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the changes in design guidance as well as reviewing its standards for design of extreme event overflow areas for new and redevelopment projects. 2.2 Topography and Drainage More than 10,000 years ago, Roseville evolved into a series of bluffs and upland hills that defined the adjacent lowlands, a network of drainage ways, lakes and marshes. The topography of northern Ramsey County (and Roseville) is irregular with ground elevations varying approximately 150 feet: from 1,000 feet above Mean Sea Level (MSL) near County Road B2 and Western Avenue to a low of 840 feet above MSL south of Lake McCarrons. Because of its topographic characteristics, the City of Roseville lies at the headwater of three subwatersheds: • The western part of the City drains northerly toward Rice Creek into the Mississippi River, which falls under the jurisdiction of Rice Creek Watershed District; • The southeasterly part of the City drains to the south and east into the Trout Brook interceptor and then to the Mississippi River, a part of the Capitol Region Watershed; and • The east - central and northeast areas drain northeasterly into Lake Owasso which overflows into Grass Lake in Shoreview. This area is a part of the Ramsey Washington Watershed District. In order to better understand how the surface -water system works, the CSWMP divides the city into sub - watershed areas based on surface drainage features and the storm sewer system. The City's sub - watershed areas are shown in Figure 2. The City's storm sewer and overall conveyance system is largely completed at this time. Future changes to the system will primarily be retrofitting to address flooding problems or to incorporate water quality treatment or improvements at the time of redevelopment. This storm sewer system consists of: • 124 miles of pipe, • 4719 catch basins, • 2728 manholes, • 128 ponds, • 13 special features (infiltration, biofiltration, water reuse, ect.) • 739 inlets and outlets, and • six storm -sewer lift stations. The citywide storm sewer map (Figure 3) shows the locations of the majority of these facilities and general direction of flow through the system. [Discuss interactive tool]* *need to discuss the tool some more * ** 2.3 Soils and Geology A large portion of the landscape is dominated by Urban land- Zimmerman complex (859B) and Urban land- Hayden - Kingsley complex (860C), as identified in the Ramsey County Soil Survey. The Natural Resource Conservation Service (MRCS) also classifies soils by the Hydrologic Soil Group (HSG) based on estimates of runoff potential (Figure 5). These are: Hydrologic Soil Group A — Low runoff potential — high infiltration rate Hydrologic Soil Group B — Moderate infiltration rate Hydrologic Soil Group C — Slow infiltration rate Comprehensive Surface Water Management Plan ROSEV120222 City of Roseville Page 4