Contemplating an Irish Bridge

I've got to make it possible to cross this stream.

I have a problem. Some of the locals pass through my land to get to their coffee plantations. There are other ways for them to get to their properties, so I’m discouraging this, to a certain extent, but not denying a moderate level of access. The more I improve my own access, however, the more likely they are to take advantage of it. The problem is not really making it possible to cross the stream, because it is already possible, it is precluding passers-through from trying to lower the water level by removing the planks at the weir, a little further downstream, so they don’t get their ankles wet.

Darned plank puller-outers at it again. I'll stop you!

Needless to say, this practice would disrupt power production, as the water source for the power will be taken from the very same place that the planks are, and sometimes are not. And the best way to discourage this practice, is to make it ineffective. So the goal is not to build a pretty bridge. I don’t really want one, but it might be possible to kill two birds with one stone, or at least frighten them both off.

Yorkshire Bridge, somewhere in Ireland.

By now you must be wondering what an Irish Bridge is (the Irish call them Yorkshire Bridges, by the way). Well, the other day, while my composting worms were plotting their escape and total conquest of the interior of my car, I was drinking with Yorkshire Bob and some other Brits in my pub. The Irish Bridge (a.k.a. Yorkshire Bridge) had been suggested to me earlier in the day by Fergus, my worm guy, who’s not from Yorkshire or Ireland, but is still a Brit, himself.  In an earlier life he worked as a civil engineer around the world for various large general contractors. He even helped build an international airport in the middle of the desert in Iraq decades ago that has never been used but can still be viewed on Google Earth. When I mentioned the concept to Yorkshire Bob, he balked, shook his head furiously, and told me not to do anything until he visits me at the site again in early January. There was lots of joking. . . yeah, Irish Bridge, because it’s under water. I thought he was going to cuff me just for suggesting such a preposterous idea. But let’s look at what Wikipedia has to say:

A low water crossing (also known as an Irish bridge, Yorkshire bridge, causeway in Australia, low level crossing or low water bridge) provides a bridge when water flow is low. Under high flow conditions, water runs over the roadway and precludes vehicular traffic. This approach is cheaper than building a bridge to raise the level of the road above the highest flood stage of a river, particularly in developing countries or in semi-arid areas with rare high-volume rain.

Irish Bridge at Whitely Woods, Yorkshire.

This is exactly what I want, although “precludes vehicular traffic” is not my goal. Even when they pull out the planks from my weir, they still get their ankles wet on their motorbikes or are mid-wheel level in their Hyundai light-weight trucks. What’s depicted in the the bridge, or ford, to the right, is what I’m looking for. Note the stepping stones for persons passing through on foot.  Any comments? Any at all?

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7 Responses to Contemplating an Irish Bridge

  1. KirstenMong says:

    There are a bunch of these bridges near Tucson. Sabino canyon is a city park that has a bunch. The road is only used by the tram, and foot traffic. The road is closed when it rains. There is a culvert under the bridge. They don’t have a separate foot path over, so you can’t avoid getting your feet wet.

    • richard says:

      Hi Kirsten, I’ve been hoping for such a reply. Have you ever heard of the “Stupid Motorist Law” in Arizona? Yeah, they should know better than to cross when it’s dangerous. If they do, they have to pay to be rescued.

  2. Bob in Stow says:

    If this ford is to be used by both pedestrians and vehicles, I don’t see how it is going to prevent the removal of planks at the weir. How deep is the water at the height of the rainy season with all the planks in? Could you move the ford upstream to a location that would be shallower?

    • richard says:

      If the water going over the ford is higher than the water level at the weir, it wouldn’t matter how many planks they pulled out– it wouldn’t change the water level for them. The intention, which I didn’t mention, is to raise the water level behind the ford just about 10cm or 15cm. That will make it easier to take water from above the ford out of the river to supply rainbow trout ponds. The water will pass through the ponds and return to river just above the weir, where it can help making power or just look pretty going over the fall. I’m hoping to make it so people passing through don’t get any wetter than they do now.

  3. Mike says:

    Why not leave an extra plank at the weir…. ?

  4. Fergus says:

    Why not return the water from the ponds to the stream just DOWNSTREAM of the weir but still above the waterfall. That way the water level at the ford and weir will remain lower.

    • richard says:

      Okay, I can see that I haven’t been very clear. Time to play with Google Sketchup. The short answer is because I may need that water for power. If I don’t need it for power, it can just go over the fall. The water level between the ford and the weir will not affect how much water people on motorbikes have to drive through on the ford, it will always be lower. I’ll post something to make this more clear, and probably just realize in the process that I’ve got it all wrong. . . anyway, I appreciate the feedback from you guys. Just what I need.

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