Welcome
Hello
everyone and welcome to May edition of “Keep Things Flowing”, the
monthly newsletter presented by Storm Water Consulting.
Over the
past few months we have brought you news and information about the
new stormwater treatment device from HUMES called the Jellyfish.
Earlier this month we were informed that Brisbane City Council has
officially accepted the HUMES Jellyfish as a form of water quality
treatment. The Jellyfish product will rival Stormwater 360’s
Stormfilter as an alternative form of stormwater treatment. Storm
Water Consulting are capable of sizing the Jellyfish product, if
you would like assistance with water quality treatment or any further
information please contact our office.
Over the
past month we have worked on several subdivisions that had an issue
with providing a lawful point of discharge. In this month’s issue
of Keep Things Flowing, we will identify potential solutions to
meet lawful point of discharge criteria. We will also take a closer
look at causes of soil erosion.
Erosion
Soil erosion
is a serious issue that can have debilitating impacts on land and
infrastructure. Soil erosion occurs when the topsoil is washed away
as a result of sudden impact or gradual weathering of the soil from
water. Soil erosion generally occurs in areas inundated by Creeks,
Rivers and Overland Flow Paths.
Presented
below are some pictures of severe erosion that we observed in an
overland flow path located on one of our project sites.
During a
site inspection it was identified that the overland flow path
located through the site was severely eroded. Without adequate
treatment the erosion would continue to worsen and would likely
impact the proposed development. Before recommending a treatment,
we first identified the likely causes of the erosion.
1.
Soil
Type – Whilst on site we identified that the soil through the
overland flow path was very fine grained and of a dispersive
nature. Dispersive soils are usually sodic and susceptible to
erosion due to their structural unstable nature.
2.
Limited
Vegetation – The ground vegetation throughout the flow path was
sparse. Plant roots help bind soil together, forming a more solid
mass that is less susceptible to erosion from water. Vegetation
also increases the permeability of soil and reduces surface flows.
The lack of vegetation would have increased the extent of erosion
on site.
3.
Overland
Flow – This particular flow path was located downstream of a
detention basin (from an upstream development). Whilst the
detention basin would have mitigated the peak discharge from the
upstream development, the development would have increased the frequency
of overland flow though the flow path and increased the likelihood
and extent of erosion.
So how did
we treat this issue? We recommended that the topsoil within the
overland flow path be replaced with a soil that is more organic or
clay like. Soils that contain high levels of organic material or
clay tend to coagulate and form tighter bonds, making them more
resistant to erosion. We also recommended that the flow path be
revegetated and rehabilitated with plant vegetation that can
withstand constant inundation. This would further increase the
soils resistance to erosion and help to reduce the volume of overland flow due to groundwater
infiltration. Finally, we recommended constant monitoring and
maintenance of the flow path to assess for continued erosion issues
so that future erosion could be addressed if required.
If you
experience erosion on a development site we would be pleased to
assist with investigations and recommend a treatment strategy.
Lawful Point of
Discharge
Over the
past month we have assessed several proposed subdivisions to
identify a lawful point of discharge. Most of these properties had
an issue because the new lots graded away from the road frontage,
thus preventing discharge to the street. To identify a lawful point
of discharge we must firstly understand the lawful point of
discharge criteria. The assessment criteria for a lawful point of
discharge are presented below.
1.
The
location of the discharge is under the lawful control of the local
government or other statutory authority from whom permission to
discharge has been received. This will include park, drainage or
road reserve or stormwater drainage easement.
2.
In
discharging to that location, the discharge will not cause an
actionable nuisance (i.e. a nuisance for which the current or some
future neighbouring proprietor may bring an action or claim for
damages arising out of the nuisance), or environmental or property
damage.
In recent
years a number of Council’s in South East Queensland have
prohibited the use of charged roof water lines and rubble pits as a
lawful point of discharge. Gravity fed roof water lines are
acceptable for use, however with lots grading away from the street
this option is often physically impossible.
Council
owned stormwater infrastructure, located
through subdivision sites is often used for discharging site
runoff (often on-site detention is still required to mitigate the
increased flow into the pipe system back to pre-developed
conditions). Filling the subdivided lots to achieve grading to the
street is an acceptable solution provided the fill would not cause
an adverse impact to neighbouring properties and that the street
constitutes a lawful point of discharge. The final solution is to
construct a stormwater line through a neighbouring property to a
lawful point of discharge. This option requires consent from the
owner of the land that the stormwater line will be located through.
Permission may be denied from neighbouring land owners. Storm Water Consulting have been
successful with implementing tank and pump solutions to pump
stormwater up to the street, however this strategy cannot be used
on every development and is considered on a site by site basis. If
a lawful point of discharge cannot be identified then the
subdivision is unlikely to be approved.
If you
require a lawful point of discharge to be identified for a
development please contact our office and we would be pleased to
provide assistance.
Wrap Up
We hope you
enjoyed this edition of Keep Things Flowing. Feedback on articles
presented is always welcomed and for further information on any of
the articles presented please don’t hesitate to contact our office.
As always,
Keep Things Flowing!
The Storm
Team
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