Stormwater & the built surface
The runoff a campus-scale impervious surface adds to the design storm.
A campus-scale impervious surface changes what a design storm does downstream. A real impact study routes that change down the reach. This site has a committed reach table of 7 navigated reaches. The design-storm hydrograph is computed here. The routed peaks, the channel attenuation, and the animated flow field all live in the annex.
Reach-network river centerlines (NHDPlus via USGS NLDI)
- Centerline geometry is real NHDPlus, display-only — no reprojection/simplification.
- Mainstem/tributary reach boundaries are a proportional cut by reaches.yaml lengths.
- Tier-0 screening geometry for the FlowLayer viz; not a calibrated hydraulic network.
The flow annex — the routed reach network →
The stormwater permit applicationrec declares the numbers this chapter turns on. The parcel is 335 acres. 195 acres will be developed. 115 acres will be permanently impervious. Rain that used to soak into 115 acres of farm ground will now run off roofs and pavement. It will also reach the ditch faster. Coverage was granted under Ohio’s statewide construction-stormwater general permitrec , and the campus sheet this record does carry — a 95 % grading and storm plan marked Not For Constructionrec — is a design snapshot rather than the built condition.
The site sends that runoff out through a 60-inch storm outfall, quoted verbatim in the engineer-of-record’s own emails.
What the routed model shows
The screen above routes a 25-year design storm of 4.25 inches down the reach network. Routing matters because a channel does not pass a flood through instantly. It stores water, spreads the wave out, and delays it.
Here that effect is small. The routed peak of 14,283 cfs is only 2.66 % below the peak you get by simply adding the sub-basins together. The routed flood arrives at 20.2 hours instead of 17.4. In a basin this flat, with channels this short, the reach does very little to soften a storm. Whatever the campus adds at the top arrives at the bottom nearly intact.
What the model still cannot see
The routed screen works on basin geometry. It does not yet include the campus’s own grading, its detention basins, or its outlet controls, because those sheets are not public.
Two records the county holds and did not produce
The Allen Soil and Water Conservation District holds the site plan sets, and they are withheld twice over. The same office answered a request about farm-tile drainage impacts with “no records”. A tile failure on the site sits photographed in a produced inspection report. A wetland determination came back the same way. Each of those answers is tracked as its own lead. Each one is a document that would let this chapter model the campus itself, rather than the basin around it.
The record behind this chapter
What this chapter stands on: the records it reads, the inputs its modeled figures rest
on, and the reference data behind its baselines — the same pages the record screens
serve, not a second copy. A figure the record does not support stays [open] and links nothing.