All three hypotheses only apply to situations involving erosion. Possible explanations for this lack of increase in velocity include increased roughness, decreased effective slope angle because of the development of vertical head cuts and a shift in energy use. The measurements showed virtually no increase in velocity and a minor increase in hydraulic radius with slope, as flow was more concentrated on steeper slopes. As Manning's n is usually assumed to be constant, this must mean that either velocity increases with slope or hydraulic radius decreases. Furthermore, for croplands, there is an apparent linear increase in Manning's n (and f) with increasing slope angle (R2=0.70). The results show that Manning's n can, just like Darcy-Weisbach f, be estimated from Reynolds number. Water was evenly applied to the top of the plot and discharge, surface velocity, flow width and slope were measured. Measurements were performed on a 2.5×0.4 m plot, on which flow was allowed to find its own path. The experiments were conducted for a range of land uses as well as for different slope angles (6–64%). The soils are typically erodible loess soils. A series of field experiments was carried out in a small catchment on the Chinese Loess Plateau to obtain reliable values of Manning's n. Hydrological and soil erosion models require calculations of flow velocity, for which either the Darcy-Weisbach or the Manning equation is generally used.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |