Question - LIDAR Data
"What is Lidar Data??
LIDAR stands for Light Detection and Ranging. It is a remote sensing method that uses light in the form of a pulsed laser to measure the distance from the light source to the Earth. These light pulses combined with other data produce three-dimensional information about the shape of the Earth and its surface characteristics.
LIDAR data is often refered to as ALS (Aerial Laser Scanning) survey data. SWC purchase LIDAR data from the State Government for use in our flood studies. LIDAR data is usually accurate to within 200mm of true ground levels.
The current extent of our LIDAR data can be viewed in the "Data"
section of our website.
Question - BCC Floodwise Property Reports
"I’m developing my property within the Brisbane City Council precinct. I’ve used Brisbane City Council’s interactive mapping and Floodwise property report data to determine that my property is inundated by two types of flood water.
1. Brisbane River
2. Overland Flow
The Floodwise property report states a flood level for the Brisbane River flood event, why hasn’t a minimum finished floor level therefore been identified?
Your initial investigations are a great way of identifying any potential flooding issues affecting your property. The level of flood water affecting your property has been identified by Brisbane City Council (BCC) through the use of hydraulic computer modelling and reported and historical flooding information. Generally if a property is only affected by Brisbane River flooding, a minimum finished floor level will be set in the Floodwise property report.
In this case your property is also subject to inundation from overland flow. Overland flow is runoff that travels across the land after it rains, either before entering a waterway, after breaking out of a waterway, or rising from the ground. There are a vast number of overland flow paths within the BCC precinct. Council does not have the resources to determine the flood level for every single overland flow path. Therefore a hydraulic engineer is required to determine the flood level due to overland flow and subsequent minimum finished floor level requirement.
The overland flow flood level may be higher than the Brisbane River flood level therefore both flood levels must be known before a minimum finished floor level can be identified.
Question - Bio-retention Basins
"What is a bio-retention basin and how does it work?"
A bio-retention basin is a vegetated area where runoff is filtered downwards through filter media and is collected at the bottom by perforated drains. Figure 1.0 presented below illustrates the layout of a bio-retention basin.
Figure 1.0 – Typical Bio-retention Section
The filter media type can vary depending on the geographical location of the bio-retention and available area for placement. Bio-retentions operate by filtering stormwater runoff through surface vegetation and allowing the runoff to percolate through the filter media. This process removes pollutants via filtration, absorption and biological uptake. The “clean” water is collected at the bottom of the basin and discharged accordingly. Bio-retention basins are designed to allow runoff to pond on the surface. Ponding increases the volume of runoff treated through the filter media.
For further information on bio-retention basins or if you require water quality treatment design for your development please don’t hesitate to contact our office.
Question - Due Dilligence
"I’m in the due diligence stage of purchasing a block that is affected by flood water, can STORM provide professional advice on the potential for development prior to the end of my due diligence?"
Yes Storm can provide assistance. It is imperative that you make contact with one of our engineers to discuss the issues affecting the block as soon as possible. In most cases (given the time constraint) we can undertake a preliminary assessment of the property to identify expected flood levels and the associated development constraints. At the very least we can provide verbal advice regarding this issue. This information is usually enough for the purchaser to make an informed decision about the risks of development when purchasing the property. A detailed assessment of the development may be required following the acquisition of the land. If you have a property that you are looking to purchase we would be happy to provide assistance with any investigations.
Question - Civil Design
"Does STORM do the civil design for project or just the conceptual design?"
Although we are civil engineers, we only undertake the conceptual design of a project.
Question - Q100 Event
"Does a Q100 event mean I will only experience the event once in every hundred years?"
No, a Q100 event is defined as an event that has a 1% chance of occurring in any single year.
Question - Form 15 & 16
"Do you provide Forms 15 and 16?"
Yes we have the ability to provide these documents.
Question - Water Quality Treatment
"Do you size water quality treatment devices?"
Yes we do. We size both traditional and propriety devices depending on the water quality targets required to be met.
Question - ALS Survey Data
"What is ALS Survey Data?"
ALS stands for Aerial Laser Scanning. Ground levels are mapped aerially and compiled into square kilometre tiles. STORM purchase these tiles from the Department of Natural Resources and Mines. We then reformat the data to form contours over the relevant study area.
Question - 1D vs 2D Modelling
"I’ve recently submitted a Stormwater Report as part of a development application and the Council have issued an Information Request in response. The Information Request stated that the hydraulic modelling presented in the Stormwater Report was undertaken using 1D modelling software, which is not considered appropriate. The Council has asked that the hydraulic modelling be redone using a 2D modelling software package. What is the difference between the two software types and is the modelling required to be redone as Council have asked? "
The difference between 1D and 2D hydraulic modelling software packages is that the 2D package has the ability to model water moving in multiple directions at the same time. In a 2D modelling package flow can move in the x, y and z planes all at the same time, whereas a in a 1D modelling package the flow is restricted to two planes.
When the direction of flow is known, either a 1D or 2D software package is adequate for modelling purposes. When the direction of flow is unknown then a 2D model would be better suited. The fact that Council have asked for a 2D model does not necessarily mean that the original 1D model was inadequate. A review of the modelling methodology and discussions with the Council would be an appropriate course of action given the request.