Figure 4

Variations in the roughness of small, medium and large gravel against increases in coverage.

Coverage of relatively small gravel (and aerodynamic roughness lengths) are 25% (0.185 cm), 45% (0.354 cm), 55% (0.352 cm) and 75% (0.471 cm); those of medium gravel are 20% (0.193 cm), 40% (0.366 cm), 50% (0.300 cm) and 60% (0.303 cm); and those of large gravel are 20% (0.211 cm), 30% (0.379 cm), 45% (0.407 cm) and 75% (0.265 cm).