Design and construction of linear flood defences across 15 sites along both banks of the river Loxley from Malin bridge to the confluence of the rivers Loxley and Don. This project is designed to alleviate flooding in the Hillsborough, Malin Bridge and Owlerton areas of Sheffield.

Project Scope

The main scope of works included the following:

– Construction of new structural concrete retaining walls – 1.5km long
– Raising and strengthening of existing walls, including the installation of steel beams to counteract flood pressures
– Ground raising – clay earthwork bunds, 1m x 60m
– Embankment construction – brick clad walls with copings along the whole section of defences
– Utilised a bulk bag dam to enable works on retaining walls
– Construction of bridge parapets along the Penistone Road Bridge
– Installation of sheet pile walls rather than demolition of pre-existing buildings
– Vibration free piling used throughout installation of the sheet piles
– Demolition of existing balconies, and installation of new balconies with demountable flood defences
– Installation of demountable flood barriers on Rudyard Mews, approximately 40m in length total

Ecology on Site

The project was a response to the rising flood risks in this area of Sheffield, with Malin Bridge subject to multiple severe flood warnings. We collaborated with the Environment Agency to secure all necessary FRA permits for this scheme.

Working with the River Stewardship Company, Natural England and the Environment Agency, we programmed the scheme to work on different sections of the river after one another, rather than move along the river in order to not disrupt the natural aquatic wildlife in and around the river beds.
Japanese Knotweed and Himalayan Balsam was found across multiple sites on the scheme. This has been treated through spraying and injecting. Other environmental mitigation measures include:

– Fish recovery – diverted river small fish
– Used aquatic ecologists for evidence of spawning activity within the area to be dewatered
– Used ecologists to look for habitat along the embankment (otters, badgers, bats, nesting birds) and gain mitigation licences to rehome the bats found on site.
– Undertook several nesting bird surveys using our ecologists at regent court to determine at what point works could be started
– Bat surveys across sites

Carbon Reduction – Hybrid Power Solutions

To power our on-site welfare facilities for our site team we engaged with Aggreko to deliver 2x 60kVa generators. They were equipped with monitoring technology to ensure efficient operation and proactively monitor mechanical faults.
Upon review, Aggreko and ourselves agreed to remove one generator and replace with a 55kW lithium-ion battery to provide a hybrid solution to our power requirements. This allowed for dual use – the generator would handle peak energy performance whilst the battery would manage the lower loads.

During the four weeks the solution was on site, we were able to make savings of approximately 2.7 litres per hour compared to a standard generator set-up, whilst also lowering noise levels to the surrounding area. In addition, we were able to make a reduction of 4.8 tonnes of carbon emissions.

Project Challenges and Solutions

Surrounding Land and Businesses to the Project

Original plans for the scheme included the demolition of parts of surrounding industrial buildings – to later be rebuilt to construct the flood defence walls on their land. Keltbray recognised the cost to the council for these works would be costly, therefore eliminated this through the installation of sheet pile walls which could be constructed much closer to the embankment and prevented interference on local stakeholders’ land.
During construction of the sheet pile walls we utilised the only vibration free Giken clamp crane in Europe. The crane picks up the piles and feeds them into the piling machine via a crane runner. This enabled us to use piling in such an environmentally sensitive area, other benefits included minimal noise or vibration caused by the works and eliminated the need to work at height. Once completed the sheet pile walls were brick clad with the coping on top specific to the landowner.

Badger Setts on Site

During the works we encountered an unidentified badger set within a culvert beneath the Regent Court car park, where we were due to construct a flood defence wall parallel to the river. The original scope included the infill of that specific culvert so we had to develop a plan to safely remove and rehome the badger living within it. In collaboration with River Stewardship Company and Wildscapes Sheffield we developed a process to seal access to the culvert and install a one-way badger gate allowing the badger to leave but not return.

Despite this the badger managed to leave and return, requiring us to develop an alternative method. Engaging with consultants and our design partner, BWB, we decided to install a concrete slab above the culvert with a concrete headwall across the opening, strengthening the structure and removing the need to infill the culvert. Prior to the pouring of the headwall we installed a concrete pipe from the culvert to the surface of the car park, including a 90 degree soft bend, allowing the badgers safe access in and out of the culvert. We coated the inside of the piping with mortar to provide grip to the badgers and at the outcrop of the pipe we segregated the area with timber fencing and soil.

Learning from this experience we incorporated specific badger sett RAMS into our Environmental Management Plan to benefit our teams going forward. The amended culvert design provided greater benefits to the surrounding environment and wildlife to the project and the badger sett remains in its existing location.

Working in Water

In order to construct the concrete retaining walls, we had to use CFA piling, this required the need to dam the river for the segments we were working on at the time. We first used a portal frame dam but as the riverbed was made of pebble and rock rather than sand, the ground was too porous and the dam failed.

As a result we decided to try a damming method using bulk bags which proved to be successful. Our CFA piling subcontractor, Van Elle had to use smaller rigs due to limited working room and constraints as a result of damming off the river.