In this issue

 

Welcome

   - Jellyfish Approved

 

 

Erosion

-  Causes

 

 

Lawful Point of Discharge

-  Subdivisions

 

 

Wrap Up

   - See you next month

 

 

Visit our website:

www.stormw.com.au 

 

 

Phone:

07 3398 4992

 

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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