I have been monitoring Cedar Grove Creek in Rockbridge County for approximately ten years and in the last two years I have been measuring turbidity monthly for the Chesapeake Monitoring Cooperative. This creek is subject to sediment runoff after rain and its clarity changes as a result of the runoff.  Since it is a shallow waterway the 120 cm turbidity tube appears to be an appropriate method to determine changes in water clarity.  If the water is sediment laden it will reflect a turbidity tube reading of less than 120 cm.  When it is clear it exceeds 120 cm.  Thank you.