Manchester Ordinary Watercourse Improvements
Manchester City Council Highways department are developing improvements to the drainage networks in several areas to reduce the likelihood of flooding to residential properties. This work is funded through the Environment Agency.
Work is underway and will continue through to March 2023 to improve the operational performance of several areas based upon recorded information, flooding incidents and input from residents and businesses. Works will include:
- removal of debris from streams and watercourses
- vegetation clearance to prevent debris blocking the existing features
- installation of a series of features to help the watercourse remain operational during flood events, while minimising risks to residents and businesses to increase the performance of the existing system
The works will be undertaken in two concurrent phases, with the first phase being maintenance operations to maximise the performance of the existing system. Ditch reprofiling, removal of silts / debris from the channel, and removing debris from the existing trash screens (grates that prevent waterborne debris such as sediment, weeds, timber, animal carcasses, litter and household and non-domestic waste from entering in advance of the culverted sections, and removal of debris from culverts).
We will introduce leaky dams through the various woodland areas. These are specifically designed and engineered to trap debris further upstream of the trash screens to reduce the likelihood of blocking and potential flooding. When significant rainfall occurs, these leaky dams are designed to breach. In more regular storm events floodwater is stored throughout the length of the drain, which reduces the risk of flooding in key areas.
The leaky dams are made from timber, constructed into the existing banks with a narrow stone track for construction and maintenance access. The location of the leaky dams is specifically engineered to permit flooding in woodland areas away from residential areas.
As part of the improvements, we will undertake a scheme of vegetation removal, which has been specifically identified in consultation with our ecological and environmental team. The vegetation clearance is a compromise. This is not a wholesale removal of vegetation, but a calculated scheme of minor clearance. Some vegetation needs thinning to aid maintenance access, some areas are cleared to reduce the potential for materials dropping into the drainage channels and obscuring the downstream outfall.
This is limited to clearance of vegetation within 2 meters of either side of the drainage ditch system for up to 30 meters from existing trash screens or new leaky dams. The vegetation clearance does not include the removal of mature trees, but self-seeded immature species and scrub.
Phase two of the work will consist of the introduction of new headwalls and trash screens at existing inlet locations within Ash Wood, Gorse Covert, Park Wood and Big Wood, to improve the resilience of the network and allow for easier maintenance.
The work will be undertaken in daylight hours, and with awareness of the noise and potential intrusion caused. During these works, it is necessary to restrict access to the four wooded areas for safety reasons. Please see map.
There is also potential for odours when the decaying vegetation is removed from the watercourses, however this material will be removed using a vacuum and disposed of within a licensed waste handling facility. We should stress the works are to a surface water system only but will advise of the potential risk.
Highway maintenance teams will be procuring the works, and they will manage day to day activities on site. They will also deliver any traffic management requirements to enable the works to be delivered quickly and efficiently.
Works are to begin at Gorse Covert, moving onto Park Wood, then Ash Wood and finally Big Wood.
Working hours will be 7.30am - 5pm.