Stillwater Associates has grown steadily since its formation in 2008 to become a successful engineering consultancy specialising in dams and reservoirs. Establishing an EOT is the next step in our company’s growth, and marks a significant milestone for us, with full ownership of the business being transferred from the company’s founder (David Littlemore) to the EOT. This change will give all our employees a greater sense of ownership and representation whilst ensuring the long-term sustainability of the company as a successful, independent business. It will also continue to strengthen our workplace culture of quality, technical expertise and teamwork, ultimately delivering an even greater service to our clients.

Congratulations to Tom Wanner and Hermann Stehle for their appointment as directors of Stillwater Associates Limited, and to Jon Holland for his appointment as a director to the board of trustees.

A huge thank you to our amazing team for their continued hard work and dedication. We’re extremely excited by the company’s continued development and growth, and are proud that our employees will share even more in this success moving forward.

In all cases the sink holes appear to have been caused by water passing through and eroding the embankment fill adjacent to overflow structures, pipework or chambers located within the embankment. The internal erosion was most likely initiated by flows entering the embankment fill through a defect in one of the structural elements leading to the formation of a void. Over time the void increases in size to a point where the roof of the void cannot support itself and the void moves towards the surface of the embankment.  Eventually the saturated topsoil layer falls into the void and the defect can be observed from the surface of the embankment.

Advice for Undertakers

As always careful regular surveillance of embankment dams is key with the following of particular importance:

• Consider making additional surveillance visits to reservoirs during and immediately after inclement weather.
• Pay particular attention to those sections of the embankment that are adjacent to overflow structures or have pipework / chambers within them.
• Look for signs of flows entering or issuing from defects in the overflow structures, pipework or culverts.
• Consider carrying out CCTV surveys of pipework / culverts to check for defects. 
• Contact your Supervising Engineer if you have any concerns or notice any changes in the appearance of your embankment or associated structures.

The photos below show a number of examples of voids that have recently appeared at reservoirs where we provide reservoir supervision services. Fortunately each of these defects were observed in a timely fashion by the Undertakers concerned and staff from Stillwater Associates were able to attend site to provide advice on the immediate actions and long term remedial works. 

Reservoir 1 - Void located immediately downstream of the scour valve chamber caused by defects in the brick culvert leading away from the chamber.

Reservoir 2 - Void located on the embankment crest close to the overflow structure side wall. This void was caused by a defect in the upstream wave wall which allowed flows to pass behind the side wall of the overflow structure creating a pipe within the embankment which eventually reached the surface.

Reservoir 3 - Internal erosion took place along the alignment of the overflow pipe which is likely to have been initially caused by a defect in one of the concrete pipes or a misaligned joint between two pipe sections.

Reservoir 4 - Void adjacent to the overflow cascade side wall caused by defects in the upstream wave wall and cascade side wall.

Stillwater Associates have had a number of inputs into this publication with a special note made to Halil Kula for his articles where he shares his impressions of his first Supervising Engineering Forum and the lessons learnt during this important event in the BDS calendar.

The 2023 BDS Yearbook can be accessed free at the following link - https://britishdams.org/assets/documents/Yearbooks/BDS%20Digital%20Yearbook%202023.pdf

Stillwater Associates has been working alongside Somerset Council and its predecessor, South Somerset District Council, since 2020 to promote this scheme through the early feasibility stages, which included a comprehensive reservoir safety risk-based assessment.  The assessment identified the need for modifications to the existing overflow stilling basin, installing erosion protection along the downstream face of the embankment, and raising the embankment crest to prevent overflowing during extreme flood events.  The various elements of the scheme were subsequently optimised by laboratory-based physical hydraulic model testing of the dam and overflow arrangements.

It is anticipated that construction of the scheme will be completed during the summer months of 2024.

Details of the technical papers can be found below:

Authors: Halil Ibrahim Kula, BSc, MSc

Dams and Reservoirs - Volume 33 Issue 4, December, 2023, pp. 141-153

ICOLD 2023, Gothenburg Sweden: Turkish experience of the February 2023 seismic event

https://www.icevirtuallibrary.com/doi/abs/10.1680/jdare.23.00100a

Authors: Hermann T. Stehle, Meng, PrEng MSAICE, SE

Dams and Reservoirs - Volume 33 Issue 4, December, 2023, pp. 167-168

ICOLD 2023, Gothenburg, Sweden: report on sessions on concrete dams

https://www.icevirtuallibrary.com/doi/abs/10.1680/jdare.23.00050

This desktop exercise provided an excellent opportunity for knowledge sharing and will go a long way to ensuring that reservoir safety remains a top priority. As a company we work hard to ensure that our clients’ dams remain safe and compliant with UK reservoir safety legislation. Reservoir emergency planning forms an integral part of this and we look forward to helping more clients plan and run more of these valuable exercises. It was a very long table! 

The British Dam Society is an Associated Society of the Institution of Civil Engineers, consisting of individual and corporate members interested in sharing experience or knowledge of all aspects of dams and reservoirs. The society exists to advance the education of the public and the profession in technical subjects relating to planning, design, construction, maintenance, operation, safety, environmental and social issues related to dams and reservoirs.

As the reservoir safety industry continues to move through a period of change the British Dam Society fulfils an incredibly important role in within this field and its an excellent opportunity for Stillwater Associates has been able to support the workings of the BDS in this particular way.

Check out the British Dam Society website (www.britishdams.org) for lots of valuable reservoir safety resources.