MS GEORGINA HOLBECHE · TS004 60 – 180 carbonate material. Thin section of quartz dominated...

Profile

Georgina grew up in Victoria where on the completion of high school she undertook a

Bachelor of Arts degree at Monash University. She moved to Perth to

undertake her PhD under Professor Bob Gilkes. She is looking at one of several

engineering options for addressing salinity in the landscape and has relished the

opportunity to get out in the thick of things as well as conduct research with real

applications.

MS GEORGINA HOLBECHE

Georgina HolbecheProf. Bob Gilkes

Dr Richard George

10,000km of drainage in the Wheatbelt, what are the issues?

Background

Salinity represents one of the greatest problems facing agricultural productivity in the south-west of Western Australia.

As traditional plant-based solutions may prove unsuccessful engineering solutions provide new options for salinity management

Engineering alternatives

Relief and siphon boresSurface water managementGroundwater pumpingDeep drainage

Area of Blackboy Creek requiring surface water management

Cox 2005

Complexity of materials

Lee 1999

The complex, highly weathered landscape of Western Australia

An agricultural problem

Valley floors are occupied by sediments and highly weathered soils and are consequently complexRising groundwaters and associated salts threaten agricultural productivityDeep drainage has resulted in inconsistent degrees of successUnderstanding the materials may make deep drainage more predictable

Deep drain design

An open deep drain with a levee on both sides

An open deep drain with a levee on one side of the drain

EEI 2005

Drainage in the Wheatbelt of W.A.

Cox 2002Solomon 2005

Herringbone design in DumbleyungDeep drain near Wubin

Aims of research

To identify and understand the materials that are being drained

To develop a user-friendly classification system for predicting the impact of deep drainage prior to construction

Components of project

Field work

General observation of materials

Mineralogy

Chemistry

Microscopy

Hydrology (known)

Develop classification tool

Development of classification

Develop a better understanding of different types of valley floor materials and their propertiesInitial basis for classification

TextureStructureCoarse materialMottlingCementation

Good micro classification can be macro useful

Development of classification

Macro + Micro + Hydrology

Macro Classification Tool

Impact of material permeability

The properties of a material determine how it well it drains

Cox 2005

Diversity of drain materials

ClaySandCarbonatesCoarse sedimentsIndurated material (silica, iron oxides)

Examples of diverse materials

Mineralogy of drainage materials in W.A.

Typical XRD patterns for  three different  materials

0

200

400

600

800

1000

1200

3 13 23 33 43 53 63

Degrees 2‐Theta

Counts

ka olinite

quartz

goethite

feldspar

calcitedolomite

hematite

Mineralogy and drainage

The common regolith consists of kaolinite, quartz and feldspar

Some regolith has been impregnated by iron oxides or carbonates which will reduce permeability

Thin section of carbonate material

TS004 60 – 180 carbonate material

Thin section of quartz dominated material

WC021 45 – 60 quartz dominated material

Image analysis of pore size distribution

0 10 20 30 40 50 60 70 80 90 100

Micropo

0

10

20

30

40

50

60

70

80

90

100

esopore

0

10

20

30

40

50

60

70

80

90

0

KandKandKandKandKandiustox (Pc) Limestone

Kandiudox (Ak) LimestoneKandiustox (Ci) BasaltKandiudox (Ti) Basalt

Cryptopores = < 0.1 μm

Ultramicropores = 1 – 5 μm

Micropores = 5 – 30 μm

Mesopores = 30 – 75 μm

Macropores = > 75 μm

Mesopores Micropores

Macropores Tawornpruek 2003

Cryptopores contribute 23 – 35% of total porosityTotal pore volume = 30 – 50%

A practical application

Understanding micro features of samples (such as porosity)

Relate these to analogous macro features (such as texture)

Relate material properties to water flow

Make drainage prediction more user-friendly

Conclusions

Drains are constructed through highly diverse materials

Materials range from sand to clay resulting in large differences in hydraulic conductivity

Comprehension at a micro scale can assist the construction of a user-friendly classification system at a macro scale

Acknowledgements

GRDC for their generous funding

Department of Agriculture and Food, WA

School of Earth and Geographical Sciences

Mr Michael Smirk