Armoured Ford / Armoured Ford / Low Water Stream Crossing
An alternative to constructing a bridge. Historically used since the beginning of mankind to cross a waterway. Bridges allow passage at all heights of water flows, but the cost and environmental impact of bridges with their abutments and approach causeways can be detrimental, liable to damage, loss of usage for a long period, expensive to build, expensive to maintain, expensive to replace as they come to the end of their service life and do not able to be upgraded to handle wider or heavier traffic.
Benefits: a) short construction time b) much lower cost than a bridge
Description: During normal stream low flows the water crossing is passable to vehicles and pedestrians. At periodic high flows vehicle passage is halted until water level drops(ie after a storm event).
Endurance: The lack of stream restriction (such as bridge abutments and built up approaches) allows the high flows to pass without costly damage to the crossing structure such as bridge failure. High-water flows that carry debris such as trees that get hung up on bridges due to lack of height clearance are not impeded with the use of an armoured ford.
Higher water volume streams: A modified armoured ford can handle larger normal water flows by the installation of one or a number of pipes underneath the armoured ford.
Durability: The usage of geotextile underlayment and articulated concrete block allow for differential movements that cause premature destruction and failure of poured concrete or cemented ford structures.
Modifiable: In the event that road usage changes such as wider vehicles or heavier loads or upgrading from one lane to two lanes is desired, the present armoured ford is able to be cheaply and quickly added to or re-built to accommodate.
Longetivety: Armoured fords built by the Romans 2,000 yrs ago are still in user today.
Environmental: A very low environmental impact compared to excavation and construction of abutments and building up of bridge approach causeways.
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FORD
.
Shallow crossing with a firm bottom
Simple effective crossing for a waterway
In use by man since we first walked
Romans were adept at designing and
constructing an armoured crossing
Ensured passage in low and regular flows
3. reproduced from the
Stream Crossing Guidebook for Fish Streams
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4. Objections to fords
Loss of access in high flows
Generation of sediments
Water contamination by users
Negative values for aquatic life
Loss of access thru site degradation by
users
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5. Long-term
successful
fords
Well designed
Expected water flows
Expected traffic use
Design shape ensures a fail-safe structure
Well constructed
Durable materials
Concrete
Rock
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New
Concept
New and novel use of a product that has been around for
many years in providing armour protection for small and
large waterways as a channel liner and on beachfronts
for wave protection.
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Flexibility
Can withstand
changes in
ground (base)
materials from;
Flexing
Heaving from ground frost
Loss of sub-surface material
8. Trilock System
Trilock blocks have a diameter of 40cm
(16”) and weight of 10kg (30lb) and
20kg (60lb)
Thickness of either 10cm (4”) or 15cm
(6”) readily available. 20cm (8”) and
30cm (12”) are used for higher loading
applications
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9. Design flexibility
Trilock has a
working radius of
One Meter (3’) and
can flex in multiple
directions
Openings can be
made for;
Bridge pilings
Trees
Large obstructions
Can withstand loss or breakage of individual
units with out serious threat to system
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10. Key design elements
Max 25% Max 25%
15% 15%
1.5 meter
stream bed
1.5 meter
apron
1.5 meter
apron
Armour to
above high
water mark
Stream shape - ensure Fish passage at low flows
Ensure passage shape for expected vehicle use
Downstream splash apron for stream gradients over 5%
(Steeper gradient streams may require installation of a
culvert underneath to ensure fish passage in low flows)
Extend approaches
Above highest high water mark
To a point where vehicle traffic will not adversely affect
(damage) road surface
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12. Mission Creek
Crossing 399
Graystokes Forest
Service Road
Penticton Forest
District, BC, CANADA
Community Watershed
High fish values
High use recreation area
Soon to be a Provincial Park
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14. Site Preparation
Excavation
Shape streambed
Shape approaches
Max 25% Max 25%
15% 15%
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15. Site Preparation
Streambed / Approaches
Excavate upstream and
downstream “heel-in” for
stream bed and for approach
aprons (compact)
Excavate “heel-in” at top of approaches (compact)
Place suitable bedding material (compact)
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16. Site Preparation
Compaction / Fabric
Compact to 90%
Density
24” plate tamper provides a firm base
Geotextile (woven monofilament) fabric is used as
a base to;
Provide additional support
Prevent migration of fines
Provide bi-directional flow of water
Strength and opening size (site specific)
Armtec AMF 245
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17. Placing of Blocks
Line and right angle laid.
out to ensure alignment.
Blocks are placed in unit .
pairs for ease of application .
Blocks are laid rapidly .
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of two .
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Bio-engineering
20% interspacing provides
many opportunities for
establishment of mature
vegetation
Shade and nutrition
Management of water energy
Use vegetation as a tool to
assist stability
Soil Plugs – local grasses,
herbs and forbs, associated
microbes, enzymes, and soil
building organisms
Live-staking - Willow whips
(through the blocks)
Planting rooted stock –
Softwoods / hardwoods
19. Backfilling
Back-fill stream channel and approach ramp flanks with suitable
well-graded cobble material and compact to 90%
Infill blocks with well-graded material within the wetted
perimeter
Infill blocks on the approaches with native sands and soils (or
gravels)
Compacting of infill material – optional – dependant on
materials and engineering objectives
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20. Articulated Concrete
Block (ACB) also
known as Flexible
Concrete Revetment
Designed to be hand-placed or machine placed
Provides protection from erosive water energy
Conforms to changes in grade while remaining
interlocked
Allows bi-directional water flows (will not build up static
pressure)
Provides a secure crossing structure for traffic
Abrasive resistance for transported bedload material
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21. ACB’s are suitable for
placing over many
different soil types
Suitable for placement over
fine-textured materials such
as sands and silts
The system employs a Geotextile
(woven monofilament fabric) as a base (site-specific)
(Armtec AMF 245 was chosen for Mission Creek installation)
(Nilex non-woven geotextile 2016 chosen for 18 mile creek)
Geotextile overlain with interlocking concrete blocks
(Trilock System was chosen for these installations for its multi-directional
installation flexibility values)
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23. When to use ACB’s
When traditional Poured Concrete
or Rock Armour is not easily available
When costs are excessive for;
Mobilization / Demobilization
Transport (trucking access / distance)
Generate rock (drilling and blasting)
Flow
When heavy equipment or truck access is difficult or denied.
Eg. The materials can be transported by smaller vehicle or by
helicopter to remote sites
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24. Long-term solution
with ACB’s
Can be cost effective
Easy to install by semi-skilled
workers
Permanent
Fish friendly
No maintenance
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26. CONTACT INFORMATION
Eric L Kay - Forest and Industrial Road Consultant
250 337-5096 erickay@kayassociates.com
Daryl Hunt, A.ScT - Ministry of Forests, Penticton District
250 490-2219 Daryl.Hunt@gems8.gov.bc.ca
Bruce Stickney / Ernie Bone - Coast Masonry, CCI Industries
604 270-8411 Bruce bstickney@cci-industries.com
Ernie ebone@cci-industries.com
David Campbell, P.Eng - Campbell Engineering Inc.
250 658-4276 dcamp@mail.islandnet.com
Ken Langedyk, P.Eng - Dobson Engineering Ltd.
250 861-5595 langedyk@dobsoneng.com
Phil Carroll, P.Eng – Armtec Industries Ltd.
604 278-3881 pcarroll@armtec.com
Doug Bennett, M.Sc. R.P.F. P.Eng. - FERIC
604 228-1555 dbennett@vcr.feric.ca
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A line in long array where they wind betwixt green islands,
They take a serpentine course, their arms flash in the sun-hark to the musical
clank,
Behold the silvery river, in it the splashing horses loitering stop to drink,
Behold the brown-faced men, each group, each person a picture, the negligent
rest on the saddles,
Some emerge on the opposite bank, others are just entering the ford-while,
Scarlet and blue and snowy white,
The guidon flags flutter gaily in the wind.
Walt Whitman - Cavalry Crossing A Ford
Located at Wycollar, Lancashire.
Armtec 245 is typically used under rip-rap and concrete revetment systems. It resists clogging while maintaining a steady flow rate in the thigh gradient and dynamic flow conditions. It also provides a high survivability rating during aggressive installations such as underwater placement or during back-dumping of rip-rap.
Bowran – 18 Mile Creek - Prince George
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