Reducing Urban Flooding: Detaining the volume of rainwater where it falls.
I had the pleasure of attending Stormwater Victoria 2023 Conference in Ballarat, where @Dr Dale Browne from E2Designlab presented, A Review on Permeable Paving: An Often Overlooked Component of the IWM Toolkit for Metropolitan Victoria.
From that presentation the key takeaway for me was; most stormwater professionals can see the benefits of traditional permeable paving, porous concrete and asphalt surfaces, but are restricted in its use due to the limited reduction in flow and the clogging effect that requires maintenance over time.
Whilst there are multiple types of pervious surfaces, the reduction in volume and flow rates is vastly different between different products
A recent publication by Dr Meenakshi Arora , Department of Infrastructure Engineering, University of Melbourne . Titled Flood Mitigation Performance of Permeable Pavements in an Urbanised Catchment in Melbourne, Australia (Elizabeth Street Catchment), sets out to answer the question that “ While #PermeablePavement systems have been widely investigated from a water quality perspective, there is limited understanding of their performance to reduce critical storm events at the watershed scale. With larger flooding events projected to occur more frequently as a result of #urbanisation and climate change, Permeable Pavement systems have the potential to #mitigatefloods by reducing peak flows and runoff volumes”.
Results within this paper indicate that the integration of traditional type #permeablepavements in urban settings is effective in mitigating surface flooding in an urbanised catchment in Melbourne, by reducing the peak flows by 7–16% leading to a delay in #peakflood times of between 3 and 6 minutes.
The paper also supports the position taken by Dr Browne that clogging is an issue and in assessing the results an infiltration rate of 360mm/hr against a non-clogged ideal rate of 3600mm/hr was used.
So what would occur if you used TRUEGRID HDPE Permeable Pavers that had an infiltration rate measured in metres not millimetres and a runoff coefficient of 0 – 0.05 for gravel fill ? These very high initial surface infiltration rates can immediately infiltrate and detain rainfall from high intensity rainstorms. In many cases, direct runoff is completely eliminated.
TRUEGRID is not like traditional permeable paving that requires routine maintenance such as power washing or vacuuming to maintain permeability. TRUEGRID is designed to use a clean/washed angular stone for the base and fill material which has 40% void space. These large void spaces allow TRUEGRID to maintain permeability over the life of the product without any routine maintenance.
A third-party geotechnical firm conducted infiltration rate tests in the USA as per ASTM C1781 in March 2019 to determine the surface infiltration rate of TRUEGRID. The tests were conducted in both the drive lane and parking spaces to compare high traffic areas. The results are presented in the summary table below.
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Conclusion:
With the inevitable impacts of climate change and urbanisation, the effectiveness of permeable pavements, within a project, can be exponentially enhanced by replacing traditional permeable paving, porous concrete, and asphalt with TRUEGRID Drive on Surface .
Traditional Permeable Paving performance can be substantially affected by the intensity and duration of the rainfall event. #TRUEGRID can be effective for any rainfall event, based on the depth of subgrade for detention and its reduced flow rate coefficient.
The traditional thought process regarding clogging and maintenance no longer apply when using TRUEGRID Drive on Surface due to nature of the subgrade and infill material.
TRUEGRID Drive on Surface , locally manufactures 100% #recycled #hdpe paving systems for, stormwater management solutions, as an engineered alternative to concrete and asphalt. They deliver cost savings against traditional pavement and permeable paving such as porous concrete and asphalt.
"Pave the way to a more sustainable future".
Philip Goodman
Director
TRUEGRID Australia Pty Ltd
Alex McMahon Leah Myers TRUEGRID Australian Made GECA Sustainability Victoria Stormwater NSW Stormwater NSW Stormwater Queensland