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Environmental Assessment Worksheet Nature's Refuge Conservation Development Lino Lakes, Anoka County, Minnesota Draft Document — September 25, 2006 Page 11 pre - settlement conditions likely did not include a surficial outlet from the area and the system developed over time as a series of landlocked basins. Historic Anthropogenic Impacts Activity at the site that has impacted the site and contributing watershed hydrology includes: • clearing / timber harvest • development including roadway networks, school, residential, commercial • agricultural activity • development of an outlet ditch from the large wetland complex and a large wetland within the site • construction of downstream ditch crossings (by others) • fire suppression (which modifies the vegetative cover) • internal unpaved roadway and all- terrain vehicle (ATV) trails Historic aerial photos indicate the wetland complexes were cut for hay in the late 1930's and all but small patches in the northeastern 80 -acre parcel were deforested for agriculture. Much of the area has reforested naturally and some areas have been planted. The majority of the southwestern 80 -acre parcel was cleared in the last 5 years by the previous owner. There is no known internal tiling or subsurface drainage network on the site. Existing Conditions Drainage Area - The existing landform is very flat. The large wetland complex is enclosed by a 904 contour at approximately 52 acres. However, the 906 contour does not close anywhere in the vicinity and loops north of Pine Street, south of Main Street and west of Wood Duck Trail. It appears to extend over a square mile. In addition, it appears there are two surficial outlets to the system. Specifically, to the southwest via the private ditch and overland to the west and eventually to the judicial ditch system CD # 10- 22 -32. The site is shown to be partially within subwatersheds MRC1 and MRC3 as defined by the Rice Creek Watershed District. However, review of the recently available 2 ft contour data indicates there is significant opportunity for interbasin transfer and a very subtle overland drainage divide. As previously described local infiltration is a significant component of the surficial stormwater drainage the area. Based upon this understanding, the following conclusions have been made: • A conventional stage - storage routing of stormwater discharge is a relatively academic exercise based upon the existing topography and watershed characteristics • A planning flood elevation for the large wetland complex has been developed for the RCWD and the City of Lino Lakes. However, this elevation must be considered within the context of the assumptions and method limitations. The incremental impact analysis is not considered a regulatory elevation, but rather presented for information and general planning purposes only. The regulatory flood level will need to be revised and established based on the grading plan for the project. • It is considered very unlikely that the flood elevation of any of these basins would reach 906. • Based upon the characteristics of the watershed and the basin, it is considered that the proposed development activity will not raise the regional flood elevation. Proposed Conditions: The project will include alterations to surface water features on the property including the filling of wetlands and the construction of a new roadway crossing of the outlet ditch. The general objectives of the stormwater management for the site have been identified as follows General Project Objectives: • Enhance the wetland community that will sustain the threatened and endangered vegetation / retain function of natural system • Maintain existing hydrologic regime as much as practicable • Maintain physical context of wetland complex • Maintain existing biochemical environment for threatened and endangered species as much as practicable.