Mt. Nusatsum

Mt. Nusatsum

Tuesday, November 9, 2010


One of the usual outcomes of any stream high water event like the Great Flood of 2010, is the transfer of silts, sand, gravel and rock - all considered part of the bedload of the stream.  The amount of bedload and the type that moves during a flood is all proportional to the size of the event.  In the Great Flood of 2010, there was a lot of bedload movement because it was a really BIG event for this watershed.  Now that the Bella Coola River and the tributaries are getting down to more normal levels, the extent of the bedload changes are really becoming evident.  Some of the side creeks like Noosgulch and Cachootin Creek also appear to have had debris torrents which are liquefied masses of gravel, rock and wood.

Fresh bedload from side creek 3-4 metres deep
The short term implications of the bedload are readily apparent and being dealt with by the digging going on in Snootli, Thorsen Creeks and Klonnik Creeks, which with dykes on both sides have resulted in full and overflowing situations.   What is less obvious and will only become apparent with time and observations during more moderate floods is the effect on the Bella Coola River.  All those 1000's of cubic metres of material that came into the system are still there somewhere - only the finest particles went to sea and added to the great Bella Coola Estuary to make it  imperceptibly but slightly larger.  Spread throughout the Bella Coola River it will now have a deeper channel in some areas, shallower and wider in others.  It's part of the long term consequences we won't know the full extent of  and how to deal with them for years.  We are not alone though - the Pemberton Valley near Whistler BC also has a long flooding history and with 40 km of dykes, it can become a complex management problem.  They seem to have a comprehensive system of monitoring and putting some science to the situation.  Grizzly

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