Chelmer-Blackwater Canal, 28th May and 26th August 2006
Ken Adams 63 Wroths Path, Baldwins Hill, Loughton, Essex IG10 1SH
Unfortunately, torrential rain had swollen the canal and it was murky with silt, on the
first survey date. Nevertheless we prodded the river at intervals for submerged vegetation
and recorded the margins along the south bank, all the way from Papermill Lock down
to the Hoemill Bridge. We were looking particularly for the large river pondweeds
Perfoliate Pondweed, Potamogeton perfoliatus and the even larger and rarer Shining
Pondweed, P. lucens, that we had found in abundance along the river in 1978. Once
abundant in the Lee and Stort and recently exterminated by cabin cruiser screws and oil
films, we feared the same might be happening along the Chelmer-Blackwater canal. A
few fragments of P. perfoliatus were found close to the southbank about halfway along
this stretch, and quite a healthy colony in a protected embayment just upstream of Rushes
Lock, but no sign of P. lucens. In all, only three clumps of the Great water Dock,
Rumex hydrolapathum, another characteristic plant of larger rivers, were found along
this segment of the canal. Mark Hanson led us to see a gigantic Crack Willow in a
hedgerow back from the canal, and we were surprised to see the abundance of Crataegus
laevigata, the Midland hawthorn in the hedgerows, all of which appeared to be of the
attractive scarlet to pink flowered var. rosea.
For the second visit to the canal, in August, there was less of a flood, and the water was
more transparent. We decided to tackle the next stretch downstream from Hoe Mill
Lock, sampling the river at intervals for macrophytes and molluscs, and eventually got
down as far as the backwater weir north of Guy's farm. Tragically, as with our earlier
visit along the upstream stretch, we found that the increase in motor cruiser traffic has
devastated the macrophytes in the centre of the canal. Peter Wilson used a grapnel and
weighted chuck bucket, and I used my 3m hooked pole to sample the river at intervals
along this stretch. Due to neglect, much the towpath on the north side of the canal is
becoming inaccessible due to the growth of scrub andbramble, and the numerous Cricket
Bat willows planted alongside the canal have also been neglected, not having been kept
trimmed of their lower shoots, they will be pretty useless for cricket bats. In the wide
section immediately below Hoe Mill a few healthy fragments of Potamogeton perfoliatus
together with the alien Elodea nuttallii were dredged up, and occasional fragments
lower down, but most of it was shredded by boat screws. The bucket sampling revealed
that the bottom of the canal is being heavily scoured, and is virtually bare of plant life.
For this reason very few molluscs were found alive, except in the less disturbed section
just below Hoem ill. The scouring is probably being caused by fast moving currents
following heavy rains, due to the lack of a protective blanket of aquatic vegetation on
the floor of the canal. Of the other higher plants, Myriophyllum spicatum was abundant
in the shallows, and Ceratophyllum demersum formed local patches, but they were
both heavily encrusted by silt. The Yellow Water lily, Nuphar lutea was present in
localised patches, but again heavily shredded. Just one patch of Arrowhead, Sagittaria
sagittifolia was noted in a segment protected by bollards on the opposite shore, one
Essex Field Club Newsletter No. 52, January 2007 21