FINAL DRAINAGE REPORT Road Improvements (MP 0.6)

Transcription

1 FINAL DRAINAGE REPORT Road Improvements (MP 0.6) Prepared for: Prepared by: Mesa County Engineering Department 200 S. Spruce Street Grand Junction, CO DOWL 222 South Park Avenue Montrose, Colorado, (970) August 17, 2018

2 Final Drainage Report 31 Road Intersection Improvements TABLE OF CONTENTS 1. INTRODUCTION BACKGROUND PROJECT LOCATION... 1 FIGURE ROAD (MP 0.6) PROJECT AREA DESIGN CRITERIA PREVIOUS DESIGN INFORMATION TOPOGRAPHY VEGETATION GENERAL SOILS AND GEOLOGY EXISTING DRAINAGE FEATURES HYDROLOGIC ANALYSIS HYDRAULIC ANALYSIS.7 4. BANK STABILIZATION RECOMMENDATIONS CONCLUSIONS AND RECOMMENDATIONS REFERENCES DOWL January 27, 2017 i

3 Final Drainage Report 31 Road Intersection Improvements Table 1: Table 2: Table 3: PFDS Rainfall Values for the Grand Valley Area Cover Conditions Hydrology Modeling Results LIST OF TABLES Figure 1: Figure 2: Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure Road (MP 0.6) Project Area Atwell Gulch Basin Map Photo of 45.5 Road at project location NRCS WSS Soil Map of Atwell Gulch Photo of RS 1110 showing erosion and temporary rip-rap HEC-RAS RS 1110 cross-section of existing conditions HEC-RAS RS 1110 cross-section with gabion wall Gabion Wall Schematic cross-section detail LIST OF FIGURES Appendix A: Appendix B: Appendix C: Appendix D: Existing and Proposed Project Site Plans NRCS Web Soil Survey Data NOAA 14 PFDS Data HEC-RAS Output Pre-Developed and Developed Conditions LIST OF APPENDICES DOWL January 27, 2017 ii

4 Final Drainage Report 45.5 Road (MP 0.6) Improvements 1. INTRODUCTION 1.1 Background As part of proposed roadway improvements at MP 0.6 on 45.4 Road in Mesa County, DOWL has prepared this Drainage Report for the region contributing runoff into the project area. Storm flows are currently conveyed by Atwell Gulch on the east side of 45.5 Road and they have eroded large portions of the roadway embankment at MP 0.6. This report is intended to present the following information: project site characteristics, identification of existing drainage system H & H components, drainage analysis and results, preliminary design for current project area improvements, conclusions and recommendations. 1.2 Project Location The 45.5 Road (MP0.6) Project (Project) is located approximately 0.6 miles north of the intersection of 45.5 Road and Colorado State Highway 330 north of Mesa, Colorado, within Mesa County. Refer to Exhibit 1 for the general project location. Figure Road (MP 0.6) Project Area DOWL March 15,

5 Final Drainage Report 45.5 Road (MP 0.6) Improvements 1.3 Design Criteria The purpose of the project is to design improvements relating to erosion of the road prism on the west bank of Atwell Gulch at the MP 0.6 locations. Surface stormwater currently flows in in a meandering stream pattern that is eroding portions of 45.5 Road and endangering the asphalt pavement of the road. The Atwell Gulch drainage channels is well established on the east side of 45.5 Road and is directed towards the road in several sections as a cut bank. The scope of work for this drainage report is to determine and design bank stabilization that will accommodate the 100-year design storm in Atwell Gulch, an ephemeral stream channel. 1.4 Previous Design Information Per Mesa County, it does not appear that any existing drainage reports were prepared or are available for the 45.5 Road (MP0.6) project area. DOWL previously prepared drainage reports for Shire Gulch, the 45.5 Road Improvements Phases I/II and the 45.5 Road 4B projects. No known Atwell Gulch drainage reports were available as a reference for this report. Figure 2. Atwell Gulch basin upstream of the project location. DOWL March 15,

6 Final Drainage Report 45.5 Road (MP 0.6) Improvements 1.3 Topography Topography of the project area for project area ranges from an elevation of approximately 7,923 feet (MSL) on the topographic highpoint to the east of the intersection, to 5,200 feet (MSL) at the low point of the project limits to the north and south. The general drainage direction of stormwater runoff is to the southwest at an average grade of approximately 413 feet per mile or 7.8%. 1.4 Vegetation Vegetation in the project area consists primarily of native grasses, shrubs. including rabbit brush and sagebrush and pinyon-juniper trees. Additionally, there are tamarisk trees adjacent to Atwell Gulch which are an invasive species and non-native to the project area. Figure 3. View looking west at vegetation adjacent to the project area. Eroded section of the 45.5 Road bank is to the lower left of the photo. 1.5 General Soils and Geology Information from the NRCS Web Soil Survey (WSS) site indicates that there are thirteen (13) mapped soil units identified in the Atwell Gulch basin. Table 1 below summarizes those soil DOWL March 15,

7 Final Drainage Report 45.5 Road (MP 0.6) Improvements units. More detailed soils descriptions obtained from the WSS website are presented in Appendix B and in the geotechnical report prepared by DOWL for the project. In general, the project area and Atwell Gulch basin are composed of approximately 79% sandstone rock outcrops of the Ohio Creek member of the Mesa Verde formation and the remaining 21% represent colluvial loam soils derived from weathering of that rock. Slopes range from 3 percent up to 90 percent for vertical rock cliffs to the west and east of the MP 0.6 site. Figure 4. Project Soils Map. (Source: NRCS-USDA Web Soil Survey) 1.6 Existing Drainage Features As evidenced by the incised nature of the Atwell Gulch drainage channel on the east side of 45.5 Road, stormwater flows to the project area are readily conveyed towards the 45.5 Road section and then south towards Plateau Creek through numerous channels within the basin in addition to the main Atwell Gulch channel. Drainage features observed during our site visits include: access drive culverts on the west side of 45.5 Road, a 12-inch CMP culvert that DOWL March 15,

8 Final Drainage Report 45.5 Road (MP 0.6) Improvements crosses 45.5 Road near Station 8+25 of the project plans and the 36-inch CMP culvert under SH 330 to the east of the 45.5 Road intersection. Figure 5. View looking downstream at right bank erosion adjacent to 45.5 road. Note sandstone bedrock at the surface of the stream channel and rip-rap placed along the bank and at the toe to minimize erosion of the bank. DOWL March 15,

9 Final Drainage Report 45.5 Road (MP 0.6) Improvements 2. HYDROLOGIC ANALYSIS This section of the report reviews the sources for hydrologic data used hydraulic analysis in Section 4. In addition to the StreamStats data, which calculated the 100-year flow using the USGS regression equation for the northwest Hydrologic Region, we used the USDA Win TR 55 software and the CDWR Unit Hydrograph spreadsheet to estimate peak flow for the Shire Gulch basin. The recently published NOAA Atlas 14 was consulted for revisions to rainfall depth and frequency-duration for the interval storms over a 24-hour period. The data for Mesa, Colorado with a 90% confidence interval was used for our analysis and is presented in Appendix C. RETURN PERIOD 24-HR TOTAL PRECIPITATION (IN) 2-year year year year year year 2.50 Table 1. Summary of NOAA Atlas 14 precipitation data for varying recurrence periods. RETURN PERIOD STREAMSTATS WIN TR-55 PEAK FLOWS (c.f.s) PEAK FLOWS (c.f.s.) 2-year year year year year year Table 2. Summary of StreamStats Peak-Flow Statistics Data for Atwell Gulch Basin 2.1 Win TR 55 Model To confirm that StreamStats returned reasonable rainfall and flow data for the Atwell Gulch basin, we also modeled the basin using Win TR 55 software form the US Department of Agriculture (USDA). Output for this model is included in Appendix C of this report. Assumptions for the TR 55 model: Basin area = 6.92 sqare miles. This is slightly smaller than the area returned by the StreamStats program (8.04 sq. miles), but was calculated from USGS maps, and aerial photos using AutoCAD and appears to better represent the contributing basin for Atwell Gulch Weighted CN = 82 for arid rangeland, from StreamStats data Channel length = 6.58 miles Lc = 3.62 miles Slope = ft/ft DOWL March 15,

10 Final Drainage Report 45.5 Road (MP 0.6) Improvements NOAA Type A Design Storm The Win TR-55 calculation resulted in a peak flow at 3,353 cfs, which was similar to the StreamStats estimate of 3,600 cfs. To be conservative, the StreamStats values were used in HEC-RAS hydraulic analysis presented in Section 4 below. Win TR-55 output is presented in Appendix C of this report. 2.2 Existing 100-Year Floodplains\Easements There is no published FEMA floodplain insurance rate map (FIRM) for the Atwell Gulch drainage. A Flood Insurance Study (FIS) for Mesa County, FIS # 08029CV000A, completed in August 2010, does not include Atwell Gulch in the analysis. 3. HYDRAULIC ANALYSES In our preliminary options analysis, we proposed eight varying solutions to stabilizing the bank along 45.5 Road while avoiding construction below the ordinary highwater mark as mapped by ERO Resources. Mesa County selected a gabion wall option with spiral soil nails anchored by a 3-4-foot concrete to wall as shown in Figure 5 below. Using the information obtained in Section 3 as input into the US Army Corps of Engineers HEC-RAS 5.03 hydraulic modeling software, we calculated the minimum required gabion wall height and length pass the estimated 100-year flow of 3,600 cfs. The following assumptions were used for the HEC- RAS culvert sizing analysis: Maximum 100-year flow of 3,600 cfs obtained from StreamStats calculations. Cross-sections of the channel were taken from topographic survey performed by DOWL, as supplemented by digital terrain mapping (DTM) provided by Mesa County for the purpose of confirming gabion wall locations for the project. In order to simulate the bank stabilization proposed using the gabion walls and anchor nails, we modeled a bridge abutment in HEC-RAS. Both pre-developed and developed conditions models were created in HEC-RAS 5.03 to simulate flow conditions with and without the proposed gabion wall stabilization structure. The model output for both analyses are presented in Appendix D and summarized in Table 3 below. Analysis for scour was also performed in HEC-RAS and scour on river right segments will be managed with the bank stabilization structures described above. Scour analysis output is also presented in Appendix D. Condition 2-YR 5-YR 10-YR 25-YR 50-YR 100-YR Existing Gabion Wall Table 3. Summary of water surface elevations for pre-developed and developed conditions at RS DOWL March 15,

11 Final Drainage Report 45.5 Road (MP 0.6) Improvements Figure 6. RS 1110 cross-section of existing conditions. 100-year W.S. elevation is Figure 7. RS 1110 cross-section of Option #2 gabion wall. Modeled as an abutment to a bridge to match structural conditions of design. 100-year water surface is at DOWL March 15,

12 Final Drainage Report 45.5 Road (MP 0.6) Improvements 4. BANK STABILIZATION RECOMMENDATIONS After reviewing and presenting eight options for bank stabilization to Mesa County, Option #2 consisting of a gabion wall with soil anchors and a concrete retaining toe wall was selected for design and final modeling. This option is similar to past bank stabilization efforts by Mesa county along Atwell Gulch except for the retaining wall at the base and the anchors. Both of these additions should minimize future maintenance of this section. In sections of the project area that had slopes greater than 2H;1V, the DOWL design uses grouted and un-grouted rip-rap to retain the slope. In general, these areas are moderately well vegetated and appear stable under current flow conditions. The proposed gabion wall structure is reserved for those section of the channel that have eroded and are nearly vertical. The concrete toe wall will be doweled into underlying sandstone bedrock which is at or near the channel surface throughout the project area. The geotechnical report prepared By DOWL for the project explains the retaining structure in greater detail. Figure 8 below provides a typical gabion wall detail at RS 110 which was used in the hydraulic analyses in Section 3. Figure 8. Gabion Wall schematic design DOWL March 15,

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14 Final Drainage Report 45.5 Road (MP 0.6) Improvements 7. REFERENCES Mesa County Colorado GIS Website, Mesa County Stormwater Management Manual (SWMM), dated December 31, 2007, issued April Natural Resources Conservation Service National Cooperative Soils Survey Website, CDOT Standards and Specifications for Road and Bridge Construction (2017) Erosion Control and Stormwater Quality Field Guide, Colorado Department of Transportation (undated) DOWL March 15,

15 APPENDIX A EXISTING AND PROPOSED SITE PLANS

16 EXISTING CONDITIONS ISSUED FOR BID R SC-VM-BA-45.5RD-ATWELL.dwg EXISTING CONDITIONS 45.5 ROAD IMPROVEMENTS MP 0.6 MESA COUNTY, CO

17 SITE PLAN ISSUED FOR BID R MC-CB-45.5 Road Design Base.dwg SITE PLAN 45.5 ROAD IMPROVEMENTS MP 0.6 MESA COUNTY, CO

18 APPENDIX B NRCS WEB SOIL SURVEY DATA

19 108 9' 27'' W Soil Map Douglas-Plateau Area, Colorado, Parts of Garfield and Mesa Counties; and Grand Mesa - West Elk... (GlobalWatershed) 108 4' 51'' W ' 27'' N 39 16' 27'' N ' 43'' N 39 11' 43'' N ' 27'' W N Map Scale: 1:42,600 if printed on A portrait (8.5" x 11") sheet. Meters Feet Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 12N WGS ' 51'' W Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/26/2018 Page 1 of 3

20 Soil Map Douglas-Plateau Area, Colorado, Parts of Garfield and Mesa Counties; and Grand Mesa - West Elk Area, Colorado, Parts of Delta, Garfield, Gunnison, Mesa, and Montrose Counties (GlobalWatershed) MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Douglas-Plateau Area, Colorado, Parts of Garfield and Mesa Counties Survey Area Data: Version 10, Oct 12, 2017 Soil Survey Area: Grand Mesa - West Elk Area, Colorado, Parts of Delta, Garfield, Gunnison, Mesa, and Montrose Counties Survey Area Data: Version 7, Oct 10, 2017 Your area of interest (AOI) includes more than one soil survey area. These survey areas may have been mapped at different scales, with a different land use in mind, at different times, or at different levels of detail. This may result in map unit symbols, soil properties, and interpretations that do not completely agree across soil survey area boundaries. Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: 2, 2017 Dec 31, 2009 Mar The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/26/2018 Page 2 of 3

21 Soil Map Douglas-Plateau Area, Colorado, Parts of Garfield and Mesa Counties; and Grand Mesa - West Elk Area, Colorado, Parts of Delta, Garfield, Gunnison, Mesa, and Montrose Counties GlobalWatershed Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 2 Badland % 3 Barx loam, 3 to 12 percent slopes 7 Biedsaw-Sunup gravelly loams, 10 to 40 percent slopes 12 Bunkwater very fine sandy loam, 1 to 8 percent slopes 32 Dominguez clay loam, 3 to 8 percent slopes 61 Rock outcrop-torriorthents complex, 15 to 90 percent slopes 66 Torriorthents, warm-rock outcrop complex, 35 to 90 percent slopes 69 Travessilla-Rock outcrop complex, 10 to 35 percent slopes % % % % % 1, % 1, % Subtotals for Soil Survey Area 3, % Totals for Area of Interest 4, % Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 102 Badland % 103 Barx loam, 3 to 12 percent slopes % 180 Rock outcrop, shale % 192 Torriorthents, cool-rock outcrop, 35 to 90 percent slopes 193 Torriorthents, warm-rock outcrop, 35 to 90 percent slopes % % Subtotals for Soil Survey Area % Totals for Area of Interest 4, % Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 1/26/2018 Page 3 of 3

22 APPENDIX C NOAA 14 PFDS DATA AND RUNOFF CALCULATIONS

23 StreamStats Page 2 of 3 StreamStats Report Region ID: CO Workspace ID: CO Clicked Point (Latitude, Longitude): , Time: :17: Basin Characteristics Parameter Code Parameter Description Value Unit DRNAREA Area that drains to a point on a stream 8.04 square miles EL7500 Percent of area above 7500 ft 0 percent PRECIP Mean Annual Precipitation inches BSLDEM10M Mean basin slope computed from 10 m DEM 25.5 percent CSL1085LFP Change in elevation divided by length between points 10 and 85 percent of distance along the longest flow path to the basin divide, LFP from 2D grid feet per mi ELEV Mean Basin Elevation 5954 feet ELEVMAX Maximum basin elevation 7920 feet I24H100Y Maximum 24-hour precipitation that occurs on average once in 100 years 2.5 inches I24H2Y Maximum 24-hour precipitation that occurs on average once in 2 years - Equivalent to precitation intensity index 1.18 inches I6H100Y 6-hour precipitation that is expected to occur on average once in 100 years 1.87 inches I6H2Y Maximum 6-hour precipitation that occurs on average once in 2 years 0.79 LAT_OUT Latitude of Basin Outlet degrees LC11BARE Percentage of barren from NLCD 2011 class LC11CRPHAY Percentage of cultivated crops and hay, classes 81 and 82, from NLCD percent LC11DEV Percentage of developed (urban) land from NLCD 2011 classes percent LC11FOREST Percentage of forest from NLCD 2011 classes percent LC11GRASS Percent of area covered by grassland/herbaceous using 2011 NLCD 0 LC11IMP Average percentage of impervious area determined from NLCD 2011 impervious dataset 0.7 percent LC11SHRUB Percent of area covered by shrubland using 2011 NLCD 73.7 LC11SNOIC Percent snow and ice from NLCD 2011 class 12 0 LC11WATER Percent of open water, class 11, from NLCD LC11WETLND Percentage of wetlands, classes 90 and 95, from NLCD LFPLENGTH Length of longest flow path 7.79 miles LONG_OUT Longitude of Basin Outlet degrees MINBELEV Minimum basin elevation 5200 feet OUTLETELEV Elevation of the stream outlet in thousands of feet above NAVD feet RCN Runoff-curve number as defined by NRCS ( RUNCO_CO Soil runoff coefficient as defined by Verdin and Gross (2017) 0.34 SSURGOA Percentage of area of Hydrologic Soil Type A from SSURGO 49 percent SSURGOB Percentage of area of Hydrologic Soil Type B from SSURGO 1.9 percent SSURGOC Percentage of area of Hydrologic Soil Type C from SSURGO 17.2 percent SSURGOD Percentage of area of Hydrologic Soil Type D from SSURGO 25 percent STATSCLAY Percentage of clay soils from STATSGO percent STORNHD Percent storage (wetlands and waterbodies) determined from 1:24K NHD 0 percent 1/10/2018

24 StreamStats Page 3 of 3 1/10/2018 Parameter Code Parameter Description Value Unit TOC Time of concentration in hours 1.89 Peak-Flow Statistics Parameters [100 Percent (8.01 square miles) Northwest Region Peak Flow] Parameter Code Parameter Name Value Units Min Limit Max Limit DRNAREA Drainage Area 8.04 square miles EL7500 Percent above 7500 ft 0 percent 0 99 PRECIP Mean Annual Precipitation inches 8 49 Peak-Flow Statistics Flow Report [100 Percent (8.01 square miles) Northwest Region Peak Flow] PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE: Standard Error (other -- see report) Statistic Value Unit SEp 2 Year Peak Flood 120 ft^3/s Year Peak Flood 371 ft^3/s Year Peak Flood 736 ft^3/s Year Peak Flood 1540 ft^3/s Year Peak Flood 2410 ft^3/s Year Peak Flood 3600 ft^3/s Year Peak Flood 5130 ft^3/s Year Peak Flood 7740 ft^3/s 79 Peak-Flow Statistics Citations Capesius, J.P., and Stephens, V. C.,2009, Regional Regression Equations for Estimation of Natural Streamflow Statistics in Colorado: U. S. Geological Survey Scientific Investigations Report , 32 p. (

25 Precipitation Frequency Data Server Page 1 of 4 NOAA Atlas 14, Volume 8, Version 2 MESA LAKES Station ID: Location name: Mesa, Colorado, USA* Latitude: , Longitude: Elevation: Elevation (station metadata): ft** * source: ESRI Maps ** source: USGS POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Deborah Martin, Sandra Pavlovic, Ishani Roy, Michael St. Laurent, Carl Trypaluk, Dale Unruh, Michael Yekta, Geoffery Bonnin NOAA, National Weather Service, Silver Spring, Maryland PF_tabular PF_graphical Maps_&_aerials Duration 5-min 10-min 15-min 30-min 60-min 2-hr 3-hr 6-hr 12-hr 24-hr 2-day 3-day 4-day 7-day 10-day 20-day 30-day 45-day 60-day PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches) 1 Average recurrence interval (years) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.17 ( ) 1.49 ( ) 1.89 ( ) 2.19 ( ) 2.45 ( ) 3.18 ( ) 3.81 ( ) 5.46 ( ) 6.80 ( ) 8.50 ( ) 9.96 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 1.06 ( ) 1.33 ( ) 1.68 ( ) 2.15 ( ) 2.51 ( ) 2.82 ( ) 3.66 ( ) 4.35 ( ) 6.15 ( ) 7.64 ( ) 9.61 ( ) 11.3 ( ) ( ) ( ) ( ) ( ) ( ) 1.03 ( ) 1.11 ( ) 1.31 ( ) 1.60 ( ) 2.02 ( ) 2.59 ( ) 3.05 ( ) 3.45 ( ) 4.45 ( ) 5.24 ( ) 7.28 ( ) 9.02 ( ) 11.4 ( ) 13.5 ( ) ( ) ( ) ( ) ( ) 1.10 ( ) 1.26 ( ) 1.33 ( ) 1.52 ( ) 1.85 ( ) 2.32 ( ) 2.98 ( ) 3.53 ( ) 4.00 ( ) 5.13 ( ) 6.01 ( ) 8.23 ( ) 10.2 ( ) 12.8 ( ) 15.2 ( ) ( ) ( ) ( ) 1.21 ( ) 1.39 ( ) 1.57 ( ) 1.64 ( ) 1.84 ( ) 2.21 ( ) 2.76 ( ) 3.54 ( ) 4.21 ( ) 4.78 ( ) 6.10 ( ) 7.08 ( ) 9.55 ( ) 11.7 ( ) 14.7 ( ) 17.5 ( ) ( ) ( ) 1.09 ( ) 1.40 ( ) 1.61 ( ) 1.81 ( ) 1.88 ( ) 2.09 ( ) 2.50 ( ) 3.12 ( ) 3.99 ( ) 4.76 ( ) 5.41 ( ) 6.87 ( ) 7.93 ( ) 10.6 ( ) 12.9 ( ) 16.1 ( ) 19.1 ( ) ( ) 1.01 ( ) 1.23 ( ) 1.58 ( ) 1.82 ( ) 2.05 ( ) 2.13 ( ) 2.36 ( ) 2.82 ( ) 3.50 ( ) 4.47 ( ) 5.33 ( ) 6.06 ( ) 7.66 ( ) 8.80 ( ) 11.6 ( ) 14.1 ( ) 17.5 ( ) 20.7 ( ) 1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS) ( ) 1.11 ( ) 1.35 ( ) 1.75 ( ) 2.02 ( ) 2.29 ( ) 2.38 ( ) 2.64 ( ) 3.16 ( ) 3.90 ( ) 4.97 ( ) 5.94 ( ) 6.75 ( ) 8.48 ( ) 9.70 ( ) 12.7 ( ) 15.3 ( ) 18.9 ( ) 22.2 ( ) ( ) 1.23 ( ) 1.50 ( ) 1.97 ( ) 2.29 ( ) 2.61 ( ) 2.71 ( ) 3.03 ( ) 3.63 ( ) 4.47 ( ) 5.65 ( ) 6.77 ( ) 7.69 ( ) 9.59 ( ) 10.9 ( ) 14.1 ( ) 16.9 ( ) 20.6 ( ) 24.1 ( ) ( ) 1.30 ( ) 1.59 ( ) 2.11 ( ) 2.48 ( ) 2.84 ( ) 2.97 ( ) 3.34 ( ) 4.01 ( ) 4.93 ( ) 6.20 ( ) 7.43 ( ) 8.43 ( ) 10.5 ( ) 11.9 ( ) 15.2 ( ) 18.1 ( ) 21.9 ( ) 25.4 ( ) Numbers in parenthesis are PF estimates at lower and upper bounds of the 90% confidence interval. The probability that precipitation frequency estimates (for a given duration and average recurrence interval) will be greater than the upper bound (or less than the lower bound) is 5%. Estimates at upper bounds are not checked against probable maximum precipitation (PMP) estimates and may be higher than currently valid PMP values. Please refer to NOAA Atlas 14 document for more information. Back to Top 6/21/2018

26 Precipitation Frequency Data Server Page 2 of 4 6/21/2018 PF graphical Back to Top

27 Precipitation Frequency Data Server Page 3 of 4 6/21/2018 Maps & aerials Small scale terrain 3km + 2mi Large scale terrain 100km + 60mi Large scale map 100km + 60mi

28 Precipitation Frequency Data Server Page 4 of 4 6/21/ km + 60mi Back to Top US Department of Commerce National Oceanic and Atmospheric Administration National Weather Service National Water Center 1325 East West Highway Silver Spring, MD Questions?: HDSC.Questions@noaa.gov Disclaimer

29 APPENDIX D HEC-RAS MODEL OUTPUT

30 Plan: existing Ephemeral Wash Creek FL RS: Profile: 100-YR E.G. Elev (ft) Element Left OB Channel Right OB Vel Head (ft) 2.94 Wt. n-val W.S. Elev (ft) Reach Len. (ft) Crit W.S. (ft) Flow Area (sq ft) E.G. Slope (ft/ft) Area (sq ft) Q Total (cfs) Flow (cfs) Top Width (ft) Top Width (ft) Vel Total (ft/s) Avg. Vel. (ft/s) Max Chl Dpth (ft) 9.53 Hydr. Depth (ft) 6.98 Conv. Total (cfs) Conv. (cfs) Length Wtd. (ft) Wetted Per. (ft) Min Ch El (ft) Shear (lb/sq ft) 4.78 Alpha 1.00 Stream Power (lb/ft s) Frctn Loss (ft) 0.21 Cum Volume (acre-ft) 8.20 C & E Loss (ft) 0.41 Cum SA (acres) 1.39

31 45.5 Road - Existing conditions Plan: exist 6/21/ Legend WS 500-YR WS 100-YR WS 50-YR WS 25-YR WS 10-YR Ground Bank Sta 5235 Elevation (ft) Station (ft)

32 HEC-RAS Plan: exist River: Ephemeral Wash Reach: Creek FL Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR

33 HEC-RAS Plan: exist River: Ephemeral Wash Reach: Creek FL (Continued) Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR

34 HEC-RAS Plan: exist River: Ephemeral Wash Reach: Creek FL (Continued) Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR

35 HEC-RAS Plan: exist River: Ephemeral Wash Reach: Creek FL (Continued) Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL 5 10-YR Creek FL 5 25-YR Creek FL 5 50-YR Creek FL YR Creek FL YR

36 Road - Gabion Option Plan: Option #2 - Run 1 6/21/2018 Gabion Wall.02 Legend WS 500-YR WS 100-YR WS 50-YR WS 25-YR WS 10-YR Ground Bank Sta 5235 Elevation (ft) Station (ft)

37 HEC-RAS Plan: gabion River: Ephemeral Wash Reach: Creek FL Reach River Sta Profile Q Total Min Ch El W.S. Elev Crit W.S. E.G. Elev E.G. Slope Vel Chnl Flow Area Top Width Froude # Chl (cfs) (ft) (ft) (ft) (ft) (ft/ft) (ft/s) (sq ft) (ft) Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL 1110 Bridge Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR Creek FL YR