Meeting new

challenges in

minesite landform

design

Rob Loch

Historically ….

Waste landforms were not designed;

Similar profiles used worldwide

No consideration of site materials & climate;

Poor aesthetics;

Commonly unstable; and

Failure to meet community expectations.

Metalliferous mines (gold)

Coal mines (Qld)

Coal mines (Hunter)

An alternative approach

Landform and erosion modelling has been used

since late 1990’s to produce:

Site- and material-specific landforms

Wide range of landforms

Demonstrated stability

Geomorphically sound landform approaches.

Example #1: Sand mine, NSW

Linear slopes;

Low gradients;

Use of tree debris

Control of flows.

December 2009

December 2010

Example #2: Gold mine, WA

Concave slopes;

Soil amelioration;

Use of tree debris;

Control of flows.

Example #3: Dredge spoil, WA

Linear slopes;

Preparation of rocky cover material;

Soil amendment and fertilisation.

What have we learnt?

Can produce a wide variety of designs and excellent outcomes

Modelling can be very accurate

Most critical where erosion hazard greatest

Provides a wide range of soil management and landscape guidance

High potential for development of aesthetically acceptable landforms

Accuracy

Performance of constructed designs has been

assessed;

Very close agreement between predicted and

observed erosion; but

Critical to use measured parameters; so

Quality in landform design planning is critical.

Accuracy of design simulations

Predicted and observed cumulative erosion rates for 20

batter slope locations on Western Australian mine sites

Using MEASURED

erodibility parameters

0 100 200 300 400 500Measured Cumulative Erosion (t/ha)

0

100

200

300

400

500

WE

PP

-Calc

ula

ted

Cu

mu

lati

ve E

rosio

n (

t/h

a)

1:1

R² = 0.987

But parameter inputs are critical

0 100 200 300 400 500Erosion Predictions (t/ha/y) UsingCalibrated WEPP Soil Parameters

0

100

200

300

400

500E

ros

ion

Pre

dic

tio

ns (

t/h

a/y

) U

sin

g

Inte

rna

lly

De

riv

ed

WE

PP

So

il P

ara

me

ters

1:1

Risk and slope height

0

5

10

15

20

25

30

35

40

45

0 100 200 300 400 500 600

Pre

dic

ted

ero

sio

n r

ate

(t/

ha

/y)

Horizontal distance (m) from crest

Risk and soil erodibility

0 40 80 120 160 200

Slope length (m)

0

100

200

300

400

Pre

dic

ted e

rosio

n r

ate

(t/ha/y

)

Topsoil

Conglomerate topsoil mix

Weathered conglomerate

Fresh conglomerate

Risk and soil infiltration capacity

0 4 8 12 16

Hydraulic conductivity (mm/h)

0

200

400

600

800

Pre

dic

ted

an

nu

al a

ve

rag

e e

rosio

n (

t/h

a/y

)

Measured conductivity = 0.4 mm/h

• Vegetation?

• Gypsum?

Potential impact of soil improvement

Risk and Climate

Impacts of vegetation

Management guidance

Modelling approach and associated assessments can guide:

Progressive rehabilitation to deal with high slopes;

Soil amendment to increase infiltration and reduce erodibility;

Identification of targets for revegetation (cover); and

Soil treatment (fertiliser) to ensure vegetation targets are met.

Risk factors

Low risk High risk

Rain >500 mm/y Rain ~300 mm/y

Non-erodible soils Erodible soils

Non-dispersive soils Dispersive & tunnel-

prone

Good vegetation growth

Poor vegetation growth

Low gradient slopes High gradient slopes

Low slopes (≤ 60 m

vertical)

High slopes (up to 200 m

vertical)

Capacity to design “natural” landforms

Concave profiles

Able to consider spatially variable materials

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

50

55

0

40

80

120

160

200

0 200 400 600 800 1000

Pre

dic

ted

ero

sio

n r

ate

(t/

ha

/y)

Lan

dfo

rm H

eig

ht

(m)

Horizontal Distance (m)

Bluff

Rock/Soil Mix

Vegetation Only

Rocky bluffs,

zones of varying

erodibility

Also able to:

• Incorporate swales and flow paths;

• Assess 3-D erosion patterns; and

• View the final vegetated product.

Considering aesthetics

No single, identifiable, "natural" landform shape or profile;

Mimicking nearby landforms may be dysfunctional;

Personal opinions of aesthetic quality may vary greatly;

Need some way to rate/assess aesthetic

Aesthetics: a “less bad” rating

1. Functionality (stability, water quality);

2. Sustainability (vegetation);

3. Non-linear batters (concave profile);

4. Non-linear plan footprint;

5. Non-linear top outline;

6. Geomorphic features (swales, cliffs).

Landloch has used a progression of: 1 star

6 star

So basically 3 design options:

1. Mimic natural landforms.

2. Mimic natural landforms, assess with erosion

and landform evolution models.

3. Design using models and typical landform

features.

Pros and cons of design options

Option 1 (Natural Design only) may well not be

stable if:

Topsoil and waste are more erodible than

“natural” soil and rock;

Vegetation performance is poorer than in

analogue areas; and/or

Climate change alters erosion risk.

Clearly best applied in low-risk situations.

Pros and cons of design options Option 2 (Natural Design followed by

erosion/landform modelling) will achieve:

Initial design based on natural landforms;

Modification of the design to ensure stability

and sustainability;

Guidance on material management and

rehabilitation practices; and

Demonstrated landform stability.

Applicable to higher risk situations.

Pros and cons of design options

Option 3 (Design using erosion/landform

modelling) can achieve:

Stable, sustainable design based on natural

landforms;

Guidance on material management and

rehabilitation practices; and

Demonstrated landform stability.

Applicable to higher risk situations.

Assessing options

Deciding the optimal approach may not be easy, but:

It IS more appropriate for a landform to be designed on the basis of site climate and soil properties than on the properties of the surrounding hills; and

landform; there is scope for considerable variation.