PROJECT EXAMPLE: Japanese knotweed and Himalayan balsam removal to enable planned development
On this contract we cleared a site of Japanese knotweed and Himalayan balsam, ready for Morris Homes to begin construction.
The site
A site deemed for development by Morris Homes (Midlands) was identified as having several areas of Japanese knotweed and Himalayan balsam. The proposal for construction of a new residential development consisting of 154 properties.
Originally an old waterworks pump station located off a residential road, with access gates that lead to a roadway through woodland to a building in the centre of the site. Surrounding the main building was soft landscaping, unkempt recreational ground and a stream.
Japanese knotweed area
One of the two Himalayan balsam areas
The stream that ran through the site
Project overview
Originally this was a project to carry out knotweed removal for a Morris Homes site, however Himalayan balsam was also found onsite. Japanese knotweed was located within the proposed rear gardens of two plots. This meant that it was going to be disturbed by development and needed to be excavated.
One area of Himalayan balsam was located to the Local Wildlife designated area and was therefore able to be controlled with herbicide treatment as part of a long-term plan. Two further areas of Himalayan balsam were in an area designated for a settling bond, which meant excavation was the preferred option.
The works
A thorough walk over of the site was undertaken to identify the presence, locations and extent of Japanese knotweed growth. During the survey Himalayan balsam was also identified, mostly within the soft landscaping areas.
We advised that all areas of infestation be fenced off before and during development to prevent accidental disturbance and spread of the plants to other parts of the site, or off-site.
The site was largely overgrown, so vegetation clearance was required to fully determine the extent of infestation. Large areas of knotweed were intertwined with bramble and small trees within a mounded area – we suspected this could have been the result of fly tipping.
Once the overgrown vegetation had been cleared the site was readied for excavation of the knotweed areas.
Excavated ground with knotweed rhizomes marked out in blue
Excavated knotweed soils being stockpiled ready for removal to landfill
Area of excavated ground with root barrier installed
Knotweed rhizomes were found within a large tree-root zone, so a vertical root barrier was installed to the tree-root zone to separate the contaminated soils from the excavated area.
The Himalayan balsam was treated with herbicide as part of a long-term plan, including yearly monitoring for two years in case of any regrowth, and all works were covered by a guarantee.
The outcome
A site that was cleared for development with knotweed removed from site and Himalayan balsam under control. The waste plant materials and soils were transported offsite as controlled waste in accordance with Duty of Care Regulations for disposal at a specially licensed landfill facility.
The excavation team commented: “This was a relatively straightforward contract, with lots of dense vegetation to tackle before we could start excavation and treatment. Knotweed and Himalayan balsam are often found together as they both thrive in woodland areas and near water.”
If you’d like us to advise on or quote for a project that requires our expertise please get in touch with the team.