4.7 SR 06-01-2020 - Laserfiche WebLink

Home Browse Search

Sherburne County Multi -Hazard Mitigation Plan, 2020 the 2007 rainfall caused seven fatalities (MN DNR, 2007). In September 2oio, a storm on the 22-23rd resulted in more than six inches of rain falling over 5,000 square miles in southern Minnesota. Rainfall totals of more than eight inches were reported in portions of io counties. The heavy rain, falling on soils already sodden from a wet summer, led to numerous reports of major rural and urban flooding. For many monitoring locations in southern Minnesota, stream discharge resulting from the deluge was the highest ever seen during an autumn flood (Minnesota Climatology Working Group, 2010). June 203.4 was the wettest month on record in Minnesota, with a state -averaged rainfall of 8.o3 inches. This broke the previous record of 7.32 inches, which occurred in both July 1.897 and June 3.93-4. Rainfall totals for much of the state ranked above the 95th percentile when compared with the historical record; in some cases the totals tripled that of the historical rainfall average for June. A presidential disaster declaration was declared due to the severe storms, winds, flooding, landslides, and mudslides (DR- 0.82), which included 37 Minnesota counties and three Indian Reservations. Vulnerability and Hazus Hazard Analysis A potential risk and economic loss analysis for a i% annual chance flood was performed using a FEMA tool, Hazus for ArcGIS. A Digital Flood Insurance Rate Map (DFIRM) defined the i%annual chance flood boundary and a io-meter Digital Elevation Model (DEM) was used to create a flood depth grid. The resulting Hazus i%annual chance floodplain output is shown in Figure 12. Losses were based on Sherburne County -specific building data. Sherburne County provided parcel tax and spatial databases that included building valuations, occupancy class, square footage, year built, and number of stories. The quality of the inventory is the limiting factorto a Hazus flood model loss estimation. Best practices were used to use local data and assumptions were made to populate missing (but required) values. Hazus reports the percent damage of each building in the floodplain, defined by the centroid of each building footprint polygon derived using LiDAR data. After formatting the tax and spatial data, 61,205 points were input to Hazus to represent buildings with a total estimated building plus contents value of $13.5 billion. Approximately 87%of the buildings (and 65%of the building value) are associated with residential housing. Page157