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,~- ~ _%~ Plan of Study for City of North Olmsted Phase I by Floyd Browne Group January 4, 2006 complaints was completed as a result of the August 20th storm, there were only two (2) complaints of flooding around the Hawkins Road culvert indicating that extreme flooding levels did not seem evident in this area. Finally, the LeBern Box Culvert under Clague Road (sub-basin A3-3) was rated as having a 2 - 5year storm duration capacity by the ODOT analysis program. This also should be further investigated. However, in this case, the City's wastewater collection maintenance personnel observed the August 20th storm flow through the culvert as they were operating the LeBern pump station. During the storm's high flow the maintenance staff reported the water only raised to about 3.5 feet of depth in the 4 foot high box culvert. There appeared to be additional capacity available through this culvert during the storm. This observation is consistent with other comments by City crews that sanitary sewers flood at the same time storm drains are not running full. Dover Pump Station Drainage The analysis of the Dover drainage area shown in Table 3 indicates that the frequency capacity of the storm sub-basins is in the range of 15-50 year storm frequencies. As in the LeBern drainage system, the storm capacities for the Dover drainage area seemed adequate relative to standard engineering design practices. Two (2) exceptions were found to this pattern. The ditch that runs perpendicular to Sweetbriar Drive (sub-basin B2-2) is only rated fora 5-year storm event but, as in the LeBern system, this was done intentionally to give the system some detention time and adequate steps were taken for a storage area upstream of this restriction. No flooding upstream of this culvert was reported in this area during the August 20th storm even though many complaints were received downstream of this detention culvert. The second area of concern is where the Dover basin empties into the City of Westlake. The restrictive culvert is in Westlake on Dunford Ave. and consists of a 7.3' X 20.0' half round corrugated metal pipe with a "V" notch weir upstream of the opening. This pipe has the capacity of approximately a 20-year storm. Floyd Browne Group performed an informal survey on this culvert, weir and the drainage area immediately upstream of the culvert and found that there seemed to be sufficient storage for the intended detention that Westlake built into the system. It is unknown if any residents flooded along the area immediately upstream of the "V" notch weir culvert as these residents are in Westlake. The flooding complaints were minimal from the North Olmsted residents who would be affected by the failure of this culvert to transport flow into Westlake. Only three (3) North Olmsted residents closest to the culvert experienced flooding. It was concluded that this structure/basin feature had little impact in North Olmsted. North Olmsted Soils Survey Review As a part of this drainage study the soil types of both drainage basins were investigated. The LeBern drainage area is predominantly Condit-Urban and Haskins-Urban land complex soil types. Both these soils are nearly level, poorly drained, and if they are not drained artificially, have a seasonal high water table to the soil surface or 12-30 inches from the surface. The run off potential of both soil types is slow to very slow to ponding. The soil survey report states that buildings in these soil types are better suited without basements. 21