Monday, December 18, 2017

Pre-Christmas Water Status Update

Water Status Reports – A Tale of Contrasting Flows
Thornton-le-Dale flow gauge in snow 30/11/17

Apart from the heavy rains prompting flood warnings in the northern England during the third week, November was a largely a relatively dry month across the UK; especially in the English lowlands, southern and central Scotland. The autumn (1st September – 30th November) rainfall total was well down in these areas, too. In southern and SE England, rainfall deficits have been building for the past 12-18 months; reflected in low groundwater and river levels and low river levels in these areas. A growing number of rivers across southern England are running well below normal: the Thames among them; with the Great Stour in Kent and the Lee in Hertfordshire exceptionally low; and hitting new record lows for November.
Great Stour, Canterbury, August 2014
The Stour gauge is just upstream Canterbury (Horton), where it is a chalkstream fed by groundwater percolating through the North Downs. The CEH and EA hydrographs show it has been running well below normal for at least the past twelve months; with no increase in flow since the summer. On 16th December, the River Lavant above and through Chichester, West Sussex was still dry. I have not seen any water in the river for the past eighteen months.Most chalk wells in southern England have yet to recharge and one in Kent (Little Bucket Farm) is dry according to CEH. Though most reservoirs are at least 80% capacity; some in the south are well below that, especially Bewl in Kent which was only 33% capacity at the end of November. The watery outlook for next year is dependent on how much rain falls over the winter and early spring. To bring the low level rivers and wells back into the normal range for the time of year will take “appreciably above average” rainfall, say CEH. If it doesn’t happen and we have, for the second year running,  another dry, anticyclone-dominated winter, this could strain water resources and lead to environmental stress by next summer.

Dry stream bed at Mid Lavant, 16/12/17

The same location in February 2013, after a wet winter
 Still Missing - River Lavant, West Dean 16/12/17

It has also been very dry in France / western Europe for much of this year, with similarly low, or even lower river flows and groundwater levels; due to high pressure over the continent to the west in the Atlantic keeping the rain away. The drought has been particularly pronounced in the south, where there were forest fires in the summer; and the wine harvest has been poor due to a combo’ of a spring frosts and summer heat. Even at the end the of November, the rainfall deficit was still 40% in some areas; and the Loire, the longest river in France with total catchment area of over 100,000km2 was still running below 200m3s-1 (Saumur, basin size here around 81000 sqkm). That’s about what they’d expected here in summer, ie estival.  Things began to change in late November when the synoptic pattern finally shifted; though more for the benefit of the east of the country than the west and Loire valley.

The Derwent-Cocker confluence, Cockermouth 25/09/17
As in November 2016, the corresponding monthly rainfall totals were very influenced by heavy rainfall falling over one or two days: most notably this year, November 22nd, when heavy rain fell in NE England and the Scottish borders affecting the Lake District, Pennines and River Tweed. During that week, the EA had a number of flood warnings out in these areas, including on the rivers I have visited this year and last: the Tweed, the Greta at Keswick and the Eden. The CEH say that  the Lune and Eden hit record high peak flows for the month of November in records going back to the 1960s; the Eden apparently exceeding its flow at the height of the November 2009 Cumbrian floods.

Eden-Caldew confluence, Carlisle, September 2016
According to the NRFA, the peak flow at Sheepmount (Carlisle) during that episode was over 1000m3s-1. However, there’s no mention of any flow figures in the November hydrological reports. The CEH November monthly hydrological summary shows a hydrograph for the Eden at Temple  Sowerby, indicating a flow of about 300m3s-1. The NRFA gives a peak flow at Temple Sowerby, 18/11/09 was just under 350m3s-1; but that figure is not exceptional in the record for that gauging station, going back to 1964. The highest recorded peak flow there was over 900m3s-1, 08/01/05, which stands out among the other readings in the data table like a sore thumb. The catchment here is around 600km2 and is upstream from everything flowing in from the Lake District via the Eamont and Caldew and far north Pennines. The Sheepmount gauge is just downstream of the Caldew confluence in Carlisle, therefore takes in the whole catchment (2287km2); though the EA is still giving near real-time river levels here, the NRFA say that during the big Storm Desmond flood, the channels shifted, meaning readings at the gauge are no longer comparable with previous ones dating back to 1968. During this year’s episode, the Swale, which rises close to the Eden, also ran high; discharging into the Ure-Ouse upstream of York. At the end of that week (24th November), the Ouse spilled onto the quays in York: when we visited it the following week, they were hosing away the mud.

Thornton-le-Dale in snow 30/11/17
After this soggy interlude, the weather pattern shifted, with high pressure extending all the way up the north Atlantic, diverting the lows up and over the British Isles and down over Scandinavia and the North Sea. This brought rain to eastern France, raising the River Seine to comfortably normal levels. The airflow, though was northerly, bringing chilly weather to Britain, with some snow. During the last week of November, it got very wintery over NE England: we know this as we were away that week in Thornton-le-Dale, in the Vale of Pickering. On Monday 27th, a bitterly cold northerly on the north facing coast at Whitby. The Wednesday, 29th, was a thoroughly miserable day in Thornton, with bitter cold, heavy rain and hail. Though the Pennine rivers had fallen, there were now flood alerts on rivers flowing off the North York Moors: the Esk and Derwent. A small rise (about 10cm) on the placid, steadily flowing Thornton Beck. Overnight the rain turned to snow. It continued snowing on the Thursday morning. A snowy walk along the Thornton Dale, followed by filling pie pub lunch at The Buck Inn. The rest of the week remained cold, with snow lingering in Thornton on Friday 1st December – likewise an ungritted Park & Ride car park on the east side of York. Snow still lingered on the North York Moors (which go up to about 300m) during the drive (road clear) to Whitby on the Saturday. Unusually during this snowy episode, the precipitation was coming in from the east, troughs in the North Sea and was mainly confined to the NE coast / far east of Yorkshire. Dry over the Pennines and NW England (which we wanted to avoid for a winter week away after Storm Desmond).

River Ouse, York, 1st December 2017
During the second week of December, it was the turn of the Midlands to get the snow (10th December. Icy in other areas, including the south on Monday 11th. This came shortly after the third named storm of the season, Caroline, which affected the far north of Scotland with strong winds. Monday 11th in southern England was wet and windy. In France, it was even windier, with gusts upto 160km/h on the west coast, according to Météo France. At Blois, on the Loire above Tours, there was a 121km/h gust, the third strongest since the station opened in 1990. Thanks to this rain, the Loire finally began to rise slowly from its estival levels; but still couldn’t quite make it to 500m3s-1 at Saumur. Often in winter there, the flow is in four figures. The Seine (Paris Austerlitz exceeded that figure on 12th and 15th December, with yellow flood alerts on some its tributaries, including the Marne, its largest.
One hopeful thing, maybe for the drier areas is, though high pressure never seems to be far away from western continental Europe, the December synoptic pattern so far is less blocked and much less anticyclonic than it was last year. Rainfall during November has wetted the soils, enabling further rain to percolate though the soil down to aquifers.

Links / sources of information:
UK Met. Office - https://www.metoffice.gov.uk/
          Weather news  releases - https://www.metoffice.gov.uk/news/releases
Met.Office (news release 01/12/17) – November and Autumn weather statistics
Environment Agency (England):
National and regional water situation reports, issued weekly and monthlyhttps://www.gov.uk/government/collections/water-situation-reports-for-england
River and Sea Levels
https://flood-warning-information.service.gov.uk/river-and-sea-levels
Flood warnings - https://flood-warning-information.service.gov.uk/warnings
Centre for Ecology and Hydrology (CEH), UK
Monthly hydrological summaries - https://nrfa.ceh.ac.uk/monthly-hydrological-summary-uk
Hydrological outlook - http://www.hydoutuk.net/latest-outlook/
National River Flow Archive – river flow data measured by gauging stations around the UK
https://nrfa.ceh.ac.uk/data/search
CEH Drought Portal - maps of dryness around the UK for the past month - 24 months. Data back to 1961
France
Météo France – forecasts and weather news, weather warnings
http://www.meteofrance.com/accueil
Vigicrues (flood warnings, links to gauging stations with real-time river levels and flows:
https://www.vigicrues.gouv.fr/
Eaufrance – national monthly hydrological reports - http://www.eaufrance.fr/

Other water news
English rivers polluted by powerful insecticides, first tests reveal | Environment | The Guardian 13/12/17
Sampling was on twenty-three rivers around the UK, mainly in England and Wales. The Eden and Twyi (Wales) and three other rivers were in the clear; but neonicotinoid insecticides were detected in all the others. The River Test, a prime angling river in Hampshire was among them; as were the Yorkshire Ouse and the Teme. Levels were particularly high / bad in the Waveney and Great Ouse in East Anglia and the Tame in the Midlands.
CEH news – Mapping ephemeral / intermittent rivers and streams across the UK and Europe. The Lavant in West Sussex is among them.
https://nrfa.ceh.ac.uk/news-and-media/news/mapping-intermittent-rivers-and-ephemeral-streams-across-europe


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