capacity is not trivial. The Miami Conservancy District engineered all five basins as an integrated set, with each structure's storage volume calculated against the watershed area it drains. The Stillwater's basin serves a drainage area that is substantial — the district's own records place the embankment at roughly 4,300 feet in length and the design storage in the hundreds of thousands of acre-feet range. The result is a structure modest in appearance and decisive in function.
