Coding classes in Denbighshire

The record gives a radius of about 54 metres and a crest length of 140.2 metres. If the crest is an arc of a circle, its angle in radians is simply the arc length divided by the radius: 140.2 over 54 is about 2.596 radians, or 148.8 degrees, well short of a full semicircle, which fits the record's description of a near-crescent. From the angle the learner computes the chord, the straight line between the two ends, which is roughly the width of river the weir spans, and the sagitta, how far the curve bulges upstream from that line.

Why curve it? Water flowing over a weir obeys a power law: the flow grows with the crest length times the height of water above the crest raised to the power one and a half. Turn that around and, for the same flow, the water above a longer crest stands lower. The learner inverts the formula in Python: with a crest 35 per cent longer than a straight one across the same river, the water over the crest stands 18 per cent lower, at every flow. The flows and weir constant in our example are invented, but the 18 per cent depends only on the ratio of lengths, which comes from the record.

One more property of power laws appears: doubling the flow does not double the height over the crest; it multiplies it by two to the power two thirds, about 1.59. The learner checks every step with a known case, a crest that is a full semicircle, where the chord must equal twice the radius exactly.

Turning a design into numbers you can check is why a Denbighshire teenager should keep learning to code in 2026. The longer argument is in why teenagers should still learn to code in 2026.