cuckoo

Hoping these 'outlier' Ops don't prove to be trendsetters. Massive 12z's later.

Better but need the limpet low to head SE

Thank you for coming on to explain the upside down graphs and to clarify that no valves were opened to release extra water before or during the weekend floods. However a lot of water was still released into the Derwent from Ladybower through the plugholes (as you confirmed this occurs when the level is at a negative number). The response of the Derwent (rising to all time records in a number of locations) was out of step with other nearby rivers (e.g. Wye, which stayed below levels where property was at risk) suggesting that the water coming through the Ladybower plugholes was making a big difference.on the Derwent. You said you didn't release any water before the floods but wouldn't it have made sense to do so? Releasing water before the well forecast rain event and taking the reservoir level to a positive number would have left Ladybower in a position to absorb a lot more water prior to the level exceeding the plughole height and starting to overflow. I don't have access to the Environment Agencys river level prediction models but prior to Thursday I would have thought the Derwent was at a level where it could cope with some extra flow and would only flood low lying land. I understand that it might have been the Environment Agency's call but it looks like the level is not being very actively managed and doing nothing prior to the weather warning may have been a missed opportunity to mitigate the level of impact of the floods.

Looking at the historical data, I've been reading your graph the wrong way round. At the time Ashopton was visible, late summer/autumn 2018, the level is given as +13.01 mBDAT, which shows the positive numbers correspond to low reservoir levels and the negative numbers are when the reservoir is full. Reinterpreting the recent graph that you posted it now looks very different. With all the rain on 07th the reservoir begins to fill and goes from +0.0 to -0.5. The normal operating level at -0.21 has been exceeded. Allow an embankment dam to overtop would be dangerous so water starts to be released into the river moving the level back towards -0.3 and the normal level. Maybe there's no conspiracy after all! If they were prepared to let it fill to -0.5 though couldn't they have held it for longer at that level before gradually releasing back to -0.2 rather than the sudden release at the worst time?

severn trent info above link about dam safety. The section that caught my attention about embankment dams like Ladybower "If the downstream face of the reservoir is saturated with water, for example after very heavy rain or due to a leak from the reservoir, it will be weaker and more prone to failure by slipping along a plane of weakness within the embankment. The strength of the embankment can also be reduced over time. This reduction in strength can be caused by: • natural weathering • tree roots • burrowing animals" Maybe there are some concerns about slope instability at Ladybower which triggered the water dump? Doubt I'll find out without working there.

Very interesting post. Not sure, but I think something similar happened on the Derwent for the 2007 event. As many people on this site posted the 24-hr rainfall totals for Thursday were typically below 50mm for a lot of the catchment areas surrounding Matlock. A wet day during a very wet autumn but still well below 2007 totals and well below the 100mm amounts that fell around the Don catchment area and onto the Derwent moors further North. The response of nearby rivers like the Wye were nothing exceptional with levels presenting a flood risk to low lying areas only. Yet the Derwent exceeded all time records at Chatsworth and in Derby. Looking at your graph I believe mBDAT stands for metres below datum. According to Google "the normal level of the Ladybower Reservoir at Ladybower Reservoir LVL in average weather conditions is between -0.21m and 13.03m". Yet it is clear looking at your medium-term data that the reservoir level is being managed to keep the reservoir at or below the datum. When the level starts to exceed the 0.0 datum there is a discharge event to move it back. As anyone who goes there regularly will know Howden and Derwent dams often fill to full capacity and brim over the dam walls but Ladybower appears to be managed differently. Maybe, as you say, there are safety concerns letting about letting Ladybower fill up and given the rainfall totals on the moors they visualised the mBDAT going strongly positive so preemptively dumped the water. Looking at the graph it looks like a big overreaction as even now the levels are still well down compared to the datum. The timing and quantity of the water dump for some of those downstream was disastrous, turning a minor flooding scenario into an all-time record breaking event. Someone should be asking Severn Trent serious questions about what happened, but as you say, a few smoke-screen stories about the plugs, Boris Johnson in town with a mop and it should soon blow over.

Why would they do that at that time? Are there structural concerns about the dam when the reservoir is full?

Ah that explains why its so much higher than average compared to other nearby rivers e.g. Wye & Amber. Makes sense I guess, empty it now to make space to hold back as much as possible over the next few days. I remember in 2007 when the dam was overwhelmed the levels became very high downstream.

Looks like the river Derwent is pretty high at Chatsworth (highest recorded level)

The gulf stream continues up towards the arctic hindering ice formation. Therefore the northerlies heading toward the UK are soon being warmed over the ocean. As others have said areas of the mid-Atlantic / north east Pacific are much closer to frigid continental land masses e.g. Greenland and Northerly flows are subject to less modification prior to reaching the low latitudes.

Fascinating conditions in the Netherlands, thanks for posting Vorticity. I can certainly verify that freezing rain is dangerous as I have discovered (painfully) on my cycle commute before. Looks like increasing possibilities for a UK cold shot now.

Looking good for The Netherlands and West / South Germany tomorrow.

This website shows lightning maps http://www.lightningmaps.org/realtime Invading the Peak District?? Sounds like a rise in Mercian nationalism happening around Birmingham!

Could it have been power lines going down? The wet snow is really accumulating on telegraph wires & tree branches

Surprised at that. I remember being near Buxton in Jan 2010 and there was just over 40cm. In December 2010 there was over 40cm near Chesterfield, so both west and east of the peak district did well, you must have been a bit unlucky on those occasions.