Hurricane proved point
My point (in a June 2 Forum) was not about just "a rainfall event" but the danger posed from "a peak rainfall event." Engineers design anything for a worst case scenario — in this instance, a 100-year peak rainfall. So, Mr. Halvorson's statement: "it is very unusual to have a natural stream that fluctuates more than two to three feet due to a rain event" has no relevance to the main point of my forum; without any dams/ponds, Traverse City is vulnerable to flood disasters including flash floods.
The statement: "Most of the soils in northern Michigan are of a sandy nature and are highly absorbent, allowing infiltration of the rain" is misleading. Sandy soils do absorb more water than non-sandy soils, but, to give the impression that, "during a peak rainfall event, a flood can be averted because sandy soils absorb water" is incorrect. In reality, the soil gets saturated near the surface and the subsequent rainwater flows as runoff.
In September 1961, the failure of the two small dams due to the accumulated water from Hurricane Carla proves that a large volume of water flowed to the dams instead of being absorbed into the soil.