Reservoir Safety Compliance

Reservoir supervision

The Undertaker of each high risk registered reservoir is required to appoint a Supervising Engineer to supervise the operation and maintenance of the reservoir between statutory inspections. The role of a Supervising Engineer is a continuous appointment, although typically the Supervising Engineer will undertake an annual inspection of the reservoir, prepare an annual statement in accordance with Section 12 of the Reservoirs Act and be available to visit at any other time in case of an emergency. Stillwater Associates has an extensive network of Supervising Engineers throughout England and Wales that are able to provide these services. 

Reservoir monitoring

Regular monitoring of reservoirs is a legal requirement under the Reservoir Act 1975 and includes features such as water levels, seepage and crest levels.

Stillwater Associates can assist Undertakers with their monitoring requirements by carrying out routine site visits, levelling surveys and the development of reservoir record systems.

Reservoir inspections

Reservoir safety legislation requires periodic inspections (safety reviews) at not less often than every 10 years and where appropriate to identify and recommend measures to be taken in the interest of safety to manage the risk to those living downstream of the dam. These can only be carried out by engineers appointed to the ”All reservoirs panel”, who also act as a ‘Qualified Civil Engineers’ to supervise and certify the completion of any safety works.

Stillwater Associates have a number of All Reservoir Panel Engineers that are able to carry out periodic safety reviews.

Construction of new or enlarged reservoirs

A Construction Engineer needs to be appointed to supervise the design and construction of any new reservoir or modification of a reservoir such that increases its capacity.

Stillwater Associates has extensive experience with the construction and modification of large raised reservoirs including the provision of Construction Engineer Services for third party reservoir designs. 

On-site emergency (flood) plans

It is a legal requirement for all Undertakers to prepare an on-site flood plan for high-risk and not high-risk, large raised reservoirs in England, including reservoirs under construction. The on-site flood plan covers the areas that could flood from a breach of a reservoir and the actions needed to prevent, control and mitigate the uncontrolled release of water. Stillwater Associates can help prepare and maintain your on-site flood plans and assist with the required testing of these plans.


Reservoir Engineering

Reservoir feasibility and planning

In planning new reservoirs and confirming their technical feasibility it is important to consider all aspects including availability of water, potential hazard to those downstream, reservoir watertightness and source of materials for construction.

Stillwater Associates has extensive experience in the feasibility planning design for new reservoir. Early involvement with our design teams have provided invaluable assistance to our clients in achieving a technically robust and cost effective solution.

Detailed design and contract procurement

We have extensive experience in the detailed design and preparation of tender documents for reservoir remedial and improvement works.

Hydrology / Hydraulics

Stillwater Associates' staff have extensive experience in carrying out reservoir safety flood studies, hydraulic modelling of reservoirs and overflow arrangements, identification and testing of potential remedies for inadequate freeboard, hydraulic analysis and design of spillways and energy dissipation structures, design of syphon overflows and drawdown arrangements, dam-break flood modelling and flood risk mapping, specification and management of physical scale modelling of hydraulic structures.

Geotechnical engineering

Geotechnical skills are essential in the design of new reservoirs, in terms of foundation requirements for structures and the dam embankment as well as sourcing and compaction of fill. Stillwater Associates have in-house geotechnical skills, to prepare ground investigation and earthworks specifications, and interpretive reports, supervise ground investigations and carry out dam stability and seepage analyses and internal erosion assessments.

Pipework and valves

Stillwater Associates carries out hydraulic analysis of reservoir pipework and valve systems including drawdown assessments in accordance with the ‘Guide to drawdown capacity for reservoir safety and emergency planning’ (EA 2017). We also carry out the design of new pipework and valve systems including drawdown facilities and syphon systems and provide assistance with the design of new valves, penstocks and gates.

Construction support

Supervision of construction or overseeing of site activities ensures that the engineering design is constructed to the standard required and that any changes undertaken on site are consistent with the design philosophy. We are able to offer project management, construction supervision or site supervisor roles in line with normal construction conditions of contract.

Independent reviewer

On many projects the client appoints an independent or peer reviewer to provide an independent review of aspects of the design which are critical to dam safety. Stillwater Associates has been appointed on this role on many projects.


Other Services

Risk assessment

Modern management of assets involves risk based balancing of the costs of safety upgrades against the benefits of that intervention, and thus judging whether the risk has been reduced “as low as reasonably practicable” (ALARP) as set out in the ‘Guide to risk assessment for reservoir safety management’ (EA 2013). Stillwater Associates staff have extensive experience of a risk based approach to dam safety works, including identification of the full range of options from minor interventions to major upgrades, quantifying the benefits of that risk reduction and thus whether the reduction in risk achieved is proportionate to the costs. This ALARP approach has been used on many dams where the consequences of failure are modest, to identify works that are proportionate to the potential consequences if the dam failed.

Asset management

Preparation of asset registers in watercourse or dam systems, including key dimensions and condition. Identification of maintenance programme and costs, including risk based prioritisation of both maintenance and upgrade works.

Water resources

Stillwater Associates offers the following water resource services:- Analysis of long term hydrometric data; catchment hydrological modelling for long term flow sequence synthesis; assessment of river abstraction potential based on possible abstraction licence and compensation flow scenarios; behavioural analysis of surface water reservoirs and river abstractions; hydraulic analysis of water transfer and distribution systems; abstraction licencing.

Flood risk and planning

Initial flood risk assessment for development proposals; detailed flood mapping using flood levels and survey data supplied by the EA; assessment of feasibility of potential flood impact mitigation measures including source control; specification and management of river channel surveys and threshold surveys to EA standards, obtaining EA approval or advising on nature and feasibility of further work required to achieve approvals; addressing PPS25 requirements including Sequential and Exception tests.

Dam break assessment

A key component of any dam safety assessment is the potential consequences if the dam failed, as this is needed to set the design standard for floods, as part of on-site flood (emergency) plans and for quantitative risk assessment. Stillwater Associates routinely produces rapid dam break assessments as part of dam safety reviews, and has produced detailed dam break maps using both 1D and 2D modelling.