The siren was sounded across the valley and could be heard in Todmorden, where one resident described it as "echoing" and "very dramatic".
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The flood warning reads: "River levels have risen rapidly as a result of recent persistent rainfall. Consequently, flooding of property is possible between 12pm and 3pm today. Areas most at risk are properties closest to the watercourse. Further rainfall is forecast into this afternoon but will pass later today. We expect river levels to peak around 1pm and remain elevated throughout the afternoon on 08/01/22. We have sounded the Walsden Siren. We are closely monitoring the situation but we are not expecting any further river rises this weekend."
In Leeds, the city has one flood siren - based at Wyke Beck in east Leeds - and sounds like a traditional Second World War air raid siren.
Based on the best available information and, where possible, in discussion with local flood wardens, the Flood Warning Duty Officer will sound the siren to provide advance warning of flooding to property.
The siren sounds like a traditional Second World War air raid siren. It is sounded continuously for two minutes. At short range, it is likely to have noise levels of 120-145 db (similar to an ambulance siren) and it may be heard up to 1,500 metres away, depending on local factors such as levels of traffic, weather conditions.