Latest Flood Report : Bridge Of Allan Flood Alleviation Scheme Optioneering Report (click here for report)
Background Extract From Report:
In late 2011, Stirling Council appointed Mouchel, through their framework with
Scotland TranServ, to conduct a flood mitigation optioneering study for the town of
Bridge of Allan. The Allan Water river flows through the town and has flooded in the
past, with the largest recorded floods in recent years being in 1993, 2006 and 2008.
Large parts of Bridge of Allan and Stirling were flooded during these events. A flood
defence scheme, Allanvale Road Flood Alleviation Scheme, was built in 1985 under
the Flood Prevention (Scotland) Act 1961, as a consequence of significant flooding
in previous years.
The Allanvale Road flood defences consist of raised river embankments and flood
walls, which run from the A9 Bridge to the fire station at the bottom of Allanvale
Road. Little work has been carried out to maintain these defences and recent reports
have found the level of protection to only be adequate for a flood with a 20% (1 in 5
year return period event) annual exceedance probability (AEP).
During the 2006 flood event (recorded as a 1 in 55 year return period event on the
River Forth and a 1 in 21 year event on the Allan Water river), it was noted that the
River Forth caused the waters of the Allan Water river to back up and the flood
defences were close to overtopping. In some sections the defences were in distress
with water passing through the embankments, ground and walls.
The level of protection provided by the defences in their current condition is far below
the 1 in 200 year flood event. A damage risk assessment carried out for Bridge of
Allan predicts losses of £12.5 million directly and indirectly by a 1 in 200 year flood
Halcrow has previously carried out a flood study of the lower reach of the Allan
Water, extending from the confluence of the Allan Water and River Forth to nearly
700m upstream of the weir2. In addition a geotechnical survey of the existing
embankment and ground conditions was carried out3, as well as a damage risk
assessment for Bridge of Allan4.