This report gives highly detailed info concerning the Shiawassee River
Midshiawasee-River-report_334332_7.pdf (application/pdf Object)
Rainfall Frequency Atlas of the Midwest, Bulletin 71, Midwestern Climate Center, 1992.
Every 2 years, there is 50% chance, of getting a heavy thunderstorm dumping
2.42 inches of rain within a 24 hr period in the region.
If the weather man says we got 3 inches of rain in a 24 hr period, it's pretty significant news.
Back in August 2007, over 5 days, this area of Michigan received 5.12 inches of rain.-
Mid-Shiawassee River Watershed - Hydrologic Study - 9/30/2010 - page 30
The Shiawassee River watershed is both a snowmelt-driven and a storm-driven system. In a storm-driven system, rainfalls during the growing season generate flood flows. Snowmelt-driven systems are usually less flashy than storm-driven systems, because the snow pack supplies a steadier rate of flow. However, a rain-on-snow event, where rain and snowmelt simultaneously contribute to runoff, can produce dramatic flow increases. The runoff from the rain and snowmelt also likely occur with saturated or frozen soil conditions, when the ground can absorb or store less water, resulting in more overland flow to surface waters than would occur otherwise. Although the Mid-Shiawassee River watershed is likely more of a snowmelt-driven system, the increasing imperviousness of urbanizing tributary watersheds may shift those watersheds toward more storm-driven systems.