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TitleMonitoring flood-related change in bathymetry and sediment distribution over the Squamish Delta, Howe Sound, British Columbia
AuthorBrucker, S; Hughes-Clarke, J; Beaudoin, J; Lessels, C; Czotter, K; Loschiavo, R; Iwanowska, K; Hill, P RORCID logo
SourceFlood-related change on the Squamish Delta, proceedings of the U.S. Hydro 2007 Conference; by Bruker, S (ed.); 2007, 16 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20070120
MeetingU.S. Hydro 2007 (Hydrographic Society of America); Norfolk, VA; US; May 14-17, 2007
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia
AreaHowe Sound; Squamish Delta; Squamish
Lat/Long WENS-123.5000 -123.0000 50.0000 49.7500
Subjectssedimentology; geophysics; floods; flood plains; flood potential; deltas; deltaic sediments; deltaic deposits; sediment distribution; sediment transport; bathymetry
Illustrationslocation maps; plots; images
ProgramGeoscience for Oceans Management
AbstractThe Squamish Delta is a particularly rapidly growing wedge of sediment that is prograding into a > 200m deep fjord. Comparisons of historic surveys since the 1970's clearly indicate annual accretion rates of over 1m per year for much of the upper delta. The first geomorphologic investigations in the early 1980's using sidescan successfully revealed the morphology but lacked the positioning confidence to prove change. More recently in 2004 and 2005, two EM1002 multibeam surveys were conducted of the lower delta face which were able to resolve the detailed morphology and prove that over a year, major change was present including deepening of channels and the build up of a distributary lobe on the lower delta slope. In 2006 two precise multibeam surveys using EM3002 were conducted of the whole delta slope, for the first time imaging up to the 5m contour. PPK GPS supplemented by local tide gauges provided the vertical control and extensive MVP profiling was conducted to minimise water mass driven error sources. The surveys reveal the same gross morphological detail but had improved accuracy and resolution revealing smaller scale change. In addition to the bathymetric surveys, the multibeam backscatter was reduced for analysis (and groundtruthed with 20 grabs). Particular complications exist as the range of water depths extended to close to the extinction limit of the 300 kHz sonar. Adjustments to the attenuation coefficient to allow for the anomalous fresh water content were necessary. In addition, as the sonar was using narrow angular sectors (as little as +/-30° in depths greater than 180m), and there was considerable short-wavelength slope variation due to bedforms and rotational slumping features, there was a strong grazing angle dependence overprinted on the sediment signature. Algorithms were implemented to estimate the local 3D grazing angle to correctly predict the location and migration of the points of near-normal incidence. Only after correction for these effects, could the variation in sediment type be separated from the strong textural overprint of the changing imaging geometry.

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