HJULSTROM’S DIAGRAM

This plot shows the average current velocities necessary for the erosion, transportation and deposition of the sediment particles of different sizes.

• For sand and gravel, the larger the particles, the stronger the current must be to erode the material. Surprisingly, though higher current velocities are needed to erode, tiny clay and silt particles than to erode fine sand. It is because the mud (clay and silt) is more cohesive and hence sticker than sand and so a stronger current is needed to dislodge a mud particle from the bottom.

The lower curve on the diagram, it shows that once eroded and moving a clay particle, but not a fine particles of sand can be transported by a week current. This is because the little settling rate of suspended particles also varies with diameter. Small particles settle more slowly than do large grains.