Course Design

This won't be fully known until the commissioning period after construction - what we hope to create is a series of rapids, eddies, playholes and waves. This will be done with a fixed concrete channel, with movable plastic obstacles inserted in the course 'bed', to create constrictions and turbulent water flow.

One advantage of the movable obstacle system is that different courses can be created in the same channel. Additionally, we are planning a choice of channels and flows, creating the most flexible course in the world. The aim is to produce the right combination of rapids, waves, 'holes' and eddies for the different user groups.

While we might all want to have the biggest flow possible, we do need to remember that it costs more to pump bigger volumes of water up a higher drop. Additionally, while we might want the most exciting course, we do have to remember that safety is the first concern.

1. the movable obstacle system - these were developed by Hydrostadium (formerly EDF) of France. They come in 3 shapes - short and long columns ('calleboitis')(see the pictures below); and flat 'toblerones' which lie on the 'river' bed. They all slot into a 'peg board' which is fixed to the 'river bed' - between 10 to 25% of the course can be covered by these boards.

2. Variable flow created by a combination of six, 2 cumec pumps

3. A choice of channels - the final result will depend on the detailed design work, still to be done but if we take the basic design ie a U shaped course and add a second channel with a choice of pump outlet at the top (eg 4.5 m high) and at (perhaps 2.5 m high, at the basin 1/3 of the way down) - then 4 or 5 variants of the course can be run dependnding upon the user group and the features required.

Remember, this is just a hypothetical example of what can be achieved with such a flexible course. However, it does take time to change the course, so instant changes are not feasible.

We have suggested the following basic parameters:

Length - overall length, 400+m.
Drop - top to bottom, approx 4.5m.
Flow -(measured in cubic metres per second - cumecs) from 6 to 12

Compare this with details from the other UK and international courses below:

To help comparison, there is an engineering formula that tries to estimate the degree of 'roughness' of whitewater called Power Surface Index - (discharge*head)/length*width. However, this formula does have it's limitations in comparing one course with another - especially natural courses versus concrete ones.

On artificial courses, the concrete allows the water to flow smoothly down the course - but a natural river bed of stones and boulders creates more friction, effectively 'sucking' some of the energy from the water. With a limited amount of energy available in an AWWC, this energy loss must be minimised.

Flow - is measured in 'cumecs' - cubic metres per second [conversion from cubic feet per second - cfs / 35.7 = cumecs] One difficult issue that the design team will be asked to face will be to ask if the course can handle different flows. The reason we are asking for a variety of flows is that - every drop of water that we paddle, we pay for. At present, we have suggested the following flows

• 4 Cumecs - If beginners don't need much beyond a grade 2 rapid to start on, and 4 cumecs can provide enough of a challenge, then pumping more water isn't required. However, if you put less water down a course that is designed for (e.g.) 12 cumecs, then it will be too shallow. This illustrates some of the difficulty with design.
• 8 - 10 Cumecs - standard flow for rafting and general use
• 12 Cumecs - for international slalom and heavy use recreational periods.

The detail of the rapids will be further down the line, at the detailed design stage and beyond; however, at the early design stage, we will likely specify where each of the 5-7 rapids will go, as well as a rough idea of the amount of drop at each.

What sort of water features do we want to see? An important thing to understand here is that there's a limited amount of energy available to make the rapids happen. If we create a fantastic wave using a lot of the drop and flow, then it leaves less to create other features elsewhere on the course.

Here's some ideas for starters

• standard "V" shaped rapid - with large eddies on each side to accommodate paddlers
• playhole - there will be a couple or more of these. However, the big question that we've asked the playboaters is - how would you build the perfect playhole using combinations of the movable obstacles [picture, right]
• standing/surf waves - can these be created on an artificial course? They are great for teaching people the 'feel' of a proper ferry glide - but will likely require some subtle design of the river-bed. Most other courses have a surf wave based on the entry gate; but the Scottish AWWC is pumped and so won't need an entry gate - and they do take up a fair amount of the energy that is available to the course.
• 'squirrely' eddy lines - for the playboaters who are always expanding new ways of going 3-D.Would a 'splat' rock be safe, and where should it go? small stoppers for intermediate paddlers to play in, and the rafts to bounce their passengers into.

please mail any comments to info@clydesmill.org.uk

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