Burnley Nelson and Colne Flood Risk Management Strategy
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Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 1 Trawden Flood Risk Reach 2 Cotton Tree Flood Risk Reach 3 Colne Flood Risk Reach 4 Lower Colne Flood Risk Reach 5 North Valley Stream Flood Risk Reach 6 Swindon Clough Flood Risk Reach 7 Barrowford Flood Risk Reach 8 Nelson College, Barrowford Flood Risk Reach 9 Lomeshaye Flood Risk Reach 10 Nelson Central Flood Risk Reach 11 Fulledge, Burnley Flood Risk Reach 12 Plumbe Street, Burnley Flood Risk Reach 13 Burnley Central Flood Risk Reach 14 Padiham Flood Risk Reach 15 Burnley East Flood Risk Reach 16 Green Brook Upper Flood Risk Reach 17 Green Brook Lower Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 1: Trawden Throughout the last ten years, flooding to properties has occurred twice in Trawden village, in 2000 and in 2001. This flooding occurred as a result of high flows and blockages in the brook. Today, 79 properties are at risk of flooding in the village with a 1% (1 in 100) chance of occurrence in any one year. 64 of these properties are at risk from more frequent events. Flooding in Trawden is caused by water coming out of the channel when river levels are too high. This is made worse when the channel becomes blocked by debris at bridge crossings. Rainfall can flow very quickly through the catchment, which means there is a limited amount of time in which to warn people of flooding. Whilst there is currently no flood warning service in place for Trawden we are looking at the possibility of providing this service. This would mean residents in the village have enough time to be warned and to act prior to a flood. New flood defence walls, constructed along the left bank (looking downstream) of the river, could provide protection against a 1.33% chance flood event in any one year. We also propose to enhance our maintenance activities and consult with other parties to see what can be done to reduce the risk of blockage from existing river crossings. Flood resilience/resistance measures could also be considered to individual properties. Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 2: Cotton Tree Cotton Tree is a small settlement at the confluence of Trawden Brook and Colne Water, situated a short distance upstream of Colne. Flooding was recorded here in 1947, and although we have no record of flooding in the area since then, there are 77 properties at risk from a 1% (1 in 100) flood, with 31 of these having a 2% chance of flooding. Flooding is caused by overtopping of the river channel from an event with a 4% chance of occurrence in any one year. Development in the area is mostly set back from the watercourse, behind the B6250 (Cotton Tree Lane), although immediately upstream of the confluence with Trawden Brook there are some properties close to the banks of Colne Water. A flood defence embankment in the park, upstream of Winewall Bridge, could reduce the chance of overland flows from Colne Water into Cotton Tree. Gaps in riverside walls, south of Cotton Tree Lane would also need to be filled. The alignment and location of this embankment is to be determined but it could be positioned so as to utilise the existing park area to store water during very high river levels. However more investigation is required to promote this scheme and the work would be dependent on funding. Key Location where new defences or wall improvements may be required. Wall improvements New embankment Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 3: Colne The Colne flood risk reach sits alongside Colne Water, which flows in a westerly direction through the South Valley area. Development in Colne is spread across the whole valley and there are a number of former textile mills situated alongside the river that are now mainly occupied by industrial units. Raised walls are in place along the banks of Colne Water, however they contain gaps so would not stop river flows coming out of the channel. Much of the flood risk reach is covered by the South Valley Area Action Plan (AAP), being produced by Pendle Borough Council to regenerate the area. 13 commercial properties in this area are affected during a flood that has a 1% (1 in 100) chance of occurring. There is no residential property identified at risk of flooding on our published flood map. As the current standard of protection is reasonably high, we propose to continue our existing inspection, maintenance and enforcement activities. Rainfall can flow very quickly through the catchment, which means there is a limited amount of time in which to warn people of flooding in Colne. Whilst there is currently no flood warning service in place we are looking at the possibility of providing this service. This would allow residents enough time to be warned and to act prior to a flood. The area is planned for redevelopment and developers will need to demonstrate to the Environment Agency how they propose to mitigate future flood risk. Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 4: Lower Colne Lower Colne is situated alongside Colne Water, downstream of Primet Bridge and the railway crossing. Although the river begins to meander here, more so than further upstream, it is constrained by the proximity of former mill buildings which form much of the river channel sides. There are no formal flood defences in Colne. There are four major crossings, over the river in this location, and they all have significantly large openings so are unlikely to block flows. Many of the larger mill buildings have been divided into smaller properties, as a result, 70 commercial properties are at risk of a flood with a 1% (1 in 100) chance of occurring in any year. There are no residential properties identified at risk of flooding on our published flood map. As the standard of protection is reasonably high we are proposing to continue our existing inspection, maintenance and enforcement activities in Lower Colne. Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 5: North Valley Stream North Valley Stream runs to the north of the major urban area of Colne. 2km in length, it runs mainly underground through culverts and flows in open channels for the last 500m, before it joins Colne Water. The area adjacent to North Valley Stream is heavily developed with several large commercial properties directly over the culverted watercourse. North Valley Stream is relatively steep causing it to be very ‘flashy’ i.e. where flood levels can rise and fall rapidly with little or no warning time. The river is contained within several culverts of varying size and condition, and flooding could occur if these sections should block, collapse or spill out due to lack of capacity. In this situation flow could escape through manholes or back-up within pipes carrying surface water or wastewater that discharges into North Valley Stream. When the culvert is at full capacity, surface water will be unable to discharge into North Valley Stream possibly leading to flooding of low lying areas. 18 properties, 5 of which are residential, are at risk from a 1% (1 in 100) chance of flooding in any one year but flooding could occur with more frequent events (from a 10% probability). This would become even more frequent if culvert conditions deteriorated as it would ultimately lead to it becoming blocked. Due to the nature and potential scale of flooding here, a flood defence scheme would be high in cost and could cause significant disruption to the area. At the moment we are focusing on opportunities to reduce the risk from the culverted sections, particularly in relation to new developments. Through the planning process our Development & Flood Risk team will take actions to ensure that the probability and consequences of flooding are reduced. Approximate line of culvert Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 6: Swinden Clough Swinden Clough is a minor watercourse that flows northwards from Gib Clough Head and joins Colne Water downstream of Colne. The watercourse enters into culverts as it passes under the Whitewalls Industrial Estate and emerges downstream where it flows through an open channel to join Colne Water. Development along this reach is industrial/commercial and sits immediately above the line of the culverted watercourse. There are a number of large modern industrial units and associated storage and parking sites too. There are 3 commercial properties are at risk from flooding. The culvert itself does not pose a significant risk. Our river modelling indicates it can manage flows with a 0.5% (1 in 200) chance of occurring in any one year. However, without continued maintenance, the potential for a blockage is high. There are no records of flooding in Swinden Clough although the local authority has reportedly prevented flooding in recent years by removing debris build up at the culvert entrance. The preferred option for this area is to provide debris screens at the entrance to the culverts to support the existing inspection and maintenance works. We will seek contributions from beneficiaries to implement these works. Key: Location of potential new debris screens Approximate line of culvert Burnley Nelson and Colne Flood Risk Management Strategy Flood Risk Reach 7: Barrowford Barrowford is situated to the north of Nelson on the A682 and sits where Pendle Water and Colne Water join. The Barrowford flood risk reach covers the area adjacent to, upstream of the confluence on Pendle Water.