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54
The general condition of the River during the past year has been fairly
good, largely due to the rush of fresh water during the second and fourth
quarters of the year.
The Conservators of the River Thames, with whom the question of
preventing the pollution of the River Thames largely rests, have done a great
deal of work in the direction of dredging the River, thus removing large
quantities of putrescible matter, and providing a larger volume of water which
is available for the oxidation of organic matter discharged into it.
The general report of the proceedings of the Conservators of the River
Thames, during the year ended 31st December, 1906, contains some valuable
information as to the work done in regard to dredging the river, and the
following extract will be of interest:—
"In Barking Reach, between Crossness and Margaretness, a distance
"of 1¾ miles, the channel was deepened to 22 feet over the greater part,
"but owing to the continual silting up, the present depth of the channel
"is 16 feet only for a width of 500 feet, and there are a few patches
"where the depth is 15 feet only.
"Continuous dredging has been carried out in this reach throughout
"the year. From January, 1901, to December, 1906, about 940,000 cubic
"yards of material have been dredged, but notwithstanding this there is
"no general improvement in the navigation channel since the work was
"commenced six years ago. The reach is, however, deeper in places.
"The cause of the continual silting up in this reach has been
"investigated, and 152 samples were taken of the effluents from the
"Barking and Crossness Outfalls on 38 days between 1st May and
"30th July. They were examined by the Conservators' Analyst,
"Mr. C. S. Groves, F.R.S., who certified that the result showed
"that one million gallons of the effluents carries into the river more solid
"matter than is sufficient to form a deposit of 100 cubic feet of mud.
"Mr. Groves also examined 24 samples of silt taken from the river
"bed in Galleons, Barking and Halfway Reaches, and he certifies that
"a considerable portion of the finer particles of mud in the silt is of the
"same nature as the solid matter passing into the river from the
"outfalls, and that the silting is due, therefore, in part, to the suspended
"matter in the affluents.
"From calculations based on the statistics of the London County
"Council, it appears that in 1904 the volume of effluent passed into the
"river was 91,216,254,000 gallons. The amount of solid matter
"contained therein would therefore represent 9,121,000 cubic feet, or
"about 337,000 cubic yards of mud, which exceeds the quantity which
"No. 1 or No. 2 Dredger raises in a year.
The Conservators have been engaged in generally dredging the river, and
have been in the habit of depositing the hard material dredged up in a