Physical Modeling of Stepped Structures. Design Methodology

Water flow behavior in open channels is mainly governed by gravity forces. Thefore, flow behavior is influenced by the channel longitudinal slope. In practical applications, water in open channels are transported with small sloped channels, which allows the flow to have a low velocity, admisible shear stresses and an adequate transport. Nevertheless, sometimes the canal bottom needs to change abruptly from higher to lower elevations in a relatively short distance due to topography, which means that the channel will have a very high slope and excessive velocities. Excessive kinetic energy dissipation can be done abruptly or gradually with hydraulic structures. Stepped structures, subject of study of the present research, dissipate energy in an open channel flow in a gradual way.

This document presents the physical modeling of three stepped structures of rectangular cross section with 25 cm base width, but with different height / length ratios of the step: 1:1, 1:3 and 1:5. The three structures have a step height of 5 cm and a total of 20 steps, that is, the fall of the three structures is 1m, but each one has a different total length.

Caracterization of nappe flow, transition flow and skimming flow for each of the mentioned stepped structures was done in this study with a flow rate from 0.5 to 40 lps. The range of flow rate for each stepped structure and for each water flow behavior was found as a result of this research. Efficiency in energy dissipation for each stepped structure was also assessed, according to slope variation and flow rate. A new methodology for stepped structures design is suggested in this research.

Besides, the built physical models were also used to verify Ohtsu design methodology for stepped strutures with skimming flow.