Hydraulic model of a braided channel to aid design of a grade-building structure

Abstract

Presented here are considerations for designing a hydraulic model involving a broad reach of braided, sand-bed channel used to aid the design of a grade-building structure (GBS) for retaining bed sediment upstream of a sediment-deposition plain formed by a sediment-retention dam. The results focus on the similitude and calibration considerations needed to simulate bed-sediment transport along a large braided channel. Key variables in this regard were flow discharge, channel slope and sediment-transport rate. Additionally, the results describe how the GBS evolved in design from initially comprising four walls that lengthened flow path (thereby causing sediment deposition) to being four walls with openings that dispersed flow and consequently spread sediment deposition across the reach. The addition of rock aprons and wall bunds (curved, wall ends), enhanced sediment retention, reduced scour, and mitigated an under-wall seepage concern. In final design, the GBS retained approximately 83% of the bed sediment entering the reach over the test duration.