Perth has always been prone to flooding by the River Tay which has the highest volume of flowing water in Britain.  Many properties have been damaged, especially after a period of heavy rain upstream and during a high tide.  To reduce the chances of the Tay bursting its banks again, a complex flood prevention scheme was built consisting of a series of embankments, walls and gates.  Today the flood gates were closed perhaps in anticipation of flooding although the river was not quite at danger level.   There is a lot of symbolism on the gate connected to the cycle of water and the destruction and renewal that water can bring.  The extra shows some of the barriers.
Thanks to Bobsblips for the challenge today of “entrance or exit.”  The gates prevent the floodwaters from entering the centre of Perth,