Bar Hill's Flood

Understanding the flooding that occurred in August 2014 is important as we, the village, could be landed with a hefty bill for work that only scratches the surface of the problem. Accurate data is needed in order to make the correct decisions and that seems to be lacking at present. There is a surfeit of guesses and incorrect information. I will try to make reliable information available here and would be pleased if anyone has more or better information. Please email the webmaster if you have more/better information.

Things that are common knowledge but incorrect
  • There are no Sluice gates on the stream through Bar Hill
  • Dry Drayton didn't open a sluice gate to let water through to Bar hill. There is no such sluice gate.
  • The golf course didn't close a sluice gate to protect the course. They have no sluice gates on their land.
  • The A14 drainage pond at the entrance to the village is not a balancing pond as it has no outlet and is not connected to a watercourse. It is an infiltration pond (a soakaway)
  • The A14 drainage pond didn't help or hinder the flooding. It seems to have only a connection to the Trafalgar road industrial estate drains. More investigation is needed to clarify this.
  • How much water fell on Bar Hill Village?

    There are several conflicting pieces of information regarding how much water actually fell.
    I have 3 different numbers. The first and largest is that 102mm fell in 30 mins. I can't remember where this came from but, as it seem to have no corroborating evidence it may be incorrect.
    The second and with a better provinence is that 53mm fell in 1 hour at the Uttons Drove Rain Gauge. This rain gauge is near Swaversey and was probably not close to the eye of the cloud burst so, although it is likely to be an understated measure it is at least official.
    The third from the Environment Agency also at the Uttons Drove Rain Gauge is that 140mm fell in 6 hours. This is an average of approx 23mm/hour

    Area of Bar Hill = 1396165.5 square metres = 345 acres Actual amount of water that fell from the sky in 6 hours onto Bar Hill = 1396165.5 x 0.140 = 195463 cubic metres or 42,995,849 gallons (say 43 million gallons) During the 1 hour of maximum rain we received 73997 cubic meters or 16,277,504 gallons.

    So, what does it mean
    If we had a pipe of a metre across that amount water would flow through in about 8 hours (assuming a speed of around 2 metres/sec) but only if the incoming rate was a constant and it is clear that nearly half the rain fell in just one hour so even a metre wide pipe would be overwhelmed. I also don't think that the flow rate would be this high as the slope of the land is too shallow. I haven't measured the pipes under the roads so my numbers are just ball park figures. Then, in addition to the incoming water from the sky, we have to take account of the water flowing off the fields above Bar Hill. The field directly behind Bar Hill is 288147 square metres in area so, taking the lower figure for the rainfall rate of 53mm in one hour. That hour would add a further 3,359,150 gallons to the water coming through the village just from that single field. There are other fields of similar size feeding into Bar Hill so it can be seen that just from our immediate locality we would have to cope something in excess of 20 million gallons of water in just one hour and a total of around 50 million gallons over the 6 hours the rail fell.
    These figures make no allowance for any water absorbed by the soil but, as there had been rain leading up to the event, the ability of the soil to absorb significant amounts of water is likely to have been reduced.

    The prediction of how fast the water will flow through a pipe is tricky. Some figures from the internet. 6" diameter pipe - 550 gallons/min or 33,000 G/Hour 500mm diameter pipe = 667 cubic Metres/hour =146,719 gallons/hour

    The A14 Drainage pond

    This infiltration pond seems to have come into existance when the A604 was upgraded to the A14. I can't remember the date but it was after 1972 and possibly around 1976. The area of the pond is 16295 square metres. I doubt that it played a significant part in our flood event. I don't think that it even fulfilled its alleged design task of stopping the A14 flooding. Water that enters it doesn't seem to have any obvious outlet so it is just a large soak-away. Assuming an even depth of 2 metres right to the edge, it has a capacity of about 7 million gallons. As the soil in the area is mainly clay the pond will only release any water into the ground slowly.