Bolingbrook, IL Environmental Rules: Flood Elevation Requirements (2026)

The freeboard and base flood elevation standards sit in the same stormwater management division as the village's drainage rules, Chapter 16, Article IV, Division 2. Section 16-115 defines base flood elevation as the elevation delineating the level of flooding from the 100-year frequency flood event, and defines freeboard as the added height above the 100-year high water elevation built in to cover uncertainties in calculations, unknown local conditions, wave action and debris jams. Section 16-120(f)(6) sets that freeboard at a minimum of one foot between the 100-year event water level and the top of embankment for wet detention basins, and Section 16-120(g)(4) applies the same one-foot minimum to dry detention basins between the 100-year high water level and the top of embankment.

Section 16-120(l)(3) extends the one-foot freeboard standard to culvert and bridge crossings, measured between the 100-year water surface elevation and the low chord of the structure at its upstream face. 5 times the volume displaced below the 100-year base flood elevation, replacing floodwater storage lost below the ten-year flood elevation with storage below the ten-year elevation and storage lost above it with storage above the proposed ten-year elevation. The village's regulatory floodways, mapped by FEMA, cover Lily Cache Creek, the Lily Cache Lane Tributary, the Naperville Road Tributary and the DuPage River.