GNS Science

P. White GNS Science

C. Tschritter GNS Science

P. Davidson Marlborough District Council

3D models of sedimentary lithologies and piezometric levels to understandgroundwater and surface water flows, Wairau Plains, New Zealand… and web-based access to 3D model data

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Acknowledgements

Thanks to:

•Harvey Thorleifson for the invitation to present this talk•GNS Science Groundwater Resources Research Programme for 3D model development (Wairau Plains) and GNS ‘seed’ funding (web site).•Groundwater managers for in-kind and direct support on model development, particularly Marlborough District Council and Bay of Plenty Regional Council (Janine Barber)

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Outline of the talk

Methods

3D models of geology and groundwater level: example of Wairau Plains

Web-based access to model data•Web site demo

Software used in talk: Earthvision and home-built including web and FORTRAN

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Methods Building 3D geological models: two main types

• Lithology (3D) These models are used to understand the distribution of

sediments relevant to aquifers systems and are particularly useful when interpreting drillers’ logs

• Chrono – stratigraphic (typically 2D surfaces) These models aim to understand strata in relation to time

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Lithological models: a statistical approach with geological logs

Useful because we are uncertain about the quality of well logs

We use ‘pseudo-logs’ e.g. blue = water bearing pink = other

Well log and pseudo logReference: White, P.A. and Reeves, R.R. 1999. Waimea Plains aquifer structure as determined by three-dimensional computer modelling. Journal of Hydrology (NZ) 38 (1) 49-75.

The 3D model itself has an important role in data-quality checking

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Lithological models: a statistical approach with geological logs

2) Pseudo-logs are plotted in 3D space

3) …and then modelled as continuous distribution in 3D as 3D grid and 3D ‘faces’ file

4) Models developed separately for: gravel;sand; silt and clay.

1) Well log data quality checks

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3D models of static groundwater level in 3D

1) Quality checks of static groundwater level data (e.g. remove wells where level is influenced by pumping)

2) Assemble as 3D points

3) Model as continuous 3D distribution in a conformal grid

Holocene Gravel aquifer

Holocene/ Pleistocene Gravel aquifer

Confined areaUnconfined area

Static groundwater level (colour) and elevation of the base of the screen.

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Web site access to model data

Aim: access to 3D model data for everybody, e.g.:•education (e.g., children)

•drillers

•groundwater managers

•Scientists

•general public

Some criteria:•not dependent of proprietary software

•intuitive

•fast

•access to models from the field (i.e., smart phones)

•uncertainty

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An example of 3D models: Wairau Plain

One purpose of this work: how does groundwater recharge travel to spring-fed streams?

•Important to water management in the area

The following slides show the results of:

•Development of 3D models (geology and piezometric level)•Comparison of 3D geology and 3D piezometric level•Groundwater budget

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Wairau Plain

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Wairau Plain geology and historic hydrology

Yellow = alluvial in westmarine/estuarine in east

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Study area: 1165 geological logs1562 static water level measurements

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Results: 3D geological model: combines chrono- and lithology modelsMain purpose is to assess the distribution of Holocene gravels, sands and silts/clay

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Results: 3D piezometric model and 2D water table

Piezo contours in 3DPiezo contours in 2D

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Results: 3D geological model, piezometric model and groundwater budget

Budget component

Groundwater budget zone

West of

transition

(m3/s)

Transition

(m3/s)

East of

transition

(m3/s)

Inflow

P 1.6 1.2 1.5

QGWIN (Wairau River) 7 0 0

QGWIN (other rivers) 1 0 0

QGWIN (boundary) 0.1 8.1 0.8

Outflow

ET -1.4 -1.1 -1.4

UGW (irrigation) -0.2 -0.2 -0.3

UGW (municipal) 0 -0.1 0

QSWBF 0 -7.1 -0.5

QGWOUT (boundary) -8.1 -0.8 -0.1

Approx 90% of nett gw inflow (Transition zone and west) flows to spring-fed streams West – east sections

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Web-based access to model data

Aims to provide model information to anyone

http://data.gns.cri.nz/ebof/

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Web access to model data: Aims to provide model information to anyone

GNS Science has a programme of sub-regional 3D model development

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Earth Beneath Our Feet web site:

Aim to represent:

Layers Properties and uncertainty

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Conclusions

3D models•Models of lithology, chrono-stratigraphic units, when combined with models of static groundwater levels are very useful in understanding coastal aquifer systems

•These models shown that most groundwater recharge in the Transition zone and west (approx 90%) flows to springs

•This has significant implications for management of the system

Web-based access to model information•shown to be great fun

•… and it’s useful for groundwater managers

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Thanks very much