i had a crossing put in on a seasonal creek and they used rock that size. My excavator guy said 6 inches of that crushed rock that's 4" makes a good base. Seems to pack down well and the water flows right over it without eroding. I think that's a perfect first layer on wet areas and and smaller gravel could be added on top once it settles.How big is that rock 4" minus? Does it settle into the mud well?