Marc B. Parlange

Regional roughness of the Landes forest and surface shear stress under neutral conditions

Mean wind velocity profiles were measured by means of radio-windsondes over the Landes region in southwestern France, which consists primarily of pine forests with scattered villages and clearings with various crops. Analysis of neutral profiles indicated the existence of a logarithmic layer between approximately z − d0 = 67(±18)z0 and 128(+-32)z0 (z is the height above the ground, z0 the surface roughness and d0 the displacement height). The upper limit can also be given as z − d0 = 0.33 (±0.18)h, where h is the height of the bottom of the inversion. The profiles showed that the surface roughness of this terrain is around 1.2 m and the displacement height 6.0 m. Shear stresses derived from the profiles were in good agreement with those obtained just above the forest canopy at a nearby location with the eddy correlation method by a team from the Institute of Hydrology (Wallingford, England).

Preferential flow influences on drainage of shallow sloping soils

The dramatic effect of flow through macropores and hardpan fissures on artificial drainage in shallow sloping soils is demonstrated. Implications of these preferential flow mechanisms on drainage design and water management are discussed. In designing drainage systems on these types of soils, more emphasis should be given to the characteristics of the hardpan.

A simple model for flow on hillslopes

Abstract A simple hillslope hydrological model predicting water movement on sloping shallow soils is developed. Unlike existing hillslope models, the new model can be used to predict flow for long records of climatological data and it can be easily extended to include preferential flow. It compares favorably to other models with more restrictive input requirements. Its application is illustrated for experimental data collected for an homogeneous hillslope at the Cooweeta Hydrological Laboratory.