QUESTIONS

1. What bedforms develop under upper regime in alluvial channel flow?

   (1) plane bed, (2) antidune standing waves, (3) antidune breaking waves, and (4) chutes and pools.

2. When do surges form in open-channel flow?

   Surges are perturbations created by sudden gate closures or rapid changes in stage or flow depth. Typically, a surge does not attenuate readily, traveling along the channel for a considerable distance.

3. What is a kinematic shock?

   Kinematic shocks are kinematic waves that have steepened to the point where they become, for all practical purposes, a wall of water, with a near vertical face.

4. What conditions are necessary for a kinematic wave to steepen into a kinematic shock?

   Four conditions: (1) the type of wave: the more kinematic a wave is, the less its tendency to attenuate and, therefore, the more its tendency to steepen; (2) the amount of baseflow: the smaller the base-to-peak flow ratio, the greater the tendency for the wave to steepen; (3) the flow regime: high-Froude number flows have less tendency to attenuate disturbances; therefore, the higher the Froude number, the lesser the attenuation; (4) the type of cross section: hydraulically wide channels have a greater tendency to steepen that triangular channels.

5. When do roll waves develop?

   Roll waves develop in open-channel flow when the Vedernikov number exceeds 1. In natural channels, this condition is seldom, if ever, met. Thus, roll waves are restricted to artificial channels lined with either concrete or masonry.

6. Do roll waves develop always in steep channels?

   The condition V > 1 is necessary, but may not be sufficient. Certain dimensionless wavenumbers have stronger amplification tendencies than others. Thus, certain scales of disturbances are more likely to be amplified than others.

7. Where are tidal bores are more likely to form?

   Tidal bores are more likely to form under a large tidal range in smooth, hydraulically wide channels of relatively constant depth.

8. What is a debris flow?

   Debris flows are sudden accumulations of runoff containing great quantities of sediment particles, usually boulder size and above. Debris flows travel downstream at great speeds, destroying everything in their path and threatening life and property.

9. What conditions are conducive to the development of debris flows in the Southern California climate?

   Five conditions: (1) Tectonism, which maximizes erosion potential, (2) Chaparral ecosystem, which develops survival adaptations based on wax-protective surfaces to suppress evapotranspiration, (3) wind, which can readily achieve speeds of more than 40 miles per hour, (4) fire, which follows wind after a long drought, and (5) rain, which follows fire due to ash particles in the air promoting coalescense and raindrop formation.

10. What is a lahar?

    Lahars are debris flows triggered by snowmelt, following a volcanic eruption and subsequent sudden melting of the snowcap.