HR: 14:20h
AN: H53L-03    [Abstracts]
TI: Channel widening due to urbanization and a major flood can alter bed particle organization and bed stability in an urban boulder-bed channel
AU: * Prestegaard, K L
EM: kpresto@geol.umd.edu
AF: Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Behrns, K
AF: Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Blanchet, Z
AF: Department of Geology, University of Maryland, College Park, MD 20742, United States
AU: Hankin, E
AF: Department of Geology, University of Maryland, College Park, MD 20742, United States
AB: The Anacostia River is a tributary of the Potomac River north of Washington D.C. that has become progressively more urbanized in the past 50 years. Bankfull discharge and bankfull width in the Anacostia have increased by 3- 4x in the past 50 years. Nearby watersheds of similar size and geology, but without significant urbanization, contain threshold gravel-bed streams. The Anacostia, however, is not a threshold channel; it exhibits break-up of boulder-bed channels in upstream reaches and significant gravel bar formation in downstream reaches. These gravel bars have grown and migrated considerably in the past 10-15 years, contributing significantly to local channel widening that can be twice that of adjacent reaches. The purpose of this study is to determine bedload transport rates and grain size distributions and their relationship to discharge, bed organization and sediment supply. Bed mobility data come from both bedload transport measurements and measurements of channel bed changes. Channel bed changes were obtained from a) repeated channel cross section surveys, b) surface and subsurface size distributions, and c) bed particle organization measurements (measurements of location of particles within reaches). These measurements were made prior to and after the floods of 2006, which equalled the largest floods on record for most parts of the Anacostia River. In some boulder bed reaches, boulders were removed from the center of the channel and deposited along and on the channel banks. The mid-channel boulders were replaced by sheets of gravel and cobbles, significantly altering the bed mobility of the channels.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1879 Watershed
DE: 4558 Sediment transport (1862)
SC: Hydrology [H]
MN: 2007 Fall Meeting