The use of artificial roughness in movable-bed models

Tests have been done in a laboratory flume, to evaluate the influence of vertical rods of 3 mm dia on the hydraulic and sedimentological characteristics of the flow. The first two tests have been done with some 10 cm waterdepth. In both tests the s ame flow rate and sediment transport was used, the only difference between the tests being the artificial roughness, which was applied during the second test. The following two tests were done in a similar way with a waterdepth of about ~ and with a reduqed flow rate and sediment transport. For both 10 em and 5 om waterdepths, the bar resistance was then measured in the flume without bakelite. The influence of the rods on the ripple factor, ~, thus on the bottom roughness, could be evaluated, after e1imination of the bar resistance. In the case of 10 em depth, the artificial roughness caused a reduction "of bottom roughness, while with a depth of 5 cm an increased bottom roughness with the bars was found. By calculating the bed load from the product of the mean ripple celerity and half the meru1 ripple height a very good agreement was found with the actually measured quantities