The comparison between the means for limiting the area of active ripples existence with observation data shows inability of earlier methods to establish the limits reliably. It is shown that the limits can be determined using functions relating sand particle dimensions or orbital radius of motion near the bed to particle Mobility characteristics or the Shields parameter; the functions are more complex than linear or power ones. The relationships between active ripple dimensions and orbital radius and mobility characteristic as developed by the authors are more reliable than previously known methods. Equations are suggested for calculation of passive ripples maximum dimensions, and a possibility of dynamic reconstruction based on the data on the forms is established.