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HomeMy WebLinkAbout007_FloodHazardReport8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 2 As-Built Condition (as of 3/27/2023) In 2022 there was a significant amount of earthwork that took place within the railroad ROW to add siding tracks and stubs for future spur lines. Some of this earthwork filled in the low-laying areas that convey floodwater to the northwest. The Red Wing Drive crossing was removed as part of this work and the existing 36” cast iron railroad culvert was extended approximately 40’ upstream to account for the additional railroad tracks. Figure 3 shows the As-Built conditions topography and site features. Track C Condition At the request of the City of Bozeman, a phase for Track C was added to the modeling. This phase involves only the crossing for the rail spur line (Track C) that is necessary to access Tract 2-B. This crossing is anticipated to be constructed in late 2024 or early 2025 and is proposed as a 144” equivalent CMPA culvert (171”x110”) with a 1’ embedment depth. Intermediate Condition The next phase of the project is to add two more crossings to Mandeville Creek. The two crossings will be for Wheat Drive and Cultivar Street. These two crossings are anticipated to be constructed in 2025 and are proposed as precast concrete box culverts with a span of 18’ and rise of 6’ with embedment depths of 1’. This phase of the project also involves upsizing the existing 36” cast iron culvert at the main rail line. The upsized culvert will need to be equal to the capacity of the upstream culvert (for Track C) and the future upsized downstream culvert at Frontage Road. We anticipate the existing 36” cast iron culvert will be replaced with a 144” equivalent CMPA culvert (171”x110”) with an embedment depth of 1’. The construction of this culvert replacement is anticipated to take place in 2025. We have been coordinating with BNSF about the design of this replacement culvert. Additional rail spurs are proposed to be constructed to the west of Mandeville Creek as well. Figure 4 shows the intermediate condition topography and site features. The intermediate condition assumes the existing culvert at Frontage Road is left as the 36” RCP/CMP. We do not recommend upsizing the existing 36” cast iron culvert at the main rail line before upsizing the Frontage Road culvert because the new overflow path that would be activated (see the Intermediate Condition described in the Hydraulic Analysis section of this report). However, it is ultimately up to BNSF on what they want to decide for replacing their culvert and the associated risks. Final Condition The final phase of the project involves replacing the existing 36” RCP/CMP culvert at Frontage Road. We anticipate this replacement will be a precast concrete box culvert with a span of 12’, rise of 8’, and embedment depth of 1.25’. The Frontage Road culvert is anticipated to be replaced in 2025. We have been coordinating with Montana Department of Transportation about the design of this culvert replacement. Figure 5 shows the final condition topography and site features. All timelines outlined above are subject to change. As of now, all crossing improvements outlined above are being included under a single general permit with the Army Corps of Engineers being a primary driver due to wetland impacts. 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 3 Hydrology Analysis A hydrologic analysis was performed for the 2016 Flood Study. The same flow values were adopted for this study which are 390-cfs for Mandeville Creek and 127-cfs the Farmer’s Canal. The 2016 Flood Study is included in this report as Attachment 1. Hydraulic Analysis The updated Flood Study was performed using The Army Corps of Engineer’s Hydrologic Engineering Center’s River Analysis System (HEC-RAS) version 6.3.1 (USACE, 2022). Mandeville Creek and the surrounding floodplain area was modeled using a steady-state 2D model consisting of a cell mesh, inflow and outflow boundary conditions, and 2D connections for the hydraulic structures. Elevation data for the model was obtained from survey data provided by Allied Engineering, Inc. and LiDAR data obtained from the 2018 City of Bozeman mapping project. The data’s vertical datum is NAVD88. Figure 1 shows the model extents and geometry of the existing conditions. Manning’s n values were obtained by referencing aerial imagery and from “Open-Channel Hydraulics” (Chow 1959). A Manning’s n value of 0.045 was appointed to the main channels describing a winding channel with some weeds and stones. The model was extended far enough downstream so the downstream boundary conditions did not affect the hydraulics in the development area. However, a normal depth boundary condition with a friction slope of 0.004 was used for the East Gallatin River outflow location. Flow hydrograph boundary conditions with constant flow values were used for the inflow locations where Mandeville Creek and the Farmer’s Canal enter the model area. A 12 hour initial conditions time was used to ramp up the flows to increase model stability. A model simulation time of 12 hours was used for all plans and the models were checked to ensure a steady-state condition was met. A Courant controlled time step was selected with a maximum and minimum courant values of 1.0 and 0.4 respectively with a base time step of 1 second. Existing Conditions The existing conditions were modeled using the 2D methodology to compare to the 1D model from the 2016 Flood Study. Figure 2 shows a comparison of the 1D and 2D flood hazard boundaries and WSEs for the existing condition. As depicted in Figure 2, the flood hazard boundary and WSEs of the 1D and 2D model are similar. The 2D model flood hazard boundary will be used as the existing condition flood hazard boundary for the remainder of this study. Where the 1D model ended, the 2D model was extended further downstream to the confluence with the East Gallatin River as well as further to the northwest and eventually to the East Gallatin River. The overflow path that flows along the southern side of the railroad ROW to the northwest from the main track railroad crossing of Mandeville Creek is shown in the 2D model. Approximately 438-cfs of the total 517-cfs is being directed along this overflow path because the culverts at Frontage Road, the main railroad track, and Red Wing Drive are undersized. 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 4 As-Built Condition (as of 3/27/2023) A plan was created with an updated geometry and terrain to reflect the As-Built conditions and the flood hazard boundary was remapped. The resulting flood hazard boundary was the same from the upstream end of the model to within approximately 400-ft of the railroad ROW. In this case, the grading associated with the railroad siding tracks requires backwater to build up more head to overtop to the northwest. This increased WSE causes backwater to extend further upstream and laterally in the adjacent floodplain. The overflow path to the northwest is maintained in this configuration with approximately 423-cfs being directed that way. Figure 3 shows a comparison between the existing condition and the as-built condition flood hazard boundary. Track C Condition A plan was created using the proposed Track C crossing overlaid onto the as-built condition terrain. This was requested by the City of Bozeman to show the flood conditions will only the Track C rail extension in place. Figure 3.5 shows a comparison between Track C and the existing condition flood hazard boundary. The flood hazard boundary for the Track C condition is nearly identical to the as- built condition. This is because the culvert proposed for Track C is capable of passing the 517-cfs flow from the 100-year event. The existing 36” culvert at the main rail line still causes roughly the same backwater scenario seen in the as-built condition. Figure 3.5B shows a comparison at a larger scale between the Track C condition and the as-built condition flood hazard boundary. Intermediate Condition The modeling for this phase of the project was completed using the anticipated culvert sizing and grading discussed in the Project Phasing section. The new crossings upstream of the main rail line in this intermediate condition have minimal impact to the flood hazard extents because each culvert is sized to handle the 517-cfs. However, there is a small backwater area at the Cultivar Street crossing where the flood hazard extent increases due to a localized increase in the WSE. This backwater area extends approximately 400’ upstream of the proposed Cultivar Street crossing. The areas are considered to be ineffective flow areas not providing conveyance. The areas will be impacted by the approved (but not yet constructed) shared use trail. The areas are noted Figure 5 and are considered to be filled as part of future development. Because the areas are considered to be ineffective flow areas, impacts to the BFEs are not anticipated. Figure 4 shows a comparison between the existing conditions flood hazard boundary and this intermediate condition. Figure 4A shows a comparison at a larger scale between existing flood hazard boundary and the intermediate condition. It is important to note that upsizing the main rail line culvert before the Frontage Road culvert creates a new overflow path on north side of the railroad tracks. In previous iterations the northwest overflow path remains on the south side of the railroad tracks until crossing under N 19th Ave and I-90. In this scenario, a large amount of backwater would form just upstream of the existing Frontage Road culvert and would overtop Frontage Road near the intersection with Reeves Road. This new overflow path has the potential to flood existing structures before the flood water reaches the East Gallatin River. Final Condition The final condition will allow the full flow from the 100-year event to reach the East Gallatin River without backwatering upstream of the railroad or the Frontage Road crossing and without activating 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 5 the northwest overflow path. In this configuration, the flood hazard boundary along Mandeville Creek is very similar to the existing condition with the exception of the area immediately upstream of the Cultivar Lane crossing as discussed in the intermediate condition section above. Figure 5 and Figure 5A shows the flood hazard boundary for the final condition. It should be noted that the elevation data used for this updated flood hazard study has been updated since the original flood hazard evaluation took place in 2016. The most recent (year 2018) City of Bozeman LiDAR was used for the current study along with finished design grading for the proposed conditions. Table 1 shows a comparison of water surface elevations at key locations during the 100- year event for the various conditions previously outlined. Table 1. 100-year Event Water Surface Elevations Comparisons (Units = Feet, Datum = NAVD 88) Location* Existing Condition (2016 Flood Study) As-Built Condition (as of 3/27/3023) Track C Condition Intermediate Condition Final Condition Cultivar Lane 4701.9 4701.9 4701.9 4706.2 4706.2 Wheat Drive 4675.0 4675.1 4675.2 4677.1 4677.0 Track C 4670.5 4673.8 4674.0 4673.2 4671.3 Railroad Main Track 4670.5 4673.8 4674.0 4671.8 4668.7 *The WSE for these were taken just upstream of the indicated location Downstream Considerations The section of Mandeville Creek from Frontage Road to the East Gallatin has likely not seen flows above 100-cfs in the history of its current configuration. The existing undersized 36” culverts at the main railroad and Frontage Road currently restrict flows to approximately 94-cfs before remaining flow overtops and follows the northwest overflow path mentioned earlier. Large rain events in June of 2022 and June of 2024 have resulted in localized flooding just upstream of the main railroad within the North Park Development. It’s unclear if the northwest overflow path was activated in these events. The localized flooding occurs because the larger upstream culverts are capable of passing more flow into the site than what the smaller culverts are able to convey from the site. The upstream culverts at Baxter Lane and Interstate 90 include a 60” equivalent CMPA and a 48” equivalent CMPA for Mandeville Creek and Farmers Canal respectively. Figure 7 shows the existing configuration and culvert sizes. The combined capacity of these culverts is approximately 220-cfs before overtopping. The overtopping path at Interstate 90 has not been modeled as part of this evaluation. The full flow rate from the 100-year event is assumed to enter Mandeville Creek within the North Park Development. However, it does appear the overtopping path for the Interstate 90 culverts would likely stay along the west side of Interstate 90 up to the North 19th Avenue interchange. By upsizing the culverts at the main railroad and Frontage Road the downstream section of Mandeville Creek would be subjected to higher possible flow rates than the existing condition. The replacement culverts would be designed to pass the entire 517-cfs from the 100-year event. The culverts at Interstate 90 would likely need to be upsized for flow rates beyond approximately 220-cfs to reach the downstream section of Mandeville Creek. 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 6 The possibility of increased flows to the downstream portion of Mandeville Creek necessitates a more detailed evaluation of impacts to the adjacent properties and structures. Mitigation strategies for the offsite properties just downstream of Frontage Road may be necessary. Exhibit 1 shows a plan and profile of the Mandeville Creek outfall to the East Gallatin River. The overall creek grade is displayed based on the 2018 city of Bozeman LiDAR. The LiDAR data likely represents only the water surface elevation rather than the actual channel bottom. The actual channel bottom has not been conventionally surveyed for the full length. Mandeville Creek has an average profile grade of approximately 1% from the downstream end of the Frontage Road culvert to the confluence with the East Gallatin River. Some shorter sections of channel appear to have average grades closer to 3%. The existing channel likely formed naturally prior to being restricted by the undersized railroad and Frontage Road crossings. It’s unknown when the railroad and Frontage Road culverts were installed. Historic maps from the railroad seem to indicate that a bridge was once used for the Mandeville Creek crossing. Exhibits 2, 3, and 4 show cross sections along Mandeville Creek and compare the 100-year event as- built condition water surface elevation to the final condition water surface elevation. The cross sections within these exhibits also compare the 100-year event water surface elevations to the surrounding topography and estimated finished floor elevations of adjacent structures. The finished floor elevations were estimated from the 2018 City of Bozeman LiDAR contours and dwelling information from Montana Cadastral. The existing structure at 27589 Frontage Road sits approximately 50-ft east of Mandeville Creek. According to Montana Cadastral, the structure has a daylight basement. The basement finished floor elevation is estimated to be roughly 4659-ft from the City LiDAR data. The adjacent water surface elevation from the 100-year event of the final condition is estimated to be 4657.87-ft, this is approximately 1.87-ft higher than the as-built condition. The water surface elevation from the 100- year event is less than 2-feet below the estimated basement finished floor elevation. Because of the relative elevations, the existing structure at 27589 Frontage Road is at risk under the final condition of this updated flood hazard study. If the adjacent existing stream bank was to erode and allow the channel to migrate it could result in damage to the structure. The existing structure is located on an outside bend of the creek which raises the likelihood of erosion/channel migration. The existing bank should be evaluated in more detail to determine if mitigation is recommended. A mitigation strategy could involve armoring the existing channel/banks. Any work on the stream bed or banks would require stream permitting. The method of stabilization would need to be evaluated and coordinated with the conservation district and other reviewing entities. Before any of these mitigation strategies could take place, the landowner would need to be amenable. We have had preliminary conversations with the landowner at 27589 Frontage Road and they are open to the possibility of upsizing the culverts and mitigation. The existing structures on the property at 27489 Frontage Road generally sit a couple feet higher in elevation and further from the creek than the residence at 27589 Frontage Road. The structures consist of a detached garage and single-family home with a basement based on Montana Cadastral. The basement finished floor elevation was estimated to be 4658-ft from the City LiDAR data. The finished floor elevation of the basement would need to be verified by a survey. This estimated finished floor elevation is approximately 1.2-ft above the final condition 100-year water surface elevation. The structure is approximately 60-ft horizontally from the edge of the flood hazard in this location. Ground 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 7 elevations around the structure are about 2-feet higher than the opposite side of the creek which do reduce the risk of flooding. However, recommended floor elevations are a minimum of 2-feet above estimated flood elevations. No other structures exist within 100-ft of the Mandeville Creek outfall. While the risks for the property on the west side of the creek seem relatively smaller, we still recommend further evaluation to better determine risks and recommend any mitigation strategies. There are three notable locations where the final condition flood hazard from the 100-year event for Mandeville Creek extend beyond the existing condition flood hazard extents. These three areas also extend beyond the effective boundary for the East Gallatin River. Figure 5B and Figure 5C show the final condition flood hazard boundary for Mandeville Creek compared to the effective FEMA flood hazard zones for the East Gallatin River. Two areas are just upstream of the confluence with the East Gallatin River, on the east and west sides of Mandeville Creek where a lower bench is visible from the topography. The third area is across the East Gallatin River on a local high point surrounded by floodway. An additional Figure 6 represents a delineation of the effective East Gallatin River base flood elevations with 2018 LiDAR from the COB. The effective flood plain boundary utilized photogrammetry from 2001 which we anticipate may not represent the true ground topography as accurately as the 2018 LiDAR. In general, LiDAR does a better job providing a “bare earth” surface whereas photogrammetry may be more impacted by vegetation. Figure 6 shows that the areas impacted by the Mandeville Creek flood hazard boundary may also already be affected by the East Gallatin River. The areas are generally relatively low benches located adjacent to the East Gallatin River and Mandeville Creek. These areas are already at risk of flooding but may have an increased risk with increased flows associated with upsizing the existing Mandeville Creek Crossings. Prior to any development in these areas, more detailed delineations and studies should be completed whether the Mandeville Creek culverts are upsized or not. In summary, two structures directly downstream of the Frontage Road and adjacent to Mandeville Creek may be at increased risk of flood damage. The cross sections described above provide good representations of estimated flood elevations, adjacent grades, and estimated floor elevations. The homes and adjacent grades are above the estimated flood elevations; however, if stream banks were to erode or migrate, the east structure in particular may be at risk of damage. Because basement elevations are within 2-feet of the estimated flood elevations, and in particular the location of the home on the east side of the creek on an outside bend, additional work should be completed to better understand the risks and mitigation alternatives. Additional ground survey of the channel may provide more accurate elevations as the flood hazard model for this stretch is based on 2018 LiDAR from the COB. 8/23/2024 Allied Engineering Services, Inc. Flood Hazard Evaluation Page 8 Attachments: 1. Figure 1 – 2D Model Set Up – Existing Conditions 2. Figure 2 – Existing Conditions – 1D/2D Comparison 3. Figure 3 – As-Built/Existing Conditions Comparison 4. Figure 3.5 – Track C Condition Comparison 5. Figure 3.5B – Track C Condition Comparison Overall 6. Figure 4 – Intermediate/Existing Conditions Comparison 7. Figure 4A – Intermediate/Existing Condition Comparison Overall 8. Figure 5 – Final/Existing Conditions Comparison 9. Figure 5A – Final/Existing Conditions Comparison Overall 10. Figure 5B – Final Condition Comparison to FEMA Flood Hazard Zones 11. Figure 5C – Final Condition Comparison to FEMA Flood Hazard Zones 12. Figure 6 – East Gallatin Effective Boundary vs 2018 COB LiDAR Delineation 13. Figure 7 – Vicinity Map & Existing Conditions 14. Exhibit 1 – Mandeville Creek Plan & Profile 15. Exhibits 2, 3, and 4 – Mandeville Creek Cross Sections REFERENCES Allied Engineering Services Inc. (2016). Flood Hazard Evaluation for Mandeville Creek. Bozeman, Montana. Chow, V. T. (1959). Open-Channel Hydraulics. Caldwell: The Blackburn Press. US Army Corps of Engineers. (2022). River Analysis System (HEC-RAS) V6.3.1. Davis, California. Federal Emergency Management Agency (2021). Flood Insurance Study: Gallatin County, Montana and Incorporated Areas. Volume 1 of 4. P:\2014\14-167 North Park\05 Design\H & H\2023 Flood Study\Report Update 2024\Working Doc\North Park Flood Hazard Evaluation.docx FIGURE: 1DRAWN BY: TWCDATE: 5/17/2023PROJECT: 14-167³0 540 1,080 1,620Feet NORTH PARK2D MODEL SET UP - EX. CONDITIONSBOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 1 - Model Set Up.mxd1 inch = 900 feet Mandeville Creek Legend 2D Model Area Boundary Condition Lines (Inflow/Outflow Locations) 2D Connections (Hydraulic Structure Locations) 2D Existing Conditions - 1% AC Flood Hazard Boundary East Gallatin River 466846924666470846984676470046954690471547104680 472046704730472547004685466546604665474547404730472546754670466546554650 47254720 470547004680 4655 464547304720466546704660 47354735473047304725472547154695 4675 4670466546604655 4655473046604680.44709.84707.84706.24702.947004697.54694.64691.54686.74683.54715.74672.44669.84675.5FIGURE: 2DRAWN BY: TWCDATE: 5/17/2023PROJECT: 14-167³0 240 480 720Feet NORTH PARKEX. CONDITIONS - 1D/2D COMPARISON BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 1 - Existing Conditions.mxd1 inch = 400 feet Mandeville Creek Legend 1D Cross Sections 2016 Flood Study 1D - 1% AC Flood Hazard Boundary 2D WSE Contours (2-ft Contour Interval) 2023 Flood Study 2D - 1% AC Flood Hazard Boundary Northwest Overflow Path Frontage Road Main Railroad Track Red Wing Drive 471547104690468547054700469546604655474547404735473047254670466546654660472047154675467046554650 472546704715 46954680 467046554650 47354730472547304730473047254725468046704665466546604660 46554730FIGURE: 3DRAWN BY: TWCDATE: 5/17/2023PROJECT: 14-167³0 240 480 720Feet NORTH PARKAS-BUILT/EX. COND. COMPARISON BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 3 - As-Built Conditions.mxd1 inch = 400 feet Mandeville Creek Legend Siding Tracks Existing Conditions - 1% AC Flood Hazard Boundary As-Built (3/27/2023) - 1% AC Flood Hazard Boundary Northwest Overflow Path Frontage Road Main Railroad Track Red Wing Drive crossing removed and railroad culvert extended 4715471046904685470547004695467046654660465547454740473547304725472047154675467046554650 472546654715 46954680 4660472046704670467046554645 47304735473547254725473047304730472046954680467046654665466546604660465046554730FIGURE: 3.5DRAWN BY: EJFDATE: 7/16/2024PROJECT: 14-167³0 240 480 720Feet NORTH PARKTRACK C CONDITION COMPARISON BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 3.5 - Track C Condition.mxd1 inch = 400 feet Mandeville Creek Legend Siding Tracks with Track C Existing Conditions - 1% AC Flood Hazard Boundary Track C Condition - 1% AC Flood Hazard Boundary Northwest Overflow Path Frontage Road Main Railroad Track Red Wing Drive crossing removed and railroad culvert extended Track C with CMPA Culvert FIGURE: 3.5BDRAWN BY: EJFDATE: 7/16/2024PROJECT: 14-167³0 540 1,080 1,620Feet NORTH PARKTRACK C COND. COMPARISON OVERALLBOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 3.5B - Track C Condition Comparison Overall.mxd1 inch = 900 feet Mandeville Creek Legend Siding Tracks with Track C Boundary Condition Lines (Inflow/Outflow Locations) 2D Model Area As-Built (3/27/2023) - 1% AC Flood Hazard Boundary Track C Condition - 1% AC Flood Hazard Boundary East Gallatin River Track C 471547104705469046854670466547454740473546754670 47304725467046654665466046554650 4725 4720 4700468046754715 46954680465546604645 472047054680 46704655 47354730472547304730473047254725471546954670467046654665 46604660 46554730FIGURE: 4DRAWN BY: TWCDATE: 5/23/2023PROJECT: 14-167³0 240 480 720Feet NORTH PARKINTERMEDIATE COND. COMPARISON BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 4 - Intermediate Condition.mxd1 inch = 400 feet Legend Intermediate Condition Features Existing Conditions - 1% AC Flood Hazard Boundary Intermeditate Condition - 1% AC Flood Hazard Boundary Mandeville Creek Exisintg FrontageRoad culvert Main Railroad Track Red Wing Drive crossingremoved and railroad culvertreplaced with box culvert Cultivar LaneWheat Drive Additional railroad tracks Track C with box culvert Northwest overflowpath is eliminated New flow path createdon north side of railroad ROW FIGURE: 4ADRAWN BY: EJFDATE: 7/16/2024PROJECT: 14-167³0 540 1,080 1,620Feet NORTH PARKINTERMEDIATE COND. COMP. OVERALLBOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 4A - Intermediate Condition Comparison Overall.mxd1 inch = 900 feet Mandeville Creek Legend Final Condition Features Boundary Condition Lines (Inflow/Outflow Locations) 2D Model Area 2D Existing Conditions - 1% AC Flood Hazard Boundary Intermediate Condition - 1% AC Flood Hazard Boundary East Gallatin River 471547104705469046854670466547454740473546754670 47304725467046654665466046554650 4725 4720 4700467546804715 46954680465546604645 47204680 46704655 47354730472547304730473047254725471546954690467046654665 46604660 46554730FIGURE: 5DRAWN BY: TWCDATE: 6/20/2023PROJECT: 14-167³0 240 480 720Feet NORTH PARKFINAL/EX. COND. COMPARISON BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 5 - Final Condition.mxd1 inch = 400 feet Mandeville Creek Legend Final Condition Features Shared Use Trail Existing Conditions - 1% AC Flood Hazard Boundary Final Condition - 1% AC Flood Hazard Boundary Frontage Road culvertreplaced with box culvert Main Railroad Track Red Wing Drive crossingremoved and railroad culvertreplaced with box culvert Cultivar Lane Wheat Drive Additional railroad tracks Northwest overflowpath is eliminated Track C with box culvert Area of ineffective flowand shallow flooding,anticipated impact from approvedshared use trail location Area of ineffective flowand shallow flooding Shared use trail FIGURE: 5ADRAWN BY: EJFDATE: 7/17/2024PROJECT: 14-167³0 540 1,080 1,620Feet NORTH PARKFINAL COND. COMPARISON OVERALLBOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 5A - Final Condition Comparison Overall.mxd1 inch = 900 feet Mandeville Creek Legend Final Condition Features Boundary Condition Lines (Inflow/Outflow Locations) 2D Model Area 2D Existing Conditions - 1% AC Flood Hazard Boundary Final Condition - 1% AC Flood Hazard Boundary East Gallatin River 4660465546454640 468046754680467046754670467546704650464546654670464546504655 46554655468546854680468546754665466546654670467046804650 FIGURE: 5BDRAWN BY: EJFDATE: 7/31/2024PROJECT: 14-167³0 120 240 360Feet NORTH PARKFINAL COND. COMPARISON TO FEMA BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 5B - Final Condition Comparison to FEMA Zones.mxd1 inch = 200 feet MandevilleCreekFrontage Road culvertreplaced with box culvert Main Railroad Track Red Wing Drive crossingremoved and railroad culvertreplaced with CMPA culvert Wheat Drive Additional railroad tracks Northwest overflowpath is eliminated Track C with CMPA culvert Shared use trail Legend Final Condition Features Shared Use Trail Existing Conditions - 1% AC Flood Hazard Boundary Final Condition - 1% AC Flood Hazard Boundary Flood Hazard Zones 0.2% Annual Chance Flood Hazard Regulatory Floodway 1% Annual Chance Flood Hazard 46654655 467546654670466546604650467046704670466546704655465046504650FIGURE: 5CDRAWN BY: EJFDATE: 7/31/2024PROJECT: 14-167³0 40 80 120Feet NORTH PARKFINAL COND. COMPARISON TO FEMA BOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Figure 5C - Final Condition Comparison to FEMA Zones.mxd1 inch = 80 feet MandevilleCreek Frontage Road culvertreplaced with box culvert Main Railroad Track Legend Final Condition Features Shared Use Trail Existing Conditions - 1% AC Flood Hazard Boundary Final Condition - 1% AC Flood Hazard Boundary Flood Hazard Zones 0.2% Annual Chance Flood Hazard Regulatory Floodway 1% Annual Chance Flood Hazard íííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííí íííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííí íííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííííí46504648465046504659465846574654465546534652465046694665466446634651464946564648467146664669466846664651465046474646 46474646466846674662466146604674467346664675467046694667 467046694667465146504654 46674665466646644665465346514650 46494649464846484653FIGURE: 6DRAWN BY: EJFDATE: 8/23/2024PROJECT: 14-167³0 40 80 120Feet NORTH PARKEAST GALLATIN EFFECTIVE BOUNDARY VS2018 COB LiDAR DELINEATIONBOZEMAN, MT P:\2014\14-167 North Park\08 ArcGIS\2023 - Flood Study\Zoomed In\Possible Revised East Gallatin 100-Year.mxd1 inch = 80 feet MandevilleCreek Legend Final Condition Features 1-ft Contours from 2018 COB LiDAR East Gallatin 100-year BFE Delineated with2018 COB LiDAR Terrain ííííííííííííBase Flood Elevation line and value FEMA SFHA Floodway 1% Annual Chance Flood Hazard 0.2% Annual Chance Flood Hazard Frontage Road culvertreplaced with box culvert East Gallatin River The intent of this figure is to compare the effective flood hazard boundary to the delineated boundarybased on current topography. The effective study was based on topography generated in 2001.The data used to complete this delineation is based on 2018 COB LiDAR which we anticipate producesa more accurate "bare earth" surface compared to the 2001 data. This exhibit is conceptual only aselevations have not been verified by ground survey. It does indicate that areas impacted by MandevilleCreek may also already be impacted by the East Gallatin River.