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
December 2009
December 2010
Linear slopes;
Low gradients;
Use of tree debris
Control of flows.
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.
WEPP-Calculated Cumulative Erosion (t/ha)
Accuracy of design simulations
500
400
1:1
300
Using MEASURED
erodibility parameters
200
100
R² = 0.987
0
0
100
200
300
400
Measured Cumulative Erosion (t/ha)
500
Predicted and observed cumulative erosion rates for 20
batter slope locations on Western Australian mine sites
Erosion Predictions (t/ha/y) Using
Internally Derived WEPP Soil Parameters
But parameter inputs are critical
500
400
1:1
300
200
100
0
0
100
200
300
400
Erosion Predictions (t/ha/y) Using
Calibrated WEPP Soil Parameters
500
Risk and slope height
45
Predicted erosion rate (t/ha/y)
40
35
30
25
20
15
10
5
0
0
100
200
300
400
Horizontal distance (m) from crest
500
600
Risk and soil erodibility
Predicted erosion rate (t/ha/y)
400
300
Topsoil
Conglomerate topsoil mix
Weathered conglomerate
Fresh conglomerate
200
100
0
0
40
80
120
Slope length (m)
160
200
Risk and soil infiltration capacity
Predicted annual average erosion (t/ha/y)
Potential impact of soil improvement
800
Measured conductivity = 0.4 mm/h
600
• Vegetation?
• Gypsum?
400
200
0
0
4
8
Hydraulic conductivity (mm/h)
12
16
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 & tunnelprone
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
200
55
Rocky bluffs,
zones of varying
erodibility
Landform Height (m)
45
160
Rock/Soil Mix
120
Vegetation
Only
40
35
30
25
20
15
80
10
5
0
40
-5
-10
0
0
200
400
600
Horizontal Distance (m)
800
-15
1000
Predicted erosion rate (t/ha/y)
50
Bluff
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
Landloch has used a progression of:
1.
2.
3.
4.
5.
6.
Functionality (stability, water quality);
Sustainability (vegetation);
Non-linear batters (concave profile);
Non-linear plan footprint;
Non-linear top outline;
Geomorphic features (swales, cliffs).
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.