Landcom Book 4 Maintenance - WSUD

Water Sensitive Urban Design
Item to be
Monitored
Purpose of
Monitoring
Performance
Target
Schedule
Maintenance or
Investigation
Immediate
Action Required
Maintenance
Action Required
Sediment
build up
The accumulation of sediment in the
sediment forebay of the bioretention
system is a prescribed function of
this zone. However, sediment must be
regularly removed to ensure that the
sediment trapping performance of this
zone is sustained.
If sediment accumulates on the
bioretention surface, percolation
of water into the media may be
reduced, resulting in poor treatment
performance.
Sediment absent
Sediment
accumulation
appears excessive in
sediment forebay
Fine sediment
accumulation
apparent on
bioretention media
surface
Sediment
accumulated to half
the forebay depth
Coarse sediment
or large volumes
of sediment
accumulation
apparent on the
bioretention media
surface
Schedule investigation to identify
sediment source.
Once sediment source is stabilised,
remove accumulated sediment and
replace the top 100 mm of filter media
from the bioretention system. The filter
media specifications should be as per
the design intent.
Common sense should be exercised
in deciding if plantings need to be
replaced as part of maintenance work.
If the sediment build-up is extensive
and smothering vegetation, it may be
easier and less costly to remove the
plantings and replant once the filter
media has been replaced. Conversely,
if the sediment build-up is small and
isolated or the system is planted
with trees, it may only be necessary
to scrape away the accumulated
sediment and the top 100mm of filter
media and replace without disturbing
the plants within the bioretention
system.
Lightly spread and compact replaced
filter media using either hand tools, an
excavator bucket or a pozitrack bobcat
(DO NOT drive over the media with any
vehicle but a pozitrack bobcat).
Replace any damaged plants to meet
the design plant schedule.
Compaction
Percolation into the media may be
reduced if the media surface has been
compacted, i.e. by pedestrian traffic,
poor construction methods.
No compaction
evident
Localised compaction
or subsidence
evident. Localised
ponding longer than
24 hours after storm
event
Water remains
ponding longer than
24hours after storm
event
Schedule investigation to identify
cause of compaction.
If compaction is localised, remove top
500 mm of filter media with auger.
- Break-up removed filter media so
that it is no longer compacted.
- Refill hole with uncompacted filter
media (that is, there is no need to
replace with new filter media).
If compaction is extensive, seek expert
advice.
Weeds and
invasive
plants
The growth of weeds can impair a
bioretention system’s performance by
- Changing flow paths across the
bioretention system
- Shading and out-competing plant
species that are important for water
treatment, or filter media stability.
Weeds can spread to downstream
environments, compromising
ecosystem health.
No weeds present Weeds present Noxious or
environmental weeds
present, or weed
cover more than 25
percent
Hand removal or targeted herbicide
treatment (herbicides registered for
use around waterways).
Note: Herbicides should not be
routinely used to maintain edges and
batter slopes. General spraying of
batter slopes should not be undertaken
without follow up revegetation with
native species.
Weeds compromise the visual amenity
of the bioretention system.
Book 4 | MAINTENANCE 25