Stank Beck & tributaries, Harewood Estate Advisory Visit, March 2020 Prof J Grey: [email protected] Index • Key Findings • Introduction • Catchment & Fishery Overview • Habitat Assessment Eccup Beck (upper) Sturdy Beck Eccup Beck (lower) Stubs House Beck Stank Beck • Recommendations Connectivity / Fish Passage Instream Habitat Riparian Habitat Monitoring • Making it Happen Key Findings • The Stank Beck catchment has been heavily modified historically. Major landscaping associated with creation of the Estate in the 18th Century (resulting in repeated impoundment of the becks) and the damming of Eccup Reservoir in the early 19th Century have taken their toll. • Unlike many of the other smaller tributaries within the wider Wharfe catchment, the proximity of intensive agriculture is less of an issue (aside from the deer herd), and there is copious raw woody material to work with. • While there is much historic value associated with individual structures, there is also sufficient space within the catchment to accommodate both history and ecology if so desired. Many barriers to connectivity could be simply bypassed. This alternative to removal also makes (potentially) inefficient, expensive or aesthetically- insensitive fish easements redundant. • Without restoring connectivity, fish populations will always be fragmented and challenged. However, slowing the flow of water from the land, reducing fine sediment pollution, and improving riparian and instream habitat will still provide enormous ecological benefits and ecosystem services. • Invasive non-native species, particularly rhododendron / azalea and Himalayan balsam have already been identified as issues along the channels and are gradually being dealt with – this should remain a priority to improve riparian habitat quality and resilience. • Diffuse pollution of fine sediment was rife in the Sturdy Beck sub- catchment, and a clear problem under the dense stands of INNS. It was also a clear breach of Farming Rules for Water within the deer enclosure and hence the relocation of the fence to exclude deer from the beck will improve water quality and habitat opportunities. • Encouragement of geomorphological process by judicious installation of woody material where the channel is already beginning to renaturalise will aid retention and sorting of substrate, in particular the gravels required for spawning and invertebrate habitat. To realise full potential, reinstatement of a natural gradient via weir removal or bypass will be required. 1.0 Introduction & Rationale This report is the output of a site visit to Stank Beck and associated tributaries, at the request of the Harewood Estate. The rationale was to assess habitat and connectivity throughout the Estate waters, and propose practical solutions to any issues which could either be applied by the Estate directly, or the ideas be used to form the basis of a future funding application. Prof Jonathan Grey of the Wild Trout Trust undertook a walkover, which happened to coincide with a Yorkshire Water scour test from Eccup Reservoir (recorded via time-lapse photography). Normal convention is applied with respect to bank identification, i.e. left bank (LB) or right bank (RB) whilst looking downstream. Upstream and downstream references are often abbreviated to u/s and d/s, respectively, for convenience. The Ordnance Survey National Grid Reference system is used for identifying locations. Weir numbers and bridge names were sourced from the Estate for ease of referencing – see Map 1. Map 1. Overview of Eccup / Stank Beck weirs and identification numbers, as provided by the Estate. 2.0 Catchment / Fishery Overview The Stank Beck catchment is a relatively small (20.2km2) tributary of the River Wharfe, identified by the Environment Agency (EA) as a Heavily Modified Water Body (GB104027063960). Over 4 years of assessment (2013-2016 incl.) for the Water Framework Directive, Stank Beck has improved from Bad to Moderate Ecological Potential, driven by an improvement for Fish. However, Moderate is still a failure, and Physico- chemical quality elements have remained Moderate throughout. Reasons for not achieving Good potential are listed as the barriers (to fish), pH and phosphate. The upper catchment was heavily influenced by the presence of Eccup Reservoir, constructed in the 1830s and since expanded; it is now designated as a Site of Special Scientific Interest. Eccup Beck which becomes Stank Beck was heavily modified by ‘Capability’ Brown’s designs to landscape the Estate, most of which was completed in 1786. Modifications included 14 major weirs and the impoundment of the beck to create at least five or six pools of various sizes. There are various other smaller weirs, bridges and culverts which will have added to the fragmentation of the beck system over time. A brief correspondence with a contact at Yorkshire Water indicated that no utility company pipework was associated with any weir structures within the Estate boundary but this should be investigated further. Given the steeper gradient of the upper catchment, the fish population would have been dominated by brown trout (Salmo trutta). The lower reaches probably would also have been used by Atlantic salmon (S. salar) and grayling (Thymallus thymallus) as well as smaller native species (e.g. bullhead, Cottus perifretum; brook lamprey, Lampetra planeri). Fragmentation and pollution of the River Wharfe has altered the fish community considerably over time, although those fish species should be able to access the lower reaches of Stank Beck from the Wharfe. How the modification of Eccup and Stank Beck has altered the fish community is uncertain, although EA survey data indicate a relatively healthy population of wild brown trout from the vicinity of Fancy (New) Bridge in 2013, i.e. above the main lake. West Riding Anglers have the fishing rights on Stank Beck from the Estate boundary to the confluence with the River Wharfe and have a vested interest in maintaining the habitat quality along that length to promote healthy and resilient fish populations. 3.0 Habitat Assessment The reporting that follows considers the three main becks from the most u/s point accessible on the day of the visit. The main lake essentially splits the waters. Upstream, Eccup Beck and Sturdy Beck exhibited relatively natural channel characteristics within the Estate boundary. That is not to say they were free from issues, but there is great potential upon which to build. These two becks have a confluence at SE 31276 42149 which continues to be identified as Eccup Beck. Numerous small becks and seeps contributed flow throughout the valley. Only one of these provided substantive flow: Stubs House Beck. For the purposes of this report, the upper section finished at the inflow to the main lake, below Rough Bridge, at SE 31375 43841. Below the main lake, an impoundment requiring a weir ~7m headloss, Stank Beck was heavily modified through ornamental gardens and the former laundry building. So, for the purposes of this report, the u/s limit of the Stank Beck survey began at Laundry Bridge (SE 30605 44575) and continued to the Estate boundary at SE 30489 45433. The lowest reaches, between Lady Bridge and the Estate boundary were historically straightened and walled and repeatedly fragmented by smaller weirs which have since broken up. The strongest influence on those reaches recently has been the deer herd, and it is understood that exclusion of deer from the beck banks is part of future funded work under the Water Environment Grant. This is to be applauded and will lead to significant ecological benefits; otherwise, it would have been a key recommendation based upon observations made during the walkover. 3.1 Eccup Beck to confluence with Sturdy Beck Fig 1. Upper: u/s limit of Eccup Beck and despite being only ~100m from the reservoir, there was considerable evidence of fine sediment deposition in the margins. Fencing was in place along the LB boundary, but looked in suspect condition – check responsibility for maintaining this. Lower: a presumed defunct gauging structure ~100m d/s acts as a barrier to fish passage by creating shallow, fluming flow for ~3-4m (note the hydraulic jump, standing wave at the tail end). This should be removed / broken up to return to a natural bed. Pool Ramp Fig 2. Despite the abundance of living wood, there was relatively little dead or living wood retained within the channel. Good examples in the images above demonstrate how wood helps to sculpt and diversify the channel, creating a mosaic of habitats. Upper: a relatively small double trunk of silver birch spanning the channel has trapped finer debris (& rubbish), causing deeper scour to the LB via a plunge pool and deposition to the RB. The latter was becoming colonised by plants and will stabilise over time. Finer debris like the abundant leaf litter trapped around the stems provides food resource and refuge for invertebrates (particularly shredders like gammarid shrimp – see Fig 6). Lower: a more substantial trunk has forced water down into the bed, creating a scour pool with overhead cover and a ramp of deposited cobble and gravel on the d/s side. In spate flow, water has been forced out of bank for a short distance (white arrow) but could be encouraged further; see Fig 3. Fig 3. From a higher vantage point on the RB, it was clearer to envisage where former paleo-channels and depressions lay, into which water could be encouraged under spate flow, by judicious positioning of large woody material in the channel. Out-of-bank flow would also improve water quality and channel habitat further d/s by removing and trapping fine sediments. It was also notable in this area how high and even the canopy was. All the trees were tall and whip- like with very little understory except for mosses, ferns and bluebell shoots. Fig 4. Channel diversity was reasonably good where the beck was forced around mature tree roots, and there were some natural pool-riffle-glide sequences, but in other areas the channel retained a rather consistently uniform, trapezoidal cross-section.