Metadata: 3D hydrostatigraphic model of Nanaimo Lowlands

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Abstract

The study area is a coastal strip running from Nanoose to Deep Bay on eastern Vancouver Island (~580 km2). The 3D model was developed using existing driller's logs, published cross-sections and new data which include rotosonic coring, borehole geophysics logs, seismic reflection profiles and surficial geology mapping. The detailed surficial geology consists of 31 different units which, for modelling, are grouped into 9 major hydrostratigraphic units (from youngest to oldest): Capilano-Salish (sand aquifer), Capilano glaciomarine (silty clay aquitard), Vashon-Capilano (coarse sand and gravel aquifer), Vashon (till aquitard), Quadra (sand aquifer), Cowichan-Dashwood (compact silt aquitard), Dashwood-Mapleguard (sand aquifer), sedimentary bedrock and metamorphic bedrock (aquifer near surface with potential decreasing with depth). This succession of Late Pleistocene to Holocene sediments is up to 140 m thick and is present over most of the study area, thinning to the southwest with rising topography and bedrock outcrops. Capilano-Salish and Vashon-Capilano deposits are shallow and contain unconfined aquifers with relatively high vulnerability to surface contamination and low groundwater resource potential due to their limited thicknesses. Quadra Sand is the most exploited aquifer unit. It underlies the ubiquitous and low permeability Vashon till and it overlies Cowichan-Dashwood aquitard or bedrock. Quadra sediment has an average thickness of 19 m and it is generally above sea and river levels. This would minimize the potential of seawater intrusion and direct surface water extraction, respectively, in the event of intensive groundwater extraction in Quadra unit. The Quadra is an important aquifer, however only about one-third of its thickness is saturated likely due to the overlying Vashon till aquitard that limits groundwater replenishment. Dashwood-Mapleguard sand is a lower confined aquifer unit that extends below sea level. It may have hydrogeological properties and resource potential similar to the Quadra sand, but it is present only in areas where the bedrock elevation is low, generally closer to the coastline. It may be more vulnerable to sea water intrusion, and remains poorly understood. The relatively low permeability regional bedrock aquifers of the Nanaimo Group are generally exploited only where the Quadra aquifer is not present. Their hydrogeological potential is poorly understood due to lack of subsurface data. This hydrostratigraphic model will be used to support groundwater flow modelling. The numerical files include thickness of each hydrostratigraphic unit in a georeferenced raster format.
Status:register completed
Title3D hydrostatigraphic model of Nanaimo Lowlands
Date2015-01-01 (register publication)
Date2015-01-01 (register creation)
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Edition date
Citation group
register pointOfContact
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OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada
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AddressDelivery point :
City :
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Postal code :
Country :
Email nrcan.gsc-geosciencedata-donneesgeoscience-cgc.rncan@canada.ca
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Citation group
register principalInvestigator
NameNicolas Benoît
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada - GSC Quebec
Position
Information
AddressDelivery point : 490, rue de la Couronne, 3e étage 490, rue de la Couronne, 3e étage
City : Québec Québec
Administrative region : Québec Québec
Postal code :
Country : Canada Canada
Email nicolas.benoit@canada.ca
Telephonetelephone voice; 1 (418) 6543646
Online Resource
Citation group
register originator
NameNicolas Benoît
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada - GSC Quebec
Position
Information
AddressDelivery point : 490, rue de la Couronne, 3e étage 490, rue de la Couronne, 3e étage
City : Québec Québec
Administrative region : Québec Québec
Postal code :
Country : Canada Canada
Email nicolas.benoit@canada.ca
Telephonetelephone voice; 1 (418) 6543646
Online Resource
Citation group
register custodian
NameFrancois Letourneau
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada - GSC Quebec
Position
Information
AddressDelivery point : 490, rue de la Couronne, 3e étage 490, rue de la Couronne, 3e étage
City : Québec Québec
Administrative region : Québec Québec
Postal code :
Country : Canada Canada
Email francois.letourneau@canada.ca
Telephonetelephone voice; 1 (418) 6543826
Online Resource
Presentation formregister modelDigital
SeriesOpen File7796

Related publication

  • Benoit, N., Paradis, D., Bednarski, J.M., Hamblin, T., and Russell, H.A.J., 2015. Three dimensional hydrostratigraphic model of the Nanoose-Deep Bay area, Nanaimo Lowland, British Columbia. Geological Survey of Canada, Open File 7796, 1 .zip file.

Goals

To support improved sustainable groundwater management of the Nanaimo Lowland, British Columbia (BC), a three-dimensional (3D) hydrostratigraphic model was developed for the Nanaimo Lowland aquifer system.

Keyword(s)

Thesaurus
TitleGovernment of Canada Core Subject Thesaurus
Date2004 (register creation)
Date2013-05-11 (register publication)
Edition
Edition date
Citation group
register custodian
Name
OrganisationGovernment of Canada; Library and Archives Canada
Position
Information
Typeregister
TermHydrogeology
Thesaurus
TitleNRCan - GSC - Hydrogeology - Thesaurus
Date2009-01-01 (register creation)
Edition
Edition date
Citation group
register pointOfContact
Name
OrganisationCommission Géologique du Canada - Geological Survey of Canada
Position
Information
Typeregister thème
TermGroundwater
Thesaurus
TitleNRCan - GSC - Hydrogeology - Thesaurus
Date2009-01-01 (register creation)
Edition
Edition date
Citation group
register pointOfContact
Name
OrganisationCommission Géologique du Canada - Geological Survey of Canada
Position
Information
Typeregister produit
Term3D Model
Thesaurus
TitleNRCan - GSC - Hydrogeology - Thesaurus
Date2009-01-01 (register creation)
Edition
Edition date
Citation group
register pointOfContact
Name
OrganisationCommission Géologique du Canada - Geological Survey of Canada
Position
Information
Typeregister thème
TermAquifer
Thesaurus
TitleNRCan - GSC - Hydrogeology - Thesaurus
Date2009-01-01 (register creation)
Edition
Edition date
Citation group
register pointOfContact
Name
OrganisationCommission Géologique du Canada - Geological Survey of Canada
Position
Information
Typeregister endroit
TermNanoose - Deep Bay area
Thesaurus
TitleNRCan - GSC - Hydrogeology - Thesaurus
Date2009-01-01 (register creation)
Edition
Edition date
Citation group
register pointOfContact
Name
OrganisationCommission Géologique du Canada - Geological Survey of Canada
Position
Information
Typeregister thème
TermQuaternary
Spatial representationregister grid
Resolution
Languageeng; CAN
Character encodingutf8
Thematic categorygeoscientificInformation
ExtentLocalisation
-124.833000000,49.167000000;-124.500000000,49.500000000
Supplemental information

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Specific information related to data distribution
Format
NameASCII GRID
Versionnot applicable

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register pointOfContact
Name
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada
Position
Information
AddressDelivery point :
City :
Administrative region :
Postal code :
Country :
Email nrcan.gsc-geosciencedata-donneesgeoscience-cgc.rncan@canada.ca
Telephone
Online Resource

Distributor

Contact
register distributor
NameEric Boisvert
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada - GSC Quebec
Position
Information
AddressDelivery point : 490, rue de la Couronne, 3e étage 490, rue de la Couronne, 3e étage
City : Québec Québec
Administrative region : Québec Québec
Postal code :
Country : Canada Canada
Email eric.boisvert2@canada.ca
Telephonetelephone voice; 1 (418) 6543705
Online Resource

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Lineage is the description of the sources and steps used to create the current dataset.


Introduction
Process step Sources
The unconsolidated sediment in the study area is comprised of marine, fluvial and glacial materials of Pleistocene and Holocene age. They generally form an extensive cover and can exceed 100 m in thickness. The Nanaimo Lowland is covered by a succession of two groups of glacial deposits (Vashon and Dashwood) separated by non-glacial deposits (Cowichan Head formation) and proglacial outwash deposits (Mapleguard and Quadra), which are postglacial marine and fluvial deposits. The architecture of the aquifer system is defined with 9 hydrostratigraphic units, which are ordered according to their relative chronology, as follows from top (younger) to bottom (older): I. Capilano-Salish (aquifer): Composed of deltaic and fluvial sediments close to main rivers. II. Capilano Glaciomarine (aquitard): The study area is covered by thick glaciomarine and marine deposits that are relatively impermeable due to their mostly fine grain-size. III. Vashon-Capilano Coarse (aquifer): Composed of coarse glaciofluvial outwash gravel and sand deposits located at the mountain/lowland junction. IV. Vashon Till (aquitard): Over the lowland, Vashon Drift tends to be a sandy diamicton except within some valleys where the matrix is more clayey. Vashon Drift also includes sand and gravel in eskers, kame terraces, and ice-contact fans and deltas. V. Quadra (aquifer): The Quadra Sand consists of horizontally and cross-stratified, well-sorted sand with minor silt and gravel. Quadra is interpreted to be outwash deposited during the transition from non-glacial to glacial conditions at the onset of the Fraser Glaciation. In general the Quadra sands can be regarded as proglacial outwash formed subaerially on outwash plains. It is present almost everywhere over the study area except along the main rivers where it has been eroded by rivers or cut-and-filled by the Vashon till. The Quadra Sand is the most important water-bearing unit in the study area. VI. Cowichan-Dashwood (aquitard): Dashwood Drift is generally comprised of muddy diamicton glaciomarine sediment overlain by cobbles and gravel. Cowichan Head Formation unconformably overlies the Dashwood Drift. The formation has been divided into a lower member of clayey silt and sand, and an upper member of sandy silt and gravel. VII. Dashwood-Mapleguard (aquifer): Mapleguard sediments are the oldest Pleistocene deposits present in the Nanaimo Lowland. They are composed of bedded sand, silt, clay and minor gravel. Mapleguard proglacial outwash deposits could be coarser than the Quadra Sand and are expected to have good aquifer potential; however, the vertical and spatial extend of this unit is not well constrained. The grain-size of Mapleguard sediment is expected to be finer with depth and could transition into an aquitard unit. VIII. Bedrock - Sedimentary (aquifer): The sedimentary bedrock aquifer is mostly sandstone and conglomerate in the study area and generally has low to moderate aquifer potential especially when fractures are present. IX. Bedrock - Metamorphic (aquitard). Metamorphic and Intrusion bedrock in the area is generally considered to be an aquitard unit.
Standard recognized succession. Deep rotosonic wells.
The Hydrostratigraphic Modelling defines the distribution and thickness of the hydrostratigraphic units in 3D based on a synthesis of available geological and hydrogeological information. The integration of available data for the construction of the hydrostratigraphic model was mainly completed using Leapfrog® Hydro software. The lower contact of the model is fixed at an elevation of 400 m below sea level in the bedrock, whereas the top is constrained by the DEM. The 2D plane mesh resolution of the model was set to 70 m, which was applied to each contact surface. For purposes of modelling in the Leapfrog® environment, all basal unit contacts are defined as depositional surfaces. That is, younger surfaces do not cut older surfaces. The bedrock surface was interpolated from outcrop observations and bedrock-sediment contacts identified in public water well records and seismic surveys. The bedrock elevation was thus estimated by kriging with external drift on the DEM using an omnidirectional variogram with four structures (variance proportion, range in meters): (i) nugget (0.3, 0); (ii) spherical (24.9, 1240); (iii) Gaussian (31.2, 6076); and (iv) spherical (43.6, 7688). The interpolated bedrock surface generated with SGeMS was then integrated within LeapFrog® Hydro as a grid surface. Note that some wells that were drilled in deep sediment, without intercepting bedrock, were used as a bedrock surface maximum. All other contact surfaces that correspond to unconsolidated sediments were defined in Leapfrog® Hydro and constrained between the DEM and the bedrock topography using existing stratigraphic columns and cross-sections, the updated surficial geology map, rotosonic cores and seismic surveys. Elevation constraints were also imposed on some hydrostratigraphic units according to their respective depositional environment. When well depths and geological descriptions allowed, hydrostratigraphic information extracted from public water well records were also used to interpolate sediment contact surfaces.
The hydrostratigraphic model was built from existing geological information and additional data collected specifically for this project. The compilation of existing data includes: Digital Elevation Model (DEM) at a 30x30 m grid resolution; Public wells database: After filtering and validation 708 bedrock wells and 570 surficial wells were retained. Surficial geological map including stratigraphic columns and a cross-section. Data collected for this project include: Seismic reflection surveys: 42 km of two dimensional (2D) surveys collected along 15 lines; Rotosonic coring: 3 cores of surficial sediments ranging from 65 to 140 m; Borehole geophysics: surveys in 5 wells (4 surficial and 1 bedrock) that include gamma, induction, temperature, fluid resistivity, magnetic susceptibility and compressional (p-wave) and shear (s-wave) waves logs.


Technical details and constraints

File identifierbb8e7bfc-8b29-0421-718d-a420c72a9a0d
Languageeng; CAN
Character encodingregister utf8
Hierarchical classificationregister dataset
Date2017-03-24
Metadata standardNorth American Profile of ISO 19115:2003 - Geographic information - Metadata
VersionCAN/CGSB-171.100-2009
Constraints
Update frequencyregister asNeeded

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register Frenchregister Canadaregister utf8

Geographic Reference System

Reference System codeEPSG:26910
Registerhttp://www.epsg-registry.org/
Version6.14

Metadata Contact

register pointOfContact
Name
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada
Position
Information
AddressDelivery point :
City :
Administrative region :
Postal code :
Country :
Email nrcan.gsc-geosciencedata-donneesgeoscience-cgc.rncan@canada.ca
Telephone
Online Resource
register pointOfContact
NameFrancois Letourneau
OrganisationGovernment of Canada; Natural Resources Canada; Geological Survey of Canada - GSC Quebec
Position
Information
AddressDelivery point : 490, rue de la Couronne, 3e étage 490, rue de la Couronne, 3e étage
City : Québec Québec
Administrative region : Québec Québec
Postal code :
Country : Canada Canada
Email francois.letourneau@canada.ca
Telephonetelephone voice; 1 (418) 6543826
Online Resource