Heavy, thundery downpours developed by midday across south-west England on 16 August 2004.
These showers formed bands which aligned themselves with the wind helping to maintain the heavy rain across certain areas of north Cornwall for several hours. The trigger mechanisms for these storms appeared to be convergence of winds along the coast and the high ground in the local area which also helped to generate showers. It would appear that the serious nature of these floods was exacerbated by the local topography around Boscastle.
Other similar serious flooding events that have occurred in the past include:
The following data was obtained from the Environment Agency on 19 August 2004. No quality control has yet been undertaken on the data.
|NGR||24 hour |
|Main event total (mm)|
|Otterham||SX 169 916||200.4||-|
|Trevalec, Lesnewth||SX 134 900||184.9||181.0 (11:30 to 16:30 GMT)|
|Trevalec, Lesnewth TBR||SX 134 900||155.8||152.8 (12:15 to 16:19 GMT)|
|Creddacott||SX 231 956||123.0||-|
|Slaughterbridge TBR||SX 109 857||76.5||-|
|Bude||SS 208 063||46.7||-|
TBR = Tipping Bucket Rain gauge
The 24-hour value from Otterham would give a return period in excess of 200 years (using the Flood Estimation Handbook method).
Graph below showing 15-minute rainfall totals for Lesnewth TBR (Tipping Bucket Rain gauge).
The animation below uses 15-minute data between 1030 GMT and 1930 GMT. The images are composites, based on a mixture of the best resolutions available.
Please note: The empirical relationship between radar reflectivity and rainfall rate is fixed whereas in reality this is highly dependent on precipitation type and is very different for rain and hail.