Home Transit
of Venus Sewer
History in Leeds Sundials in Leeds William
Gascoigne John Feild About
VIII. TIME FOR RENEWAL
The sort of rainstorm which produces the most intense flows from
any water-producing catchment is usually assumed to be a rainstorm which has a
duration roughly equal to the time taken for the water falling on its farthest
reaches to arrive at the outlet of the catchment. This being so, the artificial
catchments created by modern urban sewer networks and becks, are worst affected
by short, sharp storms. The convective thunderstorms of summer months fit the
bill more than the long, steady rainfalls of winter frontal systems.
The Summer of 1948 in Leeds provided ample demonstration of this
fact. Flooding was extensive, especially in the Gipton and Meanwood Valleys.
The City Engineer, Mr.D.Currie, was asked to prepare a detailed survey of the
main drainage of the city - by now comprising 850 miles of sewers - with a view
to fundamental remedial action. Such was the pace of post-war housing
development in the city, that he at first was hampered by the fact that many of
his staff were being diverted to deal with the design and construction of
housing estate sewers.
The long-awaited report appeared in 1955 and revealed, in Currie's
words, that "not only is the present sewerage system overloaded but,
more serious, sections of the most important sewers in the city are reaching
the end of their lives and in places are breaking up". It was exactly 100
years since the completion of Leather's scheme. His principal intercepting
sewer, known as the Low Level Sewer, had developed alarming distortions along
its whole length. In 1950 a complete collapse of the sewer took place in the
Hunslet railway goods yard, necessitating a major diversion. In 1958 the
4'6" x 3'6" section from Globe Road to Wellington Street had reached
a critical stage and needed emergency repairs. The potential dangers in
collapses of major sewers are evident when it is realised that this short
length of the Low Level Sewer passed underneath more than 40 railway tracks, 3
heavily trafficked roads, the River Aire and the Leeds and Liverpool Canal!
In addition to having structural problems, the Low Level Sewer was
seriously surcharged with sewage flows. Before Hewson's rising overflows,
installed over 50 years previously, could operate to relieve the flow, the
sewer had to build up water levels to a depth considerably exceeding the height
of the sewer itself. Not only did this extra weight of water put undue stresses
on the structural fabric of the sewer, it also introduced pressures which could
cause the sewage to find its way through flaws in the brickwork of the sewer.
Thus the surrounding subsoil was contaminated. Since the Low Level Sewer
frequently passed close under water mains, public health was thereby put at
risk. Currie's report therefore proposed the abandonment of the old rising
overflows.
The report highlighted also the need for either replacement or
renewal of the Low Level Sewer. Just like Hewson before him however, Currie had
to decide how to deal with the large increases in flow which had occurred since
the time when the sewer was originally constructed. It would have cost £1.5m
(at 1955 prices) to construct a new sewer large enough to convey all the sewage
to Knostrop.
SEPARATE
WAYS
Instead a £1.15m scheme was proposed, and adopted, which involved
a new departure in sewerage policy for the city: a separate system of drainage
for rainwater. Currie proposed to construct a new, 4 mile long, Low Level Sewer
(or reconstruct the old sewer) which would cater for six times the dry weather
flow from those areas which could be overflowed by gravity, but only the foul
flow from most of the remaining low lying areas. He proposed that the bulk of
the rain or surface water from the latter areas should be taken into new
surface water only sewers in other words, a separate sewerage system.
This separate system approach meant that the low lying areas
involved would have to be re sewered. These areas were generally old and
decaying: ripe for redevelopment. Re sewering on the separate system would take
place as and when redevelopment took place.
A spin off benefit from the new policy would be that rain water,
at least from the redevelopment areas, could be discharged relatively
unpolluted to the becks and the River Aire. It would not have been first mixed
with foul sewage, as was the case with the combined (foul and surface water)
sewage which predominated in the other parts of the city. The costs of treating
and pumping surface water at Knostrop would also be reduced.
The pace of development on the northern side of the city since the
completion of the High Level Sewer in 1925 was so great that this sewer too was
considerably surcharged by 1955. A series of overflow modifications and
reconstructions was proposed in order to reduce flows in the High Level Sewer.
Associated with these measures were various major flood relief sewers and
culverts in the Meanwood Valley, Gipton Valley, Sheepscar, Alwoodley and many
more parts of the city.
Currie's plan inaugurated the largest spate of sewer construction
which Leeds has witnessed in recent decades.