Water that once lingered in hollows, meandered around oxbows, and soaked into the ground now speeds downhill, shoots through pipes, and sheets off rooftops and paving. Insurance purposes require the NFIP floodplain maps to be based on existing watershed development. But unless plans and regulations are based on future watershed urbanization, development permitted today may well flood tomorrow as uphill urbanization increases runoff. Tulsa enforces the NFIP minimum regulations and maps, to retain eligibility for federal flood insurance. In addition, the city enforces its own more extensive maps and regulations, which are based on ultimate watershed urbanization as forecast in the comprehensive plan.
Floodplains are only part of flood-management considerations.
Water gathers and drains throughout entire watersheds, from uplands to lowlands. Each watershed is an interactive element of the whole. A change at one place can cause changes elsewhere, whether planned or inadvertent. Therefore, Tulsa goes above and beyond the floodplain in its regulatory program, extending its regulations watershed-wide. One way to avoid increased flooding downstream from new development is to provide stormwater detention basins throughout watersheds.