Lateral distribution of sediment and phosphorus in a two-stage ditch with partial emergent vegetation on the floodplain.

Two-stage channels are effective drainage facilities because they can decrease soil erosion and nutrient loss effectively. The lateral distribution of streamwise velocity in two-stage channels has been substantially studied. However, knowledge about the lateral distribution of sediment and phosphorus in two-stage channels with emergent vegetation on the floodplain are limited. In this work, flume experiments were conducted to investigate the relationship between current and transport of sediment and phosphorus. Results show that lateral distributions of total suspended sediment (TSS), particulate phosphorus (PP), and dissolved phosphorus (DP) are affected by the lateral variation of streamwise velocity, i.e., larger TSS and DP were found in the main channel, while larger PP appeared in the floodplain. Besides, theoretical models for the lateral distribution of TSS and DP were presented. Three models were adopted to predict the depth-averaged streamwise velocity, and corresponding results have been used to predict the TSS and DP. Comparisons indicated that with a high-precision velocity model, the newly presented analytical models can give satisfied predictions of the lateral distributions of TSS and DP.