characterising superficial deposits through 3d mapping and ... · processes and environments: •...

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Characterising superficial deposits through 3Dmapping and modelling

Andy Farrant & Jon Ford


Superficial Deposits

Extensive cover of superficial deposits:Approx. 60% of the UK is covered bysuperficial depositsThickness generally less than 10 m,but over 100 m in placesMain basins: East Anglia, The Wash,Vale of York-Teeside, Holderness,Cheshire Basin and Morecombe Bay

Huge range of materialGlaciogenic deposits (till, moraines)Glaciofluvial depositsFluvial (river terraces & alluvium)Colluvial and periglacial sedimentsBiogenic sediments (peat, tufa)Marine (raised beaches)


Superficial Deposits are inherently complicated

Processes and environments:• rapid spatial variation (e.g. ice-

margins)• rapid changes with time (e.g.

shift between deposition, erosionand deformation)

• scale of change (vertical andhorizontal) typically greater thanbedrock)

Spatial and temporal complexity directlyaffect deposit:

• geometry• properties• structure

These all affect groundwater flow

Vale of York c. 20 ka BP!


Hydrogeological properties vary considerably

• Extensive glacial deposits innorthern & eastern England:• Beneath cities and arterial

infrastructure• Concealing regional aquifers

• Existing geological mapsrepresent 2D surface data only• Don’t represent true

variability and spatialdistribution

• 3D representation and 4Dthinking is key:• resolve concealed

geometries and relationships• framework to visualise

physical properties andsimulate processes

‘Till’ (blue)– rangingfrom ‘aquitard’ stiffclay to ‘aquifer’loose sand andgravel; highlyirregular thicknessand ‘rockhead’geometry

‘Glaciolacustrinedeposits’ (orange)–ranging from‘aquitard’ stiff clayto ‘aquifer’ runningsand; concealedbeneath till and‘coversand’


Subsurface investigation and geologicalmodelling solutions

• Integrated approach combining:• Data acquisition → compilation → interpretation (3D modelling) → outputs

• Example: Buried Channel Study – Doncaster area (BGS, Yorkshire Water, Arup):• detailed geometry and properties of sub-glacial channels• informing Nitrate Vulnerability Zones for the Sherwood Sandstone Group aquifer• combining existing borehole data, drilling, geophysics and modelling

Passive seismic profile across northern edgeof buried channel

Velocity profiling from drillcore


• Integrated approach combining:• Data acquisition → compilation → interpretation → outputs

• Example: Buried Channel Study – Doncaster area (BGS, Yorkshire Water, Arup):• highly irregular rockhead relief (76 m)• >50 m deep clay-rich deposits juxtaposed against ‘bare’ sandstone at surface• highly variable bedrock weathering

Rockhead elevation based on calibrated seismicplus depth of bedrock weathering Rockhead based on seismic and BHs

22m

-54m

Subsurface investigation and geologicalmodelling solutions

Reduced uncertainty and hidden complexity

• 3D characterisation reduces uncertainty and can reveal previously unrecognised geologicalcomplexity that is hydrogeologically significant

• Example: Selby Superficial Deposit Model (BGS, EA):• detailed representation of the extensive, thick Quaternary cover• informing aquifer recharge and vulnerability of the Sherwood Sandstone

SherwoodSandstone‘rockhead’surface

WeatheredbedrockEarlyglaciolacustrinedeposits

Till sheetEsker andglaciofluvialdeposits

Lateglaciolacustrinedeposits

“Cover sands”River deposits

• Impact of 3D models increase when integrated with other data and systems:• visualised dynamically in the context of other spatial data• translated into thematic representations with applied attribution• integrated with geological data / models of the bedrock• incorporated in numerical groundwater simulations at a range of scales

5000m

10km30m

40km

SelbySuperficialDeposit Model

Buried Channel Study

UK3D – NationalBedrock Model

Reduced uncertainty and hidden complexity


Buried Valleys

Buried valleys can impact ongroundwater flow in the Chalkand other aquifers.

Poorly characterised, not wellrepresented on 2D geologicalmaps.

BGS has an on goingresearch project to useborehole data and data miningto understand the locations,geometry and fills of buriedvalleys across the UK


National Buried Valleys dataset

GIS dataset soon to be freely availableon the Open Geoscience area ofwww.bgs.ac.uk –

Contact Dr Tim Kearsey([email protected]) if you want to benotified when it released


The ChilternsChalk aquifer with an extensivesuperficial cover including:

Clay with flintsPre-Anglian Thames terraces(Vale of St Albans)Anglian glacial deposits (icemarginal setting & buried valleys)Post Anglian terraces and alluvialdeposits

Old 2D maps not suitable for modernhydrogeological modelling.

EA, water company & BGS fundedprogramme of remapping & 3Dgeological modelling

Superficial cover more extensivethan previously mappedThames terraces now subdividedBuried valleys characterisedRevised Anglian limit

Anglian limit


Runoff

Post-diversion Thames &Colne valley terraces

Anglian deposits

Pre-diversionary Thames (pre-Anglian MIS12) terraces

Thames TerracesStaircase of gravel deposits, spanning 180 m elevation and 2.5Ma. Identifiable on digital terrain models.

Not to scale


Chess & Misbournecatchments


Hemel Hempstead

Redbourn

Kensworth

Luton

St Albans

Ver catchment


Karst FeaturesKarst features are often associated withsuperficial deposits.Many stream sinks around glacial till outcrops(focussed recharge)Suffosion sinkholes often developed in glacialtill & terrace deposits over limestoneVery irregular rockhead beneath River Terracegravels and Clay-with-Flints.Evidence of deep sediment filled dissolutionpipes beneath superficial deposits (M25 SladeOak Lane, HS2 boreholes)

M25 Slade Oak Lane– sediment infilled

sinkhole 37 m deep(Gibbard 1986)

Sinks draining till outcrop, Mimram catchment


Superficial deposits are extensive and veryheterogeneous with rapid facies changes.

• 2D maps do not represent the geologicalcomplexity of superficial deposits

• 3D geological models better forunderstanding temporal and spatialvariability

3D modelling increasingly used to characterisesuperficial deposits. New datasets used to createmodels include:

• Updated geological mapping• Borehole data (including geophysical logs)• Lidar & digital terrain models• Geophysical methods (passive seismic)• Geochronology (dating & biostratigraphy)

Used to create better conceptual models forgroundwater modellingCan be attributed with physical properties and dataexported into other modelling packages

Conclusions


Thanks to:Michael Kehinde Rolf Farrell Nigel HoadMichael Jones Jo Thompson Helen SmithIlias Karapanos Keith Westhead Rowan VernonEdward Wrathmell Lou Maurice Romaine GrahamHaydon Bailey Melinda Lewis Peter HopsonRhian Kendall Tim KearseyAlessandro Marsili Mark Woods

characterising superficial deposits through 3d mapping and ... · processes and environments: •...

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