LANCASTER FLOOD ALLEVIATION PROJECT – PHASE 4.
Part 1 – Re cap of events • The most significant flooding in Lancaster was caused during Storm Desmond on the evening of the 4 th December 2015. • Lancaster City was worst affected as flows within the River Lune exceeded the capacity of the channel and resulted in flooding along both banks within the area. • Surface water was unable to drain off into the River Lune due to water levels / tide levels. • 467 reported properties flooded (227 Commercial)
(1) Photos from the media Source : Source : Lancaster Guardian Highways Operations Location : Location : View down Chapel Street from the A6 View down Damside Street on to the main Gyratory
(2) Photos from the media Source : Source : The Guardian Newspaper Highways operations Location : Location : Lancaster Bus Station / Gyratory / Damside Street Caton Road on the morning of the 05 th December 2015
(3) Photos from the media Source : Source : Lancaster Guardian Lancaster Guardian Location : Location : River level on the Morning of the 05 th December 2015 Back Caton Road / Bulk Road on the morning of the the morning after the peak flow 05 th December 2015
The impact of Storm Desmond • Both bridges were closed during the 48 hours after the storm following reports of a 20 tonne shipping 'container' striking both Skerton and Greyhound bridges. • The overtopping of the River Lune also affected an electricity substation, on Caton Road, which resulted in over 55,000 homes and businesses being without power for nearly 48 hours, many of which still experienced problems for the week after. • A major incident was called on the morning of the 5 th December 2015 which continued until power outages were stabilised.
Initial findings of the flooding event • At storm peak on 5 th December 2015, the River Lune reached its highest ever recorded flow rate, which was a flow of 1742cumecs (m3/seconds) at the Caton gauging station. • Survey of the water mark inside the station suggested that the flood level peaked at 8.15m. (Usually a range of 0.28m to 0.32m) • This was the highest flow ever recorded on the River Lune. • This was a new record for any English river. • Rain fall at Kirkby Lonsdale was 140mm through the period.
Initial findings of the flooding event • These high river levels resulted in the River Lune overtopping its banks. • Combined with the inability to disperse surface water, this lead to the flooding hundreds of properties and businesses. • The most significant areas affected were : – Lancil Industrial Estate, Caton Road (and substation) – A683 Caton Road. – City Centre. – St Georges Quay area.
Initial findings of the flooding event • The main cause of the flooding in the city centre is understood to be surface water being unable to discharge. • The outfall which drains this area could not efficiently drain the surface water into the River Lune due to excessive water levels and possibly working below design capacity. • The river contributed by over topping at Caton Road and St Georges Quay. • River levels dropped but the ‘City centre’ remain tide locked with areas of surface water flooding from the Highways drains and combined drainage systems.
Post Flood action What action has Lancashire County Council taken to date: • Inspections of all accessible drainage location to clear silt levels / blockages. • De-silting of City Centre areas using high powered vactor units. • Extensive jetting. • Additional City Centre gully cleaning. • Minor Capital improvement repair schemes. • Joint inspections of Mill race entry points (LCC / United Utilities) • Planned boat launch to inspect outlets / inlets on the River Lune. • Funding application to the E.A for major investigation.
Post Flood actions (2) Formation of a ‘Multi agency’ working group • The partner agencies, who have flood risk management functions have formed a separate group outside of the LMSW to further the post flood investigations – Lancashire County Council (lead Local Flood Authority) – Lancashire County Council (Highways Authority) – The Environment Agency (Flooding from designated Main Rivers) – Lancaster City (Urban infastructure and ordinary watercourses) – United Utilities (Flooding from sewers/combined systems)
The Mill Race, Lancaster City centre
The History of the Mill race • Lancaster is home to a historic Mill Race drainage system, dating back to 1610 when the first Lancaster Mill was present. • Over centuries the Mill race has been gradually covered over by bridges, developments & houses and upstream sections were lost with the building of railway sidings at Green Ayre and Kingsway. • The head of the Mill race sits on the banks of the River Lune on Caton Road (HSS hire on Caton Road) and is piped to the Kingsway site. • The ‘Mill Race’ is a mixture of drainage pipe (300 mm) to large scale structures (up to 5.0 m wide x 1.8 m high) and in places, it has been restricted by services.
(2) • Its outfall is usually below river at times of tidal increase or flooding and the actual functionality of the outlet is un known.
(3) • Over time, sections have been subjected to strengthening works and the risk of collapse under heavy traffic lead to repairs to the mill race in the 1990s and the construction of new overflows and a solids traps. • Due to the age of the urban development in this area, parts of the sewerage infrastructure is combined, at the lower end of the Mill race. (both surface water and foul sewage running adjacent as one system by way of over flows) • During an extreme rainfall event, surcharging or blockage of combined sewerage systems has the potential to result in contaminated foul sewage flooding areas of residential property, giving significant risk to human health .
(4) • Owner ship is complex with numerous developments having being given permission over the line of the Mill race. • The Mill Race may be in varied states of repair and will have variable effectiveness. • Some sections may be prone to failure or may be working well below their design capacity which may have a significant impact on flood risk to homes and property. • The significance of the Mill Race in the future of Lancaster City centre flood alleviation is currently un clear.
1991 Survey line of the Mill Race
Photograph 1 – Pitt Street, North Road
Photograph 2 – Centre of the Carriageway on Rosemary Lane, City centre
Photograph 3 – Junction of Damside street, Gyratory
Photograph 4 – At the outlet at the River Lune, Damside Street
(6) • We know for certain that there are significant challenges and areas of deterioration within the Mill Race. • Confined spaces and hazardous conditions could explain maintenance issues. • Tidal conditions make surveying and maintenance of the inlet /out challenging. • There is evidence to suggest that the pipe is badly damaged in a section near Kingsway. • There has been widespread development over the Mill race, which is reliant upon developers employing the correct protection techniques.
Part 1 : Questions ?
Part 2 : Post Flood strategy • It is proposed to commission a wide scale study that will investigate the known areas of flooding which have been identified : • Caton Road junction M6 out of bank flooding • City centre Surface water flooding • Lancaster Quay • Potentially a duration of 18 months with very challenging aspects.
Funding • The E.A intend to commence Phase 3 of the Lancaster Flood Alleviation programme along the banks of the River Lune. • Phase 4 has been agreed as the ‘Lancaster Flood Alleviation project’ and part 1 (Lancaster investigation) assigned for delivery as soon as possible. • LCC to present to the E.A at a Project Appraisal Review (PAR) as soon as the documentation is ready, to secure funding. • Initial funding allocation totals £4’020’000.00.
Objectives of the study / investigation • LCC needs to fully understand the flooding mechanics in the city (source's and frequencies), and have a clearer understanding of the condition of the asset and identification of any relevant issues. • It will be possible for LCC to use the outcomes to prioritise further investigations and / or actions and assess what future works are required. • The reports will also identify a potential range of measures which may be introduced in the future to reduce the current level of flood risk while considering economics and cost.
Part 1: Full Catchment Study • A full investigation of the surrounding catchment zones affecting Lancaster city centre, including the River Lune, in order to fully understand their significance in the recent floods and to establish why areas flooded and what were the affecting influences. • To locate all known and un known water sources entering the City centre drainage systems. • To include an Integrated catchment model of the City centre.
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