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Case study: RDAA / Lower Kennet

Last edited: Apr 4, 2022, 5:33 PM

This case study demonstrates how important consistency is when surveying and treating / removing floating pennywort. Any removal/treatment should be coordinated by a single point source contact (catchment officer etc). Treatment manual or otherwise should be started at the extreme upper end of any infestation and any downstream treatment timed accordingly.

Foudary Brook before and after treatment. Images: (left) Del Shackleford, (right) Angling Trust.

The project

Brief history of infestation and how the project to remove it started. Why did people want to do the removal?

Reading & District Angling Association (RDAA) and other local stakeholders first became aware of floating pennywort when it appeared in the Kennet tributary known as Foudry Brook in 2007. By 2009 it was clear to all concerned we had a potential ecological issue on our hands as Floating pennywort is a vigorously invasive plant (which is costing the Dutch waterways authority over one million euros a year).

It is widely believed to have been introduced to the area during the realignment of a part of the Foudry Brook and the creation of Longwater Lake within the Green Park Business park, which was completed in 1999.

Prior to the establishment of The Lower Kennet Project Group comprising Action for the River Kennet (ARK), RDAA, Kennet Valley Fisheries Association (KFVA) and the Angling Trust there had been numerous attempts since 2009 by the riparian owners and the Environment Agency to stop the spread of this highly invasive plant. These attempts were largely unsuccessful in halting its spread downstream to the Thames in 2017, in part due to the lack of funding and lack of practical knowledge of the management of the plant.

Failure to deal with Floating pennywort in the Foudry Brook saw the problem extend downstream to the Thames as far as Sonning and attracted negative national publicity.

Waterbody name and type
  • Longwater Lake (source), Foudry Brook (natural river), Green park flood relief channel (ditch), river Kennet (canalised river).
  • All these waterbodies feed into the river Thames to the east of Reading town centre.
Specific area worked on
  • Large. The total length of watercourse we deal with is 4.2km excluding Longwater lake.
What went well?
  • The location of ‘booms’ on the non-navigable sections of watercourse, this enabled us to section off areas for manual removal, thus limiting downstream drift.
  • The initial mechanical removal, with manual removal, followed by spot chemical treatment.

Boom placed at the confluence between Foudary brook and Kennet 2018. Image: Del Shackleford.

What did not go so well? Lessons learnt

During the initial mechanical removal large piles of Pennywort were left on the bank. It was noted that despite heavy frosts and even snow, Pennywort within the deep piles was still growing and even rooting into the subsoil due to the humidity within the pile.

Many lessons have been learnt (in fact we are still learning)
  • Any attempt to remove pennywort must start at the extreme upstream end of any infestation.
  • Water courses should be ‘divided’ into bite sided areas with the use of booms to limit downstream drift, where possible.
  • Once any large scale removal has been completed, be it mechanical or manual, disturbance of the plant should be kept to a minimum. Any contact with individual plantlets poses the potential for plant break up and downstream drift.
  • Any arisings should be removed to a DRY location at least 2m away from the waters edge. It should also be spread thinly, no more than 50mm in depth (we have witnessed pennywort continuing to grow in sub-zero temperatures within ‘piles’ due to the humidity, despite the surface appearing to die off).
  • A Kayak is invaluable, this puts you in a position to access even the most hard to reach areas.
  • Removal by hand is best achieved by using a racket of some description (Tennis racket is preferable), removal via nets or by hand breaks the delicate individual plantlets up. Any removed plants should be placed into a container, tub/bucket, again this is to reduce the potential for accidental spread. Simply into or onto a ‘deck’, constitutes a huge risk of further contamination.
  • Any hard to reach or small groups of plants are best sprayed with Glyphosate. Due to the frequency of our visits, we use between 0.5% and 0.75% of the products recommended maximum per litre dosage (dependent on conditions and time of year). By spraying we limit the potential of plant break up.
  • Weekly surveys coupled with immediate removal or treatment are an absolute must.
Methods used? What was done on site and how
  • Mechanical initially, followed by manual ‘in-stream’ removal and then a mixture of picking/chemical spot spraying from a kayak.

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Watch a video on the project

Who was involved
  • Reading & District Angling Association/ Lower Kennet project group.
  • Support from both EA & CRT, although due to historical budget constraints this is largely limited.
Timeline
  • Our project was started in February 2018. This was after numerous attempts since 2009 by the riparian owners and the Environment Agency to stop the spread of this highly invasive plant. These attempts were largely unsuccessful in halting its spread downstream to the Thames in 2017.
  • This project is still on-going.
Frequency
  • After the initial mechanical removal (Feb 2018) weekly visits covering the whole area were made. This continued until April 2020 since which visits have been reduced to 3 times a month. It is planed that these visits will be further reduced going forwards.
Resources available, including equipment used
  • After some considerable delay, the EA eventually approved the application from Thames Water to apply £140k of the Enforcement Undertaking monies on an eradication programme of mechanical removal overseen by Reading & DAA, which has been welcomed by all stakeholders.
  • This has allowed us to employ the services of a contractor. Since the start of the project up to December 2020 we have spent a total of circa 61k.
  • We have funds remaining for a further 8 years, as it is hoped that the frequency of visits by the contractor will reduce going forwards.
Access and permissions
  • This has the potential to cause major issues. Indeed, the lack of interest of riparian owners was the major cause of the spread of Pennywort within the Lower Kennet and then onto the Thames. I would suspect this is the case up and down the country.
  • Without those with the power to enforce the duties of riparian owners, actually doing so, I fear it will always be left to third parties to attempt to ‘persuade’ riparian owners to do the right thing….not always successfully.
Outcomes and what was achieved
  • Thus far, we have reduced total bank to bank infestation of the Flood relief channel/ the Foudary brook to individual plantlets.
  • We have also reduced large scale matting within the Kennet and longwater lake to the same.
Any biosecurity measures put in place
  • Any manually picked Pennywort is contained within a tub whilst in the kayak or boat.
  • ALL equipment used in the manual collection of Pennywort is taken away from the watercourse and washed off on a hard surface.
  • Any resulting vegetation that is washed off, is then treated with Glyphosate.
Any other comments?

  • Going forwards…we believe our biggest problem with dealing with this highly invasive plant is… it’s apparent ability to ‘over winter’ (leafless) in shallow margins, large stands of Phragmites, Typha and damp bankside soils.
  • We have noted spring re-growth in areas that appear during the winter months, to be totally devoid of the plant.
  • It’s root system, however small, also seems to have the ability to lay dormant in areas of bankside that is prone to fluctuating water levels during times of low growth.
  • The success of this project will be measured once we have achieved 2 complete summers pennywort free.
  • Don’t turn your back for one second!
Contact lead for further information

Contact Del Shackleford, RDAA Fisheries Officer (external link)

Return to the main floating pennywort strategy page.