4.7 SR 06-01-2020 - Laserfiche WebLink

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Sherburne County Multi -Hazard Mitigation Plan, 2020 Warning Siren Coverage— Sherburne County has a large warning siren system, however, some of the sirens are old and have not been serviced frequently. This could lead to sirens not working properly, causing residents to not receive warnings during an event. Emergency Services is currently working on updating the county's outdoor warning system. Sherburne County has implemented CodeRED, however, not everyone has enrolled in the community notification system. The outdoor warning system seems to be the best method of warning the general public. Backup Power— Not all county and city facilities have backup power in the event of a severe storm that takes out power. Storm Shelters/Community Safe Rooms — There are many areas throughout the county that do not have safe rooms or storm shelters to protect vulnerable populations from severe storm and tornadoes/extreme wind events (i.e., mobile home parks, campgrounds or schools). 4.3.5 Flash Flood and Riverine Flood Flooding is a significant natural hazard throughout the United States. The type, magnitude, and severity of flooding are functions of the amount and distribution of precipitation over a given area, the rate at which precipitation infiltrates the ground, the geometry and hydrology of the catchment, and flow dynamics and conditions in and along the river channel. Upstream floods, also called flash floods, occur in the upper parts of drainage basins and are generally characterized by periods of intense rainfall over a short duration. These floods arise with very little warning and often result in locally intense damage, and sometimes loss of life, due to the high energy of the flowing water. Flood waters can snap trees, topple buildings, and easily move large boulders or other structures. Six inches of rushing water can upend a person; another 18 inches might carry off a car. Generally, upstream floods cause damage over relatively localized areas, but they can be quite severe. Urban flooding is a type of upstream flood, which involves the overflow of storm drain systems and can be the result of inadequate drainage combined with heavy rainfall or rapid snowmelt. Upstream or flash floods can occur at any time of the year in Minnesota, but they are most common in the spring and summer. Four flash floods have been recorded in Sherburne County since 3.996. Riverine floods refer to floods on large rivers at locations with large upstream catchments. Riverine floods are typically associated with precipitation events that are of relatively long duration and occur over large areas. Flooding on small tributary streams may be limited, but the contribution of increased runoff may result in a large flood downstream. The lag time between precipitation and the flood peak is much longer for riverine floods than for upstream floods, generally providing ample warning for people to move to safe locations and, to some extent, secure some property against damage. Nationwide, floods caused 4,586 deaths from 1.959 to 2005while property and crop damage averaged nearly s8 billion per year (in 2oii dollars) from 3.981.-2011 (Georgakakos, et al., 2014). During the past several decades, agencies have used the "ioo-year floodplain" as the design standard for projects funded by the federal government. However, today floods of that magnitude are occurring far more often than once per century (Natural Resources Defence Council, 2015). In recognition of increasing risks, in January of 2015 the President issued an executive orderthat updates flood Page154