| Popis: |
Coastal Plain floodplains in the Mid-Atlantic United States are the last place for sediment storage before reaching sensitive estuarine and marine environments. Field monitoring of sedimentation rates and patterns, suspended-sediment concentrations, substrate characteristics, and woody vegetation has been conducted in eight 1-ha floodplain sites during 2000–02 to describe the main controls on sedimentation and to determine the effects of channelization and urbanization on floodplain fluvial geomorphic processes and sedimentation patterns along three tributaries to the Chesapeake Bay. These tributaries include the Chickahominy River, the Pocomoke River, and Dragon Run. Site-scale deposition patterns are spatially highly variable. Multiple regression analyses were used to determine that inundation frequency and duration, and lateral distance from the channel and sloughs jointly explain most of this variation (between 65 and 85%). Channelized floodplain reaches are flooded less frequently, have lower sedimentation rates (0.19 mm/yr to 3.2 mm/yr), less storage (700 metric t-sediment/yr to 1,090 metric t-sediment/yr) and less diversity than the nonchannelized reaches. Inundation (from 27 days/yr to 97 days/yr), sedimentation rates (3 mm/yr to 7.2 mm/yr), and diversity (0.36 to 0.84 on the Shannon-Weiner diversity index) increase with distance from urbanization along the Chickahominy River. These results suggest that understanding floodplain sediment and community dynamics and geomorphic processes with respect to dominant watershed land-use patterns is critical for effective water-quality management and restoration efforts. |
