The regional hydrology of extreme floods in an urbanizing drainage basin

The Charlotte, North Carolina, metropolitan area has experienced extensive urban and suburban growth since 1960. Five of the largest flood peaks in the 74-yr discharge record of Little Sugar Creek, which drains the central urban corridor of Charlotte, have occurred since August of 1995. A central objective of this study is to explain how these two observations are linked. To achieve this goal, a series of hypotheses of broad importance to the hydrology and hydrometeorology behavior of extreme floods will be examined. These hypotheses concern the roles of 1) space-time variability of rainfall, 2) antecedent soil moisture, 3) expansion of impervious area, and 4) alterations of the drainage network for extreme floods in urbanizing drainage basins. The methodology used to examine these hypotheses centers on diagnostic studies of flood response for the five major flood events that have occurred since August of 1995. Diagnostic studies exploit the diverse range of extreme precipitation forcing for the events and heterogeneity of land surface properties for catchments with stream gauging records. The observational resources for studying flood response in the Charlotte metropolitan region are exceptional. They include two National Weather Service WSR-88D radars that were deployed in 1995, a dense network of rain gauges and stream gauges installed by the U.S. Geological Survey in 1995, and extensive land surface datasets developed by Mecklenburg County. This study focuses on the regional hydrology of extreme flood response, as opposed to the specific effects of individual elements of the constructed environment. Of particular interest are the hydrologic, hydraulic, and hydrometeorological controls of extreme flood response at basin scales ranging from 1 to 500 km².