Pepin County's Flood Hazards
Flooding is the most common and most costly disaster in Wisconsin. Flooding can happen anywhere, even outside of the floodplain!
The history of flooding in the Pepin County, particularly along the Chippewa River, was first studied by the U.S. Corps of Engineers in the late 1880's . As a result of the study, it was determined that it would be difficult to control flooding based on the topography of the region. To this day, the waterways of Pepin County generally experience flooding to some extent on an annual basis on the Mississippi River, Chippewa River, or our smaller inland rivers/creeks. The flooding can usually be attributed to localized or regional heavy rain events or be part of a larger regional system changes (i.e. spring snowmelts). Flooding typically occurs when a river, stream, lake or other body of water overflows its banks and/or when there is an excessive rainfall that accumulates faster than it can be absorbed into the environment or stormwater infrastructure systems.
The National Weather Service uses the following terms associated with flooding:
Flash Flood: A rapid and extreme flow of high water into a normally dry area, or a rapid level rise in a stream or creek above a predetermined flood level, beginning within six hours of a causative event (e.g. intense rainfall, dam failure, ice jam). Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters.
Flood: Any high flow, overflow, or inundation by water which causes or threatens damage.
Floodplain: In hydrologic terms, the portion of a river valley that has been inundated by the river during historic floods.
Floodway: In hydrologic terms, 1) A part of the floodplain reserved for emergency diversion of waters during floods. A part of the floodplain which, to facilitate the passage of floodwater, is kept clear of encumbrances. 2) The channel of a river or stream and those parts of the floodplains adjoining the channel, which are reasonably required to carry and discharge the floodwater of any river or stream.
Flood Categories: Terms defined for each forecast point which describe or categorize the severity of flood impacts in the corresponding river/stream reach. Each flood category is bounded by an upper and lower stage. The severity of flooding at a given stage is not necessarily the same at all locations along a river reach due to varying channel/bank characteristics. The flood categories used by the National Weather Service are:
• Minor Flooding: minimal or no property damage, but possibly some public threat.
• Moderate Flooding: some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations.
• Major Flooding: extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.
• Record Flooding: flooding which equals or exceeds the highest stage or discharge at a given site during the period of record keeping.
