River channel assessment - a method for defining channel sectors on the River Glen, Lincolnshire, UK

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1 Man 's Influence on Freshwater Ecosystems and Water Use (Proceedings of a Boulder Symposium, July 1995). 1AHS Publ. no. 230, River channel assessment - a method for defining channel sectors on the River Glen, Lincolnshire, UK IAN MADDOCK Department of Geography, Worcester College of Higher Education, Henwick Grove, Worcester WR2 6AJ, UK GEOFF PETTS School of Geography, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK MELANIE BICKERTON Department of Geography, Loughborough University, Loughborough, Leicestershire LEU 3TU, UK Abstract A methodology for defining channel sectors using specific information at both the catchment and the reach scale is evaluated for the River Glen, Lincolnshire. Broad measurements from map sources and ecological records are used to define the river into types reflecting position along the river. Sectors and reaches are then defined using hydrological, geomorphological and physical habitat field data. Results support the classification of the Glen catchment into three river types (upland, intermediate and lowland) and 10 sectors. The upland type have low and intermittent discharges, morphological diversity is low and ecological communities have low diversity. Intermediate types have large proportions of riffle habitat with a diverse fauna. Lowland type sites are sustained by perennial flow with low velocities and deep run habitat with low morphological diversity. The 10 sectors are identified using the field data on hydrology and bed morphology. This information can then be used to ensure river management is applied in the appropriate places. INTRODUCTION With the increased demand for water supply, coupled with a rise in environmental awareness, there has been a growing need for improved approaches to assess the impacts of water resource schemes and especially for allocating water for the maintenance of instream habitat (Petts & Maddock, 1994). Instream habitat assessment methods attempt to describe and assess the present stream resource (Maddock, 1994), flow allocation techniques try to assess the discharge requirements of the instream biota (Gore & Nestler, 1988) and fishery enhancement recommendations often involve the use of habitat improvement structures to physically recreate the habitat that may be degraded due to engineering works (Swales, 1989). Application of all these techniques requires a multidisciplinary framework including fields such as hydrology, geomorphology, engineering, ecology and biology. However, all disciplines need a consistent frame of reference when describing river channels. One such method is the use of stream classifi-

2 220 Ian Maddock et al. cation for describing distinct channel sectors which exhibit a set of discrete variables. The general principles of classifying rivers for the purpose of assessing conservation potential have been reviewed elsewhere (e.g. Hawkes, 1975 and Naiman et ah, 1992). This definition is necessary in order to ensure that appropriate management is being applied in the most suitable location and is essential in order to provide a practical framework for ecologically-sensitive river management. For instance, a system has been developed in Britain for predicting invertebrate assemblages at given sites from a small set of physico-chemical variables based on in-channel features (Wright et al., 1984) which allows the classification of sites based on the integration of physical, chemical and biological data. RIVPACS (River Invertebrate Prediction and Classification System) has been valuable in detecting environmental stress and identifying species-rich communities across a wide range of stream types. However, the approach has been criticized for only focusing at the small scale and ignoring some of the larger landscape features of the watershed that may have an indirect impact on the biota, e.g. changes in geology which may influence water quality (Naiman et al., 1992). DATA The accurate definition and classification of channel sectors relies on specific information at both the basin and the reach scale. For the assessment of instream habitat, this study proposes a three-level classification system. First the river system may be divided into TYPES (e.g. upland, intermediate and lowland), reflecting position along the river where such variables as altitude, distance from source and the slope of the valley floor are important. Secondly, each type may be divided into SECTORS. Within, each sector, water quality, sediment load, and hydrological regime are seen as invariant between sites. Thirdly, each sector is divided into REACHES on the basis of local variations in channel morphology or river-margin vegetation. Variations between individual reaches within a sector relate to local conditions (bank sediments, riparian vegetation, spring inflows, sewage outfall etc.). Along natural rivers, channel morphology often has the same general form throughout each sector. A preliminary classification of sites along a river should be at the type and sector scale. The criteria used to define types and sectors are those variables that influence the important hydrological, geomorphological and ecological processes at the basin scale and for which the relevant information is readily accessible from published sources. These may include all or a combination of: (a) a measure of scale (stream length, drainage area, stream order, stream magnitude); (b) a measure of location (altitude); (c) a measure of hydraulic energy (slope); (d) measures influencing hydrology and water quality (rock type and land use); (e) a measure of local controls (riparian land use). More detailed (field) information should then be obtained to clarify the location of sector boundaries, requiring a complete physical habitat survey of the channel, supported by routine hydrological surveys and/or comprehensive gauging station flow data. Habitat type, condition and scale Six main habitat types and conditions are recognized in accordance with the definitions

3 River channel assessment used to define channel sectors on the River Glen, UK 221 proposed by Gorman & Karr (1978) and Helm (1985). The types are split into two main categories. Good quality habitats included riffles, glides/shallow runs and pools. Deep runs, stagnant runs and dry channels are considered to be poor quality habitats in biologically productive terms. Habitat scale is determined by measuring channel bed width and water width (to the nearest 10 cm). Measurements should be recorded at every 50 m or at every riffle site whichever is the closer. This sampling strategy is clearly biased to one specific habitat type, but has been devised to monitor a specific habitat type that is fundamental to the biological productivity of the channel and one that is commonly removed as a consequence of insensitive river engineering. Hydrological survey Sites for routine hydrological surveys should be chosen with reference to (a) the location of existing gauging stations; (b) areas known for importance in terms of water gains/ losses from the channel; (c) sites used for previous stream gauging surveys to allow comparison; and (d) ease of access e.g. road bridges, farm tracks, public footpaths. APPLICATION TO THE RIVER GLEN, LINCOLNSHIRE The River Glen, a tributary of the River Welland, lies within the Anglian region of the National Rivers Authority (NRA). The drainage area consists of two distinct zones. The upstream section is made up of two principal tributaries i.e. the West Glen and East Glen which join to form the River Glen. Kates Bridge Gauging Station (GS) separates the two zones and the basin area upstream is 342 km 2. Downstream, the River Glen possesses characteristics of a lowland river as it flows across the low gradient Fenland. Four electrofishing surveys and invertebrate records from 44 sites within the basin gave indirect evidence relating to geomorphology based on the species present and knowledge on their specific habitat requirements. It is clear from the data and related reports that the River Glen system can be divided into two separate fisheries: (a) the West and East Glen and the River Glen between the confluence and Thurlby Fen, with relatively high populations of dace, chub, brown trout with pike and eel, and (b) the River Glen below Thurlby Fen with relatively high populations of common bream and roach, but frequently dominated by pike and occasionally eel. The weirs at Greatford, Kates Bridge and Fletland Mill restrict fish movement within this zone. Analysis of the invertebrate records was undertaken by Bickerton (1992) using two multivariate methods of analysis (i.e. TWINSPAN (Hill, 1979) and CANOCO (Ter Braak, 1988)). Samples were standardized into faunal groups and analysis suggested that the invertebrate communities could be separated into three types: (a) upland type River Tham and middle West Glen, (b) intermediate type - East Glen, lower west Glen and upper River Glen, and (c) lowland type lower River Glen and Bourne Eau. The stream network was ordered using the Strahler (1952) and Shreve (1967)

4 222 Ian Maddock et al. systems based on the Ordnance Survey maps of the drainage basin at the 1: scale. A physical habitat survey of the West and East Glens from their source to the confluence was undertaken between 21 August and 28 September Measurements in the field were taken at every tenth of the reach length or at every riffle site, whichever was the closer. Each point was assigned to a habitat category as described above. Channel width and water width were recorded to the nearest 10 cm. A total of 823 measuring points were recorded along km of the West Glen and 762 points along km of the East Glen. Flows were monitored at 17 sites throughout the basin. These supplement the continuous data recorded by the network of seven NRA gauging stations. Figure 1 shows the average monthly flows experienced at the five main river gauging stations over the period compared with the long-term averages measured since each station became operational. This highlights the low flows experienced during the period. Using these data, reaches have been split into two basic groups, i.e. perennial flow and ephemeral flow. Further subdivisions highlight which perennial sections experience consistent losses from the channel bed and whether the ephemeral sections become either totally dry or contain ponded water but with no flow. Definition of channel types, sectors and reaches Results support the classification of the Glen catchment into three river types (upland, intermediate and lowland) and 10 sectors (Fig. 2). The upland type sectors comprise sectors 1, 2, 3, 4, 6, 7, 8 and sector 5. The majority of the sectors have low invertebrate community diversity with low and intermittent discharges. Flows reach zero for periods of the year and morphological diversity is low. Within sector 5, flows are maintained by spring flows and the lower Tham, in particular, sustains good quality habitat. Invertebrate assemblages are more diverse and the characteristic fish species are dace and brown trout. Intermediate type sites have large proportions of riffle habitat although the weirs at Kates Bridge and Fletland Mill create ponded reaches characterized by deep runs. These sites have a diverse invertebrate fauna and are characterized by dace and chub. The lowland type sites are sustained by perennial flow with low velocities and deep run habitat. The invertebrate fauna indicate the water quality is good. In such channels, water depth is more important than flow velocity for determining habitat diversity. Morphological diversity is distinctly lacking, due to the channelized nature of the reach. The use of the geomorphological characteristics to aid definition and describe sectors, and in particular, reaches within sectors, is illustrated in Fig. 3. This compares the physical habitat of two representative reaches within sector 9 on the West Glen, highlighting the decrease in overall channel size downstream of Greatford Cut due to the diversion of flood waters from the main channel and also the improved distribution of habitat types within this lower reach. The pie diagrams highlight the predominance (>75%) of deep and stagnant run type habitats in the upstream reach whereas they occur less frequently downstream (50%). This information can then be used for subsequent studies that require data collection on "representative" or "target" reaches and help identify the extent to which the results can be extrapolated elsewhere along the river. This approach is intended to enable definition at three spatial scales, i.e. type, sector

5 River channel assessment used to define channel sectors on the River Glen, UK 223 and reach based on both broad scale sources (e.g. maps) and standardized field methods to identify the spatial array and physical dimensions of a number of habitat units. The advantages of this type of system are that it combines important information from a Fig. 1 Long term average monthly flows (o) and actual recorded ( ) flows during 1990 and 1991 for the five main river gauging stations.

6 224 Ian Maddock et al. SECTORS 0 upland TYPE intermediate TYPE lowland TYP h t UJ 0@ tors o m S tors îctor o vu ss from channel becomes ponded becomes dry perennial flow perennial flow, lo intermittent flow, intermittent flow, tributaries.tment works 1 : j j j 1 1 rtre to 151 F II S 'c. E 0 o O a. t> o...jl.y^.. \ m L \ ; - : / \ '" to CD D) o Hî r LU CD K CO Uj O > i2 Xi H N ei S

7 River channel assessment used to define channel sectors on the River Glen, UK 225 SHILLINGTHORPETO GREATFORD REACH distance = 3.46 km n = 54 GREATFORD TO EAST GLEN CONFLUENCE REACH distance = 1.71 km n = 44 E 10 mean = o O 6 Observations r log(x) of channel width (m) - i Observations log(x) of channel width (m) riffle pool run stagnant run deep run dry channel Fig. 3 A comparison of the physical habitat of two reaches within the same sector along the West Glen. The top graph represents the size of the channel, the middle graph highlights the frequency distribution of the channel width and the pie charts highlight the relative importance of the six habitat types along the reach. range of spatial scales and attempts to integrate the physical, chemical and biological data relating to the whole river system. This more holistic approach allows the river to be partitioned into zones with similar physical and biotic characteristics, and hence enable river managers to focus their decisions and actions at the most appropriate locations along the river. Acknowledgements The work described above was undertaken for the National Rivers Authority Anglian Region. We acknowledge the guidance and constructive criticism given by Dr Alistair Ferguson and his colleagues throughout the project. REFERENCES Bickerton, M. (1992) Assessment of NRA invertebrate records. In: The River Gten: a Catchment Assessment (ed. by G. E. Pens). Report undertaken by the Department of Geography, Loughborough University for the NRA Anglian Region.

8 226 Ian Maddock et al. Gore, J. A. &Ncstler, J. M. (1988) Instream flow studies in perspective. Regulated Rivers: Research and Management 2, Gorman, O. T. & Karr, J. R. (1978) Habitat structure and stream fish communities. Ecology 59, Hawkes, H. A. (1975) River zonation and classification. In: River Ecology (ed. by B. A. Whitton), Blackwell, London. Helm, W. T. (ed.) (1985) Glossary of Stream Habitat Terms. American Fisheries Society, Western Division, Habitat Inventory Committee. Hill,M. O. (1979)TWINSPAN - A FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. In: Ecology and Systematics. Cornell University, Ithaca, New York. Maddock,I. P. (1994)Instreamhabitatassessment ageomorphologicalapproach.unpublishedphdthesis.loughborough University, UK. Naiman.R. J.,Lonzarich,D. G., Beechie.T. J.&Ralph,S. C. (1992)Streamclassificationandtheassessmentofconservation potential. In: River Conservation and Management (ed. by P. J. Boon, P. Calow&G. E. Petts), Wiley, Chichester, UK. Petts, G. E. & Maddock, I. P. (1994) Flow allocation for in-river needs. In: The Rivers Handbook, vol. 2 (ed. by P. Calow & G. E. Petts), Blackwell Scientific Publications, Oxford. Shreve, R. L. (1967) Infinite topologically random channel networks. J. Geol. 75, Strahler.A. N. (1952) Hypsometric (area-altitude) analysis of erosional topography. Bull. Geol. Soc. Am. 63, Swales, S. (1989) The use of habitat improvement methodology in mitigating the adverse effects of river regulation on fisheries. In: Alternatives in Regulated River Management (ed. by J. A. Gore & G. E. Petts), CRC Press, Florida. Ter Braak, C. J. F. (1988) CANOCO A FORTRAN program for canonical community ordination by (partial) (detrended) (canonical)correspondence analysis, principalcomponenlanalysisandredundancyanalysis(version2.1). AgncuXlutÀ Mathematics Group, Ministry of Agriculture and Fisheries, Wageningen. Wright, J. F., Moss, D., Armitage, P. D. & Furse, M. T. (1984) A preliminary classificationof running water sites in Great Britain based on macro-invertebratespecies and the predictionof community type using environmental data. Freshwat. Biol. 14,