Oldroyd Terrace Saved From Storm Ciara, Here’s How
The summer floods of 2012 and the Boxing Day flood of 2015 brought havoc to the hamlet of Oldroyd which is situated above Todmorden on the southern slopes of the Calder Valley. Five properties were flooded on those occasions. A scheme to prevent this from happening was designed by Slow The Flow engineer Stuart Bradshaw in 2016 and was described in a blog published in 2018.
Storm Ciara on 9th February 2020 brought further flooding to the Calder Valley and put the scheme to the test. Margaret, a resident of Oldroyd terrace, kindly provided some video footage and a narrative of the performance of the attenuation pond and inflow and outflow channels on the 9th February 2020.
Margaret reports as follows:
Oldroyd flood defences Feb 9th 2020: A success!
“….to summarise, the ‘lake’ filled very effectively and did its job very well indeed. All the ditches & waterways that had been introduced coped well with the volume of water, with the exception for a while of the manhole cover over the pipe taking water from the ‘lake’, to the track. It was not physically dislodged, but leaked water, creating a small steam earlier in the day. But this was very minor in relation to the success overall of the whole design & system. The end terrace usually the first to flood was under zero threat. The water was adequately channelled as it reached the bottom of the hill towards the houses. It did come down from the top fields erratically earlier, but even then was still channelled well near the houses.
The ditches at the back of the houses all fared well – none had anything more than a tiny bit of standing water, none of it surface run-off I think. There was also minimal run off down the street in front of the houses. The troughing collecting the water from the ‘lake’ and directing it down the track was very efficient – very full, but the speed of the flow conveyed it downhill more quickly than it could overflow to flood the track. The water itself was much cleaner than our flood water has been in the past, as seemingly filtered by the pond and carrying little in the way of rubble or soil. The ex-farm buildings below were safe too, very little surface run-off reached them. The only issue I could see was that the water was dispatched so efficiently down the track, that the road below was very badly flooded. But a neighbour who lives on Woodhouse Road said that she had witnessed the same amount of flooding on the road on the Boxing Day floods, long before our work was done.”
The video shows water running off the hillside, either from springs, as over land flow or down a footpath. The water is gathered by a series of interception channels that prevent it reaching the houses, the water is then fed in a short culvert below the footpath and into an adjacent field containing an attenuation pond. The attenuation pond has a capacity of about 800 m3 with a 150 mm diameter piped outlet falling steeply due to the lie of the land to a farm access track. Encouragingly given the amount of rainfall, the pond has additional capacity as can be seen in the footage. The water is slowed by the pond and stored for a while allowing any sediment to settle out before discharging at a controlled rate to the farm access track. The pond is designed to empty completely returning the field to pasture once the storm has passed. The water continues on down the access track in a concrete lined channel to Woodhouse Road where as can be seen in the footage it makes a small contribution to an already flooded road. Notice the dirty brown colour of the flood water on the right of the picture compared with the water entering from the left from the attenuation pond. The combined flows continue on down Woodhouse Road before entering a concrete lined channel which is an original highway drain and is not part of this scheme.
Opportunities are often hidden in plain sight
Finally for the observant, in the final clip look for the open and empty field adjacent and to the left of the concrete channel in the background. Adopting exactly the same principles as described here, but on a larger scale, an off line attenuation pond on this land with some of the water diverted from the channel into it would slow its journey to the Calder reducing the effects downstream at Callis Bridge, Hebden Bridge, Mytholmroyd and beyond. The scheme at Oldroyd cost around £20,000, it was completed with local labour and expertise and without any disruption to people’s lives, it took only around three weeks to complete. Already it has paid for itself preventing damage from Storm Caira and a smaller flood on the 16th March 2019.
Unfortunately due to bureaucracy, small schemes like Oldroyd elsewhere in the Calder Valley have been delayed, others have been refused permission for dubious reasons. Planning permission is required and possibly ordinary water course consent, the process is too slow and fraught by officialdom, staffed by people with little experience of these approaches. As for capital intensive flood attenuation schemes, we have seen raised flood walls constructed in the early 2000’s at Todmorden, Callis Bridge and Eastwood overtopped both in 2015 and in this latest flood. As we have seen at Mytholmroyd, in channel flood alleviation schemes adjacent to highways and houses are extremely slow to construct, highly disruptive to the local economy and costly to implement, and when finished there still remains the probability that these walls too will be overtopped in a future flood event. By holding and slowing water higher up the catchment these schemes can be reduced in scale and cost.
More, faster and at scale
The key to a meaningful reduction of flooding in the Calder Valley are more of these smaller schemes, combined with sustainable drainage systems (SuDS) holding, slowing and filtering water. If implemented at scale they can provide local flood protection and contribute significantly to the overall flooding problem here in the Calder Valley and beyond. Furthermore they are cost effective as has been demonstrated, two floods, five houses equals ten new kitchens, lets guess at £5000 each, £50,000, more than double the payback in four years. Compare that to the close on £40 million spend at Mytholmroyd, just a fraction of that budget spent on these small schemes could make a significant difference.