Downstream Hydraulic Geometry of Alluvial Channels

This study extends the earlier contribution of Julien and Wargadalam in 1995. A larger database for the downstream hydraulic geometry of alluvial channels is examined through a nonlinear regression analysis. The database consists of a total of 1,485 measurements, 1,125 of which describe field data used for model calibration. The remaining 360 field and laboratory measurements are used for validation. The data used for validation include sand-bed, gravel-bed, and cobble-bed streams with meandering to braided planform geometry. The five parameters describing downstream hydraulic geometry are: channel width W, average flow depth h, mean flow velocity V, Shields parameter ${\tau }^{*}$ , and channel slope S. The three independent variables are discharge Q, median bed particle diameter $d_{s,}$ and either channel slope S or Shields parameter ${\tau }^{*}$ for dominant discharge conditions. The regression equations were tested for channel width ranging from 0.2 to $\mathrm{1,100}\mathrm{m}$ , flow depth from 0.01 to $16\mathrm{m}$ , flow velocity from 0.02 to $7\mathrm{m}∕\mathrm{s}$ , channel slope from 0.0001 to 0.08, and Shields parameter from 0.001 to 35. The exponents of the proposed equations are comparable to those of Julien and Wargadalam (1995), but based on ${\mathrm{R}}^2$ values of the validation analysis, the proposed regression equations perform slightly better.