The water leaking through this top gate
is not as fast as the water leaking out of this bottom gate hence the lock empties in about 15 minutes. You may think that this is not the case but looking from behind the bottom gate we can see more of the problem
This isn’t as wasteful as one might think. Certainly at this time of the year we have a surplus of water and down here we have nowhere to store it. Even in the summer it is not a problem in fact it is a necessity.
Shipton Wier Lock is one of several locks (two on the Oxford) which though only designed to take one boat (72 ft) will quite happily take 3/4 smaller boats.They are wide because the step from the river is small so it is built wide to ensure a more or less standard lock full of water is used to keep the pound full. Placing more than one boat in the lock uses more water at the next lock than this lock puts into the pound eg 3 boats here going south use 1 lock of water however when those boats exit the pound at Roundham Lock (being a single) it will use three locks full of water and the pound will be deficient two locks of water. If this happens all day as it does in the summer the pound eventually empties. You might argue that boats going the other way would replace the lost water. This is not the case. For three boats coming up the canal they will use three locks of water to get into Thrupp pound. If they all exit at Shipton together they will only put in 1 lock of water. So this lock and the other at Aynho should only ever have one boat in. In the days of the 72 footers you could only get one boat in. The odd maintenance boats travelling through would not make any significant difference. This is most important at Aynho because the next lock down is 12 feet deep, so two boat using one lock at Aynho will require 4 locks of normal size water to exit the pound.
Had Shipton been built to the same dimensions as normal locks then each boat going through would only put two feet of water in the pound but it would still take 6+ feet of water to leave the pound. So the leaks are a good thing.
These thing are not always as simple as one might think!
It might seem selfish using these locks on your own but the reverse is true.