"Mike Clarke" wrote in message
...
On 05/08/2019 10:18, NY wrote:

I may have missed something in the earlier new reports, but why are they
having to *pump* water out of the reservoir? Is there a problem with
taking water out in the normal way? I think it's a canal feeder
reservoir. Can the canals not cope with a greater flow of water into them
than was originally intended?

Canals weren't designed to carry a significant flow of water.

They're a series of long thin "lakes" connected by locks where there's a
change in level. Every time a boat passes through a lock a lock's worth of
water escapes from the higher section to the lower one. Apart from that
there's very little flow.

Presumably canals have to be capable of carrying a flow of water equivalent
to each lock being opened every so often to let narrow boats up or down. How
big is "a lock's worth", typically, in terms of the amount of water the
flows into it when the upper gate is opened and flows out when the lower
gate is opened? I imagine it's fairly small compared with the 7000 litres (7
tonnes) of water that were being pumped out every *minute*. Do canals tend
to have a maximum boat movements per day limit, not just because of traffic
congestion at the locks but because of the flow of water through the canal
which could scour its sides?

The reservoir had a spillway to allow for excess water to overflow into (I
presume) non-canal waterways. Is there no way to divert water that would
normally go into the canal, so it can go into those non-canal waterways
instead in an emergency.

Is the problem essentially that the spillway had become damaged? Could the
spillway mechanism have safely coped with the excess water if the concrete
skin on the spillway hadn't been breached, allowing the earth fill to be
scoured away?