NLR_Final_Hydraulics_Report.pdf

I

Contents Section Page

I. Introduction II. Existing Conditions III. Drainage Design Criteria and Methodology IV. Hydrologic Analysis V. Hydraulic Analysis VI. Recommended Improvements VII. Erosion and Sediment Control VIII. References

Appendix

A Existing Culvert Inventory

B Hydrology

C Hydraulics

D Corrosion Test Results & Service Life Calculations

I. Introduction This report describes the hydrologic and hydraulic design recommendations for improvements to Navajo Lake Road (FSR30053). Navajo Lake Road lies within the boundaries of Dixie National Forest and provides access to Navajo Lake, multiple campgrounds and summer residences. See Figure 1 for Location Map and Vicinity Map.

Navajo Lake Road is an area road (as classified by AASHTO) with low ADT and is maintained by Kane County. The general terrain of the route is rolling with steep cut and fill slopes. The beginning 4.8 miles of the alignment from SH14 is unpaved with an aggregate base surface and the remaining 0.7 miles has an existing double chip seal surface that has reached the end of its service life.

The project proposes paving 5.7 miles of Navajo Lake Road to provide two 11-foot travel lanes with 4-foot shoulders from the intersection of SH14 to Forest Service Road 31762 along with paving four existing pullout locations along the alignment. This project is part of a larger vision to connect SH14 to SH9 with a better route.

The proposed road reconstruction will closely follow the existing road with minor realignments as appropriate to improve safety and minimize impacts. Improvements also include flattening back slopes on the cut side and adding a ditch to facilitate proper drainage and to accommodate a constant typical roadway section. Culvert replacements will be necessary and new signing and striping will be added.

Figure 1 Location Map and Vicinity Map

Utah

Project Location

II. Existing Conditions A. General

There are 39 existing culvert crossings within the project limits. These culverts were installed as a part of a road improvement project in the mid 1990’s. There are no major drainage structures (vertical opening greater than 48 in.) Existing drainage structure sizes vary from 15 to 24 inches in diameter. General culvert condition was assessed during a July 23, 2013 field visit and a detailed culvert condition assessment was made during the 30% Field Review in June of 2015.

See Appendix A for a culvert inventory and condition assessment.

In general, existing culverts on the project are in good condition, however many of them do not meet the current minimum size requirement of 24 inches. Culverts in the project area were installed in 1992. Most of the culverts are corrugated metal pipe (CMP), with a few locations being corrugated plastic pipe. Many of the existing culvert inlets have been damaged, presumably having been hit by vehicles or blades. Many existing culvert outlets extend past the slope, leaving 3 to 5 ft. of unsupported culvert. This has in turn resulted in a number of instances where the last section of pipe has dropped.

Roadside ditch overtopping was observed during the 2013 site visit, indicating that existing ditches and pipes may be undersized or filled with sediment. Signs of overtopping were not observed during the 30% field review conducted in June of 2015 or the 70% field review conducted in July of 2015. The roadway is currently maintained by Kane County, whose representatives did not recall any history of drainage issues such as washouts or overtopping since the roadway improvements were made in the mid 1990’s.

Typical Culvert Entrance

Roadside ditches within existing cut sections are poorly defined or have been filled in overtime and have reduced capacity. This appears to be a result of grading and erosion of the existing roadway base combined with limited erosion of the existing cut slopes. Channels at existing pipe outlets did not show signs of erosion, rather accumulation of roadway base that is being transported.

Drainage areas contributing to existing culvert crossings vary from less than 1 acre to 337 acres in size and have similar basin characteristics. In general, the discharge from the project is to Navajo Lake or to the area immediately downstream of the Lake. These areas then discharge either to Zion Canyon, which is a part of the Colorado River Basin or Duck Creek which in turn discharges to the Great Basin.

Windrows that are a result of grading the existing gravel surfacing have created locations of concentrated flows and erosion. Concentrated flows are conveying sediment to Navajo Lake and the area immediately east of the lake.

B. Floodplain Investigation

The project is located adjacent to (but not within) an area mapped as Zone A on FEMA Community Panel No. 490093 0001A A Zone A mapped area represents the 1-percent-annual-chance flood event determined using approximate methodologies. Base flood elevations are not shown. The project improvements are outside of any local floodplain management jurisdiction and does not impact the mapped area. See Appendix A for the FEMA map.

C. Wetlands

A wetland delineation will be performed as part of the Environmental Compliance Study and resource report preparation. It is anticipated that wetlands are located within the project area, on the west end of the lake.

III. Drainage Design Criteria and Methodology A. General

The drainage design will be in accordance with the Federal Lands Highway Project Development and Design Manual (PDDM) Chapter 7 (Reference 1).

The current (2015) ADT is 350 and the projected design year ADT is 520. The full length of the roadway is classified as a Low-Standard road, and the roadway is not designated as a critical access road.

B. Hydrology

Existing drainage areas vary from less than 1 acre to 337 acres in size and have similar basin characteristics. Peak flow rate results from the Rational Method were compared with those from the SCS hydrologic method. Based on results and engineering judgment, the SCS hydrologic method was chosen to calculate peak flows for this project.

Roadway overtopping during large rainfall events has been observed. Therefore, all existing crossings will be evaluated for contributing drainage area, peak design flow and capacity. New culvert crossing locations will be evaluated as needed.

C. Hydraulic Analysis

1. Culverts

Culvert invert elevations should match the streambed but may be as flat at 0.5% where pipe cover is an issue. Culverts should comply with the criteria below:

Table 1 – Culvert Design Criteria

Culvert Type Design Storm Minimum Diameter HW/D

Roadway Crossing 25-year 24-inch 1.2 (>48”) & 1.5 (≤48”)

Approach Crossing 10-year 18-inch 1.2

Maximum and minimum cover shall be per Standard Drawing 602-1.

There are 39 known existing culvert crossings within the project limits, two of which are approach culverts. There are no major drainage structures (vertical opening greater than 48 inches

In general, existing culverts on the project are in good condition, however many of them do not meet the current minimum size requirement of 24 inches. The project intent will be to evaluate the existing pipe crossings with regards to meeting the minimum HW/D ratio for the design event, adequate pipe condition and meeting minimum size requirements.

Existing cross pipes, 24 inches or greater in diameter, in good condition and meeting the HW/D requirement for the design event will remain in place and will be extended as needed to meet new cut or fill limits. Cross pipes less than 24 inches in diameter or not meeting the minimum HW/D ratio will be upsized. Due to concern of forest fire, all existing plastic pipes will be replaced with CMP.

Flared end sections will be specified on all pipe installations except where at locations with double or triple pipes where concrete headwalls will be used.

New metal culverts and concrete pipes shall have a minimum service life of 50 years. The gage of pipe shall be of a thickness to achieve the required minimum service life instead of using bituminous coated pipe.

The need for outlet energy dissipation and permanent erosion control will be evaluated for all crossings. Final designs for outlet energy dissipation will be based on CFLHD standard for placed riprap. Stream stability shall comply with the scour analysis methods found in FHWA’s HDS 6, HEC 14, HEC 15, HEC 18, HEC 20, HEC 23, and NCHRP.

2. Roadside Ditches

Roadside ditches are anticipated in cut situations. Ditch sizing will accommodate peak flows from a 10-year storm event. The water surface elevation (WSEL) in the ditch should not exceed the bottom of the roadway aggregate base layer. Minimum ditch slope shall be 0.5%. Maximum ditch side slopes will be per roadway and geotechnical recommendations.

Design and stabilization of roadside ditches shall comply with FHWA’s HEC 15.

3. Pavement Drainage

The roadway will continue to sheet flow through the majority of the project length. A curbed section was considered during concept design to minimize excavation due to cut slopes, however was eliminated due to maintenance concerns, thus eliminating any need for pavement spread design criteria and storm drain design criteria.

It is anticipated that current erosion issues due to flow concentration caused by windrowed roadway base will be eliminated by the surfacing improvement.

D. Erosion and Sediment Control

Best Management Practices (BMP) as shown in the standard CFL details will be used for temporary control of erosion and sediment during construction.

Seeding and riprap shall provide permanent erosion control around the replaced culvert.

E. Miscellaneous

The project is located adjacent to (but not within) an area mapped as Zone A on FEMA Community Panel No. 490093 0001A A Zone A mapped area represents the 1-percent-annual-chance flood event determined using approximate methodologies. Base flood elevations are not shown. The project improvements are outside of any local floodplain management jurisdiction and does not impact the mapped area. Neither a Conditional Letter of Map Revision (CLOMR) nor a LOMR will be submitted. See Appendix A for the FEMA map.

Fish passage will not be accommodated since all streams crossing the roadway are ephemeral.

The surfacing improvement from a gravel base to a plant mix pavement will increase the amount of impervious surface in the project area. As such, the peak flows from the project will also increase. In general, the discharge from the project is to Navajo Lake or to the area immediately downstream of the Lake. These areas discharge either to Zion Canyon, which is a part of the Colorado River Basin or Duck Creek which in turn discharges to the Great Basin.

Increase in peak discharge due to project improvements will be insignificant and thus, will not be mitigated with through detention or retention.

IV. Hydrologic Analysis A. Major Basin Analysis

No major drainage basins discharge through the project.

B. Minor Basin Analysis

The former Soil Conservation Service (SCS) hydrologic methodology for minor drainage basins has been completed within the United States Army Corps of Engineer (USACOE’s) HEC-HMS 4.0 software. This procedure requires, as its input, the rainfall distribution information, watershed time of concentration, drainage area, and runoff curve numbers (CN). The time of concentration (Tc) is defined as the travel time for a parcel of water to move from the most hydraulically remote point in the catchment to the outlet. The Tc can be calculated as the sum of the travel times within the consecutive flow segments: sheet flow, shallow flow, open channel flow, and pipe flow.

The curve number was estimated by determining the hydrologic soil group designation of the soils included in the watershed, cover type, and hydrologic condition. Utilizing the existing and proposed impervious and pervious areas, a weighted CN was calculated for each sub-basin.

Minor drainage basin delineation maps as well as hydrologic parameter maps representing soil types and curve numbers are located in Appendix B. Pertinent hydrologic input data such as rainfall characteristics, curve number designations and modeling output from HEC-HMS are also included within Appendix B.

1. Rainfall Characteristics

Precipitation values were obtained from the (National Oceanic and Atmospheric Administration (NOAA) Atlas 14, Volume 1. Four precipitation values were obtained that represent the four corners of the project limits (vertical and horizontal locations). These precipitation values were fitted to the SCS Type II rainfall distribution noted in the Utah Department of Transportation (UDOT) Manual of Instruction (MOI).

2. Basin Delineation

To aid in basin delineation, a variety of data sources were used. U.S. Geological Survey (USGS) quadrangle maps and aerial photographs were obtained to help determine watercourses and topography for all off-site drainage basins.

Digital elevation models (DEMs) obtained from the state of Utah’s Automated Geographic Reference Center (AGRC) also were used to generate topography and contours for all of the minor drainage basins. DEMs with a 1:24,000 scale and 10-meter grid spacing were obtained for this purpose. ArcGIS was used to determine flow direction, flow paths, basin divides, and areas tributary to the pertinent concentration points within all offsite minor drainage basins.

3. Land Use and Land Cover

Land use and land cover for the offsite areas draining to the project are largely undeveloped. The majority of the terrain is grassland and semi-arid shrub land. Very little commercial and residential development exists within the offsite watersheds.

In addition to aerial photographs, land use/land cover data was obtained in GIS format from the AGRC. The source of this data was the USGS’ Gap Analysis Program and Southwest Gap Analysis Project. Land use/land cover was verified during site visits and field investigations.

4. Soil Classification

Hydrologic soil groups and distribution within the drainage areas have been mapped and classified by the U.S. Department of Agriculture (USDA) and the Natural Resources Conservation Service (NRCS). For hydrologic purposes, these soils are generally classified as A, B, C, or D soils. These classifications relate to the ability of the surface horizons to infiltrate storm water at various rates.

Data from the NRCS Soil Survey Geographic database at http://websoilsurvey.nrcs.usda.gov is unavailable for our project area. Soil classifications are available within the UDOT MOI Appendix 7.C in graphical format. This data was georeferenced in ArcGIS for representation of hydrologic soil types within our delineated offsite drainage basins.

5. Losses and Abstractions (Curve Number)

The SCS Curve Number Method was used to estimate losses such as abstractions and infiltration into the ground. Remaining precipitation would become excess rainfall (runoff).

As is common practice, an initial abstraction coefficient of 0.2 was used. Individual CNs were selected from TR-55 and matched to the land use and soil type data for this project.

Individual CNs were selected from Tables 7-14 through 7-15 of the UDOT MOI and matched to the land use and soil type data for this analysis. CNs chosen within UDOT MOI account for an average (2) antecedent soil moisture condition.

Based on the land use/cover and soil type combinations, area-weighted composite curve numbers (CCN) were calculated for each delineated watershed sub-basin using GIS and Microsoft Excel.

6. Time of Concentration

Time of concentration (Tc) was determined using procedures outlined in the UDOT MOI.

This method breaks up the longest flow path (time wise) into several different segments of either sheet flow, shallow concentrated flow, open channel flow, or culvert/storm drain flow.

7. Transform Method

The SCS Dimensionless Unit Hydrograph was used within HEC-HMS to convert runoff volumes to hydrographs for each offsite minor drainage basin.

8. Modeling Results

Table 2 shows the hydrologic parameters for each offsite minor drainage basin. Also included in this table are the resulting hydrologic routing peak runoff values for the 2, 25 and 100-year storm events.

http://websoilsurvey.nrcs.usda.gov/

Table 2 - Hydrologic Parameters and Modeling Results

Drainage Basin ID

Crossing Location

(Sta.)

Input Data Resulting Peak Flows (cfs)

Area (acres)

CCN

Tc

(hours) 2-year 10-year 25-year

100-year

B011 11+76 0.7 50 1.02 0.0 0.0 0.0 0.1

B019 19+13 7.0 53 0.47 0.0 0.3 1.1 3.2

B028 28+50 3.4 49 0.35 0.0 0.0 0.2 1.1

B033 33+26 4.7 58 0.40 0.0 0.7 1.7 3.8

B039 39+15 43.0 71 0.32 10.9 35.4 54.0 87.4

B046 45+79 63.0 65 0.33 5.3 28.5 50.3 91.8

B052 51+80 14.1 74 0.15 7.2 18.7 26.9 41.3

B060 60+16 60.6 63 0.40 2.7 20.3 37.4 70.9

B066 66+62 16.6 56 0.47 0.1 1.6 4.2 10.2

B079 78+98 7.1 57 0.43 0.0 0.9 2.1 5.1

B086 85+82 180.6 57 0.38 1.1 23.4 58.9 138.7

B097 97+35 95.5 56 0.57 0.4 8.3 21.5 52.8

B102 102+99 22.7 58 0.22 0.2 5.0 11.3 24.2

B115 116+40 21.5 52 0.22 0.0 0.8 4.0 13.2

B121 121+50 33.3 56 0.22 0.2 4.8 12.8 30.4

B128 128+00 11.9 59 0.22 0.1 3.1 6.6 13.6

B133 133+42 11.2 54 0.28 0.0 0.8 2.6 7.6

B141 140+39 140.9 57 0.38 0.9 18.3 45.9 108.2

B147 146+46 16.6 59 0.17 0.2 4.5 10.0 21.5

B153 153+00 8.8 54 0.18 0.0 0.8 2.6 6.8

B158 157+74 27.6 59 0.17 0.3 7.5 16.6 35.9

B161 161+61 21.2 55 0.17 0.1 2.6 7.2 19.5

B171 171+25 5.4 52 0.20 0.0 0.2 1.1 3.3

B176 176+52 17.8 56 0.18 0.1 2.7 7.0 17.0

B181 182+06 7.5 60 0.15 0.1 2.5 5.3 10.9

B184 183+92 8.8 58 0.20 0.1 2.0 4.4 9.5

B188 188+81 217.4 59 0.52 2.5 34.9 76.1 165.2

B198 198+49 12.3 51 0.18 0.0 0.3 2.0 6.7

B205 204+78 43.5 55 0.27 0.2 4.3 12.9 34.0

B211 211+00 7.4 59 0.18 0.1 2.0 4.2 9.2

B224 223+84 23.6 58 0.48 0.2 3.3 7.7 17.0

B229 228+99 307.8 57 0.37 1.9 41.3 103.2 240.4

B234 234+00 2.0 71 0.08 0.8 2.3 3.5 5.6

B240 239+40 3.5 70 0.12 1.2 3.7 5.6 9.0

B241 240+42 3.4 71 0.10 1.4 3.9 5.8 9.2

B245 245+75 6.6 68 0.27 1.2 4.7 7.4 12.4

B248 247+61 6.6 69 0.15 1.7 6.2 9.6 15.7

B255 254+69 17.8 67 0.30 2.4 10.7 17.7 30.5

B261 261+59 161.1 59 0.25 2.0 39.5 85.8 181.0

B263 263+21 12.8 65 0.12 1.6 9.0 14.9 25.9

B269 269+32 11.4 64 0.27 0.8 5.4 9.5 17.3

B273 272+02 4.7 68 0.25 0.9 3.4 5.3 8.9

B278 277+79 13.1 58 0.22 0.1 2.9 6.5 14.0

B285 284+69 23.3 51 0.20 0.0 0.6 3.6 12.8

B291 291+35 36.8 53 0.27 0.1 2.0 7.4 23.3

V. Hydraulic Analysis A. Major Crossing Analysis and Design

There are no major crossings on the project.

B. Minor (15 to 24-inch Diameter) Culverts

All minor cross culverts were analyzed using the FHWA’s HY-8 (v7.30) Culvert Hydraulic Analysis Program. Two conditions were analyzed; the existing condition and a proposed pipe replacement condition. All culverts are recommended for replacement, therefore presentation of analysis data is limited to the proposed culverts. This data is shown in Table 3.

Three culverts, located at 39+15, 45+79 and 60+00, designed at 24-inch diameter, overtop for the design flow (25-year event). One additional culvert, located at 51+80 violates HW/D ratio criteria for the design event. These culverts are replacements for the existing 18-inch diameter culverts currently in place, each of which provide cut ditch relief. There is no evidence of an existing channel or concentrated flows on the slopes above these culverts and there is no record of flooding issues, erosion, sedimentation or maintenance problems with the existing 18-inch culverts at these locations. This area is known for sinks and based on the lack of concentrated flow evidence in the existing topography, it is unlikely that the full design flows are accurate at the crossing. These locations are recommended to remain sized at 24-inch.

C. Culvert Material Selection

Soil testing (resistivity, pH, Chloride and Sulfate) to support appropriate culvert selection was performed by Shannon & Wilson Inc. The existing soils are rated as ‘highly corrosive’ due to low soil resistivity values. Using the minimum resistivity of the project samples, the maximum soil pH, and Exhibit 7.3-B in a service life for galvanized steel culverts was determined to be 44.5 years. In order to achieve the required 50-year service life for culverts, a minimum gage of 14 will be required (0.079 inches). See Appendix D for corrosion test results and service life calculations. Most areas adjacent to the roadway are forested and due to the potential for pipe damage caused by forest fire, plastic pipe will not be considered.

D. Ditches

Ditches were evaluated for depth and velocity during the 10-year design event. In general, drainage areas contributing to cross drains on the project also contribute to the roadway cut ditch flows. Because the contributing roadway areas are minor in comparison, the design events for the offsite basins were used for the ditch hydraulics calculations. Contributing flows were proportioned by the approximate basin area contributing to the ditch. A riprap lined ditch was recommended where velocities exceeded 5 ft/sec. Ditch calculations can be found in Appendix C.

Although design flows warrant a deeper ditch and riprap in ditches upstream of culverts located at 39+15, 45+79, and 60+00, as discussed above, these flows are considered inaccurate. At these locations, riprap is recommended for ditch slopes greater than 4%.

Table 3 - Proposed Culvert Crossings

Location Dia.

(in.) Barrels Invert In

Invert Out

Length

(ft) Slope (%) HW/D

11+76 24 1 9148.11 914700 71 1.6% 0.1

19+13 24 1 9143.95 9142.48 42 3.5% 0.2

28+50 24 1 9130.00 9126.14 47 8.2% 0.1

33+26 24 1 9101.71 9098.38 54 6.2% 0.3

39+15 24 1 9088.52 9087.79 39 1.9% 1.6

45+79 24 1 9071.72 9065.10 52 12.7% 1.6

51+80 24 1 9084.28 9078.39 58 10.2% 1.7

60+16 24 1 9095.12 9090.70 47 9.4% 1.6

66+62 24 1 9107.95 9104.72 48 8.0% 0.5

78+98 24 1 9095.27 9090.50 50 9.5% 0.3

85+82 36 1 9075.86 9069.91 71 8.4% 1.3

97+35 24 1 9079.26 9076.13 50 6.3% 1.4

102+99 24 1 9073.18 9068.90 48 9.0% 0.8

116+40 24 1 9064.04 9062.61 41 3.5% 0.5

121+50 24 1 9065.73 9058.68 53 13.3% 0.9

128+00 24 1 9078.11 9071.00 49 14.5% 0.6

133+42 24 1 9085.86 9075.54 75 13.8% 0.3

139+84 18 1 APPROACH

140+39 30 2 9084.72 9080.70 54 7.5% 1.0

146+46 24 1 9100.67 9096.46 45 9.5% 0.8

153+00 24 1 9091.88 9088.82 48 6.4% 0.4

157+74 24 1 9086.02 9083.07 49 6.1% 1.1

161+61 24 1 9089.39 9083.93 54 4.6% 0.6

171+25 24 1 9075.72 9074.83 42 2.1% 0.2

176+52 24 1 9072.56 9070.60 46 4.2% 0.6

182+06 24 1 9067.81 9064.91 45 6.4% 0.5

183+92 24 1 9068.15 9062.90 61 8.5% 0.5

188+81 30 2 9073.92 9070.39 40 8.8% 1.4

198+49 24 1 9070.60 9067.43 58 5.5% 0.3

204+78 24 1 9088.00 9084.06 60 6.6% 0.9

211+00 24 1 9128.00 9123.68 56 7.7% 0.5

223+84 24 1 9110.66 9108.37 46 5.0% 0.7

228+99 36 2 9086.64 9085.27 55 2.5% 1.4

234+00 24 1 9076.30 9074.80 43 3.5% 0.4

239+40 24 1 9062.18 9061.33 42 2.0% 0.6

240+42 24 1 9061.90 9059.94 43 4.6% 0.6

244+43 18 1 APPROACH

245+75 24 1 9056.75 9056.46 50 0.6% 0.6

247+61 24 1 9063.38 9057.61 54 10.7% 0.7

254+69 24 1 9076.57 9072.27 46 9.3% 1.1

261+59 30 3 9080.00 9079.10 53 1.7% 1.1

263+21 24 1 9082.37 9081.08 49 2.6% 1.0

Location Dia.

(in.) Barrels Invert In

Invert Out

Length

(ft) Slope (%) HW/D

269+32 24 1 9084.34 9081.80 49 5.2% 0.8

272+02 24 1 9080.59 9078.58 42 4.7% 0.7

277+79 24 1 9081.25 9078.65 55 4.7% 0.6

284+69 24 1 9090.75 9089.83 50 1.8% 0.4

291+35 24 1 9106.86 9105.54 43 3.1% 0.7

298+82 18 1 APPROACH

VI. Recommended Improvements A. Minor (15 to 24 inch Diameter) Culverts

In general, existing culverts on the project are in good condition, however many of them do not meet the current minimum size requirement of 24 inches. Existing culverts were evaluated based on size, condition and capacity to accommodate the design event. In addition, the potential for forest fire caused damage to plastic pipe requires the replacement of all existing plastic pipe. This evaluation resulted in the recommendation to replace all existing culverts on the project.

The project was evaluated with respect to need for outlet energy dissipation and permanent erosion control measures. Many of the proposed culverts outfall onto steep embankment slopes. To protect the slope from erosion caused by concentrated flow, riprap pads at outlets are recommended. Culvert cleaning will not be necessary since all culverts are being replaced.

Flared end sections will be added to proposed culverts to improve inlet efficiency and reduce outlet erosion or undercutting potential.

B. New Culvert Locations

During the 30% and 70% Field Reviews, the project was also evaluated for the need for additional culverts based on capacity and existing culvert spacing. In addition, culverts were evaluated for the need to be relocated due to new or shifted low points or ditches with inadequate capacity. These evaluations resulted in the recommendation for 7 additional culverts and 7 culvert relocations. Several existing culvert locations within a cut/fill section will not match the new roadway low points. These culverts will be removed and new culverts installed at the roadway low points.

C. Ditches

As a part of the typical section, roadside ditches will be established that will provide drainage away from the road section. This will provide positive drainage away from the surfacing section, enabling a longer design life for the pavement. The existing ditches have been evaluated for capacity with respect to the requirement that the design flow WSEL be below the bottom of the road section base.

Although site investigations have indicated that the existing roadside ditches do not have a tendency to erode, they have been evaluated for erosion potential. Ditches with permanent erosion potential due to significant flow, permanent flow from springs, high velocities and/or steep grades will be lined with riprap.

D. Sub drains

Sub drains are recommended at locations where surface drainage results in ponded water between culvert sites as well as locations where seepage is actively occurring. Two such locations were identified at Station 161+00 to 165+00 and 208+00 to 215+00. See the project Geotechnical Report for additional discussion.

VII. Erosion and Sediment Control A. Construction BMPs

Fiber roll, riprap or gravel bag check dams will be utilized in disturbed cut ditches and immediately upstream of existing and proposed culvert crossings to minimize the amount of sediment leaving the project within concentrated flows. Silt fencing or fiber rolls will be used at the base of disturbed slopes to minimize sediment leaving the project via sheet flow. To minimize soil tracking off of the project on vehicles, stabilized construction entrances will be used where construction traffic is leaving disturbed areas.

B. Permanent BMPs

Many slopes on the project are designed at 2:1. Native seed and mulch mix will be applied by hydro method. Erosion control mat use will be limited to slopes steeper than 2:1 or as needed at unstable locations such as at springs.

Many of the proposed culverts outfall onto steep embankment slopes. To protect the slope from erosion caused by concentrated flow, riprap pads at outlets will be used. Ditches in steep areas will be riprap lined to prevent erosion. Ditches with seasonal flows due to springs will also be riprap lined to prevent erosion.

Windrows that are a result of grading the existing gravel surfacing have created locations of concentrated flows and erosion. Concentrated flows are conveying sediment to Navajo Lake and the area immediately east of the lake. It is anticipated that current erosion and sediment transport issues due to this flow concentration will be eliminated by the surfacing improvement.

Additional water quality mitigation measures are not proposed.

VIII. References

1. Federal Highway Dec 2012. “Federal Lands Highway Project Development and Design Manual”, U.S. Department of Transportation, Washington, DC

2. AASHTO. A Policy on Geometric Design of Highways and Streets. 2011

3. Utah Department of Transportation (UDOT). Manual of Instruction. Roadway Drainage. 2004

4. U.S. Department of Commerce. National Oceanic and Atmospheric Administration.

Precipitation-Frequency Atlas of the Western United States; Volume 1 – Version 5. May 2015.

5. U.S. Geological Survey (USGS). The National Map Seamless Server. http://seamless.usgs.gov/.

May 2015

6. U.S. Department of Agriculture (USDA), National Resources Conservation Service (NRCS). Web Soil Survey. http://soildatamart.nrcs.usda.gov/. May 2015

7. Utah Automated Geographic Reference Center. Utah Mapping Portal. http://gis.utah.gov/. May

8. U.S. Department of Agriculture, Natural Resources Conservation Division. Urban Hydrology for Small Watersheds, Technical Release 55 (TR-55). 1986.

9. U.S. Army Corps of Engineers (USACE). HEC-HMS: Hydrologic Modeling System Technical Reference Manual Version 4.0. March 2000.

http://seamless.usgs.gov/ http://soildatamart.nrcs.usda.gov/ http://gis.utah.gov/

APPENDIX A

Existing Culvert Inventory & FEMA Floodplain Mapping

Existing Culvert Crossings

Location Dia. (in.) Type June 2015 Field Inspection Notes

39+15 18 PLASTIC Fair Condition

45+79 18 PLASTIC Good Condition

51+80 18 CMP Good Condition

60+92 18 CMP Good Condition, Damaged inlet, significant sediment transport

66+62 18 PLASTIC Good Condition. Outlet does not match slope

78+98 18 PLASTIC Good Condition. Partially silted in. Outlet does not match slope

85+82 24 PLASTIC Good Condition

97+35 18 PLASTIC Good Condition

102+90 18 PLASTIC Good Condition. Culvert not at ditch lowpoint

115+04 15 CMP Fair Condition. Partially silted in.

121+50 18 CMP Fair Condition. Section near outlet is dropping. Inlet in deep hole

133+42 18 CMP Good Condition

139+84 18 PLASTIC Approach pipe, damaged FES, silted in

140+39 24 CMP

Fair condition, damaged outlet, culvert does not match lowpoint, scour at outlet

146+26 18 CMP Inlet abandoned or buried, Section near outlet has dropped

146+94 18 PLASTIC Good Condition

157+74 15 CMP Fair Condition, Section near outlet has dropped

161+61 15 CMP Fair Condition, poor ditch drainage upstream, damaged inlet

176+52 18 CMP Good Condition, damaged inlet, outlet does not match slope

181+59 18 CMP

Good Condition, partially filled with rock, outlet does not match slope

183+92 18 CMP Good Condition

188+81 18 CMP Good Condition

197+73 18 CMP Damaged inlet & outlet

204+78 18 CMP Damaged inlet, section near inlet is bent

228+99 24 CMP Good Condition

239+40 18 CMP Fair Condition, 50% silted in

240+42 18 CMP Fair Condition, 25% silted in

244+07 18 CMP Good Condition, taking groundwater, entrance in deep hole

245+00 18 CMP Good Condition, entrance in deep hole

245+84 18 CMP Fair Condition, Approach pipe in abandoned approach

247+61 18 CMP Good Condition, taking groundwater

254+69 18 CMP Fair Condition, damaged inlet

261+54 18 CMP Good Condition, inlet in large hole

263+21 18 CMP Fair Condition, damaged inlet

269+33 18 CMP Good Condition, damaged inlet

273+22 18 CMP Poor Condition, damaged inlet

277+78 18 CMP Fair Condition

284+64 18 CMP Fair Condition, debris blocking inlet

298+82 18 CMP Approach pipe, fully silted in

Notes

1. Culvert condition assessed during 30% Field Review; June 2015

APPENDIX B

Hydrology

CALC'D BY:

IM

SUBJECT: REV'D BY:

UT FLAP DB

DATE:

Navajo Lake Road 4/27/2015

PROJECT NUMBER

Precipitation Value Averaging

Source: NOAA Atlas 14

Location 2-year 10-year 25-year 100-year

East Side Road Elevation 2.10 3.04 3.63 4.59

East Side Ridge Elevation 2.10 3.04 3.63 4.59

West Side Road Elevation 2.29 3.31 3.95 4.99

West Side Ridge Elevation 2.21 3.20 3.81 4.82

AVERAGE 2.18 3.15 3.76 4.75

Storm Event Precipitation (in)

NOAA Atlas 14, Volume 1, Version 5 Location name: Duck Creek Village, Utah, US*

Latitude: 37.5135°, Longitude: -112.8097° Elevation: 9783 ft*

* source: Google Maps

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel

Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular

PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.199

(0.173‑0.232) 0.257

(0.223‑0.300) 0.352

(0.304‑0.409) 0.434

(0.370‑0.503) 0.557

(0.467‑0.649) 0.665

(0.549‑0.774) 0.789

(0.637‑0.927) 0.935

(0.735‑1.11) 1.17

(0.877‑1.42) 1.38

(1.00‑1.71)

10-min 0.302

(0.264‑0.353) 0.391

(0.340‑0.457) 0.536

(0.463‑0.622) 0.660

(0.563‑0.765) 0.848

(0.711‑0.987) 1.01

(0.835‑1.18) 1.20

(0.970‑1.41) 1.42

(1.12‑1.69) 1.77

(1.34‑2.15) 2.11

(1.52‑2.60)

15-min 0.375

(0.327‑0.437) 0.484

(0.421‑0.566) 0.665

(0.574‑0.772) 0.818

(0.698‑0.949) 1.05

(0.881‑1.22) 1.25

(1.03‑1.46) 1.49

(1.20‑1.75) 1.76

(1.39‑2.10) 2.20

(1.66‑2.67) 2.61

(1.89‑3.22)

30-min 0.505

(0.440‑0.589) 0.652

(0.568‑0.762) 0.895

(0.773‑1.04) 1.10

(0.940‑1.28) 1.42

(1.19‑1.65) 1.69

(1.39‑1.97) 2.00

(1.62‑2.36) 2.38

(1.87‑2.82) 2.96

(2.23‑3.60) 3.52

(2.54‑4.34)

60-min 0.625

(0.544‑0.729) 0.807

(0.703‑0.943) 1.11

(0.957‑1.29) 1.36

(1.16‑1.58) 1.75

(1.47‑2.04) 2.09

(1.73‑2.44) 2.48

(2.00‑2.92) 2.94

(2.31‑3.50) 3.67

(2.76‑4.45) 4.35

(3.15‑5.37)

2-hr 0.720

(0.634‑0.816) 0.914

(0.803‑1.03) 1.21

(1.06‑1.36) 1.47

(1.27‑1.67) 1.87

(1.60‑2.12) 2.23

(1.87‑2.53) 2.66

(2.18‑3.05) 3.15

(2.52‑3.65) 3.92

(3.01‑4.63) 4.64

(3.43‑5.57)

3-hr 0.825

(0.745‑0.925) 1.04

(0.936‑1.16) 1.33

(1.20‑1.50) 1.60

(1.42‑1.79) 1.99

(1.74‑2.23) 2.34

(2.02‑2.63) 2.76

(2.35‑3.14) 3.26

(2.70‑3.74) 4.04

(3.23‑4.72) 4.76

(3.70‑5.64)

6-hr 1.08

(0.979‑1.19) 1.34

(1.22‑1.48) 1.66

(1.51‑1.84) 1.94

(1.75‑2.14) 2.34

(2.09‑2.60) 2.68

(2.37‑2.98) 3.06

(2.67‑3.43) 3.53

(3.03‑4.00) 4.32

(3.62‑4.98) 5.04

(4.13‑5.89)

12-hr 1.51

(1.37‑1.67) 1.88

(1.69‑2.08) 2.30

(2.08‑2.56) 2.67

(2.40‑2.98) 3.18

(2.83‑3.55) 3.59

(3.16‑4.01) 4.01

(3.50‑4.51) 4.49

(3.88‑5.07) 5.18

(4.41‑5.93) 5.99

(5.01‑6.93)

24-hr 1.77

(1.60‑1.97) 2.21

(2.00‑2.45) 2.75

(2.49‑3.06) 3.20

(2.89‑3.55) 3.81

(3.43‑4.24) 4.30

(3.85‑4.78) 4.82

(4.29‑5.36) 5.35

(4.72‑5.98) 6.08

(5.31‑6.83) 6.66

(5.75‑7.53)

2-day 2.17

(1.96‑2.42) 2.72

(2.45‑3.02) 3.40

(3.06‑3.78) 3.97

(3.57‑4.41) 4.76

(4.26‑5.30) 5.40

(4.80‑6.01) 6.08

(5.37‑6.77) 6.79

(5.95‑7.58) 7.77

(6.72‑8.74) 8.56

(7.33‑9.69)

3-day 2.44

(2.20‑2.72) 3.05

(2.75‑3.40) 3.83

(3.45‑4.27) 4.48

(4.03‑4.99) 5.40

(4.82‑6.01) 6.13

(5.45‑6.83) 6.91

(6.10‑7.72) 7.74

(6.76‑8.67) 8.89

(7.67‑10.0) 9.81

(8.38‑11.1)

4-day 2.71

(2.44‑3.01) 3.39

(3.06‑3.78) 4.26

(3.84‑4.76) 4.99

(4.49‑5.57) 6.03

(5.39‑6.72) 6.86

(6.09‑7.66) 7.75

(6.83‑8.66) 8.69

(7.58‑9.76) 10.0

(8.61‑11.3) 11.1

(9.43‑12.6)

7-day 3.28

(2.93‑3.67) 4.12

(3.68‑4.61) 5.20

(4.64‑5.84) 6.09

(5.42‑6.84) 7.33

(6.48‑8.21) 8.31

(7.32‑9.33) 9.34

(8.18‑10.5) 10.4

(9.04‑11.8) 11.9

(10.2‑13.6) 13.1

(11.1‑15.0)

10-day 3.84

(3.43‑4.32) 4.84

(4.32‑5.43) 6.15

(5.48‑6.89) 7.22

(6.42‑8.09) 8.71

(7.70‑9.77) 9.91

(8.70‑11.1) 11.2

(9.74‑12.6) 12.5

(10.8‑14.1) 14.3

(12.2‑16.3) 15.8

(13.3‑18.0)

20-day 5.20

(4.67‑5.77) 6.50

(5.85‑7.22) 8.09

(7.27‑8.97) 9.35

(8.39‑10.4) 11.1

(9.87‑12.3) 12.4

(11.0‑13.7) 13.7

(12.1‑15.3) 15.1

(13.3‑16.9) 16.9

(14.7‑19.0) 18.4

(15.8‑20.8)

30-day 6.58

(5.95‑7.27) 8.24

(7.46‑9.12) 10.2

(9.24‑11.3) 11.8

(10.6‑13.0) 13.8

(12.4‑15.3) 15.4

(13.8‑17.0) 16.9

(15.1‑18.8) 18.5

(16.4‑20.6) 20.6

(18.1‑23.0) 22.2

(19.3‑24.9)

45-day 7.92

(7.13‑8.88) 9.95

(8.95‑11.2) 12.4

(11.1‑13.9) 14.4

(12.9‑16.2) 17.1

(15.2‑19.2) 19.1

(16.9‑21.5) 21.3

(18.7‑24.0) 23.4

(20.5‑26.5) 26.4

(22.8‑30.0) 28.7

(24.6‑32.8)

60-day 9.62

(8.63‑10.9) 12.1

(10.9‑13.7) 15.2

(13.6‑17.2) 17.6

(15.7‑19.9) 20.9

(18.6‑23.6) 23.4

(20.7‑26.4) 25.9

(22.8‑29.4) 28.5

(24.9‑32.4) 32.1

(27.7‑36.6) 34.9

(29.8‑40.0)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).

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

PF graphical

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5135&l...

1 of 4 4/27/2015 4:30 PM imatagi Oval imatagi Oval imatagi Oval imatagi Oval

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Maps & aerials

Small scale terrain

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5135&l...

2 of 4 4/27/2015 4:30 PM

Large scale terrain

Large scale map

Large scale aerial

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5135&l...

3 of 4 4/27/2015 4:30 PM

Latitude: 37.5084°, Longitude: -112.7484° Elevation: 9415 ft*

* source: Google Maps

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel

Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular

PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.182

(0.159‑0.213) 0.236

(0.205‑0.275) 0.324

(0.280‑0.377) 0.400

(0.341‑0.464) 0.516

(0.433‑0.603) 0.619

(0.510‑0.724) 0.739

(0.595‑0.872) 0.879

(0.688‑1.05) 1.10

(0.825‑1.34) 1.31

(0.943‑1.62)

10-min 0.278

(0.242‑0.324) 0.358

(0.311‑0.419) 0.493

(0.426‑0.574) 0.609

(0.519‑0.707) 0.786

(0.659‑0.918) 0.943

(0.777‑1.10) 1.13

(0.905‑1.33) 1.34

(1.05‑1.60) 1.68

(1.26‑2.04) 2.00

(1.44‑2.47)

15-min 0.344

(0.300‑0.402) 0.444

(0.386‑0.519) 0.611

(0.528‑0.711) 0.754

(0.643‑0.876) 0.975

(0.817‑1.14) 1.17

(0.963‑1.37) 1.39

(1.12‑1.64) 1.66

(1.30‑1.98) 2.08

(1.56‑2.53) 2.47

(1.78‑3.06)

30-min 0.464

(0.404‑0.542) 0.598

(0.520‑0.699) 0.823

(0.711‑0.958) 1.02

(0.866‑1.18) 1.31

(1.10‑1.53) 1.57

(1.30‑1.84) 1.88

(1.51‑2.21) 2.23

(1.75‑2.67) 2.80

(2.10‑3.41) 3.33

(2.40‑4.12)

60-min 0.574

(0.500‑0.670) 0.741

(0.643‑0.866) 1.02

(0.880‑1.19) 1.26

(1.07‑1.46) 1.63

(1.36‑1.90) 1.95

(1.60‑2.28) 2.32

(1.87‑2.74) 2.77

(2.16‑3.30) 3.47

(2.60‑4.22) 4.12

(2.96‑5.10)

2-hr 0.661

(0.581‑0.748) 0.837

(0.734‑0.945) 1.11

(0.968‑1.25) 1.35

(1.17‑1.53) 1.73

(1.47‑1.96) 2.07

(1.73‑2.35) 2.47

(2.02‑2.83) 2.94

(2.34‑3.40) 3.68

(2.80‑4.35) 4.37

(3.21‑5.25)

3-hr 0.763

(0.689‑0.856) 0.962

(0.866‑1.08) 1.23

(1.11‑1.38) 1.48

(1.31‑1.66) 1.84

(1.62‑2.07) 2.17

(1.88‑2.45) 2.58

(2.19‑2.93) 3.05

(2.53‑3.50) 3.80

(3.04‑4.45) 4.49

(3.49‑5.34)

6-hr 0.980

(0.893‑1.08) 1.22

(1.11‑1.34) 1.51

(1.38‑1.67) 1.77

(1.60‑1.95) 2.14

(1.91‑2.37) 2.44

(2.16‑2.72) 2.79

(2.44‑3.13) 3.24

(2.78‑3.67) 4.00

(3.34‑4.61) 4.68

(3.83‑5.49)

12-hr 1.41

(1.28‑1.56) 1.75

(1.59‑1.94) 2.15

(1.95‑2.38) 2.49

(2.25‑2.77) 2.96

(2.65‑3.29) 3.34

(2.96‑3.73) 3.74

(3.28‑4.19) 4.18

(3.63‑4.72) 4.84

(4.13‑5.54) 5.62

(4.72‑6.50)

24-hr 1.69

(1.53‑1.86) 2.10

(1.91‑2.33) 2.62

(2.38‑2.90) 3.04

(2.75‑3.37) 3.63

(3.27‑4.02) 4.09

(3.67‑4.54) 4.59

(4.09‑5.09) 5.09

(4.50‑5.67) 5.79

(5.06‑6.49) 6.34

(5.48‑7.15)

2-day 2.06

(1.86‑2.28) 2.57

(2.33‑2.85) 3.22

(2.91‑3.57) 3.76

(3.39‑4.17) 4.51

(4.04‑5.00) 5.12

(4.56‑5.67) 5.75

(5.10‑6.40) 6.42

(5.64‑7.17) 7.35

(6.37‑8.26) 8.10

(6.95‑9.16)

3-day 2.29

(2.07‑2.54) 2.86

(2.59‑3.17) 3.59

(3.24‑3.99) 4.20

(3.78‑4.66) 5.05

(4.52‑5.61) 5.74

(5.11‑6.38) 6.47

(5.72‑7.20) 7.24

(6.34‑8.09) 8.30

(7.18‑9.35) 9.16

(7.84‑10.4)

4-day 2.51

(2.27‑2.79) 3.15

(2.85‑3.50) 3.96

(3.58‑4.40) 4.63

(4.17‑5.15) 5.59

(5.01‑6.21) 6.36

(5.66‑7.08) 7.18

(6.34‑8.01) 8.05

(7.03‑9.01) 9.26

(7.98‑10.4) 10.2

(8.73‑11.6)

7-day 3.08

(2.75‑3.44) 3.86

(3.46‑4.32) 4.89

(4.37‑5.46) 5.72

(5.10‑6.39) 6.88

(6.11‑7.68) 7.81

(6.89‑8.73) 8.78

(7.69‑9.83) 9.79

(8.51‑11.0) 11.2

(9.61‑12.7) 12.3

(10.5‑14.0)

10-day 3.56

(3.19‑3.99) 4.48

(4.02‑5.02) 5.70

(5.09‑6.37) 6.69

(5.97‑7.47) 8.07

(7.16‑9.02) 9.17

(8.09‑10.3) 10.3

(9.05‑11.6) 11.6

(10.0‑13.0) 13.2

(11.3‑15.0) 14.6

(12.4‑16.7)

20-day 4.85

(4.37‑5.37) 6.07

(5.47‑6.72) 7.55

(6.80‑8.36) 8.73

(7.84‑9.66) 10.3

(9.23‑11.4) 11.6

(10.3‑12.8) 12.8

(11.4‑14.2) 14.1

(12.4‑15.8) 15.8

(13.8‑17.8) 17.2

(14.8‑19.4)

30-day 6.12

(5.55‑6.75) 7.66

(6.96‑8.46) 9.52

(8.62‑10.5) 11.0

(9.91‑12.1) 12.9

(11.6‑14.2) 14.3

(12.8‑15.8) 15.8

(14.1‑17.5) 17.2

(15.3‑19.2) 19.2

(16.9‑21.4) 20.6

(18.0‑23.2)

45-day 7.36

(6.63‑8.28) 9.25

(8.32‑10.4) 11.6

(10.4‑13.0) 13.4

(12.0‑15.1) 15.9

(14.2‑17.9) 17.8

(15.8‑20.1) 19.8

(17.4‑22.4) 21.8

(19.1‑24.8) 24.6

(21.3‑28.1) 26.8

(22.9‑30.7)

60-day 8.95

(8.02‑10.1) 11.3

(10.1‑12.7) 14.2

(12.7‑16.0) 16.4

(14.7‑18.6) 19.5

(17.3‑22.0) 21.8

(19.3‑24.7) 24.2

(21.3‑27.4) 26.6

(23.3‑30.3) 29.9

(25.8‑34.3) 32.5

(27.8‑37.5)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).

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

PF graphical

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5084&l...

1 of 4 4/27/2015 4:30 PM imatagi Oval imatagi Oval imatagi Oval

Small scale terrain

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5084&l...

2 of 4 4/27/2015 4:30 PM

Large scale aerial

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5084&l...

3 of 4 4/27/2015 4:30 PM

Latitude: 37.5183°, Longitude: -112.7383° Elevation: 9132 ft*

* source: Google Maps

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel

Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular

PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.185

(0.161‑0.216) 0.238

(0.207‑0.279) 0.328

(0.283‑0.381) 0.405

(0.345‑0.469) 0.522

(0.437‑0.610) 0.626

(0.515‑0.731) 0.747

(0.601‑0.880) 0.888

(0.695‑1.06) 1.11

(0.833‑1.35) 1.32

(0.952‑1.64)

10-min 0.281

(0.245‑0.328) 0.363

(0.315‑0.424) 0.499

(0.431‑0.580) 0.616

(0.525‑0.715) 0.795

(0.666‑0.928) 0.953

(0.784‑1.11) 1.14

(0.914‑1.34) 1.35

(1.06‑1.61) 1.70

(1.27‑2.06) 2.02

(1.45‑2.49)

15-min 0.349

(0.303‑0.407) 0.450

(0.391‑0.525) 0.618

(0.534‑0.719) 0.764

(0.650‑0.886) 0.985

(0.825‑1.15) 1.18

(0.973‑1.38) 1.41

(1.13‑1.66) 1.68

(1.31‑2.00) 2.10

(1.57‑2.55) 2.50

(1.80‑3.09)

30-min 0.470

(0.409‑0.548) 0.606

(0.526‑0.707) 0.833

(0.719‑0.968) 1.03

(0.876‑1.19) 1.33

(1.11‑1.55) 1.59

(1.31‑1.86) 1.90

(1.53‑2.23) 2.26

(1.77‑2.69) 2.83

(2.12‑3.44) 3.37

(2.42‑4.16)

60-min 0.581

(0.506‑0.678) 0.750

(0.651‑0.876) 1.03

(0.890‑1.20) 1.27

(1.08‑1.48) 1.64

(1.38‑1.92) 1.97

(1.62‑2.30) 2.35

(1.89‑2.77) 2.79

(2.19‑3.33) 3.50

(2.62‑4.26) 4.17

(2.99‑5.15)

2-hr 0.667

(0.586‑0.754) 0.845

(0.742‑0.953) 1.12

(0.977‑1.26) 1.36

(1.18‑1.54) 1.74

(1.48‑1.97) 2.08

(1.74‑2.37) 2.49

(2.04‑2.85) 2.96

(2.35‑3.43) 3.71

(2.83‑4.38) 4.41

(3.23‑5.29)

3-hr 0.771

(0.696‑0.865) 0.972

(0.874‑1.09) 1.25

(1.12‑1.40) 1.49

(1.33‑1.67) 1.86

(1.64‑2.09) 2.19

(1.90‑2.47) 2.60

(2.21‑2.96) 3.08

(2.55‑3.54) 3.84

(3.06‑4.49) 4.54

(3.52‑5.39)

6-hr 0.991

(0.903‑1.09) 1.23

(1.12‑1.36) 1.53

(1.39‑1.69) 1.78

(1.61‑1.97) 2.16

(1.93‑2.39) 2.47

(2.19‑2.75) 2.82

(2.46‑3.17) 3.27

(2.81‑3.71) 4.04

(3.37‑4.66) 4.73

(3.87‑5.54)

12-hr 1.44

(1.30‑1.58) 1.78

(1.61‑1.97) 2.18

(1.98‑2.42) 2.53

(2.29‑2.81) 3.01

(2.69‑3.35) 3.40

(3.01‑3.79) 3.80

(3.33‑4.25) 4.25

(3.69‑4.79) 4.92

(4.20‑5.62) 5.71

(4.79‑6.60)

24-hr 1.69

(1.53‑1.86) 2.10

(1.91‑2.33) 2.62

(2.38‑2.90) 3.04

(2.76‑3.37) 3.63

(3.27‑4.02) 4.10

(3.68‑4.54) 4.59

(4.09‑5.09) 5.09

(4.51‑5.68) 5.79

(5.07‑6.49) 6.34

(5.49‑7.16)

2-day 2.06

(1.87‑2.28) 2.57

(2.33‑2.85) 3.22

(2.91‑3.57) 3.76

(3.39‑4.17) 4.51

(4.04‑5.01) 5.12

(4.56‑5.68) 5.76

(5.10‑6.40) 6.43

(5.64‑7.17) 7.36

(6.38‑8.27) 8.10

(6.95‑9.17)

3-day 2.28

(2.07‑2.53) 2.85

(2.58‑3.17) 3.58

(3.23‑3.98) 4.19

(3.77‑4.65) 5.04

(4.51‑5.60) 5.73

(5.10‑6.36) 6.45

(5.70‑7.18) 7.22

(6.32‑8.07) 8.28

(7.16‑9.32) 9.14

(7.82‑10.4)

4-day 2.50

(2.27‑2.78) 3.13

(2.84‑3.48) 3.94

(3.56‑4.38) 4.61

(4.16‑5.13) 5.57

(4.98‑6.19) 6.33

(5.63‑7.04) 7.15

(6.31‑7.97) 8.01

(7.00‑8.97) 9.21

(7.95‑10.4) 10.2

(8.69‑11.6)

7-day 3.06

(2.74‑3.42) 3.85

(3.45‑4.30) 4.87

(4.35‑5.44) 5.70

(5.08‑6.37) 6.85

(6.08‑7.65) 7.77

(6.86‑8.69) 8.74

(7.66‑9.79) 9.74

(8.47‑11.0) 11.1

(9.57‑12.6) 12.2

(10.4‑14.0)

10-day 3.54

(3.18‑3.97) 4.46

(4.00‑5.00) 5.67

(5.07‑6.34) 6.66

(5.95‑7.44) 8.04

(7.13‑8.98) 9.13

(8.06‑10.2) 10.3

(9.02‑11.6) 11.5

(9.99‑13.0) 13.2

(11.3‑15.0) 14.5

(12.3‑16.6)

20-day 4.84

(4.36‑5.36) 6.06

(5.46‑6.71) 7.54

(6.79‑8.34) 8.72

(7.83‑9.65) 10.3

(9.22‑11.4) 11.5

(10.3‑12.8) 12.8

(11.3‑14.2) 14.1

(12.4‑15.7) 15.8

(13.8‑17.7) 17.1

(14.8‑19.4)

30-day 6.09

(5.53‑6.73) 7.64

(6.93‑8.43) 9.48

(8.59‑10.5) 10.9

(9.87‑12.0) 12.8

(11.5‑14.2) 14.3

(12.8‑15.8) 15.7

(14.0‑17.4) 17.2

(15.2‑19.1) 19.1

(16.8‑21.3) 20.6

(17.9‑23.1)

45-day 7.35

(6.62‑8.27) 9.24

(8.31‑10.4) 11.6

(10.4‑13.0) 13.4

(12.0‑15.1) 15.9

(14.1‑17.9) 17.8

(15.8‑20.1) 19.8

(17.4‑22.4) 21.8

(19.1‑24.7) 24.6

(21.2‑28.0) 26.7

(22.9‑30.7)

60-day 8.97

(8.04‑10.1) 11.3

(10.1‑12.8) 14.2

(12.7‑16.0) 16.5

(14.7‑18.6) 19.5

(17.3‑22.1) 21.8

(19.3‑24.7) 24.3

(21.3‑27.5) 26.7

(23.3‑30.4) 30.0

(25.9‑34.4) 32.6

(27.9‑37.5)

1 Precipitation frequency (PF) estimates in this table are based on frequency analysis of partial duration series (PDS).

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.

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PF graphical

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5183&l...

1 of 4 4/27/2015 4:29 PM imatagi Oval imatagi Oval imatagi Oval

Small scale terrain

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5183&l...

2 of 4 4/27/2015 4:29 PM

Large scale aerial

Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=37.5183&l...

3 of 4 4/27/2015 4:29 PM

Latitude: 37.5321°, Longitude: -112.8167° Elevation: 9115 ft*

* source: Google Maps

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel

Brewer, Li-Chuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring, Maryland

PF_tabular | PF_graphical | Maps_&_aerials

PF tabular

PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)1

Duration Average recurrence interval (years)

1 2 5 10 25 50 100 200 500 1000

5-min 0.212

(0.185‑0.246) 0.274

(0.238‑0.319) 0.375

(0.324‑0.434) 0.461

(0.393‑0.532) 0.589

(0.495‑0.684) 0.701

(0.580‑0.815) 0.831

(0.671‑0.974) 0.982

(0.773‑1.17) 1.22

(0.922‑1.48) 1.45

(1.05‑1.79)

10-min 0.322

(0.281‑0.375) 0.416

(0.363‑0.485) 0.570

(0.493‑0.661) 0.701

(0.598‑0.811) 0.897

(0.753‑1.04) 1.07

(0.883‑1.24) 1.26

(1.02‑1.48) 1.49

(1.18‑1.77) 1.86

(1.40‑2.25) 2.20

(1.60‑2.72)

15-min 0.399

(0.349‑0.464) 0.516

(0.450‑0.602) 0.707

(0.611‑0.820) 0.869

(0.741‑1.00) 1.11

(0.934‑1.29) 1.32

(1.09‑1.54) 1.57

(1.27‑1.84) 1.85

(1.46‑2.20) 2.30

(1.74‑2.79) 2.73

(1.98‑3.37)

30-min 0.538

(0.469‑0.626) 0.695

(0.606‑0.811) 0.952

(0.823‑1.10) 1.17

(0.998‑1.35) 1.50

(1.26‑1.74) 1.78

(1.47‑2.07) 2.11

(1.71‑2.48) 2.50

(1.96‑2.96) 3.10

(2.34‑3.76) 3.68

(2.67‑4.54)

60-min 0.666

(0.581‑0.774) 0.861

(0.750‑1.00) 1.18

(1.02‑1.37) 1.45

(1.24‑1.68) 1.85

(1.56‑2.15) 2.21

(1.82‑2.56) 2.61

(2.11‑3.06) 3.09

(2.43‑3.66) 3.84

(2.90‑4.65) 4.55

(3.30‑5.62)

2-hr 0.765

(0.673‑0.865) 0.971

(0.853‑1.10) 1.28

(1.12‑1.45) 1.56

(1.35‑1.76) 1.98

(1.69‑2.24) 2.36

(1.98‑2.67) 2.80

(2.30‑3.21) 3.31

(2.65‑3.83) 4.12

(3.17‑4.85) 4.87

(3.61‑5.84)

3-hr 0.874

(0.789‑0.979) 1.10

(0.993‑1.23) 1.41

(1.27‑1.58) 1.69

(1.50‑1.89) 2.10

(1.84‑2.35) 2.46

(2.13‑2.78) 2.91

(2.48‑3.31) 3.42

(2.85‑3.93) 4.24

(3.41‑4.95) 4.99

(3.90‑5.91)

6-hr 1.14

(1.04‑1.26) 1.42

(1.29‑1.57) 1.76

(1.60‑1.94) 2.05

(1.85‑2.27) 2.48

(2.21‑2.74) 2.83

(2.50‑3.14) 3.22

(2.82‑3.61) 3.71

(3.19‑4.20) 4.54

(3.81‑5.23) 5.28

(4.35‑6.18)

12-hr 1.61

(1.46‑1.78) 2.00

(1.81‑2.22) 2.46

(2.21‑2.73) 2.85

(2.56‑3.17) 3.39

(3.01‑3.78) 3.83

(3.37‑4.28) 4.28

(3.73‑4.81) 4.78

(4.14‑5.41) 5.52

(4.69‑6.32) 6.37

(5.33‑7.37)

24-hr 1.84

(1.66‑2.04) 2.29

(2.07‑2.55) 2.85

(2.58‑3.17) 3.31

(2.99‑3.69) 3.95

(3.54‑4.40) 4.45

(3.99‑4.96) 4.99

(4.44‑5.57) 5.54

(4.89‑6.20) 6.29

(5.49‑7.09) 6.90

(5.95‑7.82)

2-day 2.26

(2.03‑2.52) 2.82

(2.54‑3.14) 3.53

(3.17‑3.93) 4.12

(3.69‑4.59) 4.95

(4.41‑5.51) 5.61

(4.98‑6.25) 6.31

(5.57‑7.05) 7.05

(6.17‑7.89) 8.08

(6.98‑9.11) 8.90

(7.61‑10.1)

3-day 2.54

(2.29‑2.83) 3.17

(2.86‑3.54) 3.99

(3.58‑4.45) 4.66

(4.18‑5.20) 5.62

(5.01‑6.26) 6.39

(5.67‑7.12) 7.20

(6.35‑8.04) 8.06

(7.04‑9.04) 9.26

(7.99‑10.4) 10.2

(8.73‑11.6)

4-day 2.82

(2.54‑3.14) 3.53

(3.19‑3.94) 4.44

(4.00‑4.96) 5.21

(4.68‑5.80) 6.29

(5.62‑7.00) 7.16

(6.36‑7.98) 8.09

(7.12‑9.03) 9.07

(7.92‑10.2) 10.5

(8.99‑11.8) 11.6

(9.85‑13.1)

7-day 3.41

(3.04‑3.83) 4.28

(3.82‑4.81) 5.42

(4.82‑6.09) 6.34

(5.63‑7.13) 7.63

(6.74‑8.57) 8.65

(7.61‑9.73) 9.73

(8.50‑11.0) 10.9

(9.40‑12.3) 12.4

(10.6‑14.2) 13.7

(11.6‑15.7)

10-day 4.01

(3.58‑4.51) 5.05

(4.51‑5.69) 6.42

(5.71‑7.21) 7.54

(6.70‑8.46) 9.10

(8.03‑10.2) 10.3

(9.08‑11.6) 11.7

(10.2‑13.1) 13.0

(11.3‑14.7) 14.9

(12.7‑17.0) 16.5

(13.9‑18.8)

20-day 5.44

(4.88‑6.04) 6.80

(6.11‑7.55) 8.46

(7.59‑9.39) 9.77

(8.75‑10.9) 11.6

(10.3‑12.8) 12.9

(11.5‑14.4) 14.3

(12.7‑16.0) 15.8

(13.8‑17.6) 17.7

(15.4‑19.9) 19.2

(16.5‑21.7)

30-day 6.91

(6.24‑7.64) 8.65

(7.81‑9.57) 10.7

(9.68‑11.9) 12.4

(11.1‑13.7) 14.5

(13.0‑16.0) 16.1

(14.4‑17.9) 17.8

(15.8‑19.7) 19.4

(17.1‑21.6) 21.6

(18.9‑24.2) 23.2

(20.2‑26.1)

45-day 8.32

(7.48‑9.32) 10.4

(9.39‑11.7) 13.1

(11.7‑14.6) 15.1

(13.5‑16.9) 17.9

(15.9‑20.1) 20.0

(17.7‑22.6) 22.3

(19.6‑25.1) 24.5

(21.4‑27.8) 27.6

(23.9‑31.4) 30.1

(25.7‑34.4)

60-day 10.1

(9.08‑11.4) 12.8

(11.4‑14.4) 16.0

(14.3‑18.0) 18.5

(16.6‑20.9) 21.9

(…