Final answer:
The minimum size for a circular rainwater leader is generally determined by factors such as the roof area, the maximum expected rainfall intensity, and local building code requirements. However, the question seems to contain unrelated information about agricultural fields and center-pivot irrigation, which does not directly relate to the sizing of rainwater leaders.
Step-by-step explanation:
The question asks about the minimum size for a circular rainwater leader. A rainwater leader, also known as a downspout, is part of a building's stormwater drainage system, which guides rainwater from the roof to the ground or drainage system. While the question does not provide a specific context or building code reference that would define the exact minimum size, we can reference a general principle in engineering practices regarding fluid dynamics and capacity requirements. A circular rainwater leader's size is often determined by factors such as the roof area it needs to drain, the maximum expected rainfall intensity, and local building code regulations.
However, given the additional information provided, which seems unrelated to the specific question about rainwater leaders but rather describes agricultural fields, it appears there may be some confusion. The descriptions provided refer to center-pivot irrigation systems and geometrical constraints for circles fitting within squares. These references do not directly help in determining the minimum size for a circular rainwater leader unless we are considering the drainage for such agricultural setups, which would require significantly different considerations and is not typically the scope of urban building drainage systems.