Editing Severn bore (section)

==Timing==
[[File:Severn Bore near Over Bridge, Gloucester - geograph.org.uk - 346180.jpg|thumb|left|The Severn bore near Over Bridge]]
[[File:Severn Bore imminent - geograph.org.uk - 1735599.jpg|thumb|This bore, near the Severn Bore Inn, was smaller than predicted.]]
The largest bores occur around the times of the equinoxes but smaller ones can be seen throughout the year. There are about 260 bores in each year occurring twice a day on 130 days. Because the bores are associated with the phases of the moon, one occurs between 7 a.m. and noon on bore days, and the other between 7 p.m. and midnight [[Greenwich Mean Time|GMT]], with the largest bores occurring between 9 and 11 in both the morning and evening. Maximum bores occur between one and three days after new and full moons, and smaller ones on the days that precede and follow the maxima.<ref name=Facts/>

Timetables for the bore and predictions of bore heights are published each year;<ref>{{cite web| url= http://www.severn-bore.co.uk/2016_times.html| publisher= The Severn Bore| title= The Severn Bore: 2016 timetable| access-date= 1 September 2016| archive-url= https://web.archive.org/web/20160907210421/http://www.severn-bore.co.uk/2016_times.html| archive-date= 7 September 2016| url-status= live}}</ref> however, the heights and timings are subject to minor variations. The bore height is increased by a strong southwest or west wind, low barometric pressure, about {{convert|2|ft|m|order=flip|abbr=on|sigfig=1}} of fresh water below Gloucester and well-scoured channels in the estuary. The height is decreased by strong winds from the east or north, high barometric pressure and little fresh water below Gloucester or excessive fresh water.<ref name=Rowbotham1967>{{cite book |title=The Severn and its Bore |last=Rowbotham |first=F.R. |year=1967 |publisher=The Raleigh Press |pages=12–19 }}</ref> The bore is made earlier by strong southwest or west wind, low barometric pressure, between two and five feet of fresh water, and shorter and well-scoured channels in the estuary. Conversely, it is delayed by strong winds from the east or north, high barometric pressure, little fresh water and more meandering, poorly scoured channels. The wind direction out at sea is of more significance than the local air-flow.<ref name=Rowbotham1967/>

Being the onset of the flood tide, the bore is accompanied by a rapid rise in water level which continues for about one and a half hours after the bore has passed. The Severn bore is not a self-reinforcing solitary wave or [[soliton]] but rather a shock wave which is formed because the wave is travelling faster than the wave speed in water above the bore (see [[tidal bore]] for more details). The passing of the bore causes a churning of the water, and the myriads of tiny bubbles popping contributes much of the roaring sound made by the bore.<ref name=Rowbotham1967/> The largest recorded bore was on 15 October 1966, when it reached a height of {{convert|9.2|ft|m|order=flip|abbr=on|sigfig=2}} at Stonebench.<ref name=Facts>{{cite web |url=http://www.severn-bore.co.uk/facts.html |title=Facts |work=The Severn Bore |access-date=18 August 2016 |archive-url=https://web.archive.org/web/20161007214857/http://www.severn-bore.co.uk/facts.html |archive-date=7 October 2016 |url-status=live }}</ref>