AZ FLAP 261(1) Eagar to Crescent Lake_Final Hydraulics Report_07282021.pdf

Eagar to Crescent Lake Apache County, AZ

AZ FLAP 261(1)

Final Hydraulics Report

Federal Highway Administration Central Federal Lands Highway Division

July 28, 2021 i AZ FLAP 261(1) - Final Hydraulics Report

Signature Sheet

Report prepared by: ____________________________________________________

Cassidy Cote, Hydraulics Engineer

Report reviewed by: ____________________________________________________

Aaron Estep, P.E., Hydraulics Engineer

Approved for distribution by: ____________________________________________________

Aaron Estep, P.E., Hydraulics Engineer

Distribution

Electronic:

N:\projects\AZ\az261(1)\Hydraulics\9_Final-Report Dustin Robbins, Project Management Alice Gustafson, Roadway Design Ray Golden, Right of Way and Utilities Opal Forbes, Environmental Protection Robert Norick, Pavement and Materials ii AZ FLAP 261(1) - Final Hydraulics Report

Executive Summary Hydrologic and hydraulic analyses were conducted for the AZ FLAP 261(1) Eagar to Crescent Lake project located in Apache County, AZ. The scope of work includes roadway improvements, culvert cleaning, paved invert culvert rehabilitation, and the replacement of culverts in need of services along the project corridor.

The ADOT pipe inventory in conjunction with CFLHD survey were utilized to determine an initial scope of work. An on-site condition assessment was then conducted at each crossing to refine the recommendations. A summary of the proposed drainage related recommendations along the 11.63-mile corridor is provided in Table 1. A breakdown of Recommendations specific to each of the 107 culverts identified along the project corridor is provided in Appendix F.

The hydraulic design frequency is the 25-year flood based on a low-standard roadway classification.

Design flows were estimated using both the USGS and ADOT Regression Equations for basins over 0.5 square miles. The USGS method resulted in more conservative design flows and was selected as the hydrologic method of choice for these crossings. The Rational method was utilized for basins below the

0.5 square mile threshold. Hydraulic performance was evaluated using HY-8 and the Hydraulics Toolbox.

The following report summarizes hydraulic design criteria, computational methods, and draft hydraulics recommendations.

Table 1: Recommendation Summary

Service or Description Number of Locations/Culverts Crossings Hydrologically Evaluated 32 crossings Hydraulically Inadequate Crossings 15 crossings

Culvert Replacements 18 crossings (one of which is a double-barreled culvert) Paved Invert Culvert Rehabilitation 3 crossings (one of which is a four-barreled culvert)

Riprap Installation 26 locations Culvert Cleaning 57 culverts

Ditch Reconditioning 6 locations Flared End Sections (FES) 53 total FES installed at 30 culverts

No Culvert Specific Services Proposed 15 culverts iii AZ FLAP 261(1) - Final Hydraulics Report

Table of Contents

1 Project Background Information

2 Hydraulic Design Criteria

3 Site Selection

4 Hydrology

4.1 Hydrologic Setting

4.2 FEMA Flood Insurance Study

4.3 Available Hydrologic Data

4.4 Regression Equation Estimates

4.4.1 Regression Methods Results Comparison

4.5 Rational Method

4.6 Recommended Design Discharges

5 Hydraulic Analysis

5.1 Hydraulic Model Development

5.1.1 Generalized Inlet Control Analysis

5.2 Hydraulic Model Results

5.2.1 Replacement

5.2.2 Rehabilitation

5.2.3 Stability Design

5.3 Entrance Treatment

6 Discussion

6.1 Breakdown of Proposed Services

6.2 Sedimentation

6.3 Maintenance

6.4 Replacement on the Basis of Corrosion

7 Appendices

References iv AZ FLAP 261(1) - Final Hydraulics Report

Tables

Table 1: Recommendation Summary ............................................................................................................ ii

Table 2: PDDM Hydraulic Design Criterion

Table 3: Available General Flow Statistics

Table 4: Regression Methods Results Comparison

Table 5: Inlet Control Capacity Analysis – Traditional HW/D

Table 6: Inlet Control Capacity Analysis – Debris/Sediment HW/D

Table 7: Culvert Replacement Summary

Table 8: Proposed Flared End Section Replacements

Table 9: Appendix Summary

Figures

Figure 1: Project Location

Figure 2: Drainage Basin Excerpt

Figure 3: FEMA National Flood Hazard Layer - FIRM Excerpt of AZ-271 and Mexican Hay Lake

Appendices

Appendix A: FEMA Flood Insurance Study Map

Appendix B: Hydrology

Appendix C: Hydraulic Summary

Appendix D: Capacity Design

Appendix E: Stability Design

Appendix F: Recommendation Summary

Appendix G: Culvert Rehabilitation Candidate Photographs

Appendix H: HY-8 Output Reports

AZ FLAP 261(1) - Final Hydraulics Report

1 PROJECT BACKGROUND INFORMATION

The Central Federal Lands Highway Division (CFLHD) in cooperation with USFS Apache Sitgreaves and the Arizona Department of Transportation (ADOT) plan to improve the existing AZ-261 corridor. The proposed project includes pulverization of the existing surface, the addition several inches of asphalt, and a final roadway section of 11-foot lanes with 3-foot shoulders. The scope of the project also includes culvert and drainage related services, such as cleaning, culvert rehabilitation and culvert replacement. AZ-261 is located within Apache County, AZ and provides access to the USDA Forest Service Apache Sitgreaves. The project begins at the intersection of AZ-273 and AZ-261 (N 33.911833°, W 109.414472°) and proceeds northerly toward the Town of Eagar for approximately 11.63 miles, ending at N 34.047361°, W 109.360139°.

Figure 1: Project Location https://www.google.com/maps/place/33%C2%B054'42.6%22N+109%C2%B024'52.1%22W/@33.9119064,-109.4154456,349m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d33.911833!4d-109.414472 https://www.google.com/maps/place/34%C2%B002'50.5%22N+109%C2%B021'36.5%22W/@34.0475236,-109.3612074,293m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d34.047361!4d-109.360139 https://www.google.com/maps/place/34%C2%B002'50.5%22N+109%C2%B021'36.5%22W/@34.0475236,-109.3612074,293m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d34.047361!4d-109.360139

2 HYDRAULIC DESIGN CRITERIA

The Federal Lands Highway Project Development and Design Manual (PDDM) establishes the hydraulic design criteria for this project (Federal Lands Highway 2012). The scoping report indicates a design speed of 45 mph, a design average daily traffic (ADT) of 380 vehicles and does not designate this roadway as a critical access road. Based on these parameters, the roadway is classified as a low-standard road for hydraulic design purposes. The corresponding PDDM hydraulic design criterion are detailed in Table 2.

Hydraulic adequacy for roadway culverts is determined by conformance to all applicable design criterion including allowable headwater (AHW) and the respective headwater to depth ratio (HW/D).

Table 2: PDDM Hydraulic Design Criterion

Low-Standard Roadway

Design Frequency

Check Frequency Design Criteria

Roadway Culverts 25-Year Overtopping

New: AHW ≤ bottom of aggregate base layer

Existing: AHW ≤ shoulder hinge point

Where D ≤ 48", HW/D ≤ 1.5 & Where D > 48", HW/D ≤ 1.2

Heavy debris or sediment load concerns: 0.8 ≤ HW/D ≤ 1.0

Crossing is stable at the design flood

Temporary Culverts 2-year -

Seasonal construction may justify a lower design flood

WSE ≤ shoulder hinge point

3 SITE SELECTION

The Arizona Department of Transportation (ADOT) has provided a culvert inventory for AZ-261 from Mile Point (MP) 394.37 – MP 406.00. This inventory provides details on each culvert crossing along the project corridor, including ratings pertaining to debris accumulation, extent of corrosion, and likelihood of collapse (ADOT 2019). This information was utilized to establish the preliminary scope of work, identifying rehabilitation or replacement candidates, and where culvert cleaning would be best utilized. The scope of work was further refined following a site visit to each of the 107 culvert crossings along the project corridor.

Field review identified 57 structures that would benefit from varied levels of cleaning. These structures have been identified as having debris or sediment accumulations and do not have apparent deficiencies indicating replacement is necessary. The condition of many of the culverts recommended for cleaning is difficult to ascertain in the existing condition, inundated with sediment. It is suggested that the engineer on site during construction be given the leeway to specify replacement of specific culverts, should he find after cleaning that the culvert condition is in fact poor and warrants replacement.

The ADOT culvert inventory and on-site condition assessment were utilized to determine where hydrologic and hydraulic evaluation was warranted. The criteria used to make this selection includes any structure listed as having a debris accumulation of ‘100%’, an erosion rating of ‘severe’, a corrosion or collapse rating of ‘25% - 50%’ or higher, or any culvert with a 42-inch diameter or larger. In this way, major drainage crossings and culverts identified as having significant existing issues have been selected for evaluation. Field review identified 3 additional culverts that warrant replacement based on existing disposition. A total of 32 crossings were selected for hydraulic and hydrologic evaluation.

4 HYDROLOGY

4.1 HYDROLOGIC SETTING

The project is situated in the high elevation terrain of Apache County, Arizona. The contributing drainage basins for the crossings of interest along the project corridor were delineated in ArcMap using 1/3 arc-second National Elevation Dataset (NED) information obtained from the USGS National Map (U.S.

Geological Survey 2018). Precipitation information was obtained using the USGS StreamStats Program (U.S. Geological Survey 2016) or the NOAA National Weather Service Precipitation Frequency Data Server (NOAA 2011), as applicable to the hydrologic method for the basin of interest. Figure 2 details the drainage basins for the three major culvert crossings (diameter larger than 48-inches), located at MP 396.21 (STA 106+64), 397.23 (159+85), and 399.79 (294+24).

Figure 2: Drainage Basin Excerpt

4.2 FEMA FLOOD INSURANCE STUDY

The Federal Emergency Management Agency (FEMA) provides flood insurance rate maps that detail Special Flood Hazard Areas. Land that is inundated by the base (100-year) flood are subject to National Flood Insurance Program (NFIP) floodplain management regulations. The National Flood Hazard Layer indicates that Zone D encompasses the AZ-261 roadway within the project limits. Zone D is defined as area with possible but undetermined flood hazards where no flood hazard analysis has been conducted (FEMA). There is also a Zone A floodplain on the west side of AZ-271 encompassing Mexican Hay Lake as shown in Figure 3. Zone A is defined as areas with a 1% annual chance of flooding. Because detailed analyses are not performed for such areas; no depths or base flood elevations are shown within these zones (FEMA).

The project will not be subject to NFIP floodplain management regulations. Fill is not proposed adjacent to Mexican Hay Lake. The project resides on the existing bench and avoids encroachment on the Mexican Hay Lake floodplain. The image below depicts the Zone A floodplain limits. Flood Insurance Rate Maps for the entire project limits are included in Appendix A (FEMA 2007).

Figure 3: FEMA National Flood Hazard Layer - FIRM Excerpt of AZ-271 and Mexican Hay Lake

4.3 AVAILABLE HYDROLOGIC DATA

There are no active USGS streamflow stations within the project limits. There are however two inactive stations within the vicinity of the project corridor. Table 3 summarizes the station location, period of record and general flow statistics for the continuous stream gages (Wolock 2003). Station 09489040 is located approximately 0.1 miles downstream of the STA 294+24 crossing. Station 09489030 does not have a directly associated crossing. Due to the relatively small period of record, this data has not been used in the development of design flows for this project.

Table 3: Available General Flow Statistics

Station Number 09489040 09489030

Station Name WF SEVEN SPRINGS DRAW NR

SPRINGVILLE, AZ

EF SEVEN SPRINGS DRAW NR

SPRINGERVILLE, AZ

Latitude 33.97616004° 33.96504909° Longitude -109.373698° -109.37175329°

Drainage Area 0.75 mi2 1.17 mi2 Period of Record 10/1/1979 - 9/30/1980 10/1/1979 - 9/30/1980

Total Days of Record 366 366 Status Inactive Inactive

Minimum Daily Flow 0.01 cfs 0.01 cfs Maximum Daily Flow 21 cfs 15 cfs

Standard Deviation of Daily Flows 2.264 cfs 1.532 cfs Average Daily Flow 0.425 cfs 0.392 cfs

4.4 REGRESSION EQUATION ESTIMATES

Two regression equation methodologies are available for the State of Arizona and have been utilized to compute the design flows for applicable basins along the project corridor. The two sources of Arizona regression equations are presented in USGS Report 2014-5211 (Paretti 2012), and the Arizona Department of Transportation (ADOT) Highway Drainage Design Manual (JE Fuller Hydrology and Geomorphology 2014).

The project limits are in the USGS High Elevation Region, hydrologic flood region 1. The equations developed for hydrologic flood region 1 relate peak discharge to drainage area, using exploratory predictor variable (EPV) ranges of 1.26 to 711 square miles. The average standard error of prediction is reported as 55.1% for the 25-year event and 56.3% for the 100-year event (Paretti 2012).

The project limits are in the ADOT High Elevation Region, hydrologic flood region 1. The equations developed for hydrologic flood region 1 relate peak discharge to drainage area and mean annual precipitation, using EPV ranges of approximately 0.5 to 1,000 square miles and 12 to 44 inches, respectively. The estimated average standard error of regression is reported as 46% for both the 25-year event the 100-year event (JE Fuller Hydrology and Geomorphology 2014).

4.4.1 Regression Methods Results Comparison

Design flows were computed using both the ADOT and USGS regression methodologies for each of the five basins exceeding the ADOT drainage area EPV range of 0.5 square miles. It is important to note that the drainage area EPV lower bound using the USGS method is 1.26 square miles. Along the project corridor, this criterion is only met by the crossing at STA 106+64. The resulting design flows using both regression methodologies are detailed in Table 4. The results of the ADOT method appear under-conservative when compared to Rational method results for smaller basins and the corresponding USGS method results. To be conservative and not disproportionately under-represent flows at the larger drainage crossings, the design flows produced by the USGS method have been selected for the five crossings detailed in Table 4.

Table 4: Regression Methods Results Comparison

Crossing Station

Drainage Basin

(sq. mi.)

Method Q2

(cfs) Q5

(cfs) Q10 (cfs)

Q25 (cfs)

Q50 (cfs)

Q100 (cfs)

Q200 (cfs)

Q500 (cfs)

106+64 6.80

ADOT 81 130 164 208 241 273 N/A N/A

USGS 61 139 212 328 430 545 678 879

159+85 0.78

ADOT 13 23 30 39 47 54 N/A N/A

USGS 15 36 56 89 117 149 185 241

294+24 0.67

ADOT 12 21 28 36 43 49 N/A N/A

USGS 13 33 51 81 107 136 169 220

474+17 0.86

ADOT 14 24 32 42 50 58 N/A N/A

USGS 16 38 60 94 124 158 196 255

539+18 1.00

ADOT 15 26 35 46 55 63 N/A N/A

USGS 17 42 66 103 136 173 215 280

4.5 RATIONAL METHOD

Of the 32 crossings selected for hydrologic evaluation, 27 crossings had drainage basins below the 0.5 sq.

mi. EPV threshold used to develop the ADOT regression equations for hydrologic region 1. These basins were evaluated in the Hydraulics Toolbox (FHWA 2018) using the Rational Method as presented in HDS-2 (FHWA 2002). The contributing drainage areas for these culverts were delineated using the NED information described in Section 4.1.

Rainfall intensity was obtained from the National Oceanic and Atmospheric Administration Precipitation Frequency Data Server (NOAA 2011). Runoff coefficients (C) of 0.22 – 0.40 were used to represent these undeveloped basins (VTrans 2015), which range from hilly forest to open rangeland with soils predominantly in hydrologic soil group D (NRCS 2015).

4.6 RECOMMENDED DESIGN DISCHARGES

AZ-261 is designated as a low-standard roadway in accordance with the PDDM. The design storm for this roadway designation is the 25-year event. An event of this magnitude has a 4% Annual Exceedance Probability (AEP). To be conservative and not disproportionately under-represent flows at the larger drainage crossings, the design flows produced by the USGS method have been selected for the five crossings detailed in Table 4. The Rational Method has been utilized for basins that fall below the 0.5 square mile drainage area threshold. Appendix B summarizes basin characteristics, hydrologic method selection and recommended design discharges for each of the 32 crossings selected for evaluation.

5 HYDRAULIC ANALYSIS

5.1 HYDRAULIC MODEL DEVELOPMENT

The hydraulic performance of the existing culverts was evaluated using HY-8 (Federal Highway Administration 2017). A generalized inlet control analysis was conducted for each of the 32 crossings evaluated. Structures exceeding a 42 in. diameter replacement size were also selected for site-specific hydraulic models. This criterion was met by a total of six crossings (STA 71+00, 106+64, 159+85, 294+24, 474+17, 539+18), including the three major culvert crossings (diameter larger than 48-inches) where culvert rehabilitation was proposed in the project scope (STA 106+64, 159+85, 294+24).

Two sources of topographic information were used to develop the hydraulic models: 1/3 arc-second National Elevation Dataset information obtained from the USGS National Map (U.S. Geological Survey 2018) and field survey information collected by CFLHD in along the project corridor in October 2019.

Elevations reference the North American Vertical Datum of 1988 (NAVD88).

5.1.1 Generalized Inlet Control Analysis

A generalized inlet control analysis was conducted using HY-8 (Federal Highway Administration 2017) to evaluate hydraulic adequacy and develop recommended replacment sizes. Results of the model were used to determine the discharge that would require upsizing to the next incremental size for the respective HW/D ratio. This model employs a culvert slope of 2%, a projected structure length of 50 feet, and a 5% factor of safety applied to the resulting flows.

Table 5: Inlet Control Capacity Analysis – Traditional HW/D

Pipe Diameter (in.)

Waterway Area

(sq. ft.) HW/D

Maximum Flow (cfs) Mitered Headwall

18 1.8 1.5 9 10 24 3.1 1.5 17 19 30 4.9 1.5 30 34 36 7.1 1.5 48 53 42 9.6 1.5 71 79 48 12.6 1.5 99 110 54 15.9 1.2 108 118 60 19.6 1.2 141 154

Table 5 details the results of the generalized inlet control capacity analysis for traditional HW/D ratios. A total of 10 of the 32 sites selected for H&H evaluation have been identified as having substantial issues associated with sedimentation as determined by the on-site condition assessment. In accordance with the PDDM, more stringent HW/D ratios have been applied to these crossings. This alteration in HW/D approach results in upsizes to 3 of the 10 structures subject to this condition (STA 316+06, 320+80, 604+43).

Table 6: Inlet Control Capacity Analysis – Debris/Sediment HW/D

Pipe Diameter (in.)

Waterway Area

(sq. ft.) HW/D

Maximum Flow (cfs) Mitered Headwall

18 1.8 1.0 5 6 24 3.1 1.0 11 12 30 4.9 1.0 20 21 36 7.1 1.0 31 34 42 9.6 1.0 47 50 48 12.6 0.9 56 61 54 15.9 0.8 63 68 60 19.6 0.8 82 89

Table 6 details the results of the generalized inlet control capacity anaylsis with respect to the selected HW/D ratios, increased to accommodate sedimentation. To promote sediment transport and mitigate deposition, it is desirable for for any structure, particularly those with identified sedimentation issues, to be constructed on a gradient matching that of the local channel.

5.2 HYDRAULIC MODEL RESULTS

Results of the hydraulic investigations for the 32 crossings evaluated are compiled in the appendices.

Appendix C summarizes the generalized inlet control analysis. Results for the six crossings selected for site-specific models have been compiled in Appendix D, pertaining to capacity design, and Appendix E, pertaining to stability design.

5.2.1 Replacement

The models indicate that 15 of the 32 structures selected for evaluation do not meet the hydraulic standards as established in this report. It is recommended that all 15 of these structures be replaced.

Three additional structures have been selected for replacement on the basis of corrosion, located at STA 71+00, 477+47 and 528+69. Modeling indicates that he crossing at STA 71+00 is hydraulically adequate at a 42-inch size, however it is proposed that this crossing be replaced with a 48-inch diameter to match the existing size. Table 7 summarizes the 18 locations in which replacement is proposed. The minimum replacement size recommended to limit maintenance problems associated with debris and sedimentation is 24-inches (Federal Lands Highway 2012).

Structure size and type has been modified in some locations to accommodate local geometric limitations.

Customary Standard 602-1 provides minimum cover requirements (Federal Lands Highway 2005). Several crossings are recommended to be replaced with corrugated metal pipe arch (CMPA) to accommodate limited cover or headwater depths that exceed relief elevations or the allowable headwater depth.

Further increases to the roadway profile is considered outside the scope of the project and is generally not recommended as an increase in roadway elevation could effectively create a dam, thereby raising floodwaters upstream.

Table 7: Culvert Replacement Summary

Crossing Station

(STA)

Existing Culvert Diameter (in.)

Is Existing Structure Hydraulically Adequate?

Replacement Culvert Size and

Type (dia. or w x h)

Entrance Treatment

17+94 24 No 30 in. CMP FES 30+94 24 No 49 in. x 33 in. CMPA FES 71+00 48 Yes 48 in. CMP FES

141+36 36 No 57 in. x 38 in. CMPA FES 166+68 24 No 49 in. x 33 in. CMPA FES 182+11 30 No 49 in. x 33 in. CMPA FES 205+49 30 No 42 in. CMP FES 224+28 24 No 36 in. CMP FES 316+06 24 No 49 in. x 33 in. CMPA FES 320+80 24 No 36 in. CMP FES 370+74 24 No 30 in. CMP FES 474+17 36 x 2 Pipes No 42 in. x 2 CMPs FES 477+42 24 Yes 24 in. CMP FES 528+69 24 Yes 24 in. CMP FES 574+75 18 No 24 in. CMP FES 580+43 24 No 30 in. CMP FES 586+26 18 No 24 in. CMP FES 604+43 18 No 35 in. x 24 in. CMPA FES

5.2.2 Rehabilitation

The crossings located at STA 106+64, 159+85, 294+24, culverts with diameters larger than 48-inches, were evaluated for culvert rehabilitation. Site-specific hydraulic models were generated for the existing configuration, as well as various culvert liner rehabilitation alternatives including a paved invert, spray-on liner, and a slip liner. The on-site condition assessment conducted for these structures revealed that the primary concern with existing disposition pertains to the corroded inverts. Photographs taken during the condition assessment have been included as Appendix G. Field investigations indicate that these structures are well suited for a paved invert rehabilitation. The project partner confirmed that this is the preferred culvert rehabilitation alternative.

A paved invert culvert rehabilitation should encapsulate existing rust lines, at a minimum. Geometric recommendations for the paved inverts are provided in Appendix F based on the rust line dimensions measured in the field. Flowable fill should be employed to fill any holes beneath the structure inverts to mitigate undermining and the development of sinkholes in the roadway surface (e.g. STA 106+80).

Hydraulic modeling indicates that equipping these structures with a smooth interior surface will result in increased outlet velocities. It is proposed that existing outlet protection riprap aprons be improved.

Recommended riprap class and apron dimensions for each of the proposed culvert rehabilitation crossings are detailed in Appendix E and summarized in Appendix F.

There is an outstanding erosion concern upstream of the crossing located at 106+80. It is proposed that the riprap embankment protection be improved to mitigate risk of undercutting the roadway. The existing upstream riprap embankment protection should be extended an additional 40 ft. to address toe of slope erosion. Riprap Class IV may be utilized for economy of scale, consistent to the size proposed for the riprap outlet apron at this site. Consistent with HEC-23 Volume 2, Design Guideline 4, Figure 4.3, a mounded toe configuration is proposed to avoid extending the riprap below the streambed elevation to the scour depth (P.F. Lagasse 2009). The desired toe down depth is 3-feet for this location, consistent with the bankfull depth of the channel.

5.2.3 Stability Design

The results of HY-8 models (Federal Highway Administration 2017) in coordination with the Hydraulic Toolbox (FHWA 2018) were used to develop recommendations for riprap outlet protection in the locations selected for site specific modeling. Standard Detail C-251-50 may be used to size riprap aprons for culverts with diameters 48-inches and below and proposed culvert slopes less than 10% (CFLHD 2015). Appendix E summarizes proposed outlet protection and invert elevations for applicable crossings along the project corridor. The cross-functional design team identified two locations where it is desirable to downsize the riprap from class V to class IV for economy of scale (STA 159+85 and 539+18).

5.3 ENTRANCE TREATMENT

For the design of new structures, flared end sections are recommended for 48-inch equivalent and smaller pipes. A headwall entrance treatment is recommended to offset buoyant forces for structures exceeding a 48-inch diameter (Federal Lands Highway 2012). Culvert replacements are summarized in Table 7. The models indicate that the crossings approaching the 48-inch diameter threshold (STA 71+00, 141+36, 474+17) are hydraulically adequate equipped with flared end sections (FES). A headwall entrance treatment is not proposed for any of the structures along the project corridor.

6 DISCUSSION

Appendix F provides site-specific recommendations for each of the 107 culverts along the project corridor.

Table 1 summarizes these recommendations, which include a range of services such as culvert rehabilitation (3), culvert replacement (15), culvert cleaning (58), and various other minor improvements such as replacement of flared end sections and ditch reconditioning. It is proposed that side road culverts be cleaned wherever an asphalt apron is being installed. In an effort to accommodate culvert crossings inundated with sediment, it is suggested that the engineer on site during construction be given the leeway to specify replacement of specific culverts should they find after cleaning that the culvert is in poor condition and warrants replacement.

6.1 BREAKDOWN OF PROPOSED SERVICES

Table 1 provides a summary of the recommended services along the project corridor. The following information summarizes culvert related services proposed along the project corridor. Recommendations specific to each of the 107 crossings may be found in Appendix F.

• Culverts Hydrologically Evaluated – 32 crossings o Hydraulically inadequate crossings – 15 crossings

Replace based on hydraulic inadequacy: 15 crossings (includes one 2-barrelled culvert) o Hydraulically Adequate Crossings – 17 Culvert rehabilitation – 3 crossings (including one 4-barrelled culvert) Replace based on corrosion: 3 crossings Minor culvert services (cleaning, riprap installation, etc.) – 11 crossings

• Riprap Installation – 26 locations o Replacement culvert crossings – 18 locations (includes one 2-barrelled culvert) o Culvert rehabilitation – 3 locations (includes one 4-barrelled culvert) o Additional riprap installation – 5 locations

• Culvert Cleaning – 57 crossings o Includes 7 side route structures (culvert cleaning wherever an asphalt apron is installed)

• Ditch Reconditioning – 6 locations

• Installation of FESs – 53 total FES installed at 30 culverts o 18 replacement culverts, one of which is double barreled: 38 total FES o 8 structures to be left in place, replace corroded inlet FES: 8 FES o 1 structure to be left in place, replace corroded outlet FES: 1 FES o 3 structures to be left in place, replace both inlet and outlet FES: 6 total FES

• No Culvert Specific Services Proposed – 15 crossings

6.2 SEDIMENTATION

The condition of several of the culverts was difficult to ascertain in the field due to the existing barrels being inundated with sediment. It is recommended that the Contracting Officer (CO) on site during construction be given specify the replacement of specific culverts, should they find after cleaning is conducted that the culvert condition is poor (e.g. advanced corrosion or abrasion) and warrants replacement. Locations in which sedimentation prevented an assessment of the existing pipe condition include 37+12, 386+37, 401+33, 449+70, 461+71, and 600+73. The cross functional design team has been consulted and determined that a contingency would be applied to the quantities in an effort to allow the CO to specify additional replacements based on existing disposition after the culverts are cleaned and the barrels are visible.

6.3 MAINTENANCE

Services for this project include the cleaning of approximately half the structures along the route. It is anticipated that the culverts along the project corridor will require intermittent maintenance to keep the existing structure openings from being obstructed by sediment and/or debris. Plugged culverts can result in overtopping and can lead to erosion of the roadway prism. The culverts should be maintained regularly, particularly after large flow events, to maintain hydraulic openings and mitigate clogging.

6.4 REPLACEMENT ON THE BASIS OF CORROSION

Several culvert crossings and end sections have been recommended for replacement on the basis of existing corrosion. If left in place these features have the potential to continue deteriorating. This complication can result in holes within the invert, allowing water to carry sediment from beneath the structure, commonly referred to as undermining (piping). This complication has the potential to result in deterioration of the roadway embankment, including but not limited to the development of sink holes.

It is recommended that the flared end sections showing signs of advanced corrosion be replaced as part of this project. As detailed in Table 8, this includes the replacement of 15 flared end sections at 12 different culverts. If budgetary constraints preclude the inclusion of all the culvert related services recommended in this report, these replacements could be considered for exclusion from the current project, leaving the existing flared end sections in place until a subsequent project or maintenance operations are conducted.

Table 8: Proposed Flared End Section Replacements

Crossing Station Proposed Replacement FES 37+12 Inlet 56+06 Inlet 75+62 Inlet

188+86 Outlet 246+20 Inlet 335+35 Inlet 407+25 Inlet & Outlet 446+71 Inlet 480+21 Inlet 501+46 Inlet & Outlet 520+81 Inlet 560+67 Inlet & Outlet

Three hydraulically adequate culvert crossings are recommended for replacement based on existing disposition (STA 71+00, 477+42, 528+69). These structures are showing signs of corrosion, particularly along the culvert inverts. If budgetary constraints preclude the inclusion of all the culvert related services recommended in this report, these replacements could be considered for a leave in place alternative. If these crossings are selected for a leave in place alternative, it is recommended that they be monitored for any holes in the invert that could lead to material loss from beneath the structure.

7 APPENDICES

Table 9 summarizes the appendices included in this report. Appendices B and C provide supplemental information on hydrologic and hydraulic investigations respectively. Appendices D, E and H provide information on the six structures selected for site-specific modeling. Appendix F provides a summary of recommendations for each of the 107 crossings along the project corridor. Appendix G provides photographs of the culvert rehabilitation crossings.

Table 9: Appendix Summary

Appendix Name Description

A FEMA Flood Insurance Study Map National Flood Insurance Rate Maps for the project corridor.

B Hydrology Hydrologic method, basin characteristics and resulting design flows.

C Hydraulic Summary Minimum hydraulic openings and recommended sizes considering inlet control hydraulics and the minimum 24-inch replacement diameter.

D Capacity Design Site-specific model results pertaining to hydraulic capacity design.

E Stability Design Site-specific model results pertaining to stability design and outlet protection.

F Recommendation Summary Recommendations pertaining to each of the 107 drainage crossings.

G Culvert Rehabilitation Candidate Photographs Photographs of the three crossings evaluated for culvert rehabilitation.

H HY-8 Output Reports Hydraulic modeling output reports for the structures that received site specific models.

REFERENCES

ADOT. 2019. Pipe Inventory for SR-261 MP 394.37 - 406.00. Arizona Department of Transportation.

CFLHD, Central Federal Lands Highway Division. 2015. "Placed Riprap at Culverts (C-251-50)." Detail Drawings: FP-14.

Federal Highway Administration. 2017. HY-8 Culvert Analysis Program. Version 7.50.

Federal Lands Highway. 2005. Metal Pipe Culvert, U.S. Customary Standard 602-1. June.

https://flh.fhwa.dot.gov/resources/standard/Std602-1.pdf.

Federal Lands Highway. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics." https://flh.fhwa.dot.gov/resources/design/pddm/.

FEMA. n.d. "Definitions of FEMA Flood Zone Designations."

https://snmapmod.snco.us/fmm/document/fema-flood-zone-definitions.pdf.

FEMA. 2007. "Flood Insurance Study Apache County, Arizona and Incorporated Areas." Map Number 04001C4700E.

FHWA. 2002. Hydraulic Design Series No. 2, Second Edition, FHWA -NHI-02-001. Washington, DC: Federal Highway Administration.

FHWA. 2018. Hydraulic Toolbox. Federal Highway Administation, Aquaveo.

JE Fuller Hydrology and Geomorphology, Inc. 2014. "Highway Drainage Design Manual." Arizona Department of Transportation, Pheonix, AZ. https://azdot.gov/business/engineering-and-construction/roadway-engineering/drainage-design/manuals-drainage-design.

NOAA. 2011. Precipitation Frequency Data Server. Silver Springs, MD.

https://hdsc.nws.noaa.gov/hdsc/pfds/.

NRCS. 2015. Soil Survey Geographic (SSURGO) database. Fort Worth, TX.

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

P.F. Lagasse, P.E. Clopper, J.E. Pagán-Ortiz, L.W. Zevenbergen, L.A. Arneson, J.D. Schall, L.G. Girard. 2009.

"HEC-23, Bridge Scour and Stream Instability Countermeasures." FHWA-NHI-09-112. Vol. 2. Fort Collins, CO: U.S. Department of Transportation.

Paretti, N.V., Kennedy, J.R., Turney, L.A., and Veilleux, A.G. 2012. "Methods for estimating magnitude and frequency of floods in Arizona, developed with unregulated and rural peak-flow data through water year 2010." U.S. Geological Survey Scientific Investigations Report 2014-5211.

http://dx.doi.org/10.3133/sir20145211.

U.S. Geological Survey. 2016. StreamStats Program. http://streamstats.usgs.gov.

U.S. Geological Survey. 2018. The National Map. https://viewer.nationalmap.gov/advanced-viewer/.

VTrans. 2015. "Hydraulics Manual." Montpelier, VT: Vermont Agency of Transportation, May 28.

Wolock, D.M. 2003. Flow characteristics at U.S. Geological Survey streamgages in the counterminous United States. Open-File Report 03-146, digital data set, U.S. Geological Survey.

Appendix A – FEMA Flood Insurance Study Map

Project Corridor

Project Start

Project End

Appendix B – Hydrology

Appendix B - Hydrology AZ FLAP 261(1) - Final Hydraulics Recommendations

17+94 25 31 Rational 28 0.04 N/A N/A 30+94 45 56 Rational 41 0.06 N/A N/A 61+03 13 16 Rational 16 0.03 N/A N/A 71+00 64 79 Rational 112 0.17 N/A N/A

106+64 328 545 USGS 4351 6.80 29.3 9144

141+36 70 86 Rational 66 0.10 N/A N/A

159+85 89 149 USGS1 500 0.78 29.2 9127

166+68 46 57 Rational 40 0.06 N/A N/A 182+11 57 71 Rational 36 0.06 N/A N/A 205+49 53 66 Rational 28 0.04 N/A N/A 224+28 37 45 Rational 21 0.03 N/A N/A

294+24 81 136 USGS1 429 0.67 30.6 9349

316+06 38 46 Rational 60 0.09 N/A N/A 320+80 26 32 Rational 31 0.05 N/A N/A 370+74 24 30 Rational 43 0.07 N/A N/A 386+37 9 12 Rational 18 0.03 N/A N/A 401+33 8 10 Rational 19 0.03 N/A N/A 407+25 24 30 Rational 48 0.07 N/A N/A 446+71 3.6 4.5 Rational 5.5 0.01 N/A N/A 449+70 4.5 5.6 Rational 5.0 0.01 N/A N/A 458+71 3.5 4.3 Rational 4.8 0.01 N/A N/A 461+71 4.5 5.6 Rational 5.2 0.01 N/A N/A

474+17 94 158 USGS1 550 0.86 29.2 9200

477+42 3.5 4.4 Rational 2.6 0.00 N/A N/A 528+69 16 21 Rational 30 0.05 N/A N/A

539+18 103 173 USGS1 642 1.00 28.1 9118

574+75 15 19 Rational 46 0.07 N/A N/A 580+43 19 24 Rational 11 0.02 N/A N/A 586+26 9 12 Rational 6.3 0.01 N/A N/A 589+96 6 7 Rational 3.7 0.01 N/A N/A 600+73 8 10 Rational 5.0 0.01 N/A N/A 604+43 13 17 Rational 8.1 0.01 N/A N/A

25-Year Design Flow (cfs)

100-Year Check Flow (cfs)

Crossing Station Hydrologic

Method Mean Annual

Precipitation (in.)

Mean Basin

Elevation (ft.)

Drainage Area

(acres) Drainage Area

(sq. mi.)

1 - The drainage area for these crossings falls below the range of explanatory variables used to develop the regional regression equations for the USGS Arizona High Elevation Region. The ADOT hydrologic method was also used to compute flows for these crossings. The USGS results were selected as they are more conservative than the flows produced by the ADOT method. See the Hydrology section for further discussion on the selected hydrologic methodologies.

Appendix C – Hydraulic Summary

Appendix C - Hydraulic Summary AZ FLAP 261(1) - Final Hydraulics Recommendations

(dia. or w x d, in.) 3 WWA (sq. ft.) 4 (dia. or w x d, in.) 3 WWA (sq. ft.) 4 (dia. or w x d, in.) 3 WWA (sq. ft.) 4 17+94 25 HY-8, Generalized Inlet Control Traditional 24 3.1 30 4.9 30 4.9 30+94 45 HY-8, Generalized Inlet Control6 Traditional 24 3.1 36 7.1 36 7.1 61+03 13 HY-8, Generalized Inlet Control Traditional 24 3.1 24 3.1 24 3.1 71+00 64 HY-8, Site Specific Traditional 48 13

106+64 328 HY-8, Site Specific Traditional 66 x 4 pipes 95 141+36 70 HY-8, Generalized Inlet Control6 Traditional 36 7.1 42 9.6 42 9.6 159+85 89 HY-8, Site Specific Traditional 60 20 166+68 46 HY-8, Generalized Inlet Control6 Traditional 24 3.1 36 7.1 36 7.1 182+11 57 HY-8, Generalized Inlet Control6 Traditional 30 4.9 42 9.6 42 9.6 205+49 53 HY-8, Generalized Inlet Control Traditional 30 4.9 42 9.6 42 9.6 224+28 37 HY-8, Generalized Inlet Control Traditional 24 3.1 36 7.1 36 7.1 294+24 81 HY-8, Site Specific Traditional 60 20 316+06 38 HY-8, Generalized Inlet Control6 Debris 24 3.1 42 9.6 42 9.6 320+80 26 HY-8, Generalized Inlet Control Debris 24 3.1 36 7.1 36 7.1 370+74 24 HY-8, Generalized Inlet Control Traditional 24 3.1 30 4.9 30 4.9 386+37 9 HY-8, Generalized Inlet Control Debris 24 3.1 24 3.1 24 3.1 401+33 8 HY-8, Generalized Inlet Control Debris 24 3.1 24 3.1 24 3.1 407+25 24 HY-8, Generalized Inlet Control Traditional 30 4.9 30 4.9 30 4.9 446+71 4 HY-8, Generalized Inlet Control Traditional 24 3.1 18 1.8 24 3.1 449+70 5 HY-8, Generalized Inlet Control Debris 24 3.1 18 1.8 24 3.1 458+71 4 HY-8, Generalized Inlet Control Traditional 24 3.1 18 1.8 24 3.1 461+71 5 HY-8, Generalized Inlet Control Debris 24 3.1 18 1.8 24 3.1 474+17 94 HY-8, Site Specific Traditional 36 x 2 pipes 14 477+42 4 HY-8, Generalized Inlet Control Traditional 24 3.1 18 1.8 24 3.1 528+69 16 HY-8, Generalized Inlet Control Traditional 24 3.1 24 3.1 24 3.1 539+18 103 HY-8, Site Specific Traditional 48 13 574+75 15 HY-8, Generalized Inlet Control Traditional 18 1.8 24 3.1 24 3.1 580+43 19 HY-8, Generalized Inlet Control Debris 24 3.1 30 4.9 30 4.9 586+26 9 HY-8, Generalized Inlet Control Debris 18 1.8 24 3.1 24 3.1 589+96 6 HY-8, Generalized Inlet Control Traditional 18 1.8 18 1.8 24 3.1 600+73 8 HY-8, Generalized Inlet Control Debris 18 1.8 24 3.1 24 3.1 604+43 13 HY-8, Generalized Inlet Control6 Debris 18 1.8 30 4.9 30 4.9

1 - Based on a generalized inlet control HY-8 model for the 25-year capacity design flow.

3 - Diameter or width x depth, given in inches unless otherwise noted.

4 - Waterway opening area in square feet.

5 - These crossings were evaluated with site-specific hydraulic models as detailed in Appendix D - Capacity Design.

N/A 5

N/A 5

N/A 5

N/A 5 N/A 5

N/A 5

6 - Site specific models were also generated for these locations to investigate local geometric constraints. The models indicate that these crossings are conducive to CMPAs due to low cover or low relief elevations. A 57 in. x 33 in. CMPA is recommended for 141+36. A 35 in. x 24 in. CMPA is recommended for 604+43. A 49 in. x 33 in. CMPA is recommended for 182+11, 166+68, 316+06 and 30+94.

Crossing Station Hydraulic Model 25-Year Design

Flow (cfs) Existing Structure Opening

2 - Using the results of the required hydraulic opening column and upsizing meet the minimum 24-inch diameter replacement size recommended to limit maintenance problems associated with debris and sedimentation (Federal Lands Highway 2012).

Minimum Replacement Opening 2Minimum Hydraulic Opening 1HW/D Approach

Appendix D – Capacity Design

Appendix D - Capacity Design AZ FLAP 261(1) - Final Hydraulics Recommendations

Span (in.) Depth (in.)

Existing 48 48 CMP FES 8975.5 8978.4 1.5 0.94 118 Yes

Proposed 48 48 CMP FES 8975.5 8978.2 1.5 0.94 121 Yes

Existing 66 x 4 pipes 66 x 4 pipes 4 CMPs Mitered 8931.3 8938.3 1.2 0.68 1146 Yes

Proposed 66 x 4 pipes 58 x 4 pipes 4 CMPs with 8in.

paved inverts Mitered 8930.7 8938.1 1.2 0.63 1181 Yes

Existing 60 60 CMP Mitered 8982.2 8985.5 1.2 0.82 193 Yes

Proposed 60 52 CMP with 8in.

paved invert

Mitered 8981.4 8985.4 1.2 0.75 295 Yes

Existing 60 60 CMP Mitered 9211.0 9216.1 1.2 0.77 228 Yes

Proposed 60 52 CMP with 8in.

paved invert

Mitered 9210.4 9215.9 1.2 0.73 230 Yes

Existing 36 x 2 pipes 36 x 2 pipes 2 CMPs FES 8956.4 8956.3 1.5 1.35 94 No

Proposed 42 x 2 pipes 42 x 2 pipes 2 CMPs FES 8955.6 8956.1 1.5 0.95 117 Yes

Existing 48 48 CMP FES 8928.6 8929.1 1.5 1.49 122 Yes

Proposed, Retain Existing Structure

48 48 CMP FES 8928.6 8928.9 1.5 1.49 124 Yes

Headwater Elevation (25-

Year, ft.)

Target HW/D Ratio

HW/D Ratio Overtopping

Flow (cfs) Crossing Station

71+00 64

Meets Capacity Design Criteria?

Structure Type Model Inlet

Configuration 1

25-Year Design Flow (cfs)

Structure Size AHW Elevation (ft.)2

474+17 94

294+24 81

106+64 328

159+85 89

Proposed or Existing

539+18 103

1 – The mitered inlet configuration has been used in HY-8 as a substitute for a flared end section inlet configuration.

2 – Allowable headwater elevation (AHW) criteria is established by the PDDM (Federal Lands Highway 2012). New structure: AHW ≤ bottom of aggregate base layer; Existing: AHW ≤ shoulder hinge point.

Appendix E – Stability Design

Appendix E - Stability Design AZ FLAP 261(1) - Final Hydraulics Recommendations

Span (in.) Depth (in.) Stone Class Apron Length

(ft.)

Apron

Thickness (ft.)

Apron End Width (ft.)

71+00 64 48 48 CMP FES 8971.7 8969.9 90.0 2.0% II 16 3.0 20.0

106+64 328 66 x 4 pipes 58 x 4 pipes 4-barrel CMP with paved inverts Mitered 8927.6 8925.9 97.4 1.7% IV 22 3.0 25.0

159+85 89 60 52 CMP with paved invert Mitered 8978.1 8975.8 67.7 3.4% IV2 35 3.5 32.5

294+24 81 60 52 CMP with paved invert Mitered 9207.2 9205.7 103.7 1.4% IV 30 3.0 29.5

474+17 94 42 x 2 pipes 42 x 2 pipes 2-barrel CMP FES 8952.3 8947.1 119.5 4.4% III 18 2.5 19.5

539+18 103 48 48 Retain existing CMP FES 8922.6 8918.9 76.2 4.9% IV2 24 3.5 25.5

1 - Proposed invert elevations reflect the elevation of the invert at the entrance to the closed conduit. For applicable sites this is the juncture between the enclosed pipe and the flared end section.

2 - Downsized from Type V for economy of scale based on input from the cross-functional design team.

25-Year Design Flow (cfs)

Outlet Protection Proposed Structure

Type Crossing Station

Inlet Invert Elevation (ft.)1

Outlet Invert Elevation (ft.)1

Projected Structure

Length (ft.)

Structure Slope

Proposed Structure Size End Treatment

Appendix F – Recommendation Summary

Appendix F - Recommendation Summary AZ FLAP 261(1) - Final Hydraulics Recommendations

Number MP STA Clean Replace

Structure Culvert Rehab

Regrade Ditch

Side Road Culverts

New FESs Missing

Delineators No Culvert

Work Photos

Is Existing Structure Hydraulically

Adequate?

Replacement Culvert Diameter and Type

Riprap Riprap Class Riprap Length Riprap

Thickness Riprap End

Width H3 Recommendation

1 394.53 17+94 X X X No 30 in. CMP X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 30 in. CMP with flared end sections at the inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

2 24+56 X X Clean existing structure. Regrade ditch to drain on west side of road approx. STA 24+00.

3 30+94 X X X No 49 in. x 33 in. CMPA X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 49 in. x 33 in. CMPA with flared end sections at the inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

4 37+12 X Inlet 24 in. CMP (if replace) Clean existing structure. Replace inlet FES. Add note for CO once to assess condition of pipe after cleaning. If existing condition is unsatisfactory, remove and replace with 24 in. CMP with flared end sections at the inlet and outlet and place outlet riprap apron per Standard Detail C251-50.

5 40+44 X Clean existing structure.

6 395.01 43+43 X Clean existing structure inlet. Outlet is visible and should not be listed as DIR only.

7 56+06 X Inlet Clean existing structure.

8 395.32 59+91 X X This is a side route structure. Clean side route structure wherever an asphalt apron is being installed.

9 395.33 61+03 X Yes Place outlet riprap apron per Standard Detail C251-50. Clean existing structure outlet.

10 395.53 71+00 X X X Yes 48 in. CMP X II 16 3 20 Remove and replace with 48 in. CMP with flared end sections at inlet and outlet. Place outlet riprap apron as specified.

11 75+62 Inlet Replace inlet FES.

12 81+41 X Regrade ditch to drain west side of road, approx. STA 81+50 - 82+20

13 86+38 X X X No culvert specific work is proposed for this crossing. Asphalt apron noted in the plans does not appear necessary at this location (no existing side road intersection).

14 100+89 X Clean existing structure outlet.

15 396.21 106+64 X X Yes X IV 22 3 25

Install paved invert culvert rehabilitation extending a minimum of 5.0 ft. horizontally and 2.0 ft. vertically along the bottom of the invert to fully encapsulate the existing rust lines. This should be undertaken for each barrel of the four-barrel structure. Flowable fill and/or grout should be utilized to fill any holes in the structure inverts, such as those in the RTC barrel (right most structure looking downstream) to mitigate undermining and the development of sinkholes in the roadway surface. Improve outlet riprap apron as specified (min). The width of the riprap apron should extend to encompass all four barrels between existing guide banks. Extend existing upstream riprap embankment protection an additional 40 ft. to address toe of slope erosion using a mounded toe configuration with a mound height of 3 feet, 1:1.5 maximum slope, depth of 2.5' on the slope and 5' at the mound location.

16 106+75 X This is a 4-barrel culvert crossing. See 106+64 recommendation.

17 106+87 X This is a 4-barrel culvert crossing. See 106+64 recommendation.

18 106+99 X This is a 4-barrel culvert crossing. See 106+64 recommendation.

19 109+00 X X Clean existing structure.

20 115+40 X Place outlet riprap apron per Standard Detail C251-50. Improve outlet apron per Standard Detail C251-50.

21 396.44 118+50 X X No culvert specific work is proposed for this crossing.

22 141+36 X X X X No 57 in. x 38 in. CMPA X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 57 in. x 38 in. CMPA with flared end sections at inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

23 151+36 X X No culvert specific work is proposed for this crossing.

24 397.23 159+85 X X Yes X IV 35 3.5 32.5 Install paved invert culvert rehabilitation extending a minimum of 3.5 ft. horizontally and 1.5 ft. along the bottom of the invert to fully encapsulate the existing rust lines. Improve outlet riprap apron as specified.

25 163+35 X Clean existing structure.

26 397.36 166+68 X X X No 49 in. x 33 in. CMPA X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 49 in. x 33 in. CMPA with flared end sections at inlet and outlet. Place outlet riprap apron per Standard Detail C251-50. Inlet is visible and should not be listed as DIR only.

27 170+95 X Clean existing structure.

28 175+87 X X Clean existing structure. Regrade ditch on northwest side of road to drain, approx. STA 176-177.

29 181+05 X No culvert specific work is proposed for this crossing.

30 182+11 X X X No 49 in. x 33 in. CMPA X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 49 in. x 33 in. CMPA with flared end sections at inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

31 184+85 X X No culvert specific work is proposed for this crossing.

32 397.78 188+86 X Outlet Clean existing structure inlet.

33 192+81 X No culvert specific work is proposed for this crossing.

34 199+62 X Clean existing structure.

35 202+33 X Clean existing structure.

36 205+49 X X X No 42 in. CMP X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 42 in. CMP with flared end sections at inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

37 224+28 X X No 36 in. CMP X Place outlet riprap apron per Standard Detail C251-50. Remove and replace with 36 in. CMP with flared end sections at inlet and outlet. Place outlet riprap apron per Standard Detail C251-50.

38 398.80 242+25 X Clean existing structure.

39 246+20 X Inlet X Clean existing structure inlet.

40 271+30 X X Clean existing structure inlet.

41 275+80 X Clean existing structure outlet.

42 281+09 X Clean existing structure.

43 399.59 283+72 X X Clean existing structure outlet.

44 399.79 294+24 X X Yes X IV 30 3 29.5 Clean existing structure invert of sediment. Install paved invert culvert rehabilitation extending a minimum of 3.5 ft. horizontally and 1.5 ft. along the bottom of the invert to fully encapsulate the existing rust lines.