Why do we need location plans and technical drawings?

These allow us to see how the design of structures for your hydropower scheme may affect the river environment. You will need to provide good quality location plans and drawings of permanent works for any licence or planning application.

Plans and technical drawings should detail the location and design of any structures associated with the impoundment, distribution, abstraction, conveyance and discharge of water. You will also need to include information detailing the current river channel, including banks and bed, in your drawings and show how these may change with your scheme.

For a typical high head, run-of river hydropower scheme this will include:

  • the impounding weir and/or associated screened intake
  • the penstock from the intake to the bank
  • penstock route including stream crossings
  • wings walls, ancilliary structures and the extent of any proposed bank or bed stabilisation measures
  • a fish pass or easement

Whilst we advise on design principles for outfall structures in our hydropower guidance, these structures, the penstock route, stream/river crossings and any bank or bed stabilisation works associated with them are regulated through Ordinary Watercourse consents, Flood Risk Activity Permits and Town and Country Planning consent, not abstraction and impoundment licensing. We will however seek to ensure that our design principles are applied through these routes.

You will also need to provide drawings of any temporary works associated with the construction process for Flood Risk Activity Permits or Ordinary Watercourse Consents.

We will assess technical drawings submitted with an application to see if the hydraulic structures will operate in accordance with the proposed abstraction regime and to ensure it meets other requirements for protecting the in-river environment as we have set out in our guidance. This includes design checks to ensure that the low flow notch is correctly sized and that the fish easement will provide suitable flow conditions for fish passage.

A well-designed hydropower scheme that is clearly presented in technical drawings can be easily assessed, leading to a quicker licensing decision. An application for a poorly designed scheme that fails to incorporate our environmental design principles or that is presented in low quality or incomplete drawings may be returned, lead to extended licence determination time or a refusal.

The technical drawings that we approve will form part of the abstraction and impoundment licences. They will be used for compliance purposes. This means that the intake weir and associated structures must be built to the approved design. Where they have been built at a different location or to an alternative design than those specified on the licensed drawings, then we may take enforcement action requiring you to correct this in line with our Enforcement and Sanctions policy.

What drawings are needed?

You will need to provide the following drawings for all hydropower schemes:

  • A location map or block plan at 1:5,000, 1:10,000 or larger scale, subject to the extent of the development showing where the proposed structures will be sited in relation to other local features.
  • Plan, profile and cross-section drawings for the impounding and/or intake structure, fish pass/easement and outfall at a scale of 1:20 or higher resolution to show existing topography, natural features and proposed design detail including modification to channel bed and banks.

Note that these drawings are in addition to any maps showing ownership boundaries demonstrating rights of access.

For small schemes the details of the fish pass/easement can usually be included in the drawings for the intake structure. On larger schemes or sites where the fish pass/easement is located away from the main intake structure or where formal fish pass approval is required, then additional drawings may be needed to show the design detail of the fish pass.

A set of example drawings illustrating a typical high-head, run-of-river hydropower scheme are presented in this guidance. These have been drawn to show a generic design of passive control, overspill weir and intake with associated outfall. They include the key design features and information that should be included on technical drawings.

The list of information requirements for technical drawings may initially appear extensive but are necessary for the proper design and construction of a hydropower scheme of any size.

A checklist of requirements is provided at the end of this section to help applicants complete their drawings.

What standard of drawings are required?

Drawings must be clearly presented and include key design details which are listed in the next section. They will normally be completed using computer aided design (CAD) software and submitted digitally in paper document format (pdf). We will accept hand drawn plans on A4 or A3 paper providing that they are good quality and drawn with ink, including the details listed below. We will not accept pencil drawings.

What information is needed on the drawings?

All drawings should:

  • have a title describing the drawing
  • include a site and project name
  • be drawn to scale with scale specified in relation to paper size (e.g. 1:50 at A3)
  • have a drawing date, author and version number

We will require key levels and dimensions to be included on the drawings.

Dimensions should be provided in metric units. In detailed drawings they should be provided in millimetres e.g.1250mm.

Levels should be provided as an absolute value in metres Above Ordnance Datum (mAOD) to 3 decimal places e.g.68.395m. Absolute levels can be derived from topographic survey using GPS surveying equipment or transferred from a local benchmark. Details of the location and elevation of the local benchmark(s) should be included with your technical drawings.

Topographic information

Drawings will need to include information about the characteristics of the natural river channel, adjacent landform and other natural physical features prior to any construction work being carried out. This information can be collected by undertaking a topographic survey of the proposed intake and outfall sites to obtain site measurements. These should include but not be limited to:

  • the outline of the river channel (bottom of bank) and measurements of channel width at, upstream and downstream of the proposed points of intake and outfall
  • cross sections of the river channel at the point of the proposed intake and outfall
  • the outline and elevations of the bank tops (the point at which the bank slope changes from the river channel to the surrounding land use)
  • a long profile of the natural river bed in reaches where structures are developed
  • the location of prominent natural in-channel or bankside features such as tributaries, areas of erosion, gravel bars, rock outcrops or boulder stones.

Details of the impounding weir and intake structure

The hydraulic design of the impounding weir and intake structure is key to ensuring that the flow is appropriately distributed between that licensed for abstraction and that required to protect ecology in the depleted river reach.

It is therefore essential that the hydraulic performance of the weir and intake structure has been correctly assessed and incorporated into the design. The key dimensions and elevations of the weir and intake structure that provide hydraulic control must be detailed in technical drawings and should include:

  • the crest height and width of the intake and residual flow sections of the proposed weir
  • existing and proposed bed levels at the structure plus the length and extent of backwater created by the impoundment
  • the invert level, width and depth of the low flow notch and any other point of discharge such as stop log opening, eel pass or route for fish passage
  • the static water level, width, length and depth of the plunge pools
  • the invert level, width and depth of the outflow notch of the plunge pool
  • penstock and diameter
  • eel pass

We also consider wing walls and any bank or bed stabilisation works, such as boulder stone, to be part of the impounding weir and intake structure as they are engineered features affecting the natural morphology of the river channel. The use of engineered bank and bed stabilisation measures should be minimised and only used where design calculations show there that there is proven need for them to retain channel and structure stability and bioengineering approaches can be shown to be unsuitable.

The type, location, extent and elevations of all proposed stabilisation measures should be included in the technical drawings.

Details of the fish pass or easement

As detailed earlier in this guide, formal fish passes, and more formal designs of easements should be designed to standards set out in the Fish Pass Manual to provide specific flow conditions for fish passage. Certain elevations and dimensions of these passes will be quite precise and should be included in technical drawings. They include:

  • the static water level, length, width and depth of pools
  • the invert level, width and depth of notches between pools
  • the crest height of weirs between pools
  • the total length of the pass structure

Rocky ramp type easements are less formal structures for which it can sometimes be more difficult to provide a detailed design. For larger rocky ramps based on Fish Pass Manual design standards then dimensions and elevations like those of formal fish passes above should be included in drawings. For smaller rocky ramp structures seeking to replicate local in-river features then the technical drawings should include as a minimum:

  • the outline of the ramp structure including dimensions of total length, width and height
  • static water level, width, length and depth of the first pool downstream of the intake weir low flow notch
  • the central low flow channel route through the ramp

The location, dimensions and elevations of pools and intermediate channels should be included where possible.

Details of the outfall structure

The key information required to show the design of the outfall is that detailing the position of the outfall relative to the river channel, the measures taken to dissipate outfall velocities and the structures used to build the headwall, outfall channel and any bank or bed stabilisation. Key requirements for technical drawings for outfalls are:

  • location and diameter of tailrace pipe
  • invert levels of the tailrace pipe at the point of discharge
  • structure of outflow channel
  • bed level in the main river channel at the confluence with the outflow channel
  • elevations of velocity dissipation structures on the outfall
  • outline and elevations of any works for bank and bed stabilisation including headwall

Drawings checklist

You should include the following drawings with your licence application

  • location plan (including intake, penstock route, turbine house and outfall)
  • plan, cross section and long profile of intake structure
  • plan, cross sections and long profile of fish pass/easement (where required separately)
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