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• Table 4 -Storm Events <br />Recurrence <br />Interval Probability of <br />Exceedance % ~4-hour Rainfall <br />..Amount in) <br />1 100 2.4 <br />2 50 2.8 <br />5 20 3.6 <br />10 10 4.2 <br />25 4 4.8 <br />50 2 5.3 <br />100 1 5.9 <br />Additional description of the climate of the area is provided in the CRWD Water <br />Resources Management Plan. <br />Topography <br />The City of Falcon Heights is part of the Anoka Sand Plain. This is a glacial outwash <br />plain and consists generally of fine sand with small depressions. <br />• Geology <br />Geologic maps of the City area are published in the Geologic Atlas of Ramsey County, <br />Minnesota (Minnesota Geological Survey, 1992). <br />The uppermost geologic formation is quaternary deposits. Figure II-1 in the CRWD Plan <br />shows the extent of these deposits. The quaternary deposits are associated with the Des <br />Moines Lobe (Grantsburg Sublobe) and Superior lobe of the Wisconsin Glaciation. In the <br />District, these consist mainly of meltwater deposits. In the central portion of the <br />watershed, quaternary deposits consist of meltwater stream sediment, generally coarse <br />sand with pebbles. As mentioned above, the Anoka Sand Plain extends into the northwest <br />part of the District. In the north central and northeast portion of the watershed are <br />deposits of till, consisting of loamy sand and clay. <br />Figure II-2 in the CRWD Plan shows the bedrock for the District. Bedrock geology in the <br />City of Falcon Heights consists of Decorah Shale, which acts as a confining layer. The <br />Decorah Shale is green calcareous shale with thin limestone interbeds. <br />The Platteville and Glenwood Formations underlie the Decorah Shale. The Platteville <br />consists of fine-grained dolostone and limestone. The Glenwood consists of thin green <br />sandy shale (3-5.5 feet thick). <br />• <br />Falcon Heights Comprehensive Plan 2008 Draft -January, 2008 Part III: Infrastructure, Page III-27 <br />