On the 18th Feb 2020, the River Severn peaked at 4.665 m at the Mythe Gauging Station. This was the third highest level on record here, with the still yet-to-be-beaten 5.50 m record recorded in 2007. I sent the drone up on the 18th, which was risky as it was raining and there was a fairly strong wind. You can see those photos above, reminiscent of the famous 2007 Tewkesbury island shot.
At one point, three of the four main routes out of the town centre were cut off, with only Mythe Road to the north east of the town still holding its head above the water. It's difficult to comprehend how much water there actually is, even with the aerial shots. Water stretches to the foggy horizon in all the photos, in almost all directions. The Severn's floodwater has backed up the Avon and all the other smaller rivers which converge in Tewkesbury, creating an incredibly wide-reaching impact.
Why is Tewkesbury so prone to flooding?
Tewkesbury is unlucky in the fact that it is the converging point of the great River Severn, Britain's longest river, and the Warwickshire Avon. On top of this, a number of smaller but still significant tributaries also converge here. Tewkesbury is susceptible to both immediate, local-storm-induced flash flooding and the more delayed cumulative flooding that the Severn and Avon bring.
Why did this flood event not break the record level like it did upstream?
Although extremely significant, this flood event was still almost a metre off the record in Tewkesbury, but broke records higher upstream. Here's my theory: The Severn's floodplain at Tewkesbury has an incredibly big capacity and can support floodwater from the Severn and Avon without closing any major roads and hardly any minor ones. During this flood event in Feb 2020, although the Severn was bringing almost record-breaking amounts of water to Tewkesbury, the other rivers were not. Due to the delay, the small, quick-response rivers were back to normal levels and the Avon was not in significant flood, except for what backed up from the Severn. In record-breaking 2007, the quick-response rivers in Tewkesbury were all bringing record-breaking amounts of water into the Severn's floodplain, as well as the Severn and the Avon. The cumulative effect of all the rivers in flood, as opposed to just the Severn, was enough to push the level at the Mythe Gauge up to the 5.50m record.
In reality, there are an enormous amount of reasons why a significant flood may be experienced in certain places on a river and not others. For example, imagine a heavy rain storm drops a significant amount of water in both the Severn and the Avon upstream. Then imagine these two rivers as having a 'wave' of flood. The water level increases before decreasing, like a wave. Then imagine these waves travelling down to Tewkesbury. If it happens that the route the wave takes in the Severn is shorter than that in the Avon, the wave from the Severn will arrive in Tewkesbury before the wave in the Avon, so Tewkesbury may see two small floods or one prolonged but small flood. However, if these waves arrive in Tewkesbury at the same time, their amplitudes will add together to create a wave double the size, creating a short but big flood.
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