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HomeMy WebLinkAboutEver Vail Hydraulic Design Report 112108f t lA AIin IOM 91* leek ■:gals]: IMPORTANT NOTICE This report was prepared exclusively for the Town of Vail by AMEC Earth & Environmental, Boulder Office (AMEC). The quality of information, conclusions and estimates contained herein is consistent with the level of effort involved in AMEC's services and based on: i) information available at the time of preparation, ii) data supplied by outside sources and iii) the assumptions, conditions and qualifications set forth in this report. This report is intended to be used by the Vail Resorts Development Company only, subject to the terms and conditions of its contract with AMEC. Any other use of, or reliance on, this report by any third party is at that party's sole risk. AMEC Earth & Environmental Boulder Office 1002 Walnut Street, Ste. 200 Boulder, CO 80302 Phone: 303.443.7839 Fax: 303.442.0616 Principal Investigator: Bob Weaver 303.443.7839 Bob.Weaver @amec.com ' CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek ' Page i Table of Contents ' 1. Introduction .................................................................................. ............................... 1 2. Hydrology ...................................................................................... ..............................3 ' 2.1 Red Sandstone Creek Basin ................................................... ............................... 3 2.2 Red Sandstone Creek Channel ............................................... ..............................4 2.3 Precipitation Data ............................................................. ............................... 4 2.4 Flood History .................................................................... ............................... 4 2.5 Design Flood Frequency .................................................... ..............................5 3. Existing Structure .......................................................................... ..............................7 4. Design Discussion ......................................................................... ..............................9 4.1 General Design Discussion ................................................ ..............................9 4.2 Channel Armoring and Scour Analysis under the South Frontage Road Bridge 11 4.3 Red Sandstone Creek Realignment and Design Discussion .......................... 13 4.4 Permitting ....................................................................... ............................... 15 4.5 Evaluation of Structural Alternatives ............................... ............................... 15 5.0 Recommended Design ........................................................... ............................... 18 6.0 References ............................................................................... .............................19 List of Figures Figure 1. Project Site for the New Frontage Road Bridge ................. ............................... 1 Figure 2. Red Sandstone Creek Watershed ...................................... ..............................3 Figure 3. Daily mean discharge for Red Sandstone Creek at USGS Gage ..................... 5 Figure 4. Estimated daily mean discharge for Red Sandstone Creek Flows Gore Creek (Period of Record October 1963 — September 2006) ................ ............................... 6 Figure 5. Annual peak flow for Red Sandstone Creek Flows at junction with Gore Creek (Period of Record October 1963 — September 2006) ................ ............................... 6 Figure 6. Existing Scour Hole at 1 -70 Culvert Discharge .................... ..............................7 Figure 7. Red Sandstone Creek 20 ft downstream of existing 1 -70 Culvert Discharge ..... 8 Figure 8. Debris downstream of 1- 70 ................................................ ............................... 8 Figure 9. Existing and proposed ground elevation and 100 yr water surface elevations as producedby HEC RAS ........................................................... ............................... 10 List of Tables Table 1. Proposed 100 yr Water Surface Elevations at Key Design Locations .............. 10 Table 2. Velocities and Rip Rap Diameter at which bed motion will begin ..................... 12 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek ii of 2 List of Appendices Appendix 1. Floodplain Map Appendix 2. HEC RAS Analysis 2.1 HEC RAS Summary 2.2 HEC RAS Sections 2.3 HEC RAS Profile 2.4 HEC RAS Results in Tabular Format 2.5 HEC RAS Scour Analysis Results Appendix 3. Calculations Appendix 4. Hydraulic Design Sheets AMEC Earth & Environmental ' CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 1 of 21 1. Introduction The Town of Vail plans to realign a section of the 1 -70 South Frontage Road in the West Lionshead area in Vail, Colorado. The new alignment will move the South Frontage Road to the north so that it is immediately adjacent and parallel to the eastbound lanes of 1 -70. This realignment will require the construction of a bridge across Red Sandstone Creek directly south of the 1 -70 right -of -way. The purpose of this report is to evaluate the hydraulic implications of the new South Frontage Road Bridge across Red Sandstone Creek. This report is organized in accordance with the outline for a Hydraulic Report as ' specified by CDOT (CDOT Design Drainage Manual). The existing South Frontage Road crosses Red Sandstone Creek approximately 350 ' feet south of the proposed location for the new crossing as shown in Figure 1 (USGS Quadrangle Vail West, Co, Sections 6 and 7 of Township 5S, Range 80W). The area where the new bridge will be located is highlighted in Figure 1. The proposed design for the new frontage road bridge across Red Sandstone Creek will ' require realignment and reconstruction of the creek channel from the 1 -70 Culvert discharge location to approximately 30 ft downstream of the new frontage road bridge. Figure 1. Project Site for the New Frontage Road Bridge CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 2of91 24 The realignment of the creek is necessary due to the angle of the existing Red Sandstone Creek culvert under 1 -70 and a sharp bend in the stream channel to the east and then west below the culvert outfall. Bridging the existing channel would require a span of at least 120 feet, which was not practical due to cost and aesthetic considerations. The design objectives for this project are: armor the new channel under the bridge to prevent scour and maintain channel stability; include channel geometry that is similar to the existing stream geometry; and provide sufficient channel conveyance capacity to minimize changes in the designated floodplain. AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 3of21 2. Hydrology 2.1 Red Sandstone Creek Basin The Red Sandstone Creek watershed encompasses 13.9 sq mi. Elevations in the drainage area range from over 13,000 feet at the headwaters in the Gore Range 8,070 feet at the Gore Creek confluence. The upper reaches of the watershed are in pristine areas within the Eagles Next Wilderness. Parts of the watershed are impacted by road development, timber harvesting, and urbanization within the Town of Vail. A map of the watershed is shown in Figure 2. AMEC Earth & Environmental Figure 2. Red Sandstone Creek Watershed CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 4of2' 2.2 Red Sandstone Creek Channel Red Sandstone Creek in the project area is a perennial, small, shallow, cobble bed mountain stream located in a mountain valley setting in Vail Colorado. The banks are vegetated with slopes generally less than 30% with a few exceptions where slopes approach 50 %. The creek has sinuosity between 1.06 and 1.25, is not braided, but exhibits local anabranching. The estimated D 50 of the stream substrate is between 9 and 12 inches. The channel gradient of Red Sandstone Creek varies from 3% to 9% from the 1 -70 culvert exit to the junction with Gore Creek. At the location of the new bridge, the channel slope averages approximately 4.6 %. The existing bank to bank width of Red Sandstone Creek ranges from 30 -45 ft. The edge of water width at low flow ranges from 10 -20 ft downstream of the 1 -70 culvert. The width at low water's edge at the proposed bridge location is 16 ft. The stream channel is stable through the project area and there is no evidence of significant recent flood disturbance. A visual inspection of rock diameter shows rock diameters ranging in size from a few inches to 1 '/2 ft. Based on these observations and the hydrologic conditions it is highly unlikely that hydraulic forces resulting from ice will impact Red Sandstone Creek, particularly because during the months when ice does exist flows in Red Sandstone Creek are minimal (< 2 cfs). Woody debris does enter the channel from areas to the north of 1 -70 during spring runoff, but the existing culvert under 1 -70 prevents large debris from reaching the project area to the south of 1 -70. Channel reconstruction will be with materials that prevent channel destabilization from ice or debris. A USGS gage (9066400) is located on Red Sandstone Creek approximately 3 miles upstream of the proposed frontage road bridge at Lat 39 40 58, long 106 24 03, NAD 1937. Base flow conditions occur in the late fall and winter months. Flows start to increase in April in response to the snow melt and runoff and generally tend to peak in June with peak flows generally ranging from 60 to 135 cfs just upstream of the new frontage road bridge. 2.3 Precipitation Data The average total precipitation in Vail ranges between 1.3 inches during December and 2.2 inches during April, the wettest month. The average annual total rainfall is 21.97 inches and is relatively consistent for each month of the year. Vail receives an average of 184.3 inches of snow per year, with a maximum depth accumulated in February averaging at 31 inches. 2.4 Flood History There are no published flood records or anecdotal accounts of property damage caused by flooding on Red Sandstone Creek. Annual peak flows occur in late May or early June as shown in Figure 5. AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek ' 5of21 2.5 Design Flood Frequency ' The 10 yr. flood event flow is 330 cfs, 50 yr flood event flow is 440 cfs, the 100 yr. flood event flow is 490 cfs, and the 500 yr flood event flow is 590 cfs (FEMA Insurance Study, FEMA, December 2007). The existing 100 yr flood plain is shown in Appendix 1. Figure 2 provides USGS gage discharge measurements for Red Sandstone Creek. This gage is approximately 3 miles upstream of the Ever Vail Site. Figure 3 provides the estimated discharge at the mouth of Red Sandstone Creek. These flows were estimated ' by assuming that the Red Sandstone Creek watershed receives a uniform amount of precipitation and that the USGS gage measures approximately 31 % of the total Red Sandstone Creek runoff. The USGS gage discharge values were multiplied by a factor ' of 1.69 to estimate the estimated flows at the mouth. This factor accounts for the additional runoff from the remaining watershed downstream of the gage captured at the mouth, providing an estimate stream flow rates at the Ever Vail site. ' Figures 3 and 4 show the median of daily mean discharge measurements, 80 percentile of daily mean discharge (representative of a typical wet year), and 20 percentile of daily mean discharge (representative of a typical dry year). Peak flows were evaluated using the same multiplier as above. Figure 5 shows the peak flow data for the period of record, adjusted to the confluence with Gore Creek. 90 80 70 60 y w 50 m rn t 40 ° 30 20 10 0 J F M A M J J A s 0 N D — Median (50th Percentile) — Dry (20th Percentile) Wet (80th Percentile) Figure 3. Daily mean discharge for Red Sandstone Creek at USGS Gage AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 6of21 160 140 120 100 80 0 60 40 20 0 -, 1 1 1 1 J F M A M J J A s O N D — Median (50th Percentile) — Dry (20th Percentile) —Wet (80th Percentile) Figure 4. Estimated daily mean discharge for Red Sandstone Creek Flows Gore Creek (Period of Record October 1963 — September 2006). 600 500 ♦ - U 400 - a� 300 • • N 200 ♦ ♦ ♦ ♦ ♦♦ ♦ ♦♦ ♦ ♦ • ♦ ♦ • • 100 ♦ • ♦ • 0 1960 1970 1980 1990 2000 2010 Year Figure 5. Annual peak flow for Red Sandstone Creek Flows at junction with Gore Creek (Period of Record October 1963 — September 2006). AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 7of21 3. Existing Structure The only existing structure in the project area is the culvert that conveys the creek under 1 -70 from the north. The 1 -70 culvert will be cut back 13' from the existing outfall and a new headwall and retaining wall will be built adjacent to the 1 -70 right -of -way. The existing culvert invert elevation is 8107.9 ft. The new culvert invert elevation will be 8108.39 ft. The water surface elevation during the 100 yr event under existing conditions is 8130.30 (7', full) at the upstream end of the culvert, and 8111.86 (3.47 ft) at the downstream end. There is a natural scour hole at the existing culvert discharge location (Figure 6) that is approximately 4 ft deep. The banks at this location appear to be stable (Figure 7). There is some woody debris 20 -50' downstream (Figure 8) that has been deposited during past high flow events. r r . ! _'-e `">'- Figure 6. Existing Scour Hole at 1 -70 Culvert Discharge AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 8of21 Figure 7. Red Sandstone Creek 20 ft downstream of existing 1 -70 Culvert Discharge AMEC Earth & Environmental Figure 8. Debris downstream of 1 -70. � I � I CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 9of2 4. Design Discussion ' 4.1 General Design Discussion As described above the Red Sandstone Creek channel will be realigned from the 1 -70 ' culvert discharge location to 30' downstream of the new bridge edge to accommodate the new frontage road and associated bridge. AMEC Earth & Environmental ' The primary design criteria are: • Convey the drainage from Red Sand Stone Creek under the new South Frontage Road. • Construct a high quality and economical structure that will serve the public with a minimum service life of 75 years and have minimal maintenance requirements. ' • Tie into the existing culvert under 1 -70 while minimizing the impacts to 1 -70 during construction. • Minimize impacts to the floodplain. ' • Accommodate the utilities proposed for the South Frontage Road. Meet the aesthetic requirements of the adjacent community while adhering to CDOT policy. • Create channel geometry that is similar to the existing Red Sandstone Creek and ' to effectively manage all flow conditions (low flow to high flow) • Design a new creek bed that will not allow scour under the 500 yr flow event under the South Frontage Road Bridge. ' • Realign Red Sandstone Creek to meet the existing grade at the designated junction with the existing channel HEC -RAS computer modeling was used to compute the water surface elevations and ' velocities for the 100 -yr flow event for the new creek alignment. HEC -RAS results indicate the impacts to the water surface elevations associated with the 100 year flood are minor ( <1.0 ft), and only impact water surface elevations in the new creek section N (Table 1). At a location 45' downstream of the bridge edge, HEC RAS (section 404.5) results show the water surface elevation has returned to its existing elevation for the entire downstream reach. Figure 9 shows the existing and proposed ground elevations and 100 yr water surface elevations as produced by HEC RAS. ' HEC -RAS cross sections of the new stream alignment, and downstream existing cross sections, can be found in Appendix 2, along with a summary of the modeling process. Water surface elevations and velocities at representative key design locations are shown ' in Table 1. The existing and proposed floodplains are shown in Appendix 1. AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 10 of 21 Table 1. Proposed 100 yr Water Surface Elevations at Key Design Locations Location WSE Velocit Culvert Exit (405-7)* 8111.86 25.74 Proposed Stream Section 8108.32 8.13 at upstream edge of bridge 405.6 Proposed Stream Section 8103.53 6.41 at downstream edge of bride 404.9 Existing Channel (405)*** 8103.34 5.15 Proposed Stream Section 8099.98 6.16 45' Downstream of Brid a ** ' I he culvert will be cut back 13' and has been shortened in the model. I his elevation represents the elevation at the culvert discharge 13' farther north from the existing discharge location. " This location is the only HEC -RAS section cut that has not changed location in the proposed model. The existing WSE at this location is 8099.98; the existing velocity is 6.16. There is a match in WSE and velocity at this location. " *"The existing cross section is located 10ft upstream from the southern end of the proposed bridge. The location of section 405 is shown in Appendix 1. 8140 8130 8120 8110 8100 8090 8080 8070 0 �- Proposed Ground Elevation —n-- Proposed 100 yr WSE Existing Ground Elevation x Existing 100 yr WSE Figure 9. Existing and proposed ground elevation and 100 yr water surface elevations as produced by HEC RAS The water surface elevation increase seen in the stretch of creek 45' downstream of the bridge will not impact downstream users. The new Ever Vail development will be constructed in this area but will be outside the 100 yr floodplain. ■r am M AMEC Earth & Environmental 200 400 600 800 1000 r CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek ' 11 of 21 j 4.2 Channel Armoring and Scour Analysis under the South Frontage Road Bridge r The realignment of Red Sandstone Creek to accommodate the new South Frontage Road Bridge requires the construction of a new stream channel. The purpose of the scour analysis is to determine the design requirements needed to prevent scour under ' the bridge during the 500 yr flood event. The secondary goal of this analysis is to develop design requirements needed to control grade downstream of the bridge to prevent channel degradation in the new channel below the bridge. The design details for r the second objective are discussed in detail in Section 4.3 Red Sandstone Creek Realignment. Because of the design constraints and the space limitations resulting from the existing circular culvert discharging into the larger structural arch culvert for the new bridge, and the need to quickly transition flows while dissipating energy, typical design conditions do r not exist. For this reason, several analytical approaches were use to develop design criteria for channel armor that will prevent scour under the bridge. The design approach taken uses the following concepts and variables: • Use large grouted rip rap on the sloped culvert discharge rundown for energy dissipation that will mimic a concrete baffle design. • Size the D 50 under the bridge using the assumption that the bottom of the rundown will act as an energy dissipation basin. The riprap basin will not have an upslope on the downstream side. • Treat the sloped rundown below the 1 -70 culvert as the incoming rundown for the riprap basin. The elevation loss (culvert invert — stream bed invert) was used as the design variable (h to select D 50 using the FHWS guidelines for riprap basin design. • Maintain the stream invert within 1 ft. of the existing stream invert at the existing culvert discharge location • Enter the D 50 values into HEC -RAS to verify that scour will not occur under the proposed design conditions under the new frontage road bridge. • Use the incipient motion equation to verify that the D 50 value selected using the riprap basin design concept will not scour under the 500 yr flow conditions. HEC No. 14 (FHWA July 2006) was used as guidance in selecting a D 50 value that will prevent scour under the bridge. As mentioned above, a riprap basin computation was completed that used equations from HEC No. 14, chapter 10, equation 10.1: -0.55 h, = 0.86 D50 VO —C Equation 10.1 ' Y, Y, gy, r This equation was used to size riprap under the bridge when the sloped culvert discharge ramp is assumed to be the rundown to the bottom of the riprap basin. Using the existing design criteria of a drop of 4.47 ft with a 2:1 slope, the D 50 calculated using r AMEC Earth & Environmental 1 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 12 of 21 Equation 10.1 is: 27 inches. A full scour pool design was not completed on the downstream end because it is believed that a complete scour pool located under a bridge is not advisable. In addition, there is no need to decrease the velocity at the downstream end because velocities are within an acceptable range of existing velocities along Red Sandstone Creek and under a bridge. Tables 1 -4 in Appendix 2 show existing and proposed design velocities. The calculations for D 50 using this method are shown in Appendix 3. In addition to using HEC No. 14, equation C.12 from HEC -18 (FHWA May, 2001) was used to verify the D 50 value selected is larger than the diameter at which bed motion will begin under the proposed design during the 500 yr flood event. Using equation C -12 from HEC -18: 3 D = y Equation C -12 11. 17(y' 16 ) y = average depth of water in channel v = velocity in channel Average depth (y) and average velocity (v) were derived from HEC RAS modeling results based on design stream geometry. Results of Equation C -12 are listed in Table 2. These results indicate the smallest size of riprap shall not be less than 159 mm under the arched culvert to prevent scour from occurring under the 500 yr flood event. Table 2. Velocities and Rip Rap Diameter at which bed motion will begin. Location 100 r 500 r Velocity (fps) Rip Rap Diameter mm Velocity (fps) Rip Rap Diameter mm 2 Feet Below Culvert Exit 10.39 132 11.25 159 At upstream End of Bride 8.13 75 8.53 82 At downstream Edge of Bride 6.41 33 6.73 37 Velocities and depth are from the HEC RAS Modeling Results. HEC RAS modeling was then used to determine the D 50 value at which scour will begin to occur under the bridge. A new section (405.61) was added 1 ft upstream of the section 405.6 to utilize as the approach section since the existing upstream section is on the other side of the 1 -70 culvert. The contraction scour function was the only scour analysis computed since there are no piers or abutments. Using a trial and error method D 50 values entered into HEC RAS were reduced until it was found that scour will begin to occur when the D 50 is at or below 60 mm. The default scour option function was chosen, and resulted in a clear water contraction scour, which is consistent with the FHWA AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 13 of 21 guidelines: the critical velocity (Vc) at the specified D 50 diameter is greater than the mean velocity in the channel. For example, at the downstream end of the proposed bridge the 500 yr event yields a V, =7.79 ft/s and the V a „ 9 = 6.73 ft/s. It is understood that a high flow event would most likely not result in clear water scour, but that is what HEC RAS indicates, and since a clear water scour yields more conservative results than a live bed scour function, a live bed scour function was not forced. In conclusion, it is believed that using the HEC 14 design equation 10.1 for specifying riprap sizing is conservative and will ensure that scour will not occur at the bottom of the grouted riprap rundown or under the new frontage road bridge. The riprap basin scour pool concept utilized above has been chosen as the final design requirement. Using this method the D 50 value will be 27 inches (686 mm) under the bridge and the riprap thickness shall be 40.5 inches (1028 mm). The D 50 value will be lower downstream of the bridge. See below discussion on realignment and design of Red Sandstone Creek. Final design drawings will indicate specific details riprap design under the bridge. 4.3 Red Sandstone Creek Realignment and Design Discussion The re- alignment of Red Sandstone Creek was chosen as an alternative to a 120' span bridge and found to be ecologically viable as it will have minimal impacts on aquatic habitat and riparian wetlands. The new alignment will provide improved fish habitat via 2 drop structures resulting in pool and riffle habitat. This section focuses only on the reach of Red Sandstone Creek that requires a new channel to accommodate the new frontage road bridge. The project area begins at the 1 -70 culvert discharge and ends approximately 30 ft downstream of the proposed bridge edge. The new creek alignment will mimic the existing morphology in width and slope. The existing length of Red Sandstone Creek from the culvert exit to the location where the new stream will tie into the existing stream is 132 ft. The new alignment will be 10 ft shorter, with a total length of 122 ft. Part of the reason for the relatively short increase in length is the 13 ft in gain of creek length that will occur as a result of the shortened 1 -70 culvert. The channel slope of Red Sandstone Creek varies from 3% to 9% from the 1 -70 culvert exit to the junction with Red Sandstone Creek. At the location of the new bridge, the channel slope is approximately 4.6 %. Downstream of the new frontage road bridge the slope increases to 9.6 % for 50 ft, then drops back down to 4.4% for another 30 ft, where it then approaches an 8% slope. The reach of RSC below this point will not be discussed in this report because it will not be impacted by construction and modeling results that indicate there will be no change in the elevation or velocity of 100 yr flood flows. The objective for the stream realignment is to create a new average creek bed slope of 4% down to the location where the new creek will meet grade with the existing creek bed at 8098.00, and bank elevation at 8102.42. See the Hydraulic Sheets in Appendix 4 for the proposed channel alignment. The existing bank to bank width of Red Sandstone Creek ranges from 30 -45 ft through ' the project area. The edge of water width at low flow ranges from 10 -20 ft along the reach. The width at water's edge at the proposed bridge location is 16 ft. The new channel width will be 20 ft at the bottom of the bank and range from 36 -40 ft depending AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 14 of 21 on thalweg and bank elevations. The bank slopes will not be less than 2:1. The new channel will meet existing creek width approximately 30 ft. downstream of the newly proposed bridge. The existing channel width at this location is 16'. The new channel alignment is shown on Hydraulic Sheet 2 in Appendix 4. The new cross section topography has been modeled in HEC -RAS and is shown in Appendix 2. The new floodplain is shown in Appendix 2. 4.3.1 Drop Structures and Scour Pool Design To maintain the design slope of 4% under the bridge, grade control drop structures will be placed downstream of the downstream edge of the bridge to decrease the existing slope and increase habitat. The drop structures have been sized using an iterative method defined by the need for adequate pool length and the need to meet existing grade and channel where the new creek channel will connect with the existing Red Sandstone Creek. Pool length is dependent on longitudinal slope and step height. In addition, the pools are designed as pre- formed scour pools as outlined in Colorado's Urban Drainage and Flood Control District, Volume 2, Chapter 3, Hydraulic Structures, Section 3.4.3. Red Sandstone Creek has gradients greater than 3 -5 %, which often lead to distinctive stepped -bed morphology. Alternation of steps and pools having a stair -like appearance are a characteristic feature of mountain streams flowing over slopes greater than 3 -5% (Knighton, 1998). To restore the creek to a state which will mimic natural morphology, drops are being placed downstream of the new frontage road bridge to minimize slope and create a stable stream environment. Step length in natural mountain creeks and streams is negatively correlated to slope. A few equations have been developed that address this correlation. The equation chosen for this design was illustrated by Abrahams et al. (1995) where he found a relationship to step and pool morphology based on field and laboratory data, H 1.Ss L H = step height L = pool length s = longitudinal slope Using this equation, the objective slope of 0.04, and the calculated step heights based on the need to meet the existing grade at the junction with the existing Red Sandstone Creek alignment, the following pool lengths were calculated. Structure Step Height (H), ft Pool Length (L), ft 1 1 16 .9 .9 15 Pre - formed scour pool dimensions were calculated using the method for the design of riprap basins for culvert discharges with low tailwater (Colorado's Urban Drainage and Flood Control District, Volume 2, Chapter 3 Hydraulic Structures, section 3.4.3). The AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 15of21 upstream cross section of Red Sandstone Creek is treated as a rectangular culvert using the water surface elevation bank width at the design flow condition. The result was the need for a basin that is 14 ft in length, 34 ft in width, and 1.75 ft below the top of the drop structure. The rock used for the drop structure must be 1.75 ft above grade and buried a minimum of 1.45 ft below grade. These dimensions indicate the stepped -pool morphology calculated above will work well with a preformed scour pool design. The pre- formed scour pool dimensions will be embedded in the proposed stepped -pool morphology. The calculations for this are shown in Appendix 3. The pre- formed scour pool computations calculated a D 50 based on the design inputs listed above. The D 50 in this reach shall be 9 inches. Calculations can be found in Appendix 3. Note this does not include sizing for the drop structure riprap. Detailed drop structure design shall be submitted in the next submittal. 4.4 Permitting A construction dewatering permit, issued by the Colorado Department of Public Health and Environment will be required under Section 402 National Pollutant Discharge Elimination System (NPDES). Applying for and obtaining this permit will be the responsibility of the construction contractor. The creek realignment and wetland disturbance will require a U.S. Army Corps of Engineers Permit under Section 404 of the Clean Water Act. A Conditional Letter of May Revision (CLOMR and /or Letter of Map Revision (LOMR will be submitted to FEMA for approval and adoption of the proposed floodplain modification. A Floodplain Modification Permit application will be submitted to the Town of Vail. 4.5 Evaluation of Structural Alternatives Section 4.5 is based upon information from the 1 -70 Frontage Road Over Red Sandstone Creek Structure Type Selection Report prepared by Tsiouvaras Simmons Holderness Inc. ' Single Span Bridge with 60 Foot Clear Opening This option would consist of a single span bridge with integral abutments supported on a single row of steel H pile. The superstructure consists of precast, prestressed concrete box girders with a cast in place concrete deck. To minimize the height of the abutment and allow for the use of integral abutments, 2 to 1 slopes are utilized down to the creek. The bridge would have 16 foot long wing walls cantilevered from the abutment. The 6' -0" wide girders are spaced at 14' -0" to provide sufficient space for utilities to pass beneath the deck. The girders are 2' -6" deep. ' This option provides adequate vertical clearance over the existing culvert under 1 -70 and meets the hydraulic requirements for the project. The slopes and abutment do infringe into the 100 -yr floodplain, causing a slight localized water surface rise. It also has the ' flexibility of being able to be skewed to fit the site. AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 1 16 of 21 ' Arched Culvert with 42 Foot Clear Opening This option consists of precast arched culvert sections supported on a cast in place foundation supported on steel H pile. The precast sections cannot be skewed so the culvert is offset from the existing pipe culvert by 11 feet to re- direct the flow. Each end of the culvert will require a concrete headwall. The up stream headwall will retain the 1 -70 fill and allow the existing culvert to penetrate the wall. It will also extend above the culvert to make up grade between 1 -70 and the frontage road. The downstream head wall will support the approximate 8 feet of fill over the culvert and tie into the adjacent retaining walls. This option has adequate vertical clearance over the existing culvert under 1 -70 and meets the hydraulic requirements for the project. The relatively flat bottom of the culvert minimizes the impacts to the floodplain. Architectural Requirements The down stream headwall and adjacent retaining walls are an important part of the aesthetic vision for the development. They will be covered with stone veneer and incorporate pilasters as shown on the preliminary elevation. The stone will be 4" thick Telluride Gold. See Structure Type Selection Report for more details on architectural requirements. Preliminary Cost Comparison The following is a summary of the structure cost estimates located in Appendix B. The cost data used for the estimates was derived from the historical cost data from the previous three years of the CDOT cost Data Book. These costs were adjusted for the size of the job, location and construction inflation. The cost of the precast arch culvert was provided from Contech and contractor mark up and erection were added. For comparison purposes, the roadway quantities for the roadway section above the arched ' culvert were included into its estimate for the length equaling the distance from the end of approach slabs. Structure Type Cost Estimate 60 Foot Bridge With Precast Concrete Girders $952,519.00 Precast Arched Culvert $860,617.00 I � I � The cost estimate for Red Sandstone Creek realignment will be added in a later submittal. I � I � AMEC Earth & Environmental ' CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 17 of 21 Recommended Alternatives The Arched Culvert option is selected as the preferred option for the following reasons: • Reduced impacts to the floodplain • Improved aesthetics ' Reduced construction duration • Slightly lower cost I I AMEC Earth & Environmental CDOT Hydraulic Report 30% Design , South Frontage Road Bridge at Red Sandstone Creek 18 of 21 ' 5.0 Recommended Design _ The size, location and skew of the new South Frontage Road Bridge is shown in Hydraulic sheet 2. Because of the space limitations and proximity (5 ft) of the new South Frontage Road Bridge to the existing 1 -70 culvert, a grouted riprap rundown will be constructed that will extend from the 1 -70 Culvert exit down to the new stream invert. Wing walls will be put in place to divert flow through into the 42 -ft structural arch culvert. At the bottom of the rundown the riprap will be sized and modeled after a riprap basin per FHWA standards. Riprap shall be D =27 inches, to a depth of 40.5 inches (3.36 ft) through the entirety of the bridge. The bank to bank width of the channel through the bridge will range from 36 -40 ft. The longitudinal slope under and downstream of the bridge shall be 4 %. Two grade control drop structures shall be constructed downstream of the bridge to maintain a steady 4% slope and decrease velocities below and downstream of the bridge. There will be no excavation of the thalweg or encroachment since there will be a newly aligned creek that will be designed within the parameters of the arched culvert. The structure will have a clear span of 42 feet and a minimum height to the crown of the arch of 8 feet. The water surface elevation of the 100 -year flood is 8,108.32 at the upstream and 8103.53 ft at the downstream end. A profile of the ' proposed ground and water surface elevation at the 100 yr event is shown in Figure 8. Red Sandstone Creek will be realigned as specified in the Hydraulic sheets in Appendix 4 and as discussed in detail in Section 4.2 Red Sandstone Realignment. Detailed design drawings will be submitted in the next submittal. I i I � I � I � AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek 19 of 21 6.0 References CDOT Drainage Design Manual. 2004 Flood Insurance Study. Eagle County, Colorado and Incorporated Areas (08037CV000A). FEMA. December 4, 2007. HEC -14 Third Edition (July 2006). Hydraulic Design of Energy Dissipators for Culverts and Channels. Federal Highway Association. HEC -15 Third Edition (September 2005). Design of Roadside Channels with Flexible Linings. Federal Highway Association. HEC -18 Fourth Edition. Evaluating Scour At Bridges (May 2001). Federal Highway Association. HEC -20 Third Edition. Stream Stability at Highway Structures (March 2001). Federal Highway Association. Knighton, Davis (1998). Fluvial Forms and Processes. New York, Oxford University Press. Urban Storm Drainage Criteria Manual (2008) Urban Drainage and Flood Control District. Volume 2. AMEC Earth & Environmental � Appendix 1 Flood Plain Map 1� 1 1 n Appendix 2 HEC RAS Analysis F] Appendix 2 2.1 HEC RAS Modeling Summary CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Modeling Summary Floodplain Modeling using HEC RAS The existing Flood Insurance study (08037CV000A). was adopted by FEMA on December 2, 2007 The HEC RAS files were received from FEMA in October of 2008 and represent the most recent mapping efforts adopted by FEMA December 4, 2007. The map number for Red Sandstone Creek is 0837C046D. The existing FIRM is shown in Figure 1. Red Sandstone Creek is modeled from the confluence with Gore Creek to approximately 2,900 feet upstream, just past Potato Patch Drive. Figure 1. FIRM for Red Sandstone Creek The existing cross section geometry modeled in HEC RAS was examined for accuracy with recent survey data to verify the accuracy of the geometry prior to modeling the new AMEC Earth & Environmental flood insurance is available in this community, contact LIMIT OF DETAILED STUDY tional Flood Insufanee Program at 18001638 -6620. 823 MAP SCALE 11 = 500' c^ ^^ ^ ZONEAE 8 732 1% ANNUAL CHANCE FLOOD DISCHARGE TE LI MITS — CONTAINED IN CULVERT ._ 9210 TOww O y PANEL 016w 8200 ZONE X UBIIO 819 FIRM C 19 RED SANDSIDNE AOAD KLO FLOOD INSURANCE RATE MAP EAGLE COUNTY, 8110 COLORADO 3 Red Sandstone 711 AND INCORPORATED AREAS ONE X Creek eeso 8160 PANEL 469 OF 1125 aP" ZONEAE °m 16H IMP INWI ree iPM P�kFl lAYOUI mmaac 8140 m sa rearxm yew rely � ° clacLE ZONE 3W 8 � s� AE mpD t ZONEX P 1 %ANNUAI,C E 810 FLOOD DISC CON T AED I C ERT P oP ° Bike o $ A MAP NUMBER Path rn ° y 08037C0469D ° � P °� e Fap8 8080 Z WEST ® EFFECTIVE DATE: ° Pty w „c' DECEMBER 4, 2001 r,Fa Path o X $ Footbridge p m o Faded Emagwj Manage— Agency 0 ® 0 roRe caeeA Z *1va ro an aalca cop/ f a poNm dthe above r,b—d 1-1 p cc N lP O S °� -- .d uia9 F'MIT OrvU- Thia map 1a net eAM charpee — — — « amenmenn wHCn mry hm been mane su<eep.�a m the Bate on the O — — — CORPORATELIMITS a ioa hmk FE �S-st mv�ma. q 11l FlO� l po Figure 1. FIRM for Red Sandstone Creek The existing cross section geometry modeled in HEC RAS was examined for accuracy with recent survey data to verify the accuracy of the geometry prior to modeling the new AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Modeling Summary South Frontage Road bridge. Upon comparing these cross sections to more recent topographic data discrepancies were revealed between topographic elevations. The survey data used for the existing effective FEMA HEC RAS modeling was done in October 1999 by Peak Land Consultants. Vail Resorts and Development Company contracted Peak Land Consultants to resurvey the existing cross sections at the same locations along Red Sandstone on October 7, 2008. Cross sections 406.5 to 401.5 were re- surveyed . In addition, new cross sections were added to better model the existing floodplain prior to proposed modifications. The location of these cross sections is shown in Appendix 1. The notable changes to the existing model are listed below. 1. Sections 406.5 and 406 have updated horizontal geometry and the sections have been expanded to show flow in the horizontal plane, rather than rising above 1 -70 during high flow conditions. 2. The culvert invert on the upstream side at 1 -70 has been updated to 8120.3. The previous culvert invert measurement was 8124.3. 3. The culvert invert on the downstream side of 1 -70 has been updated to 8107.90. The previous culvert invert measurement was 8105.00. 4. Section 405.3 was added 5' below section 405.5 to represent the actual stream geometry just outside of the culvert because the existing section 405.5 shows the wing walls of the culvert and misrepresents the existing channel geometry in that reach. 5. Sections 404.5 and 405.25 were added to provide more floodplain elevation accuracy downstream of the new frontage road bridge. 6. The culvert diameter has been changed to reflect the actual measurements of 7 ft. The previous diameter measurement was 6 ft. This new cross sectional data was then entered into the existing effective HEC RAS model and used to model new baseline conditions. HEC RAS cross sections are shown at the end of this summary. Results The original effective model was updated with the above changes. HEC -RAS results varied slightly with the cross sectional data. The more significant results are listed below. 1. Sections 406 and 406.5 north of 1 -70 saw a decrease in water surface elevation of 3.8'. This is most likely due to the increased length of the horizontal cross section showing the water flowing over the banks rather than up and over 1 -70 as it did in the original model. 2. Section 405.5 shows a higher water surface elevation. This is most likely a result of the existing model not showing the wing walls here while the new cross section geometry represent the wing walls. 3. The water surface elevation at 405 is lower in the new model. This is mostly likely a result of more detailed geometry that shows a more incised channel. 4. The largest variation in velocity observed was 4.6 %. This varied between cross sections. In some instances the velocity was higher at individual cross sections, while in others it was lower. CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Modelinq Summary Table 1. Existing FIRM vs New Baseline WSE and Velocities from HEC RAS Modeling New Effective Existing Firm River W.S. Elevation Vel Chnl W.S. Elevation Vel Chnl Station ft) (ft/s) (ft ft/s 415.5 8253.94 1.18 8253.94 1.18 415 8253.93 1.43 8253.93 1.43 414 8238.11 8.37 8238.11 8.37 413.8 8235.6 7.95 8235.6 7.95 413 8232.39 0.94 8232.39 0.94 412.4 8232.39 1 8232.39 1 412.2 8215.28 8.38 8215.28 8.38 412 8214.19 7.79 8214.19 7.79 411 8201.96 7.13 8201.96 7.13 410.5 8192.12 9.09 8192.12 9.09 410 8189.59 6.69 8189.59 6.69 409.3 8187.42 8.54 8187.42 8.54 409.2 8182.61 8.4 8182.61 8.4 409 8181.22 7.42 8181.22 7.41 408 8158.02 7.66 8158.02 7.66 407 8140.04 7.62 8140.04 7.64 406.5 8135.03 1.48 8139.21 0.93 406 8135.02 1.73 8139.21 0.84 405.5 8110.01 10.01 8109.39 8.8 405.3 8108.83 8.41 405 8106.76 5.98 8107.13 6.11 404.91 8103.34 5.15 404.5 8099.98 6.16 404.25 8097.96 6.08 404 8096.35 7.68 8096.39 7.32 403 8088.6 8.04 8088.34 8.2 402.5 8088.2 6.25 8087.71 6.03 402 8085.42 7.71 8085.54 7.69 401.5 8083.16 7.55 8083.53 7.55 401 8077.8 8.98 8077.2 5.79 "Blank values indicate those cross sections do not exist in the model. Proposed Changes 3 The new effective baseline geometry has been modified to reflect the new South frontage Road Bridge and the realignment of Red Sandstone Creek. The bounding cross sections are 407, which is located 3 cross sections and 211 ft upstream of the 1 -70 culvert inlet, and section 404, which is located 208 ft downstream of the 1 -70 culvert discharge. The water surface elevations and velocities return to existing values at or before these bounding sections. AMF;C Larth &- IAuvironiiiemal CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Modeling Summary Modeling Assumptions The following are assumptions that were used in the existing adopted HEC RAS modeling. The Mannings n values have not been adjusted to represent the increased size in boulders. Nor, were the original Manning's n values adjusted to represent the steep slope of Red Sandstone Creek. Manning's n values used were consistently 0.04 and 0.05 throughout the model. Flow regime modeled is subcritical Downstream boundary condition was kept at normal depth = 0.04, as exists in the current model. The primary changes to the HEC RAS geometry are listed below. 1. The downstream end of the culvert has been cut back 13 ft. The new culvert invert elevation is 8108.39. 2. Sections 405 and 405.5 have been deleted. 3. A bridge has been added 5 ft downstream of new culvert discharge location. The east and west sides of the bridge will be filled to accommodate the new roadway. The bridge width is 90'. 4. Sections 405.61, 405.6, and 405.59 have been added in- between the new bridge and the new retaining wall to model the 2:1 grouted riprap rundown coming out the 1 -70 culvert. 5. Section 405.4 was added as internal bridge geometry to model the stream inside the bridge. 6. Section 404.9 was added to model the new stream morphology at the downstream end of the bridge. 7. Section 404.8 was added to represent the morphology 1 ft downstream of the bridge. 8. The following sections were added to represent the two drop structures located downstream of the new frontage road bridge: 404.79, 404.78, 404.77, 404.76, 404.75, 404.74, 404.73, and 404.72. Results of this new geometry are shown in Tables 3 and 4. HEC RAS sections for the proposed geometry are shown at the end of the summary. The existing FIRM, the proposed new effective baseline floodplain, and the proposed floodplain with the ' new South Frontage Road Bridge are shown in Appendix 1. Proposed vs. existing ground and water surface Elevations are shown in Figure 2. I i I � I � I � Y N Ql L U m c 0 c co c � rn � � � a C) co J. o L l y U Z = C o a U� 0 C OU L 7 � � Z 0 c� W v s, c �a 0 > W �i 0 s, C7 wo W > 0 CL 0 s. a N S■ to w 0 W w U w e ro w cn L (D O O 2 O o p N }� U) +� CaL W O O Cl) •X •x a_ W a W W W O O O O 00 O O O O d" O O N O O O O O O O O O M N O 07 00 1— � 0p 00 00 00 Co 00 00 00 0 c� W v s, c �a 0 > W �i 0 s, C7 wo W > 0 CL 0 s. a N S■ to w 0 W w U w e ro Appendix 2 2.2 H EC RAS Sections CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 1 of 15 HEC RAS Cross Sections For the longitudinal location of cross sections see the floodplain map in Appendix 1. AMEC Earth & Enviromiental Red Sandstone Creek Plan: Plan 73 11/19/2008 406.5. As survey by PLC 100708. 8138 Legend WS 100 -yea 8136 WS 10 -year Ground 8134 • Bank Sta 8132 O q, w 8130 8128 8126 8124 -50 0 50 100 150 200 Station (ft) AMEC Earth & Enviromiental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 2of15 AMEC Earth & Enviromnental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections �SRP: x:31 8120 c 0 w 8115 8110 8105+ 10 Red Sandstone Creek Plan: Plan 73 11/19/2008 Interstate 70 culvert Legend C rit 100 -yea Crtt 10 -year WS 10 -year WS 100 -y ea E � ` Ground Levee • Bank Sta 20 30 40 50 60 Station (ft) 3 of 15 AMEC Earth & Enviromnental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 4 of 15 AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 5 of 15 81 8115 c 0 d w 8110 8105 8100+ -20 Red Sandstone Creek Plan: Plan 73 11/19/2008 Legend WS 100 -yea c rit 100 -y ea WS 10 -year Crit 10 -year Ground Bank Sta 0 20 40 60 80 Station (ft) AMEC Earth & Envirorunental. Red Sandstone Creek Plan: Plan 73 11/19/2008 8125 Legend WS 100 -yea C rit 1100-year 8120 WS 10 -year Crit 10 -year Ground 8115 Bank Ste m w 8110 1 8105 8100 0 20 40 60 80 100 Station (ft) AMEC Earth & Envirorunental. CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 6 of 15 8105 8104 8103 c 0 a� w 8102 8101 8100+ 0 Red Sandstone Creek Plan: Plan 73 11/19/2008 404.9 PROPOSED STRM. ALIGNMENT ATS.END OF BRIDGE Legend WS 100 -yea Crit 100 -yea WS 10 -year Crit 10 -year Ground • Bank Sta 20 40 60 80 100 Statio (ft) 8105 8103 c 0 m w 8102 8101 8100+ 0 Red Sandstone Creek Plan: Plan 73 11/19/2008 404.8. 1/2 downstream of bridge edge Legend WS 100 -y ea - -+ - -- Crit 100 -y ea WS 10 -year Crit 10 -year Ground Bank Sta 20 40 60 80 100 Station (ft) AMEC Earth & Environtnental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections Red Sandstone Creek Plan: Plan 73 11/19/2008 404.79. top of drop strucutre 1. 81 8104 8103 - c .s w w 81 81 WS 100 -yea c rit 100 -yea WS 10 -year Crit 10 -year Ground Bank St. 40 50 7of15 AMEC Earth & Enviromnental 81 -10 0 10 20 30 Station (ft) CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections Red Sandstone Creek Plan: Plan 73 11/19/2008 404.76. End of Scour Pool 8105 8104 8103 c 4 8102 m w 8101 8100 8099 -10 0 10 20 30 40 50 Station (ft) WS 100 -year Crit 10 -year Ground • Bank Sta 8of15 AWC Earth & Envirotunental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections AMEC Earth & Environmental 9 of 15 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Se ctions 10 of 15 ANMC Earth & Enviromnental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections AMEC Earth & Enviromnental 11 of 15 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections AMEC Earth & Enviromnental 12 of 15 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 13 of 15 AMEC Earth & Enviromiental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 14 of 15 i✓ c w W Station Legend • WS 100 -yea C rit 100 -yea WS 10 -year Grit 10 -year Ground Bank Sta AMEC Earth & Environmental Red Sandstone Creek Plan: Plan 73 11/19/2008 South frontage road CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Cross Sections 15 of 15 AMEC Earth & Environmental Appendix 2 2.3 HEC RAS Profiles CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Profiles 1 of 2 Figu re 1. 190 yr Event - 49U Ms CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek HEC RAS Profiles 1 2 of 2 ' Figure 2. 10 yr Event - 330 cfs Red Sandstone Creek Plan: Plan 73 11202008 Red Sandstone Creek Plan: Plan 73 11202008 RIVER -1 Reach -1 L r RIVER -1 Reach -1 Legend WS 10-year 8180 - - -� - - - Crk 10 -year WS 600-year 8180 Ground - - Crlt 600 -year Left Levee Right Levee 8160 8140 c, Right Levee 8160 w 8120 3 8100 m 8120 8080 8100 0 200 400 600 800 1000 1200 1400 Main Channel Distance (ft) -il Figure 2. 10 yr Event - 330 cfs Figure 3.500 Yr Event - 590 cfs Red Sandstone Creek Plan: Plan 73 11202008 L r RIVER -1 Reach -1 Legend WS 600-year 8180 - - Crlt 600 -year Ground Left Lev ee Right Levee 8160 8140 m 8120 8100 -il 8080 0 200 400 600 800 1000 1200 1400 Main Channel Distance (ft) Figure 3.500 Yr Event - 590 cfs Appendix 2 2.4 HEC RAS Results in Tabular Format v r` co Cp M Ln _ > a) 00 N co U O r M M O 0 O M � N N N 7 (n U C, co O M co N N N N N 10 O O O 0 0 0 0 0 0 r O co O 0 0 0 0 0 0 0 0 O O O O O o O O r- O O — 0 a O L U O) M CO M M N D) M 0 M N M M o0 M N O M M o V' M Q O co M Cfl Cl) O r c0 N 00 co O r O —� 6 �- co O co r O LO LO co r N (0 00 r- CD O I� M O l!� I� O M 'V N tf') CO CO O O LC7 O a0 Cl) CO N 5 LO r- N CO N N N— M M O O N r- N r- t'- M M N co Q _ M r co N co V r CO r 0) M V' O M M U) LO LO co r- N (D M 00 U') V CD M M LO CO r — d' co 0 o N N Cl) M O 0) 4— u') o 00 O) LO D) 10 r O co LO M CO Q M co u M O N co CO Lr) N co CD M Ln M r In M Lo 6 W co M CD lfl co M co co V LI) O O 00 co co O (D co co M LO cr M LO V O 0 LL M CO r U) V co O) co 0) O V V N Cfl N A co co U ( 00 00 'T L in co d' co O 0) CO r- — o (D LO M (D M r O V O o CD O N f� LO 0) C CO r O m r-- r (A (fl m � r- r- O M u LP Co o r- m cO � r-� o0 m N aO M **I 00 r- r- q - - LO 'T co 't (o o (D V LO M (D (0 N 00 N V N 00 O o O LO M Lf) — M O) O N 00 M r- M (0 V O LO O 00 N d' <- r- V CO r- O N n O O O CO Q0 O (D It N o 6) N LO 00 N LO 0 N CO LO O CO 0) O O 07 O O O M O o 0 r O O O o 0 0 O V (fl 'I M N O O O M O a) O O M O O O N N N N N O O N N N N N N O N N 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O O O O O O O O O O o O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O O O W U) r- M N 00 r M LO rt M LO t'- M LO t` (fl (fl CO LO r- M CO LO 'T M > d7 o D) L O CV Cl? � r M N LO O O O o 0 Ln o M r Ln LO N CD M M O O M M M (O N M M LO N O) O co co N 00 O LO 0) t` CO O 00 r 0) M O V' o W LO LO N M CO N O �-- 0) 00 00 M CO M M 0 0 0 0 m o M M 00 00 r N N 00 N N 00 N N N 00 — 0 0 0 0 O O O (� 00 M 0O 00 CO 00 00 00 M 00 M 00 00 M M M M M 00 00 00 00 00 co 00 W � O CD 00 00 0) CD N N N N IT 0) e- co (D IT 00 (fl U (O Cl) N (D 00 LO Lr) N— O) —. r- IT N O Cl r- O 00 r- M O M M 00 LC) � 7 r (D 00 Cl) Lr) V N 0) r- 00 o r- O 00 Co Cl) o r- (0 00 r- to M r- V M N N � 0 O 00 00 00 CO N c- 0 0 0 0) 0) 0) 0 00 M M O N N 00 N N N N .-- - 0 0 0 00 O o 0 00 co 00 00 00 00 00 00 00 M M W oD a0 00 c0 N co co co N 00 U � 'T c) — (.9 0) 0 00 O (o N O N N N V' co N M M V 00 co LO O N N (0 M > O o — Lr ) M M N O— LO q CO N 0 0 0 0 O cO t` M O O M 00 00 'IT r O LL1 M M 00 M N N 6 V N 00 N � 00 o LO L0 O M (.D M O r- C) M Ljr) M r LO N LO N Cl) N N M M N M N N N O N o co M of M M CO M M 0 0 0 0) O 0 O 0) 0 O 0 CO 0 CO 00 00 o 00 o 0 CO W 00 00 00 M 00 M M 00 c0 M ao of of M M a0 00 co M M M 00 W cO 00 M > Z 00 00 't 1-- 0) co O 00 �t '7 r O M M Lo M a0 It O Cl) N (fl O LO V' L _ W N LO N N N O 00 to M LO N (D O L!') V O d1 N M 00 V V M co N M ao co r co OO a0 d' O M N Lt) �f i N o O U N N N N N N N N N O O O O O Q) M M M t` O M M oo M 00 c0 00 00 00 M � -- O o 0 00 0 00 0 00 0 00 0 co 00 OO 00 00 00 00 O o 0 0 0 000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O o 0 O o O O m 0) 0) O o O) O d7 0) o 0 6) 0') 6) 07 6) 0) 0) O 0) 0 0) 0) 0) O O 0') M 0) +-' V V V V V N m x O O 0 � m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m to a) a) m m m m m a) m a) a) m a) a) a) a) m m a) a) a) m m a) a) a) m a) m (1) m a) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o 0 O o 0 0 0 0 2 o 0 O o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 - c- U LO Ln CO CO � CO N N �- LC) O Ln CO N o co r- U') (D r- U) M Liz LO LO It M LO co N LO M N N N O O) o O o 0 0 CD 0 0) N O o N N o o V � V V V' V 0 0 0 � d' V' O V 0 0 0 V � CD d' 'V V 00 V O 't 'IT It V V V V O V 0 Nt � V U a) W � 2 cr r L L L L r .0 _C L L L 7 � , L L L L L L s-. t-. 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N m o CO M CO M M O M N N O N V r O W CD (D M M W I` M Ln V M N M M co N O m M W W W Ln V N 0 0 O O O 0 0 0 0 m m M M 00 m I` N M N 00 N 00 N 00 N M N 00 N N M r co N M 00 00 M M M 00 00 00 co 00 co M r 00 00 0 00 0 co 0 M 0 00 0 00 0 00 0 00 U > m M M 7 M V m M m M Ln I-- r 0o V V M (D i- M M I� r of Ln M M m M m I- (O V (D N 00 (D (0 Ln V M t` M V N N M M N N CD M M O ( ,.j N N o N '7 V (.0 co Ln M V N W I� t` co Ln Ln Ln Ln V N N m r- N M O M 0 m 00 M M M O M N N O N O W M W N Ln M N W (n Ln N Ln N M N M N M N Cl) N N r- N O N m W W of W Ln V' M M 0 0 O O O M O O o .- of O O o m O m O 00 O co O co O co O I` O > O0 00 M 00 c0 N M co 00 M 00 M M W 00 00 00 M 00 00 00 00 M W M W M M M W 00 M c0 M 00 00 (0 00 00 V I` 0) M V O co V v m CD N Ln M m v m Ln Ln N I` I` N N Ln Ln M M N CD m Ln V LlJ .- N Ln N N N 0 0 CD M (D ^ in M Ln N M co m Ln M Ln Ln M m Ln Lt') 00 "t O 0) V N M 00 I O L V V M M N 00 M N M W 0J M r M M O Ln r M If) O O O CO CO m m I� r m 0 o N Ln Ln N m o co O U N N N N N N N N N O O O O O O m 6 m 0 m 0 O M m o m O O co m 0 m 0 m 0 W 0 M 0 M O r O C M M 00 M M co M M 00 Co co co co co co m of M M M M N M 00 00 00 co c0 co co (D N O 00 O O O O O O O O O O 0 0 0 0 0 0 0 0 0 0 0 O O O O O O O O O O O O o 0 o O O O 0 m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m m Q Ln Ln Ln Ln Ln u) u U In Ln Ln Ln Ln Ln Ln t(') U) X) In S) Ln Lo Ln Ln Ln Ln u) u) u) u) u) Ln Ln Ln Ln Ln Ln U) Ln Ln LO LO 0 m a N a m N r m `m m a) a) a) aJ a) a) a) a) Q) a) Q) w a) ! a) a) a) a) a) a) m a) a) a) a) a) .. a) N . N N O 0 0 0 0 0 O o 0 0 0 0 0 0 0 0 0 0 0 0 O o CD o Cj O O o O O O o C7 o CD a O O O O O o O O O O O O O 0 0 0 0 0 0 0 0 0 0 0 O O O L O 0 0 0 0 LO 0 0 0 0 0 0 O O O Lf') li) li) W M c} M N N lt) O Ln M N m N f� Ln CD I� CD m In m W m 00 I� CD l N Ln Ln a m n V M N N N O m m m O O O O M m Ln V V I� r r r r - r n . r N O 0 O N N O � O (n � 0 0 0 O 0 o O O Ln o O O O V V 1 1 , o O 0 0 O� U Q) -T t{ V V V V 7 V V V V O 0 v O v V V V O v O v o O v Z O v 0 O v 0 0 v 0 0 v 0 0 v 0 0 v V V V W �T Q) L L L t L t t-r- L L L L t L t t L L L L L L L L L L L t L L L L L L L L r L L t L L L L L L U m U m U m U m U m U m U m U m U m U m U m U m U m U m U (a U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m U m to a o a m o m m o o m o 0 o a) o Q) m o o a) o 0 o a) w o a) w a) w w o o a) o a) a) a) a) m a o 0 Appendix 2 2.5 HEC RAS Bridge Scour Results HEC RAS Modeling Bridge Scour Results Inputs: 500 yr flow — 590 cfs Section — 405.4 Default tab for Live bed vs Clear Bed K1= 0.64 Hydraulic Design -Bridge Scour River- Reach= Reach -1 RS = 405.4 BR Contraction Scour Left Channel Right Ys (ft): 0.02 Vc (ft/s): 7.79 Equation: Live Bridge Scour RS = 405.4 8125 L eg en d WS 500 -y ear 8120 Ground • Bank Ste Contr Scour 8115 c W 8110 8105 8100 -20 0 20 40 60 80 Station (it) Hydraulic Design -Bridge Scour River- Reach= Reach -1 RS = 405.4 BR Contraction Scour Left Channel Right Ys (ft): 0.02 Vc (ft/s): 7.79 Equation: Live Appendix 3 Calculations ' CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek ' Calculations for a Riprap Basin at the 1 -70 Culvert Exit ' Calculations for a Riprap Basin at the 1 -70 Culvert Exit 1. Objective ' Size a pre- formed scour pool using the 500 yr flood event flow conditions that will utilize the existing design conditions at the 1 -70 Culvert Exit to prevent scour from occurring under the arched culvert. 2. Source FHWA HEC No. 14. Chapter 10. Section 10.1. Titled ` Riprap Basin'. 1 3. Assumptions • Use large grouted rip rap on the sloped culvert discharge rundown for energy dissipation that will mimic a concrete baffle design. • Size the D 50 under the bridge using the assumption that the bottom of the rundown will act as an energy dissipation riprap basin. The riprap basin will not have an upslope on the downstream side. • Treat the sloped culvert rundown as the incoming rundown for the riprap basin. The elevation loss (culvert invert - stream bed invert) was used as the design variable (h to select D 50 using the FHWS guidelines for riprap basin design. • Maintain the stream invert within 1 ft. of the existing stream invert at the existing culvert discharge location • Tail water depth divided by equivalent brink depth at culvert exit is less than 0.75 • No downstream apron will be included as part of this design. The design will include only the length required to dissipate the energy. • The riprap floor is constructed at the approximate depth of scour, h that would occur in a thick pad of riprap. The h /D of the material should be greater than 2. • All values are for the 500 yr flood event, 590 cfs (FIS FEMA 2007). • Velocity and water depth values are from HEC -RAS modeling results 4. Calculations I h ` = 0.86 ] - 0.55 [D50 V ° - C .ye .ye gye C =1.4 L =10h, ' W = W O + 2 Lb 3 h = dissipater pool depth, (ft) Ye = equivalent brink (outlet) depth, (ft) ' D50= median rock size by weight, (ft) C = tailwater parameter as defined in equation 10.2. Ls - Length of pool W = width AMEC L u L Li roninental Equation 10.1 CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek Calculations for a Riprap Basin at the 1 -70 Culvert Exit W = width of conduit 2 An iterative method was used to calculate the h value based on changing the D 50 value and the need to match the h with the existing predetermined depth from bottom of culvert to riprap basin floor. Equation 10.1 was solved using excel. The results are shown below. Parameter Value Dimension Culvert diameter 7 ft Ye 3.67 ft Velocity 26.39 ft/s Froude number 2.43 n/a Dso 2.3 ft C 1.4 n/a h /y 1.30 n/a h s 4.77 ft h /D 2.07 n/a D50/ye 0.63 n/a Downstream WSE 8106.77 ft Invert of Basin 8104 ft Tail Water Depth 2.77 ft TW /ye 0.75 n/a L 47.69 ft L b 71.54 ft W b 54.69 ft 5. Results and Conclusions The above values have been used to size riprap for pre- formed scour pond to avoid scour at the 500 yr flood event. In conclusion: • The riprap D50 will be 2.2 ft (27 inches) • The riprap thickness will be 2D 54 inches (4.5 ft) • The h value adequately satisfies the design conditions of 4.39ft with a value of 4.77 ft. • The width is larger than the width of the Culvert but it is believed that the existing culvert width of 42 ft will adequately manage the energy dissipation and the armoring specified armoring identified above. In addition the riprap rundown will be specified so as the rundown mimics a concrete baffle design. AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek Calculations for Drop Structures and Scour Pools below Drop Structures Calculations for Drop Structures and Scour Pools below Drop Structures 1. Objective Design drop structures and scour pools downstream of the new arched culvert that will accommodate the required spacing between steps and pools that would occur in a natural mountain setting with a similar slope. 1 2. Source: Colorado Urban Drainage & Flood Control District. Volume 2. Hydraulic Structures 3.4.2. 3. Assumptions: • The upstream cross section can be approximated as a rectangular culvert using the bottom width and a height that is above the high water surface elevation. • The depth of water above the drop is 2.5 ft. This value is taken from the HEC RAS modeling results • The velocity used is taken from the average velocity calculation in the HEC RAS section modeling the top of the proposed drop structure and is assumed to be synonymous with the culvert exit velocity. • Tail water depth is assumed to be less than 1/3 of the height of the discharge object (i.e. conduit or cross section) 4. Calculations These equations are taken from Colorado Urban Drainage & Flood Control District. Volume 2. Hydraulic Structures 3.4.2. P, = (V +gxd) / T= 1.75xA. L, =4D or L _ (D) /2 x 2 W = w +4D B= D +T 2 Excel was used to solve the above equations. Results are listed in the table below. Parameter I Value Dimension Description AMEC Earth & Environmental CDOT Hydraulic Report 30% Design South Frontage Road Bridge at Red Sandstone Creek Calculations for Drop Structures and Scour Pools below Drop Structures d 2.5 ft normal depth V 7.84 ft/s Velocity at Outlet g 32.2 ft/s2 H 3.5 ft Height of channel W 20 ft Width of conduit Pd 11.91493 non dim. Rip rap sizing parameter RiprapType ** L non dim. look up this value in Figure 4 D50 9 inches look up this value in Figure 4 L, 14 ft Length of Basin L2 7.333648 ft Length of Basin B 17.5 inches Depth of cutoff wall T 15.75 inches Minimum thickness of riprap W 34 ft Width of basin Ld 5.6 Location of deepest scour D 1.75 depth of basin (height channel /2) *Assume rectangular shape * *if HG+ is indicated riprap needs to be grouted * ** Choose the L, or L values based on the higher of the two 5. Results and Conclusions The design parameters are listed below: • D 9 inches • Depth of Scour Pool = 1.75 ft • Length of Pool = 14 ft • Width of Pool = 34 ft • Minimum thickness of riprap = 15.75 inches • Depth of Cutoff Wall (depth of drop structure below grade) = 17.5 inches In conclusion, the specified pool lengths and widths can be accommodated in the stepped -pool morphology that is typical in mountain streams with similar slopes. 2 AMEC Earth R. Environmental Appendix 4 Hydraulic Sheets G 3�tjno1A NAAOHS Sty V/N 'ON 3unou :31V0S :NO1103rONd upaldpooij p;asodOJd peon 96eluoiA qjnoS OZOL i. 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