Site Description

The Cuckmere river is located in South East England, stretching  approximately 25km in length, with its source rising in Heathfield, (Figure 1) and mouth located between Seaford and Eastbourne. The mouth of the river empties into the English Channel. The Cuckmere has an approximate catchment area of 134.7km2 (Eastbourne Borough Council and Wealden District Council, 2008) which, for administrative purposes, is often split into two catchments, the lower being tidal and the upper being fluvial.

Figure 1. The Cuckmere River 

The main thread of the channel forms near Hellingly, at the confluence of the Waldron Gill  and Cuckmere river. In its headlands, the Cuckmere tributaries lie within a steeply sloping, narrow valley. The channel flows through mixed clayey geologies (Mainstone and Holmes, 2010). The valley rises northwards, sharply, before reaching the mouth at Cuckmere haven. The floodplain boundaries are demarcated by the break of slope between the flat floodplain and rising valley sides.

The tidal section was straightened in 1846 to allow the Cuckmere to discharge quickly into the sea, and prevent natural meandering. The catchment is predominantly rural with only a few urban areas within the study area, namely Heathfield, Hailsham, and Alfriston (Environment Agency, 2009).  In the headlands, the land use has a greater urban fraction with increasingly rural land use, with increasing distance downstream.

Habitats

The Cuckmere river has a wide variety of diverse habitats, supported by the diversity of the of fluvial geomorphological environments within the channel, floodplain and its wider catchment. Throughout its course, the Cuckmere is known to support a number of species with high conservation values (Southgate, 2012) associated with acidic, iron rich, Wealden stream and wetland habitats (figures 2 and 3).

The wider catchment also features woodland (ancient and semi-natural), and multiple ponds (The River Restoration Centre, 2003). Across the catchment, there are a number of sites assigned with protected statuses such as SSSI (Vines Cross Stream, Ashbourne Stream, Powdermill stream) (The River Restoration Centre, 2003), Ramsar, Local Nature Reserves, and areas of Outstanding National Beauty (Environment Agency, 2007).

The river also supports a variety of freshwater and migratory fish including brown trout and sea trout (Environment Agency, 2007).

See here for more information on the diverse habitats the Cuckmere River supports.

 

Stakeholders

The history of the catchment remains relatively unmodified in the upper- and mid-reaches, with previous interventions including flood embankments, channel resectioning and ditching.

Despite being one of the least developed river estuaries in Sussex, Management of the channel, specifically in its lowest course, can be reliably dated back to the 1840’s, through the canalisation of the channel (Southgate, 2012) . This channel was constructed to divert the river channel towards the sea, in order to protect the adjacent farmland from flooding, during high tides. The engineered channel disconnected the natural meandering reaches, however some connectivity is still apparent, though overland flow via drainage channels. However, some existing hard-engineered flood defences within the Cuckmere valley have weathered and eroded so much so they are no longer fit for purpose (Krolik-Root et al., 2015).

Most recently, the straightened channel has been enhanced with embankments, reinforcement, timber walls etc, at the terminus of the river. Catchment management, and its maintenance, is undertaken by a variety of Key stakeholders the majority of which have formed a partnership, with a shared objective to provide integrated catchment management within The Cuckmere basin.  These stakeholders  (including Sussex Wildlife Trust, the South East Rivers Trust and the Environment Agency) aim to deliver the Water Framework Directive at the local level. This Partnership is called CuRE – Cuckmere Restoration project.

CuRE – Cuckmere Estuary Restoration Project

Amongst other factors, the physical modification of the channel has been highlighted as a potential management issue, impeding the passage of migrating fish. Further, the upstream installation of weirs has degraded the some habitats, by impounding sediment, ultimately drowning the natural bed features, such as riffles –  critical to the life-cycle of spawning fish (South East Rivers Trust, 2017). CuRE has lead a number of initiatives, resulting in the identification of wider catchment issues, which have aimed to ultimately increase connectivity between the catchment and its sub-catchments. These project have been implemented to improve habitat diversity (e.g. removal of floating pennywort management), flood peak attenuation to (e.g. Sussex Flow initiate interaction of large woody debris), and improve understanding of the catchment dynamics through public participation (Water Week scheme).

Given the catchment has a number of key stakeholders and national habitat designations, efficacy in the allocation of limited recourse is vital. Well considered management techniques are vital in the protection and management of the habitats the Cuckmere sustains, as required under international law (both the Habitats Directive and  Water Framework Directive) (The River Restoration Centre, 2003). This is achieved through the production of a River Basin Management Plan (RBMP). The South East RBMP includes the Cuckmere river, of which can be found here.

Why does the Cuckmere River need a Fluvial Audit?

Sear et al (2010) have identified potential drivers that are likely to induce changes in catchment sediment and fluvial dynamics. These may induce changes to the habitats supported by the channel’s geomorphology. These drivers are what the Fluvial Audit describes as Potentially Destabilising Phenomena (PDP’s) (Sear et al., 2010).

A number of maintenance, rehabilitation, and management approaches have been proposed for the wider Cuckmere and Pevensey Levels catchment (see here). Some of these interventions could be considered as, or have the ability to introduce, PDP’s. These interventions include increased urbanisation, sea level rise (resulting in saltwater intrusion), increased abstraction, changes in management techniques coastally (managed realignment, withdrawal of maintenance, sustaining existing coastal defences) and within the wider catchment (i.e. where there are embankments).

The Cuckmere catchment, as a whole, must be considered, prior to the implementation of these methods, to account for the unanticipated changes that me induced as a result of these interventions. Undertaking a broad Fluvial Audit assessment of the geomorphological properties of the Cuckmere, by breaking the catchment down into reaches of similar geomorphology, allows for the identification of areas of high sensitivity to change. This promotes efficient decision making and resource allocation into the maintenance and management of channel.

 

MAYBE ADD SOME PHOTOS OF DEGRADED HABITATS ON THE CUCKMERE OR EVIDENCE

References

Eastbourne Borough Council and Wealden District Council, (2008). Strategic Flood Risk Assessment – Level 1: Final. Hampshire: Scott Wilson, p.4.

Environment Agency, (2007). planning for the future Cuckmere estuary draft flood risk management strategy. [online] Environment Agency. Available at: <https://democracy.eastsussex.gov.uk/Data/Lead%20Member%20for%20Transport%20and%20Environment/20071119/Agenda/LMTE19Nov07item8appendix.pdf> [Accessed 7 May 2021].

Environment Agency, (2009). Cuckmere and Sussex Havens Catchment Flood Management Plan. Worthing: Environment Agency, pp.3 – 24.

Krolik-Root, C., Stansbury, D.L. and Burnside, N.G., (2015). Effective LiDAR-based modelling and visualisation of managed retreat scenarios for coastal planning: An example from the southern UK. Ocean & Coastal Management, 114, pp.164-174.

Mainstone, C.P. and Holmes, N.T., (2010). Embedding a strategic approach to river restoration in operational management processes—experiences in England. Aquatic Conservation: Marine and Freshwater Ecosystems, 20(S1), pp.S82-S95.

Sear, D., Newson, M. and Thorne, C., (2010). Guidebook of applied fluvial geomorphology. London: Thomas Telford, pp.126-140.

South East Rivers Trust, (2017). How Weirs Affect Fish Communities      – South East Rivers Trust (& the Wandle Trust). [online] Southeastriverstrust.org. Available at: <https://www.southeastriverstrust.org/how-weirs-affect-fish-communities/> [Accessed 7 March 2021].

Southgate, F., (2012). The Wetland Potential of Sussex. [online] Sussex Wildlife Trust, pp.36-40. Available at: <https://assets.sussexwildlifetrust.org.uk/the-state-of-sussex-wetlands-report-final-1.pdf> [Accessed 1 April 2021].

The River Restoration Centre, (2003). High Weald AONB Integrated Catchment Management & River Restoration Study. HIGH WEALD AONB INTEGRATED CATCHMENT MANAGEMENT & RIVER RESTORATION STUDY. [online] London, pp.7-55. Available at: <https://www.highweald.org/downloads/publications/uk-landscape-research-reports/1492-integrated-catchment-management-river-restoration-study/file.html> [Accessed 7 February 2021].