Shannon, We are almost done reviewing your last submittal. It seems each time you make a submittal, we have more questions. We are trying to figure out how to reach a point where the back and forth ends. It may be Wed. next week but we want to give you something that helps resolve the ongoing questions. Thank you, Nancy From: SLN [mailto:shannon@nave-eng.com] Sent: Thursday, February 03, 2011 6:03 PM To: Bruce Grantham; Nancy Cline; Clay Barnett; Mathew Thomas Cc: Lea Dunn Subject: RE: Plan comments and further discussion That would be great. Thanks, and stay warm. sln 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: Thursday, February 03, 2011 5:58 PM To: SLN; Nancy Cline; Clay Barnett; Mathew Thomas Cc: Lea Dunn Subject: RE: Plan comments and further discussion Shannon: I’m sorry to have missed your recent calls but this week which has been a disrupted one for us due to the weather. I’m tied up tomorrow morning but hope to have time to call you tomorrow afternoon. Would 3 p.m. be a good time? Regards, Bruce From: SLN [mailto:shannon@nave-eng.com] Sent: Thursday, February 03, 2011 5:39 PM To: Nancy Cline; Bruce Grantham; Clay Barnett; Mathew Thomas Cc: Lea Dunn Subject: RE: Plan comments and further discussion All, I haven’t heard back from you and my Friday February 4th trip to Dallas has been canceled. I recommend the following course of action. 1. Bruce please give me a call at your earliest convenience 817-992-8031. Perhaps we can find some common ground. 2. My meeting for Dallas will take place next week. If Bruce and I can’t see eye to eye over the phone I think we will need to get together. Perhapse the same day I am in Dallas. Thanks, sln 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: Nancy Cline [mailto:ncline@addisontx.gov] Sent: Tuesday, February 01, 2011 3:55 PM To: SLN; Bruce Grantham; Clay Barnett; Mathew Thomas Cc: Lea Dunn Subject: RE: Plan comments and further discussion Shannon, I hope your trip went well last week. It appears there are some disagreements on the analysis of the modeling of the impact of the proposed fill for the Bankston site. Would you prefer to meet (this Thursday at 3:00 pm works for me and I can check with the others) or would you rather we send a formal, specific comment letter detailing our requirements on the modeling for this site? It does not seem productive at this time to continue the e-mailing back and forth. Please let me know your preference. Thank you, Nancy Cline From: SLN [mailto:shannon@nave-eng.com] Sent: Sunday, January 23, 2011 10:07 AM To: Bruce Grantham; Nancy Cline; Clay Barnett; Mathew Thomas Cc: Molly Pierson Subject: RE: Plan comments and further discussion Bruce, I understand this stream and its flooding are a particularly sensitive subject with City of Addison. I appreciate the care in which you have reviewed my work. I hope the following will convey the thought processes that went into modeling the stream as I have. I contend that the area of the Bankston parking lot is flooded on a regular basis. There are two primary flow paths in the area 1) the main channel which flows east to west from the east Lindbergh culverts to Midway and 2) north to south from the west Lindbergh culvert to the main channel. I believe that as flow and depth increases in the channel, there is a back water effect from the main channel that inundates the Bankston parking lot. There may be some minimal north-south flow in the parking lot when the 100-year flood event is peaking, but I contend that the only truly active conveyance in the parking lot and just south of it is from the east to the west in the main channel. During the 100-year storm event peak, the majority of the north-south flow would transpire in the north-south channel east of the parking lot. Further the buildings along the right (north) overbank, along with debris, vehicles, and shallow ponding conditions in the right overbank limits the active conveyance of the right overbank in either westerly or southerly direction in the parking lot and westerly west of the parking lot. In short, when the channel is experiencing the 100-year peak flow the right overbank is acting as a pond. During the 100-year storm event the area east of the Bankston parking lot is currently inundated. This is due to the backwater of the main channel. This is not helped by the fact that Bankston parking lot acts more like a pond that means of conveyance during the 100-year storm event. I believe the parking lot is inundated before the 100-year peak arrives and has become an area of ineffective flow when the 100-year storm event does arrive. Therefore there the filling of the parking lot would cause no loss of conveyance during the peak of the 100-year storm event and the loss of valley storage, in this case, would be very, very minor. If the volume were larger, or had a more controlled release and or held up, to one degree or another, the entire flow in the basin I could see how that might affect the flow downstream, but not at the parking lot or east of the parking lot. However, the area of ineffective flow (and volume of proposed fill) is small, is off channel, and really is a condition of backwater rather than detention. Therefore I see the filing of the parking lot as not effecting flow or water surface. With this in mind I don’t believe the loss of the valley storage at Bankston effects the west or east culverts or channels east of Bankston since there is no loss of conveyance. The stream itself is in a subcritical flow regime so the filling does not impact downstream. Because the area of proposed fill is currently inundated before the 100-year peak arrives it is filled with water at the time of the peak and its filling with another material should have little to know impact on the downstream flows. The proposed fill will not, in my mind, impact either upstream or downstream. If I had a larger basin to model with an area of minimal incoming lateral flows beside and partly through an area of ineffective flow, I would model as I have this one, with the exception that if it was over 200 ac I would Unit Hydrograph method to generate the peak flows rather than the Rational Method. I don’t believe the use of the Unit Hydrograph method on a basin less than 200 ac is well founded or in this case well suited. I also don’t believe a 2-D model would provide a level accuracy that would compensate for its cost. There is a law of diminishing returns that provides that doubling, tripling, or quadrupling time and cost does not double the level of accuracy. I don’t expect the filling of the Bankston parking lot to have any impact, either in a model or in the field. I don’t believe that a 2-D model will show a much different answer. If the right overbank had been free of buildings, not been a parking lot of cars which impede flow, and or had deeper depths it would not be an area of ineffective flow. However, the building on the west property line prevents water from flow west. The building on the south property line limits the flow to the south. And the south building coupled with the west building and the other downstream buildings prevents westerly flow in the right overbank. This, together with a parking lot that is routinely packed tight with cars and flow depths of less than a foot indicates to me an area of ineffective flow. I believe the cross sections should run north to south as the flow is in the east to west direction. The existing parking lot is an area of inundation, but also ineffective flow. The area is small and filled with water before the peak 100-year discharge arrives. Therefore I believe I have modeled the pre- and post project correctly and the proposed filling of the parking lot will have no describable impact on the adjacent property owners. I am sorry but I am leaving after I send this e-mail. I hope it was some small help into conveying my thoughts and modeling practices in this case. Thank you, sln 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: Saturday, January 22, 2011 3:39 PM To: SLN; Nancy Cline; Clay Barnett; Mathew Thomas Cc: Molly Pierson Subject: RE: Plan comments and further discussion Shannon: Unfortunately, I missed your call yesterday. However, I have made some additional comments below in black that may help to clarify our respective points of view. If you have an opportunity to respond via e-mail, I will talk to Nancy while you are out of town next week. Regards, Bruce From: SLN [mailto:shannon@nave-eng.com] Sent: Friday, January 21, 2011 3:45 PM To: Bruce Grantham; Nancy Cline; Clay Barnett; Mathew Thomas Subject: RE: Plan comments and further discussion 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 . · Your position is that the sheet flow in the parking lot, which is primarily north-south, should dictate the orientation of the main channel cross sections. · Our position is that the parking lot is part of the channel overbank; consequently, the cross sections should be orientated at right angles to the main east-west channel flow starting at the four elliptical pipes under Lindbergh to the east. · Your position is that the east-west 100-year flow that overtops the north-south parking lot high point and spills between the two buildings into the channel can be ignored because the parking lot slopes from north to south, and the buildings and cars in the parking lot completely block the flow. · Our position is that the parking lot flow is only north-south until the high point (which acts as a weir) is overtopped during the 100-year storm, at which time, the flow is west across the parking lot and south between the two buildings. We would also contend that parked cars do not completely block the channel 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. · Your major concerns are the 24” RCP (25 cfs) and the main channel west of and along the south Bankston property line. As a result, your position is that a wall can be constructed along the east and south Bankston property lines under proposed conditions with no impact on the 100-year water surface elevation anywhere. · Our major concern is that the existing condition model represent actual field conditions which include the primary flow (300+cfs) originating at the four elliptical pipes to the east, valley storage occurring on and east of the parking lot prior to the high point being overtopped, and east-west flow across the parking once it is. 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. I’m curious if you were dealing with a similar situation to Bankston on a much larger scale (add zeros to the respective flows), like the Rowlett Creek hydraulic model that our team in currently working on for Garland, would you take the same approach? Another way to think about Bankston is to visualize how the flow would be represented if it were modeled in 2D. What are your thoughts in this regard, and would you still block off the whole Bankston property to the 100-year flow? 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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