This report relates peak discharges for recurrence intervals ranging up to 100 years to drainage area, stream length, stream slope, and percent of basin covered by impervious surfaced. The relations are based on analysis of flood information for approximately 200 sites, 42 of which are in metropolitan areas of the North Carolina Piedmont providence. The estimating relations are limited to providing flood discharge estimate at open-channel sites in the Piedmont province of North Carolina where runoff is unaffected by artificial storage or diversion. The estimate are most reliable for smaller size floods at sires where the drainage area ranges between 0.3 and 150 square miles, where the L/√s ratio ranges between 0.1 and 9.0, and where impervious cover of less than 30 percent is uniformly distributed over the basin.
Changes from rural to urban conditions significantly affect flood flows. Urban development may reduce the basin laf time to one-sixteenth that of comparable natural system. This reduction in basin lag time, along with the increased storm runoff resulting from impervious cover, increases the flood-peak discharge by a factor that ranges up to five. The increase in flood-peak discharge depends on the drainage-basin characteristics and the recurrence interval of the flood.
