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| Description |
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Channel bank remodelling is employed by many water authorities
in Australia. It is a form of compacted earthen lining undertaken
when damage to the channel banks is thought to be the main cause
of seepage. Banks are at least partially rebuilt with compacted
clay material.
| Experience |
|
Murrumbidgee Irrigation undertook the remodelling of a channel
bank on the Lateral No. 9 Channel as part of the IAL Channel
Seepage Remediation Project.
| Site
preparation |
|
Before commencement of remodelling, willow trees were removed,
and the left-hand bank was stripped back to natural surface and
all tree roots removed. Earthen blocks were placed across the channel
at regular intervals to allow easy access for trucks and earthmoving
equipment.
| Installation |
|
In the trial section on Lateral No. 9, only the left-hand bank
of the channel was remodelled as seepage was only evident on this
side. In total 1,500m of bank was reconstructed, with only 800m
of the channel was the subject of the pondage test before rehabilitation.
Clay material was sourced for this project from a storage site
approximately 20km away. An assessment of the soil type (plasticity,
dispersion, and permeability) concluded that the material was suitable
for channel bank construction, given 95% compaction was achieved
and moisture content was within 3% of optimum. The clay fill was
compacted in layers of around 150mm until the bank level was raised
above the design water profile (including some freeboard). Remodelling
work was undertaken during late July and early August 2001.
| Site
conditions |
|
Light rainfall during construction made conditions greasy for trucks
and earthmoving equipment, causing some down time.
| Weather
conditions |
|
Fog caused delays in the construction by restricting the travel
speed of trucks bringing borrow material from 20km away.
| Maintenance |
|
Properly constructed channel banks require little maintenance in
the short term, but they should be inspected at least annually
for erosion, dispersion, shrinkage cracks and other damage. It
is recommended that stock be prevented from accessing the channel
bank, as they can cause significant damage, particularly below
the water line.
| Durability |
|
Remodelled channel banks are estimated to last for 100 years.
| Seepage
reduction |
|
Baseline seepage rates at Lateral No. 9 ranged from 2.0-3.5L/m2/day.
A post-construction pondage test was not undertaken by Murrumbidgee
Irrigation, as the success of the seepage remediation work was
evident by reclamation of 20ha of adjacent farmland. Previously
only suitable for grazing due to its permanently wet state, the
land is now under cereal crop production.
| Cost |
|
A breakdown of the costs is presented in the table below. The total
cost of $45,728 corresponds to a cost of $28.58/m for the 1,600m
section or $9.53/m2 based on a surface area of 4,800m2 for the
left-hand channel bank only.
The unit rates for the remodelling of the left-hand bank cannot
simply be doubled to determine the remodelling costs for both banks.
This is due to the differences between the conditions of the two
banks.
The left-hand bank had numerous willow trees and associated
roots, which required removal at an additional cost to normal remodelling.
Table 1 Breakdown of costs for channel bank remodelling
|
| Item |
Cost ($) |
Cost ($/m)1 |
Cost ($/m2)2 |
|
| Earth works (haul, compact and shape) |
$40,829.10 |
$25.52 |
$8.51 |
| Tree removal |
$4,900.00 |
$3.06 |
$1.02 |
| Total (for one bank) |
$45,729.10 |
$28.58 |
$9.53 |
| Estimated total (for two banks) |
$81,658.20 |
$51.03 |
$17.01 |
|
1. Cost per metre based on remodelling 1,600m.
2. Cost per square metre based on a surface area of 4,800m2 (a
perimeter of 3m on the left-hand bank only)
| Advantages
and disadvantages |
|
Advantages
Channel remodelling is a standard and straightforward technique
for channel rehabilitation, for which water authorities have expertise
and equipment.
Disadvantages
The availability and proximity of suitable clay material for bank
construction may be limiting in some cases.
Rehabilitation works are undertaken only on the banks and not the
bed of the channel, thus only remediating horizontal, and not vertical,
seepage.
| Related
pages |
|
Earthen lining techniques
Compacted earthen liners
Clay
lining example: Channel 12
Clay
lining example: Waranga Western Channel
Other
Australian examples
Loose earthen linings
Bentonite treatments
Modified soil earthen linings
Soil sealants |
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