The Hogsmill in July 2020 Cloudy skies and early “browning” of the grass have often left the Hogsmill corridor looking drab this month. But when the sun has been out, the meadows have been looking “sweet”; and for a splash of bright colours, the Tolworth roundabout with its wonderful new Hogsmill murals is the place to visit. Six Acre Meadow Tolworth Roundabout The most noteworthy news this month - both good and bad - has been from the Bonesgate tributary. There have been glimpses of “red” and “silver” as some of our rarer critters have lightened the gloom by the stream near Park Farm; but there have also been major pollution incidents at 2 of its large outfalls that have led to the water matching the grey/brown of the sky and meadows. Kite Park Farm Fritillary This newsletter reports on volunteer activities to monitor and restore the habitat along the Hogsmill river, working with the South East Rivers Trust and local groups, and alongside the Environment Agency (EA) and local water companies, mainly Thames Water (TW). This month it also looks further at the Bonesgate, the largest and the most interesting tributary of the Hogsmill. The Hogsmill in July Another month of relatively low rainfall has led to a steady fall in water depth in the Hogsmill, though with aquifer levels still above recent year lows, the sharp dips in the last 3 summers have so far been avoided. 1 Average Daily River Level Average Monthly River Level 0.6 1.3 0.5 1.2 0.4 0.3 1.1 Metres 0.2 Metres 1.0 0.1 0.0 0.9 Ewell Bourne Hall Worcester Park Water levels were down at most of our sampling sites, in some cases markedly so, but perhaps because flows have been holding up, there seems to be much less of the algae that has clogged the river in recent years; and some river residents have obviously been thriving – he said he would put it back! Bonesgate confluence Green Lanes Stream confluence Elmbridge Meadows (Photo thanks to Anita) But we seem to be having a bumper season for Himalayan balsam. The flowers may look attractive at this time of year, but massive clumps are now lining the banks along virtually the whole stretch from around the Bonesgate confluence to the Berrylands STW. Long Meadow Bonesgate confluence Elmbridge Meadows 2 There has been another spate of outfall pollution incidents this month. A blocked sewer in Chessington led to a major spill through the Moor Lane outfall on the Bonesgate, killing fish and requiring a large clean-up from TW. There were also signs of pollution further upstream at the same time. Later a burst water main in Chessington led to large flows of brown water from the Moor Lane and Cox Lane outfalls. Although hopefully mainly silt, this still resulted in fish “gasping” as far away as the Hogsmill Tavern; and later there was another spill of brown water by the Tavern, again apparently caused by a leaking main. Moor Lane Cox Lane Hogsmill Tavern (photo thanks to Kim) If you see pollution along the river or indications of possible pollution, such as dying fish, please call the Environment Agency Hotline: 0800 80 70 60, and ideally take a photo. Hogsmill RMI in July The River Monitoring Initiative (RMI) is a national scheme that uses counts of “water quality sensitive” invertebrates to assess river health. This month all our 7 sites were surveyed, between 15th and 18th July. Results were again mixed. At the 4 upstream sites, some scores fell but more notably olive and gammarus numbers fell sharply. This could partly reflect lower water levels as olive counts have dropped in previous summers. But at 3 sites it might indicate some impact from recent pollution incidents, albeit not a large one: • At Ewell Storms Tanks invertebrates were “scarce and tiny” in July. Although a month since the overflow there, it would presumably take some time numbers to recover; • Downstream at Green Lanes, the closest site to the Epsom Tanks which may also have overflowed in June, gammarus numbers have been unusually low in both samples since then; and • At Bonesgate, the score rose this month, but this reflected higher caddis scores which tend to be variable. Olive and gammarus numbers were very low and several dead specimens were found. By contrast, scores rose at the 3 downstream sites reaching a “10” at Middle Mill and with some impressive individual counts, including the largest number of gammarus for 6 years at Berrylands. There is no obvious 3 reason for these improvements, but they match what happened in July last year when there were also sharp rises in score and a “10” at Middle Mill. Hogsmill RMI Scores July 2020 12.0 10.0 8.0 6.0 4.0 RMI Score 2.0 0.0 GL Upstm GL Dwnstm Storm Tanks Bonesgate Tol Brook Berrylands MiddleMill Olives Caseless caddis Cased caddis Gammarus The Bonesgate: a mysterious and diverse stream The Bonesgate is the largest tributary of the Hogsmill, flowing over 5km from near Epsom and Ashstead Commons to Tolworth. It is believed to be named after a “gap in a wall belonging to Bone”, rather than anything more sinister. It is cloaked by overhanging trees and vegetation and is a stream of contrasts, impacted by urban/industrial areas but also flowing through a rural landscape of farms and woods. Diversity starts at the confluence. Ruxley Sewage Works once stood on its south bank until replaced by the Watersedge, for a long time a “sink” estate that blighted the stream: in the 1970s it was called a “river of shame” choked with rubbish and scrap metal, including old cars. It is much better now: just bicycle wheels! Ruxley Sewage Works 1938 Confluence with the Hogsmill Watersedge 2020 But on its north bank is the “hidden gem” of Tolworth Court Farm Fields, over 100 acres of largely unspoilt landscape with an ancient drovers’ road still clearly visible and extensive hay meadows that in early summer are full of flowers and insects and at present are also home for some other unfortunate creatures! 4 Tolworth Court Farm Fields For over 2 km upstream from Tolworth, the Bonesgate flows in a heavily modified channel with urban development closeby. The trees and brambles that line the stream provide good habitat for some wildlife, such as bats and butterflies. But being overshadowed by pylons, this is not the most attractive stretch and it is where the Bonesgate “flirts” with industry with the Cox Lane outfall; for a long time a source of “noxious substances” dumped in the Chessington Industrial Estate, though this has improved of late. Bonesgate by Watersedge Cox Lane outfall 2016 Riverbank at Drakes Road But upstream of Filby Road the Bonesgate enters a “new world” as a rural stream. It passes close to Castle Hill, an Ancient Monument and Nature Reserve. “Cisendene” mill recorded in the Domesday Book was probably located here. Then it bursts into “Big Sky” country along the edge of the fields of Park Farm now full of ripening crops with carpets of flowers near the banks of the stream. Bonesgate at Castle Hill Park Farm fields Flowers by the riverbank A short distance upstream, it splits into 2 and later 3 “hard-to-track” branches. The first “east” branch heads into Horton Country Park, “hiding” in the hedgerows dividing the farm fields and the thickets of Pond Wood 5 before reaching a series of ponds and reed beds in West Park on the edge of Epsom Common. Even at this time of year, there seems to be plenty of water here, though some of the signage seems surprising! “Is there a stream in there?” Pond Wood West Park Horton The other branches pass under Chalky Lane at the entrance to Park Farm house and yard, though apart from the tell-tale glimpses of balsam, the presence of a stream could easily be missed. Here the “middle” branch heads south by fields that seem to be a regular haunt of predators, before passing under Rushett Lane and then petering out in thickets by Rushett Farm on the edge of Ashstead Common. Bonesgate “hiding” at Park Farm “Are there any sparrows around?” Rushett Farm The “west” branch, which also seems to have a fair flow of water even at this time of year, fringes fields that provide pasture for rather more impressive equines, passes through Chessington Wood before “disappearing” in a large culvert by Malden Rushett crossroads. Park Farm “thoroughbreds” Chessington Wood Malden Rushett 6 .