Till de Vashon

Hydrostratigraphic Unit

Project
Nanaimo Lowlands

Datasets

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Till de Vashon unit description

Update:2016-02-02
The Vashon Till overlies the Quadra Sand with thickness generally up to 30 m, except where depressions left by deeply eroded Quadra Sand were filled by approximately 60 m of drift (Fyles, 1963). Vashon Till is composed of gravel, sand, but mostly silt and clay. The unit is considered an aquitard. The till of this unit was deposited during the last deglaciation. Over the lowland, Vashon Till tends to be a sandy diamicton except within some valleys where the matrix is more clayey. The Vashon Drift unit is composed of two hydrostratigraphic units: Vashon coarse Sediments (of the Vashon-Capilano) and the Vashon Till. The geochemical signature of Vashon Drift has a number of complicated trends over the unit thickness (Knight, 2015).
Physiography
Hydrogeological regionCordillera
Hydrogeological context
ReliefThe regional topography ranges from sea level at the coast, up to 1819 m (Mount Arrowsmith). The coastal plain terrain is sub-horizontal with slopes lower than 6% except along incised rivers valleys (up to 20%).
Area425.00 km2
Lithology
DescriptionThe Vashon Till is composed of gravel, sand, but mostly silt and clay. The till of this unit was deposited during the last deglaciation. It is interpreted to be ground moraine deposits.
Source
Aquifer
Aquifers

Unit properties

Groundwater storage
Description Specific storage: 8.0E-5 (1/m)
Surficial sediment thickness
Hydrogeological unit thickness
Description mean thickness 12 m and median thickness 7 m
Well depth
25 m
Surficial unit hydraulic conductivity
Range: [8e-08 to 5e-06] m/s
Source Aquifer Hydraulics: A Comprehensive Guide to Hydrogeologic Data Analysis
Regional precipitation
Description The total precipitation is typically up to 5000 mm in the mountains (Mount Arrowsmith) (Waterline, 2013).
Source Regional District of Nanaimo Phase One Water Budget Project
Regional recharge
Description Recharge for the unit: 50 mm/yr