LONG POST ON #ELNINO / #FLOODING
As we hear of the effects of the #ClimateEmergency round the world, and see #flooding in #Norway I am reminded of #StormDesmond that hit #Cumbria between 5th & 6th Dec 2015. In 48 hours #Thirlmere in #LakeDistrict recorded 405mm of rainfall in combination with severe gales up to 81mph. This was an El Nino year.
It was the 4th major storm of the autumn. The ground and the lakes were already saturated.
The Thirlmere reservoir, built in 1888 to supply Manchester (153km away) with water, is owned by the #UnitedUtilities a private water company and has an agreement to supply water to Manchester throughout the year.
At the time of #StormDesmond the reservoir was already at full capacity. It is reported that engineers were helicopted to the site to open ancient dam release valves, and the water pumping station was flooding.
2/
Locals report that the reservoir was overtopping a stone wall designed for traffic safety (not designed to hold water) which runs across the reservoir dam. #UnitedUtilities report they have no data about reservoir level during the storm.
Maximal flows were released into the outflow river, St Johns Beck, which leads into the River Greta, which follows through the middle of the town of #Keswick , then drains onward to the town of #Cockermouth .
3/
#Keswick’s newly installed flood defences were breached, and downstream hundreds of homes were flooded
The combination of the heavy rainfall through the autumn, heightened with #StormDesmond, and then in combination with the reservoir opening its overflow pipes caused massive disruption from the flooding, hundreds made homeless, and a massive £500 million cost to the economy.
4/
#StormDesmond caused landslides which closed the main road, north-south, through Cumbria (A591) for months. Many trees in the pine forest surrounding Thirlmere were damaged.
#UnitedUtilities at the time had no requirement to prevent flooding, despite earlier serious flooding in the area, and were primarily focused on ensuring they preserved water in the reservoir to supply their customers.
/5
After the disaster #KeswickFloodActionGroup #KFAG worked with the #EnvironmentAgency #EA and #UnitedUtilities to petition that during the flood risk season (autumn – winter) the reservoir is maintained 3m below full, to prevent flooding, and also, when there is heavy rainfall to gradually release increased amounts out to the St Johns Beck.
6/
As we wait for the effects of #ElNino to come this autumn, it will be testing the commitment of the #EA & #UU to work to prevent or mitigate severe #flooding again.
However, questions remain about the flood outflow system for the reservoir, and changes made during recent placement of a pipeline to West Cumbria are still to be tested in highflows:
7/
- The overspill weir drains through a rough-hewn tunnel, which in combination with increased storm debris from the surrounding forest, could become blocked
- Beyond the overspill weir, the water drains down a rough tree lined channel, which also is at risk of being blocked, either the impeding the overspill weir or diverting the water course towards the dam wall
8/
- The control centre for the lower valves built into the dam wall stands within the reservoir and is reached by a bridge. It is not clear if this can be reached safely in high flood levels
- The valves built into the reservoir dam wall are relatively small, and it is not clear if they would be able to provide sufficient drainage in the case of failure of the main weir.
9/
- We lack parliamentary oversight of the flood management role of the reservoir, at present the communities of Cumbria rely on nothing more than some promises to keep the reservoir level low when there is flooding risk.
10/
The Environment Agency now regularly have the local flood action group at their meetings with United Utilities - apparently a first in England. They are pushing to change the contractual requirement for the reservoir operator to help prevent flooding, as well as the requirement to supply drinking water, as the contract is coming up for renewal.
It's still a worry that with increasingly erratic weather the reservoir is vulnerable, & thus the 10 000s of people downstream
Stingray's Badger Friend
Emma Bee
Gary 