From: Rob GordonTo: Richard Collier (RCollier@mckimcreed.com); Craig NurseyCc: Trent Butler; Jeff Walton; Denise FreundSubject: Eng Review - RiverplaceDate: Wednesday, August 02, 2017 3:19:52 PMAttachments: StormCAD Tables.pdf

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Engineering has reviewed the Riverplace calculations and have the following comments:1. Please organize your output tables similar to how Riverlights is submitted (see attached) –

this breaks the analysis up into spread calcs and HGL calcs, with all required info for reviewincluded with each type of analysis. I do not need the stormCAD profiles, although you arewelcome to provide them.

2. Please carry the HGL analysis into the receiving MH. The only place HGL is specified is onthe spread calc sheets and there are no spread calcs for MH’s, therefore no HGL shown forMH’s. Also, there are a few locations where the HGL matches the rim exactly, some where Imight expect surcharge (Chestnut/Water St) and some areas where I would not expect HGLissues. Please verify these HGL values.

3. The bypass target for bypass flows is not specified on calcs provided. Also, I cannot tell ifbypassed flows are actually being accounted for in the downstream structure. Please clarify.

4. Why do the tables have different flow values? For example GB1 – cfs listed on 10-yrcatchment table is 2.83 cfs, but stormdrain system/HGL table lists flow as 3.46 cfs (providedc, I and area values calculates out closer to 2.83…). There does not appear to be any otherinflows. This type of discrepancy exists throughout the tables. Please clarify.

5. Is a one hour time of concentration value for tower downspout really appropriate? Thatrunoff has to travel a long way within the building, so I can see how it would be greater than5-min but 1 hr seems excessive. Please justify or use a more conservative figure.

6. I’m not sure the DA’s for the inlets near the grace St entrance are correct. The gradingshows a low point along the North side of the crosswalk (near the deck entrance). Incontrast, the DA map indicates GB 7 & 8 are at LP’s. The rim of GB 7 is 7.08, but the rim ofthe adjacent Ex MH is 6.93, so 7 & 8 may pick up some water, but most will just bypass downGrace to CB’s 5 & 17A, which is not consistent with the model. Please either revise themodel or the grading. Perhaps an inlet could be added to EX SDMH 8 if it is located at theLP?

7. The calcs list GI 6 & 7 as “2GI’s”. Are these double inlets? They are not shown as 2GI’s onthe plans.

8. I don’t see where a pipe schedule has ever been submitted. That is fine, but all pipes willhave to be labeled clearly on the grading sheets. There is rim & invert for most structurescalled out, but without a pipe schedule one would assume all pipes are matching inverts (nodrops), which is not consistent with the calcs. Please clarify pipes.

9. Has a profile for Nutt St been prepared? I do not see any grading detail beyond the rimelevations of the structures and the 1 ft contours provided. If this alley is going to bereconstructed, some grading detail has to be provided – preferably a profile.

10. I am just going to make a generic comment to coordinate the drainage structures and pipesbetween the grading sheets, the DA map and the calculations. I found at least a dozendiscrepancies. The Grace St structures were especially hard to follow.

11. I do not see how the bijou park pipe through the wall comment made previously has been

mailto:Rob.Gordon@wilmingtonnc.govmailto:RCollier@mckimcreed.commailto:CNursey@mckimcreed.commailto:Trent.Butler@wilmingtonnc.govmailto:jeff.walton@wilmingtonnc.govmailto:Denise.Freund@wilmingtonnc.gov

addressed. The detail is exactly the same as it was last time.Please note – the addition of these flows to the downstream system created additional flooding inthe water street model. Staff is determining the best way to proceed. Some reconfiguration may benecessary to address this flooding. Please submit a full set of plans calcs and revised forms toEngineering for additional review. Please call or email if there are any questions. Thank you. Robert Gordon, PEPlan Review Engineer City of Wilmington, Engineering Division212 Operations Center DriveWilmington, NC 28412Office: (910) 341-5856 | Fax: (910) 341-5881Email: rob.gordon@wilmingtonnc.govwww.wilmingtonnc.gov

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