In 1874 there were no dams upstream holding back the water for irrigation and power generation. O'Sullivan's photo was probably taken in the fall. If it had been taken in the spring it would have looked more like this:
I wasn't sure if that was a dam, running across the middle of the picture, in your photo or just the (very) slightly different viewpoint. Did you know of the earlier photos when you took yours - or is it like Uluru (Ayers Rock) in Australia: the bus stops there, so that's where almost every photo is taken from?
Dave: What you see in the background is more of a diversion barrier than an actual dam. The real dams are farther up river. I wasn't aware of previous photos. It just seemed like the best place to shoot from.
Wayne, so a water diverter system - you'll have to go up in a helicopter and take photos of the whole system so we can all see the full lie of the land river.
Communication: When Liverpool started building up as a port a system was set up so that when ships were sighted rounding Anglesey the owners in Liverpool could be informed. A series of semaphore stations and beacons was set up round the coast of North Wales and Wirral. The system was tested recently for the BBC series Coast against the phone system. Semaphore was quicker! (Though thick fog tends to cause a problem!)