Installed Cost Comparison of 3 Surface Drainage Solutions
Whether light rainfall is frequent or heavy rain pours deluge on the pavement, surface drainage is necessary to prevent damage to pavement and property, and reduces safety hazards caused by the ponding of water. However, there is some diversion within the drainage design industry about which method of surface water drainage is the most affordable and effective. So, recently, a report was prepared by an independent quantity surveyor, Rider Levett Bucknall, to compare the installation costs of three alternative surface drainage methods.
The methods investigated were grated pit and pipe systems (Figure. 1) and grated trench drain systems (Figure 2) in two varieties: cast-in-situ and precast modular. The report compared the installation costs of the three surface drainage methods for the car park of the Homebush Aquatic Centre in New South Wales.
The results showed a clear difference in price between the three methods. Costing the highest, the full expense of installation of the cast in-situ trench drainage system reached $393,000. At 4% cheaper, the grated pit and pipe system cost $377,000 to install. The cheapest of the three surface drainage systems to install was the ACO Drain®, a factory manufactured modular trench drainage system at $340,000 – 13% cheaper than its cast in-situ competitor.
As well as comparing the costs of the systems, there is a strong design argument which focuses on four primary areas which would determine the overall efficiency and suitability to the Aquatic Centre car park: hydraulics, safety & convenience, installation and maintenance. In each of these areas, the modular ACO Drain® system would be the superior choice.
Hydraulic Performance
ACO Drain® leads in hydraulic performance. When compared to conventional concrete, which exists as cast in-situ installations, Polycrete® Channels ultra-smooth internal surfaces and V-shape design allows uninterrupted flow for increased velocity. The roughness of the concrete in cast in-situ installations, as well as its angular box profile, renders it less efficient than Polycrete® Channels.
Safety and convenience
The major downside caused by inefficient surface drainage is slipping and people getting splashed or standing in puddles. Polycrete® Channels reduce the risk of this hazard as they are assembled in pavements built on simple falls capturing liquid along its length. In the grated pit and pipe scenario, overland flow is a hazard in the space between the pits. This also increases the risk of ponding which can cause severe damage to the pavement. As a further risk to safety, the linear cast in-situ system, due to concrete deterioration, exposes frames and grates from coming loose under traffic
Installation
Polycrete® Channels require simple, one-way sloping of the pavement which is easy to grade and fast to construct. The minimal underground piping means that excavation and site work are limited and less costly than the extensive excavation, formwork and construction required for the grated pit and pipe system. .
Linear cast-in-situ installations rely heavily on the experience of the installer, which can be inconsistent from project to project. The advantage of Polycrete® Channels is that they are factory manufactured for a precise and consistent end product. During installation of Polycrete® Channels, a non-level grate seat is avoided, which is often a cause for early failure in cast in-situ installations.
Maintenance
Trench drainage generally is easier to maintain as access to the system is as easy as removing the grates. The polymer concrete that constitutes ACO Drain® requires little maintenance. The smooth surfaces of the Polycrete® Channels resist the buildup of mould and biological growth which often forms on the rough surfaces of cast in-situ drainage channels.
The modular ACO Drain® Polycrete® Channels excelled in all areas of comparison to the grated pit and pipe system and cast in-situ installations. ACO Drain® was deemed the most affordable and efficient for the Homebush Aquatic Centre car park. In addition to this it has many intrinsic benefits. A technical bulletin featuring the results of Rider Levett Bucknall’s report can be read here.
