Configuring mine
disturbed landforms for
long-term sustainability
By Les Sawatsky and Anil Beersing
Golder Associates Ltd., Canada
ONLY TWO KEY MESSAGES
1. The most common cause of mine
closure failures is erosion
2. Examples of doing it right are all
around you
Purpose of this presentation: Challenge you to replicate
natural systems to achieve long term sustainability in
mine closure.
Evolution of Best Practices
 No regulation; no design for closure
 Regulations for closing mines
 Conceptual mine closure planning in
advance of mining
 Detailed mine closure plans updated
regularly
 Detailed mine closure planning for
long term sustainability
Meaning of long term sustainability
 No catastrophic failure or serious
deterioration, ever
 All extreme events are
accommodated
 Desired land use and/or ecological
productivity is delivered forever
 Minimal erosion similar to the
natural environment
 Same level of robustness as natural
terrain
Methods of Achieving Long Term Sustainability
1.
Perpetual Maintenance
On the positive side, it can be characterized as custodial
transfer that sustains mining town economy.
 It forces future generations attend to the mess created by the
current generation.
 Cannot guard against failure caused by extreme events

2.
Targeting Maintenance-Free


Complexity of processes and many unknowns may make
‘maintenance-free’ condition unachievable
On the positive side, durability of final landscape depends
entirely on the target. Maintenance-free condition is much
more likely achievable if you plan to achieve it.
Choose Maintenance-Free Closure
Because:
• Perpetual maintenance does not
deliver long term sustainability
• Natural terrain shows that
maintenance-free condition is
achievable, but only if you care to
understand natural processes
(geomorphology)
Why Geomorphology?
 It enables proper recognition of long
term processes
 Erosion is a dominant geomorphic
process that can lead to deterioration of
landforms
 It explains how natural topography
results from many years of land form
evolution
 Long term sustainability can be defined
by natural topography. Hence the target
for mine closure long term sustainability
is the natural environment.
I
t
e
Replicating Nature - Importance of Shape
• Configuration (contouring, shape) of a landform
strongly affects geomorphic processes like:
• Surface runoff
• Erosion
• Mass wasting
• Ground water effects, seepage and soil salinization
• Sustainability of natural terrain is strongly related to
configuration of the landform, including contouring features
such as slope, relief, drainage density, regime of drainage
channels.
• Most mine closure failures caused by disregarding hydrology
and surface erosion
State of Practice in Oil Sands of Alberta
• Geomorphic Approach to mine
closure had it origins in mid 1990’s.
• Today it is mandatory by regulation
• Oil Sands firms have embraced it
because it delivers:
•
•
•
•
Minimum long term liability
Compliance with regulations
Natural appearance
Delivers sustainability
Remaining Challenge
• Integrate landform contouring into mine
operations to reduce costs
•
•
•
While mining equipment is still available
Avoid double handling of material
Contouring managed by knowledgeable operators
Geomorphic Design Guidelines
Topographic Irregularity (relief)
• Benefits vegetation diversity
and wildlife escape habitat
• Controls soil salinization
• Controls drainage courses
• Appears like natural terrain
Geomorphic Design Guidelines
Provide a Mature Profile
• Mature profile is concave up with reduced
slope downstream
GEOMORPHIC
GEOMORPHIC
GEOMORPHIC
MATURE
MATURE
PROFILE
MATUREPROFILE
PROFILE
IMMATURE
IMMATURE
IMMATURE
PROFILE
PROFILE
PROFILE
Mature
Mature
profile
patterned
after
natural
landscape
Matureprofile
profilepatterned
patternedafter
afternatural
naturallandscape
landscape
Geomorphic Design Guidelines
Water courses in well defined swales or valleys
• Natural channels remain within a defined valley
Depth
Depth
of
valley
exceeds
Depthof
ofvalley
valleyexceeds
exceeds
any
any
extreme
flow
anyextreme
extremeflow
flow
Absence
Absence
of
valley
Absenceof
ofvalley
valley
makes
makes
this
configuration
makesthis
thisconfiguration
configuration
vulnerable
to
vulnerable
spillage
vulnerable to
tospillage
spillage
Well
Well
Defined
Swales
or
Valleys
to
Prevent
Spillage
WellDefined
DefinedSwales
Swalesor
orValleys
Valleysto
toPrevent
PreventSpillage
Geomorphic Design Guidelines
Suitable Drainage Density
• Reduces overland flow path • Drainage Density =
Function of climate,
length
slope and soils
• Enables maximum use of
vegetated watercourses
High
Drainage Density
High
HighDrainage
DrainageDensity
Density
Low
Drainage Density
Low
LowDrainage
DrainageDensity
Density
Selection
of Appropriate
Drainage Density
Selection
Selection of
of Appropriate
Appropriate Drainage
Drainage Density
Density
Geomorphic Design Guidelines
Do not exceed MOFPL
(Maximum Overland Flow Path
Length)
• MOFPL threshold is clearly
indicated in natural terrain
• Watercourse must be present
before end of MOFPL
A
A
A
• Exceeding this threshold results
in erosion and gullying
MAXIMUM OVERLAND
MAXIMUM OVERLAND
MAXIMUM
OVERLAND
FLOW
PATH LENGTH
FLOW PATH LENGTH
FLOW PATH LENGTH
A
A
A
Drainage
Drainage
Density
Required
to
Avoid
Excessive
DrainageDensity
DensityRequired
Requiredto
toAvoid
AvoidExcessive
Excessive
Path
Lengths
for
Overland
Flow
Path
Path Lengths
Lengths for
for Overland
Overland Flow
Flow
Geomorphic Design Guidelines
Maximize use of Vegetated
Watercourses
• Examine nearby natural terrain
to determine applicability of
Vegetated Watercourses
• Specifications for Vegetated
Watercourses include base
width (distributed flow) and
soil depth (moisture storage)
Geomorphic Design Guidelines
Avoid Terraces or Benches
• Concentrates flow
• Eventually will spill at single
point and cause severe gullying
• Never found in mature natural
terrain
Geomorphic Design Guidelines
Avoid Dams
• Eventually will breach and
cause catastrophic
consequences
• Never found in mature
natural terrain
Geomorphic Design Guidelines
• Must not violate natural regime
• Natural alluvial channel regime
• Meander wave length
• Sinuosity
• Width, depth & w/d ratio
• Must consider dominant flow,
bed/bank material, gradient,
sediment load.
0.01
0.01
0.01
Slope
ChannelSlope
Slope
Channel
Channel
Drainage works should replicate
natural systems
ss =
s ==00.0
0..0000011100/ 444
0// QQ
Q
ss =
s ==00.0
0.001
0.001
0.001
0..0000011177/ 444
7// QQQ
0.0001
0.0001
0.0001
0.00001
0.00001
0.00001
1.0
1.0
1.0
Braided
Braided
streams
Braidedstreams
streams
Meandering
Meandering
streams
Meanderingstreams
streams
10
10
10
22
10
10
10 2
33
10
10
10 3
44
10
10
10 4
Mean
Mean
annual
discharge
(cfs)
Meanannual
annualdischarge
discharge(cfs)
(cfs)
Characteristic
CharacteristicPattern
Pattern
55
10
10
10 5
66
10
10
10 6
Geomorphic Design Guidelines
Channels located in incised
valleys
• Natural channels are deeply
incised in valleys
Maximum
Flow Level
Norm
al
Flow
Level
Geomorphic Design Guidelines
Provide Flow Attenuation
• Reclamation soil moisture
storage
• Floodplains
• Wetlands and lakes
Geomorphic Design Guidelines
Design Sustainable Lakes
• Need sufficient drainage area
2m
2mmax
max
2m
max
2m
2mmax
max
Lake
Lake Shoreline
Shoreline Protection
Protection by
by Littoral
Littoral Vegetation
Vegetation
• Shoreline protection
Lake
Lake
Shoreline
Protection
by
Littoral
Vegetation
LakeShoreline
ShorelineProtection
Protectionby
byLittoral
LittoralVegetation
Vegetation
• Located downstream of mine
• No dams
• Outlet on suitable ground
Lakes
Lakes
and
Wetlands
to
Attenuate
Floods
Lakesand
andWetlands
Wetlandsto
toAttenuate
AttenuateFloods
Floods
Geomorphic Design Guidelines
Provide Second Lines of Defense
• Need redundancy
• Sources of material for rearmouring and self-healing
Geomorphic Design Guidelines
Avoid excessive changes in
drainage area
• Must not increase natural
drainage area of a natural
stream; otherwise it will
change regime
Follow the Rules and Avoid this!
Geomorphic Approach - Mine in Washington
Geomorphic Approach - Mine in Washington
Geomorphic Approach - Mine in Washington
Geomorphic Approach - Mine in Washington
Geomorphic Approach - Mine in Washington
OBRIGADO
THANK YOU
ANY QUESTIONS?