Hydromorphological conditions are a key factor for the habitat diversity in riverine ecosystems. The Hydromorphological Index of Diversity (HMID) is a tool to quantify the habitat diversity in a river reach based on local flow depths and flow velocities. The work presented here analyzes the sensitivity of the HMID value towards input data. Since the evolution of the HMID, values of most of the 12 analyzed reaches arrive at a saturation value, after which the HMID value does not change anymore with additional data. This indicates that an over-sampling took place and a sub-sampling can be applied. Thereby, 50%, respectively 66%, of the input data were removed for the HMID computation. Results show that more measurement points are needed for reaches with a high geomorphological diversity in order to compute a representative HMID value than for reaches with uniform conditions.