Drainage_and_Flooding_Final_Report-dated_06-16-2008

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li June 16, 2008 P,age 3 of 6 klutz 1,'11 associates performance of North H Street system. Table I shows the comparison of Hydraulic Grade Line (HGL) difference from the existing and proposed Alternative 1. There will be adverse affect along North H Street. Table I shows LiDAR elevations and Hydraulic Grade Line elevations. Table I shows that at a 10 year storm event, the system will be filled to capacity and ponding will occur. Table 4 shows the pipe sizes and cost estimates for the 5-, 10-, 25-, 50-, 100-year storms that will lower the Hydraulic Grade Line the most without upsizing any part of North H Street. Alternative 1, while helpful, will be able to convey the sheet flow from a 5 year storm event. This alternative does not meet our goal and is therefore not recommended. MMMMIFV37�� Alternative 2 requires placing inlets at the entrance of the park to collect the sheet flow from a larger storm event and directing the flow with storm sewer pipes to the storm sewer system in North H Street and placing a new parallel system on the north side of the street to handle the additional flow (see Exhibit 6). This alternative will add flow to the existing storm sewer system in North H Street and affect the current system in place. However, a parallel system is sized to have no adverse effect. The systems will be connected to North H Street with modifications downstream of the connection to accommodate the additional flow. A parallel system in combination with the existing system will be adequate to accommodate the additional flow. Alternative 2 will have inlets and manholes at the entrance of the park and in the park that will drain into a storm sewer pipe system and connect to North H Street. The existing Hydraulic Grade Line is above the Critical Elevation for the larger storm events (see Table 2). A Hydraulic, Grade Line comparison is shown in Table 2. Calculations were done to estimate the needed capacity of North H Street system that would handle the additional flows. Alternative 2 was designed to not have any adverse effects and have the saint or lower Hydraulic Grade Line along North H Street as the existing system that is in place now. Table 4 shows the pipe sizes and cost estimates required for the 5-,. 10-, 25-, 50-, 100- year storms. The existing system drains both North H Street and Underwood Street and it was not designed to handle the 100 year storm event. Alternative 2 will handle Creekniont Subdivision Section 2 flow for the 100-year event and also have positive benefits for both North H Street and Underwood Street. Alternative 2 will require HCFCD review and approval since new outfall would be required. Right -of -Way (ROW) or easement will be needed for this alternative and the costs for the easement or ROW is not included in the cost estimate. There are several properties that could provide a reasonable route to North H Street.