Abstract: A modular scour monitoring device which employs magnets located within a weighted descending collar is designed for placement about bridge piers, abutments and the like, such that the occurrence of scour causes descent of the collar. This descent is carefully monitored against the initial reference point using one of two systems: a magnetic detecting probe unit or a magnetic switch array. The probe unit utilizes a graduated cable with a magnet detector mounted at one end and a signalling device at the other. The switch array system employs electrical components which are selectively activated with the descent of the collar, permitting periodic readings of the arrays various electrical properties to reveal the new depth. A wide variety of accessory systems may be used in conjunction with the present invention to permit remote monitoring, visual, audible or other warning signals, and data storage and control.