Friday, April 04, 2008

Lost Rivers

part of the River Quaggy Longer term residents may remember the meanders in the River Roding that were lost when the M11 was built. There are now long straight channels with concrete banks for much of it that do nothing for wildlife or visual amenity.

Of course some of London’s rivers are not seen at all, being channeled along man-made drains and through culverts beneath our ever-growing city. The stretch of track to the north of Farringdon tube station is the bed of the old River Fleet, the river now being in a drain underneath the adjacent, and 30 feet higher, Farringdon Road.

But some are reappearing, like the River Quaggy in Greenwich. Its return has transformed what were once featureless playing fields into a watery haven for wildlife. The reappearance of the Quaggy’s meandering waters has attracted a stunning array of birds and insects, including grey heron, jack snipe, wagtails and large numbers of dragonflies. This was brought about by a review of flood defences including lowering the parkland to create a floodplain.

We have a “Wetlands” project here for the River Roding and our colleagues at Riverside Concern are actively involved along with the Flood defence issue. Don’t want a repeat of the 2000 floods do we.

4 comments:

  1. Even our own Roding is trying to re-establish itself in the areas where it was straightened under the A406 . After heavy rainfall it appears both sides, on its original position. Unfortunately, because of the concrete sides of the re-directed river the old man can only flood, not get back to the river. I wonder how many people realise they cross over another river 'The Wynne' when they use the Chigwell Road between Broadmead Road and the Petrol Station towards Charlie Browns. It starts, I'm told, high on the Epping Forest ridge and runs underground up by the Castle, via Brackley Sq , visable only at the bottom of the Orchard Estate Broadmead Rd/ Chigwell Rd. for about 100 metres. They may however, have seen the playing field there often flooded.
    Ron King

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  2. I have to stand by my comments regarding the Wetland Area and here given evidence of the great loss we have, indeed suffered by the process chosen for the establishment of the wetland area opposite Ray park on the River Roding.

    From February to May in any year, the River is ‘critically essential’ for wildlife, of this there can be no doubt whatsoever, yet there are those who wish to challenge, and have done so covertly, my right to mention that the highest grade of precautions should be applied to such a large project.

    On my walk along the River Roding 04042008 there was evidence of the “damage” done by the process used to form this wetland area.

    From Redbridge Roundabout up to Snakes Lane East bridge there was evidence of Butterfly emerging from various undergrowth – mainly nettles which are growing well now – there are numerous pairs of duck, coot, moorhen, also nesting in various places along this stretch.

    However, from Snakes Lane East bridge northwards – there is little or no such activity. The Heron have moved up-river, the Swans have also moved out. There is some evidence of plant regeneration – evidenced by seedling growth – but none that can be considered ‘significant cover’. These plantlets appear in the scattered top-soil but their growth indicates that thin scattering of top-soil is on virgin soil, for there is little vigour in these seedlings. Other areas – the great majority of the area – bears only a few tougher grasses and wind-blown seeds – the top surfaces have been scoured by recent rain washing any soils into the excavations with the resulting sediment offering little in the way of nutrients as there are no plants establishing in the excavations, the lakes and surrounding stretches. The best evidence is the lack of water-born creatures in the water areas.

    All of this could have been remedied, and simply, by the mulching of the ground area with the River Dredge Material, which would have offered some sustenance to life forms, and given them a starting-place to colonize the areas so devastated by these excavations.

    The River Dredge Material contained eggs, and larvae-stage species, as well as plant seeds, rhizomes etc., yet all of this was carted away to places afar. Our great loos has been, hopefully, someone’s gain, but we have been left with a huge gap in our eco-system, environment, and essential habitat regime.

    I am informed by the many, “that the area will establish” some qualifying “quite rapidly”, yet none bareing to admit the extreme losses this area has suffered by some most inappropriate management.
    None have taken on-board the simplicity and economical continuation that this Wetland Area could have been offered, by nothing more than the recycling of Local River Dredged Material.

    The devastation and barrenness that has been inflicted here proves, quite simply, that the main breeding and establishment of habitat season can not “happen” in this part of Redbridge. There is a “promise” that ‘planting’ will begin in late April – Early May, but there is no public record to show what planting is proposed!
    The London Wetland Scheme took many months, years to get to a habitat-point, but even at this late date, there are “admitted” gaps in the ecology, and the environment is struggling to provide essential links in the “chain” due to this laid-bare area.

    I agree that the area will eventually benefit from this “construction” – but at what cost – short-term?

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  3. What Ron and Richard have to say about the Roding is most informative, thank you.

    It also appears that all this is yet another example of 'unintended consequences' and allowing 'them upstairs' to play havoc with our lives and our environment.

    It rather reminds me of when the new (and ugly) municipal building in Epping was being planned. I gather that local longterm residents kept saying "don't put it there, the ground is very wet and boggy". They were assured that all was well, everything had been surveyed etc, and then (I think) someway through the building everything had to be expensively redone because ....ta da!! the ground was indeed discovered to be too wet and boggy quite a way down to support the building.

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  4. Dear B21:

    Your article on rivers/tributaries reappearing stirred me to find my notes taken around the 1976 drought or near-drought conditions which affected the River Roding.
    During the 1976 drought the river-bed became dessicated in some parts, and although this brought a dramatic decline prosobranch molluscs and even caddisfly larvae, there was a naticeable increase in invertebrate specie populations, which was largely found to be due to stranded chemical changes in that environment.
    This drought period brought about many Papers on the effects of low flows in rivers and, of course effects by artificially reduced flows.
    Low water volume plays an effect-condition on habitats of the invertebrate community structure, their behaviour, and biotic interactions. Less water volume requires several points to be investigated if only because each bear a relationship to the others; water depth, velocity and the width of channel affected by wetting and drying-out, changes in the sedimentary distribution and types of sediment; fissures in the bed of a river can bring introductions of normally unseen sediments from the sub-strate, as can these fissures decrease/increase the ambient temperatures, so the thermal ranges have to be considered along with the water chemistry.
    Invertebrates can increase or decrease in direct response to all or any of these conditions; however, invertebrate ‘richness’ is greatly affected by these often rapid changes, showing the specie effectiveness to cope with an uncommon (that is say a drought once in ten years) set of conditions. The speed of the drought and the intensity of evaporation are not similar to the species adaption to the ‘normal’ autmnal and winter lowering of water temperatures of the river, although some invertebrate taxa are more responsive to changes in the river environment than others. We also have to include the problems and consequences where a large development scours the top-soil of all plant growth and displaces the natural communities which used to condition those soils and growing mediums, it is of major importance that bare-soils should be protected (a simple sowing of “green-manure”) from the elements and that sub-soil strata be recognized only as in need of a long-term ‘conditioning’ if the landscape is to become, again; productive for flora and fauna habitat environments.
    Because a ‘main’ river can have so many environments, a simplicitudinal manipulation of spot experiments are used to get a broad understanding of the ecological consequences of any period of flow of a river.
    The shortcoming of these ‘used standards’ can be seen locally in the habitat changes and habitat condition, for at one point in the main river, there may be two tributaries entering the regime of waters; say one one the left bank and one on the right bank, this is the classic for it may be ( but is not necessarily the case) that one tributary has its source in chalk while the other comes from a lake of a disused gravel or clay pit. These two types of water are obvious, but did you consider that the lake water would be a few degrees richer in temperature that that from the underground chalk source tributary?
    Other stretches of the main river may have no water contribution than the mean ground water table, while another section may be greatly affected by a displaced brook or tributary by a large development complex. Natural underground water, can in this way be pushed, forced, or trapped into a subdued consequence known as “loss of natural direction”, only regaining the natural drainage complement when the development becomes faulted by time or poor-quality materials breaking down over time, or, of course, demolition of the deveolpment for say – An Olymic Exercise.
    I trust this piece; adapted from my notes – opens the ‘little grey cells’ of your reader, showing the consequence of action, both natural (drought or flood, eathquake) and artificial (development, piling pipe-work, motorways) will, in time, come to light, life and original ‘consequence’. And, or course there is erosion – but that’s another story.

    Richard Cooper

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