Chichester Canal – Erosion control

A large (40m) erosion hole produced by the action of turning boats coming out of a bend in the canal


Background

The Chichester Ship Canal is a leisure waterway linking historic Chichester to the sea. The canal runs 4 miles from the Basin to the Harbour at Birdham and, today, the 2 miles as far as Donnington is navigable.

It is valued by local residents and holidaymakers who enjoy the many activities – narrow boat trips, rowing, canoeing, rambling, fishing, and cycling. Management of the activities and maintenance of the canal is the responsibility of Chichester Ship Canal Trust, who lease the canal from West Sussex County Council.

The Canal Trust is a registered charity with c 450 members, whose aims are the preservation, maintenance and improvement of the navigation between Chichester and the harbour – a historical monument to the transport revolution in Britain in the 19th century. The Trust is entirely manned by around 140 volunteers who crew the boats, run the shop, bailiff the angling and carry out maintenance and restoration work.

Project Brief

Part of a set of maintenance works carried out in the Chichester Canal, this project was directed at repairing a large (40m) erosion hole produced by the action of turning boats coming out of a bend in the canal.

As shown in the photographs below,  the eroding bank-line was getting dangerously close to the footpath, raising serious health and safety concerns. Cain Bio-engineering was hired to design and build  a heavy duty double-tier Coirnet/rock revetment to stabilise the bank, and protect it from further erosion. The bio-engineered solution, seeded with native plants, is designed to allow the regrowth of vegetation that will restore the canal bank to a desirable condition.

The Solution

Installation of a 40m length double tier revetment, constructed of coirnet and rock netting, with back-wired hardwood posts and scaffolding poles for support. A backfill of gravel held in place by geo-textiles provides the structure with additional support. A top-dress of site-won soil promotes the growth of native plants, making the protective revetment a living structure.

Before

The eroded bank-line at the site where the turning boats had generated an erosion hole.

During

Construction of the double tier-revetment, increasing the width of the bank.

After

The construction of a sturdy structure, strong enough to stop the erosion of the bank was completed.

The native plants that were seeded into the fibre-rolls will now regrow and restore the bankline to an aesthetic and healthy condition, more resistant to erosion.