[Written in May, posted today] Saturday was the chance for my one of my favourite kinds of parenting: the kind where I can go on a journey with my daughter at her pace, stop and look at various bits of engineering infrastructure along the way, and then move on when we are ready.

This weekend’s excursion was along the Frome Valley in East Bristol. Near where we live the river cuts a steep gorge through the limestone landscape that forms a lush green necklace that weaves its way through our neighbourhood. It is an excellent off-road route for cycling.

We begin at Eastville boating lake and follow the river northwards. Our first stop is Colston Weir. We lean our bikes against a bench, and spend a good half-an-hour leaning against the railings watching all that’s going on around the weir.

The weir structure itself is a long diagonal wall running almost down the centreline of the river. (Most of the weirs on this strectch are – why is that? Is it to have a longer length overwhich the water can fall, thereby reducing the amount of energy dissipated on one part of the river bed?)

In the foreground, by-passing the weir is a series of stepped pools, through which water cascades. I speculate, when asked, that this watery flight is to allow fish to swim upstream, but realise that maybe that’s just something that happens on salmon rivers. Whatever the original engineering brief, it provides an interesting flow pattern that seems to capture flotsam in a never-ending eddy.

We watch unsuspecting leaves and sticks float down the shoot and into the first pool. They disappear under water, dragged under by the force of the water, emerge in the front of the pool, look as if they will escape, but then get drawn inevitably across the event horizon and into the swirling mass of flotsam. It’s strangely captivating.

On we cycle, over a footbridge and round a curving glade. The trees are in full verdent glory, and growing as they do up such steep valley sides, the canopy seems to cascade down in stages from high above down to the river level.

Our next stop is the water wheel at Snuff Mills. Queue conversation about how this whole area was full of factories driven by the power of water. A sign explains that an older boiler was part of a machine to cut stone – what, cut stone? This concept seems not to compute.

The valley winds on. We are cold in the shade but bask in the sunshine. We stop to pick wild garlic. Every 200 metres or so we pass large mushroom-shaped concrete structures with a manhole on top. I’ve always wondered what these are. Following the river like this I have always assumed they give access to some sort of relief tunnel or water supply pipe that follows the river underground.

Whatever it is that is following us underground, a group of people went to a great deal of effort, probably decades ago, to build what is likely to be important infrastructure. It feels like such a shame for there to be no information provided about it. It’s a missing link in our understanding of the fabric which supports us. And it’s a missing set of stories about people and what they built and how they tried to improve the world.

I felt the same a few weeks ago, walking in the hills of Snowdonia, and passing under high voltage transmission lines that march inexorably across the landscape. Who built those? What was it like to put those towers up on exposed mountain passes? What did it change? Who was grateful? (Trying to find answers to those questions led me to discover the Pylon Appreciation Society. I’ve sent my cheque off in the post but I’m still waiting for my membership card to arrive).

By now the cyclepath had dried up and we were pushing our bicycles along a rocky path high above the river. Down below, another hydraulic structure peaked our interest: the river flows along a massive V-shaped concrete channel for twenty metres or so. The sign above it says ‘Environment Agency Flow Monitoring Station’. This seems like rather a massive intervention in the river environment just to enable engineers to measure the flow rate. Why can’t the flow be measured at a weir?

My daughter watches as I type this engineering question into Twitter, but so far no response.

Time to go home, but our trip along the river has left it’s mark. The next day, while riding in the ferry through the floating harbour in Bristol, my daughter points out to the boat driver where the Frome enters the Avon. I am quietly pleased with this transmission of enthusiasm for engineering from one generation to the next.