Newsletter - June 2018

From the Riverbed - editorial roundup

Plus ça change… If you look closely at the back page of the Newsletter, you might spot something a bit different—not just the Data Protection statement, but that the RWT’s charity number has changed and with it the type of Charity that we are: over the last few months, thanks to the hard work of Trustee Bob Wilson (with invaluable advice from Bill Wain of—among other organisations—the Woolmer Forest Heritage Society and the Deadwater Valley Trust) we are now a Charitable Incorporated Organisation (“CIO”).
Previously the legal entity comprised the individual trustees themselves (four of whom held our land on behalf of the Trust), but now it is the Trust itself, as a CIO, that is the entity, and all assets (especially the land—once it’s transferred) become the property of the Trust itself.
CIO is a relatively new charity status—previously the only alternative was a charitable company limited by guarantee, which worked for larger charities with a strong ‘trading’ activity (like the Hampshire Buildings Preservation Trust): this involved onerous things like registering with Companies House, so clearly was not for the RWT!

Trustee David Lee resigned at our APM in November after many years’ hard work for the Trust (particularly in filling the hon. secretary rôle—still vacant!) and although a hard act to follow, Alistair Young has stepped forward to become a Trustee … he of the SandBox (see elsewhere in this Newsletter), our Webmaster and Data Protection guru.

We wait expectantly as the planning application for the land at Radford Bridge is scheduled—at last—to be lodged by the end of June!


THE INVASIVE SKUNK CABBAGE

The American Skunk Cabbage (Lysichiton americanus) is perhaps not as aggressive an invader as our old friends Himalayan Balsam or Japanese Knotweed but when grown near watercourses the seed—although shortlived—can rapidly spread downstream: it seems to prefer growing away from stronger flows (so that the seed can establish—it’s a herbaceous perennial with tough rhizomes).
Introduced (like many of our ‘intended’ invasives) by Victorian gardeners for wetland gardens attracted by its scale and its spectacular flowers (like a giant, yellow Lords-and-Ladies plant) the first report of its escaping into the wild in the UK was in 1947—near Haslemere! This was in fact into the Arun catchment, not the Wey—the watershed is somewhere near Haslemere High Street—but either from that introduction or (more likely) from a planting within the upper Wey catchment it is spreading down the Southern Wey and is now seen (in small quantity) at least as far downstream as Liphook.

Whilst it makes an impressive — if smelly — garden plant, growing four feet high, it does, like ‘our’ other invasives have the ability to colonise large areas of wetland and to do what invasives do best, which is to suppress or even eliminate competition from our natives. When it dies back in winter, it can leave the soil below vulnerable to erosion at time of flooding or high flows in adjacent watercourses, leading to siltation of the rivers and instability of riverbanks.

Controlling can be hard work—for new establishments just removing the (immature) seed heads may do it; for longer-established plants there may still be viable seed left on the ground after the plant itself is removed, and it can re-establish from broken-off sections of its rhizomes. On larger stands, glyphosate can (at the moment) be used … albeit by trained personnel.

The images are taken from Skunk Cabbage guidance published by Scottish Natural Heritage and GB Non-Native Species Secretariat http://www.nonnativespecies.org/index.cfm?pageid=413


CATCHMENTS/WATERSHEDS/HEADWATERS/TRIBUTARIES

These terms are all interrelated: the catchment is the topologically bounded extent of where rainwater runoff (and to some extent groundwater—depending on how deep down is the aquifer) finds its way into a river system.
There are catchments and sub-catchments (and indeed sub-sub-catchments): the Southern Wey is a sub-catchment of the Wey catchment which, in turn, is a sub-catchment of the Thames catchment.

Where the Northern Wey joins the southern Wey at Tilford, then these two sub-(sub-)catchments form the upper part of the main Wey catchment, and so on. We keep reminding our colleagues on the Northern Wey that ‘we’ captured them some 30 thousand years ago when a drop in the river level through the North Downs/Hogs Back gap at Guildford meant that ‘we’ stole the headwaters of the Blackwater at Farnham to become the Northern Wey.
More tributaries join the Wey upstream of Guildford, notably the Cranleigh Waters (and with them the Wey and Arun Canal) and the Tillingbourne (which powered the Chilworth gunpowder mills, dating from the mid-17th century—go to https://www.guildford.gov.uk/article/19506/Chilworth-Gunpowder-Mills for more details).

Back to our own sources: the watershed is a (notional) line drawn along the highest sequence of points that separate one river system from another, and defines the limits of the catchment—to take a local example, the (relatively) high ground that the B3004 follows along from Liphook to Standford defines the watershed between the main Southern Wey and the Holly Water (and then Dead Water) tributary, which joins the main river at Deadwater in Bordon.

Watersheds can ‘hang’ where the high “point” is in fact fairly flat—it may be a boggy area which drains in both directions, or it could be and area of standing water where the watershed is at a relatively low elevation, such as Wolmer Pond at Longmoor which at times of longterm high rainfall can feed both into the Wey catchment (via the Dead Water) and into the Rother catchment (itself a sub-catchment of the Arun).
Our headwaters are spring-fed: this may be at the actual source, or it may from groundwater emerging along the valley-side either at an identifiable point or as a more generalised seepage, but in any case where a permeable aquifer emerges on top of an impermeable (or less permeable) stratum (clay or relatively unbroken rock layer): where this stratum is relatively permeable, then depending on the amount of water in the aquifer layer, some will descend to deeper more long-range and longer-term aquifers. We are fed by Blackdown and then by Hindhead (around which the Wey circles clockwise for much of its length), giant sponges both—serving tributaries that join the Wey at Weyhill (Haslemere), Pitfold, Bramshott, Arford, and both Frensham Ponds. On the outer side of the curve come the stream from Marley (via Shottermill Ponds) and the Slea (from Selborne and Binsted) … and there are other, smaller contributors as well.