COAL CREEK FLOODPLAIN MAPPING

Transcription

1 COAL CREEK FLOODPLAIN MAPPING 51-3 rd Ave., Box 19 Fernie, BC VB 1M FINAL REPORT 214 October 16 (Reissued 216 February 25) NHC Project No.: 3372

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4 Executive Summary Coal Creek is a steep mountain stream with headwaters originating in the Fernie basin of the Rocky Mountains. It flows predominately east-west towards the Elk River at the. A large flood event occurred in 1995 which caused overbank flooding, channel shifting, bank erosion, coarse sediment deposition, and damage to private and public property. Brewery Creek is a small seasonal stream that drains into Coal Creek which has been reported to flood along with Coal Creek. To provide guidelines for development, the City is interested in identifying flood hazards and developing floodplain mapping within its boundaries. Flood hazards include flooding, bank erosion and channel migration, bed lowering or degradation, and avulsion or high velocity overbank flows; any of which could lead to damage to buildings, bridges, pipes or infrastructure. The Coal Creek active fan area which includes relic side channels and possible channel migration/avulsion points are identified through a review of historical air and satellite photographs and Lidar data collected by Focus Corporation (Cranbrook) in 28 and the in 214. Hydrologic estimates of the 2-year instantaneous design flow using the rational method are 79.7 m 3 /s and 3.92 m 3 /s for Coal Creek and Brewery Creek, respectively. The estimates account for a % increase for climate change (APEGBC, 212). Floodplain mapping is developed for Coal Creek using one-dimensional (1D) hydraulic modeling (HEC-RAS). Model channel geometry is developed from bathymetric survey data of 48 cross-sections collected by Focus Corporation (Cranbrook) in May 214, Lidar data and supplemental topographic data collected by NHC in June 214. Approximated 2-year flood depths are also provided for Brewery Creek. 2-year estimated inundation extents and depths are provided on the floodplain mapping for Coal and Brewery Creek. A.6 m freeboard allowance for Coal Creek is applied to account for uncertainties in the discharge estimates, the potential to raise water levels from log jams, sediment deposition, and the fluctuation in water surface levels due to large velocity heads. For Brewery Creek, a.3 m freeboard is applied. In the Mountainview neighbourhood the combined Elk River and Coal Creek floodplain mapping extents incorporate NHC 26 Elk River floodplain mapping. Flood construction levels (FCLs) are mapped along with the 2-year floodplain boundary. The floodplain and FCLs are based on waterlevels determined for the 2-year flood event, potential bridge blockage scenarios at the existing five (5) bridge crossings along Coal Creek, a.5 m sediment deposition allowance in the channel, and a.6 m freeboard allowance for recognized uncertainties. Three (3) flood hazard management zones are identified on the floodplain map and recommendations for future development in these areas are provided. Flood hazard Zone A is considered the 2-year floodway and setback area where no further development is recommended. Zone B is outside the 3 m setback area but within the active fan where overland flow and potential avulsions can occur. It is recommended that development in Zone B be limited to park, open-space recreation and agricultural uses. Any buildings or structures constructed in this area should apply the BC MWLAP Flood Hazard Area Land Use Management Guidelines (24) for specific land uses. Zone C identifies areas within the 2-year floodplain that have largely been developed. Any new construction in Zone C should be such that the floor system of any habitable building, business, or building for the storage of commercial goods be constructed to a level at or above the FCL, or have another means of flood proofing. Coal Creek Floodplain Mapping ii

5 Credits and Acknowledgements The authors would like to thank the for initiating this study. Bruce Lennox Director of Planning Dave Cockwell Director of Operational Services Terry Nelson Snr. Engineer, Technologist Lisa Janssen Engineering Technologist The following NHC personnel participated in the study: Dale Muir, PEng Principal Joanna Glawdel, PEng Hydrotechnical Engineer Piotr Kuraś, PEng, RPF Hydrologist Tim Argast, GIT Geomorphologist Monica Mannerström, PEng Technical Reviewer Joe Drechsler, GISP GIS Professional Sarah North, GISP GIS Professional Coal Creek Floodplain Mapping iii

6 Table of Contents 1 Introduction Study Area Description Geomorphic Assessment River Morphology and Channel Processes Reach-Specific Channel Changes Bed Elevation Changes along Coal Creek 22 to Hydrology Historic Floods Previous Peak Flow Estimates Accounting for Climate Change Updated Peak Flow Analysis... 4 Coal Creek Hydraulic Assessment Field Investigation Hydraulic Model Development Model Geometry Model Boundary Conditions Model Calibration and Verification Design Flood Profiles Sensitivity Analysis Bridge Blockage Scenarios Brewery Creek Hydraulic Assessment Channel Aggradation Flood Hazard Assessment Flood Inundation Mapping Floodplain and Hazard Boundaries Flood Construction Levels Hazard Zones Limitations, Conclusions, and Recommendations References Coal Creek Floodplain Mapping iv

7 List of Tables Table 1. Summary of watershed characteristics for Water Survey of Canada (WSC) gauges and project locations.... Table 2. Summary of 2-year instantaneous peak flows (m 3 /s) using various methods. Values include % increase to account for climate change Table 3. Comparison of surveyed and modelled 1995 highwater levels (HWL) within Coal Creek Table 4. Comparison of June 19 th, 214 surveyed and modelled water levels with Coal Creek Table 5. Sensitivity test results for the HEC-RAS model; assessed at the 2-year flood Table 6. Elevation at upstream face of bridges with and without blockage, calculated through model simulations of 2-year design flood List of Figures Figure 1. Overview map of project Figure 2. Coal Creek active channel bed, relic channels, and active fan Figure 3a. Coal Creek thalweg profile changes between 22 and 214. Stationing from confluence with Elk River (St. ) to St Figure 3b. Coal Creek thalweg profile changes between 22 and 214. St 1+4 to St Figure 4. Project watersheds and Water Survey of Canada (WSC) gauges and watersheds Figure 5. Regional curve based on 2-year instantaneous peak unit discharge estimates for Water of Survey Canada (WSC) gauges, with upper and lower envelopes Figure 5. June 19th, 214 surveyed and modelled water levels within Coal Creek Figure 6. Coal Creek floodplain map Figure 7. Coal Creek flood hazard map List of Photographs Photo 1. Coal Creek at the mouth, view facing downstream to Elk River Photo 2. Coal Creek, view facing upstream from Farm Access Bridge Photo 3. Dike protection works between Railway Bridge and Park Avenue Bridge, view facing downstream Photo 4. Brewery Creek springs, view facing upstream from farm access road Photo 5. Brewery Creek wetland, view facing upstream of Cokato Road Photo 6. Brewery Creek wetland outlet, view from right bank at edge of wetland Photo 7. Pine Avenue Bridge, view facing upstream Photo 8. Railway Bridge, view facing upstream Photo 9. Cokato Road Bridge, view facing upstream from railway embankment Coal Creek Floodplain Mapping v

8 Photo. Farm Access Bridge, view facing downstream. Bank protection works along left bank at bottom left corner of photo Photo 11. River Road extension bridge, view facing downstream List of Appendices Appendix A. Appendix B. Hydraulic modelling results Hydraulic modelling sensitivity results Coal Creek Floodplain Mapping vi

9 1 INTRODUCTION The is located along the banks of the Elk River with substantial tributaries also crossing through the city, such as Fairy Creek, Mutz Creek, Coal Creek, McDougall Creek, and Lizard Creek. Sections of the city are prone to flooding and a series of dikes help to protect the city from frequent flooding. Historic Elk River flood events occurred in 1948, 1995, and 213. Other high flow years include 1956, 1972, and In 1975, the Ministry of Environment (MOE) prepared floodplain mapping for the Elk River. The purpose of the mapping was to delineate the limits of the 2-year floodplain and display flood construction levels (FCL). In 26, Northwest Hydraulic Consultants (NHC) assessed the flood hazard and updated the FCLs for the and West Fernie along the Elk River (NHC, 26). No floodplain mapping was updated at that time. Floodplain mapping within the has been limited to the Elk River with no flood mapping of Coal Creek or Fairy Creek. Development along the creeks has largely been managed by the requirements contained in the Floodplain Management Bylaw 178 (1998) which defines flood setbacks and FCLs and identification of potential hazard zones developed by the Provincial Ministry of Land, Water, and Air Protection along with the Fraser Basin Council (MWLAP, FBC, 24). The City is interested in identifying flood hazards and developing floodplain mapping to provide guidance for evaluating development requests. Flood hazards include flooding, bank erosion and channel migration, bed lowering or degradation, and avulsion or high velocity overbank flows; any of which could lead to damage to buildings, bridges, pipes or infrastructure. The retained Northwest Hydraulic Consultants (NHC) to prepare a flood hazard study and produce floodplain mapping for Coal Creek within the city s boundaries. The floodplain mapping will identify areas with a flood hazard risk and update current FCL s within the Coal Creek floodplain. Brewery Creek drains into Coal Creek from the south within the study area and has been reported to flood along with Coal Creek (i.e., 1995 flood). The lower sections of Brewery Creek are included in this work. The Mountainview neighbourhood which is bounded by Coal Creek to the north, Elk River to the south and west and the CP railway to the east is subject to flooding from both Coal Creek and Elk River. Existing Elk River floodplain mapping (NHC, 26) is used to assess flooding in this area. 1.1 Study Area Description Coal Creek is a steep mountain stream with headwaters originating in the Fernie basin of the Rocky Mountains. It flows predominately east-west towards the Elk River at the (Photo 1). The upper slopes are steep and have historically been logged, with much of the channel confined within its valley. The creek transitions as it flows from the Coal Creek valley and into the Elk River valley. Here the channel is no longer confined by valley walls, allowing the creek to meander and channel slope to decrease (Photo 2). This causes a reduction in the sediment transport capacity; resulting in the deposition of transported sediment and the formation of an alluvial fan. The municipal boundary is near this point of transition, roughly 3 km upstream of the Coal Creek s confluence with the Elk River (Figure 1). Cokato Road Bridge, located roughly 6 m from the Coal Creek Floodplain Mapping 1

10 confluence provides a break in historic land use, with little to no development upstream of the crossing and substantial residential development downstream. Downstream of the Cokato Road Bridge the channel is confined by training berms and dikes along the left 1 bank (Photo 3). Brewery Creek is a relatively small seasonal stream which originates in the Morrissey Range and joins Coal Creek from the left bank (south) between the Cokato Road Bridge and Canadian Pacific Railway (CPR) Bridge. Brewery Creek meanders through a densely vegetated floodplain of coniferous and deciduous trees with low shrubs and grasses. Approximately 2 m upstream of Cokato Road, there appears to be additional subsurface water contribution to Brewery Creek at Brewery Creek Springs (Photo 4). Flow continues through the Brewery Creek wetland (Photo 5) prior to discharge through a 12 mm corrugated steel pipe (CSP) (Photo 6), which runs under Cokato Road and then continues between Cokato Road and the CPR embankment before discharging into Coal Creek. An armoured swale duplicates the overland path between Cokato Road and the CPR embankment, presumably to convey flow that exceeds the culverts capacity and overtops Cokato Road. 1 River left and right based on downstream facing view. Coal Creek Floodplain Mapping 2

11 OWEN ST GLOVER ST HARTLEY ST ««11 BreweryCrek MathesonCrek Coal Crek BEACH AVENUE LOUGH AVENUE AND AVENUE STEWART AVENUE HOATH ST HESKETH ST COMMONS ST ECKERSLEY ST CROWSNEST HIGHWAY 3 McLEOD AVENUE McDONALD AVENUE BEAVER ST RIVERSIDE DRIVE COLCLOUGH AVE HAND AVENUE ELK RIVER MT MINTON STREET RIVERSIDE DRIVE VANDERBERGH «1 MILL ST «2 4th STREET WILSON 6A AVENUE 3rd STREET 6th AVENU 5th STREET 4th STREET 3rd STREET 2nd STREET PARK CRES 4A AVENUE 1st STREET B2 B1 PARK AVENUE 7th STREET 5th AVENUE 4th AVENUE 3rd AVENUE 2nd AVENUE BREWERY CREEK OUTFALL PINE AVENUE B3 1st AVENUE PINE AVENUE COAL CREEK RD PINE CRES SILVER RIDGE DR SILVER RIDGE WAY CANADIAN PACIFIC PLACE RIDGEMONT ST MARGARET'S ROADRIDGEMONT D R IVE COAL CREEK CRESCENT B4 RIDGEMONT AVENUE RIDGEMONT DRIV RIDGEMONT LANE ST MARGARET'S ROAD COAL CREEK RD D.O.C. CREEK «43 BLACK BEAR CREEK «44 «45 «46 «47 B5 «48 Fernie COAL CREEK RD MT PROCTOR AVENUE MT INGR AM MT VA NBUS KIR K MT TRINITY AVENUE MT TRINITY AVENUE MT HERCHMER PARK MT KLAUER «3 ELKVIEW MT WASHBURN ST «4 PL AVENUE MT McLEAN STREET Streams «5 ELKVIEW DRIVE ELKVIEW Hec Ras Sections «6 «8 «7 «9 CRESCENT Flood Protection (Approximate Location) Dike Attack Dike Bin Wall Dike Riverbank Protection CANADIAN PACIFIC RAILWAY COKATO ROAD BREWERY CREEK CULVERT CASTLE MOUNTAIN ROAD CRE EK PL «13 «12 ESTATE DR «14 ««15 16 «17 LiDAR Extent «18 BLACK ROCK PL RDEK Parcel Fabric Fernie ICF Fernie Boundary Railway «19 «2 SLALOM BREWERY CREEK SPRINGS DRIVE CRES CEDAR BOWL DRIVE WHITE TAIL DRIVE PLACE «21 SPRUCE PL «22 «23 «25 «24 «28 «27 «26 «29 «3 «31 «33 «32 «34 «35 BREWERY CREEK «36 TUBER CREEK «37 «38 DATA SOURCES: SCALE - 1:8, ± BACKGROUND - CITY OF FERNIE (MAY 24) STREAM LINES - BASED ON BC FRESHWATER ATLAS M FLOOD PROTECTION - CITY OF FERNIE CADASTRAL - CITY OF FERNIE Job: 3372 «39 «4 «41 «42 Coordinate System: NAD 1983 UTM ZONE 11N Units: METRES Date: 18-AUG-214 FERNIE FLOODPLAIN MAPPING STUDY AREA OVERVIEW FIGURE 1 JXD/JXG, \\mainfile-van\projects\projects\3375 Fraser River Bank Erosion\GIS\3372_JXD_Fig1_Overview.mxd

12 2 GEOMORPHIC ASSESSMENT 2.1 River Morphology and Channel Processes Coal Creek drains a steep watershed in the Rocky Mountains in south-eastern British Columbia. Although historically this valley was explored and mined as its name suggests, no active mines have been operating for several decades. Unlike the large open pit mines of the Crowsnest Coal field, the Coal Creek mines were underground and did not leave any significant impacts on the surface hydrology. As part of this study, a review of available air photos (years 1968, 1979, 1984, 1994, 25) was conducted to determine the history of the watershed and channel dynamics on the alluvial fan. Available Google Earth air and satellite photographs (years 24 and 2) as well as Lidar data collected by Focus Corporation (Focus) were also reviewed (Figure 2). Between 1968 and 2 development in the upper watershed has been primarily limited to industrial logging and clearing for transmission line right-of-ways. Logging may cause a shift in the sediment supply regime in a drainage basin. In the case of the upper Coal Creek watershed, logging appears to have not been concentrated enough to significantly increase sediment supply. However, numerous steep side tributaries maintain a steady supply of sediment to Coal Creek. Some of this sediment is temporarily stored in bar complexes along the channel margins, but much is transported downstream to the lower Coal Creek alluvial fan. 2.2 Reach-Specific Channel Changes Alluvial fans are dynamic landforms that regularly reconfigure themselves in response to episodic changes in sediment input and hydrologic events. Channel bifurcation, avulsion, and abandonment are all common processes on fans and can have large consequences for development. Over the period of record covered by the air photos, the channel course appears relatively stable with no major changes. The 28 Lidar data reveals numerous relic channels on the fan. Although the Lidar data is limited by tree cover and human alteration of the floodplain, it provides first approximation of the area of the floodplain that is subject to possible channel avulsion and can be considered geomorphically active. The active channel and relic channels are shown in Figure 2. Many of these channels are likely active during flood events. It also appears that the confluence of Tuber/Brewery and Coal Creek has migrated downstream from its former location. During the 1995 flood event, Coal Creek was noted to transport a large amount of debris (BC MELP 1995). Wood can be an important factor in channel avulsions as wood jams can quickly form during flood events, causing the channel to plug or become constricted and diverting water over the banks or into relic channels. Taking into the consideration the aforementioned process and relic landforms, an area of the active fan has been delineated where there is a fluvial geomorphic hazard from the upstream municipal boundary to the study extents (Figure 2). It is expected that any future channel avulsions will be Coal Creek Floodplain Mapping 4

13 contained within this area. The active fan at the left bank in the area downstream of the Cokato Avenue Bridge is limited by the binwall dike. Figure 2. Coal Creek active channel bed, relic channels, and active fan. 2.3 Bed Elevation Changes along Coal Creek 22 to 214 Focus surveyed 28 cross sections in 22 for a proposed development along the left floodplain of Coal Creek (Hay & Co, 23). Focus surveyed 48 cross-sections from the upstream municipal boundary to the confluence with the Elk River in May 214. The thalweg profiles from these surveys have been plotted on Figure 3a and Figure 3b for comparison. Comparison of profiles is limited to the density of survey points across the channel and spacing of sections. It is likely more changes exist in the reach than those apparent in Figure 3a and Figure 3b. In general, there is no specific trend observed between the 22 and 214 thalweg profiles, however, local areas of deposition and scour are notable such as: The deposition of material immediately downstream of the River Road Bridge (Sta. 27). In all but the largest flood events, sediment from upstream sources is expected to be deposited in this region where the channels transport capacity reduces due to a decrease in slope and increase in channel width (lack of confinement). Material deposited here is expected to be gradually re-mobilised, sorted, and moved down the fan. There are several sites of local scour at approximately Sta. 19, Sta. 135, and Sta. 8 (measured in metres from the Elk River confluence). The local scour at Sta. 135 is likely a Coal Creek Floodplain Mapping 5

14 result of the Farm Access Bridge constricting the flow. Other local scour sites may be due to bank protection works or other local constrictions. Figure 3a. Coal Creek thalweg profile changes between 22 and 214. Stationing from confluence with Elk River (St. ) to St Coal Creek Floodplain Mapping 6

15 Figure 3b. Coal Creek thalweg profile changes between 22 and 214. St 1+4 to St. 3+. Coal Creek Floodplain Mapping 7

16 3 HYDROLOGY 3.1 Historic Floods In 1995 a high precipitation event combined with rapid snow melt resulted in a flood event on Coal Creek. During this event considerable damage was sustained to the left bank (south) upstream of Cokato Bridge, the Park Avenue Bridge, and the right bank (north) downstream of the Railway Bridge (Armstrong, 22; BC MELP, 1995; and Hay & Co., 23). Sediment from this event was transported to and deposited within the Elk River at and downstream of the Coal Creek confluence. BC MELP 1995 estimate the peak flow of this event to be 53 m 3 /s; Armstrong (22) estimated the flow between 7-8 m 3 /s. Following this event, the Coal Creek binwall dike was installed. The Elk River flood of record occurred in June 213. Parts of the City were flooded but no dikes were overtopped in the 213 event (NHC, 213). Although water levels were likely high in Coal Creek, overbank flooding or major damage was not reported on Coal Creek. 3.2 Previous Peak Flow Estimates NHC has reviewed the hydrology components of the following reports for prior peak flow estimates at Coal Creek: Hay & Co. (23), NHC (26), and NHC (213). Hay & Co. (23) estimated the 2-year instantaneous peak flow (QPI-2) 2 for Coal Creek at the mouth using the following Water Survey of Canada (WSC) gauges: Fording River below Clode Creek 8NK21 (WSC Fording) Grave Creek at the Mouth 8NK19 (WSC Grave) Michel Creek below Natal 8NK2 (WSC Michel Natal), and Line Creek at the Mouth 8NK22 (WSC Line) Hay & Co. (23) developed a regression using the QPI-2 estimates for the gauges above with drainage area, and estimated that the QPI-2 for Coal Creek at the mouth is 68 m 3 /s. The Streamflow Inventory Peak Flow map (BC MELP, 1998) indicates a -year instantaneous peak flow (QPI-) of 57.3 m 3 /s. The average QPI-2: QPI- ratio determined for the four WSC gauges above is 1.23, and multiplying this by the QPI- estimate provides a QPI-2 of 7.5 m 3 /s, which supports the regional estimate. NHC (26) provides a comparison of three sources of QPI-2 estimates for Coal Creek: Graphs prepared by Reksten and Bar (1989), with the QPI-2 estimated to be 83 m 3 /s Hay & Co. (23) as noted above, with the QPI-2 estimated to be 68 m 3 /s 2 A 2-year return period flood event represents a hypothetical flood with a.5% annual likelihood of exceedance; that is a % chance of exceedance in 2 years. Coal Creek Floodplain Mapping 8

17 Estimates by Hay & Co. (23) were checked using the Creager Method. The Creager coefficient was computed for the daily peak flow return period estimates for WSC Grave, WSC Line, and WSC Michel, and the average of Creager coefficients was applied to estimate the corresponding flows for Coal Creek. An average instantaneous/daily ratio of 1.12 for the WSC gauges was applied to the Coal Creek daily peak flow return period estimate to estimate an instantaneous value. This was not found to be significantly different from previous estimates by Hay &Co. (23). NHC (213) relies primarily on the estimates provided in NHC (26). 3.3 Accounting for Climate Change BGC (213) describe the potential effects of projected climate change on flood hazards in the Regional District of East Kootenay (RDEK) based on various climate change studies conducted at a regional and provincial level. The PCIC (212) and Murdock and Sobie (213) use global climate models to project changes to precipitation and temperatures within BC and are summarized for the RDEK by BGC (213) as: increasing mean annual temperatures; decreasing average summer precipitation volumes; increasing winter precipitation volumes; decreasing spring snowfall; decreasing extreme snow packs; and increasing intensity and frequency of occurrence of short duration, high intensity precipitation events, and precipitation events in general. These climate change study findings are limited to qualitative statements of potential changes to average conditions and not directly to proportional to changes in extreme events (i.e., flood events). The Columbia Basin Climate Change Scenarios Project (CIG 2) conducted a climate change study of the Columbia River basin based on global climate models (GCMs) and two emission scenarios. They developed a simplified hydrologic model to predict streamflow at various stream gauges including the WSC Fording River gauge (WSC 8NK21). Using the simulated flow data CIG (2) project the 2, 5, -year return period daily flows three periods (2-24, and 27-2). For WSC 8NK11, the mean peak flow increase of the GCMs is less than % for both emission scenarios and all reported temporal periods. There are numerous uncertainties and complexities in the climate change modelling data which make it difficult to include in estimating extreme flood events at Coal Creek. There are two ways of addressing the uncertainty: 1) conduct further study to define potential effects of climate change to extreme flood events in the Coal Creek watershed; 2) apply a factor of safety to provide a buffer for such events. Local effects of climate change on rainfall intensity and flood flows are beyond the scope of the current project. In this study, a % increase applied to peak flow estimates to account for the Coal Creek Floodplain Mapping 9

18 potential impacts of climate change. This is in accordance with the Association of Professional Engineers of BC suggested approach to account for climate change up to the year 2 (APEGBC, 212). 3.4 Updated Peak Flow Analysis Peak flows at Coal Creek and Brewery Creek were calculated using relevant WSC gauges which include: WSC Fording WSC Grave WSC Michel Natal WSC Line Hosmer Creek above Diversions 8NK26 (WSC Hosmer) Michel Creek above Corbin Creek 8NK28 (WSC Michel Corbin) Drainage areas were delineated for Coal Creek and Brewery Creek as well as the WSC gauges using BC TRIM mapping (Figure 4). Watershed characteristics are provided in Table 1. Table 1. Summary of watershed characteristics for Water Survey of Canada (WSC) gauges and project locations. Location Drainage Area (km 2 ) Mean Elevation (m) Min Elevation (m) Max Elevation (m) WSC Hosmer WSC Michel Corbin WSC Grave WSC Fording WSC Line WSC Michel Natal Brewery Creek Coal Creek Coal Creek Floodplain Mapping

19 Fording River ") WSC Fording Brewery Creek Creek Matheson Coal Creek WSC Line ") Line Creek WSC Grave ") Grave Creek WSC Michel ") KM Description Gauge Drainage Area (km²) Mean Elevation (m) Min Elevation (m) Max Elevation (m) WSC Grave 8NK WSC Michel 8NK WSC Fording 8NK WSC Line 8NK WSC Hosmer 8NK WSC Michel Corbin 8NK Coal Upstream Coal At Mouth Brewery Watersheds Grave Ck Michel Ck Fording Rv Line Ck Hosmer Ck Michel Corbin Brewery Ck Coal Ck DS Coal Ck US ") WSC Gauges Streams Fernie WSC Hosmer Coal Creek (At Mouth) Brewery Creek KM Hosmer Creek ") Coal Creek ± DATA SOURCES: BACKGROUND - NATIONAL GEOGRAPHIC WORLD MAP SCALE - AS SHOWN WATERSHEDS AND STREAM LINES - BC FRESHWATER ATLAS Job: 3372 Michel Creek Coordinate System: NAD 1983 UTM ZONE 11N Units: METERS ") Corbin Creek Date: 22-JUL-214 WSC Michel Corbin FERNIE FLOODPLAIN MAPPING PROJECT WATERSHEDS AND WSC GAUGES FIGURE 4 JXD, \\van-mainfile\projects\projects\3372 Coal Cr Floodplain Map\GIS\3372_JXD_Fig3_Watersheds.mxd

20 Estimates of the QPI-2 for the project watersheds were determined through the development of a regional curve (Figure 5), the Creager method, and scaling by drainage area (Eaton et al., 23). An estimate of the QPI-2 was also determined for the Brewery Creek watershed using the Rational Method combined with the Intensity-Duration-Frequency curve for the Environment Canada Sparwood station (Sparwood IDF). QPI-2 estimates for each method are provided in Table 2. The values in the table include a % increase to account for the potential impacts of climate change. This is in accordance with the Association of Professional Engineers of BC suggested approach to account for climate change up to the year 2 (APEGBC, 212). Figure 5. Regional curve based on 2-year instantaneous peak unit discharge estimates for Water of Survey Canada (WSC) gauges, with upper and lower envelopes. Coal Creek Floodplain Mapping 12

21 Table 2. Summary of 2-year instantaneous peak flows (m 3 /s) using various methods. Values include % increase to account for climate change. Drainage Regional Creager Area Scaling Rational Area Regression Upper Mean Max Mean Max Sparwood Site (km 2 ) Envelope IDF Brewery Creek Coal Creek n/a * bold indicates design flow For Coal Creek, the mean Creager estimate of 79.7 m 3 /s is recommended for design. For Brewery Creek, the upper envelope value estimated using regional regression of 3.62 m 3 /s is recommended for design. Coal Creek Floodplain Mapping 13

22 4 COAL CREEK HYDRAULIC ASSESSMENT HEC-RAS (Version 4.1), a one-dimensional hydraulic modeling software developed by the US Army Corp of Engineers, was used to determine flood profile elevations in Coal Creek. HEC-RAS uses a steady state standard-step computational hydraulic method for calculating water surface profiles and cross-sectional averaged hydraulics. 4.1 Field Investigation NHC conducted field investigations June 19 th to 2 th, 214. On June 19 th, the estimated discharge in Coal Creek was 19.6 m 3 /s, approximately a 2-year return period flow. During the field investigation, data was collected to define channel roughness (i.e., channel bed and bank materials, floodplain characteristics), bed and channel forms, presence and transport of debris, channel stability, and locations of structures with potential to affect hydraulics. The geometries of the five bridge crossings were also collected for modelling input which included: location of abutments; bridge span length and width; and elevation of bridge deck and soffit. Bathymetric data was previously collected by Focus in May 214. Additional cross-sections were not gathered during the field investigation due to high flow (highwater depth and velocity prevented accessing much of the channel). Notes on channel geometry to produce interpolated cross-sections at specific locations were collected. No highwater marks were identified during the site visit but water levels were collected at various locations in the study reach associated with June 19 th flow. 4.2 Hydraulic Model Development Model Geometry The Coal Creek hydraulic model geometry was developed from three primary sources: 1. Lidar data collected by Focus in 28; 2. Bathymetric survey data of 48 cross-sections collected by Focus in May 214; 3. Topographic survey conducted by NHC in June 214 of areas not captured by the Lidar and bathymetric survey. Additional Lidar data was made available by the in September 214 following the hydraulic model development. The data sources were combined into a Digital Elevation Model (DEM) in ArcGIS following the verification of vertical datum. Cross-section data for modeling were extracted at the bathymetric survey locations. The model consists of 55 cross-sections on Coal Creek extending from the mouth at the Elk River to 3.2 km upstream (Figure 1). Two un-surveyed cross-sections were added at the upstream boundary using Lidar data and noted channel geometry. An additional five interpolated cross-sections were added to stabilize flows at the bridge crossings. Coal Creek Floodplain Mapping 14

23 4.2.2 Model Boundary Conditions The water surface elevation at Elk River at the confluence of Coal Creek provides a downstream boundary condition for the model. Flood profiles for the 2-year Elk River flood event were prepared by MOE in 1975 and updated by NHC in 26. June 21 st, 213 Elk River peaked at a WSC reported flow of 97 m 3 /s. Following this event, the 2-year Elk River instantaneous peak flow was recalculated to be 4 m 3 /s (NHC, 213). Using the NHC 213 flow and the Elk River hydraulic model from NHC (26) the downstream boundary condition for Coal Creek was calculated as El m 3. Highwater marks along the Elk River were surveyed by NHC following the June 213 flood event. A highwater elevation of El m was recorded on the right bank of the Elk River at the confluence of Coal Creek. Assuming co-occurrence of flood events within two watersheds of sizable difference in watershed area may arguably be considered excessively conservative. However, during the June 1995 flood event, the peak flow within Coal Creek was reported to have occurred between 6 pm and 8 pm June 6 th, and the same event peaked on the Elk River at :26 am June 7 th Model Calibration and Verification Hydraulic modeling offers a snap-shot of a river, corresponding to the channel configuration at the time of survey. In a steep-mountain stream with substantial sediment and debris load such as Coal Creek, flood profiles calculated by the hydraulic model may vary over time in response to long-term aggradation/degradation and channel adjustments. Also, the riverbed may significantly scour during a high flood followed by a period of gradual build up over several years. For accurate calibration, it is important that both the recorded flood profile and surveyed cross-section date from roughly the same time. No comprehensive calibration data for high flows was available for this project. The model was developed based on previous experience with similar type water systems, and major assumptions were tested using a sensitivity analysis. Efforts were made to verify highwater surface profiles for the 1995 flood. Highwater levels were recorded by Armstrong in 1995 and were limited to the reach between Cokato Bridge and the Elk River. For model verification the 1995 flood event was simulated with a discharge of 53 m 3 /s and downstream boundary of El Table 3 compares the 1995 recorded water levels to those computed in the model. Calibration of the model to the 1995 highwater marks was discarded due to a number of deficiencies associated with the data set including: unguaged flow estimate for the event; unknown elevation datum used to collect highwater marks; poor documentation of highwater mark description; and channel aggradation/degradation which likely has taken place since Elevations are geodetic. Coal Creek Floodplain Mapping 15

24 Table 3. Comparison of surveyed and modelled 1995 highwater levels (HWL) within Coal Creek. Cross-section River Station 1995 Surveyed HWL (m) 1995 Modelled HWL (m) Variance (m) Water levels recorded by NHC on June 19 th, 214 at an estimated flood flow of 19.6 m 3 /s (i.e., approximately 2-year return period) were used to verify the model. Figure 6 and Table 4 allow comparison of the June 214 recorded water levels to those computed in the model (river station is distance in metres from the Elk River confluence). The average absolute error between recorded and computer water levels was.8 m. Table 4. Comparison of June 19 th, 214 surveyed and modelled water levels with Coal Creek. Cross-section River Station (m) June 19th 214 Surveyed Water Level (m) June 19th 214 Modelled Water Level (m) Variance (m) Coal Creek Floodplain Mapping 16

25 Figure 6. June 19th, 214 surveyed and modelled water levels within Coal Creek. 4.3 Design Flood Profiles The designated flood flow for floodplain mapping in BC is the 2-year return period flood. Water surface profiles for Coal Creek for the 2-year instantaneous peak flow event were calculated using a steady-state subcritical simulation. 2-year estimated water levels at the cross-sections are provided in Appendix A. Inundation extents and approximate depths of the 2-year flood including a.6 m freeboard allowance are shown on the attached floodplain map. The freeboard allowance is further discussed in Section 5.3. The Mountainview neighbourhood is subject to flooding from both Coal Creek and the Elk River. The Elk River 2-year daily maximum flood with at.6 m free board allowance as defined in NHC 26 are used to define the Coal Creek and Elk River combined floodplain in the area. 4.4 Sensitivity Analysis The sensitivity of the model output for 2-year flood profiles was tested by varying key input parameters such as the magnitude of the flow; channel roughness (Manning s coefficients) and the Coal Creek Floodplain Mapping 17

26 downstream boundary condition. Detailed results of the sensitivity analysis are provided in Appendix B. The sensitivity analysis results are summarized in Table 5. Table 5. Sensitivity test results for the HEC-RAS model; assessed at the 2-year flood. Parameter Base Value Upper Limit (UL) Tested Lower Limit (LL) Tested Max Flood Level Variance (m) UL/LL 1 Mean Flood Level Variance (m) UL/LL 2 2-Year Peak Flow 79.7 (+3%) (-3%) +.41/ /-.25 Channel Roughness (+25%) (-25%) +.27/ /-.8 D/S Water Elevation (+.5 m) (-.5 m) +.5/ /-.1 Note: 1. Flood level variance reported is the max difference at all the cross-sections in the study reach. 2. Flood level variance reported is the mean difference at all the cross-sections in the study reach. The design 2-year flow event was varied by ±3% to assess the uncertainty in the hydrological estimate. Water levels increase by +.1 m and +.4 m over the base condition when discharge is increased by 3%. The higher variation is noticed in the lower reach, where channelization has occurred and flow is confined within the dike. The channel roughness coefficients were not calibrated in the model and were chosen based on previous experience with similar channels. Model sensitivity to changes in the roughness coefficient by ±25% resulted in average water level variation in the study reach between ±.5 m and ±.27 m (increased channel roughness results in increases water levels). The downstream boundary condition Elk River water elevation was varied by ±.5 m. Variation of this boundary represents possible changes in the flood elevation on the Elk River associated with the Coal Creek flood event. Due to the relatively steep slope of Coal Creek, a change of.5 m in Elk River water level is diminished to negligible value within m upstream of the confluence. The sensitivity analysis is conducted to give context on how modelled water level results change with uncertainty in the model input parameters. For the Coal Creek hydraulic model, the greatest uncertainties are in channel roughness due to lack of calibration data and the design discharge due to lack of flow data for Coal Creek and Brewery Creek and the uncertainty of the effects of climate change on local flood flow over the next years. 4.5 Bridge Blockage Scenarios Coal Creek transports a large amount of sediment and debris during flood flow events. In the 1995 flood event, floating trees were noted with lengths up to 25 m and diameters of 1 m (BC MELP, 1995). Large trees can block bridge openings particularly if there is inadequate conveyance to pass floating debris; such as low lying bridges with inadequate freeboard 4 and/or narrow bridge openings that can be spanned by a single log of size expected to be transported during a flood. 4 Freeboard is often in the range of 1.5 to 2. m above the 2-year flow for crossing in British Columbia. Coal Creek Floodplain Mapping 18

27 Existing freeboard for the 2-year design events at the five (5) bridges on Coal Creek (Figure 1) were analyzed in the HEC-RAS model based on geometries surveyed by NHC in June 214. The results of the analysis and associated bridge freeboard, defined as the distance from water level to the soffit, are provided in Table 6. Bridges with inadequate freeboard include Park Avenue, Cokato Road, and Farm Access Bridge. Bridge blockage scenarios were modelled to investigate flood conditions assuming reduced conveyance capacity at these crossings. The following bridge blockage scenarios were modelled. Park Avenue Bridge (B1) The existing freeboard for the 2-year design event is 1.4 m at the Park Avenue Bridge (Photo 7). Flow is constricted through a 21 m wide bridge opening from an upstream flow width of 31 m. Partial debris blockage can occur at the bridge soffit and abutment, increasing water levels upstream and encroaching on the dike freeboard (MELP, 1995; Armstrong, 22). A potential blockage scenario where the soffit elevation is lowered by 2 m and 1 m of material accumulates on the right abutment was simulated in the hydraulic model. This scenario represents a 54% reduction in the bridge conveyance area. Waterlevels are increased by a maximum of.12 m over the 2-year design condition. The influence of the bridge blockage is diminished approximately 5 m upstream of the bridge (Table 6). Canadian Pacific Railway Bridge (B2) Freeboard at the railway bridge (Photo 8) is in excess of 1.5 m and it is unlikely that debris will be captured by the bridge soffit. The upstream flow width is 32 m. The bridge abutments extend into the main channel constricting flow to a 3 m opening. In high flow events debris can become trapped by the abutments, further constricting the flow. A scenario where 2 m of debris on the both the left and right banks of the bridge abutments was simulated to determine the potential increase in waterlevels. The scenario represents a 9% decrease in the bridge conveyance area. Hydraulic simulations results (Table 6) show there is little influence on upstream water levels under this blockage scenario. Cokato Road Bridge (B3) The Cokato Road Bridge (Photo 9) is located approximately 5 m upstream of the railroad bridge. There is inadequate freeboard at the bridge under the 2-year design scenario (i.e.,.69 m) (Table 6) and debris may reduce bridge conveyance if trapped by the soffit or the abutments. Flow is constricted through the bridge to a 18 m wide bridge opening from an upstream flow width of 24 m. A hydraulic analysis was simulated with the bridge blocked by 2 m of debris on the bridge soffit and 2 m on both abutments. This represents a 59% reduction in the bridge capacity. The bridge is not overtopped in this scenario and flow is maintained through the opening. Upstream water surface elevations are increased by.25 m upstream of the bridge with effects diminished within 6 m upstream (Table 6). Overland flow at the upstream face of the bridge would be directed towards Brewery Creek. Coal Creek Floodplain Mapping 19

28 Farm Access Road Bridge (B4) The Farm Access Road Bridge constricts channel flow. Upstream of the bridge the channel width is approximately 5 m (Photo 2) and is constricted to 17 m wide at the bridge (Photo ). The channel is migrating towards the left bank and bank protection works have been put in place to limit this. Freeboard at the bridge is inadequate for the 2-year event (i.e.,.74 m) and debris can block the conveyance area by catching on the bridge soffit and against the abutments. A potential blockage scenario where the bridge conveyance area is reduced by 51% was simulated in the hydraulic model. Water levels upstream of the bridge are increased by.8 m over the 2-year design scenario and the blockage has an influence on upstream water levels for approximately 8 m upstream (Table 6). Given the large constriction this bridge has on the flood flows, there is potential that the bridge may be overtopped in a high flow event. Overtopping flows would move onto the Coal Creek floodplain towards Brewery Creek. River Road Bridge (B5) Hydraulic analysis results of the River Road Bridge (Photo 11) show there is adequate clearance to pass the 2-year flood flow (i.e., 2.55 m) Table 6. The bridge is skewed to the flow which is slightly constricted by the bridge where the upstream water width is 25 m and the bridge span width is 2 m. Downstream of the bridge, the channel widens to approximately 35 m and bank protection works have been constructed along the left bank. A blockage scenario where 1.5 m of debris material is caught on the soffit and 2 m of debris is trapped on the left and right bank was simulated in the hydraulic model; a 46% reduction in bridge conveyance capacity. This bridge blockage scenario has little influence on upstream water levels (Table 6). Table 6. Elevation at upstream face of bridges with and without blockage, calculated through model simulations of 2-year design flood. Bridge Station 1 (m) Soffit Elevation (m) Blockage Free Flood Elevation (m) Bridge Freeboard (m) Reduction in Conveyance Area with Blockage Flood Elevation with Debris Blockage (m) Flood Elevation Increase at u/s Face (m) Upstream Distance of Influence (m) Park Avenue % CP Rail % Cokato % Farm Access % River Road % Stationing from the confluence with the Elk River. Coal Creek Floodplain Mapping 2

29 4.6 Brewery Creek Hydraulic Assessment It has been reported that during the 1995 flood event overbank flow from Coal Creek entered Brewery Creek (BC MELP, 1995). The introduced flow in addition to the already high flow within Brewery Creek led to flooding within lower Brewery Creek. Prior to 1995, Brewery Creek flows were directed through a mm culvert in the railway embankment and empty through a flood box to Coal Creek. During the 1995 flood event, the flap gate on the floodbox culvert was closed and the culvert s capacity was exceeded. Flows were directed over Cokato Road and ran between the Cokato Road and railway embankments, draining through culverts in the railway embankment and into the Mountview neighbourhood (Armstrong, 1995). In response to the 1995 flood, the installed a 12 mm diameter corrugated steel pipe (CSP) in 1996 under Cokato Road. After passing under the road the CSP continued northward conveying Brewery Creek subsurface between Cokato Road and the CPR embankment directly to Coal Creek. An armoured overflow channel with berm was also constructed along a similar alignment but above ground to capture flow that overtops the culvert. Brewery Creek water surface elevation east of Cokato Road is controlled by the culvert invert elevation and capacity. HY-8 (Version 7.3) is a culvert analysis program developed by the US Department of Transportation. A HY-8 model was created to develop a rating curve for the Brewery Creek outlet culvert using details of culvert inlet, outlet, provided by the, details in Drawing 3943-AB1 (Armstrong, 1997), and top of road details surveyed by NHC in June 214. The 2-year water level of Coal Creek at the outlet was used as the downstream condition. Modeling results of outlet controlled conditions show the culvert capacity is exceeded at a discharge of 1.45 m 3 /s. Flow in excess of 1.45 m 3 /s is directed over the road and into the overflow surface conveyance channel. A simple model of Brewery Creek within the Coal Creek floodplain was developed in HEC-RAS. The outlet rating curve was used as a downstream boundary condition and channel geometry was developed from the Lidar data and field notes. The included floodplain map indicates the approximate inundation during a 2-year flood of Brewery Creek incorporating a.3 m freeboard; further discussed in Section Channel Aggradation A review of the thalweg profile between survey years 22 and 214 is discussed in Section 2.3. No trend of aggradation or degradation is consistent throughout the study reach, although local scour and deposition is identifiable. An average sediment deposition of.43 m is calculated for the areas where sediment has accumulated over the 12 years between surveys. There is limited information on how much sediment is transported by Coal Creek. However, the deposition experienced at the outlet of Coal Creek during the 1995 flood event and localised aggradation over the past 12 years suggests incorporation of aggradation is warranted for flood modelling. Therefore, a consistent aggradation of.5 m was applied to the Coal Creek channel throughout the study reach. The resulting 2-year water profile with the aggraded channel is on average.4 m higher than what is simulated using the current bed profile. Coal Creek Floodplain Mapping 21

30 5 FLOOD HAZARD ASSESSMENT Potential flood hazards within the Coal Creek active floodplain have been evaluated through this study. Hazards in the active fan (Figure 3) include flooding, bank erosion and channel migration, bed lowering or degradation, and avulsion or high velocity overbank; any of which could lead to damage to buildings, bridges, pipelines or infrastructure near the river. 5.1 Flood Inundation Mapping The attached floodplain map identifies the expected flood inundation based on the 2-year instantaneous peak flood. In addition to flood inundation, the 2-year floodplain boundary, active fan, and flood construction level are presented. The Mountainview neighbourhood which is bounded by Coal Creek to the North, Elk River to the west and south and the CP railway to the East is subject to flooding from both Coal Creek and Elk River. The 2-year daily maximum peak flood induration depths for the Elk River from NHC 26 were projected onto the floodplain map. Elk River flood inundation depths are subject to future revisions to Elk River floodplain mapping. 5.2 Floodplain and Hazard Boundaries The floodplain boundary was calculated as the extent of flooding based on the: 2-year instantaneous peak flood determined by regional analysis, + % of flow to help account for climate change effects to flow,.5 m channel aggradation above the 214 Coal Creek channel bed, debris blockage at a number of the Coal Creek crossings, and.6 m freeboard for Coal Creek and.3 m freeboard for Brewery Creek The resulting waterlevel was projected horizontally across the surface developed using the Lidar data. The floodplain boundary delineates the expected flood extent. However floods in excess of the 2-year event may go beyond this boundary and channel changes may result in alteration of the boundary. The most likely expansion of the floodplain boundary is identified on the map as the active fan boundary shown on the floodplain map. 5.3 Flood Construction Levels For Coal Creek, the 2-year maximum instantaneous flood profile (QPI-2 of 79.7 m 3 /s) is used as the design event. Previous Provincial guidelines suggest design elevations be set to the maximum of.3 m freeboard above the instantaneous flood profile and.6 m freeboard above the daily flood profile (MWLAP, 23). Due to the uncertainties involved with the 2-year instantaneous discharge and climate change and the potential local increase in water level due to sediment, debris, Coal Creek Floodplain Mapping 22

31 and local turbulence, a freeboard allowance of.6 m has been applied to the instantaneous flood profile for Coal Creek. Downstream of the Railway Bridge, the Coal Creek fan lies within the floodplain of the Elk River where water levels from Elk River flooding are potentially much higher than the flood levels from Coal Creek. FCLs from Elk River floodplain mapping in NHC 26 were projected in the Mountainview neighbourhood. The higher of flood construction levels of Coal Creek and the Elk River is used in this area. Mountainview neighbourhood FCLs are subject to any future revisions to Elk River floodplain mapping. A freeboard of.3 m above the approximated 2-year instantaneous flood profile has been applied for Brewery Creek. The FCLs for Brewery Creek were incorporated into the Coal Creek floodplain mapping and are shown in the attached floodplain map. Flood construction levels (FCL) have been shown as isolines on the floodplain map. It is recommended that the underside of any floor system, or the top of any pad supporting any space or room, including a manufactured home, that is used for dwelling purposes, business or the storage of good which are susceptible to damage by floodwater shall be constructed to the appropriate FCL. New constructions (including replacements of existing structures), would require the review and sign off by an appropriate water resource professional as defined by APPEGBC (212) and the design of foundations by the appropriate qualified registered professional. In some cases, erosion protection of fill pads may be required. 5.4 Hazard Zones Development is to be limited within the active fan boundary to keep development from areas that have high hydrotechnical hazards (i.e., channel migration and avulsion) and to avoid restricting flow capacity of the channel and floodway (BC MWLAP, 24). The mapped floodplain extents and flood hazard boundary have been categorised with a number of zones that outline the acceptable development as delineated on the flood hazard management zone map. These zones are based on the risk to properties within the zone, potential to other properties if developed, and on the level of current development. The hazard areas only identify areas with flood hazard; other hazards (i.e., geotechnical, fire) or ecological are not identified on the mapping. Zone A Floodway and setback area This zone includes the 2-year floodway and setback area. This zone may experience moderate to high velocities and depths from overbank flooding and has the greatest potential for channel migration and avulsion. Development within this zone may affect conveyance or storage of flood flows. Due to the flood risk it is recommended that no development permits or building permits for the construction of dwellings or structures for use or occupation be permitted within this zone. The setback of any development also helps to maintain the diversity of the existing channel and riparian habitat. Zone B Overflow and potential avulsion area Coal Creek Floodplain Mapping 23

32 This zone includes the area of the undeveloped floodplain that is not included in Zone A, but is still as risk to flood hazard, either due to being located within the projected current 2-year floodplain or within areas susceptible to channel migration and or avulsion. It is recommended that use of this land be limited to non-intensives uses such as parks, trails, open-space recreation, and agriculture. Any buildings or structures constructed in this area should apply the BC MWLAP Flood Hazard Area Land Use Management Guidelines (24) for specific land uses within flood hazard areas, which include: Agricultural uses: o o Open-sided livestock structures do not required flood proofing by elevation; Farm dwellings and closed-sided livestock housing shall be located with the underside of the wooden floor system or the top of the pad (or in the case of a manufacture home the top of pad or the ground surface on which it is located) at or above the FCL elevation. Recreation, Park, and Open Space: o Closed-sided recreational buildings and/or equipment damageable by floodwater are to be built to the FCL. Recreational shelters, kiosks, washhouses, and other facilities may be considered for lower elevations. Provision for accommodations or intensive commercial or institutional development is not recommended. If non-intensive building or development is permitted, the risk of such works should be documented and provided prior to any property transfers, such as through the use of covenants. Zone C- Overflow area This area includes the largely developed Mountainview neighbourhood downstream of the Railway Bridge and Brewery Creek south of Whitetail Drive. The Mountainview neighbourhood is protected by standard dikes maintained by the. The site south of Whitetail Drive is within the projected current 2-year floodplain and is not protected by dikes, but is substantially set back from Coal Creek. All new construction of buildings in these areas used for habitation, business, or storage of goods, should be constructed such that the underside of the floor system is at or above the FCL. A reduced FCL may be acceptable if detailed dike break modelling and/or overland flow modelling is conducted by a qualified registered professional. Coal Creek Floodplain Mapping 24

33 6 LIMITATIONS, CONCLUSIONS, AND RECOMMENDATIONS The developed floodplain map of Coal Creek shows the potential for flooding at the time in which the data input was created. Changes in the floodplain, channel bed, and structures (i.e., bridges, bank protection works, set back dikes, etc.) can result in changes to the estimated flood extents and levels. The floodplain maps do not account for any other source of water that can also affect local flood levels. Channel obstructions, local stormwater inflows, groundwater, or other land drainage can cause flood levels to exceed those indicated on the map. Lands adjacent to the floodplain may be subject to flooding from tributary streams that are not indicated on the floodplain map. The design 2-year flood flow is based on a regional analysis of gauged systems. There is benefit to gauging flows on Coal Creek to improve flood flow predictions. Estimates of 2-year water levels and design flood construction levels are based on an uncalibrated model. Following high flow events, highwater elevations along with measured discharges should be recorded for Coal Creek to both calibrate the model roughness factor and verify the modelling results. Coal Creek was modelled using a 1D model. Two-dimensional modeling (2D) with probabilistic dike breach routines and possible outflow discharge scenarios can provide more refined estimates of 2-year flood elevations (and associated flood construction levels). These estimates are also improved for areas where overland flow is shown to occur such as upstream of the blocked Farm Access Road Bridge. Flood inundation depths and flood construction levels provided in the Mountainview neighbourhood are subject to any future revisions to Elk River floodplain mapping. Coal Creek Floodplain Mapping 25

34 7 REFERENCES APEGBC (212). Professional Practice Guidelines - Legislated Flood Assessments in a Changing Climate in BC (V1.1). 139 pp. Armstrong and Nelson Engineers and Land Surveyors (22). Preliminary Hydrotechnical and Geotechnical Review. Lot 2, Plan 11238, DL 4588, Fernie BC. BC Minstry of Environment Lands and Parks (1995). Investigation of the Coal Creek Training Berm Failure. BGC Engineering Inc. (BGC). (213). Regional District of East Kootenay: Regional Flood Hazard Study: Phase 1. Prepared for the Regional District of East Kootenay (RDEK). April, 213. Climate Impacts Group. (2). Columbia Basin Climate Change Scenarios Project. Eaton, B. C., Church, M., and Ham, D. (23). Scaling and regionalization of flood flows in British Columbia. 22, 16(16), Hay & Company Consultants Inc. (23). Coal Creek Flood Management. Prepared for Schickedanz Properties Inc. (BC). 14 pp. Ministry of Environment, Lands and Parks (1998). British Columbia Streamflow Inventory, Water Inventory Section, Resources Inventory Branch. Ministry of Water, Land and, Air Pollution (MWLAP) (23). Dike Design and Construction Guide, Best Management Practices for British Columbia. Prepared for the Flood Hazard managemetn Section by Golder Associates and Associated Engineering. Ministry of Water, Land and, Air Pollution (MWLAP) (24). Flood Hazard Area Land Use Management Guidelines. Ministry of Water, Land and Air Pollution (MWLAP) and Fraser Basin Council (FBC) (24). Flood Hazard Mapping, Mapsheet 8G/6. Murdock, T. Q. and S.R. Sobie. (213). Climate Extremes in the Canadian Columbia Basin: A Preliminary Assessment. Pacific Climate Impacts Consortium, University of Victoria. NHC (26). Elk River Flood Hazard Assessment. Prepared for. 41 pp. NHC (213). West Fernie Dike Improvements: Phase 3 and 4. Assessment of Design Post 213 Flood Event. Pacific Climate Impacts Consortium (PCIC) Plan2Adapt: East Kootenay. Accessed September 22, 214. Reksten, and Bar (1989). Guide to peak flow estimation for ungauged watersheds, British Columbia Ministry of Environment. Coal Creek Floodplain Mapping 26

35 Figures Coal Creek Floodplain Mapping 27

36

37 CI TY OF FE RN C Flood Protection (Approximate Location) Dike Attack Dike 5 Bin Wall Dike Riverbank Protection Active Floodplain Flood Construction Line (FCL) (m) 2 Year Floodplain Boundary Active Fan Boundary FF Year Inundation Extents, including Freeboard (.6 m for Coal Creek,.3 m for Brewery Creek) Depth (m) REEK E RE YC CI T YO RC WER E TUB BRE 5 ER NI E Combined Coal Creek and Elk River Floodplain K > 2.4 Municipal Boundary Contours 5 m interval Streams Limitations of floodplain map: 1. The hydrodynamic modeling, flood inundation extents and depths are based on bathymetric surveys conducted in May 214 and LiDAR surveys in 28 by Focus Corporation. Additional topographic data collected by Northwest Hydraulic Consultants Ltd. (NHC) in June 214 was used to supplement the other topographical data. 2. Changes to the channel, floodplain, or climate may affect the flood levels and render site-specific map information obsolete. The accuracy of the location of the floodplain boundary as shown on this map is limited by the accuracy of the bathymetric and topographic data. 3. Floodplain maps are an administrative tool that indicate the flood elevations and floodplain boundaries for the designated design flood (2-year flood). Flooding may occur outside the designated boundaries. NHC does not assume any liability by reason of the designation or failure to designate areas on the map. 4. Floodplain maps do not provide information on site-specific hazards such as land erosion or sudden shifts in the water courses. 5. Changes to roads, railways or other barriers can restrict water flow and affect flood levels locally. Changes, such as these, are not accounted for on the map. 6. Channel obstructions, local stormwater inflows, groundwater, or other land drainage can cause flood levels to exceed those indicated on the map. The floodplain maps do not account for other sources of water that can also affect local flood levels. 7. Lands adjacent to the floodplain may be subject to flooding from tributary streams that are not indicated on the floodplain map. 8. Professional assistance and detailed site-specific engineering alysis are required to address any of the above issues. Notes to users: 1. The flood levels are based on water surface profiles simulated using a one-dimensional hydrodynamic model developed by NHC (214). This map delineates the Coal Creek and Lower Brewery Creek flood potential under present (Year 214) conditions for a current 2-year return period flood event. A 2-year return period flood means that, on average, the flood will occur once in 2 years and that there is a.5% chance that the flood levels mapped could be equaled or exceeded in any one year (or that there is about a % chance that the flood level mapped could be equaled or exceeded in a period of 2 years). 2. Flood construction levels (FCLs) were computed using the 2-year instantaneous flood and account for a.6 m freeboard allowance above Coal Creek calculated water level and.3 m above Brewery Creek calculated water level. 3. The required setback of buildings from the water courses is shown based on a flood hazard assessment and is not based on other hazards (i.e., geotechnical), ecological value, or other regulations. 4. This map is available from the. The does not warrant that the information contained on this map is accurate, or guarantee that areas outside of the designated boundaries will not be subject to flooding. 5. Combined Coal Creek and Elk River flood hazard should be determined from the greater of Coal Creek and Elk River FCLs. DATA SOURCES: Background Orthophoto - (May 24) Stream Lines - Based on BC Freshwater Atlas Flood Protection - Cadastral - Bathymetry - Focus Engineering (May 214) LiDAR - Focus Engineering (28) and (214) SCALE - 1:5, 2 3 M Coordinate System: NAD 1983 UTM ZONE 11N Units: METRES Elevations: GEODETIC Engineer GIS JXG Job Number Reviewer JXD, MSN DPM Date FEB-216 COAL CREEK FLOODPLAIN MAPPING FIGURE 7 \\mainfile-van\projects\inactive\bc_3_to_3999\3372 Coal Cr Floodplain Map\GIS\3372_JXD_Map_Floodplain_R1_3.mxd Fernie REE K CO A LC STUDY EXTENT 1 5 YE B R I T I S H C O L U M B I A 7 D. O D STU R 3 Gostick Place North Vancouver, B.C. V7M 3G3 Canada Office: Fax: T 6 2 ELK RIVE N XTE CR EE K A BL AC K BE R C CITY OF FERNIE E EK IE R

38

39 CI TY OF FE RN E BL AC K 6 CR EE O. C Gostick Place North Vancouver, B.C. V7M 3G3 Canada Office: Fax: B R I T I S H C O L U M B I A STUDY EXTENT B 99 5 C LC A A RE E K Flood Protection (Approximate Location) Dike Attack Dike 5 Bin Wall Dike Riverbank Protection B 3 Metre Setback CO A Fernie Recommended Flood Hazard Management Zones NI E Floodway and setback area. No development. Overflow and potential avulsion zone. Limited development. Overflow potential zone. Conditional development. Streams Municipal Boundary Contours 5 m interval ER FF CI T YO EK RE YC 3 REE K RC WE R 3372 Coal Cr Floodplain Map\GIS E TUB BRE 5 A B C C Limitations of floodplain map: 1. The hydrodynamic modeling, flood inundation extents and depths are based on bathymetric surveys conducted in May 214 and LiDAR surveys in 28 by Focus Corporation. Additional topographic data collected by Northwest Hydraulic Consultants Ltd. (NHC) in June 214 was used to supplement the other topographical data. 2. Changes to the channel, floodplain, or climate may affect the flood levels and render site-specific map information obsolete. The accuracy of the location of the floodplain boundary as shown on this map is limited by the accuracy of the bathymetric and topographic data. 3. Floodplain maps are an administrative tool that indicate the flood elevations and floodplain boundaries for the designated design flood (2-year flood). Flooding may occur outside the designated boundaries. NHC does not assume any liability by reason of the designation or failure to designate areas on the map. 4. Floodplain maps do not provide information on site-specific hazards such as land erosion or sudden shifts in the water courses. 5. Changes to roads, railways or other barriers can restrict water flow and affect flood levels locally. Changes, such as these, are not accounted for on the map. 6. Channel obstructions, local stormwater inflows, groundwater, or other land drainage can cause flood levels to exceed those indicated on the map. The floodplain maps do not account for other sources of water that can also affect local flood levels. 7. Lands adjacent to the floodplain may be subject to flooding from tributary streams that are not indicated on the floodplain map. 8. Professional assistance and detailed site-specific engineering alysis are required to address any of the above issues. Notes to users: 1. The flood levels are based on water surface profiles simulated using a one-dimensional hydrodynamic model developed by NHC (214). This map delineates the Coal Creek and Lower Brewery Creek flood potential under present (Year 214) conditions for a current 2-year return period flood event. A 2-year return period flood means that, on average, the flood will occur once in 2 years and that there is a.5% chance that the flood levels mapped could be equaled or exceeded in any one year (or that there is about a % chance that the flood level mapped could be equaled or exceeded in a period of 2 years). 2. Flood construction levels (FCLs) were computed using the 2-year instantaneous flood and account for a.6 m freeboard allowance above Coal Creek calculated water level and.3 m above Brewery Creek calculated water level. 3. The required setback of buildings from the water courses is shown based on a flood hazard assessment and is not based on other hazards (i.e., geotechnical), ecological value, or other regulations. 4. This map is available from the. The does not warrant that the information contained on this map is accurate, or guarantee that areas outside of the designated boundaries will not be subject to flooding. 5. Combined Coal Creek and Elk River flood hazard should be determined from the greater of Coal Creek and Elk River FCLs. DATA SOURCES: Background Orthophoto - (May 24) Stream Lines - Based on BC Freshwater Atlas Flood Protection - Cadastral - Bathymetry - Focus Engineering (May 214) LiDAR - Focus Engineering (28) and (214) SCALE - 1:5, 2 3 M Coordinate System: NAD 1983 UTM ZONE 11N Units: METRES Elevations: GEODETIC Engineer GIS JXG Job Number Reviewer JXD, MSN DPM Date FEB-216 COAL CREEK FLOOD HAZARD MANAGEMENT ZONES FIGURE 8 \\mainfile-van\projects\inactive\bc_3_to_3999\3372 Coal Cr Floodplain Map\GIS\3372_JXD_Map_FHMZ1_R1_3.mxd YE 1 5 D STU T 5 R N XTE ELK RIVE 99 7 D K BE A CITY OF FERNIE CR 116 EK IE R

40 Photographs Coal Creek Floodplain Mapping 32

41 Photo 1. Coal Creek at the mouth, view facing downstream to Elk River. Photo 2. Coal Creek, view facing upstream from Farm Access Bridge. Coal Creek Floodplain Mapping 33

42 Photo 3. Dike protection works between Railway Bridge and Park Avenue Bridge, view facing downstream. Photo 4. Brewery Creek springs, view facing upstream from farm access road. Coal Creek Floodplain Mapping 34

43 Photo 5. Brewery Creek wetland, view facing upstream of Cokato Road. Photo 6. Brewery Creek wetland outlet, view from right bank at edge of wetland. Coal Creek Floodplain Mapping 35

44 Photo 7. Park Avenue Bridge, view facing upstream. Photo 8. Railway Bridge, view facing upstream. Coal Creek Floodplain Mapping 36

45 Photo 9. Cokato Road Bridge, view facing upstream from railway embankment. Photo. Farm Access Bridge, view facing downstream. Bank protection works along left bank at bottom left corner of photo. Coal Creek Floodplain Mapping 37

46 Photo 11. River Road extension bridge, view facing downstream. Coal Creek Floodplain Mapping 38