Development of a Stage-Discharge Rating for Site Van Bibber Creek at Route 93

Transcription

1 Development of a Stage-Discharge Rating for Site Van Bibber Creek at Route 93 Prepared for: Urban Drainage and Flood Control District 2480 W. 26 th Avenue Suite 156-B Denver, CO May 19, 2006 (Rev May 2007) 1225 Red Cedar Circle, Suite A Fort Collins, CO (970)

2 Table of Contents 1.0 Certification Introduction Field Survey Methods Data Reduction, Modeling And Analysis Rating Development References Field Survey Notes Table of Figures Figure 1. Site 330 Location Map Figure 2. Site 330 Looking Downstream... 7 Figure 3. Site 330 Approximate Cross Section and Bench Mark Locations Figure 4. Site 330 Cross-Section 1.0 At The Downstream End of the Bridge Wing Walls Figure 5. Site 330 Cross-Section 2.0, Left Side Looking Downstream Figure 6. Site 330 Cross-Section 2.0, Right Side Looking Downstream Figure 7. Site 330 Inside of the Left Bridge Culvert Figure 8. Site 330 Inside of the Right Bridge Culvert Figure 9. Site 330 Cross-Section 3.0, Left Side Culvert Looking Downstream Figure 10. Site 330 Cross-Section 3.0, Right Side Culvert Looking Downstream Figure 11. Site 330 Cross-Section 4.0 at the PT, Looking Downstream Figure 12. Site 330 Cross-Section 5.0 At The Upstream End of the Bridge Wing Walls Looking Downstream Figure 13. Site 330 Distances Between Surveyed Cross Sections Figure 14. Site 330 Instrument Elevations and Closure Error Calculation Figure 15. Site 330 CDOT Bench Mark Figure 16. Site 330 Reduced Channel Cross Section Survey Notes Figure 17. Site 330 Graphical Description of the HEC-RAS Cross-Sections 1.0 and Figure 18. Site 330 Graphical Description of the HEC-RAS Cross-Sections Figure 19. Site 330 Graphical Description of the HEC-RAS Cross-Sections Figure 20. Site 330 Water Surface at Maximum Discharge for Cross-Sections Figure 21. Site 330 Water Surface at Maximum Discharge for Cross-Sections Figure 22. Site 330 Water Surface at Maximum Discharge for Cross-Sections Figure 23. Site 330 Predicted Water Surface Elevation Profile Plot Figure 24. Site 330 HEC-RAS Output for Cross-Sections Figure 25. Site 330 HEC-RAS Output for Cross-Sections Figure 26. Site 330 HEC-RAS Output for Cross-Sections Figure 27. Site 330 Stage-Discharge Relationship at the PT Figure 28. Site 330 Stage-Discharge Comparison Relationships Figure 29. Site 330 Stage-Discharge Relationship Log-Log Plot Table of Tables Table 1. Site 330 Predicted Stage-Discharge Relationship Tabular Data Table 2. Current UDFCD Rating for Site Table 3. Depth-Discharge Rating for an Alternate PT Installation Inside The Culvert at Cross- Section UDFCD Site 330 Rating Development 2 Water and Earth Technologies, Inc.

3 1.0 CERTIFICATION I, Richard Spotts, state that the information presented in this report entitled, Development of a Stage-Discharge Rating for Site Van Bibber Creek at Route 93, prepared for The Urban Drainage and Flood Control District, Denver, Colorado was prepared by me or by persons under my supervision and is correct to the best of my knowledge and information. Richard Spotts, P.E. Registration No UDFCD Site 330 Rating Development 3 Water and Earth Technologies, Inc.

4 2.0 INTRODUCTION Water and Earth Technologies, Inc. (WET) was contracted by The Urban Drainage and Flood Control District (UDFCD) to develop a hydraulic rating at Site 330, Van Bibber Creek at Route 93. This station, located upstream of a box-culvert bridge under Route 93 is already instrumented to measure river stage. Stage information for this site is telemetered in real time to local base stations that assess the flooding potential during large runoff events. In addition to stage, discharge information is valuable for decision-making. Stage-discharge rating relationships (ratings) are used to convert the stage, represented as a water depth in feet above a reference elevation monitored by a pressure transducer (PT) in the stream to values of discharge in cubic feet per second (cfs). The discharge rating developed in this report is based on precise measurement of the river channel and physical structures controlling flow and mathematical approximation of the hydraulics at this site. This report includes the following sections: an introduction, a discussion of field survey methods, a discussion of office procedures for data reduction and analysis, a description of each site and a discussion and presentation of survey data and model results (including model output, a stage-discharge rating table and a plot of the rating curve, and recommendations relevant to the results), a compilation of references, and cross section field survey notes 3.0 FIELD SURVEY METHODS A theoretical step-backwater technique using the U.S. Army Corps of Engineers HEC-RAS computer model (USACOE 2002) was used to develop the stage-discharge ratings. The modeling typically requires data for five cross sections at a site. Typically, the cross section in which stage is observed is bracketed by one or more cross sections both upstream and downstream. Cross sections were surveyed from left to right looking downstream. Cross sections were numbered from downstream to upstream. Bench marks and end points of each cross section were marked as appropriate. A mapping grade GPS unit was used to determine the latitude and longitude of monument bench marks at each site, the stage measurement sensor housing (with the cap removed) and each cross-section end point so that cross sections and bench marks can be easily located in the future. Additionally, the coordinates were used to establish cross section orientation in the HEC-RAS model. A self-leveling level, tape and survey rod were used to measure each point in the cross section and to relate streambed and water-surface cross-section elevations to the bench mark elevation. Variations in channel roughness (Manning s n value) were determined for each cross section. The main channel and overbank areas within each cross section were subdivided into n-value break points (locations where n-values change), and n-values specific to each subdivision were estimated. Photos of the site and each surveyed cross section were taken. Cross-section location selection, spacing, and orientation; surveying techniques; roughness parameter selection (Manning s n UDFCD Site 330 Rating Development 4 Water and Earth Technologies, Inc.

5 values); and photographic and methods documentation followed standard protocols (Arcement and Schneider 1990; Barnes 1987; Benson and Dalrymple 1984; Dalrymple and Benson 1984; Harrelson et. al. 1994; U.S Army COE 2002; U.S. Geological Survey 1977). 4.0 DATA REDUCTION, MODELING AND ANALYSIS As previously mentioned, the U.S. Army COE HEC-RAS computer model was used to analyze the field data and develop the stage-discharge rating relationships. HEC-RAS is an integrated system of software, designed for interactive use in a multi-tasking environment. The steady flow water-surface profile component of the modeling system was used to calculate water surface profiles and elevations for a wide range in flows, from very low flow to flood flows, or flow that would occur at the highest stage contained within the channel and surveyed overbank. The basic computational procedure is based on the solution of a one-dimensional energy equation describing gradually varied uniform flow through the channel. Energy losses are evaluated by friction (Manning s equation) and contraction/expansion (coefficient multiplied by the change in velocity head). WET s HEC-RAS modeling input applied the initial assumption that the downstream modeling boundary condition was controlled by normal depth as defined by measured channel conditions and slope. At higher flows however, other cross sections (such as the location of the bridge contraction) may control the flow. These controlling locations and conditions are additional valuable output from the HEC RAS model. Output values from the HEC-RAS model include the predicted water surface elevations at each cross section for a range of known discharges. The water surface predictions at the pressure transducer cross section were used to develop the stage discharge rating for the site. 5.0 RATING DEVELOPMENT A general site investigation was performed by WET staff on January 10, The site was surveyed by WET staff on January 23, River cross sections were surveyed to describe the channel and used as input data to the HEC-RAS hydraulic model in order to develop a stage discharge relationship at the PT cross section. Site 330, Van Bibber Creek at Route 93, is located at the upstream end of a twin 14-ft x 9-ft box culvert bridge under Route 93, just north of Golden, CO (circled in red in Figure 1). UDFCD Site 330 Rating Development 5 Water and Earth Technologies, Inc.

6 Figure 1. Site 330 Location Map. UDFCD Site 330 Rating Development 6 Water and Earth Technologies, Inc.

7 The standpipe, PT riser pipe and bridge at the site are shown in Figure 2. Figure 2. Site 330 Looking Downstream. 5.1 Site 330 Channel Survey On January 23, 2006 WET surveyed five channel cross sections and four geometry cross sections of the inside of the box culvert bridge. A Colorado Department of Transportation bench mark on the bridge was used as vertical control for the survey. An aerial photo with the approximate locations of the surveyed cross sections and landmarks is presented in Figure 3. UDFCD Site 330 Rating Development 7 Water and Earth Technologies, Inc.

8 Xsec 5.0 Xsec 4.0 Xsec 3.0 Flow Xsec 2.8 Xsec 2.6 Xsec 2.4 Xsec 2.2 BM1 PT Standpipe Xsec 2.0 Xsec 1.0 Figure 3. Site 330 Approximate Cross Section and Bench Mark Locations. Photos of each cross section are presented in Figure 4 - Figure 12. Cross-Section 1.0 is located at the downstream end of the bridge wing walls (Figure 4) and describes the channel shape below the box culvert bridge. Cross-Section 2.0 is located upstream of Cross-Section 1.0 at the downstream opening of the twin box culvert bridge. Views of the two openings, left and right looking downstream are shown in Figure 5 and Figure 6. The inside of the box culvert bridge is shown in Figure 7 and Figure 8. Note that the photos in Figure 7 and Figure 8 were taken looking upstream for better lighting. Each culvert opening contains four concrete weir structures, each approximately 14 feet wide and 0.7 feet thick and sloping towards the center. Profiles of the weirs and concrete ceiling heights were surveyed and denoted as Cross-Sections 2.2, 2.4, 2.6, 2.8 from downstream to upstream. Cross-Section 3.0 is located at the upstream opening of the box culvert bridge shown in Figure 9 and 10. The PT cross section, Cross-Section 4.0 is located upstream of the bridge culvert opening (Figure 11). The upstream point of the survey, Cross- Section 5.0, is located at the upstream end of the bridge wing walls, upstream of the PT cross section (Figure 12). UDFCD Site 330 Rating Development 8 Water and Earth Technologies, Inc.

9 Figure 4. Site 330 Cross-Section 1.0 At The Downstream End of the Bridge Wing Walls. UDFCD Site 330 Rating Development 9 Water and Earth Technologies, Inc.

10 Figure 5. Site 330 Cross-Section 2.0, Left Side Looking Downstream. UDFCD Site 330 Rating Development 10 Water and Earth Technologies, Inc.

11 Figure 6. Site 330 Cross-Section 2.0, Right Side Looking Downstream. UDFCD Site 330 Rating Development 11 Water and Earth Technologies, Inc.

12 Figure 7. Site 330 Inside of the Left Bridge Culvert. Figure 8. Site 330 Inside of the Right Bridge Culvert. UDFCD Site 330 Rating Development 12 Water and Earth Technologies, Inc.

13 Figure 9. Site 330 Cross-Section 3.0, Left Side Culvert Looking Downstream. UDFCD Site 330 Rating Development 13 Water and Earth Technologies, Inc.

14 Figure 10. Site 330 Cross-Section 3.0, Right Side Culvert Looking Downstream. UDFCD Site 330 Rating Development 14 Water and Earth Technologies, Inc.

15 Figure 11. Site 330 Cross-Section 4.0 at the PT, Looking Downstream. UDFCD Site 330 Rating Development 15 Water and Earth Technologies, Inc.

16 Figure 12. Site 330 Cross-Section 5.0 At The Upstream End of the Bridge Wing Walls Looking Downstream. UDFCD Site 330 Rating Development 16 Water and Earth Technologies, Inc.

17 The measured distances between the surveyed cross sections are presented in Figure 13. Figure 13. Site 330 Distances Between Surveyed Cross Sections. A CDOT right of way bench mark with stated elevation of 5, ft amsl was located on the top of the downstream bridge wing wall at Site 330. The bench mark and the location indicated by a red arrow are shown in Figure 15. The CDOT bench mark elevation (CDOT BM) was used as a vertical control for the survey. During the survey, the level was moved to four locations in order to provide line of sight for the leveling. The survey loop was closed back to the CDOT bench mark with an acceptable vertical error of 0.01 feet. The instrument elevations and closure calculation are presented in Figure 14. Figure 14. Site 330 Instrument Elevations and Closure Error Calculation. UDFCD Site 330 Rating Development 17 Water and Earth Technologies, Inc.

18 Figure 15. Site 330 CDOT Bench Mark. UDFCD Site 330 Rating Development 18 Water and Earth Technologies, Inc.

19 The reduced survey notes are presented in Figure 16. For Cross-Sections , two different instrument locations (and corresponding HI values) were used to measure the two bridge culverts. Negative rod readings presented in the survey notes are calculated values based on actual rod readings for weir tops and ceiling height from weir top to ceiling measured with a tape. Figure 16. Site 330 Reduced Channel Cross Section Survey Notes. UDFCD Site 330 Rating Development 19 Water and Earth Technologies, Inc.

20 5.2 Site 330 HEC-RAS Modeling Graphical descriptions of the cross sections, as described in HEC-RAS are presented in Figure 17 - Figure 19. Figure 17. Site 330 Graphical Description of the HEC-RAS Cross-Sections 1.0 and 2.0. UDFCD Site 330 Rating Development 20 Water and Earth Technologies, Inc.

21 Figure 18. Site 330 Graphical Description of the HEC-RAS Cross-Sections UDFCD Site 330 Rating Development 21 Water and Earth Technologies, Inc.

22 Figure 19. Site 330 Graphical Description of the HEC-RAS Cross-Sections The Manning s n value for modeling has been set to for the main channel area, 0.05 for the overbank area and 0.03 for the bridge concrete interior. A steady flow simulation was performed using the HEC-RAS model, assuming downstream flow control and normal depth in the channel below the culvert opening. The downstream slope was assigned to be the measured slope over the surveyed reach, ft/ft. A range of flows were simulated with the HEC-RAS model, from 0.1 cfs to the highest discharge the culvert was predicted to flow with a free surface (3,700 cfs). Water is predicted to meet the culvert ceiling on the downstream end of the culvert, near Cross-Section 2.2 first. Under these UDFCD Site 330 Rating Development 22 Water and Earth Technologies, Inc.

23 conditions, water is predicted to be out of the channel and pooling both upstream and downstream of the box culvert bridge, but the culvert opening is the primary control of flow at the site. The model-predicted water surfaces for each cross section at the maximum modeled flow (3,700 cfs) are presented in Figure 20 - Figure 22. Figure 20. Site 330 Water Surface at Maximum Discharge for Cross-Sections UDFCD Site 330 Rating Development 23 Water and Earth Technologies, Inc.

24 Figure 21. Site 330 Water Surface at Maximum Discharge for Cross-Sections UDFCD Site 330 Rating Development 24 Water and Earth Technologies, Inc.

25 Figure 22. Site 330 Water Surface at Maximum Discharge for Cross-Sections The HEC-RAS model calculates normal depth flow upstream of the culvert inlet. The model calculates the normal depth below the critical depth at Cross-Section 1.0 and therefore assumes the downstream control to be critical flow below the culvert (Figure 23). The control of flow at Site 330 is the culvert inlet, Cross-Section 3.0. Predicted water surface profiles for a range of flows through the site are shown in Figure 23. Output from the HEC-RAS model for a range of flows is presented in Figure 24 - Figure 26. This figure shows that for a given discharge, water is deeper upstream of the bridge opening compared to inside the box culvert. This is due to the hydraulic control of the upstream culvert entrance and the constriction of flow at the bridge wing walls. The predicted Froude numbers for Cross-Sections 2.8, 3.0 and 4.0 in Figure 24 - Figure 26 indicate that the PT is located in sub-critical flow but near a flow regime transition from subcritical flow to critical flow through the culvert. The exact location of the transition point is likely to move up or downstream for different flow conditions. Therefore, the rating at the PT location is subject to some computational error given the hydraulic transition. UDFCD Site 330 Rating Development 25 Water and Earth Technologies, Inc.

26 Flow Best alternate PT location Box Culvert Bridge PT cross section Figure 23. Site 330 Predicted Water Surface Elevation Profile Plot. Figure 24. Site 330 HEC-RAS Output for Cross-Sections UDFCD Site 330 Rating Development 26 Water and Earth Technologies, Inc.

27 Figure 25. Site 330 HEC-RAS Output for Cross-Sections UDFCD Site 330 Rating Development 27 Water and Earth Technologies, Inc.

28 Figure 26. Site 330 HEC-RAS Output for Cross-Sections A HEC-RAS predicted stage-discharge relationship is developed for Cross-Section 4.0 at the PT, where stage is water surface elevation in feet above mean sea level (Figure 27) Discharge (cfs) Water Surface Elevation (ft amsl) Figure 27. Site 330 Stage-Discharge Relationship at the PT. UDFCD Site 330 Rating Development 28 Water and Earth Technologies, Inc.

29 5.3 Site 330 Depth Above PT Discharge Rating The rating desired by UDFCD is expressed as stream discharge as a function of water depth at the PT. The reference elevation for zero depth at the PT has been assigned to the measured elevation of the concrete at the box culvert inlet (5, ft amsl). The minimum channel elevation at Cross-Section 2.8 was measured as 5, ft amsl, 0.4 ft higher than the floor of the culvert opening. This elevation is considered the zero flow elevation, where water could pool to a depth of 0.4 ft before water begins to flow through the culvert. These values are used to calculate depth of water above the PT from the HEC-RAS water surface elevation predictions for a range of discharge values (Table 1). Table 1. Site 330 Predicted Stage-Discharge Relationship Tabular Data. Predicted Water Surface Elevation (ft Depth above PT (ft) 1 Discharge (cfs) Condition amsl) 5, , , , , , , , , ,260 5, ,440 5, ,016 Top of PT riser flooded 5, ,460 5, ,940 5, ,360 Downstream end of culvert flowing full 5, ,700 1 Depth is calculated as predicted water surface elevation minus minimum surveyed channel elevation at Cross-Section 3.0 (5, ft amsl) 2 The zero flow elevation is the minimum measured channel depth at Cross-Section 2.8 (5, ft amsl) The UDFCD rating data currently in use for this site are presented in Table 2. Comparison of the HEC-RAS predicted rating and the current UDFCD rating is shown in Figure 28. A Log-Log plot of the rating is presented in Figure 29. UDFCD Site 330 Rating Development 29 Water and Earth Technologies, Inc.

30 Table 2. Current UDFCD Rating for Site 330. Depth (ft) 1 Discharge (cfs) , , , , , , , , Discharge (cfs) Depth at PT (ft) Top of PT riser pipe flooded Downstream end of box culvert full UDFCD rating HEC-RAS rating Figure 28. Site 330 Stage-Discharge Comparison Relationships. UDFCD Site 330 Rating Development 30 Water and Earth Technologies, Inc.

31 HEC-RAS rating Discharge (cfs) Depth at PT (ft) Figure 29. Site 330 Stage-Discharge Relationship Log-Log Plot. 5.4 Site 330 Discussion of Rating Results The water surface elevation of the bottom of the culvert entrance has been assigned as the reference level for zero depth at the PT (and measured at 5, ft amsl. Channel bed elevations inside the bridge culvert have been measured to be higher than the zero depth at the PT. At very low flow, a small weir located at Cross-Section 2.8 will pool water slightly before allowing flow through the culvert bridge. Water is predicted to pool slightly before flow through the culvert begins. The point where flow begins has been measured to be 5, ft amsl (at a PT depth of 0.4 ft). The culvert opening controls the flow at Site 330. The water surface at the bridge wing walls is predicted to be higher than inside the bridge at high flows. At discharges above approximately 2,000 cfs, the top of the PT riser pipe and adjacent land upstream of the box culvert is predicted to be flooded. Upstream flooding is allowed in the model, even though overbank of surveyed cross sectional area, the model simulates pool of water of that elevation inundating adjacent land, controlled downstream by the culvert. The depth at the PT when the box culvert is predicted to be full is feet. The rating of the depth of water above the PT is based on the reference level of the concrete floor of the box culvert opening of 5, ft amsl or 7.40 ft below the top of the PT riser pipe with the cap removed. Before using this rating with confidence, the elevation of the installed PT should be verified in the field and a field verification of water depth above the reference level should be performed using the installed PT reading and a field measurement of water surface elevation. During the site survey it was noted that sediment deposition had occurred upstream of the bridge entrance at the PT cross section and two small low-flow channels existed in the sediment. This indicates that the hydraulic connectivity of the PT to the river at low-flow is most likely compromised. Also, the channel shape at the PT cross section has probably changed since PT UDFCD Site 330 Rating Development 31 Water and Earth Technologies, Inc.

32 installation and is likely to change again through scour and sediment deposition. Furthermore, the current location of the PT riser is possibly near a flow regime transition point between subcritical and critical flow. A PT installation inside the culvert (at Cross-Section 2.6, see Figure 23) is possibly a better location for the measurement of stage for a computation of discharge. The concrete rib of the culvert was exposed at this cross section during the survey indicating that this cross section shape has not changed significantly. Model predictions indicate that flow at this cross section is at critical depth through much of the rating range, but this location is not near a flow regime transition point so a rating at this location would be stable and can be used with confidence. To facilitate a change in PT installation inside the culvert, a rating for this location has been included (Table 3). Table 3. Depth-Discharge Rating for an Alternate PT Installation Inside The Culvert at Cross-Section 2.6. Depth Above PT (ft) Discharge (cfs) (if PT located at Cross-Section 2.6) , , , , , , ,700 UDFCD Site 330 Rating Development 32 Water and Earth Technologies, Inc.

33 6.0 REFERENCES Arcement, G.J., and Schneider, V.R. (1990). Guide for Selecting Manning s Roughness Coefficients for Natural Channels and Flood Plains. United States Geological Survey Water- Supply Paper Barnes, H.H. (1987). Roughness Characteristics of Natural Channels. U.S. Geological Survey Water-Supply Paper United States Government Printing Office, Washington. D.C. Benson, M.A., and Dalrymple, T. (1984). General Field and Office Procedures for Indirect Discharge Measurements. Techniques for Water-Resources Investigations of the United States Geological Survey, Book 3 Applications of Hydraulics, Chapter A1. United States Government Printing Office, Washington, D.C. Dalrymple, T., and Benson, M.A. (1984). Measurement of Peak Discharge by the Slope-Area Method. Techniques for Water-Resources Investigations of the United States Geological Survey, Book 3 Applications of Hydraulics, Chapter A2. United States Government Printing Office, Washington, D.C. Harrelson, C.C., Rawlins, C.L., and Potyondy, J.P. (1994). Stream Channel Reference Sites: An Illustrated Guide to Field Technique. General Technical Report RM-245. U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. Fort Collins, Colorado U.S. Army Corps of Engineers, Hydrologic Engineering Center. (2002). HEC-RAS River Analysis System. Version 3.1 User s Manual, Hydraulic Reference Manual, and Applications Guide. Institute for Water Resources, Davis, California. U.S. Geological Survey. (1977). National Handbook of Recommended Methods for Water- Data Acquisition. U.S. Department of the Interior, Prepared under the sponsorship of the Office of Water Data Coordination, Geological Survey, Chapter 1, Surface Water. Reston, Virginia. U.S. Geological Survey. (2005). Aerial Photography via Terraserver. UDFCD Site 330 Rating Development 33 Water and Earth Technologies, Inc.

34 7.0 FIELD SURVEY NOTES UDFCD Site 330 Rating Development 34 Water and Earth Technologies, Inc.

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