Urban Drainage and Flood Control District. Goldsmith Iliff Pond E-19 Survey

Transcription

1 Urban Drainage and Flood Control District Goldsmith Iliff Pond E-19 Survey GOLDSMITH ILIFF ALERT ID: 653/654 LID: ILFC2 Prepared by: HDR Engineering, Inc. 303 E 17 th Ave. Suite 700 Denver CO, 80203

2 Table of Contents TABLE OF CONTENTS... 2 INTRODUCTION... 3 SITE... 3 SURVEYED LOCATIONS... 4 RATING CURVE DEVELOPMENT... 7 SITE PHOTOGRAPHS...12 STUDY DATA...15 HISTORIC RECORDS...16 APPENDIX...18 Table 1 Rating Curve... 8 Table 2 HEC-RAS Profile Output Table...10 Table 3 Frequency/Discharge Table...15 Table 4 Survey Data...16 Figure 1 Location Map... 3 Figure 2 Vicinity Map... 4 Figure 3 Surveyed Points (Aerial - DRCOG 2004)... 5 Figure 3 Detailed Surveyed Points (Aerial - DRCOG 2004)... 6 Figure 4 HEC-RAS Cross Section with all Profiles... 9 Figure 5 HEC-RAS Log-Log Plot of Rating Table...11 Figure 6 Looking Downstream...12 Figure 7 Looking Upstream with Side Lateral Detention Culverts...12 Figure 8 Transmitter and Iliff Pond...13 Figure 9 Downstream Iliff...13 Figure 10 Side Lateral Culvert Outlets into Detention Pond...14 Figure 11 Scour Hole Downstream of Side Lateral Culvert Outlets...14 Figure Year Floodplain...15 Figure 13 June 3, 2005 Iliff Road Overtopped...16 Figure 14 June 3, 2005 Iliff Road Overtopped...16 Figure 15 June 3, 2005 Bike path overtopped into Iliff Pond...17 Goldsmith Iliff Pond E-19 Survey 2

3 Introduction HDR Engineering Inc. was contracted by the Urban Drainage and Flood Control District to survey and provide information about flood warning stream gage sites in a manner consistent with National Weather Service E-19 procedures. On October 13, 2006, HDR personnel surveyed the Goldsmith Gulch gages located at Iliff Pond. This report is a summary of the work done and information gathered for the dual gage configuration on Goldsmith Gulch at Iliff Pond. Included in this report are elevations of critical points in the vicinity of the site, estimates of stages causing flood damage in vicinity of the gage, and a rating curve. Site The stream gage is located on the south side, upstream, of Iliff Avenue on Goldsmith Gulch. The ALERT ID numbers for these gages are 653 (Goldsmith Gulch channel) and 654 (side channel detention pond). The National Weather Service LID is ILFC2 and is referred to as Goldsmith Gulch at Iliff Pond. There is an off channel detention pond to reduce the peak flood flows at this gage site. The Goldsmith Gulch floodplain at Iliff is fully developed at this location. Potential flooding at the gage itself would consist of flooding of homes, overtopping a recreation trail and Iliff Avenue. Figure 1 shows the location of the site on the Southeast District ALERT map. Figure 1 Location Map Goldsmith Iliff Pond E-19 Survey 3

4 Figure 2 Vicinity Map Surveyed locations Ground elevations were surveyed along a cross section for a rating curve for the site. In addition, the elevations and locations of hazard locations, along with low flow channel water surface elevations up and downstream from the gage. Figures 3-4 show the locations of the surveyed points in the vicinity of the gage. The base of the ALERT transmitter was surveyed at an elevation of for a temporary benchmark. The flow line elevation is 95.2 feet. The low flow channels banks will be overtopped at 2.5 feet above the invert elevation. Water will begin to overtop side weir to the detention pond at 4.6 feet above the invert elevation. Iliff Avenue will begin overtopping shortly after 653 reaches a stage of 7.5 feet. Based on the water surface elevations in the low flow channel, the estimated channel energy slope is 0.6 percent. Goldsmith Iliff Pond E-19 Survey 4

5 Flow Base of Transmitter Iliff Pond Figure 3 Surveyed Points (Aerial - DRCOG 2004) Goldsmith Iliff Pond E-19 Survey 5

6 Base of Transmitter Inlet Lateral Culverts Outlet Lateral Culverts Flow Figure 4 Detailed Surveyed Points (Aerial - DRCOG 2004) Goldsmith Iliff Pond E-19 Survey 6

7 Rating Curve Development Hydraulics for the weir and lateral culverts were evaluated using the HEC River Analysis System (HEC-RAS) program developed by the U.S. Army Corps of Engineers, Hydrologic Engineering Center 1. HEC-RAS uses the standard step method to calculate water surface profiles. The following assumptions are used by HEC-RAS in computing water surface profiles: Steady flow; Gradually varied flow; One-dimensional flow; Channel slopes are small, less than 1:10 A rating curve was established for the gage using the surveyed cross-sections and the Army Corps of Engineers computer program HEC-RAS. The resulting rating curve from the analysis is in Table 1. 1 U.S. Army Corps of Engineers, Hydrologic Engineering Center, HEC-RAS Water Surface Profiles, Computer Program, Davis, California, March Goldsmith Iliff Pond E-19 Survey 7

8 Q (U/S of Lateral Culverts) Q (D/S of Lateral Culverts - Gage Flow) Gage Stage Comments (cfs) (cfs) (ft) Out of Low Flow Channel Flow into Iliff Pond from Lateral Culverts Iliff Road and Side Weir Overtop Table 1 Rating Curve Goldsmith Iliff Pond E-19 Survey 8

9 Iliff Plan: Iliff with downstream culvert 4/25/2007 River =. Reach =. RS = Legend WS 1000 cfs WS 900 cfs WS 870 cfs WS 850 cfs WS 800 cfs WS 700 cfs Elevation (ft) Station (ft) WS 600 cfs WS 500 cfs WS 300 cfs WS 250 cfs WS 200 cfs WS 50 cfs WS 100 cfs WS 25 cfs Lat Struct Ground Bank Sta Figure 5 HEC-RAS Cross Section with all Profiles Denver County E-19 Surveys Goldsmith Iliff Pond 9

10 River Profile Q Total D/S of Side Culverts Min Ch El W.S. Elev E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Goldsmith Gulch Table 2 HEC-RAS Profile Output Table Denver County E-19 Surveys Goldsmith Iliff Pond 10

11 Iliff 10 Depth (ft) Flow (cfs) Figure 6 HEC-RAS Log-Log Plot of Rating Table Denver County E-19 Surveys Goldsmith Iliff Pond 11

12 Site photographs Figure 7 Looking Downstream Figure 8 Looking Upstream with Side Lateral Detention Culverts Denver E-19 Surveys Goldsmith Iliff Pond 12

13 Figure 9 Transmitter and Iliff Pond Figure 10 Downstream Iliff Denver E-19 Surveys Goldsmith Iliff Pond 13

14 Figure 11 Side Lateral Culvert Outlets into Detention Pond Figure 12 Scour Hole Downstream of Side Lateral Culvert Outlets Denver E-19 Surveys Goldsmith Iliff Pond 14

15 Study Data According to the November 17, 2005 City and County of Denver Colorado the Flood Insurance Study (FIS) for Goldsmith Gulch has a drainage area of approximately 8.0 square miles at the Mouth. The following table includes estimates of the frequencydischarge data from a December 2004 study entitled Evaluation of Debris and Flood Control on Goldsmith Gulch I-225 to Iliff Avenue : Frequency Peak Discharge (cfs) 10-year 1, year 1, year 2,200 Table 3 Frequency/Discharge Table Figure Year Floodplain Denver E-19 Surveys Goldsmith Iliff Pond 15

16 Historic records Since the installation date, a peak stage of 9.5 feet above the invert was recorded on June 3, Split flow occurs when the flow gets above the road and therefore an exact flow rate cannot be established with HEC-RAS. The following pictures are from this event. Figure 14 June 3, 2005 Iliff Road Overtopped Figure 15 June 3, 2005 Iliff Road Overtopped Denver E-19 Surveys Goldsmith Iliff Pond 16

17 Figure 16 June 3, 2005 Bike path overtopped into Iliff Pond Denver E-19 Surveys Goldsmith Iliff Pond 17

18 Appendix Goldsmith Gulch at Iliff Pond Point ID Northing (ft) Easting (ft) Elevation (ft) Description OP BS XSGR XSSIDEWALK XSSIDEWALK XSGR XSGR XSGR XSGR XSGR XSFL XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSSIDEWALK XSSIDEWALK LOWDAMAGE XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR TOPPEDBRDG FL FL XSSIDEWALK XSSIDEWALK XSGR XSGR XSGR Denver E-19 Surveys Goldsmith Iliff Pond 18

19 XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR FL FL FL XSSIDEWALK XSSIDEWALK XSGR XSGR WEIR WEIR XS XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSGR XSSIDEWALK XSCULDESAC WEIR WEIR LC TOPPTTUBE FL WATERSURFACE XSSIDEWALK XSSIDEWALK XS XSGR XSGR XSGR XSGR XSGR XSGR XSGR Denver E-19 Surveys Goldsmith Iliff Pond 19

20 XSGR XSGR XSGR XSGR WATERSURFACE CVLVERT LCTRASHRACK LCCULVERTT TOPTRASHRACK ROADCURB ROADCROWN TOPPOND BOTTOMPOND BOTTOMPOND BOTTOMPOND TOPOND INTERSECTION BOTTOMPOND TOPPOND BOTTOMPOND BOTTOMPOND BOTTOMPOND TOPPOND CENTERPOND TOPPTTUBE CNTROUTWEIR EDGECONCRETE BOTMSCURHOLE BOTTOMPTTUBE BASETRANSMITTER Table 4 Survey Data Denver E-19 Surveys Goldsmith Iliff Pond 20