GeoGraph - photograph every grid square

There are 5 sluice gates that control the level of water in Cardiff Bay. Each gate is 9 metres wide and 7.5 metres high. Nearly 400,00 litres of water per second can flow through each sluice gate. The system is designed to cope with 1 in 100 year combined river flows and annual highest astronomical tides.
In this picture, which is taken from the seaward side, it is low tide in the Bristol Channel and water is being discharged from the bay. At extreme high tides the sluices are closed to prevent sea water from entering the bay.