Quadra Sand

Hydrostratigraphic Unit

Project
Nanaimo Lowlands

Datasets

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Quadra Sand unit description

Update:2016-02-02
Quadra Sand overlies the Cowichan Head Formation and is generally found above current sea level and below 100 m. It can exceed 75 m in thickness. The Quadra hydrostratigraphic unit aquifer is present across the study area except along the main rivers where the Quadra Sand has been eroded by rivers and where locally eroded and infilled by Vashon Till. It consists of horizontally and cross-stratified, well-sorted sand with minor silt and gravel with wood and peat lenses in its lower portions. Geochemically the Quadra is distinguished from other units by the Sr concentrations throughout the unit (including the upper Cowichan Head Formation; Knight et al., 2015). Quadra is interpreted to be outwash deposited during the transition from non-glacial to glacial conditions at the onset of the Fraser Glaciation (Armstrong and Clague, 1977; Clague, 1977, 1976). In general the Quadra Sands can be regarded as proglacial outwash formed subaerially on outwash plains extending across and along the margins of the present-day Strait of Georgia. The Quadra Sand is the most important water-bearing unit in the study area. The upper part of the Quadra Sand has a fluvial erosional contact. Large incised and subsequently sediment-filled channels can be observed at the top of the unit.
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%).
Area227.00 km2
Lithology
DescriptionQuadra Sand consists of horizontally and cross-stratified, well-sorted sand with minor silt and gravel with wood and peat lenses in its lower portions.
Source
Aquifer
Aquifers

Unit properties

Surficial aquifer media
Typical value:porous
Description sand and gravel
Confinement
Typical value:confined
Description The aquifer is mostly confined in the north-west region while it is mixed (semi-confined to confined) in the south-east region.
Source Three dimensional hydrostratigraphic model of the Nanoose - Deep Bay area, Nanaimo Lowland, British Columbia
Methode To determine the confinement conditions of the Quadra aquifer, the hydrostratigraphic relationships of the different units were used (Benoit et al., 2015). The following confinement conditions were used: (1) unconfined aquifer when sand and / or gravel is present and when the till thickness is <3 m; (2) semi-confined aquifer when the till thickness is> 3 m and clay and / or silt is present with a thickness <5 m; (3) confined aquifer when the clay and / or silt thickness is &#8805;5 m.
Groundwater storage
Description Specific storage: 1.5E-4 (1/m)
Surficial sediment thickness
Hydrogeological unit thickness
Description Mean thickness 19 m; median thickness 15 m
Well depth
Range: [9.9 to 81] m
Surficial unit hydraulic conductivity
Range: [2e-06 to 0.0046] m/s
Source Compendium of Re-evaluated Pumping Tests in the Regional District of Nanaimo, British Columbia
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 For the lowland area, recharge calibrated values range from 112 to 396 mm/yr. Recharge for the unit: 400 mm/yr
Regional discharge
Description The regional analysis of the water budget reveals that 71% of the groundwater is discharging to surface water bodies, whereas the remaining 29% discharges along the coast of the Strait of Georgia.
Hydrogeological unit potential
Typical value:high
Description The Quadra Sand is the most important water-bearing unit in the study area.
Groundwater usage
Typical value:porous
Description The total annual anthropogenic groundwater extractions (from private wells, agriculture and community systems) is approximately 22,336,047 m3. The main users are: - City of Qualicum Beach (serving approximatively 9 350 people): 1 574 962 m3 - City of Parksville (serving approximatively12 685 people): 1 239 550 m3 - Regional District of Nanaimo (serving approximatively 4 576 people): 434 390 m3
Source Nanoose Bay - Deep Bay Area, Nanaimo Lowland Groundwater Study Atlas, Regional District of Nanaimo, British Columbia
Aquifer vulnerability
Threats
Description The Quadra is likely to be only slightly affected by seawater intrusion, even under intensive pumping near the coast.