Services

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.

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

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 a ‘Qualified Civil Engineers’ to supervise and certify the completion of any safety works.

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.

Schedule 4 Sections 20 to 24 of the Flood and Water Management Act 2010 provides powers for the Secretary of State to direct flood plans. These detail how reservoir owners or those responsible for the operation of a reservoir will respond to a potential or real reservoir failure. It is good practice for all reservoirs to have on-site plans.

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.

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

Standard reservoir safety flood inflow assessment; 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 arrangements; 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 skills are essential in 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, including a UK Registered Ground Engineering Adviser and geology and MSC in sol mechanics.

Stillwater Associates work in association with a firm of structural engineers, Hewson Consulting, to provide detailed structural design and detailing. Hewson won the NCE/ACE Small Consultant of the Year Award.

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.

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.

Modern management of assets is risk based balancing 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). 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 of the dam failed.

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

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

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.

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 routinely produce rapid dambreak assessment as part of dam safety reviews, and have produced detailed dam break maps using both 1D and 2D modelling.