Road gully trap - what's the purpose of the stopper?

[Hugh Jaleak]

They didn't direct some of the rainwater into the sewer, it was all directed in and storm overflows incorporated at strategic points in the system to send excess to rivers etc.

In my area, we have various Victorian streets, where the rainwater from the rear of the properties goes into the combined sewer. All runoff from roofs at the front is directed into the road, where the road Gullies are connected to a separate storm drain. There are several CSO's dotted around the town, but these are all recent additions in the last 50 odd years, to ease surcharging on the older parts of the system, which have become under increased pressure as the town has expanded.

Treatment Works also have Storm Tanks to contain excess flows during wet weather and retain as much effluent as possible to return for treatment as incoming flows subside.

 

[Malcolm Leighton]

They didn't direct some of the rainwater into the sewer, it was all directed in and storm overflows incorporated at strategic points in the system to send excess to rivers etc. Sewers designed to take 6DWF, normal peak flow about 2.5DWF. DWF (dry weather flow) is a flow factor based on population and average daily usage per capita (about 135litres currently I believe) In times of storm flow into sewers can be 20- 30DWF+ depending on storm intensity. At one time they would actually place an automatic dosing chamber at the head of a sewage system, a bit like a toilet cistern ( but bigger), that would discharge a cleansing flow down the system at a predetermined period although these are not in vogue anymore

Wow..Yep, it is a BIG,... little understood subject, but facinating nevertheless.
Thanks
BUT
Why were stoppers apparently phased out?