Wednesday, 7 March 2012

River Environments-Fieldwork

Describe how you would measure the velocity of the river flow? (4m)

Equipment needed:

  • clipboard with paper and pen, and drawn table to record results 
  • 2 ranging poles
  • a measuring tape
  • a flowmetre with a datalogger
By using a measuring tape between 2 ranging poles on either side of the riverbank to get the width, and dividing the width into 6, you can measure the velocity at 5 equal spaces in the river. A person can stand with a flowmetre in the river, with the flowmetre's impellor facing the water flow so that their body does not block the river flow and disrupt results. The impellor is turned by the water and data is recorded on the datalogger. By taking the average of the 5 readings, accuracy is achieved and you can get the velocity of the river flow.

Describe the fieldwork techniques you would use to collect data about a river's discharge.  (6m)

River's discharge= cross sectional area x velocity of the river (cumecs-cubic metres per second)

Cross sectional area can be calculated by multiplying the average depth of the river by its width. To get the width, 2 people hold a ranging pole each on each end of the river bank-on the edge. Connect a measuring tape across it and record the width, easier if the '0' mark is on one end of the bank. Calculate depth by dividing the width by 11, and measuring depth at each regular interval of the width. Should have 10 sites to collect data from. At each of the 10 sites, a person stands in the river channel with a metre ruler resting gently on the river bed with the '0' mark on the river bed. It's better if the ruler is sideways on the river flow so water flows around it-making the measurement more accurate. Calculate the average of the 10 measurements, multiplying this average depth by the width to get cross sectional area. To get velocity, divide width by 6. Collect data from 5 sites in the river channel in regular intervals of the width. A person should hold a flowmetre with an impellor and a datalogger attached to it. The person should stand behind flowmetre with impellor facing the river current. Record velocity reading from datalogger. Calculate the mean of the readings from all 5 sites and multiply this by cross sectional area to get river discharge. 


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