I start modeling by following the instructions of the assignment: making a grid → adding a pebble → aligning the height of cylinders to a sine wave → adjusting the height to reflect distance → adding the effect of another pebble. I found the most challenging parts were 1) adjusting the factors to make the waves look good and 2) adding the waves of another pebble. I simply added up the wave values from different drop locations, and the resulting waves appeared quite realistic.
The waves from two pebbles have the same frequency. The heights/intensity of the waves are however separate, since different pebble sizes can reasonably produce waves of different strength. Both the frequency and height, along with other variables such as base offset, grid range and cylinder sizes, are all adjustable.