VoidSaver™ Stormwater Detention System
Stone void contamination is one of the leading threats to the long term reliability of underground stormwater detention systems. Contamination from solids can compromise stone void storage before site stabilization and present a compounding downstream flooding risk each year with long term accumulation.
Industry assumptions of stone voids available for storage are often incorrect in practice. A recent study found 39% of stone backfill samples taken had less than the commonly used 40% void ratio1. Also, construction site sediment runoff often fouls the stone before site stabilization, and one month without proper erosion and sediment management during construction can do more damage than years of sediment accumulation from a paved surface.
The VoidSaver stormwater detention system alleviates these problems by containing the majority of storm events within the pipe, and only utilizing the stone void storage during infrequent events. As a result, solids are contained within the pipe, and not the stone.
How the VoidSaver Works
As water fills the gasketed system, trash, debris, and suspended solids settle within the solid pipe rather than filling the stone void space and compromising the system. During large events, water fills the pipe, and the clean water discharges into the surrounding stone via the stone overflow vent. After the storm subsides, water within the pipe continues discharging, creating differential head pressure between the water within the pipe and water within the stone. This external driving head opens the one-way water return valves, allowing the pipe and stone to fully drain down together.
VoidSaver Features and Benefits
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FEATURES
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BENEFITS
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1. Protects stone void space from solids contamination
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1. Protects long term storage capacity and reduces the opportunity for downstream flooding
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2. Leverages stone storage to allow smaller system footprints
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2. Lower system material and installation costs
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3. Does not rely on fabrics for pretreatment to protect surround backfill.
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3. No geotextile clogging and more reliable protection of stone voids
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4. Provides easier access for maintenance compared to chamber systems.
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4. Reduced long-term maintenance costs
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Long Term Reliability
The VoidSaver provides a long-term, reliable solution compared to pretreatment systems that use infiltration methods alongside geotextiles.
By their nature, lower structures such as chambers are naturally more sensitive to occlusion because a high percentage of the designed storage depends on stone voids protected by geotextile. Lab tests of geotextile pretreatment show that geotextiles allow 27-46% of TSS to pass into the voids.1 In addition, clay/silt particles can build up on and clog geotextiles over time requiring extensive and difficult maintenance. This buildup of clay/silt can then make its way over the weirs and into the surrounding backfill compounding the issue over the lifetime of the site. The VoidSaver stores the majority of storm events in the pipe and does not rely on fabrics for pretreatment to protect the surrounding backfill, thus providing a more reliable solution.
VoidSaver Maintenance
Like conventional pipe systems, inspection and maintenance are easily conducted through large access risers where trash and sediment can be removed manually or with a vacuum truck.
1 Cashatt, J.C. (2020), Viability of Stone Void Space in Underground Detention/Retention Systems, Proceedings of EWRI 2020, Henderson, NV, American Society of Civil Engineers