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52
scheme designed to serve an ultimate population of two million was
started in 1931. By 1936 the 28 old sewage works including five in this
district were closed down. The sewage from the whole area is drained
by gravitation along the main sewers to the purification works at Mogden,
Isleworth, being treated by the activated sludge process. The works
include the sewage pumping station, screening and disintegrating plant,
grit chambers, sedimentation tanks, biological purification by the activated
sludge process using compressed air, final separating tanks, storm water
tanks, first stage sludge digestion plant with gas collection and a methane
operated power station. The purified effluent is discharged into the
River Thames at Isleworth Ait. The sludge after digestion is pumped
to the Perry Oaks works where it is pumped on to beds for drying. The
dried sludge is either tipped on to land or is used for agricultural purposes.
The capacity of the local trunk sewers and main outfall sewers is such
that it is estimated on a dry weather flow at 40 gallons per person per
day, they can serve an ultimate population of 330,000. At South Vale,
Sudbury, a pumping station lifts sewage some 80 feet from the South
Vale area to the high-level sewer in South Hill Avenue.
There are still a few houses on the northern fringe of the district
from which the sewage is treated mostly in small plants in the grounds of
the houses, the effluent finding its way to a water course.
Drainage
The district is served by the separate system of drainage. The
County Council maintained all the important water courses in Middlesex
until the passing of the Land Drainage Act, 1930. The object of
this Act was to overcome conditions prevailing in certain parts of the
country where the neglect of water courses had resulted in serious
deterioration of agricultural land. On the passing of that Act all the
water courses falling within the catchment areas of the River Thames
and the River Lee passed from the control of the County Council to
that of the Thames or of the Lee Catchment Boards. The County Council
still retains control of the water courses in the catchment areas of the
Rivers Brent and Crane which discharge into the Thames below Teddington
Lock. Legislation about the prevention of pollution of streams
was consolidated in the Rivers (Prevention of Pollution) Act, 1951. In
areas for which river boards had to be formed under the River Board
Act, 1948, the powers of the Act are exercised exclusively by those
bodies; in the Thames and Lee catchment areas it is enforceable by the
Thames Conservators and the Lee Conservancy Catchment Board.
Open water courses generally are under the jurisdiction of the
County Council or of the Thames Conservators, but long lengths running
through developed land have been culverted and so have become the
responsibility of the district council. In some cases, the Council has
acquired land along the banks. There are five main water courses in
the district. The River Pinn (under the control of the Thames Conservators
up to where it crosses St. Thomas' Drive) rises in the Royston
Park Estate and runs in a southerly direction to High Street, Pinner,
during which part is open and part culverted. It is joined near Leighton
Avenue by a tributary which crosses from Pinner Park. It crosses