Little boats with a serious job to do

Among our many roles, we are responsible for the collection of information about the water cycle. We gather a variety of river level/flow data, weather and climate information and groundwater data.

Across Midlands region we have almost 500 measurement sites along our rivers. These range from our primary sites where a telemetry system automatically takes 96 readings each day, to logger sites where data may be manually downloaded once a month.

Much of this river level information is available online via the environment agency website here:

http://www.environment-agency.gov.uk/homeandleisure/floods/riverlevels/default.aspx

As well as measuring levels of water in rivers, we also need to measure flow. We can do this by using either a structure such as a weir or flume, or by putting equipment in the river. The results we get always have to be calibrated (checked) and this is where our lovely mobile boats and acoustic measurements are used.

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The level and flow data we get is of vital importance as it is used to make key decisions in areas such as flood warning and forecasting, water resource management & abstraction and discharge management.

Our telemetry data also provides the triggers for flood warnings to be issued as well as the building blocks for our flood models which trigger flood defence deployment and the advice we give to our partners during times of flooding and drought.

We measure flow using sounds waves and the Doppler effect. This is the change in frequency of a sound wave for an observer moving relative to its source (so I’m told!).

Sensitive sensors are mounted on the underside of small boats and manoeuvred across the river. This is done either with ropes, cableways (bit boring) or more recently using our remote controlled boat (great fun).

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As the sensor moves across the water surface, it fires high frequency sound waves to the bed of the river. These waves are then bounced back from the bed of the river and the return waves are altered by the Doppler effect of the flowing water. We measure this shift to give an accurate measurement of water speed or velocity.

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The sound beam also measures the river depth and a GPS and built-in compass measures the width.

We then use basic maths to calculate flow – Q (flow) = V (water speed) x A (Area) (Width x depth)

As well as telling us the flow of the river, our boats also give a screenshot of the river channel shape. This is useful to establish if there are any underwater blockages within the channel that need removing or whether future erosion is going to affect the site.

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Our little Q boats have been doing brisk business over the last few weeks’ flooding, helping to ensure our flood information and advice is as accurate as it can be.

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