The hydraulics of steep streams
This thesis describes research carried out to study steep streams. Step-pool sequences, a typical feature of such streams, were found to occur on every steep stream studied in the field. The most important control on the spacing of the steps was width. Flume experiments produced steps (at an average Froude number of 0.88), and showed that the presence of steps increased resistance to flow at lower than step-forming flow and decreased resistance at above step-forming flows. In the field, flow resistance was found to be controlled by sediment characteristics and the amount of step protrusion. The hydraulic geometry of the steep streams was also studied, and was found to differ considerably from hydraulic geometry characteristics of lowland streams. The formation of steps and pools was not found to be related to antidune processes; rather they were built up individually as large particles captured other large particles that had been entrained by the near critical flow. It was concluded that it is not the absolute values of slope and discharge that determines whether steps form. Near critical flow and high relative roughness appear to be the only requirements necessary. Previous equations were generally found to perform poorly when used with the experimental data, and an attempt to model the velocity profile using sediment characteristics and considering stresses on the flow also produced poor correlation with the actual field data. Modifications to these were made with some success, especially in the ability to predict friction factor based on relative roughness using D84 . Flume velocity profiles identified characteristic velocity profiles at different locations within the step-pool sequence and the presence 'S-shaped' profiles downstream of the step.