Hydrology, hydraulics, sediment transport and geomorphology of the Central Amazon floodplain / Leal Anne Kerry Mertes.

Tese (Ph.D.)- University of Washington, 1990

In large and small alluvial rivers the fluxes of water and sediment onto and from floodplains follow a predictable sequence. The resulting hydrologic, hydraulic, and sediment transport patterns form the basis for a conceptual model developed in this dissertation that predicts the spatial and temporal distribution of erosional and depositional processes responsible for construction of landforms on a floodplain during inundation. Field measurements of water and sediment discharge and floodplain topography and soil composition, satellite data on sediment concentrations, and numerical simulations of hydrodynamics were combined to test this conceptual model for a 200-km reach of the Amazon River. Results from field data collected July, 1986, and November-December, 1988, Landsat data for 7/31/77, 8/15/88, and 812/89, and numerical simulations of the hydrodynamics for these times indicate that non-channelized and channelized floodplain environments had distinct hydraulic and sediment-transport characteristics. More than 80% of the sediment supplied to the entire floodplain during these times was transported across non-channelized surfaces with sediment transport rates at the main channel-floodplain boundary ranging from 1 to 10 t/d-m. Over 80% of the sediment supplied to these non-channelized sites was deposited, and the highest vertical rates of 19.5 cm of sand deposition and 3.7 cm of silt-clay deposition were computed for the 1989 flood. Much lower rates of vertical deposition were computed for floodplain drainage channels, with an average of 0,5 cm of sand deposition in drainage channels varied with respect to the time from the crest of the flood. In the Iauara channel the proportion of sediment that was deposited increased from 9% to 28% over the crest of the 1986 flood. In the Barroso channel the proportion of sediment that was deposited decreased from 37% in 1986 at 8 days after the crest, to an average of 8% in 1977 and 1989 at about 29 days after the crest, to 0% in 1988 at 46 days after the crest. The spatial and temporal patterns of these results are consistent with the conceptual model. .