Drainage_and_Flooding_Report-dated_03-10-08

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Mr. Ron Bottoms March 10, 2008 Page 7 of 15 k I o t z associates some new telephone and fiber optic stations on the south side of the street which could restrict the ability to construct improvements on the south side of the street. The City provided Klotz Associates a plan dated 2-21-08 for this location that is aimed at removing a blockage to overland or sheet flow and will be helpful when the street becomes full during heavy rainfall events. Klotz Associates agrees that enhanced sheet flood relief paths are helpful to release waters backing up on streets from overflowing sewers. The drawing the City provided shows that about 94 feet of Catlett Street will be removed at the east end of Catlett and then rebuilt at a lower elevation to provide a sheet flow path for the local drainage system. Two residential driveways will have to be adjusted to account for the changes to the lowered roadway. The City did not indicate any changes to the underground storm sewer system, but increased sewer capacity would reduce the amount of backup surface water which currently sheet flows across the area. The previous embankment on the west edge of Big Island Slough has been cut down somewhat and a small swale exists on the south edge to the ditch. This area could be enlarged to provide some additional flow capacity but during high flow conditions there could be large amounts of flow trying to get through that small area. An easement may also be required to address the path of sheet flow in the restricted area. We feel that the current City plan for this location does have merit and some adjustments could be made to the current plans to make the proposed project as effective as possible. Listed below are some comments to the current City plans: 1. Was a new or enlargement to a storm sewer line investigated for this location that could convey the drainage area flows and not require that the street be removed and constructed and a lower elevation? A new or enlarged storm sewer would still require some work within the street and would require more inlets and curb cuts to make use of the larger or new storm sewer. 2. How was the location and elevation determined for the roadway removal? A review of the proposed grading shows that the revised roadway could still pond up to an elevation of 18.08 which still could pond in the street up to 1.3 feet at the intersection of Rosemary and Catlett. Removing more of the road to lower the ponding elevation could reduce the ponding but will require more excavation and construction costs than currently shown on the plans. Removing 25' more of pavement could reduce the ponding elevation by about 0.3' to 1.0'. What was the target water surface elevation or target house slab elevation? The plans indicate that the slab elevations of the two homes shown on the plan are approximately 20.1 and 20.4. 3. Has there been coordination with the owners of the two driveways to make sure they arc agreeable to the local changes and interim impact to them during construction? 4. Have the grades been checked to make sure that the new proposed grades for the driveways will work for the homeowners and their vehicles compared to the new lower roadway elevation?