Integrated fisheries, RHS and ecological data model for the river Lee Report to Environment Agency NE Thames Area P. M. Scarlett M O’Hare CEH Dorset Winfrith Technology Centre Winfrith Newburgh Dorchester Dorset DT2 8ZD Telephone (01305) 213500 Main Fax (01305) 213600 www.ceh.ac.uk Integrated fisheries, RHS and ecological data model for the River Lee P. M. Scarlett , M O’Hare Project leader: P.Scarlett Report to Environment Agency NE Thames Area CEH Project No: C01019 Date: January 2006 INTELLECTUAL PROPERTY RIGHTS CONFIDENTIALITY STATEMENT ‘In accordance with our normal practice, this report is for the use only of the party to whom it is addressed, and no responsibility is accepted to any third party for the whole or any part of its contents. Neither the whole nor any part of this report or any reference thereto may be included in any published document, circular or statement, nor published or referred to in any way without our written approval of the form and context in which it may appear’ Contents 1 Background 1.1 Introduction 1 1.2 Objectives 1 1.3 General description of the Lee catchment 3 2 Habitat Quality of the catchment 6 2.1 Habitat Quality and impacts 6 2.2 Land Use 6 2.3 Matrix of high quality and degraded sites 6 2.4 Substrates and flows 7 2.5 Stream Power 8 2.6 Fine Sediment Sources and bank Sensitivity Index 8 2.7 Nuisance and invasive species 8 3 Analysis of fish data 12 3.1 RHS data and its relationship with guild composition 12 3.2 RHS and fisheries data 17 3.3 Identification of suitable sites for guilds using RHS variables 18 3.4 Migration and movement 20 3.5 Siltation 20 3.6 Channel morphology and habitat quality 23 3.7 Early life stages 23 3.8 Water levels 23 3.9 Chemical water quality 23 3.10 Species specific habitat requirements 24 4 Conclusion 25 References 26 Figures Figure 1 Location of RHS sites on the river Lee catchment 2 Figure 2a Solid geology of the river Lee catchment 4 Figure 2b Drift geology of the river Lee catchment 5 Figure 3 Substrate compositions of the river Lee and tributaries 7 Figure 4 Flow compositions of the river Lee and tributaries 7 Figure 5 Distribution of invasive species on the Lee catchment 10/11 Figure 6 Location of fisheries data on the river Lee catchment 14 Figure 7 Relationship between RHS scores and fish survey data 17 Figure 8 Distribution of weirs, culverts and fords 21 Figure 9 Distribution of abstraction, silting and drought 22 Tables Table 1 Species recorded on the River Lee catchment and their spawning guilds 12 Table 2a Summary of fisheries data on tributaries of the river Lee 15 Table 2b Summary of fisheries data on the river Lee 15 Table 3 Adult habitat flexibility of different species 16 Table 4 Sites most suitable for Lithophils, Phytophils and Psammophils 18 Table 5 Count of potential barriers to migration and areas of silting 20 Table 6 Sites with habitats suitable for chubb and bleak larvae 20 Table 7 Sites with habitats suitable for Roach 24 Table 8 Sites with habitats suitable for Roach, derived from RHS data 25 Appendix Appendix 1 Habitat Quality – High quality and degraded sites 29 Appendix 2 Summary maps of each tributary and section of the main river Lee 31 1 Background 1.1 Introduction The Centre for Ecology and Hydrology (CEH) was commissioned by the Environment Agency, Thames Region, to analyse fisheries and River Habitat Survey (RHS) data from the River Lee, Hertfordshire, and five of its tributaries – Mimram, Stort, Ash, Rib and Beane (figure 1). Three hundred and thirty-five RHS surveys were used for analysis. The surveys were conducted between 2000 and 2004 by different surveyors. Most surveys were done using the most recent (2003) version of the RHS methodology (Raven et al 1997 and 1998). In order to provide more detailed information of variation along the main river Lee it was split into three sections namely upper (source - Hertford), middle (Hertford - Enfield) and lower (Enfield - Thames). The project is a continuation of the development of an integrated model to further a strategic approach to maintaining and enhancing local rivers for fish and other wildlife. 1.2 Objectives The objective of this part of the project is to incorporate a selection of previous analyses placed in reference to fisheries interests within the River Lee Catchment. This work will complement the current efforts to improve fish populations outlined in the Lee Fisheries Action Plan (Lee FAP, 2005). 1 Beane Rib ll Quin Ash Stort l ll l ll Lee l l l l lll lll l ll l l l ll l l l Luton Mimram l l ll l l ll l Stevenage ll l l l l l ll Bishops l l lll l ll l lll l Stortford l lll l l l ll l l l ll l l l lll l l l l l ll ll l ll l l lllllll l l l lllll l l ll l ll lll l ll ll l l l l llll ll ll ll ll ll llll llll l l llll llllll l ll l l l l l llll lll l ll ll lll l ll lll l ll ll lll ll llll ll llllll l l lllllllll ll l ll l l Pincey l l Hertford l l l l ll ll lll ll l l l brook l lllllllllllllllll l l ll ll ll ll lll lll lllll lll l l lll lll Enfield l l ll Tottenham l l l l Figure 1. Location of RHS sites on the River Lee catchment 2 1.3 General Description of the Lee Catchment The River Lee rises near Luton at an altitude of approximately 120m and flows in a southerly direction for 85 km where it joins the River Thames at Canning Town (Environment Agency 2004). The total catchment area is 1,420 sq. km of which the upper Lee area comprises 1033km2. The upper half of the catchment and all of the tributaries mentioned in this report have a solid geology which is based on chalk (figure 2). The lower half of the Lee catchment is based on London clay. As a result, the upper Lee and its tributaries are mostly fed from groundwater, and the flow of the lower Lee is mostly derived from overland run-off from the clay and urban areas. The chalk is only permeable to a limited degree. The drift geology is more mixed though it is dominated by boulder clay/morainic drift and glacial sand and gravel with river terrace deposits in the lower reaches. Ground slopes are mostly gentle though there are some steeper areas around the Chilterns in the Luton area. The upper part of the catchment is mostly a shallow valley, which opens out downstream into the floodplain of the Thames. There are a large number of Sites of Special Scientific Interest in the Lee valley, mainly due to the unique habitats provided by multiple river channels and the areas of standing water provided by flooded gravel workings. The Lee supports good fisheries especially in the upper reaches. Roach, bream, barbel, chub, eel, tench, dace, perch, pike and carp are all present in parts of the catchment. Agriculture is the main land use in the Upper Lee area, though urban areas cover 16% (169 km2) of this area. In the lower part of the catchment, urban areas are more extensive. Water quality of the tributaries is generally better than that of the main river Lee which is impacted by run-off from urban areas. Abstraction has a significant impact on the Lee catchment. Water is abstracted from the Lee at Ware to supply water for London and it is also subtracted further downstream to fill the Lee reservoirs. Some of the water is returned via sewage treatment works. Re- development of urban areas and agricultural intensification also threaten the catchment. 3 Solid Geology in the River Lee Catchment Legend Main tributaries in Lee catchment Solid Geology Barton, Bracklesham and Boagshot Beds Chalk including Red Chalk London Clay No program output Oldhaven, Blackheath, Woolwich, and Reading and Thanet beds Figure 2a Solid geology of the river Lee catchment 4 Drift Geology in the River Lee Catchment Legend Main tributaries in Lee catchment Drift Geology Alluvium Boulder Clay and Morainic drift Clay with flints Galcial Sand and Gravel No Drift Geology River Terrace deposits (mainly sand and gravel) Sand and Gravel of uncertain age or origin Figure 2b Drift geology of the river Lee catchment 5 2 Habitat Quality of the catchment Data collected from the RHS surveys provides detailed information on habitat characteristics of the Lee catchment is available. In order to provide an overview of theses characteristics and to illustrate both areas of high conservation value and areas where enhancement of habitats may be beneficial, a number of maps were generated (appendix 2). These are summarised below. 2.1 Habitat Quality and Impacts Using RHS data, scores were calculated for each site which indicate the extent of habitat modification and habitat quality. The Habitat Modification score (HMS) measures artificial modifications to the physical structure of the channel such as resectioning and man-made structures. The Habitat Quality assessment score (HQA) is based on the presence and extent of habitat features of known value to wildlife. Much of the catchment shows signs of having been extensively impacted with nearly all sites being designated as either severely or significantly modified.