Drainage_and_Flooding_Report-dated_03-10-08

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Mr. Ron Bottoms March 10, 2008 Page 10 of 15 kIotz��/jassociate5 good to hydraulically evaluate connecting both storm sewer systems to see what benefits might be derived by the connection. 2. The plans show utilities in the area when the outfall pipes arc proposed. Will utility adjustments to be needed to 12" water line, SBC line, electrical line or other utilities at the two new proposed outfalls? 3. The plans show a new junction box, near the existing 60" and 36" outfalls, to divert the flows from the north more directly into the basin. We discussed the possibility of using HDPE pipe in the area that is not under the pavement and also placing a weir type structure in the new junction box to force low flows into the basin. Could these two items be considered for the project to make it easier and more economical to construct and to make more use of the detention basin volumes? Recommend adding rip rap to the end of both new outfall pipes for this project to reduce erosion potential. Should the pipc(s) be extended to go more fully into the detention basin? 4. The proposed outfall could be directed at a 30 to 45 degree angle (not 90 degrees as currently shown on the plans) from the road into the basin to make the flow transition from the storm sewer into the basin easier and thereby reducing the HGL of the system. 5. A curb cut could be provided from the low spot(s) of the road to allow ponded flows to get off of the road and into the detention basin or ditch easier, thereby reducing the ponding depth in the roadway. However, the sidewalk elevation would require adjustment to provide the desired sheet flow path. Appropriate erosion control measures would also need to be included in the improvements. The project as currently designed by the City may not produce the desired reduction in ponding depths. It is our opinion that an overland or sheet flow path is needed to drain the collective areas from Mesquite Street south. Recommend that curb cuts and overland sheet flow paths be constructed from Driftwood into the outfall ditch and another overland sheet flow path be constructed from Driftwood into the detention pond to the east. Both of these two overland or sheet flow paths should help to drain the street easier during major rainfall events and could be constructed today with minimal cost. Other more expensive options exist to the drainage and to address sheet flow or overland flow include: 1.) including an above ground sheet flow path along the west edge of Driftwood, adjacent to the roadway, to the outfall ditch, 2.) lowering a portion of Driftwood to the outfall ditch or by 3.) adding in a larger pipe from Mesquite Street to the outfall ditch or to the detention basin. Each of these other options are more expensive and would require more easements. Recommend that further evaluation be prepared of these other options. Coordination with HCFCD will be required if a new outfall pipe is constructcd. Short Term Drainage Project 4.) Fleetwood Drive Qut all Pipe Upa•izin Fleetwood Drive is located near Driftwood Drive (see Exhibit 9). The City has informed Klotz Associates about a city project for upsizing the outfall of Fleetwood Drive. Currently the outfall pipe is a 60 inch pipe and serves an area of approximately 120 acres.