Attenuating reaches and the regional flood response of an urbanizing drainage basin

Abstract The Charlotte, North Carolina metropolitan area has experienced extensive urban and suburban growth and sharply increasing trends in the magnitude and frequency of flooding. The hydraulics and hydrology of flood response in the region are examined through a combination of numerical modeling studies and diagnostic analyses of paired discharge observations from upstream–downstream gaging stations. The regional flood response is shown to strongly reflect urbanization effects, which increase flood peaks and decrease response times, and geologically controlled attenuating reaches, which decrease flood peaks and increase lag times. Attenuating reaches are characterized by systematic changes in valley bottom geometry and longitudinal profile. The morphology of the fluvial system is controlled by the bedrock geology, with pronounced changes occurring at or near contacts between intrusive igneous and metamorphic rocks. Analyses of wave celerity and flood peak attenuation over a range of discharge values for an 8.3 km valley bottom section of Little Sugar Creek are consistent with Knight and Shiono’s characterization of the variation of flood wave velocity from in-channel conditions to valley bottom full conditions. The cumulative effect of variation in longitudinal profile, expansions and contractions of the valley bottom, floodplain roughness and sub-basin flood response is investigated using a two-dimensional, depth-averaged, finite element hydrodynamic model coupled with a distributed hydrologic model. For a 10.1 km stream reach of Briar Creek, with drainage area ranging from 13 km2 at the upstream end of the reach to 49 km2 at the downstream end, it is shown that flood response reflects a complex interplay of hydrologic and hydraulic processes on hillslopes and valley bottoms.

[1]  P. Bates,et al.  Predicting floodplain inundation: raster‐based modelling versus the finite‐element approach , 2001 .

[2]  P. Bates,et al.  Modelling floodplain flows using a two-dimensional finite element model , 1992 .

[3]  H. Barnes Roughness characteristics of natural channels , 1967 .

[4]  Paul D. Bates,et al.  Development and testing of a subgrid-scale model for moving-boundary hydrodynamic problems in shallow water , 2000 .

[5]  M. Horritt Calibration of a two‐dimensional finite element flood flow model using satellite radar imagery , 2000 .

[6]  A. Miller Debris-fan constrictions and flood hydraulics in river canyons: Some implications from two-dimensional flow modelling , 1994 .

[7]  J. T. Hack Physiographic divisions and differential uplift in the Piedmont and Blue Ridge , 1982 .

[8]  Kenneth W. Potter,et al.  An empirical study of flood measurement error , 1985 .

[9]  Andrea Defina,et al.  Two‐dimensional shallow flow equations for partially dry areas , 2000 .

[10]  P. Bates,et al.  Integration of high-resolution topographic data with floodplain flow models. , 2000 .

[11]  Paul A. Carling,et al.  Velocity and turbulence measurements for two overbank flow events in River Severn , 2002 .

[12]  J. Cady Rock Weathering and Soil Formation in the North Carolina Piedmont Region1 , 1951 .

[13]  C. Woltemade,et al.  A watershed modeling analysis of fluvial geomorphologic influences on flood peak attenuation , 1994 .

[14]  J. Robinson,et al.  Effects of August 1995 and July 1997 Storms in the City of Charlotte and Mecklenburg County, North Carolina , 1998 .

[15]  M. Anderson,et al.  Large‐scale floodplain modelling , 1990 .

[16]  Paul D. Bates,et al.  The Regional Hydrology of Extreme Floods in an Urbanizing Drainage Basin , 2002 .

[17]  Stephen J. Burges,et al.  An analysis of the influence of river channel properties on flood frequency , 1994 .

[18]  J. Smith,et al.  Scaling Properties of Flood Peaks , 2001 .

[19]  Fred L. Ogden,et al.  Green and Ampt Infiltration with Redistribution , 1997 .

[20]  D. Knight,et al.  Energy losses due to secondary flow and turbulence in meandering channels with overbank flows , 1999 .

[21]  J. Hervouet,et al.  Malpasset dam-break revisited with two-dimensional computations , 1999 .

[22]  Andrew J. Miller,et al.  Modeling Considerations for Simulation of Flow in Bedrock Channels , 2013 .