the river Harbourne

River velocity

Measuring the velocity allows us to determine the speed, at which the river travels. If a high quantity of rain falls close to the source of the river there will be a greater amount of water travelling down stream and as a result the volume of water will be travelling at a higher speed. In the section of the river harbourne that that this measurement was taken in a high river velocity can indicate that Harbertonford is susceptible to flooding, a hazard that the flood defences in place in the village are designed to deal with. In order to gain a figure of river velocity a count box and an impellor are needed. Firstly the impellor must be put together and the wire placed into the count box, then the impellor is placed into the water (approximately a third of the depth) facing into the flow of the river. It is essential that the impellor is kept vertical and steady otherwise a false reading will be acquired. The count box will give an average reading of the velocity of the river; the box gives off a sound when an average has been taken. This measurement should be taken at 3 places along the width of the river and then a final average reading taken. The reason for this is the velocity of the river can differ depending on the section of the river the velocity is taken from for reasons such as river debris e.g. logs. Finally in terms of the method it is essential that no one stands in front of the impellor, as this will obscure the reading.