Orono Community Management Plan 2020-2040

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City of Orono Surface Water Management Plan February 2019 8 16,000 years ago. The dominant geological feature in Orono is the remnant of the deteriorating Grantsburg sublobe of the Wisconsin glaciation, which covered the area until about 16,000 years ago. The landscape of Orono was formed by three glacial processes: ·the Lonsdale-Lerdal Till, which left mounds of glacial drift (small rocks up to boulders) that were “dropped out” of the glacier as it “stood still” for a period of time and then retreated ·the Emmons-Faribault Moraine formed hills where variably sized till was pushed to the edge of an advancing glacier ·irregularly shaped depressions, referred to as “kettles”, were formed by large blocks of ice and were filled as the ice melted After glaciation ended, the hills were “worn down” due to natural processes, resulting in the rolling landscape with filled depressions that became the many wetlands and water bodies seen in Orono today. Additional geological information can be found in the Geological Atlas of Hennepin County (Minnesota Geologic Survey, 1989). 2.3 TOPOGRAPHY AND SOILS Most of Orono can be described as gently to steeply rolling with numerous depressions, many of which contain wetlands. Along the shorelines of Lake Minnetonka, the terrain includes steep slopes that sharply grade down to the shoreline, low lying areas just a few feet above lake level, or wetlands that extend away from the main body of water. Elevations generally decrease north to south, with a high elevation of about 1,060 feet above sea level in the northwestern part of the City to the surface elevation of Lake Minnetonka, 930 feet above sea level. There are three major soil associations in the City of Orono. The association in the eastern region of Orono is Lester/Peaty Muck. This association is defined as rolling and hilly medium textured and moderately fine textured soils that developed in glacial till. The western half of Orono consists of the Erin/ Kilkenny/Peaty Muck association; gently undulating to hilly, medium textured and moderately fine textured soils that developed in glacial till. Big Island in Lake Minnetonka (southeastern Orono) consists of the Hayden/Cordova/Peaty Muck association. This soil is nearly level to rolling, medium and moderately fine textured, developed in glacial till. The soils within the City of Orono have generally moderate infiltration rates and create a high to moderate susceptibility to groundwater contamination. The hydrologic soil classification map is shown in Figure 4. The four soil classifications are defined as follows: Group A – These soils have high infiltration rates even when thoroughly wetted. The infiltration rates range from 0.3 to 0.5 inches per hour. These soils consist chiefly of deep, well drained to excessively drained sands and gravel. Group A soils have a high rate of water transmission, therefore resulting in a low runoff potential. Group B – These soils have moderate infiltration rates ranging from 0.15 to 0.30 inches per hour when thoroughly wetted. Group B soils consist of deep moderately well to well drained soils with moderately fine to moderately coarse textures. Group C – These soils have slow infiltration rates ranging from 0.05 to 0.15 inches per hour when thoroughly wetted. Group C have moderately fine to fine texture.