Agenda item

Executive Summary

An area of the cliff and slope at Overstrand is contaminated with Japanese knotweed, a highly invasive plant species that has strict legal responsibilities associated with its control, disposal, and the prevention of its spread.

The Council has a responsibility to address the issue, and this is made even more critical due to the nature of the area it inhabits. The cliffs are inherently unstable and the slip material appearing on the sea wall contains knotweed, the dispose of which is very expensive.

The Council commissioned a specialist report into the issue, seeking advice on its legal responsibilities as well as a management approach for addressing the problem. The contents of the report have been considered, and recommendations have been made as to the most appropriate actions to pursue.

Options considered

There are various potential options for managing the infestation and those are detailed in the consultant’s report appended to this report. There are no realistic alternatives to the immediate actions recommended, as to allow the knotweed to remain untreated, would inevitably lead to increased costs associated with removal and disposal of slip material, which might delay the planned refurbishment of the sea defences, and might breach the Council’s legal responsibilities to prevent its spread.

Consultation(s)

The matter has been referred to in notices placed in the vicinity of the site and has been discussed at drop-in events held in the village. The local member has been briefed, and the Parish Council have been made aware, together with members of the public, at the 2025 annual parish meeting.

Recommendations

It is recommended that the Cabinet resolves to provide a total budget of up to £120,000 from the ‘reactive coastal works’ budget (approved by Cabinet in March 2025) and the CTAP budget, to undertake the actions recommended in this report to address the knotweed issues over the period between autumn 2025 and autumn 2027.

The actions will include:

1. Complete a programme of four containment foliar sprays by lance/stem injection between 2025 and 2027, for a 3-metre strip at both the base and the top of the coastal slope
2. Complete works for clearance of promenade and licenced disposal of slump material containing Japanese Knotweed
3. Complete works to stabilise the base of the coastal slope, landwards of the top of the sea wall in the immediate proximity of promenade clearance works, to inhibit further encroachment of slump material potentially containing Japanese Knotweed
4. Further investigate the potential for annual foliar spraying, utilising appropriate methods, across the entire area containing the Japanese Knotweed infestation, then implement treatment by the most appropriate means (potentially between 2025 and 2027)
5. Implement and promote stakeholder engagement and community awareness, through stakeholder coordination, raising public awareness and education of the knotweed issue
6. Investigate approaches to maintaining vegetative cover during treatment of Japanese Knotweed and re-establishing vegetation post-treatment of Japanese Knotweed, in order to reduce the potential impact of rainfall-induced surface water run-off upon cliff instability
7. Implement long-term monitoring of Japanese Knotweed infestation, covering 2025 to 2027 treatment period and subsequent treatment/post treatment periods, as required. Long-term monitoring to track changes in infestation size and vegetation cover and review and refine initial treatment approaches, potentially including further foliar spraying and/or stem injection.

Reasons for recommendations

To ensure appropriate action is taken in a timely manner to meet the Council’s legal responsibilities and allow other works to proceed.

Background papers

Reports to Cabinet on 31^st March 2025 relating to Coastal Management – budget for reactive coastal works; and Coast Protection Works at Overstrand

A (Haskoning) consultant’s report on the subject of this report is included as appendix 1

Wards affected

Poppyland

Cabinet member(s)

Portfolio Holder for Coast: Cllr Harry Blathwayt

Contact Officer

Robert Young; Assistant Director for Sustainable Growth; robert.young@north-norfok.gov.uk