US social scientist Kenneth Boulding : ‘If you believe exponential growth can go on in a finite world, you are either a madman or an economist’.

Thursday, 10 September 2009

9+10/9/09: In and around the River Cray

Two consecutive days out by and in the River Cray with the Thames21 volunteer group and the indefatigable Riverkeeper, Ashe Hurst, a man who appears to have an inexhaustible supply of 'Tales of the Riverbank'.


for events listing. More recruits always welcome.

On the Tuesday we spent a bit of time watching an Environment Agency team electro-fishing a sample length of the river to see what species were present, and to measure all the fish caught. Amongst other things, a fair-sized Pike was observed. Later we did some wading and measuring just north of the upriver bridge in Crayford town centre for the installation of flow deflectors (there were some fine patches of Liverwort just above the waterline on old stonework here). The purpose of these is to help clear the build up of silt under one side of the bridge, and to provide areas of differing water speed to create a greater variety of conditions for wildlife.

On Wednesday we heaved a large number of lorry tyres dumped on the bank by Crayford industrial estate across the river, then down a footpath to a skip. After that it was a case of wading up and down the river picking litter, including quite a lot of cans etc. embedded in the riverbed. A selection of clothing prompted speculation about the likelihood of a dead body or two ....... There were also several plastic bags-worth of takeaway establishment menus that had been dumped in riverside vegetation, presumably by deliverers who didn't bother to do what they were paid for.

A Chinese Mitten Crab was found under the bridge arches at the upstream end of Crayford Riverside Gardens in a bag containing a rotting display stand of some sort. Thought to have arrived in ship ballast, this species burrows into riverbanks, eventually causing their collapse along with any reeds or other vegetation above, which can diminish suitable habitat for endangered Water Voles.

Whilst cleaning up the river, water plants such as Watercress, Brooklime, Water Mint, Water Forget-me-not, Fool's Watercress and Water Figwort were seen.

My favourite plant in this sort of habitat - for the name at least - is Trifid Bur-marigold, of which there was a lot at the Waterside gardens. It looks rather like a Dahlia on a diet, but with rather less conspicuous flowers.

Non-native Giant Hogweed and Himalayan Balsam are troublesome invaders along the Cray, and concerted attempts are being made to eliminate the former and limit the latter.

After all the work, I did a fair amount of additional wildlife recording in the vicinity of the river.

Along Footpath 106 by the river, 'behind' Crayford Way, a pristine Comma, Red Admiral, Painted Lady and Small White were all feeding on the same smallish Buddleia, a sight that wouldn't have merited a mention in my childhood when it was commonplace. A couple of Geranium pyrenaicum were also noted.

I then headed downriver from Maiden Lane towards Thames Road.

A fabulous stand of Purple Loosestrife by the Cray between Maiden Lane and Thames Rd

A rather late-flowering specimen of Dittander (Lepidium latifolium) - with the narrow leaves, foreground - a fairly uncommon Crucifer, seen not far from the Thames Rd bridge

Dittander was once cultivated. Young leaves can be eaten raw or cooked and are said to have a very hot cress-like flavour and may be used in small quantities in salads. The roots can be grated and made into a horseradish substitute.

Various larger Dragonflies were seen but I couldn't get a close enough view for a positive ID. I did, however, get to see my first Brown Hawker (though it's quite a common species) at close range when a female stopped, apparently to lay eggs, on a bit of rotting log emerging from the water up near the Thames Rd bridge.

A rather naff bit of 'landscaping' by the river where the Thames Rd bridge was recently widened

Various native shrubs have been planted in plastic tubes here, but some of the species do not naturally occur in the local area. Rather than doing this and covering the mound with bark chip, which is inevitably slipping away, it would probably have been better - and certainly cheaper - to have left it to get overgrown naturally!

I then surveyed and took quite a lot of photographs of the 'field' bordered by the Cray, Thames Rd, the Slade Green to Dartford railway line and the Sewer Pipe embankment. Thames 21 will be tasked with monitoring and managing this, after it was excavated to below water table level, landscaped for Water Voles and planted up with lots of Great Reedmace, sedges and rushes as a mitigation measure for loss of land to housing nearby. But I'll do a separate 'feature' on this site another time.

I also had a distant view of what was almost certainly my first Little Egret, just west of the railway line in a water body in the field south of the Sewer Pipe embankment.

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