The existing large diameter sewer from Larbert fed into a small bore siphon beneath the river Carron, and under storm conditions, screened discharge overflowed into the watercourse.
Purac Leslie Consortium developed the solution which involved constructing a 15m diam x 12m deep shaft to provide a combined, on-line storm storage tank and wet well pumping station, which also incorporated a stilling chamber / tumbling bay and a dry weather flow channel. The existing CSO was modified, with the installation of additional screening and a downstream stop-log chamber, which enabled isolation of the storage tank for maintenance.
To accommodate the widely fluctuating flows, the structures were connected by large diameter GRP pipework with an integral dry weather flow channel and on the downstream side of the storage tank a new valve chamber was built to measure and control the forward flows.
The existing siphon arrangement was replaced by a new twin 200mm diam HPPE rising main under the River Carron which was extended across farmland to tie in to the Cauldhame CSO and the existing sewage network. A new MCC and storage building, access road with hardstanding for hiab and tanker access, and a new security fence completed the works.
Integral to the development of the design, was the extensive site investigation undertaken which included boreholes and pumping trials, to determine the ground conditions and movement of groundwater in an area where site condition were known to be difficult. This enabled a detailed method of construction to be developed as the outline design evolved which alleviated many of the potential problems of undertaking heavy civil engineering construction works in poor ground conditions.
Key Facts
| Client: | Scottish Water Solutions |
| Engineer: | |
| Contract Value: | £2.27m |
| Duration of works: | January 2003 – April 2004 |