In order to predict the risk of flooding on the flood plain, the river's
level is constantly monitored at several points along its course. This is
carried out automatically and past records of river levels can be used as
a gauge by the Environment
Agency to alert people downstream that there is a risk to their property.
The gauging station at Hammoon is used as an indication of the areas likely
to flood.
| River Level (m) |
Effect |
Time Lag (hrs) |
| 2.56 |
Bank full at gauging station |
0 |
| 2.56 |
Roads flood in Shapwick |
6-14 |
| 2.6 |
Hammoon to Manston Road will flood |
0 |
| 2.6 |
Spetisbury to Tarrant Crawford road will flood |
5-10 |
| 2.6 |
Sturminster Marshall to Shapwick road will flood |
7-15 |
| 2.7 |
Blandford car park will start to flood |
4-8 |
| 2.9 |
Flood water onto roads in Hammoon village Bull
Inn, Sturminster Newton will flood (with continued rise) |
1.5-3 hrs before Hammoon |
| 2.9 |
Blandford car park flooded, water on to road at
Blandford St Mary |
4-8 |
| 3.0 |
Risk of flooding to property at West End, Spetisbury
- Clapcotts Farm |
5-10 |
| 3.0 |
Roads in Sturminster Marshall will flood |
7-15 |
| 3.0 |
Risk of flooding at Christchurch Iford Caravan
Park (depending on tides) |
24-36 |
| 3.0 |
Property at risk of flooding at Corfe Mullen |
|
| Time |
Event |
| 3.00 |
Flooding as before with the addition of some isolated
houses |
| 3.05 |
Houses in Hammoon may flood |
| 3.09 |
February 1990 peak flood level |
| 3.10 |
Gateway car park at Blandford will flood if gates not
closed |
| 3.50 |
Houses and A350 at Charlton Marshall at risk in 5.9 hours |
| 3.64 |
[December 1979 peak flood level, 1 in 65 year flood]
Risk of overtopping at Holdenhurst |
| 3.75 |
Risk of overtopping at Shapwick |
| 3.80 |
Risk of overtopping at Sturminster Marshall
[Approx a 1 in 100 year flood at Sturminster Marshall and
Christchurch] |
| 3.90 |
[Approx a 1 in 200 year event at Blandford] |
It takes time for rain which falls over the catchment area to
be converted into river flow and any floodwater which builds
up takes time to flow downstream to the sea.
