Twice a month the Sun and Moon and Earth line up - that's called syzygy. You know it's happened because we see a full moon or a new moon in the sky, depending. The alignment of gravitational pull creates a greater bulge in the world's oceans, so high tides are higher than they usually are - they're called spring tides. Periodically the Moon is at the closest point within its orbit - that's called perigee - and high tides then rise slightly higher still. These perigean spring tides, as they're called, occur around the time of so-called supermoons, and we've just had one of those. Which is why yesterday afternoon the Moon caused minor flooding along the Thames and its tidal tributaries, thanks to supermoontides - as absolutely nobody yet calls them.
Richmond's waterfront often gets hit, and Twickenham, and Putney Embankment, and the walkwayalongside the Pool of London by Old Billingsgate Market. But another place mentioned in yesterday's flood warning was Three Mills Island, and that's near me, so I went along to observe the rising water.
Three Mills marks the upper tidal limit on the River Lea, blocked upstream by Bow Locks, the tide mill itself and the barely-used Olympic lock on the Prescot Channel. Twice a day at high tide the pool outside the House Mill fills up, but at supermoontide it almost overflows. The water level stops rising three bricks below the Clock Mill's windows (and if you come back quarter of an hour later it's down to four, as a freshly wet line around the water's edge attests).
Although all looks contained, the waterwheels of the Clock Mill are now fully submerged, which causes the river to spill out underneath the building and gurgle through a drain into the yard. The cobbles outside the entrance to Three Mills Studios become wet with puddles - nothing unduly serious but enough to make employees popping over to Tesco look slightly surprised, and tread carefully.
A thin strip of land wends south from Three Mills carrying the footpath which one day will be otherwise known as the Leaway. To one side are the tidal waters of Bow Creek and on the other side the tamed channel of the Lea Navigation (leading down to the Limehouse Cut). The water level in the Lea Navigation remains constant, but Bow Creek has a considerable vertical range which means, just occasionally, its water almost doesn't fit.
South of the District line Bow Creek is held back behind a low concrete wall, usually irrelevant but at supermoontide breachable. River water trickles through gaps between the blocks, particularly at a single point just before Twelvetrees Bridge, oozing through onto the path and adjacent grass. As high tide approaches you can watch the water's edge encroach gradually along the footpath until it's submerged to a point where only someone in decent boots would risk using it.
Numerous pedestrians and cyclists arrive not expecting anything to be amiss, because it usually isn't. Some stare at the squidgy grass and turn back, while others make for the stones along the edge of the navigation and tread carefully along, taking care not to slip on the water flowing from one side to the other. A lady with a pushchair decided against. Two joggers splashed through. Three police officers strode nonchalantly on. The lady from the nearest narrowboat popped out to take photos. A large group of young half-term cyclists stopped and waited while their significant adult tried to work out an alternative route.
Within an hour everything on the banks will be back to normal, and within six hours the supermoontide will have completely drained away. For every extra-high high tide there's an extra-low low tide, when even more of the muddy bed of Bow Creek will be visible than usual. Today expect that bottom-scraping low around 10am, and another spring tide overtopping just before four in the afternoon.
Supermoontide will return in a month's time, around 22rd March, and then again in the autumn around 1st October. You could go and watch the Severn Bore instead, if spectacle's your thing, but the Moon puts on a show of minor overtopping a lot closer to home.
