Killarney Storm Water Channel designed by Maccaferri

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31 May 2023

Killarney Storm Water Channel designed by Maccaferri

Longitudinal Protection
The Client Challenge

The Killarney Golf Course is situated parallel to the M1 highway, which has a storm water network running through it. This is one of the catchments for Parktown, Killarney and Houghton (Johannesburg). The rapid urbanisation of these areas has resulted in an increase in impermeable surfaces. This has led to a higher volume of water flowing through the storm water channel. This caused extensive erosion of the banks and multiple failures of earth-retaining structures implemented within the channel. The client required a sustainable solution that could effectively manage storm water flow surges while preserving the golf course’s natural beauty. Maccaferri designed, supplied, and supervised the solution construction.

The Maccaferri Solution

The channel was designed to cater for a 1:2-year flood of 39 m3/s up to a 1:100-year flood of 152 m3/s. The initial design was a 4m wide and 4m high channel. However, due to space and budgetary constraints the constructed channel (4m wide and 2m/3m high) can only contain up to the 1:10 year flood of 85 m3/s if the channel remains unvegetated. To address the high water velocity and prevent scour, the channel bed was constructed with concrete capped gabions. Gabion anchors were implemented at ±20m intervals to prevent outflanking. It was advised that continuous maintenance should be carried out to minimize vegetation growth within the channel as this would decrease its discharge capacity. Stepped weirs, of 1m, were strategically placed along the first 100m of the channel to decrease water velocity by reducing the channel bed gradient.

Maccaferri worked closely with the consulting engineers and contractors from conception to implementation. The design of the gabion retaining structures was analysed using limit equilibrium analysis through MacStars W* to check the stability of the system. The channel and weirs were designed using steady flow analysis through MacRa Studio* and MacRa 2* software. The gabion baskets used in the project were manufactured with hexagonal woven galfan wire mesh, coated in PoliMac to achieve an anticipated working life of 120 years according to EN 13383 and ASTM D6711.

 * In-house software

The Macstars W software has been developed to check the stability of gabion and reinforced soil support works, it also allows the user to conduct the stability checks using the Limit Equilibrium Method for reinforced or unreinforced structures.

The MacRa 2 software was developed to provide engineers with a rapid and efficient tool to conduct hydraulic and static analysis of weirs built with Maccaferri products. This program allows the user to check many hydraulic conditions and different types of weirs.

The MacRa Studio is an open channel flow software designed to check the erosive effects within the channel and the discharge variation caused by longitudinal structures

This was an emergency works project and required quick and efficient design, supply, and installation of the solution. The design started in May 2021, and after approval, construction started in July 2021. The project was completed at the end of 2022 after delays due to sewage spills and heavy rainfall were experienced during the construction of the project.

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