Appendix L: SSSI Assessment (Site of Special Scientific Interest Source Pathway Receptor Analysis for Drought Permit Options)

Our Dry Weather Plan

South East Water’s 2021 draft drought plan

Appendix L: SSSI Assessment (site of special scientific interest source pathway receptor analysis for drought permit options)

March 2021

South East Water Rocfort Road Snodland Kent ME6 5AH

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Contents

1.1 Groundwater drought permits - site of special scientific interest source pathway receptor analysis 3 1.1.1 Halling No. 8 - site of special scientific interest source pathway receptor analysis 3 1.1.2 Balcombe- site of special scientific interest source pathway receptor analysis 5 1.1.3 Tangier / Chasewood - site of special scientific interest source pathway receptor analysis 6 1.1.4 Southlands / Oaklands - site of special scientific interest source pathway receptor analysis 8 1.1.5 Hackenden - site of special scientific interest source pathway receptor analysis 10

1.2 Surface water - Site of special scientific interest source pathway receptor analysis 11 1.2.1 RIVER OUSE Drought Plan - SSSI Source Pathway Receptor Analysis 2020 11 1.2.2 RIVER CUCKMERE - site of special scientific interest source pathway receptor analysis 14

Annex – Assessment of the hydrological links between the River Cuckmere and the West Dean Brooks. 19

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1.1 Groundwater drought permits - site of special scientific interest source pathway receptor analysis

In support of the assessment of potential effects associated with the drought permit it has been assumed that:

• All appropriate infrastructure is in place at the source • Pump testing will have been undertaken and used to confirm the extent of any surface water drawdown and inform the need to re- scope this assessment with respect to potential groundwater effects • Abstracted water meets all quality criteria associated with both Environment Agency consenting requirements and requirements for potable supply • All abstracted water is transferred to supply via existing pipe works

1.1.1 Halling No. 8 - site of special scientific interest source pathway receptor analysis

PRESENCE OF HYDROLOGICAL / POTENTIAL FOR DISTANCE FROM WATER SENSITIVE SSSI NAME REASON FOR NOTIFICATION HYDROGEOLOGICAL SIGNIFICANT ABSTRACTION (km) FEATURES OF PATHWAY IMPACT INTEREST

Halling to Chalk grassland and beech 0.5 km NW NO Depending on distance NO Trottiscliffe woodland on chalk. Outstanding and elevation, there may Escarpment SSSI assemblages of plants and be a hydrological invertebrates. relationship. However,

the habitats are typically found on freely draining soils and as such groundwater will not be a critical factor in their ongoing resilience and success.

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Holborough to Floodplain habitat of the tidal 1.7 km SE YES This is possible because NO Burham Marshes Medway including reedbeds, of the presence of more SSSI open water, fen, grassland, permeable strata. However, the small scrub and quantity being woodland. Supports a wide abstracted is highly variety of breeding birds and is unlikely to have a also important for wintering drawdown cone wildfowl and waders. affecting surface habitats beyond 1km.

This SSSI is located beyond this distance, with intervening tidal creeks and a hydrological/hydrological relationship will not be evident.

Houlder & Sediments found provide 1.1 km SW NO This is possible because NO Monarch Hill Pits of the presence of more Lithostratigraphic/biostratigraphic SSSI permeable strata. evidence for environmental However, the small changes during the Late quantity being Devensian. abstracted is highly unlikely to have a

drawdown cone affecting exposed geological features to the point where accelerated weathering occurs.

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1.1.2 Balcombe- site of special scientific interest source pathway receptor analysis

PRESENCE OF HYDROLOGICAL / POTENTIAL FOR REASON FOR WATER SENSITIVE DISTANCE FROM SSSI NAME HYDROGEOLOGICAL SIGNIFICANT NOTIFICATION FEATURES OF ABSTRACTION (km) PATHWAY IMPACT INTEREST

Worth Forest SSSI Ancient Wealden ghyll YES 1.5 km N This is possible because NO woodland which is an of the presence of more example of a base-poor permeable strata. springline alder wood, However, the small supporting assemblage quantity being of water dependant abstracted is highly plants. unlikely to have a drawdown cone affecting surface habitats beyond 1km. This SSSI is located beyond this distance and a hydrological/hydrological relationship will not be evident.

Cow Wood & Harry’s Ancient woodland with YES 1.9 km SW This is possible because NO Wood SSSI several moist ghylls that of the presence of more have a moist warm permeable strata. microclimate favouring However, the small ‘Atlantic’ bryophytes and quantity being ferns. Ponds are also abstracted is highly present which are unlikely to have a important for dragonflies. drawdown cone affecting The SSSI supports a surface habitats beyond 1km. This SSSI is

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rich community of located beyond this breeding birds. distance and a hydrological/hydrological relationship will not be evident.

1.1.3 Tangier / Chasewood - site of special scientific interest source pathway receptor analysis

PRESENCE OF HYDROLOGICAL / POTENTIAL FOR REASON FOR WATER SENSITIVE DISTANCE FROM SSSI NAME HYDROGEOLOGICAL SIGNIFICANT NOTIFICATION FEATURES OF ABSTRACTION (km) PATHWAY IMPACT INTEREST

Eridge Park SSSI Parkland and ancient YES 1km SW NO. ABSTRACTION NO woodland particularly IS CONSIDERED TO

rich range of epiphytic BE FROM A lichens. Varied habitats CONFINED SOURCE also support diverse insect and bird communities, and it is recognised as being nationally important for dragonflies. .

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1.1.4 Southlands / Oaklands - site of special scientific interest source pathway receptor analysis

PRESENCE POTENTIAL OF WATER HYDROLOGICAL / REASON FOR DISTANCE FROM FOR SSSI NAME SENSITIVE HYDROGEOLOGICAL NOTIFICATION ABSTRACTION (km) SIGNIFICANT FEATURES PATHWAY IMPACT OF INTEREST

SOUTHLANDS

Shortheath Common Mires and bog habitats, YES 1.5 km N NO. ABSTRACTION IS NO SSSI (part of Shortheath together with dry heath CONSIDERED TO BE Common SAC) and bog woodland. FROM A CONFINED Significant populations SOURCE

of invertebrates including important assemblages of dragonflies and butterflies.

Wick Wood and Woodland with slopes, NO 0.9 km NW NO. ABSTRACTION IS NO Worldham Hangers rich in vascular plants, CONSIDERED TO BE SSSI (part of East bryophytes and old FROM A CONFINED Hampshire Hangers pollards. SOURCE SAC)

Coombe Wood and The Woodland with slopes, NO 0.9 km NW NO. ABSTRACTION IS NO Lythe SSSI (part of East rich in vascular plants, CONSIDERED TO BE Hampshire Hangers bryophytes and old FROM A CONFINED SAC) pollards. SOURCE

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Woolmer Forest SSSI Wet and dry YES 1.7km SE NO. ABSTRACTION IS NO (part of Woolmer Forest heathland, valley bogs, CONSIDERED TO BE SAC/SPA) broad FROM A CONFINED SOURCE leaved and coniferous woodland, permanent grassland and open water. The only site in Britain known to support all twelve native species of reptiles and amphibians and supports a nationally important heathland flora, with associated birds and invertebrate fauna.

OAKLANDS

Binswood SSSI Habitats include acidic NO 0 NO. ABSTRACTION IS NO poorly CONSIDERED TO BE

FROM A CONFINED drained unimproved SOURCE pasture with scattered old oaks and beeches, areas of denser woodland with a sparse shrub layer and ground flora, and former encoppicements now

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open to grazing. Very rich invertebrate assemblage.

Wick Wood and Woodland with slopes, NO 0.9 km NW NO. ABSTRACTION IS Worldham Hangers rich in vascular plants, CONSIDERED TO BE SSSI (part of East bryophytes and old FROM A CONFINED Hampshire Hangers pollards. SOURCE SAC)

Shortheath Common Mires and bog habitats, YES 0.4 km SE NO. ABSTRACTION IS NO SSSI (part of Shortheath together with dry heath CONSIDERED TO BE Common SAC) and bog woodland. FROM A CONFINED Significant populations SOURCE

of invertebrates including important assemblages of dragonflies and butterflies.

1.1.5 Hackenden - site of special scientific interest source pathway receptor analysis

PRESENCE OF HYDROLOGICAL / POTENTIAL FOR REASON FOR WATER SENSITIVE DISTANCE FROM SSSI NAME HYDROGEOLOGICAL SIGNIFICANT NOTIFICATION FEATURES OF ABSTRACTION (km) PATHWAY IMPACT INTEREST

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NO SSSI RECORDED WITHIN AT LEAST 2KM OF PROPOSED ABSTRACTION. GROUNDWATER SOURCE IS CONSIDERED TO BE A HIGHLY- CONFINED SOURCE OF GROUNDWATER. NO SIGNIFICANT IMPACTS PREDICTED.

1.2 Surface water - Site of special scientific interest source pathway receptor analysis

1.2.1 RIVER OUSE Drought Plan - SSSI Source Pathway Receptor Analysis 2020

PRESENCE DISTANCE OF WATER HYDROLOGICAL / POTENTIAL FOR FROM SSSI NAME REASON FOR NOTIFICATION SENSITIVE HYDROGEOLOGICAL SIGNIFICANT ABSTRACTION FEATURES PATHWAY IMPACT (km) OF INTEREST

Asham Quarry Geological. Key site for quaternary 8km from point of NO NO – no hydrographical NO studies, key reference site for abstraction connection indicated using biostratigraphical and (downstream) EA flood zone and surface lithostratrigraphical evidence. water extent mapping.

Primarily geological. It is a nationally 15km from point NO NO – Coastal site, no NO important reference section for the of abstraction hydrographical connection Brighton to Newhaven upper Cretaceous. Locally important (downstream) indicated using EA flood Cliffs colony of breeding seabirds, a zone and surface water diverse community of beetles, and extent mapping. pockets of unimproved chalk grassland.

Buxted Park Biological. Diverse variety of 8km point of YES NO – no hydrographical NO unimproved grassland communities, abstraction connection indicated using the site is of exceptional importance (upstream)

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for the conservation of invertebrates. EA flood zone and surface River Uck, ponds, marshy grassland water extent mapping. are water dependent features

Clayton to Offham Biological. Good quality chalk 4km from point of NO NO – no hydrographical NO Escarpment grassland habitat is prevalent and abstraction connection indicated using the site supports a rich community of (downstream) EA flood zone and surface breeding birds. water extent mapping.

Firle Escarpment Biological. Extensive stretch of chalk 8km from point of NO NO – no hydrographical NO grassland supporting several abstraction connection indicated using unusual and rare plant species. (downstream) EA flood zone and surface water extent mapping.

Lewes Brooks Biological. Supports a wide diversity 6km from point of YES NO – although majority of NO - Offham Marshes of invertebrates within the flood plan abstraction the sites is within flood SSSI is situated within of the River Ouse. Salinity of key (downstream) zone 2 and 3, flood the floodplain of the ditches varies across the site. defences limit hydrological Ouse over 3km connectivity. downstream of Barcombe Mills. Previous studies (e.g. Entec UK Ltd, 2004) have demonstrated that this site is not hydrologically linked to the Ouse.

Lewes Downs Biological. Contains extremely rich 4km from point of NO No – no hydrographical NO chalk grassland which supports a abstraction connection indicated using nationally important orchid, (downstream) EA flood zone and surface invertebrates, as well as locally water extent mapping. important breeding community of downland birds.

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Offham Marshes Biological. Alluvial grazing marsh 4km from point of YES NO – although majority of NO - Lewes Brooks supporting large amphibian abstraction the sites is within flood SSSI is downstream populations atypical of this habitat in (downstream) zone 2 and 3, flood of Offham Marshes Sussex. Freshwater field ditches are defences limit hydrological and is adjacent to the key breeding sites. connectivity. much more tidally- influenced reaches of the Ouse and does not receive direct in- flow from the river.

Plashett Park Wood Biological. Area of ancient woodland 1.5km point of NO NO – no hydrographical NO that contains a rich community of abstraction connection indicated using breeding birds and also supports (upstream) EA flood zone and surface nationally restricted plant and water extent mapping. invertebrate populations.

Rock Wood Biological. Small area of ancient 10km point of No – no hydrographical NO woodland that supports a number of abstraction connection indicated using different broadleaved woodland (upstream) EA flood zone and surface types. water extent mapping.

Southerham Grey Pit Geological. Site is the only inland 6km from point of NO Yes – a majority of the site NO exposed section of Chalk Marl and abstraction is within flood zone 3. Grey Chalk in southern England / (downstream) Northern France. Single most important section of these two beds in western Europe.

Southerham Machine Geological. Provides an exceptional 6km from point of NO No – no hydrographical NO Bottom Pit diversity of fossil fish. abstraction connection indicated using (downstream) EA flood zone and surface water extent mapping.

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Southerham Works Pit Geological. Site provides the best 6km from point of NO No – no hydrographical NO remaining exposures through the abstraction connection indicated using Ranscombe, Lewes, and Seaford (downstream) EA flood zone and surface Members. water extent mapping.

1.2.2 RIVER CUCKMERE - site of special scientific interest source pathway receptor analysis

PRESENCE DISTANCE OF WATER HYDROLOGICAL / SSSI REASON FOR FROM SENSITIVE POTENTIAL FOR SIGNIFICANT HYDROGEOLOGICAL NAME NOTIFICATION ABSTRACTION FEATURES IMPACT PATHWAY (km) OF INTEREST

Arlington Biological. Adjacent to point YES YES – apart from the NO – because the water is impounded at Reservoir Important of abstraction. water intake from the the intake, raising levels locally and the ornithological site, river to the reservoir, channel is deep and slow flowing, and over 170 species of the only ‘natural’ contained within a concrete lined channel. birds on passage relationship is between Even if there are minor hydrological have been the river and the connections to the riparian area of the recorded, with adjacent right hand SSSI the channel water level is unlikely to wintering bird banks that are included significantly change and the riparian counts regularly in the SSSI boundary. corridor habitats are not dependant on the exceeding 10,000. channel.

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Firle Biological. 4km from point NO NO – no hydrographical NO Escarpme Extensive stretch of of abstraction connection indicated nt chalk grassland (downstream) using EA flood zone supporting several and surface water unusual and rare extent mapping. plant species.

Lower Geological. 4.6km from point NO NO – no hydrographical NO Dicker Provides the most of abstraction connection indicated southerly exposure (upstream) using EA flood zone of Weald Clay sand and surface water members in Britain. extent mapping.

Lullington Biological. Site 3km from point NO NO – no hydrographical NO Heath contains nationally of abstraction connection indicated uncommon chalk (downstream) using EA flood zone heath, and chalk and surface water grassland habitats. extent mapping.

Milton Biological. Site 0.6km from point YES Yes – approximately NO - Entec (2005) undertook a review of Gate contains a rich of abstraction half of the site is within the likely hydrological functioning of SSSIs Marsh mosaic of marshy (downstream) flood zones 2 and 3. associated with the River Cuckmere. grassland habitats The wet grassland habitat, that forms part that supports a rich of the Milton Gate Marsh SSSI, depends assemblage of on natural inundation from the Cuckmere invertebrates and during the winter-time. As the proposed locally important Drought Permit relates to a reduction in bird species. MRF and therefore potential effects being more likely with low flows (not floods), there will be minimal impact on the frequency and duration of over-bank

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events and therefore on the hydrological functioning of the SSSI. Water from the Cuckmere enters the West Dean Brooks though a series of ditches which are fed though a sluice above Milton Lock. Figure 4.1 shows that the level at Milton Lock fell below the feeder sluice invert level on 4 occasions in 2005. This also happened on occasions in 2001, 2002, 2003 and 2004. Section 5.3 of this report considers the potential effects of the proposed Drought Permit on this SSSI. The Arlington Reservoir SSSI site boundary includes a component of the River Cuckmere and its floodplain. The reservoir also has a ‘hydrological’ relationship with the river through the abstraction of river water.

Seaford to Biological and 5.6km from point YES – the majority of NO - Entec (2005) undertook a review of Beachy geological. Diverse of abstraction the northwestern the likely hydrological functioning of SSSIs Head – range of nationally (downstream) portion of the site is associated with the River Cuckmere West Dean important habitats within flood zones 2 and Water from the Cuckmere enters the West Brooks that support 3. Dean Brooks though a series of ditches nationally rare, which are fed though a sluice above Milton scarce, and Lock. The report considers that with significant plants, appropriate operation of the lock, it should invertebrates, and be possible to maintain head that could birds. The cliffs are provide some water along the feed to West of outstanding for

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their geological and Dean Brooks, even at times of low flow in geomorphological the Cuckmere. interest.

St. Biological. 13km from point NO NO – no hydrographical NO Dunstan's Unimproved of abstraction connection indicated Farm grasslands (upstream) using EA flood zone Meadows representing a and surface water good example of extent mapping. species-rich grassland: being managed through traditional techniques.

Wilmington Biological. 3km from point NO NO – no hydrographical NO Downs Nationally of abstraction connection indicated uncommon chalk (downstream) using EA flood zone grassland which and surface water supports diverse extent mapping. flora and fauna including two nationally rare and several notable invertebrates.

South East Water

Assessment of the Hydrological Links Between the River Cuckmere and the West Dean Brooks

Final Report

June 2006

Entec UK Limited

Report for South East Water Emma Goddard Environmental Co-ordinator The Lodge Assessment of the Arlington Reservoir Berwick Hydrological Links Polegate East Sussex Between the River BN26 6TF Cuckmere and the

Main Contributors West Dean Brooks Mike Barker Final Report

Issued by June 2006

………………………………………………………… Mike Barker Entec UK Limited

Approved by

………………………………………………………… Matthew Johns

Entec UK Limited 155 Aztec West Almondsbury Bristol BS32 4UB England Tel: +44 (0) 1454 822000 Fax: +44 (0) 1454 822010

C006i1 h:\projects\ea-210\16000 projects\16805 west dean brooks\c006i1 (final report issued).doc

Certificate No. EMS 69090 Certificate No. FS 13881

In accordance with an environmentally responsible approach, this document is printed on recycled paper produced from 100% post-consumer waste, or on ECF (elemental chlorine free) paper

Contents

1. Introduction 1 1.1 Background 1 1.2 Purpose and layout of this document 1

2. Summary of Information Gathered to Date 3 2.1 Seaford to Beachy Head SSSI Description 3 2.2 Hydrology of West Dean Brooks 3 2.2.1 Feed/Siphon 4 2.2.2 SEW Abstraction 4 2.3 Site visit 4 2.3.1 Method 4 2.4 Results 5 2.4.1 Sherman Bridge Weir 5 2.4.2 Milton Lock 5 2.4.3 Long Bridge 5 2.4.4 Ditches between Long Bridge and West Dean Brooks 5 2.4.5 West Dean Brooks 6

3. Evaluation and Conclusions 7

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Figure 1.1 Location of the West Dean Brooks System and Features After Page 2

Appendix A Photographs

1. Introduction

1.1 Background South East Water (SEW) supplies water to 259,000 properties in south-east England. SEW’s supply area is split into its Northern and Southern Regions. Following a prolonged absence of rainfall in 2003, SEW successfully applied for a Drought Permit to reduce the Mean Residual Flows (MRF) in the River Cuckmere. There is the potential for the operation of this Drought Permit to effect the hydrological functioning of Sites of Special Scientific Interest (SSSIs) associated with the river system. SEW have undertaken a review of each SSSI (in association with the Environment Agency (EA) and English Nature (EN)) to confirm their status. Entec were commissioned in 2004 to undertake a qualitative desk top assessment of the hydrological functioning of the SSSIs associated with the Cuckmere river system and potential for effects upon them as a consequence of implementing the Drought Permit issued to SEW by the EA (Entec, 20041). The assessment was based on the range information available from SEW, including the Drought Permit application, the EAs Drought Permits and the water level management plans for the SSSIs. The report concluded that the reduction in MRF was unlikely to affect any of the SSSIs apart from potential affects on part of Seaford to Beachy Head SSSI know as West Dean Brooks. The 2004 report states that “On the occasion that the reduced MRF is reached, there may be an associated reduction in feed to the Brooks, although with appropriate operation of Milton Lock, it should still be possible to maintain levels above the feed sluice invert”. This conclusion could not be validated and therefore the uncertainty around the potential for effects on West Dean Brooks remained. As a result of the 2004 report, Entec was commissioned in 2005 to further investigate the relationship between the reduced MRF, from the drought permit, and water levels within West Dean Brooks. The remainder of this Technical Report presents the findings of this study.

1.2 Purpose and layout of this document This report describes the methods used to investigate the relationship between water levels in the River Cuckmere and water levels within West Dean Brooks. It summarises the results of the study and evaluates whether there is enough evidence to determine if maintaining the flows in the Cuckmere at the MRF does provide sufficient water levels to continue to feed the SSSI. The remainder of this document sets out:

• a summary of the information already gathered, primarily by Entec (2004) (Section Two);

1 Entec (2004). River Ouse and River Cuckmere Drought Permits - Review of Hydrological Functioning of SSSIs and Potential Impacts. Report for SEW.

• the site visit methods and results (Section Three); and

• evaluation and conclusions (Section Four).

2. Summary of Information Gathered to Date

2.1 Seaford to Beachy Head SSSI Description The Seaford to Beachy Head SSSI covers some 1102 ha at the eastern end of the South Downs. The site mostly lies on chalk along the length of coastline from Seaford to Beach Head, as well as extending inland to include the Cuckmere valley from the Haven upstream to Litlington. A section of canal exists near the mouth of the Cuckmere up to Exceat Bridge, although the original meandering watercourse remains. The area of the SSSI upstream (north) of Exceat Bridge is referred to as West Dean Brooks. Milton Lock, several kilometers upstream of the extent of the SSSI, is the tidal limit on the Cuckmere. The SSSI supports a diverse range of biological and geological features. Habitats include herb- rich chalk grassland, chalk heath, maritime grassland, foreshore and chalk cliffs, river meanders and greensand reef. Alluvial habitats include meadows and drainage ditches (ranging from fresh to brackish water) that support unusual plants, and saltmarsh communities. The Cuckmere valley is also important for breeding birds and birds on passage. Although rarely flooded, the alluvial meadows are important for overwintering species including teal (Anas crecca), wigeon (Anas penelope) and snipe (Gallinago gallinago). Grazing marshes near the sea support the great green bush cricket (Tettigonia viridissima).

2.2 Hydrology of West Dean Brooks West Dean Brooks receives water from several sources: • feed provided at Milton Lock (shown in Figure 1);

• some local runoff (likely to be minimal at times of low rainfall); and

• groundwater resurgence along the edge of the floodplain from the chalk aquifer. The feed from the Cuckmere to West Dean Brooks is taken via a sluice on the western bank of the impoundment behind Milton Lock (the tidal limit of the Cuckmere), providing fresh water to the SSSI via a cross river siphon at Long Bridge (between the feed intake and the brooks, Photograph 1, Appendix A) and a network of ditches (Figure 1). Some water also flows past Milton Lock via a Denil type fish pass. In order to maintain flow through the feed (and to drive it in a southerly direction), a certain amount of water is required at Milton Lock. Data at Milton Lock, recorded between 2000 and 2003, shows the water level did not fall below the invert of the sluice gate during this time. Hence, with appropriate operation of the lock, it should be possible to maintain head that could provide some water along the feed to West Dean Brooks, even at times of low flow in the Cuckmere.

The Lower Cuckmere Water Level Management Plan (WLMP) Interim Statement2 sets out the preferred conservation objective to maintain the water level in the ditches of West Dean Brooks as being 20 to 30 cm below the mean level of the meadows between November and June, noting that during periods of drought, there is unlikely to be sufficient water to meet this objective. During the summer and autumn of 2003, part of the Brooks were noted to have dried up (Emma Goddard, SEW, pers. comm.). In addition, water has been observed (Emma Goddard, SEW, pers. comm.) to flow in a northerly direction in the Brooks, which is atypical of its normal (southerly) flow direction.

2.2.1 Feed/Siphon No information on flow capacity of the feeder sluice and channels, or the hydro-ecological flow requirements of West Dean Brooks has been gathered (by any party) to date. However, the Environment Agency undertook a review of the operation of the feed sluice in early 2004 (‘PB Report’ emailed to Kevin Clark [SEW] by Chris Wick [EA] on 15/3/04). This report confirms that due to a difference in levels, water cannot flow out of the SSSI and discharge into the Cuckmere via the sluice at West Dean Locks. However, the report does accept a comment made by SEW that water has been observed to flow in a northerly direction. This potentially may be due to a lack of head, in the Cuckmere, that is required to drive flows in the Brooks over a topographic high point. Data provided by the Environment Agency on 13 February 2004 (faxed comments on an early draft of Entec, 2004 report, sent to SEW) specifies an invert level of 2.52 m AOD and 2.397 m AOD, for the feed sluice and fish pass, respectively. This means that the upstream water level (i.e. behind Milton Lock) provides a slightly greater head (0.123 m) to drive flows via the fish pass rather than the feed sluice.

2.2.2 SEW Abstraction SEW abstract water from Sherman Bridge, which is upstream of Milton Lock (where the feed to West Dean Brooks is located). During the summer, water is abstracted to the MRF level of 4.55Ml/d and during the winter the MRF level is 9.1Ml/d. SEW also has a drought permit to exact more water during the winter, from the winter MRF to the summer MRF.

2.3 Site visit

2.3.1 Method The site was visited, by Entec, SEW and English Nature3 (on the same day but separately), on the 28th September 2005. At this time SEW had, for a period of at least 48 hours, been operating at close to the summer MRF value (approximately 4.55Ml/d). Hence the water level of the river was at the lowest limit it should be. On the 1st October, the MRF is changed to the winter value (9.1ml/d).

2 Compiled by the EA but unknown reference. 3 John Curson, Sussex and Surrey Team.

The field assessment included visual inspections at Sherman Bridge, Long Bridge and West Dean Brooks. Milton Lock was not visited as land access was not available. The water levels, approximate flow and general observations at each location were recorded. Additionally, in West Dean Brooks the following were noted; • the amount and type of vegetation in the ditches;

• flow direction and level;

• artificial modification to the channels; and

• channel connectivity. EN revisited the site on Friday 14th October 2005. This second visit provided the opportunity to assess the effect of changing the MRF from the summer level to the winter level

2.4 Results

2.4.1 Sherman Bridge Weir The depth of the water at the top of the weir was 4.12m and at the bottom of the weir was approximately 3m. The water flowing over the weir was approximately 10cm deep and was estimated to be flowing at a rate of 55 l/s-1. There was little evidence of flow along the downstream section of the River Cuckmere below the weir. Photograph 2 (Appendix A) illustrates the flow of water passing over the weirs.

2.4.2 Milton Lock The lock itself could not be accessed during the survey. However, the level of the river below Sherman Bridge indicates that the feed is likely to be adequately submerged and therefore will provide a flow into the SSSI.

2.4.3 Long Bridge Photograph 1 (Appendix A) shows the siphon crossing the River Cuckmere via Long Bridge.

2.4.4 Ditches between Long Bridge and West Dean Brooks The siphon ends at a concrete structure (approximately one metre in width) in the corner of a field east of Alfriston and the River Cuckmere (TQ524035). At this point the siphon is approximately 20cm in diameter and has a tidal flap on the outside. The water from the siphon discharges into a small ditch and was visually estimated to be flowing about 0.1m/s. From observations on the channel cross section, the flow through the siphon was estimated as approximately 20 l/sec. Floating sweet grass (Glyceria fluitans) and water forget-me-not (Myosotis scorpioides) are the predominant species present in the channel. Bramble (Rubus fruticosus) is present along the top of the bank around the structure; otherwise the land is semi- improved, permanent pasture. The water from the River Cuckmere then follows a series of ditches into West Dean Brooks.

2.4.5 West Dean Brooks The water level at the level board (approximately TQ517004) within West Dean Brooks was 1.89cm on the day of the survey (Photograph 3, Appendix A). This reading coincides with observations made by EN staff during the same week. There was no perceptible flow in the channels, this far down in the SSSI. At the time of the second October visit to West Dean Brooks by English Nature, after the MRF had increased from the summer level to the winter level, the water level had risen to 1.97m. This is an increase of approximately 0.08m. However, heavy rain immediately prior to the level reading is likely to have resulted in more water being present in the Brooks at that time. The channels support a range of emergent and marginal species, with sedges and rushes common. The level in the channels appeared to be close to the normal optimal summer level, as there was no indication of marginal vegetation stranded by a large drop in water level (Photograph 4, Appendix A). The grassland, including the depressions, was generally dry, although the depressions did show signs of winter flooding, as the sward includes abundant sedge species.

3. Evaluation and Conclusions

The site was visited when SEW were abstracting the maximum amount of water from the River Cuckmere at Sherman Bridge. Downstream of the bridge the water level within the river was above the minimum required to feed into the West Dean Brooks. There was also sufficient head to drive water through the siphon to the Brooks. Consequently, the water level within the ditches at West Dean Brooks were at, what had been agreed between Entec/SEW and EN as an acceptable summertime level. It is likely that Milton Lock has the greatest influence on maintaining the water level around the feed to the Brooks, because water is held behind the lock, ensuring the feed is always submerged. Additionally, EN considers the current input and the recent improvements to water control structures provides a level of water within West Dean Brooks which is at an acceptable level to maintain the integrity of the SSSI features (Jon Curson, pers. comm.). EN has observed the flow in the West Dean Brooks during the winter/spring 2005-6 and was satisfied with the levels maintained. It considers4 that such levels should be able to be maintained through the application of any drought permit. Therefore, it is considered that abstractions to the summer and winter MRF in the River Cuckmere during periods of drought do not affect the water level within the SSSI, provided the operation of Milton Lock continues to maintain the level of water behind the lock.

4 Email from Jon Curzon (EN) to E Goddard (SEW) on 19/06/06.

Appendix A Photographs

Photograph 1 – The feed to the SSSI along Long Bridge

Photograph 2 – Sherman Bridge Weir

Photograph 3 – The water level marker within West Dean Brooks

Photograph 4 – Channel within the Brooks showing no stranded emergent vegetation