D₅₀ riprap is a riprap with 50% of its rocks' diameters smaller or, at times, larger than its recommended rock size. The other 50% of the rocks have the D₅₀ diameter. On the other hand, a D₅₀ riprap has 90% of its rocks, either smaller or larger than the recommended D₅₀ diameter. Only 10% of them are around the D₅₀ diameter. Read more