17/02/2016 1 Tidal Ribble – Overview of the Geomorphology Causes Workshop 2, 10 July 2012 Tidal Ribble Evidence & Measures project Prepared by the Environment Agency Geomorphologist in the North-West Copyright and status 2 Copyright This document (set of slides) contains data and information licensed to Environment Agency and provided by the Environment Agency to pjHYDRO Limited and to RUKHYDRO Limited. © Environment Agency – February, 2016. All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Document Status Working document provided for the use of stakeholders at workshop. Reviewed by the Environment Agency 2016. Dissemination Status Reviewed and approved for external release by Defra and the Environment Agency 2016. 1 17/02/2016 *Cited in Cracknell, 2005: Outrageous Waves – Global Warming and Coastal Geomorphology – Context Change in Britain through Two Thousand years. ^King, 1976: The Geomorphology of the British Isles, Northern England. (Fylde and the Ribble) † Porter, 1876: History of the Fylde of Lancashire. 3 . Present situation reflects past events: – 22 to 12.5Ka BP - Deglaciation during the Late Devensian Glaciation o Deposition of the Kirkham End Moraine [relatively higher ground - headwaters] o Cutting of meltwater drainage channels [e.g. Savick Brook] – Post glacial - Sea level rise and initial formation of Ribble Estuary o Up to 10 phases of sea level rise (transgression) then fall (Tooley, 1974*) o Erosion of glacial deposits, inlet formation and deposition of sediments – Roman period coastline approx 2 miles further west – AD185 to 610 - Romano-British Transgression (rise) - sea level approx 1.8m above present – Sea level fall circa AD 700 – AD1100-1250 - Medieval Warm Period Transgression (rise) – coastal erosion – AD1610 coastline around Lytham St Anne’s was at least 0.5 miles further inland than present [tidal deposits around main drain] – Sand dune accumulation – advance of the coastline [headwaters of Liggard Brook] – 1600s - Erosion of north shore of the Ribble Estuary between Lytham and Freckleton – Estuary infilling (offshore sediment sources), land reclamation and drainage – 1837 Ribble Navigation Improvement Company confined the channel of the Ribble within stone embankment and deepened the channel by dredging† – Land reclamation at this time on both sides of the estuary † [impact on the lower sections of Dow Deepdale, Savick] – Dredging was required to maintain navigation (Preston Navigation)^ – Dredging no longer takes place – estuary in-filling and readjusting Geomorphology – Context (Fylde and the Ribble) cont. 4 Channels likely to be very modified in areas underlain by old estuary deposits (yellow) Valleys formed by drainage during late glacial (melt water) Sand dues Area enclosed (improved) 1845 – 1890* Old inlet Wider areas where glacial deposits removed by erosion * Source: http://www.coastalguide.org 2 17/02/2016 Controls on hydromorphology quality elements 5 . Hydro (Quantity and Dynamics of flow and continuity) – Topography (geomorphological evolution of the landscape) . flow velocities – Channel morphology . variation in velocity and pattern) – Flow regulation (locks, tidal sluices, weirs) . Morphology (depth, width, bed, riparian, continuity) – Topography (geomorphological evolution of the landscape) – Flow Linked by feedback – Geology/soils (geomorphological evolution of the landscape) – Engineering Hydromorphology Quality Elements: Hydrological Regime: Quantity and Dynamics of water flow Connection to groundwater bodies River continuity Morphological conditions: River depth and width variation Structure and substrate of the river bed Structure of the riparian zone Morphological Pressures (1) 6 . Historic channel modification for land drainage/improvement involved varying degrees of: – Straightening – Deepening Promote drainage, enhance flow and create space – Re-sectioning . Consequences include: – Uniform bed and banks – Uniform flow patterns (slow glide) – Siltation (soft, uniform bed) – Degraded/absence of riparian vegetation . Diagnostic evidence: straight channel planform shown on OS map, lack of riparian trees, hints of old alignment in aerial photography and topography. 3 17/02/2016 Unofficial Classification 7 . Channel morphological classification scheme (developed for this project): o Semi-natural . Limited modification, close to natural condition . Catchment land use change has impact on flow and sediment supply o Minor planform (straight or sinuous etc.) modification (but re-sectioned . Planform relatively natural . Re-profiling of the banks and bed suspected – likely to be deepened modification Increasing o Straightened and re-sectioned . Modification of relatively low sinuous channel to create straighter channel planform (removing/reducing bends) . Re-profiling of the banks and bed suspected – likely to be deepened . Limited change in the overall alignment of the channel o Realigned, straightened and re-sectioned . Relocation of channel into new position (as opposed to removing or reducing bends) . Re-profiling of the banks and bed suspected – likely to be deepened o Canalised (straightened, widened, deepened) . Straightening, widening and deepening of pre-existing channel to allow navigation by boats o Artificial (drain or canal) . Creation of new channel where no natural channel previously existed o Culverted (estimated from GIS) . Complete enclosure of channel in pipe or box Unofficial Classification (Cont.) 8 Based on a desk based assessment and expert judgement OS maps: © Environment Agency copyright and/or database rights 2015. © Crown copyright and database rights 2012 Ordnance Survey 100024198. 4 17/02/2016 Savick Brook 9 . Headwaters – Relatively natural – sinuous, tree lining – Follow route of glacial melt water streams . Urban reaches – Localised channel engineering (straightening/re-sectioning) Fullwood 1849 1894 OS maps: © Environment Agency copyright and/or database rights 2015. © Crown copyright and database rights 2012 Ordnance Survey 100024198. Ribble Link 10 . Opened in 2002 . Link is tidal, which governs its operating times . Contains nine locks (seven canal, one river and one sea lock) . Channel widened to allow navigation by 10ft 6in beam boats . Sediment sink with significant build-up during floods . Local scour at structures during floods . Closed in 2003/4 and 2006/7 for 'maintenance and repairs' after flooding* . De-silting required June 2012 – over pumping proposed . Annual dredging required to maintain navigation* *More info at: http://en.wikipedia.org/wiki/Ribble_Link 5 17/02/2016 Deepdale Brook 11 . Upper catchment rural – channel modified: o removing bends and re-sectioning o uniform morphology, soft bed . Channel confined through BNFL works (?culvert) . At BNFL the channel follows the line of glacial melt water route . Appears to be impounded at southern boundary of BNFL works . Semi-natural downstream of BNFL . Meets estuary deposits at Clifton Aerial Maps . Channel modified here: In the original slides screenshots of satellite maps were shown. These o removing bends and re-sectioning cannot be shared publicly so they have been removed. o uniform morphology Dow Brook 12 . Headwaters in the Wesham area; influence by development . Main north to south section follows line of glacial melt water route . Map/aerial photographs suggests majority of channel is modified: o removing bends and re-sectioning o uniform morphology, soft bed . Flows into area of estuary deposits to west of Newton-with- Scales at old Sewage works - channel divides . Channels are modified: o Aerial Maps removing bends and re-sectioning In the original slides screenshots of o satellite maps were shown. These uniform morphology, soft bed cannot be shared publicly so they have been removed. OS maps: © Environment Agency copyright and/or database rights 2015. © Crown copyright and database rights 2012 Ordnance Survey 100024198. 6 17/02/2016 Pool Stream 13 . Located on area of glacial deposits throughout . 2 main channels fed by network of open drains . Upper catchment rural – channel modified: o removing bends and re-sectioning o uniform morphology, soft bed . Channel confined through Freckleton . Culverted under aerodrome runway . Channel modified downstream of aerodrome o removing bends and re-sectioning, local embanking Aerial Maps o uniform morphology, soft bed In the original slides screenshots of satellite maps . Tidal sluice structure regulates flow were shown. These cannot be shared publicly so they have o Freckleton Pool Outfall Flaps been removed. OS maps: . Relatively short tidal reach © Environment Agency copyright and/or database rights 2015. © Crown copyright and database rights 2012 Ordnance Survey 100024198. Wrea Brook 14 . Upper section near Wrea Green has hard bed and is steeper than middle and lower reaches (still relatively flat) . Channel (further downstream) has been modified by removing bends and re-sectioning o Slow flow, uniform morphology, soft bed . Tidal sluice structure regulates flow: – Brook Bridge Doors – slow draining by gravity below high tide – locked at high tide – slow flow will promote fine sediment deposition on bed 7 17/02/2016 Main Drain 15 . Artificial channel designed to drain low lying former tidal deposits (historic inlet) – Very uniform morphology – Prior to creation of the drain the area is likely to have been drained by a network of shallow tidal creeks (traces of which can been seen on aerial photographs) – We need to consider what we want to achieve Aerial Maps In the original