* To work out the wetted perimeter to work out the friction of the river from the banks of the water it is also needed for a cross section of the river and a volume measurement
* The width also helps you work out the volume of a river or the amount of water as we can times the width by the depth this allows us to work out how much water is not coming in to contact with the bank so is flowing unimpeded
* This helps us to work out the cross section of the river and the wetted perimeter which helps us to work out how much water is running unimpeded.
The bank full width.
Once again you stretch the tape measure from one bank to another to the width where it is obvious the river has reached the highest point in the past this will help us start to draw a cross section of the river.
The next thing we did was measure the river depth to do this we measured the depth every 50cm with a meter rule this enables us to calculate the volume and also the wetted perimeter and a cross-sectional diagram can be made. Also the volume will help to measure discharge.
Every half meter across the stream we would pick up a stone measure its long axis and say whether it was angular, sub angular, rounded and sub rounded .we did this to see the velocity as the smaller the stone the less friction there will be and the opposite is slower. And these would also so help us measure erosion as corrosion corrasion attrition and hydraulic action.
Here are some examples of types of stones.
Angular Sub-Angular Rounded Sub-Rounded
The last thing we did was measure velocity to do this we measured ten meters and dropped an orange which floats and then we would time how long the orange would take to travel the set distance. We would repeats this 3 times in the middle, 3 times left and 3 times right and then took an average.
We did this as the speed of the water would affect the amount of erosion we would expect there to be more erosion if the water is faster and there would be more erosion on the outside bend of the river. Velocity also helps us measure discharge or the amount of water passing at any one moment. The last thing we did was measure gradient. To measure gradient we used a clinometer. To measure this we had 2 people of equal heights ten meters apart put the clinometer at eye level and took a reading in degrees we did this as this would affect gradient because usually the steeper the gradient the faster the velocity .
We measured Gradient using the Clinometers with the technique given earlier. The importance of gradient is that the steeper the gradient the quicker the river will flow and the quicker the stream flows the more erosion will take place which will affect the bed load.
The reason we need to find out the cross-section of a river is so that we can work out the volume and the wetted perimeter of the river so all this information is needed to get a river cross-section we need the stream width and the depth .
The discharge is the amount of water flowing at any given time not the velocity which is the speed of a river so as the river gets nearer the mouth the discharge should increase as the river gets bearer the mouth as it will have a higher volume as it will have been joined by more tributaries causing and increase in volume the importance of discharge is that the more discharge there is the river will be wider and deeper as the more water will result in both lateral and vertical erosion. To work this out you need to know the volume and the velocity.