Answer:
Turbidity
Step-by-step explanation:
The variable that is the best to help a student to measure in order to know the impact of soil erosion which was caused by the construction project that took place on the river TURBIDITY will be the best variable reason been that TURBIDITY help to measure the cloudiness in a water which means that the higher the cloudiness in a water the higher the TURBIDITY and Secondly a situation where their is a high soil erosion it will often lead to reduction in clarity of water which is why TURBIDITY is a vital tool to help measure all the particles in water which a physical eyes cannot see.