Thick boundary layers at zero pressure gradient are produced by generators kept along the leading edge of a flat surface and sustained by roughness elements distributed over the surface. Size, shape and spacing of the generators, distribution of the roughness elements and the roughness fetch are varied and the mean velocity profile measured at various locations. The results obtained show that layer thicknesses of about 25 cm can be obtained in a relatively short fetch of 1 m and that mean velocity profiles corresponding to both rural and urban terrain conditions can be simulated.