CITY OF KIMBERLEY HYDROLOGICAL & HYDRAULIC ASSESSMENT

Transcription

1 HYDROLOGICAL & HYDRAULIC ASSESSMENT ISSUED FOR USE January 31, 2012 FILE: LACAS CONSULTANTS INC. CONSULTING ENGINEERS & HYDROLOGICAL SPECIALISTS, SINCE 1991 Suite 200, 1311 Howe Street, Vancouver, BC, Canada, V6Z 2P3 Telephone: Facsimile:

2 EXECUTIVE SUMMARY LaCas Consultants Inc. () was retained by Aqua-Tex Scientific Consulting Ltd. on behalf of the City of Kimberley to update the hydrology of Mark Creek and to assess the hydraulic capacity of the existing Mark Creek flume, located within the City of Kimberley, BC (Figure 1). The purpose of this report is to evaluate the existing flood risk to the City of Kimberley based on a 1 in 200 year recurrence interval instantaneous peak flood flowing through the existing Mark Creek flume. This initial report will lay the ground work for the following report by, Mark Creek Flume Stream Rehabilitation Project, in which multidisciplinary criteria is integrated into the design of a new stream channel. This is not a design report for a new stream channel replacing the existing flume. The study area includes a 480 m long reach bracketing Mark Creek flume. The reach upstream of the flume appears to have been channelized and armoured with rock riprap. The flume itself is a rectangular concrete channel flowing through the city and re-enters a channelized open channel downstream in the vicinity of Jenning s Street. The existing Mark Creek flume was constructed in the 1950 s as flood control solution to the devastating 1948 flood which caused extensive flood damage to the town of Kimberley. The 1948 flood avulsed and flowed down city streets creating channels and washing several buildings away. The US Army Corps of Engineers, River Analysis Model (v ) was used as the hydraulic model to determine the water surface profile for the 200-year flood in Mark Creek and the average channel velocities. The 200-year flood at the downstream end of the project is estimated to be 66 m 3 /s, which includes Kimberley Creek inflows. The hydraulic modeling results indicated that Mark Creek channel is steep enough to sustain supercritical flow throughout its length which results in relatively shallow water depths coupled with extreme average channel velocities. Within the flume the average channel velocities exceed 16 m/s which would be a risk to life for anyone in the channel during a flood event. Furthermore, the higher than normal flow velocities would leave very little warning to the public if a flood event approaches the City. The water surface profiles indicated that it would be desirable to reduce the flow inputs into the flume by a separate upstream diversion of Kimberley Creek directing water at the Kimberley Creek intake point through to Taylor s Slough with adequate channelization downstream returning the flow into Mark Creek downstream of the flume. The diversion of Kimberley Creek is discussed in a separate report by. PAGE (i)

3 The hydraulic modeling also showed that with the exception of possible overbank flooding upstream of the entrance to the flume, the 200-year clear-water flood of 66 m 3 /s would be contained within the flume. However, the flow is expected to jump out of the channel upstream of the flume inundating properties and roads. Furthermore, when a debris flood is considered a minimum 1.5 m freeboard is recommended for the flume; which appears to be difficult to maintain through the length of the existing flume with the current flume geometry. The conclusion from a hydrological and hydraulic engineering perspective is that the flume in its current state is a danger to the public during a major flood event. It is recommended that the flume be replaced with a combination of wider channel reaches and drop structures to reduce the extreme velocity. It is recommended that the City erect signs along the existing flume warning the public of high velocity flow and flooding. Furthermore, the City should prepare emergency procedures to ensure the protection of the public and mitigate floodwater damage to properties during a flood event. PAGE (ii)

4 TABLE OF CONTENTS EXECUTIVE SUMMARY Page i 1. INTRODUCTION 1 2. MARK CREEK HYDROLOGY Hydrological Analysis 2.2 Peak Flow Estimates 3. HYDRAULIC MODELING Hydraulic Modeling Parameters 3.2 Hydraulic Modeling Results 4. CONCLUSIONS AND RECOMMENDATIONS 6 5. CLOSURE AND REPORT LIMITATIONS 7 LIST OF FIGURES Figure 1 - Location Plan Figure 2 - Mark Creek Flume, Hydrological & Hydraulic Assessment Plan View Figure 3 - Mark Creek Flume, Hydrological & Hydraulic Assessment 200-Year Flood Profile APPENDIX Table 3 - Mark Creek Flume Modeling Results for 200-Year Flood (66 m 3 /s) PAGE (iii)

5 1. INTRODUCTION LaCas Consultants Inc. () was retained by Aqua-Tex Scientific Consulting Ltd. on behalf of the City of Kimberley to update the hydrology of Mark Creek and to assess the hydraulic capacity of the existing Mark Creek flume located within the City of Kimberley, BC (Figure 1). The purpose of this report is to evaluate the existing flood risk to the City of Kimberley based on a 1 in 200 year recurrence interval instantaneous peak flood flowing through the existing Mark Creek flume. The Mark Creek flume was constructed in the 1950 s as flood control solution to the devastating 1948 flood which caused extensive flood damage to the town of Kimberley. The 1948 flood avulsed and flowed down city streets creating channels and washing several buildings away. The flume is 380 m long, about 2 m deep and 6 m wide at an average slope of 8 percent. There are several crossings of the flume including vehicular bridges, a pedestrian bridge, waterlines, gas lines and the Sullivan mine acid rock drainage treatment waterline (Figure 2). The US Army Corps of Engineers, River Analysis Model (v ) was used as the hydraulic model to determine the water surface profile for the 200-year flood in Mark Creek and the average channel velocities. In addition, the report addresses the possible impact of debris floods which are characterized by a combination of bedload movement, suspended sediment load, and floating organic debris. The movement is part of the flood process in which the flow behaves as a water flood, rather than a hillslope process such as a debris flow or / channelized landslide. Previous pertinent reports 1,2, photographs and historical memoranda were reviewed. 1 Klohn-Crippen, April 1999, City of Kimberley, Mark Creek Flood Assessment, Project No BC Environment, Water Management Branch, June 1995, Mark Creek Hydrology Data Summary and Analysis. PAGE 1 of 9

6 2. MARK CREEK HYDROLOGY 2.1 Hydrological Analysis Located in Kootenay Valley, Mark Creek flows southward to its confluence with the St. Mary River just south of the City of Kimberley. The drainage area of Mark Creek at the end of the concrete flume in the City of Kimberley is approximately 135 km 2. The median basin elevation of the watershed is approximately 1780 m. It should be noted that a concrete dam and reservoir are located within the Mark Creek watershed upstream of the City of Kimberley. Kimberley Creek is one of the major tributaries of Mark Creek, and it has a drainage area of approximately 25 km 2 at its mouth. The median basin elevation of the Kimberley Creek watershed is approximately 1300 m. There are a number of hydrometric stations on Mark Creek, but most of them are designated as regulated. There is a hydrometric station on Mark Creek (08NG085) with a relatively long period of record, measuring natural flows, and it was operated by Water Survey of Canada (WSC) from 1989 to 1998 and has been operated by the City of Kimberley since Historical hydrometric data from this station (Mark Creek Above Diversions) was obtained both from the Water Survey of Canada and from available Mark Creek resource inventory reports. The Water Survey of Canada has one natural hydrometric station on Kimberley Creek near Kimberley (08NG057), but this station was only operated from 1968 to 1973 and has limited peak flow data. Other useful regional hydrometric stations operated by the WSC include the Mather Creek below Houle Creek (08NG076), St. Mary River below Morris Creek (08NG077), and St. Mary River near Marysville (08NG046). The hydrometric stations used in this study are listed in Table 1. Table 1: Regional Hydrometric Stations Station ID Station Name Drainage Area (km 2 ) 08NG046 ST. MARY RIVER NEAR MARYSVILLE 08NG076 MATHER CREEK BELOW HOULE CREEK 08NG077 ST. MARY RIVER BELOW MORRIS CREEK 08NG085 MARK CREEK ABOVE DIVERSIONS Period of Record Years of Peak Flow Data Status Daily, 20 Instant. Active Daily, 38 Instant. Inactive Daily, 35 Instant. Inactive Daily, 25 Instant. Inactive PAGE 2 of 9

7 By analyzing available peak flow data at the Mark Creek Above Diversions station, it was determined that peak flows in the study area usually occur in May or June, as a result of snowmelt. Four methods were carried out by EBA Engineering Consultants Ltd. (EBA) were applied in determining the flood estimates for various return periods at two points of interest: Location 1 Mark Creek at the end of the concrete flume in the City of Kimberley (approx. 135 km 2 ) Location 2 Kimberley Creek at its mouth (approx. 25 km 2 ) Method 1: Station Frequency Analysis Method A flood frequency analysis was performed based on the historical maximum instantaneous flow record available at the Mark Creek above Diversions station (08NG085) using Environment Canada s Consolidated Frequency Analysis (CFA) software version 3.0. The distributions providing the best fit to the data record were selected in estimating the floods for various return periods at the station. Results of the station frequency analysis were then transposed to the project site drainage areas by applying an accepted watershed scaling method. Method 2 Regional Analysis with Index Flood Method The regional analysis in this case involves the application of an index flood method. Flood frequency analyses were conducted for the four selected regional hydrometric stations. To make use of all available peak flow data, the maximum instantaneous flow records were extended by applying an average ratio of maximum instantaneous to maximum daily flows for the three largest floods at the stations. The distributions providing the best fit to the extended data records were selected in estimating the floods for various return periods at the stations. Results of the frequency analyses were then used in the index flood method, using the 10-year flood as the index flood. A relationship was determined between the unit index flood discharge (L/s/km 2 ) and drainage area. An envelope curve was then drawn to determine the unit 10-year flood at each site. The median ratios for various return period floods to the index flood were calculated from the regional flood frequency analysis. These ratios were used to determine the peak flood estimates for various return periods at the points of interest. Method 3 Regional Analysis with Design Flood versus Drainage Area Method In addition, plotting the flood estimates against drainage area using results of the frequency analyses from the four selected hydrometric stations yields a set of regression relationships. These regression equations were used in determining the flood estimates for various return periods at the points of interest. PAGE 3 of 9

8 Method 4 - Streamflow in Kootenay Region Envelope Curve For comparison purposes, the 2002 Streamflow in Kootenay Region Envelope Curve prepared by the BC Ministry of Environment, Land and Parks was also used as a reference. In this regional study, a design curve for the 10-year peak flow as a function of drainage area was developed for Eastern Kootenay Region (Subzone Y). The regional median ratios of the flood estimates for various return periods to the 10-year floods were then applied. 2.2 Peak Flood Estimates The peak flood estimates obtained from the four methods were compared, and results indicate that the estimates determined from the station frequency analysis with the shortest period of data record available are generally the lowest. The index flood method provides the second highest flood estimates, slightly lower than the estimates obtained from the 2002 Streamflow in Kootenay Region Envelope Curve. To be reasonably conservative, peak flood estimates for Mark Creek and Kimberley Creek determined from the index flood method are recommended for design purposes by EBA (Table 2). Table 2: Recommended Peak Flood Estimates (m 3 /s) Return Period (yrs) Mark Creek Kimberley Creek Reference: Ministry of Environment, Lands and Parks, Report on British Columbia Streamflow Inventory. As a review on the results, the US Army Corps of Engineering Hydrological Modeling System (v. 3.4) based on the Clark instantaneous unit hydrograph method using the Intensity- Duration-Frequency (IDF) curve for Kimberley, BC (Kimberley PCC # ) yielded results reasonably close to the 200-year index flood method results for Mark Creek recommended by EBA. PAGE 4 of 9

9 3. MARK CREEK EXISTING FLUME HYDRAULIC MODELING 3.1 Hydraulic Modeling Parameters Kimberley Creek flows from a 1,100 mm dia. pipe into the Mark Creek flume at just downstream of the Wallinger Road bridge (north side) contributing to the flows in the existing flume. However, during the 200-year flood on Kimberley Creek 14 m 3 /s it is expected that the capacity of the Kimberley Creek diversion pipe (about 1 km long) would be exceeded and the remaining flow would be overland through the City of Kimberley eventually flowing into Mark Creek. To be conservative, the hydraulic modelling used 66 m 3 /s for the flood flow in the entire flume. Forty-nine cross sections of the Mark Creek channel and flume were input into the hydraulic model extending from the just downstream of the end of Jennings Street to about 480 m upstream to the Kimberley Street footbridge. The cross sections were based on a land survey carried out in Variation of Manning s n with flow was not considered in this study and there was no data available to calibrate roughness values. It should be noted that there is a degree of modelling uncertainty associated with 1-D hydraulic models, which assume an average cross-sectional velocity not fully representing complex hydraulic variations. The upstream and downstream boundary conditions were assumed to be normal depth. The results of the hydraulic modeling are shown in Table 3 (Appendix). The hydraulic modeling results indicated that the existing flume capacity would contain the 200-year clear-water flood under supercritical flow with associated extreme velocities up to 16 m/s as shown in Table 3 (without the formation of hydraulic jumps and debris floods). However, Table 3 shows that there is zero freeboard to -0.3 m remaining freeboard between River Station and just upstream of the pedestrian bridge along the west side of Deer Park Avenue at the bottom of Reach 8. This area is subject to overbank flooding and channel avulsion whereby the river jumps its channel. Mark Creek is susceptible to debris floods which are characterized by a combination of bedload movement, suspended sediment load, and floating organic debris. To represent the bulking of the flow a bulking factor of 2 times was applied to the 200-year clear-water flood. The bulked flow resulted in raising flood levels up to 1.2 m higher. PAGE 5 of 9

10 4. CONCLUSIONS AND RECOMMENDATIONS 1. Mark Creek which flows through the City of Kimberley through a concrete flume constructed in the 1950 s is subject to flooding and erosion / scour. 2. The hydrological assessment indicates that including Mark Creek s tributaries at the end of the existing flume the 200-year clear-water flood was estimated to be 66 m 3 /s. The chance that the 200-year flood could occur at least once in 50 years is about 22 percent. 3. The hydraulic modelling results indicated that the existing flume capacity would contain the 200-year clear-water flood under supercritical flow with associated extreme velocities ranging up to 16 m/s without the formation of hydraulic jumps and debris floods. At the pedestrian bridge upstream of the flume entrance on Deer Park Avenue (River Station to River Station 0+440) there is zero or negative freeboard for the 200-year flood therefore bankfull and overbank flooding is expected in Reach 8 (Figure 1) The estimated remaining freeboard at each River Station is shown in Table 3 (Appendix). 4. Mark Creek is susceptible to debris floods which are characterized by a combination of bedload movement, suspended sediment load, and floating organic debris. To represent the bulking of the flow a bulking factor of 2 times was applied to the 200-year clear-water flood. The bulked flow resulted in raising flood levels up to 1.2 m higher. Furthermore, when a debris flood is considered a minimum 1.5 m freeboard (1.2 m plus 0.3 m) is recommended for the flume; which appears to be difficult to maintain through the length of the existing flume with the current flume geometry (Figures 3-1 and 3-2). 5. Debris jams could conceivably occur at the entrance of the flume and cause a channel avulsion spilling floodwaters onto the floodplain inundating properties and roads. In addition, debris jams in the channel itself are likely at narrow sections which could facilitate a hydraulic jump raising water levels and reducing freeboard, and causing spillage of flows and transferring flood risk to private properties and municipal infrastructure. 6. It is evident that the concrete flume is deteriorating with holes in the concrete channel bottom and unstable concrete walls. It is apparent that the flume has exceeded its service life and requires rehabilitation. Immediate remedial works are required to stabilize the channel walls and the channel should be closely monitored during flood events. 7. The extreme velocities in the channel during flooding would be life threatening for anyone entering the channel. The City of Kimberley should erect signs prohibiting entering the channel and warning the public of the dangers of extreme velocities during flooding. PAGE 6 of 9

11 8. The City of Kimberley should have a flood action plan to deal with the immediate removal of debris jams and an emergency plan for residents affected by possible flooding from overbank flows along the channel. 9. Upon historical review of the 1948 flooding and site inspection of the Mark Creek fan, it evident that the creek fluvial and geomorphological nature is to widen itself. Channel widening, debris structures, proper crossings and controlled energy dissipation drop structures should be considered in the rehabilitation of the flume. 5. CLOSURE AND REPORT LIMITATIONS This report: Mark Creek Flume Existing Flume Flood Risk; provides updated peak flows for the assessment of hydraulic capacity and flood risk for the existing Mark Creek flume located within the City of Kimberley, BC. trusts that this report meets your present requirements. Prepared by: Original Signed and Sealed, Issued for Use, January 31, 2012 Brian LaCas, P.Eng. Hydrotechnical Engineer LaCas Consultants Inc. As mutual protection to the Client, the public and LaCas Consultants Inc., this document, its drawings, figures, and appendices, are submitted for the exclusive use of the Client for this project only and no other project. This report supersedes all previous reports by LaCas Consultants Inc. regarding Mark Creek for the City of Kimberley, BC PAGE 7 of 9

12 No person, other than the Client, is authorized to use this document or reproduce this document in whole or in part in hardcopy or electronically without the express written permission of LaCas Consultants Inc with the exception of the City of Kimberley, Aqua- Tex Scientific Consulting Ltd. and the Provincial Ministry of Natural Resource Operations who are each authorized only to review this document for the purposes of this project only. LaCas Consultants Inc. specifically disclaims any responsibility for losses or damages incurred through the use of this document for any purpose other than for this project. In order to properly understand the suggestions, recommendations and opinions expressed in this document, reference must be made to the whole document. LaCas Consultants Inc. will not be responsible for use by any party of portions of this document without reference to the whole document. The figures in this document are not meant as construction drawings and the illustrated flood inundation levels along the existing flume are based on existing site conditions as of the date of issue of this document. The inundation levels shown in the figures of this document shall not be interpreted as dike crest elevations or Flood Construction Levels. Any future uncertainty of global warming has not been taken into account in this document. When LaCas Consultants Inc. submits both electronic file and hardcopies of this document, including drawings and other documents and deliverables (LaCas Consultants Inc. s instruments of professional service), only the signed and sealed hardcopy versions shall be considered final and legally binding. Such hardcopy versions shall be the original documents of record and working purposes and, in the event of a dispute or discrepancy, shall govern over the electronic versions. The original hardcopy sealed and signed version archived by LaCas Consultants Inc. shall be deemed to be the overall original for the project. This document, and all previous reports, calculations, computer modeling, files, notes, drawings, plans, designs, techniques, technologies, methods, concepts, water surface profile data input / output, inventions, specifications and data associated with the project, is the intellectual property of LaCas Consultants Inc., and LaCas Consultants Inc. holds the copyright in all such intellectual property. This document represents LaCas Consultants Inc. s best professional judgment based on the information available at the time of its completion and as appropriate for the project scope of work. Services performed in developing the content of this document have been PAGE 8 of 9

13 conducted in a manner consistent with that level and skill ordinarily exercised by members of the engineering profession currently practising under similar conditions. LaCas Consultants Inc. provides no warranty, express or implied, with respect to its work for this project or this document. Use of this document is subject to LaCas Consultants Inc. s Standard Terms and Conditions. LaCas Consultants Inc. does not take any responsibility for the work carried out by any third party on the project. PAGE 9 of 9

14 APPENDIX Table 3: Mark Creek Flume Modeling Results for 200 Year Flood (66 m 3 /s) MODEL SECTION & RIVER STATION WATER SURFACE ELEVATION (m. elev.) AVERAGE CHANNEL VELOCITY (m/s) PAGE A1 REMAINING FREEBOARD LEFT* (m) REMAINING FREEBOARD RIGHT* (m) Section 47 Sta ** Section 46 Sta ** Section 45 Sta ** Section 44 Sta ** Section 43 Sta ** Section 42 Sta ** Section 41 Sta Section 40 Sta Section 39 Sta Section 38 Sta Section 37 Sta Section 36 Sta Section 35 Sta Section 34 Sta Section 33 Sta Section 32 Sta Section 31 Sta Section 30 Sta Section 29 Sta Section 28 Sta Section 27 Sta Section 26 Sta Section 25 Sta Section 24 Sta Section 23 Sta Section 22 Sta Section 21 Sta Section 20 Sta Section 19 Sta Section 18 Sta Section 17 Sta Section 16 Sta Section 15 Sta Section 14 Sta Section 13 Sta Section 12 Sta Section 11 Sta Section 10 Sta Section 9 Sta Section 8 Sta Section 7 Sta Section 6 Sta Section 5 Sta Section 4 Sta ** Section 3 Sta ** Section 2 Sta ** Section 1 Sta ** * Convention looking downstream. ** Rock riprapped channel, no existing flume.

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