07-09-18 Drainage and Flooding Committee Meeting

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IML Aprons 1, 2, and 3 Since the method of rehabilitation on each of the aprons is the same, they are grouped here. As part of the investigation of designs for the apron rehabilitation, Civil PEs reached out to Ameriseal of Ohio to discuss other projects that are similar to LaPorte. Out of that discussion, the following was developed to make improvements to the aprons. The block cracks can be sealed using the same specification as the other crack seals on the airport. The depressed areas that hold water will be filled. This will be achieved by spreading a thickened version of the seal coat and screeding off the surface to fill the low spot. In addition, some of the cracks have become very wide. In instances where the crack opening exceeds the maximum gap of the P-605 specification, the crack sealing will use the thermoplastic screed material but with a higher aggregate content to thicken the material so it can be spread into the cracks. Once the low areas are filled and the cracks are sealed, the entire apron is to be seal coated with a sprayed, thin layer of the thermoplastic seal coat — without aggregate — to top the surface. Since the surface already has a good friction component, the addition of a thin surface top should not dramatically lower the friction component of the pavement. 4.2. DRAINAGE REHABILITATION Drainage Ditches and Swales The multiple drainage improvements are proposed to keep the runways and taxiways free from flooding in a 10-year storm event. The proposed improvements include enlarging the existing culverts, improving open drainage ditches, and adding linear detention. The linear detention system will drain within 48 hours or less. The significant proposed improvements include: 1) The expansion of the ditch system draining the northeastern quadrant of the airport. The flowline of the main drainage ditch running along the border of the airport is proposed to drop by 2.5 ft. This allows the runoff to stay off the pavements and lower the hydraulic grade line. This will also function as linear detention and the water level will rise and fall in the same manner as it does in the existing conditions. 2) Replacement and/or enhancement of 12 culvert structures. 3) The expansion of roadside ditch along Farrington Road. The linear detention is proposed at three locations: 1) Ditch Segment 16 (See Exhibit 5) -For approximately 1000 LF, the existing swale will be expanded to 24 ft. bottom width channel, and the average depth is about 2.0 ft. The existing drainage structure 24 will be replaced by a 24" pipe. This pipe functions as a restrictor for this linear detention basin. This detention provides approximately 2.66 ac-ft. of storage. 2) Ditch Segments 7 and 21 - The right bank of the ditch (towards the airport side) will be sloped at 1 % from the channel bottom to the existing ground elevation. The Ditch segments 7, 16, and 21 are proposed to function as linear detention. The Page 125