Other
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.h23a..04w&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #H23A-04
Other
1640 Remote Sensing, 1824 Geomorphology (1625), 1860 Runoff And Streamflow
Scientific paper
Bedrock incision from streams is an important process that controls landscape evolution for many areas. Although the mechanisms that control incision rates are controversial, there is general acceptance that incision rates are a function of the streams ability to do work and are related to the amount of discharge. The stream gradient and sediment flux are considered to be the factors controlling incision into bedrock. Stream gradient can be measured from maps. Sediment flux is a more difficult quantity to measure, and the contributing drainage area is used to approximate this quantity. From this the "stream power law" has evolved to model incision, where erosion E is related to the stream gradient S and drainage area A by, E = kSmAn, k is a constant that is related to the channel geometry and other factors such as sediment supply, m and n are exponent coefficients, where the ratio of m/n represent the cancavity of the stream long profile. Although the availability of moderate resolution DEMs has facilitated the testing of this model, many questions remain unresolved such as the role of sediment supply and the erodability of the bedrock in the streambed. In this study, a high resolution DEM derived from LIDAR (Light Detection and Ranging), for the Annapolis Valley, Nova Scotia that is part of the Mesozoic Fundy Rift Basin. The area has relief (on the order of 260 m), that is in part due to the bedrock geology, and has a variety of rock types ranging from the elevated Paleozoic metasedimentary rocks of the South Mountain Batholith (SMB) granites of the Meguma Terrane to the south, Jurassic sedimentary rocks that underlie the valley floor, and the Triassic North Mountain Basalt (NMB) which forms a cuesta on the northern flank of the valley. In addition to the variable relief due to the bedrock geology, the area has had a complex glacial history with up to 4 different ice phases from the last glaciation. A thick blanket of till covers half of the North Mountain, while the rest of the North Mountain has a thin veneer of till. This contrast in cover material allows us to test the role of sediment supply to incision rates using the stream power model. Bedrock incision rates are determined by examining stream longitudinal profiles and relief derived from the LIDAR DEM. The high resolution and minimum artifacts in this DEM allow the generation of stream profiles with accuracies that previously were only available from field surveys. The three flow units within the NMB have been mapped using the DEM based on their topographic expression that results from their contrasting resistance to erosion. The effect of bedrock resistance to erosion will be tested by comparing the NMB stream profiles and relief with the streams on the SMB that are underlain by homogeneous granite.
Brendan Murphy J.
Gosse J.
Spooner Ian
Webster T. L.
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