Please see below Shannon L. Nave, P.E., CFM President Nave Engineering, Inc. Civil Engineers - Hydrologists Texas Registered Engineering Firm F-7457 P.O. Box 759, Weatherford, TX 76086 110 W. Josephine Ave., Weatherford, TX 76086 Off: 817-596-7575, Cell: 817-992-8031 e-mail Shannon@Nave-Eng.com Fax 817-887-3016 From: Bruce Grantham [mailto:bgrantham@gra-ce.net] Sent: Friday, January 21, 2011 11:13 AM To: Nancy Cline; SLN Subject: RE: Plan comments and further discussion Shannon & Nancy: I have attached a plan sheet from our Lindbergh channel project which includes the topo survey. Below are some conceptual comments related to the Bankston flood study: 1. Two FS cross sections are marked on the plan and they confirm that the 100-year water surface elevation is higher than the parking lot high point. 2. Consequently, stormwater that is flowing from east to west overtops this high point in a 100-year storm and flows between the two buildings to the channel. 3. This is consistent with what we have been told by Bankston representatives. 4. Bankston reps have also confirmed that prior to overtopping the high point, stormwater drains south across the parking lot to the channel on the east side of the small building. Eventually, this building floods. 5. As the parking lot conveys flow during a 100-year storm, we do not believe that modeling it as an ineffective flow area is an accurate representation of the field conditions. 1 – 5 It is recognized that the parking lot floods, but the flow there is typically from north to south. Therefore the HEC-RAS model that depicts channel flow from east to west should not consider it as active flow since the flows are perpendicular. Additionally the buildings as well as cars (in the parking lot) along the north bank also give reason not to count the north portion of the overbank as active flow. Therefore the HEC-RAS model was set up with the right (north) overbank as ineffective flow . 6. The plan also shows two stormwater discharge points on the south side of Lindbergh. The eastern point shows four elliptical pipes that convey most of the flow from the southern airport. The western point shows one RCP which conveys a smaller airport drainage area. 7. The FS cross sections are oriented as if the RCP conveys all the airport runoff. In reality, it acts as a small tributary to the main channel with originates at the elliptical pipes. 6 -7 The channel from the west RCP and the east-west channel south and west of the project area are the major concerns to this project. Therefore the channel from the west RCP south to the east-west channel and then west to Midway are what was modeled. The upstream of the channel starting at the west RCP is modeled with 25.0 cfs at X-Section 1755 and 27.09 cfs at X-Section 1631. When the flow from the east pipes join the flow from the west RCP at X-Section 1584 the flow is increased to 385.01. I believe we have this modeled correctly. It seems to us that coming to terms with these conceptual issues is important before a detailed analysis of the hydrology and hydraulics is performed. Shannon, if you would like to discuss these comments, please call my cell at 214-869-8856. Regards, Bruce From: Nancy Cline [mailto:ncline@addisontx.gov] Sent: Wednesday, January 19, 2011 4:28 PM To: Bruce Grantham Subject: FW: Plan comments and further discussion Bruce, I am ok if you want to call him and discuss your concerns. Please call me if you want. Nancy From: SLN [mailto:shannon@nave-eng.com] Sent: Wednesday, January 19, 2011 8:18 AM To: Nancy Cline Cc: Clay Barnett; Bruce Grantham Subject: Re: Plan comments and further discussion Nancy, I would be glad to come, but I am going out off town next week and my schedule is very tight for this week. I can not make it today, but maybe Friday. Is there any way I can get your questions, could we do a conference call, or if it is your consultant that has questions maybe he and I can talk and work this out. Shannon L. Nave, P.E., CFM Nave Engineering, Inc. www.Nave-Eng.com 817-596-7575 (O) 817-992-8031 (C) Sent from my iPhone On Jan 18, 2011, at 5:02 PM, "Nancy Cline" wrote: Shannon, If possible, we would like to discuss some questions on the submittal you made. We are available to meet either tomorrow (Wednesday) afternoon at 2:00 pm or 3:00 pm or on Friday afternoon at 3:00 pm. Do either one of these times work for you? Thank you, Nancy Nancy Straub Cline, P.E. 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