This alternative route keeps clear of the River Frome except for the length between Whitminster Lock and the site of Lockham Aqueduct but shares the existing M5 bridge over the river but in a separate channel. Map
This route starts by using the River Frome to the site of Lockham Aqueduct and then follows the existing section of the 1779 canal to the A38. In order for the river and canal to be connected, consideration has to be given to the current flood and land drainage arrangements.
The river is bounded by flood banks on both sides at Lockham and the water level could exceed the level of the canal and its banks by a considerable amount before the existing banks would over top. A direct connection would, in effect, represent a 5m wide breach in the flood defenses.
There are two alternative methods of overcoming this problem:
1) Build up the southern canal bank to the same height as the river bank at Lockham. details
2) Retain the integrity of the flood bank at Lockham through a flood lock or barrier. details
3) Reduce the height of the flood bank on the north side of the
river
giving environmental and flood benefits. details
The next obstacle is the culverted causeway which has replaced the
former humpback bridge at Stonepitts. A new fixed bridge with adequate
headroom could be built at this site which can carry modern loads,
is easier to maintain and more convenient to users than a swing or lift
bridge. However, there may be some advantages to installing a swing
bridge to enable craft with a higher air draught (than the rest of the
Cotswold Canals will provide) to reach Fromebridge Mill.
The next obstruction is an MOD fuel pipeline which crosses at a low level. The MOD have indicated that they will only accept dropping the pipeline under the canal. This work could be scheduled to coincide with one of the regular maintenance shutdowns.
The canal continues through Occupation Bridge, which has already been restored, to the A38. Dredging is likely to be necessary in a number of places, especially as the canal approaches the A38.
The existing length of canal terminates at the A38 roundabout where it was originally raised by 8ft 9ins by Bristol Road Lock. A restored canal would have to cross through the middle of the A38 roundabout. Road bridges would have to be built under the NW and SE quadrants and a smaller bridge would have to be built in the centre to carry a number of services across the waterway. The roadway would need to be raised by about 0.6m to provide adequate headroom.
alternative canal route requiring a new bridge under the M5
A new lock would need to built just to the SE of the roundabout to lift the canal about 1m, a level suitable for passage under the M5 river bridge. The canal would then pass across the fields to the M5 river crossing in a shallow cutting, its level being about 1m below that of the Frome. Because of this level difference, any water overflowing from the Frome would soon find its way into the canal. The new lock at the A38 would therefore have to be designed with at least one set of tall gates to prevent flood water rushing over the lock and under the A38.
The M5 Bridge - diagram
The M5 river bridge has a span of approximately 20m and its abutments are supported on substantial deep concrete piles. The normal river level as governed by the weir at Fromebridge Mill offers a headroom of about 1.5m .
The river passes roughly through the centre of the span and is bounded by significant silt banks. In a few places, the sheet steel piling designed to protect the concrete abutments from scouring can be seen. picture
In order to facilitate the shared use of the bridge by both the river and canal, the river would be moved to the southern side of the bridge hole and a separate 5m wide canal channel would be constructed on the north side. The normal canal level would be about 1m lower than that of the river and its bed needs to provide a draft of at least 1.5m. The overall effect of the works should be to increase, rather than decrease, the capacity of the M5 bridge to handle floodwaters as the river would overflow into the canal if its flood banks over topped.
Navigation in times of flood would be precluded by the limited headroom under the M5 but the rate of flood development is unlikely to pose a threat to craft in transit.
The M5 Bridge - Eastington Lock Flight
Having passed under the M5 Bridge, the canal channel would diverge slightly from the course of the river before passing through a new lock to raise the channel by about 1.7m. The canal channel would now follow a similar route to that described in the River Route to rejoin the 1779 route at Westfield Bridge and Lock.