Slide 13 of 75
Notes:
The combination of increased peak flows and bankfull flows also greatly impacts the floodplain. The floodplain is the wider channel outside the bankfull channel that accommodates the rare large storm events. In a post-development situation, increased upstream impervious cover and increased peak discharges cause the floodplain to widen and increase vertically, subjecting more homes, properties, and people to the risks of flooding.
This figure shows how upstream development can widen the floodplain limit and is usually accompanied by encroachment into a larger floodplain.