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elevation, water surface elevation, and overflow rate for existing conditions at each of the four <br />study points. <br />Table 5 Farrington Drive Water Surface Elevations Existing Conditions <br />Study <br />Point <br />Road <br />Elevation <br />WSE <br />100-yr <br />50-yr <br />25-yr <br />10-yr <br />5-yr <br />2-yr <br />1 <br />21.81 <br />22.22 <br />22.19 <br />22.14 <br />22.04 <br />21.91 <br />21.60 <br />2 <br />20.61 <br />21.17 <br />21.14 <br />21.10 <br />21.04 <br />20.97 <br />20.60 <br />3 <br />20.79 <br />20.86 <br />20.77 <br />20.71 <br />20.59 <br />20.49 <br />20.04 <br />4 <br />19.75 <br />20.39 <br />20.18 <br />20.14 <br />20.02 <br />19.95 <br />19.43 <br />Study <br />Point <br />Road <br />Elevation <br />Difference (WSE <br />- Road El.) [ft] <br />100-yr <br />50-yr 25-yr <br />10-yr 5-yr <br />2-yr <br />1 <br />2 <br />3 <br />21.81 <br />20.61 <br />20.79 <br />-0.02 <br />-0.08 <br />� <br />-0.20 <br />-0.30 <br />021 <br />-0 02 <br />-0.75 <br />4 <br />19.75 <br />0.32 <br />Table 6 Farrington Drive Overflow Rates Existing Conditions <br />Study <br />Overflow Rate (cfs) <br />Point <br />100-yr <br />50-yr <br />25-yr <br />10-yr <br />5-yr <br />2-yr <br />1 <br />14.41 <br />10.39 <br />6.13 <br />1.93 <br />0.17 <br />0.00 <br />2 <br />36.28 <br />30.36 <br />24.47 <br />17.32 <br />10.76 <br />0.00 <br />3 <br />0.07 <br />0.00 <br />0.00 <br />0.00 <br />0.00 <br />0.00 <br />4 <br />35.37 <br />8.29 <br />5.20 <br />2.16 <br />0.82 <br />0.00 <br />Total: <br />86.12 <br />49.04 <br />35.80 <br />21.41 <br />11.75 <br />0.00 <br />Table 5 indicates the overtopping of roadside ditch along Farrington Drive at 5-year storm event, <br />and the maximum depth is about 0.64 ft. near Creek View Drive. The City of La Porte design <br />standards require the neighborhood storm sewer system to maintain an HGL below the street gutter <br />elevation during the 5-year storm event. However, this is beyond the scope of this report and HT&J <br />did not evaluate the neighborhood storm sewer system. <br />A total of approximately 86 cfs of sheet flow is introduced to the neighborhood during the 100-year <br />storm event, and approximately 12 cfs is introduced during the 5-year storm. This likely results in <br />roadway conveyance during this storm event. Total sheet flow introduced will result in an increase <br />flooding in the neighborhood, but the extent is not uniform throughout. The resulting additional <br />flooding depth varies from 0.07 ft. to 0.64 ft. in the existing conditions. We expect the <br />neighborhood storm sewer system reaches its capacity when this additional sheet flow is <br />introduced. Thus increasing the overall sheet flow depth within the neighborhood. <br />La Porte Municipal Airport - Offsite Drainage Analysis <br />HT&J, LLC, January 2018 Page 12 <br />