Effects of Abstraction on Salinity Regime – Ant Broads and Marshes

Effects of abstraction on salinity regime – Ant Broads and Marshes

Summary

• This paper looks at a 17 page report produced by Mr Linford-Wood of the Environment Agency, which considers the potential relationship between water abstraction and increased salinity. • The Ant Valley fens are highly vulnerable to saline incursion; salinity having been demonstrated by various researchers to have a negative impact upon the distribution of rare plant species, SAC Annex 1 fen communities and uncommon species of invertebrate. • There are some indications of an ongoing upward trend in salinity in the Ant catchment with this trend having been identified by the early 1990s. • Groundwater and surface water abstraction has a direct effect on river flows. • The EA consider that the effect of real fully licenced abstraction has been to reduce freshwater river flows in the Ant system by approximately 5%, however this value is disputed. • Other hydrologists suggest that the in-combination effects of abstraction are considerably in excess of the suggested 5% of river flow quoted by the EA. • In some of the Ant floodplain fens, the reduction in diffuse flow through the model cells under ‘average’ conditions is above 10% and in some cases up to 50%. At low flows, the figure is in excess of 50% in parts of Catfield Fen, Broad Fen, Reedham Marshes and Snipe Marsh. • Flows in the River Bure upstream of the confluence with the Ant are reduced by as much as 50% at Q95; and between -10 and -20% at Q10 conditions. It is clear that the very considerable reduction in modelled flows in the Bure under all flow conditions will be significantly increasing the likelihood of saline incursion into the Ant. • Mr Linford-Wood’s analysis suggests that there is “no evident salinity impacts from seawater incursion” further upstream than Barton Broad. The Environment Agency’s own monitoring data shows that high chloride levels resulting from saline incursion can be seen as far upstream as Wayford Bridge, which is well above the upper extent of the Ant Broads and Marshes SSSI and c4km upstream of Barton Broad. • In the mid Ant valley the mean water electrical conductivity levels are already well above the tolerance of species in the ‘Freshwater’ category as developed by Panter et al (2011). • Data from a range of sources show the extreme sensitivity of a number of plant species and communities to salinity. Recent work indicates that the upper limit of the freshwater category proposed by Panter et al of 300mg/l chloride may be set too high for freshwater fen plant species and should be ‘fine-tuned by the introduction of a ‘very fresh’ category with an upper limit of 100mg/l chloride as proposed by Dutch researchers. • Mean chloride levels in the River Ant above and below Barton Broad are already well in excess of 100mg/l, and thus fen plant species and communities in the mid and lower valley should be regarded as already being at a ‘tipping point’. • In this context, the maintenance of strong freshwater flow downstream and flushing through the fens on either side of the river is critically important in preventing river water from penetrating far into these fens. • The net change in flushing resulting from reduced flows as a consequence of abstraction, whether an ‘average’ of 5% as hypothesised by Mr Linford-Wood or the much higher figure suggested by Dr Bradley could prove to be critically important.

Background and context

A 17 page report prepared by Simon Linford-Wood of the Environment Agency which considers the potential relationship between water abstraction and increased salinity was circulated to the group on the 18th September1.

Mr Linford-Wood’s report summarises the main contributing factors to the salinity regime of Ant Broads and Marshes (ABM) and assesses the potential impacts of abstraction. Mr Linford-Wood is a hydrologist and groundwater specialist and consequently his paper is focussed upon the salinity regime and not the implications of salinity for freshwater organisms, and fenland plants and invertebrates.

By way of background, it may be helpful to consider the points made in a document by Drs Bradley and Parmenter in November 2017 “The hydroecology of the Ant Valley, Norfolk, and the environmental implications of abstraction”, the main conclusions of which were:

• It is widely acknowledged that the fen system of the Ant Valley is perhaps the finest in Western Europe and this is recognised in its European and international designations as a SAC and Ramsar site. • The habitat types for which the SAC is designated are dependent upon irrigation of the fen by calcareous water, either directly from groundwater, or indirectly from groundwater via the river network. • The Broadland fen habitats support the great majority of the species for which this area is important, and the most valuable area in this respect is the Ant valley fen system. • The Ant Valley fens are vulnerable to saline incursion; salinity having been demonstrated to have a negative impact upon the distribution of both rare plant species and uncommon species of invertebrate. • Sea level is projected to rise by ~24cm by 2050, and the Broadland Fens, including those of the Ant Valley, are likely to come under increased pressure both from storm surge events and an overall increase in salinity. • There are some indications of an ongoing upward trend in salinity in the Ant catchment, either due to increased incursion of saline water, or reduced down-stream flow. • Groundwater and surface water abstraction has a direct effect on river flows: for example the combined total of groundwater and surface water abstractions represents approximately half of the flow of the River Ant at Honing Lock.

The effect of abstraction on river flows Mr Linford-Wood has concluded that, relative to estimated naturalised (i.e. no abstraction or discharge) flow conditions, the net result of historic and real fully licenced abstraction has been to reduce freshwater river flows in the Ant system by approximately 2% and 5% respectively and considers that, as a simple rule of thumb it might be expected for flushing periods to be extended by a similar extent. The Environment Agency’s comparison of modelled flow differences out of Barton Broad under the different abstraction scenarios suggest indicative ‘turnover’ times (the ratio of outflows to volume of water stored) are increased by 2-5% and some specific time estimates are provided for high storage and low storage conditions. These figures of 2% and 5% appear, although this is not expressly stated in Mr Linford-Wood’s paper, to be derived from a paper by Mr Gavin Sharpin, of the Environment Agency, entitled ‘The

1 Linford-Wood, S. 2018 Effects of abstraction on salinity regime – Ant Broads and Marshes. September 2018 Impact of artificial influences on surface water levels in Ant Broads and Marshes SSSI’ dated September 20182, which was also circulated on the 18th September. We are aware that there is some considerable dispute amongst other hydrologists as to whether these figures are actually correct; for example Dr Chris Bradley3 observes that these figures are “difficult to reconcile with the licensed abstraction volumes”, and that “there appears to be a discrepancy between modelled freshwater flows and observed freshwater flows, which suggests the figure of 2-5% should be regarded with extreme caution”. In the context of the monitored freshwater flows the inference being that “the in-combination effects of abstraction … will be considerably in excess of the suggested 2%-5% of riverflow quoted in the Sept. 2018 papers”. Prof. Gilvear of the University of Plymouth has also criticised the findings of the paper by Mr Sharpin and concludes that “the hydrological significance, and associated hydro-chemical effects, of reduced flows on the River Ant due to water abstractions has still not been firmly established …. it is poor practice to quote precise values for the impact on water levels when it is acknowledged within the report that there are some very large uncertainties and likely that there are significant errors associated with the analysis ….”. This is of particular concern, when the figures produced by Mr Sharpin are then used by other authors as a representation of the degree of change. Prof. Gilvear notes “I am also concerned that any studies which go on to develop on and extrapolate from the figures presented in the Sharpin report would be subject to similar uncertainty.”4 We also note that whilst Mr Linford-Wood reports that a “….net result of historic and real fully licenced abstraction has been to reduce freshwater river flows in the Ant system by approximately 2% and 5% respectively”, Mr Sharpin refers to a 5% reduction in the variation of the observed Barton Broad water level record under the fully licensed scenario and 3% under the historic scenario but fails to state (or estimate) the consequent reduction in river flows. Irrespective of the true value of the in-combination effect of abstraction upon flows in the main river, the impact of reduced freshwater flow in one part of the Ant system may well be higher than in another and so a figure of 5%, if correct, should be taken as the average change for the main river and not the entire floodplain system. For example, we know from recent modelling work undertaken by the Environment Agency (Appendix 2) that the fully licensed impact of combined surface and groundwater abstraction is to reduce freshwater flows through some of the fen sites (notably Catfield Fen, Mrs Myhills Marsh, Broad Fen, Snipe Marsh and the western part of Reedham Marshes) by over 50% under ‘dry’ Q95 conditions. Flows through Catfield Common and Hickling Broad under the same scenario are reduced by between 30 and 50%. Even during the very wettest part of the year under high flow Q10 conditions (likely to be in the winter period) the surface flow through Mrs Myhills Marsh, Reedham Marshes and Catfield Fen is reduced by between 10 and 20% and at Snipe Marsh by between 30 and 50%. In the main River Ant, the Q95 reduction in flows immediately upstream of the Ant Broads and Marshes SSSI and up to and above Broad Fen is between 10 and 20%; the remainder of the River Ant as it flows through the SSSI experiences a 5-10% at Q95. At Q10 (high flow conditions during a wet period) the flow reduction under the fully licensed scenario is between 5 and 10% through the entire length of River Ant from upstream of Broad Fen to downstream of Reedham Marshes with the exception of a short section of river at Irstead and Barton Broad itself. It is difficult to reconcile these flow reduction figures with the 2-5% change suggested by Mr Linford-Wood. In that portion of the River Bure modelled by the Environment Agency as part of the recent tranche of work, the flows in the Hoveton-Horning section immediately upstream of the confluence with the Ant are reduced by as much as 50% at Q95; and even at high flow Q10 conditions, the impact upon

2 Sharpin, G. 2018 The impact of artificial influences on surface water levels in Ant Broads and Marshes SSSI. September 2018 3 Bradley, C. 2018 Comments on Water Quality papers on the Ant Broads and Marshes, Oct. 2018. 4 Gilvear, D. 2018 Comments on Version II of a report titled “Impact of artificial influences on surface water levels in Ant Broads and Marshes SSSI”. 30th September 2018

flows under the fully licensed scenario is between -10 and -20%. Although this paper concentrates upon the impact of salinity in the River Ant, we know from Mr Sharpin’s work that salinity incursion into the Ant is strongly influenced by downstream flows in the Bure and it is clear that the very considerable reduction in modelled flows in the Bure under all flow conditions will be significantly increasing the likelihood of saline incursion into the Ant as well.

The total flow impacts for key locations within the Ant Broads and Marshes are summarised in the table below (see also Appendix 2).

SSSI Total Flow Impact – maximum % flow reduction resulting from Real Fully Licenced abstraction scenario (and component sites) Q10 (high flow Q50 (moderate – Q95 (low flow conditions – near average) conditions – v wet period flow conditions)* dry period) Smallburgh Fen SSSI 10-20 10-20 10-20 Broad Fen SSSI 5-10 10-20 >50 Ant Broads and Marshes SSSI Barton Fens 1-5 10-20 10-20 Sutton Fen & Broad 1-5 10-20 10-20 Catfield Fen 10-20 30-50 >50 Reedham Marshes 10-20 20-30 >50 Alderfen 1-5 10-20 30-50 Snipe Marsh 20-30 30-50 >50 Upper Thurne SSSI Catfield Common 5-10 5-10 10-20 Hickling Broad 1-5 5-10 20-30 Mrs Myhills Marsh 10-20 20-30 >50 Calthorpe Broad SSSI 1-5 5-10 10-20 Ludham-Potter Heigham SSSI 5-10 10-20 >50

* It should be noted that for most river systems the typical or average flow is best represented by the Q40 value

The effect of abstraction upon salinity Mr Linford-Wood’s analysis suggests that “no evident salinity impacts from seawater incursion” further upstream at Woodfarm Fen at the northern end of Barton Broad are indicated from the monitoring record over a 5-year period between 2003 and 2008. This is contradicted by Sharpin’s recent paper which on pg 14 suggests that saline water does enter Barton Broad “salinity readings show that some seawater can reach the Broad under particular conditions”.

Mr Linford-Wood also reports that “Seawater incursion into the Barton Broad is a rare occurrence and reporting evidence is limited” and cites Innes 1912 (quoted in Giller and Wheeler 1986a) who “reports an event that resulted in a chloride measurement of 430 mg/l (2.5% seawater).” In actuality, the Environment Agency’s own monitoring data shows a maximum chloride value of 2200 mg/l at Woodfarm Fen at the northern end of Barton Broad and a value of 1170 mg/l at Wayford Bridge, which is well above the upper extent of the Ant Broads and Marshes SSSI and c4km upstream of Barton Broad.

It should be noted that a 5 year period is a very short window of time on which to base this sort of judgement, but irrespective of this, a spike in salinity of 3640 μS/cm, which is likely to have been caused by an incursion event recorded at this monitoring point in November 2007, and during the storm surge of December 2013 an electrical conductivity of 4325μS/cm was recorded by the Environment Agency at Wayford Bridge a further 4km upstream.

For clarity, the data quoted by Mr Linford-Wood are set out in the following table, along with data derived from the EA’s regular river water quality monitoring programme. No attempt has been made to convert from electrical conductivity to mg/l chloride or vice versa due to the proportionately greater contribution of ions other than chloride at low conductivity; as explained in Panter et al5 (p23) electrical conductivity is a poor proxy for salinity at values of less than 1000 μS/cm. In such instances, measurement of chloride may be a more reliable indicator of salinity.

5 Panter, C., Mossman, H. and P.M. Dolman (2011) Biodiversity Audit and Tolerance Sensitivity Mapping for the Broads. Broads Authority Report. UEA Norwich. Original data Sample Point Grid ref Data source Chloride (mg/l) Electrical Conductivity μS/cm

Monitoring Monitoring No. records Min. Max. Mean No. records Min. Max. Mean period period

Ludham Bridge (downstream of SLW from EA TG372171 2000-2016 203 61 2060 142 lower end of SSSI) monitoring data

Ludham Bridge (downstream of TG372172 1981-2017 602 49 8460 257 1981-2017 431 412 20800 1292 lower end of SSSI)

SLW from EA Irstead Church (Catfield Fen) TG366205 1991-2018 289 45 2080 138 monitoring data

EA monitoring Irstead Church (Catfield Fen) TG366206 1981-2015 490 45 2080 135 1981-2017 419 80 7240 973 data

Catfield Fen (assumed close to BA monitoring 2003-2008 21 775 3670 1154 Irstead Church monitoring point) data BA monitoring Woodfarm Fen 2003-2008 21? 717 data 1982-1985; 1981-1997; EA monitoring Barton Broad (at Woodfarm Fen) TG361221 462 62 2200 140 1995-1997; 158 106 3640 899 2006-2017 data 2007-2017

BA monitoring Sutton Fen 2003-2008? 21? 617 data

Wayford Bridge (upstream of EA monitoring TG348248 1981-2017 800 35 1170 80 1981-2017 493 356 4325 853 Sutton Fen) data

Figures in black are taken from the SLW report. Figures in red are taken from the EA’s own monitoring record

The ecological consequences of increasing salinity

The seasonal timing of saline incursions is important in determining in how damaging they may prove to be; evidently, an incursion event which corresponds to a period of high river flows is likely to penetrate less far upstream than one that occurs at a time of low flow conditions and incursions during the early spring and summer growing period may be more damaging, at least to plant species, than a surge event during the winter Typically, the more significant surge events occur during the winter months, when river flows are generally higher; however surges associated with high tides can take place during the early spring and summer, when they may coincide with periods of very low flow. It is these events which might be expected to be most damaging to plant life. Further, different parts of the Ant system are more sensitive to salinity than others in terms of the salinity levels tolerated by the species and communities present, and the duration of time for which salinity is tolerated prior to species extinction taking place. Mr Linford-Wood observes that “…with respect to the associations between salinity and ecology, Panter et al. (2016) presents some of the long term chloride monitoring in the Broads. This attests to the general absence of trends in chloride at upstream sampling points not affected by incursion events, and in contrast, the periodic chloride spikes expressed at those sites monitored downstream that are subject to tidal influence”. Mr Linford-Wood further observes that the mean electrical conductivity of 717 μS/cm at Woodfarm Fen is typical of ‘freshwater’ systems. It is important to note that 717 μS/cm is at the upper end of the Panter et al. ‘Freshwater’ category and given that this is a mean value it is important to also consider the maximum value recorded and how often salinity levels rise above the 800 μS/l (300mg/l chloride) limit for freshwater flora and fauna cited by Panter et al and the value of 100mg/l chloride cited by Runhaar (2006) for plant communities.

At Catfield Fen, the mean electrical conductivity (derived from Broads Authority data) was 1154 μS/cm with a range of 775-3670 μS/cm. A mean value of 1154 μS/cm at Catfield Fen) is high, and well above the tolerance of species in the ‘Freshwater’ category as developed by Panter et al. (see extract from that report, Table 2 below). The Agency’s own monitoring data showed a broadly similar mean electrical conductivity, but a maximum which, at 7240 μS/cm was approximately double that recorded by the Broads Authority.

At Ludham Bridge, at the downstream end of the Ant system, Mr Linford-Wood observed that the “mean chloride level at Ludham is however well below the 300 mg/l threshold indicative of a freshwater habitat but this is intermittently exceeded”. It is important to consider here the maximum value (8460 mg/l), timing (seasonality) and duration of incursion events, and not simply the mean. A 300mg/l threshold is notably well above the both the ‘fresh’ and ‘very fresh’ categories adopted by some Dutch researchers for similar habitats.

Data for Barton Broad and Wayford Bridge shows very considerable fluctuations in electrical conductivity indicative of upstream penetration of brackish water and the analysis undertaken by Drs Bradley and Parmenter (outlined in the November 2017 paper) indicates a slight, albeit non statistically significant upward trend over time and background salinity levels (i.e. with major surge events removed from the dataset). This upward trend was, in fact, reported by Martin George, as far back as 1992 “… although the influx of saline water into the river system is to some extent prevented by fresh water flowing downstream, in recent years it has been observed that the length of water course influenced by salt water is increasing. This is thought to be due to a combination of factors including channel widening, dredging, reduced flow as a result of abstraction in the upper catchments and a rise in sea level relative to the land (George, 1992)”6. The analysis undertaken by Drs Bradley and Parmenter demonstrated that at both Barton Broad and Wayford Bridge, salinity levels are now regularly above the upper tolerance limit for many freshwater taxa of 800 μS/cm (as identified by Panter et al 2016) (see excerpt from their report above: Table 2). Indeed the Environment Agency’s monitoring data shows that the mean electrical conductivity at the northern inflow to Barton Broad (Woodfarm Fen) is 899 μS/cm and that levels of up to 3640 μS/cm have been recorded under surge conditions. It should further be noted that electrical conductivity levels of less than 800 μS/cm and chloride concentrations of below 300 mg/l do not necessarily mean that conditions are optimal for freshwater species. These values should be regarded as the upper limit of tolerance (although the duration of exposure is also important); and it should be noted that the salinity tolerance categories set out in Panter et al are for all taxa of conservation importance, including birds, plant and invertebrates and consequently, because of the range of such species present in The Broads and the range of habitats they occupy, from fully freshwater to saline, the salinity tolerance categories adopted by Panter et al are necessarily broad ones.

A classification system which specifically links plant species to salinity developed by Runhaar et al (2004)7 and Runhaar (2006)8 introduces a further tolerance category of ‘Very Fresh’ where chloride levels are below 200 mg/l and 100 mg/l respectively and is considered to be of greater relevance in identifying the potential impact of changes in salinity upon wetland plants. Den Held & Den Held (1976), in looking at wetland plant communities also use 100 mg/l as a threshold for ‘fresh water fens’9. These classification systems were adopted and set out in tabular form by Stofberg et al (2014)10 as reproduced below and allow a ‘fine-tuning’ of the broad categories developed by Panter et al and one which is specific to plant species and vegetation communtiies.

6 Parmenter, J.M. 2000 The development of the wetland vegetation of the Broadland region: A study of the sociohistorical factors which have influenced and modified the development of fen vegetation in Broadland. DPhil Dissertation, University of East Anglia. 7 Runhaar, J. van Landuyt, W., Groen, C.L.G., Weeda, E.J., & Verloove, F. 2004 Herziening van de indeling in ecologische soortengroepen voor Nederland en Vlaanderen. Gorteria 30; 12-26. 7 Runhaar, J., 2006 Natuur in de Verdringingsreeks, Wageningen: Alterra. 7 Den Held, J.J. & Den Held, A.J., 1976 Het Nieuwkoopse Plassen gebied, Zutphen: Thieme

10 Stofberg, S.F., Klimkowska, A., Paulissen, M.P.C.P., and Witte, J.P.M. 2014 Potential sensitivity of fen plant species to salinity. National Research Programme Knowledge for Climate, Utrecht.

In the report by Runhaar (2006) these salinity classes were used to assess salinity risk to wetland ‘nature areas’. Runhaar proposed that increased concentrations in the range of 100 - 1000 mg/L chloride may kill sensitive species within several weeks. However, it was unclear at precisely which level and duration such effects will occur. In his recent paper, Mr Linford-Wood inferred that ‘salinity impacts’ following an incursion are flushed within the 4 week sampling interval. However, the incursion event recorded in September 1991 and cited on pg 16 of Mr Linford-Wood’s report, was clearly significant and resulted in a chloride concentration at Irstead (adjacent to Catfield Fen) of 2570 mg/l. Elevated chloride levels “apparently persisted for at least 54 days” (this was during a drought period). This suggests that maintaining constant surface water movement through the adjacent fen system (in ditches and across the fen surface) so as to prevent the incursion of saline water from the river into the fens is critically important to the safeguard of the plant and invertebrate species present in these fens.

The table appended to this report (Appendix 1) ranks fen species according to their sensitivity to chloride and electrical conductivity using data gathered by one of the authors11, with the most sensitive species at the top and the least sensitive at the bottom. Some of the species listed at the very bottom of the table might be regarded as obligate halophytes. We have marked up the table to show the mean electrical conductivity levels quoted in the report by Mr Linford-Wood and also the mean and maximum levels derived from the Agency’s own monitoring data.

As can be seen from this table, a number of important wetland plant species present in the Ant valley fens and fen ditches could be regarded as being at a ‘tipping point’ (and in the lower parts of the valley may have already gone past that tipping point) in terms of their salinity tolerance and the current mean salinity levels within the system. The red box indicates which freshwater plant species would be lost from most of the sites in which they are present, or would have declined very significantly as electrical conductivity in the wetland system increases above 500 μS/cm; the pink box

11 Barendregt, A. 1993 Chapter 2 (The contribution of chemical diversity in Dutch polder waters to the diversity in ecosystems, page 25-56) in: Hydro-ecology of the Dutch polder landscape. Ph.D. thesis, Universiteit Utrecht. Netherlands Geographical Studies 162. Utrecht. 200 pp. ISBN 90-6809-175-1. shows the species which would be lost from most of the sites in which they are present, or would have declined very significantly as electrical conductivity increases above 1000 μS/cm. The black line shows where the 100mg/l chloride threshold for very fresh systems set out in Stofberg et al.’s summary table would fall. As can be seen from the bold highlight the ‘preferred’ electrical conductivity and chloride levels for many of these species are at the lower end of the ‘salinity range’. Although it is recognised that mean electrical conductivity and chloride levels in the main river do not necessarily equate to that same level being experienced in the adjacent fens, a major incursion at low flow conditions could potentially force brackish water into the fen.

The orange highlight represents an indicative ‘population integrity threshold’ of 10%. By the time salinity increases to the right hand end of the orange bar, there is only a c10% chance that the species in question is still present. Furthermore the plant community in which that species occurs might be substantially modified to the extent that it may no longer be considered to be the Annex I habitat. For example if the populations of Juncus acutiflorus, Carex rostrata, Menyanthes trifoliata and Comarum palustre within a stand of S27 vegetation decline so as to be within significantly fewer than 80% of quadrats then arguably that stand of vegetation is no longer S27 and may no longer correspond to the definition of the Annex I habitat Transition mires and quaking bogs (7140). Similarly, as Cladium mariscus within a stand of vegetation declines so as to no longer be a constant component of the vegetation, then that stand of vegetation may no longer qualify as Calcareous Fen with Cladium and species of the Caricion davallianae (7210).

The main NVC communities and, where relevant, the typical SAC habitat types associated with these species are shown to the right hand side of the table in Appendix 1. Although it is acknowledged that not all Cladium mariscus plants will be found in SAC-quality habitat, and not all Carex rostrata will be found in S27 fen, it is nevertheless very apparent that the SAC Annex I habitats for which the Broads are designated have a strong association with the species within the red and pink boxes; the species in the bottom third of the table are arguably either ‘generalist’ wetland species or might be considered to be halophytes.

The pattern can also be seen in mapping produced by Natural England (see Figure 01). ‘Annex 1 Wetland features and associated calcareous fen’ shows that for the most saline-sensitive habitat, Transition Mire and Quaking Bog the majority of examples are either to be found away from the main river, in the northern part of the Ant fen system above Barton Broad or are in areas of fen which are embanked from the river (Hall Fen, Hulver Ground and the internal system at Catfield Fen) and so less likely to be subject to saline incursion. A similar pattern is exhibited by the Calcareous Fen with Cladium and species of the Caricion davallianae: the majority of stands are either set back from the river or are in the upper part of the fen system.

For comparative purposes, a fairly strong negative correlation was demonstrated between electrical conductivity and plant species richness in Parmenter 200012, with the species rich vegetation(15+ species) tending to occur under conditions of moderate to low electrical conductivity (<750 µS/cm). Parmenter (2000) also considered and discounted alternative explanations. High electrical conductivity is sometimes associated with higher nutrient levels, but this was not confirmed by a plot of phytometric fertility against electrical conductivity. However, conditions of very high electrical conductivity were typically recorded in the largely unmanaged fen vegetation adjacent to the brackish broads of the Upper Thurne system. Where management is not undertaken, the vegetation becomes tall and rank and species richness is consequently reduced and this may be contributing to the strong correlation between high conductivity and low species diversity. This is unlikely, however, to be the case in the Ant valley, where some of the best-managed fens, found at Reedham Marshes, nevertheless do not support the very diverse vegetation of the Caricion davallianae to the same extent as fens further upstream.

12 Parmenter, J.M. 2000 The development of the wetland vegetation of the Broadland region: A study of the sociohistorical factors which have influenced and modified the development of fen vegetation in Broadland. DPhil Dissertation, University of East Anglia. In several instances, the mean electrical conductivity associated with a particular community type is influenced by one or two uncharacteristically high or low readings. Similar observations were made by Wheeler & Shaw (1987)13. Examples include the electrical conductivity ranges associated with the B91, B329 or B331 communities, and this could be taken to suggest that some vegetation communities have a degree of tolerance to extreme environmental conditions. When the stands of vegetation from which these anomalous results were obtained were examined, however, they usually proved to be impoverished or otherwise atypical. The above analysis indicates that not only are many of the plant species of the most important fen communities entirely intolerant of salinity in excess of c900 μS/cm or c160 mg/l chloride, but that some ‘very fresh’ fen species such as Utricularia minor, Carex rostrata and Juncus acutiflorus and aquatic plants such as Hottonia palustris appear potentially to be lost once levels much exceed c500 μS/cm or c65 mg/l chloride. This suggests that the 100mg/l ‘very fresh’ threshold for chloride in freshwater systems set out in the summary table produced by Stofberg et al is perhaps a more appropriate indicator of tolerance limits than that put forward by Panter et al., at least for wetland plant species and vegetation communities. The summary table below shows where the plant species for which chloride tolerance limits are known lie on this spectrum. Refer also to Appendix 1 for the supporting data.

Species Approx. % of positive observations where chloride levels below 100mg/l Carex rostrata 100 Nitella flexilis 100 Utricularia minor 100 Sphagnum squarrosum 99 Juncus acutiflorus 99 Hottonia palustris 99 Menyanthes trifoliata 97 Groenlandia densa 97 Comarum (Potentilla) palustre 96 Potamogeton obtusifolius 94 Potamogeton acutifolius 94 Ranunculus lingua 93 Carex elata 92 Lysimachia vulgaris 92 Juncus bulbosus 92 Veronica scutellata 92 Ranunculus aquatilis 90 Cladium mariscus 89 Thelypteris palustris 89 Potamogeton compressus 88 Myrica gale 88 Stellaria palustris 87 Filipendula ulmaria 86

13 Wheeler, B.D. & Shaw, S.C. 1987 Comparative survey of habitat conditions and management characteristics of herbaceous rich-fen vegetation types. Peterborough: Nature Conservancy Council. (Contract surveys No. 6).

Carex paniculata 86 Stratiotes aloides 86 Equisetum palustre 85 Juncus subnodulosus 84 Carex pseudocyperus 84 Epilobium tetragonum 83 Equisetum fluviatile 83 Lythrum salicaria 79 Potamogeton crispus 79 Peucedanum palustre 79 Veronica beccabunga 78 Juncus conglomeratus 78 Juncus effusus 77 Callitriche spp. 76 Lotus pedunculatus 76 Utricularia vulgaris 75

By the time average levels of 100mg/l chloride are reached, the vegetation communities in which the most sensitive plant species (those at the top of the table) occur may have been substantially modified through loss or reduced frequency of those species. With mean chloride levels in the River Ant at Irstead Church and Woodfarm Fen (upper end of Barton Broad) already well in excess of 100mg/l, it is evident that strong freshwater flow through the fens on either side of the river is critically important in preventing river water from penetrating far into these fens and a strong downstream flow in the main Rivers Ant and Bure is similarly important in preventing saline water from entering the Ant in the first place.

Conclusions

Although salinity data is only available for the main River Ant channel and in all probability salinity levels in the river will generally be higher than in the fen dykes and over the adjacent fen surface, the combined data strongly suggest that the flushing of brackish water down through the system following an incursion event and constant surface water movement through the adjacent fen system (in ditches and across the fen surface) prevent the penetration of brackish water into the floodplain fen and fen ditches. This is critically important in safeguarding the plant species, and the associated invertebrate species present in these fens. In this context, the very substantial reduction in flows seen in the fen system at Catfield Fen, Broad Fen and Reedham Marshes is extremely concerning.

Mr Linford-Wood’s paper concludes that “Given the breadth and transitional nature of the salinity regime in a lowland river, it is likely that for more salinity tolerant ecosystems, the estimated magnitude of the net change in flushing indicated resulting from abstraction in this catchment would be of only marginal significance” but goes on to say that “…at the more sensitive freshwater dependent end of the regime, the ecological significance may be more critical but the frequency of incursion events during summer low flow periods is reduced.”

We agree that for freshwater dependant systems the ecological significance of reduced flushing - even at the disputed value of 5% - is likely to be critical, but consider that the statement regarding the ‘reduced’ frequency of incursion events during the summer period is misleading: a single event during the growing season may be enough to cause a local extinction of the most sensitive plant species and the thresholds suggested by the 300mg/l / 800uS/cm ‘freshwater’ categorisation of Panter et al appear to be set too high to ensure the safeguard of the plant species, and vegetation communities of the Broads SAC which are least tolerant of salinity. Moreover, we consider that a threshold of 300mg/l chloride is too high and that a ‘very fresh’ threshold of 100mg/l chloride as proposed by Dutch researchers should be adopted for the Ant valley fens and other saline-sensitive fen communities elsewhere in the Broads.

Specific to plant species and vegetation communities, many of the special interest features of the Ant Broads and Marshes SSSI, and notably several of the SAC features (e.g., Calcareous fen with Cladium and species of the Caricion davallianae, Alkaline Fen and Transition Mires and Quaking Bogs) do not fall within the category of ‘salinity tolerant ecosystems’ and the net change in flushing resulting from reduced flows as a consequence of abstraction, whether an ‘average’ of 5% as hypothesised by Mr Linford-Wood or the much higher figure suggested by Dr Bradley, could prove to be critically important. Certainly the modelled change, of over 50% reduction in flushing through Catfield Fen at Q95 would be highly significant if a surge were to occur at a time when flows were low. It only takes one major incursion event with reduced flushing to cause significant species extinctions. The ecological evidence presented above suggests that there is already a salinity ‘problem’ in the Ant valley, that much of the Ant valley is already at a ‘tipping point’ or may have gone beyond that point and are at immediate risk. We consider that the reduction in flushing is likely to be significantly greater than the 5% figure put forward by Mr Linford-Wood; but even a 5% reduction could prove to have damaging consequences for fens throughout much of the Ant valley.

Dr Jo Parmenter The Landscape Partnership

Dr Aat Barendregt Utrecht University (input to text relating to ecological impact of salinity)

18th October 2018

Wayford Bridge Conductivity Chloride concentration Mean 853 μS/cm 80 mg/l Maximum 4325 μS/cm 1170 mg/l

Broad Fen Flow Reduction Q95 RFL >50% Q50 RFL 10-20% Q10 RFL 5-10%

Barton Fens Flow Reduction Q95 RFL 10-20% Sutton Fen & Broad Q50 RFL 10-20% Flow Reduction Q10 RFL 1-5% Q95 RFL 10-20% Q50 RFL 10-20% Q10 RFL 1-5%

Barton Turf (Woodfarm Fen) Conductivity Chloride concentration Mean 899 μS/cm 140 mg/l Maximum 3640 μS/cm 2200 mg/l

Catfield Fen Flow Reduction Q95 RFL >50% Q50 RFL 30-50% Q10 RFL 10-20%

Irstead Church Mrs Myhill’s Marsh Flow Reduction Conductivity Chloride concentration Q95 RFL >50% Mean 973 μS/cm 135 mg/l Q50 RFL 20-30% Maximum 7240 μS/cm 2080 mg/l Hall Q10 RFL 10-20% Fen

Alderfen Flow Reduction Q95 RFL 30-50% Snipe Marsh Flow Reduction Q50 RFL 10-20% Q95 RFL >50% Q10 RFL 1-5% Q50 RFL 30-50% Q10 RFL 20-30%

Reedham Marshes Flow Reduction Q95 RFL >50% Q50 RFL 30-50% Q10 RFL 10-20%

Ludham Bridge Conductivity Chloride concentration Mean 1292 μS/cm 257 mg/l Hulver Maximum 20,800 μS/cm 8460 mg/l Ground

with annotations by The Landscape Partnership Response (in relative percentage) of some plant species to the salinity of surface water n = the number of observations in each class and the number of positive observations for each species. Species optima in bold. Data from

Mean conductivity at Woodfarm Fen (717μ S/cm BA; 899μ S/cm EA) Mean conductivity at Irstead (1154μ S/cm BA; 973μ S/cm EA) Mean chloride at Irstead Church (135mg/l EA) and Woodfarm Fen (140mg/l EA) Mean chloride at Ludham Bridge (257mg/l EA) Mean conductivity at Sutton Fen (617μ S/cm BA) Maximum chloride at Wayford Bridge (1170mg/l EA) Mean chloride at Wayford Bridge (80mg/l EA) Maximum chloride at Irstead Church (2080mg/l EA) Maximum chloride at Woodfarm Fen (2200mg/l EA) Maximum chloride at Ludham Bridge (8460mg/l EA)

Classification of plant species to salinity (after Runhaar: 2,3) very fresh fresh slightly brackish brackish Ecological species groups used for Witte indicator values (4) very fresh fresh slightly brackish brackish Class number 1 2 3 4 5 6 7 8 9 10 Median Cl concentration in meq/l 0.25 0.48 0.85 1.8 2.9 4.5 8.7 19 66 195 Median Cl concentration in mg/l 8.9 17.0 30.2 63.9 103.0 159.8 308.9 674.5 2343.0 6922.5 Median Electro-conductivity in μ S/cm 194 276 361 476 687 917 1,715 2,555 6,613 16,165 Ellenberg Runhaar Indicator Salinity Stofberg Example Value for Class (2) Salinity Very NVC Example SAC Feature Species Salinity 0=uncertai Class (6) n = 14 126 215 483 507 405 116 108 44 28 fresh Example NVC Community Community (Annex 1 Habitats) Sphagnum squarrosum 17 77 4 5 7 5 1 0 0 0 0 Transition mires & quaking bogs (7140) Carex elata 0 2 3.5 13 63 0 17 6 7 0 8 0 0 0 Potamogeton compressus 0 2 25 62 17 6 3 1 12 0 0 0 0 Potamogeton obtusifolius 0 50 56 14 8 11 4 2 2 2 0 0 Natural eutrophic lakes (3150) Carex rostrata 0 1 3 48 54 18 16 10 1 0 0 0 0 0 Carex rostrata - Potentilla palustris tall herb fen S27 Transition mires & quaking bogs (7140) Carex lasiocarpa 0 1 4 0 Peucedano - Phragmites australis fen, Carex lasiocarpa variant S24eii Calcareous fens (7210) Juncus subnodulosus 0 3 75 44 12 11 10 7 5 5 2 4 0 Comarum (Potentilla) palustre 0 1 4.5 86 42 20 16 13 5 4 0 0 0 0 Carex rostrata - Potentilla palustris tall herb fen S27 Transition mires & quaking bogs (7140) Dryopteris cristata 0 2 0 Betula-Dryopteris cristata vegetation (BS5) Transition mires & quaking bogs (7140) Lysimachia vulgaris 0 2 136 41 8 22 12 10 6 1 1 0 0 Menyanthes trifoliata 0 1 5 31 37 29 17 12 3 3 0 0 0 0 Carex rostrata - Potentilla palustris tall herb fen S27 Transition mires & quaking bogs (7140) Filipendula ulmaria 0 2 168 33 21 12 11 10 6 3 2 3 0 Epilobium tetragonum 0 2 193 35 18 12 10 9 8 6 3 0 0 Juncus acutiflorus 0 3 32 33 31 26 8 1 1 0 0 0 0 Carex rostrata - Potentilla palustris tall herb fen S27 Transition mires & quaking bogs (7140) Hottonia palustris 0 1 5 103 32 30 25 10 1 1 0 0 0 0 Hydrocharis morsus-ranae - Stratiotes aloides community A4 Natural eutrophic lakes (3150) Lythrum salicaria 0 346 24 20 20 12 12 10 9 2 0 0 Stellaria palustris 0 2 69 22 20 17 12 12 5 5 3 0 0 Peucedano - Phragmites australis fen, Cicuta virosa subcommunity S24e Calcareous fens (7210) Groenlandia densa 1 1 52 28 30 16 16 7 3 0 0 0 0 Potamogeton crispus 1 3 104 36 19 9 9 8 7 6 8 0 0 Juncus effusus 0 2 614 23 13 14 13 14 14 6 3 0 0 Veronica beccabunga 0 2 127 25 17 11 13 11 10 10 2 0 0 Equisetum palustre 0 2 354 20 21 20 15 11 8 3 1 3 0 Equisetum fluviatile 0 2 4.5 735 20 17 16 17 12 11 5 2 1 0 Callitriche spp. 0-1 0-3 721 15 19 17 14 13 10 7 6 1 0 Alisma plantago-aquatica 0 3 2 719 14 17 18 14 10 11 7 9 1 0 Ranunculus lingua 0 2 5 30 0 59 17 17 0 7 0 0 0 0 Peucedano - Phragmites australis fen, Cicuta virosa subcommunity S24e Calcareous fens (7210) Juncus bulbosus 0 1 5 14 0 52 23 10 6 8 0 0 0 0 Utricularia minor 0 0 4 5 0 58 34 8 0 0 0 0 0 0 Potamogeton acutifolius 0 1 18 0 48 34 10 2 6 0 0 0 0 Natural eutrophic lakes (3150) Nitella flexilis 19 0 52 18 11 18 0 0 0 0 0 Hard oligo-mesotrophic waters (3140) Veronica scutellata 0 3 10 0 25 29 32 6 8 0 0 0 0 Myrica gale 0 3 35 0 7 43 27 4 18 0 0 0 0 Peucedano - Phragmites australis fen; Myrica gale subcommunity S24g Calcareous fens (7210) Cladium mariscus 0 3 2.5 19 0 0 21 60 9 11 0 0 0 0 S2, S24e, S25 Calcareous fens (7210) Juncus conglomeratus 0 2 150 13 18 12 18 17 12 8 2 0 0 Thelypteris palustris 0 3 175 22 14 17 18 18 10 1 0 0 0 Peucedano - Phragmites australis fen S24 Calcareous fens (7210) Carex paniculata 0 2.5 189 22 10 16 15 22 12 1 1 0 0 S24a, W5 Alluvial forests (91E0) Galium palustre 0 2 880 14 12 13 12 14 14 1 10 1 0 Peucedanum (Thyselium) palustre 0 2 3.5 201 10 17 19 15 18 13 1 7 0 0 Peucedano - Phragmites australis fen S24 Calcareous fens (7210) Schoenoplectus lacustris 0 3 1.5 110 15 17 13 9 18 9 5 6 10 0 Lycopus europaeus 0 2 446 19 11 18 11 12 13 10 4 1 0 Lotus pedunculatus 0 2 657 18 16 15 13 12 11 8 5 0 0 Carex pseudocyperus 0 2 3.5 149 0 18 21 21 23 12 2 2 0 0 Utricularia vulgaris 0 3 2.5 93 0 11 27 18 20 10 9 6 0 0 Ranunculus aquatilis 0 3 20 0 0 36 12 42 10 0 0 0 0 Ranunculetum aquatilis A19 Hydrocharis morsus-ranae 0 3 2.5 792 8 15 14 17 18 18 6 4 0 0 Hydrocharis morsus-ranae - Stratiotes aloides community A4 Natural eutrophic lakes (3150) Ranunculus flammula 0 490 9 14 18 15 19 18 4 3 1 0 Stratiotes aloides 1 1 4.5 128 0 16 20 14 25 14 10 0 0 0 Hydrocharis morsus-ranae - Stratiotes aloides community A4 Natural eutrophic lakes (3150) Scutellaria galericulata 0 2 453 9 13 19 17 16 16 8 2 0 0 Chara globularis 2 121 0 7 11 22 23 20 8 8 0 0 Hard oligo-mesotrophic waters (3140) Spirodela polyrhiza 1 3 ## 7 9 12 17 18 19 11 7 0 0 Spirodela polyrhiza - Hydrocharis morsus-ranae community A3 Natural eutrophic lakes (3150) Najas marina 0 3 18 0 0 0 11 57 32 0 0 0 0 Natural eutrophic lakes (3150) Hydrocotyle vulgaris 1 136 28 3 9 9 7 10 13 18 3 0 Cicuta virosa 0 2 4 296 17 12 12 10 13 13 14 8 0 0 Peucedano - Phragmites australis fen, Cicuta virosa subcommunity S24e Calcareous fens (7210) Nymphaea alba 0 3 3.5 222 10 9 14 15 19 19 13 1 0 0 Nuphar lutea community A8 Oenanthe fistulosa 0 3 2 675 12 10 10 12 16 20 12 8 0 0 Potamogeton lucens 0 85 16 19 11 7 11 7 4 10 15 0 Thalictrum flavum 0 2 19 0 13 23 34 10 4 0 15 0 0 Butomus umbellatus 0 3 683 6 6 10 16 14 19 15 12 1 0 Carex disticha 0 2 311 6 13 10 13 16 15 17 9 0 0 Ceratophyllum demersum 1 3 746 3 4 6 13 19 19 16 16 4 0 Alisma lanceolatum 0 3 24 0 9 5 12 16 17 30 11 0 0 Potamogeton pusillus 1 3 761 7 6 8 14 14 13 14 14 9 0 Potamogeton pectinatus - Myriophyllum spicatum community A11 Apium nodiflorum 0 3 130 0 0 0 4 13 21 27 37 0 0 Hippuris vulgaris 1 3 19 0 0 5 18 4 3 29 41 0 0 Potamogeton pectinatus - Myriophyllum spicatum community A11 Myriophyllum spicatum 0 3 57 0 3 9 9 15 5 17 41 0 0 Potamogeton pectinatus - Myriophyllum spicatum community A11 Myriophyllum verticillatum 0 3 34 0 12 7 18 9 9 19 27 0 0 Hydrocharis morsus-ranae - Stratiotes aloides community A4 Natural eutrophic lakes (3150) Chara vulgaris 2 213 0 3 6 14 11 14 17 32 3 0 Cochlearia officinalis 3 7 0 0 0 0 0 0 55 45 0 0 Eleocharis uniglumis 3 1 107 0 4 1 2 5 7 20 30 27 5 Ceratophyllum submersum 2 0 18 0 0 0 0 3 0 27 24 47 0 Potamogeton pectinatus 2 3 250 0 2 1 3 7 8 17 25 30 6 Potamogeton pectinatus - Myriophyllum spicatum community A11 and A12 Carex otrubae 2 49 0 0 0 1 4 6 16 28 21 25 Schoenoplectus tabernaemontanii 3 4 52 0 0 0 0 1 1 24 31 36 6 Zannichellia palustris 2 3 229 0 1 2 3 12 12 16 16 34 3 Bolboschoenus maritimus 4 309 0 1 1 3 3 7 16 21 27 21 Juncus gerardii 3 41 0 0 0 0 0 0 1 3 30 66 Puccinellia distans 4 32 0 0 0 0 0 0 0 1 34 65 Glaux maritima 4 23 0 0 0 0 0 0 0 1 30 69 Triglochin maritimum 4 22 0 0 0 0 0 0 1 1 21 76 Puccinellia maritima 5 22 0 0 0 0 0 0 0 0 19 81 Spergularia media 5 13 0 0 0 0 0 0 0 0 16 84 Salicornia europaea 9 13 0 0 0 0 0 0 0 0 5 95 Sea water Key Species of fen and fen meadow Freshwater species which Freshwater species which Stofberg et al : 100 mg/l Grazing marsh ditch species would be lost or would would be lost or would Cl threshold (6) Upper and middle saltmarsh species decline very significantly as decline very significantly Lower saltmarsh species salinity increases above Species occurring in several habitat types Species where approximately 90% of their population would be lost if salinity rose above 500 or 1000μ S/cm. The right hand end of the bar indicates the rounded approximate 10% population integrity threshold.

Refer to the Salinity Data table for conductivity and chloride figures for all sampling points.

Example SAC Feature (Annex 1 Habitats) Abbreviated Full description Hard oligo-mesotrophic waters (3140) Hard oligo-mesotrophic waters with benthic vegetation of Chara (3140) Natural eutrophic lakes (3150) Natural eutrophic lakes with Magnopotamion or Hydrocharition (3150) Transition mires & quaking bogs (7140) Transition mires and quaking bogs (7140) Calcareous fens (7210) Calcareous fens with Cladium mariscus and species of the Caricion davallia Alluvial forests (91E0) Alluvial forests with Alnus glutinosa and Fraxius excelsior (91E0)

References 1 Barendregt, A. (1993) Hydro-ecology of the Dutch polder landscape , Ph.D. thesis at Universiteit Utrecht, Netherlands Geographical Studies 162, Utrecht. 2 Runhaar, J., Van der Linden, M. & Witte, J.P.M. (1997) Waterplanten en saliniteit , RIZA, Lelystad. 3 Runhaar, J. (2006) Natuur in de verdringingsreeks , Alterra-rapport 1302, Wageningen, Alterra. 4 Runhaar, J., van Landuyt, W., Groen, C.L.G., Weeda, E.J., & Verloove, F. (2004) Herziening van de indeling in ecologische soortengroepen voor Nederland en Vlaanderen, Gorteria 30, pp. 12-26 (Appendix 1, p. 21). 5 Final values from Hill, M.O., Mountford, J.O., Roy, D.B., and Bunce, R.G.H. (1999) Ellenberg's indicator values for British plants, ECOFACT Volume 2 , Technical Annex, Institute of Terrestrial Ecology, Huntingdon. 6 Stofberg, S.F., Klimkowska, A., Paulissen, M.P.C.P., and Witte, J.P.M. (2014) Potential sensitivity of fen plant species to salinity , National Research Programme Knowledge for Climate, Utrecht. 632000 633000 634000 635000 636000 637000 638000 639000 640000 641000 642000 Key

Assessment Cells

Calthorpe GWDTE's 326000 Broad SSSI Habitats Directive (RoC) Broad Fen, Other SSSI (other RSA and Dilham Priory Agency GWDTE List (July 2007)) Meadows, Cell 2 Hickling Other Designations Cell 1 ! RSA Site (Site Boundary Not Defined) 325000 Rivers Smallburgh Fen Cell Z Western Limit of London Clay Subcrop

Western Extent of Crag Subcrop 324000 Total Flow Impact, RFL 6nea881 minus Cell F Cell Q Naturalised 6nea712, as % of Naturalised Flow Cell R Cell P ! > 1000% ! 0.1 to 1%

! 500 to 1000% ! negligible impact ! 200 to 500% ! -1 to -0.1%

323000 Cell N ! 100 to 200% ! -5 to -1% ! 50 to 100% ! -10 to -5% ! 40 to 50% ! -20 to -10%

! 30 to 40% ! -30 to -20% ! 20 to 30% ! -50 to -30% 322000 ! 10 to 20% ! < -50% Cell S Upper Thurne Broads & ! 5 to 10% Nat flow 0 m3/d Ant Broads Marshes & Marshes ! 1 to 5% Cell T Cell H Cell 3 Cell D Cell M Cell I Grey background symbols sized to schematically indicate the naturalised 321000 Cell U ! total flow at Q30 and thereby highlight the main channels in the model.

Cell L Cell C 320000 Cell J Cell A Alderfen Broad Cell V

Cell W 0 500 1,000 1,500 2,000 m

Scale at A3: 1:35,000

Cell X Ant Broads and Marshes RSA

318000 Cell Y Ludham-Potter Heigham Marshes Q10 Total Flow Impact RFL 6nea881 minus Naturalised 6nea712 as % of Naturalised Flow

Shallam September 2018 Bure Broads Bure Broads Dyke Marshes, & Marshes & Marshes Thurne

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Assessment Cells

Western Extent of Crag Subcrop 324000 Total Flow Impact, RFL 6nea881 minus Cell F Cell Q Naturalised 6nea712, as % of Naturalised Flow Cell R Cell P ! > 1000% ! 0.1 to 1%

! 500 to 1000% ! negligible impact ! 200 to 500% ! -1 to -0.1%

323000 Cell N ! 100 to 200% ! -5 to -1% ! 50 to 100% ! -10 to -5% ! 40 to 50% ! -20 to -10%

Cell L Cell C 320000 Cell J Cell A Alderfen Broad Cell V

Cell W 0 500 1,000 1,500 2,000 m

Scale at A3: 1:35,000

Cell X Ant Broads and Marshes RSA

318000 Cell Y Ludham-Potter Heigham Marshes Q50 Total Flow Impact RFL 6nea881 minus Naturalised 6nea712 as % of Naturalised Flow

Shallam September 2018 Bure Broads Bure Broads Dyke Marshes, & Marshes & Marshes Thurne

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Assessment Cells

Western Extent of Crag Subcrop 324000 Total Flow Impact, RFL 6nea881 minus Cell F Cell Q Naturalised 6nea712, as % of Naturalised Flow Cell R Cell P ! > 1000% ! 0.1 to 1%

! 500 to 1000% ! negligible impact ! 200 to 500% ! -1 to -0.1%

323000 Cell N ! 100 to 200% ! -5 to -1% ! 50 to 100% ! -10 to -5% ! 40 to 50% ! -20 to -10%

Cell L Cell C 320000 Cell J Cell A Alderfen Broad Cell V

Cell W 0 500 1,000 1,500 2,000 m

Scale at A3: 1:35,000

Cell X Ant Broads and Marshes RSA

318000 Cell Y Ludham-Potter Heigham Marshes Q95 Total Flow Impact RFL 6nea881 minus Naturalised 6nea712 as % of Naturalised Flow

Shallam September 2018 Bure Broads Bure Broads Dyke Marshes, & Marshes & Marshes Thurne

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