Time and (Semi) Tide

Signs of spring and thoughts of trips to come. March 1st and the daffodils are out on the roundabouts and roadsides near us. British Waterways is nearing the end of its annual stoppage programme and we'll have a free run up the canal again.

I've been researching the journey up the Thames to Oxford and beyond. We have to buy an additional visitors boat licence for this, costing £75 for 15 days. Ouch! Should we wish to venture up the Wey Navigation (belonging to the National Trust) on our way past, that would be another £26 for 3 days or £51 for 7 days. Hmmm. All that is on top of our standard BW licence which this year is £540 odd. At least with the BW licence you can moor overnight almost anywhere on the canals for free. On the Thames you often have to pay a few quid.

Just before we enter the Thames from the canal, we go through a short stretch described as "semi tidal". I had to find out what this means. The Thames itself at Brentford is fully tidal and sealed off from the canal by a lock. Surplus water in the canal spills over a weir alongside the lock. When the tide below the lock goes out, the level in the canal stays at the level of the weir, but when a high tide comes in, it overtops the weir and raises the level above the lock. Semi tidal - geddit? Beyond the next lock further up the canal the tide has no effect.

Once we get on to the tidal Thames we dash upstream an hour and a half to Teddington, where there is a big lock above which the tide cannot reach.