10-17-2005 Planning Commission Packet

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' The definition of appropriate hydrology according to the 1987 Manual includes two important terms that must be clarified. First, the definition of a growing season is needed. The growing season is defined in the 1987 Manual as: "...the portion of the year when soil temperature (measured 19.7 inches below the siirface) is above biological zero (5° C or 41°F)." According to the 1987 Manual this period of time can be approxirnated by using thc "starting and ending dates for the growing . season based on a 28° F air temperature threshold at a frequency of 5 years in 10," Based on this definition the growing season ranges approximately 160 days to 180 days in the Minneapolis/St.Paul metropolitan area (160 in tlle northern suburbs and greater to the south). Therefore, the required inundation or saturation to the surface for 5% of the growing season would be $ or 9 consecutive days that ground water would need to be at the surface or saturated to the surface, The second term in the appropriate hydrology definition from the above paragraph to be clarified is "in most years". This means in 5 of 10 years hydrology must exist within a"jurisdictional wetland" for the 8 or 9 consecutive days of the growing season, This means that one observation date or even one whole year warth of detailed hydrology data may be deemed insufficient to determine if appropriate hydrology exists at a given location. In the event that precipitation events accumulate to above or below normal duririg just prior to a site visit or during a more intensive hydrology study, the data may be confounded by non-normal circumstances and may be considered outside the bounds of "most years". Ideally,both antecedent soil moisture eonditions and precipitation would be normal during aIl delineations. However, this is not a realistic impression of climate: Therefore, primary indicators of hydrology must be zeviewed with scrutiny prior to determinirig if hydrology indeed exist5. jlVetland hydrology may be observed as standing �vater (inundation), or may be observed as freestanding water within a soil pit or auger hole (saturation) usually within the upper 12 inches. This is what would be considered primary hydrology indicators. Examination of this indicator requires digging a soil pit to a depth of 16 inches and observing the level at which water stands after sufficient time has been allowed for water to drait� into the hole. The required time will vary depending on soil textuze. This level represents�the depth to the water table; the depth to saturated soils will always be nearer the surface due to the capillary fringe. According to the �ydrolagy criteria in the 1987 Delineation Manual,f�r soil saturation to impact vegetation,it must occur within a major portion of the root zone, typically within 12 inches of the surface. Only one primary indicator is necessary to make the determination that wetland hydrology is present. However,since a single observation zs not enough evidence, based on the percentage of the growing season this inundation or saturation is required, these data are only valid when reviewed while also considering the abundance of recent precipitation events oz•the seasonal trend of climate when the site visit was made(this may be done through review of precipilation records where available). �n addition to the primary indica�ors of wetland hydrology, there are secondary indicators(e.g.oxidized root channels, �valer-stained leaves, local soil survey data, F'A�-T�Teutral test), of which two must be present to consider the sample point as having wetland hydrology. 3 Svoboda Ecological Resources Mackinnon �arcel Project No, 2005-308-03 Gronberg & Associates