Upper Alt Misconnections

Overview

The Upper Alt Catchment is urban in nature and suffers in places from the impact of poor water quality, man-made modification and flood risk. Some locations are suitable for creation of wetlands and other features that would help reduce these impacts and enable the River Alt to become healthier. This project aimed to scope, prioritise and provide designs for these features and deliver one intervention.

Water Quality: The Upper Alt is failing under the Water Framework Directive (WFD). Investigations into these failures consistently identified misconnections, urban drainage and physical modifications as being the reasons.

Flood risk: Recent Natural Flood Management (NFM) modelling & opportunity mapping identified the Alt as having potential for Natural Flood Measures to reduce the risk of flooding to properties.

 

Opportunity mapping for both WFD and NFM indicated that the creation of wetlands in the upper Alt could provide water quality improvements and flood attenuation. These wetlands could also increase channel and habitat diversity, contributing to the creation of valuable habitat in an otherwise urban environment.

 

 The project was delivered over 3 phases: 

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Phase 1 - Design and Feasibility

The feasibility phase of this project was completed in 2018/19. Three interventions were designed, costed and prioritised based on value for money and effectiveness in achieving NFM and WFD benefits. Risks including landowner agreement and land contamination were also considered. As a result of the prioritisation, the creation of a wetland within Croxteth Country Park was selected as the preferable option.

Phase 2 - Consultation

This phase, completed in 2020, involved liaison and consultation with the landowners - Liverpool City Council and the Croxteth Park Volunteer Group to explore the possibilities for delivering the interventions identified in phase 1. Land contamination and unexploded ordnance also had to be investigated to ensure the digging works could be carried out safely and excavated material was disposed of appropriately.

Phase 3 - Delivery

This phase involved the creation of the wetland within Croxteth Country Park at a point where the River Alt splits into two channels . The wetland will act as a filtration system to improve poor water quality caused by an accumulation from pipes and misconnections upstream; provide flood water storage; and create 1075m² of habitat.

Ecology survey - July 2020

Before any construction or scrub removal work was undertaken, an ecology survey was carried out by Mersey Rivers Trust staff to ensure any works would not have a negative impact on local wildlife. The survey was a combination of local records from Merseyside Biobank and a walkover survey of the site with the help of the Croxteth Park Volunteer Group.

Scrub removal - September 2020

Trained Mersey Rivers Trust staff spent two days removing scrub and brambles from the wetland site using brushcutters and hand tools in order to clear the area ready for digging works to commence. It was hoped that this would be a task that volunteers could get involved in however this was not possible due to local COVID-19 restrictions at the time.

Wetland construction - October 2020

In October 2020 contractors CCNW began construction work on the wetland. This involved further site clearance, digging the pond and landscaping the excavated material around the site. The work took two weeks to complete.

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