The continuous flow in a horizontal, frictionless rectangular open channel is subcritical. A smooth step-up bed is built downstream on the channel floor. As the height of the step-up bed is increased, choked condition is attained. With further increase in the height of the step-up bed, the water surface over the step-up bed will decrease to the extent that it will be above the critical depth. flow will stop. upstream will increase to the extent that it will create supercritical flow over the step-up bed. over the step-up bed will decrease to the extent that it will be below the critical depth.

With further increase in the height of the step-up bed in a subcritical flow, the water surface over the step-up bed will decrease to the extent that it will be below the critical depth.

This will cause the flow to transition from subcritical to supercritical over the step-up bed. The upstream water level will increase to the extent that it will create supercritical flow over the step-up bed, leading to increased velocities and changes in flow behavior.

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This is an excerpt from- Sexual selection and special design authored by Steven W Gangestad, in the Annals New York academy of Science. Answer the questions based on the excerpt provided below. "…..Women claim men’s scent importantly affects their attraction to them. Moreover, evidence suggests that women’s olfaction changes across menstrual cycle. For instance, women tend to rate androstenone, a steroid found in men’s sweat, more positively near ovulation than during non-fertile phases.
In an initial study, we asked 41 men to wear T-shirt for two consecutive nights. During the two-day period, they were to wash only with unscented soap, not to wear any fragrances or colognes, not eat certain strong foods, and not to sleep with another person. They dropped shirts off at our lab on a designated morning. Later that same morning and throughout the next day, women came in, smelled each T-shirt and rated its attractiveness (a composite of two ratings: pleasantness and sexiness). For each woman, we regressed her rating on men’s symmetry to yield "a preference for symmetry" score (the regression slope, a measure of the change in rating as a function of a change in symmetry). We then examined the correlation of these preference scores with women’s estimated fertility based on their self-reported day of the cycle and actuarial data on probability of conception for each day. Across 28 normally ovulating women the correlation was 0.54, p<0.001. Examination of the bivariate plot revealed that when women’s fertility was near zero (very early and late in the cycle), they had no systematic preference for the scent of either symmetrical or asymmetrical men. As their fertility increased, however, they increasingly preferred the scent of symmetrical men.
A subsequent study replicated and extended that result in a larger sample of about 50 normally ovulating women and 80 men. Women’s preference for symmetry correlated 0.42 with their fertility based on the day of their cycle, p<0.001. We asked men how many times they showered and whether they wore any fragrances. The number of times men showered predicted the attractiveness of their scent. When this variable was partialled out and all men who wore fragrances were eliminated from the analysis, the correlation between women’s symmetry and their fertility actually increased, r=0.48, p<0.001. In a third study in our lab, this result was once again replicated, r=0.26, p<0.05. When data from all three studies were pooled, the correlation between women’s preference for symmetry and the fertile phase of their cycle was r=0.40, p<0.0001." [Note: p values reported here means that correlation r is statistically significant]
From this scenario, the immune systems of humans should be exceptionally high. Yet, there is a rising incidence of autoimmune diseases and lack thereof immunity. What form of selection do you think is at play here? Explain.