Final answer:
The question covers principles of physics, specifically fluid mechanics related to pressure changes underwater and the necessary mass of chlorine to maintain a safe concentration in pool water. It also addresses water management and energy potential in environmental engineering contexts.
Step-by-step explanation:
The question relates to the principles of physics, specifically fluid mechanics and how pressure changes with depth in a fluid. The fact that water is denser than air and the density's role in the pressure felt underwater is a key concept. Swimming pool barriers are also discussed, although the precise height above grade required for such barriers is not provided. Pool water sanitation and the calculation of chemical concentration introduces an application of chemistry within the context of physics.
To maintain a sanitary pool environment, the addition of chlorine is necessary. For a pool with 21,200 kg of water, achieving a chlorine concentration of 3.0 ppm will require a very specific mass of chlorine to be added. When dealing with the collection and utility of rainwater, certain percentages regarding how much water is collected, how much falls on land, and the efficiency of collection for use in dams are provided. These scenarios introduce calculations that can be used to address environmental engineering challenges and the principles of water management.
The reference to decreasing water heights and the available height for a dam indicates an understanding of potential energy in relation to water's altitude. The provided figures, such as 5 km evaporation height, 800 m typical land height, and 50 m height utilized by a dam, could be used in calculations involving energy, volume, and mass in fluid systems.