TX FLAP FM 709(1) Navarro Mills Lake Access_Final Hydraulics Report.pdf

Navarro Mills Lake Access Final Hydraulics Report

TX FLAP FM 709(1)

In Partnership With:

Texas Department of Transportation

Navarro County, TX

Federal Highway Administration Central Federal Lands Highway Division

September 12, 2022

2 | Page TX FLAP FM 709(1) – Final Hydraulics Report

Signature Sheet

Report prepared by: ____________________________________________________

Cassidy Cote, Hydraulic Engineer

Report reviewed by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Approved for distribution by: ____________________________________________________

Luis Calderón, Lead Hydraulic Engineer

Distribution

Electronic:

N:\projects\TX\FM709(1)\Hydraulics\9_Final-Report Solomon Haile, Project Management Stacy Diccicco, Project Development, Lead Designer Trevor Moulton, Environmental Protection Dominic Monarco, Geotechnical Design Samir Sidhom, Bridge Martin Fey, Materials

3 | Page TX FLAP FM 709(1) – Final Hydraulics Report

Executive Summary Hydrologic and hydraulic analyses have been conducted for the TX FLAP FM 709(1) Navarro Mills Lake Access project located in the Town of Dawson, Navarro County, TX. Based on a high-standard roadway classification, the hydraulic design frequency is the 50-year event for the six cross-route structures along the project corridor. The hydraulic design frequency for the 51 parallel structures along the route is the 10-year event. Design flows were estimated using the Rational method. Hydraulic performance was evaluated in HY-8. A summary of recommendations for the cross-route structures are provided in Table

1. Additional information pertaining to the capacity and stability deign for these structures may be found in Appendix B and C, respectively. Photographs of cross-route structures are provided in Appendix F.

Recommendations pertaining to the parallel structures are provided in Appendix A. The following report summarizes hydraulic design criteria, computational methods and final hydraulics recommendations.

Table 1: Recommendation Matrix

Crossing Station

Existing Size

(w x h or diameter)

Existing Structure

Type

Existing Hydraulic Adequacy

Proposed Size

(w x h or diameter)

Proposed Structure

Type Hydraulics Recommendation

30+55 54-in. 4-Cell RCP with HW Adequate 54-in.

4-Cell RCP with HW and WW

Existing condition warrants replacement.

Replace with the same structure configuration (4-Cell 54-in. RCP), equipped with concrete HW, WW, and Class 3 riprap outlet protection.

67+80 5-ft.

x 3-ft.

3-Cell CBC with HW and WW

Adequate 5-ft.

x 3-ft.

Existing

CBC,

Extended, with new HW and

WW

Retain existing structure. Replace inlet and outlet sections of the pipe and extend length on both sides to accommodate proposed roadway geometry. Remove and replace HW and WW. Install Class 3 riprap outlet protection.

96+80 24-in. RCP with DI Adequate 24-in. RCP with

FES

Existing condition warrants replacement.

Replace structure with 24-in. RCP with FES, removing the existing DI configuration.

Install Class 3 riprap outlet protection.

113+30 30-in. RCP with DI Inadequate 42-in. RCP with

FES

Hydraulic modeling indicates that this structure is undersized. Remove and replace with 42-inch RCP with FES, removing the existing DI configuration.

Install Class 3 riprap outlet protection.

137+65 54-in. RCP with DI Adequate 4-ft.

x 4-ft.

CBC with HW and

WW

TxDOT has requested that this structure and the DI configuration be replaced with a CBC. Remove and replace existing structure with 4-ft. x 4-ft. CBC equipped with concrete HW and WW. Install Class 3 riprap outlet protection.

176+30 30-in. RCP Adequate 30-in.

Existing

RCP,

Extended, with new

FES

Retain existing structure. Replace inlet and outlet sections of the pipe and extend length on both sides to accommodate proposed roadway geometry. Install FES at inlet and outlet and Class 3 riprap outlet protection.

Acronyms: RCP – Reinforced Concrete Pipe, CBC – Concrete Box Culvert, CMP – Corrugated Metal Pipe, HW – Headwalls, WW – Wingwalls, DI – Drop Inlet, FES – Flared End Sections, LWC – Low Water Crossing, w x h – width x height

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Table of Contents

1 Project Background Information 2 Hydraulic Design Criteria

2.1 Minimum Culvert Size

3 Crossing Summary 4 Project Specifications

4.1 Drop Inlets

4.2 Culvert Material Preference

4.3 Treadwell Bridge Crossing

4.4 Culvert End Treatment

4.5 Cross-Route Culvert Replacement

4.6 Parallel Culvert Replacement

5 Cross-Culvert Site Observations 6 Hydrology

6.1 Hydrologic Setting and Topographic Data

6.2 FEMA Flood Insurance Study

6.3 Available Hydrologic Data

6.4 Regression Equation Estimates

6.5 Rational Method Estimates

6.6 Recommended Design Discharges

7 Hydraulic Analysis

7.1 Hydraulic Model Development

7.2 Hydraulic Model Results

8 Ditch Capacity Analysis

8.1 Hydrologic Investigations

8.2 Hydraulic Model Development

8.3 Hydraulic Model Results

9 Recommendations

9.1 Cross-Route Structures

9.2 Roadside Drainage

9.2.1 Existing Parallel Structures

9.2.2 Intersecting Roads without Parallel Structures

9.2.3 Roadside Ditches

9.3 Entrance Treatment

9.3.1 Cross-Route Structures

9.3.2 Parallel Structures

9.4 Outlet Protection

10 References

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Tables

Table 1: Recommendation Matrix

Table 2: PDDM Hydraulic Design Criterion

Table 3: Hydrologic Summary

Figures

Figure 1: Project Location Map

Figure 2: Example Barrel of the STA 30+55 Crossing

Figure 3: Cross-Culvert Drainage Basins

Figure 4: Flood Insurance Rate Map Excerpt

Figure 5: Example Existing Ditch Line

Appendices

Appendix A: Parallel Structures

Appendix B: Capacity Design

Appendix C: Stability Design

Appendix D: Ditch Capacity

Appendix E: HY-8 Output Reports

Appendix F: Cross-Culvert Photographs

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1 PROJECT BACKGROUND INFORMATION

The Central Federal Lands Highway Division (CFLHD) in cooperation with Texas Department of Transportation (TxDOT) plan to rehabilitate 3.8 miles of FM-709, providing access to the Navarro Mills Lake. Proposed improvements include full depth reclamation, shoulder widening, culvert replacements, culvert extensions, and the installation of drainage structure end treatments. The project scope includes increasing the existing 22-foot travel way to a 28-foot width, consisting of two 11-foot lanes with 3-foot shoulders. Culverts along the route will be extended or replaced, based on the existing condition, partner preference, and/or hydraulic capacity. The project begins at the intersection of FM-709 and SH-31 (31.901789, -96.717508) and extends 3.8 miles north along FM-709 to the intersection of FM-709 and Farm to Market 709-N (31.945527, -96.716289). No improvements have been proposed for the Treadwell Branch bridge crossing, located along the project route at 31.934484, -96.712493.

Figure 1: Project Location Map https://www.google.com/maps/place/31%C2%B054'06.4%22N+96%C2%B043'03.0%22W/@31.9017901,-96.7180565,213m/data=!3m2!1e3!4b1!4m14!1m7!3m6!1s0x0:0x0!2zMzHCsDU2JzQzLjkiTiA5NsKwNDInNTguNiJX!3b1!8m2!3d31.945527!4d-96.716289!3m5!1s0x0:0x0!7e2!8m2!3d31.9017894!4d-96.7175076 https://www.google.com/maps/place/31%C2%B056'43.9%22N+96%C2%B042'58.6%22W/@31.9455315,-96.718483,853m/data=!3m2!1e3!4b1!4m5!3m4!1s0x0:0x0!8m2!3d31.945527!4d-96.716289 https://www.google.com/maps/place/31%C2%B056'04.1%22N+96%C2%B042'45.0%22W/@31.9344754,-96.7129103,213m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d31.934484!4d-96.712493

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2 HYDRAULIC DESIGN CRITERIA

The Federal Lands Highway Project Development and Design Manual (PDDM) establishes the hydraulic design criteria for this project (FLH 2012). The scoping report indicates a design speed of 55 mph, a design average daily traffic (ADT) of 600 vehicles and does not designate this roadway as a critical access road.

Based on these parameters, the corridor is classified as a high-standard roadway for hydraulic design purposes. Corresponding hydraulic design criteria are detailed in Table 2. Hydraulic adequacy for roadway culverts is determined by conformance to all applicable design criteria including allowable headwater (AHW) and the respective headwater to depth ratio (HW/D). Cross-culverts along the project corridor have been designed for a 50-year design flood. Parallel culverts, such as those in roadside ditches beneath driveways or cross-roads, have been designed for a 10-year design flood.

Table 2: PDDM Hydraulic Design Criterion

High- Standard Roadway

Hydraulic Capacity Design Criteria

Roadway Culverts

Cross-Culvert Design Flood: 50-year

Parallel-Culvert Design Flood: 10-year

Check Flood: 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

Ditches 10-year

New: WSE ≤ bottom of aggregate base layer

Existing: WSE ≤ shoulder hinge point

Ditch is stable at the 10-year flood

2.1 MINIMUM CULVERT SIZE

The PDDM establishes minimum recommended culvert sizes, intended to facilitate access to culverts and limit maintenance problems associated with debris and sedimentation. A 24-inch diameter (or equivalent) is the minimum size recommended for cross-culvert replacement. An 18-inch diameter (or equivalent) is the minimum size recommended for parallel-culvert replacement (FLH 2012).

3 CROSSING SUMMARY

There are seven cross-route drainage structures along the project corridor, including one bridge and six culvert crossings- two of which are multi-cell structures. CFLHD survey indicates that there are a total of 51 parallel structures along the project corridor. The following information serves to summarize existing culverts along the route. Specific information pertaining to parallel and cross-structure locations and sizes are included in Appendix A and B, respectively.

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• Parallel Structures – 51 culverts composed primarily of CMP and RCP

• Cross-Route Structures – 7 crossings o One bridge (no services proposed) o A 4-Cell RCP (48 in.) with concrete headwalls o A 3-Cell CBC (5 ft. x 3 ft.) with concrete headwalls and wingwalls o A 24-in. RCP with DI o A 30-in. RCP with DI o A 54-in. RCP with DI o A 30-in. RCP

4 PROJECT SPECIFICATIONS

4.1 DROP INLETS

A total of three existing drop inlet structures are present along the project corridor (STA 96+80, 113+30, 137+65). Appendix F provides photographs for reference. At the request of TxDOT, all drop inlet configurations will be replaced with improved inlet configurations. TxDOT initially suggested pre-cast replacement for these crossings using standard details Precast Base (PB), Design Data (PDD) and Precast Slab Lid (PSL, FG lid), as provided within the TxDOT bridge standard online catalog (TxDOT 2021). However, at the site visit, it was requested that the drop inlet structures be replaced with concrete culverts with FES (for RCP), or headwalls and wingwalls (for CBC), as applies to the structure of interest. This will require regrading at the structure inlet to tie the upstream channel to the invert of each culvert. TxDOT has requested that the slopes adjacent to each of the proposed DI replacement structures be armored with riprap. Details in this regard are provided in the plans in the culvert plots and roadway cross sections.

4.2 CULVERT MATERIAL PREFERENCE

At the preference of TxDOT, and for economy of scale, concrete has been proposed for all replacement structures along the project corridor including parallel structures. Reinforced concrete pipe and concrete box culvert are the two structure types proposed.

4.3 TREADWELL BRIDGE CROSSING

As specified by TxDOT, improvements to the Treadwell Bridge crossing located at STA 158+60 are not included within the scope of this project. As such, the Treadwell Bridge crossing has not been evaluated with respect to hydrology or hydraulics.

4.4 CULVERT END TREATMENT

Recommendations pertaining to entrance treatment as detailed in the PDDM are summarized in Section

9.3. Typical end sections for include flared end sections, headwalls and wingwalls. TxDOT has indicated that this approach is acceptable for cross-route structures. For all parallel structures, TxDOT has requested use of safety end treatments (SET), discussed in further detail in Section 9.3.2.

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4.5 CROSS-ROUTE CULVERT REPLACEMENT

The scope of this project includes replacement of any hydraulically inadequate structures along the project route. In collaboration with TxDOT it was identified that it is also desirable to replace any corrugated metal pipes that run beneath the project corridor. As reported by TxDOT, the crossing at 30+55 was believed to be the only existing cross-route CMP along the project corridor. On-site field investigations, however, indicate that this structure, reported as a 4-Cell 48-inch CMP, is in fact a 4-Cell 54-inch RCP, as shown by Figure 2 below. Additional photographs of each cross-route structure are provided in Appendix F.

Figure 2: Example Barrel of the STA 30+55 Crossing

4.6 PARALLEL CULVERT REPLACEMENT

CFLHD survey indicates that there are approximately 51 parallel structures adjacent to the project corridor running beneath field drives, driveways and intersecting roads. TxDOT recommends replacing all of the parallel culverts due to the extent of impact on the ditch flow line needed to accommodate the widened roadway corridor and proposed side slopes. Proposed culverts should match into the new ditch flow line at the toe of the roadway prism.

Due to geometric constraints associated with cover limitations, a 12-in. minimum size was considered where the existing structure size does not already exceed this threshold. TxDOT requested that the standard 18-in. minimum size for parallel culverts, however, understanding that this may result in lowering of the culvert invert, the top of the culvert protruding from the intersecting road surface (a ‘bump’ in the traveled surface), not meeting cover requirements, or some combination therein. TxDOT has further requested that any parallel replacement culvert meet or exceed the size of its predecessor.

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5 CROSS-CULVERT SITE OBSERVATIONS

A site visit was conducted by the CFL cross-functional design team and TxDOT in March 2022. The existing condition of each cross-culvert was evaluated on site. In the field, it was identified that TxDOT would like to replace all drop inlet structures. TxDOT also indicated that they would like to limit riprap outlet protection within the limitations of existing right of way. The following information serves to summarize site-specific existing condition evaluations for each of the cross-route structures:

• 30+55: Significant pipe separation was observed at several culvert joints, specifically on the outlet side. Sinkholes behind both inlet and outlet headwalls extended up to 2-ft. in depth. An approximate 3.5-ft. deep headcut extending approximately 40-ft. longitudinally was observed in the ditch upstream of the inlet, in the channel approaching the culvert from the northwest. Discussion with TxDOT indicated that this structure was a good candidate for replacement on the basis of existing condition.

Riprap was recommended to stabilize the existing erosion hole.

• 67+80: The existing structure appears to be in acceptable shape. At the preference of TxDOT, it was determined that this structure was a good candidate for extension. It is anticipated that the proposed services will need to cut through existing wingwalls to facilitate the culvert extension.

• 96+80: This existing structure is equipped with an open drop inlet and an outlet that is nearly fully filled with sediment. Discussion with TxDOT indicated that this structure is a good candidate for replacement based on existing condition and a desire to remove DI configurations along the corridor.

TxDOT has requested that the new structure be equipped with an improved inlet configuration and understands that this may require regrading and armoring in the vicinity of the structure inlet to facilitate an invert that matches into local topography. It is desirable to raise invert elevations to mitigate future sedimentation at the outlet. These details are captured in the proposed pipe plots include in the plan set.

• 113+30: This existing structure is equipped with an open drop inlet, and an outlet that has a large scour hole. Discussion with TxDOT indicated that this structure was a good candidate for replacement based on existing condition and a desire to remove DI configurations along the corridor. TxDOT has requested that the new structure to be equipped with an improved inlet configuration and understands that this may require regrading and armoring in the vicinity of the structure inlet to facilitate an invert that matches into local topography. Outlet protection is recommended to stabilize the existing scour hole and mitigate continued erosion.

• 137+65: This existing structure is equipped with a large open drop inlet. TxDOT would like this structure replaced with a CBC with headwalls and wingwalls at the inlet and outlet due to a desire to remove DI configurations along the corridor. They have requested that riprap and wingwalls stay within existing right of way. It is anticipated that the wingwall at the outlet will need to be parallel the road to stay within right of way. The ditches that approach the culvert outlet on both sides of the roadway are recommended to be armored with riprap to mitigate erosion in front of the wingwalls.

• 176+30: The existing structure appears to be in acceptable shape. Little to no erosion was observed at the crossing. Flow within the drainage basin appears to attenuate in the pond directly upstream of the culvert. Discussion with TxDOT indicated that this structure was a good candidate for extension.

Flared end sections are recommended for inlet and outlet treatment of the extended structure.

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6 HYDROLOGY

6.1 HYDROLOGIC SETTING AND TOPOGRAPHIC DATA

The project is located in a low gradient setting in the town of Dawson, Texas. Major drainage basins along the project corridor were delineated using Worldwide Elevation Data obtained from WMS, the Watershed Modeling System (Aquaveo 2016), supplemented with CFLHD site-survey from March 2021. Drainage basin delineations for the cross-route culverts along the project corridor are detailed in Figure 2.

Figure 3: Cross-Culvert Drainage Basins

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6.2 FEMA FLOOD INSURANCE STUDY

The Federal Emergency Management Agency (FEMA) provides Flood Insurance Rate Maps (FIRMs) that detail special flood hazard areas. Lands inundated by the base flood (100-year) are subject to National Flood Insurance Program (NFIP) floodplain management regulations. The FIRMs indicate that Zone X encompasses the project limits with the exception of the Treadwell Branch bridge crossing, located in Zone A at STA 158+60 (31.934484, -96.712493). Zone X is defined as area of minimal flood hazard, determined to be outside the 500-year flood and/or protected by levee from 100-year flood (FEMA n.d.).

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. TxDOT has indicated that no improvements to the Treadwell Branch bridge crossing are included within the scope of this project. As the remainder of the project corridor resides within Zone X, no other locations along the project will not be subject to NFIP floodplain management regulations for backwater.

The Treadwell Bridge approaches are receiving a 2-in. mill and overlay, matching existing grade. The roadway through the bridge is wider than the rest of the corridor. However, there is approximately 100-

ft. along the road that is within the floodplain along the southern approach that has not been previously widened. To facilitate the proposed roadway geometry, it has been proposed that this area receive approximately 29 cubic yards of fill within the boundary of the Zone A floodplain. The Navarro County Floodplain Administrator has been consulted in this regard and has indicated that no County permit will be required for this project pertaining to properties under the jurisdiction of TxDOT.

Figure 4: Flood Insurance Rate Map Excerpt

Project Corridor

Treadwell Bridge https://www.google.com/maps/place/31%C2%B056'04.1%22N+96%C2%B042'45.0%22W/@31.9344754,-96.7129103,213m/data=!3m1!1e3!4m5!3m4!1s0x0:0x0!8m2!3d31.934484!4d-96.712493

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6.3 AVAILABLE HYDROLOGIC DATA

There are no United States Geological Survey (USGS) stream gage stations within the immediate project limits. The closest stream gage is USGS 08063100 located on Richland Creek near Dawson, TX (USGS 2021).

The drainage area for this gage is 333 square miles, outside the range of comparison for the crossings along the project corridor, which span from 0.01 to 0.45 square miles.

6.4 REGRESSION EQUATION ESTIMATES

The regression equations presented in USGS Report 2019-5087 for the State of Texas is one method used to estimate design flows for the cross-route drainage structures along the corridor (Roussel 2009). The project limits are located in the Arkansas-Rio Grande-Texas-Gulf Hydrologic Region (Region 6). The equations developed for this region relate peak discharge to drainage area, using explanatory predictor variable (EPV) ranges of 0.1 to 9,329 square miles. The TxDOT Hydraulics Manual indicates that the regression equation method should not be used for drainage areas less than 1 square mile (Camille Thomason 2019). Due to this guidance, USGS flows were not used in the hydraulic design of this project.

6.5 RATIONAL METHOD ESTIMATES

The Rational Method was also used to estimate design flows. The TxDOT Hydraulic Design Manual indicates that the Rational method is appropriate for estimating peak discharges for basins up to approximately 200 acres with no significant flood storage. Of the six crossings along the corridor, the crossing at STA 30+55 was the only drainage area outside of this threshold. Due to the relatively close basin size (288 acres), and the desire to have a level basis of comparison across all cross-culverts, the Rational method was selected as the hydrologic method of choice for all basins evaluated.

Precipitation data was obtained from the National Oceanic and Atmospheric Administration Precipitation Frequency Data Server (NOAA 2011). Runoff coefficients of 0.29 – 0.39 were used to represent these undeveloped basins, which range from grassland/herbaceous to partially developed, with soils predominantly in hydrologic soil group D (Natural Resources Conservation Service 2015). Runoff coefficients were estimated in accordance with the computation methodology for rural watersheds described in Table 4-11, Runoff Coefficients for Rural Watersheds, of the TxDOT Hydraulics Manual (Camille Thomason 2019).

6.6 RECOMMENDED DESIGN DISCHARGES

FM-709 has been designated as a high-standard roadway for hydraulic design purposes. The design storm for this roadway designation is the 50-year event. An event of this magnitude has a 2% Annual Exceedance Probability (AEP). The Rational Method was used to compute design flows. Table 5 summarizes recommended design discharges for cross-route structures along the project corridor.

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Table 3: Hydrologic Summary

Crossing Station 30+55 67+80 96+80 113+30 137+65 176+30 Drainage Area (acres) 288 152 7.8 19 41 18

Drainage Area (sq. mi.) 0.45 0.24 0.01 0.03 0.06 0.03 Hydrologic Method Rational Rational Rational Rational Rational Rational

Runoff Coefficient (C) 0.33 0.36 0.36 0.33 0.39 0.29 2-Year Peak Flow (cfs) 164 90 6.3 23 39 13 5-Year Peak Flow (cfs) 203 111 7.8 28 48 16

10-Year Peak Flow (cfs) 236 129 9.1 33 56 18 25-Year Peak Flow (cfs) 282 154 11 39 67 22 50-Year Peak Flow (cfs) 320 174 12 44 76 24

100-Year Peak Flow (cfs) 356 195 14 49 84 27

7 HYDRAULIC ANALYSIS

7.1 HYDRAULIC MODEL DEVELOPMENT

Hydraulic performance was evaluated using HY-8 (Federal Highway Administration 2017). Site specific hydraulic models have been generated for the six cross-route culverts. Stability design was evaluated for all cross-route culverts using the results of the site specific HY-8 models in conjunction with the Hydraulics Toolbox (FHWA, Hydraulic Toolbox 2018).

Topographic Information was obtained from CFLHD site surveyed from March 2021. The geometric layout of the existing structures was derived from survey information collected by CFLHD. Geometric layout of proposed structures was derived from pipe plots provided by the roadway design group on 06/29/2022.

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

7.2 HYDRAULIC MODEL RESULTS

Based on the capacity standards established in this report, five of the six cross-route structures were found to be hydraulically adequate. These structures received on-site condition assessments to assess if replacement is warranted on the basis of existing condition. Hydraulically adequate structures found to be in satisfactory condition have been recommended for culvert extension. The structure found to be hydraulically inadequate is recommended for replacement. A summary of the hydraulic capacity design results is included as Appendix B, detailing information pertaining to both the existing and proposed configurations. HY-8 output reports have been included as Appendix E. Recommended riprap class and outlet apron dimensions are detailed in Appendix C. Outlet apron dimensions have been updated on a site-by-site basis in coordination with the roadway design discipline to account for local geometric constraints and right-of-way limitations.

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8 DITCH CAPACITY ANALYSIS

8.1 HYDROLOGIC INVESTIGATIONS

A supplemental analysis was conducted to evaluate ditch capacity. The increased width of the roadway, including the proposed side slopes, will result in impacts to the existing ditches. Hydrologic investigations were conducted along the left (LT) and right (RT) ditches for the entire project corridor. Using WMS (Aquaveo 2016), the Kirpich Method for overland flow on grassy earth was used to compute Time of Concentration. The Rational method was then used to generate the 10-year design flow at points of interest. Runoff coefficients were estimated using the suggested TxDOT Manual computation methodology for rural watersheds as described in Section 6.5.

A relationship was developed to interpolate estimated design flows at any point along either side of the proposed corridor. These relationships were used to estimate the 10-year runoff at each of the 51 parallel culverts along the corridor, as well as at mid-point and end-condition locations along each ditch segment.

Appendix D displays the resulting flows for the ditch lines and Appendix A displays the resulting flows at each of the parallel culvert locations.

8.2 HYDRAULIC MODEL DEVELOPMENT

Hydraulic investigations were conducted to estimate the area of flow that would be required to convey the 10-year capacity design flow. The longitudinal slope captured along the new proposed ditch line was extracted from the roadway design model as reported in Appendix D. A channel capacity analysis was then conducted using the Hydraulics Toolbox (FHWA, Hydraulic Toolbox 2018) to determine the required flow area.

8.3 HYDRAULIC MODEL RESULTS

The resulting flow area required to convey the 10-year design flow at midpoints and endpoints along each ditch flow segment is summarized in Appendix D. New ditches should provide the 10-year flow area measured below the bottom elevation of the aggregate base layer. In this way the resulting 10-year water surface elevation will be less than or equal to the bottom elevation of the proposed aggregate base layer, meeting the design criteria detailed in Table 2.

9 RECOMMENDATIONS

9.1 CROSS-ROUTE STRUCTURES

Of the six cross-route structures, 113+30 was the only structure found to be hydraulically inadequate and is recommended for replacement. Modeling indicates that the remaining five cross-route structures were found to be hydraulically adequate. As described in Section 5, on-site field investigations were conducted to determine if any of the hydraulically adequate structures warrant replacement on the basis of existing condition. Based on these findings, crossings at 30+55 and 96+80 are recommended for replacement. At the field review, TxDOT also requested that all DI crossings be replaced (96+80, 113+30, 137+65). The hydraulically adequate cross-route structures at 67+80 and 176+30 were found to be in satisfactory condition and are recommended to be extended to accommodate the widened roadway prism.

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At the onsite field visit, TxDOT and maintenance personnel indicated a preference to replace the crossing at 30+55 in kind (4-cell 4.5-ft. RCP). The existing structure is laid out with approximately 3-ft. between barrels, results in the crossing exceeding 20-ft. in length, as measured along the roadway centerline. A structure exceeding a 20-ft. threshold is considered a bridge class structure and may have additional requirements, such as regular inspection. However, FHWA-PD-95-001 provides an exception to this rule for multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening (FHWA 1995). In the event that it is identified that TxDOT has alternate requirements for bridge class structures and it is desirable to select a configuration that does not exceed a 20-ft. threshold, Appendix B provides an alternate structure opening, consisting of a 3-cell 5-ft. x 4-ft. CBC. Modeling indicates that both structures are hydraulically adequate at the 50-year capacity design event. Compared to the 3-cell CBC alternate, the proposed 4-cell RCP alternative provides slightly larger waterway area, lower headwater depths, and a higher overtopping flow, all of which are hydraulically desirable.

9.2 ROADSIDE DRAINAGE

9.2.1 Existing Parallel Structures

A total of 51 parallel culverts were identified along the project corridor. Appendix A provides recommended replacement sizes, upsizing to an 18-in. minimum parallel culvert size, or larger as required by the generalized inlet control analysis, or matching the existing size if the existing structure size exceeds both the 18-in. threshold and the size required for hydraulic capacity at the 10-year design event. At the request of TxDOT, it is recommended that all parallel culverts along the project be replaced with RCP.

9.2.2 Intersecting Roads without Parallel Structures

There are a number of intersecting roads and driveways that are not equipped with culverts (parallel to the project corridor). Cross-referencing the proposed ditch profile provided by the roadway design group, the majority of these locations are at crests, where ditch flow direction changes from one side of the embankment to the other. Three of these locations are believed to be currently operating as low water crossings (154+70, 165+50, 167+60), conveying relatively small ditch drainage. In collaboration with the roadway design discipline, it has been proposed that the resulting intersection match the existing low water crossing configuration. The following details summarize the intersecting roads and driveways that do not have parallel structures, their respective side of the project corridor (LT/RT), location (latitude/longitude), and drainage designation (crest/LWC):

o 58+40 (RT) - 31.913378°, -96.724997° - Crest o 58+35 (LT) - 31.913270°, -96.725248° - Crest o 82+40 (LT) - 31.918931°, -96.729467° - Crest o 97+10 (LT) - 31.922053°, -96.725940° - Crest o 99+70 (LT) - 31.922581°, -96.725358° - Crest o 116+10 (LT) - 31.925950°, -96.721836° - Crest o 140+80 (LT) - 31.931006°, -96.716505° - Crest o 141+00 (RT) - 31.930905°, -96.716325° - Crest o 154+70 (RT) - 31.933640°, -96.713270° - LWC o 165+50 (RT) - 31.935807°, -96.710860° - LWC o 167+60 (RT) - 31.936322°, -96.710504° - LWC o 197+60 (RT) - 31.943642°, -96.714944° - Crest

17 | Page TX FLAP FM 709(1) – Final Hydraulics Report

9.2.3 Roadside Ditches

New ditches are recommended to provide the 10-year flow area measured below the bottom elevation of the proposed aggregate base layer. In this way, the resulting 10-year WSE will be less than or equal to the bottom of the aggregate base layer. Appendix D displays the flow area required to convey the design flow at midpoints and endpoints along each ditch flow segment. The PDDM recommends a minimum longitudinal slope of 0.5% where possible, and a minimum of 1.0% is desired where practical (FLH 2012).

Grass lined ditches are present along the existing project corridor as shown in Figure 5. At the request of TxDOT, grass ditches are proposed for the majority of the project corridor. The exception are locations that have steep roadway cross-slopes or existing erosion issues. This condition occurs in the vicinity of the three largest cross-route structures (30+55, 67+80, 137+65). At the request of TxDOT and for economy of scale, riprap type 3 is recommended throughout the project corridor, including as a lining in these locations, which require slopes up to 1:1.5 (V:H). In locations where riprap enters the ditch flow line, TxDOT has requested a V shape ditch, with riprap on both sides to mitigate toe erosion.

Figure 5: Example Existing Ditch Line

18 | Page TX FLAP FM 709(1) – Final Hydraulics Report

9.3 ENTRANCE TREATMENT

9.3.1 Cross-Route Structures

A headwall entrance treatment is recommended to offset buoyant forces for structures exceeding a 48-inch diameter (FLH 2012). Headwalls and cutoff walls also serve to mitigate undermining (piping), which is known to lead to embankment failure. Headwalls with beveled edges are recommended to maximize hydraulic efficiency (FLH 2012). It is also desirable for structures in excess of 48-inches to be equipped with flared wingwalls, matched into the channel banks at the inlet and outlet, to smoothly transition flow and protect the structure and roadway approaches from erosion. Standard Detail C601-5, Concrete Headwall/Wingwall for Single Normal 42-inch to 84-inch Pipe Culvert is recommended to be included the plan set as a reference for the 30+55, 67+80, and 137+65 structures (FLH 2005). Locations in which right-of-way precludes the use of a flared wingwall configuration, wingwalls set square to the structure opening may be used. Flared end sections are the recommended end treatment for cross-route structures at or below the 48-inch threshold.

9.3.2 Parallel Structures

For all parallel structures, TxDOT has requested use of safety end treatments (SET), as illustrated in the TxDOT standard detail, Parallel Drainage for 12-inch to 72-inch diameter (SETP-PD), included in the TxDOT Bridge Standards online catalog (TxDOT 2021). This detail has been modified and included in the plan set as Special 602-B. As shown in this detail, SETs are not used for single barrel parallel pipes with diameters 30-in. or smaller. It is recommended that any parallel structure below this threshold be equipped with FES at inlet and outlet.

9.4 OUTLET PROTECTION

Culverts with diameters less than 48-inches and pipe slopes less than 10% can be sized in accordance with Standard Detail C251-50, Placed Riprap at Culverts (CFLHD 2015). However, at the request of TxDOT and for economy of scale, it is proposed that all riprap throughout the project corridor be class 3. Site-specific recommendations for minimum riprap class and outlet apron dimensions for all cross-route structures have been included in Appendix C. TxDOT has also indicated that they do not want any right of way acquisition at culvert outlets. Proposed outlet apron dimensions will need to be truncated to stay within existing right of way.

19 | Page TX FLAP FM 709(1) – Final Hydraulics Report

10 REFERENCES

Aquaveo. 2016. Watershed Modeling System (WMS). Software Version 10.1.11.

Camille Thomason, P.E. 2019. TxDOT Hydraulic Design Manual. September 12.

http://onlinemanuals.txdot.gov/txdotmanuals/hyd/manual_notice.htm.

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.

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

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

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

—. 1995. "Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges."

Department of Transportation, December. https://www.fhwa.dot.gov/bridge/mtguide.pdf.

FLH. 2012. "Project Development and Design Manual, Chapter 7 Hydrology and Hydraulics."

https://flh.fhwa.dot.gov/resources/design/pddm/.

FLH, Federal Lands Highway Division. 2005. "Concrete Headwall/Wingwall For Single Normal 42" to 84" Pipe Culvert." FLH Standard Drawings.

Natural Resources Conservation Service. 2015. Soil Survey Geographic (SSURGO) database. Fort Worth, TX. Accessed April 2019. http://websoilsurvey.nrcs.usda.gov.

NOAA. 2011. Precipitation Frequency Data Server. Silver Springs, MD. Accessed April 2019.

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

Roussel, William H. Asquith and Meghan C. 2009. Regression equationsfor estimationof annual peak-streamflow frequency for undeveloped watershedsinTexasusingan L-moment-based, PRESS-minimized, residual-adjustedapproach:. USGS, DOI, TxDOT.

TxDOT. 2021. "Texas Department of Transportation Bridge Standards." Austin, TX, December 17.

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

USGS. 2021. National Water Information System: Web Interface. 4 20.

https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=08063100.

A | Appendix TX FLAP FM 709(1) – Final Hydraulics Report

Appendix A

Parallel Structures

Appendix C - Parallel Structures TX FLAP FM 709(1) Navarro Mills Lake Access - Hydraulics Report

(diameter, in.) WWA (sq. ft.) 4 (diameter, in.) WWA (sq. ft.) 4 (diameter, in.) WWA (sq. ft.) 4 Structure Type 3 11+50 3.4 HY-8, Generalized Inlet Control Traditional 18 1.8 15 1.2 18 1.8 RCP 15+80 13 HY-8, Generalized Inlet Control Traditional 24 3.1 24 3.1 24 3.1 RCP 19+20 2.3 HY-8, Generalized Inlet Control Traditional 18 1.8 12 0.8 18 1.8 RCP 22+80 29 HY-8, Generalized Inlet Control Traditional Unknown Unknown 30 4.9 305 4.9 RCP 24+80 3.7 HY-8, Generalized Inlet Control Traditional 24 3.1 15 1.2 24 3.1 RCP 28+80 4.7 HY-8, Generalized Inlet Control Traditional 30 4.9 15 1.2 30 4.9 RCP 34+10 42 HY-8, Generalized Inlet Control Traditional 24 3.1 36 7.1 36 7.1 RCP 35+70 39 HY-8, Generalized Inlet Control Traditional 48 12.6 36 7.1 48 12.6 RCP 38+70 34 HY-8, Generalized Inlet Control Traditional 24 3.1 36 7.1 36 7.1 RCP 46+30 20 HY-8, Generalized Inlet Control Traditional 30 4.9 30 4.9 30 4.9 RCP 50+80 12 HY-8, Generalized Inlet Control Traditional 24 3.1 24 3.1 24 3.1 RCP 53+10 2.2 HY-8, Generalized Inlet Control Traditional 18 1.8 12 0.8 18 1.8 RCP 54+00 6.7 HY-8, Generalized Inlet Control Traditional 24 3.1 18 1.8 24 3.1 RCP 54+80 1.5 HY-8, Generalized Inlet Control Traditional 18 1.8 12 0.8 18 1.8 RCP 65+50 2.6 HY-8, Generalized Inlet Control Traditional 18 1.8 12 0.8 18 1.8 RCP 69+90 3.1 HY-8, Generalized Inlet Control Traditional 24 3.1 15 1.2 24 3.1 RCP 70+20 20 HY-8, Generalized Inlet Control Traditional 24 3.1 30 4.9 30 4.9 RCP 71+20 2.7 HY-8, Generalized Inlet Control Traditional 24 3.1 12 0.8 24 3.1 RCP 72+30 16 HY-8, Generalized Inlet Control Traditional 22 2.6 24 3.1 24 3.1 RCP 81+00 0.4 HY-8, Generalized Inlet Control Debris 18 1.8 24 3.1 24 3.1 RCP 81+80 0.2 HY-8, Generalized Inlet Control Traditional 18 1.8 8 0.3 18 1.8 RCP 89+70 1.6 HY-8, Generalized Inlet Control Traditional 30 4.9 12 0.8 30 4.9 RCP 90+40 1.7 HY-8, Generalized Inlet Control Traditional 30 4.9 12 0.8 30 4.9 RCP 91+10 1.9 HY-8, Generalized Inlet Control Traditional 30 4.9 12 0.8 30 4.9 RCP 92+00 2.1 HY-8, Generalized Inlet Control Traditional 24 3.1 12 0.8 24 3.1 RCP 93+00 2.3 HY-8, Generalized Inlet Control Traditional 24 3.1 12 0.8 24 3.1 RCP 93+60 2.4 HY-8, Generalized Inlet Control Traditional 24 3.1 12 0.8 24 3.1 RCP 94+30 2.6 HY-8, Generalized Inlet Control Traditional 28 4.3 12 0.8 30 4.9 RCP

100+60 0.9 HY-8, Generalized Inlet Control Traditional 18 1.8 8 0.3 18 1.8 RCP 107+00 2.8 HY-8, Generalized Inlet Control Traditional 12 0.8 12 0.8 18 1.8 RCP 110+80 13 HY-8, Generalized Inlet Control Traditional 15 1.2 24 3.1 24 3.1 RCP 114+20 0.6 HY-8, Generalized Inlet Control Traditional 15 1.2 8 0.3 18 1.8 RCP 115+20 5.2 HY-8, Generalized Inlet Control Traditional 15 1.2 18 1.8 18 1.8 RCP 124+00 5.0 HY-8, Generalized Inlet Control Traditional 24 3.1 18 1.8 24 3.1 RCP 124+60 16 HY-8, Generalized Inlet Control Traditional 22 2.6 24 3.1 24 3.1 RCP 127+50 20 HY-8, Generalized Inlet Control Traditional 24 3.1 30 4.9 30 4.9 RCP 132+50 26 HY-8, Generalized Inlet Control Traditional 36 7.1 30 4.9 36 7.1 RCP 149+10 13 HY-8, Generalized Inlet Control Traditional 18 1.8 24 3.1 24 3.1 RCP 149+60 3.2 HY-8, Generalized Inlet Control Traditional 18 1.8 15 1.2 18 1.8 RCP 150+50 3.4 HY-8, Generalized Inlet Control Traditional Unknown Unknown 15 1.2 185 1.2 RCP 152+20 3.9 HY-8, Generalized Inlet Control Traditional 18 1.8 15 1.2 18 1.8 RCP 153+40 4.2 HY-8, Generalized Inlet Control Traditional 18 1.8 15 1.2 18 1.8 RCP 160+00 1.6 HY-8, Generalized Inlet Control Traditional 12 0.8 12 0.8 18 1.8 RCP 163+60 10 HY-8, Generalized Inlet Control Traditional 24 3.1 24 3.1 24 3.1 RCP 169+20 5.6 HY-8, Generalized Inlet Control Traditional 18 1.8 18 1.8 18 1.8 RCP 169+50 5.4 HY-8, Generalized Inlet Control Traditional Unknown Unknown 18 1.8 185 1.8 RCP 173+30 2.3 HY-8, Generalized Inlet Control Traditional 12 0.8 12 0.8 18 1.8 RCP 179+20 5.6 HY-8, Generalized Inlet Control Traditional 32 5.6 18 1.8 30 4.9 RCP 201+30 0.7 HY-8, Generalized Inlet Control Traditional 12 0.8 8 0.3 18 1.8 RCP 202+50 0.4 HY-8, Generalized Inlet Control Traditional 12 0.8 8 0.3 18 1.8 RCP 204+90 0.6 HY-8, Generalized Inlet Control Traditional 18 1.8 8 0.3 18 1.8 RCP

1 - Based on a generalized inlet control HY-8 model for the 10-year capacity design flow using the specified HW/D approach and a projecting inlet configuration.

3 - At the preference of TXDOT and for economy of scale, all parallel culvert replacement structures are recommended to be composed of reinforced concrete pipe (RCP).

4 - Waterway opening area in square feet.

5 - CFL survey did not capture structure sizes for these crossings. Existing structure sizes will need to be field verified to ensure that the proposed structure size meets or exceeds the existing structure size.

Minimum Replacement Structure 2Crossing Station Hydraulic Model 10-Year Design

Flow (cfs) Existing Structure Opening

2 - Using the results of the required hydraulic opening column and upsizing meet the minimum 18-inch diameter replacement size requested by TXDOT for this project, or the existing structure size, whichever is larger.

Non-standard sizes have been rounded to the nearest standard size.

Minimum Hydraulic Opening 1HW/D Approach

B | Appendix TX FLAP FM 709(1) – Final Hydraulics Report

Appendix B

Capacity Design

Appendix B - Capacity Design TX FLAP FM 709(1) Navarro Mills Lake Access - Hydraulics Report

Span (in.) Depth (in.)

Existing 54 54 RCP, 4-Cell 64 Headwall 482.8 485.6 1.2 0.86 648 Yes Proposed 54 54 RCP, 4-Cell 64 Headwall 482.9 484.9 1.2 0.83 688 Yes

Proposed, Alternate 60 48 CBC, 3-Cell 60 Headwall 483.2 484.9 1.2 1.02 634 Yes Existing 60 36 CBC, 3-Cell 45 Headwall 505.9 508.6 1.2 0.88 406 Yes

Proposed 60 36 Existing 3-Cell CBC Extended 45 Headwall 506.0 508.2 1.2 0.88 442 Yes Existing 24 24 RCP 3.1 Mitered 511.4 511.9 1.5 0.99 18 Yes

Proposed 24 24 RCP 3.1 Mitered 510.6 512.7 1.5 0.99 26 Yes Existing 30 30 RCP 4.9 Mitered 496.5 496.0 1.5 1.28 24 No

Proposed 42 42 RCP 9.6 Mitered 494.0 495.3 1.5 0.91 86 Yes Existing 54 54 RCP 16 Mitered 470.2 471.3 1.2 0.89 118 Yes

Proposed 48 48 CBC 16 Headwall 469.0 470.6 1.5 0.94 154 Yes Existing 30 30 RCP 4.9 Mitered 454.8 455.1 1.5 1.10 29 Yes

Proposed 30 30 Existing RCP Extended 4.9 Mitered 454.8 455.8 1.5 1.08 34 Yes

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.

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

113+30 44

30+55 320

Meets Capacity Design Criteria?

Structure Type Model Inlet

Configuration 1

Design Flow (50-Year, cfs)

Structure Size AHW Elevation (ft.)2

67+80 174

Hydraulic Model Evaluated

Waterway Area

(sq. ft.)

Headwater Elevation

(50-Year, ft.)

Target HW/D Ratio

HW/D Ratio Overtopping

Flow (cfs)

137+65 76

176+30 24

96+80

Crossing Station

C | Appendix TX FLAP FM 709(1) – Final Hydraulics Report

Appendix C

Stability Design

Appendix C - Stability Design TX FLAP FM 709(1) Navarro Mills Lake Access - Hydraulics Report

Span (in.) Depth (in.) Riprap Class4 Apron Length

(ft.)

Apron

Thickness (ft.)

Apron End Width (ft.)

30+555 320 60 48 RCP, 4-Cell Headwall 479.1 478.6 50.6 1.0% 2 20.0 3.0 23.5

67+80 174 60 36 Existing 3-Cell CBC Extended

Headwall 503.4 502.4 48.5 2.0% 1 17.5 2.0 20.5

96+80 12 24 24 RCP FES 508.6 507.5 45.4 2.4% 1 8.0 2.0 9.5

113+30 44 42 42 RCP FES 490.8 490.0 42.0 1.9% 2 14.0 3.0 16.5

137+65 76 48 48 CBC Headwall 465.3 464.0 54.0 2.4% 3 20.0 2.5 21.5

176+30 24 30 30 Existing RCP

Extended

FES 452.1 451.7 61.3 0.8% 1 10 2.0 12.5

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 - Geometric layout has been derived from structure profiles provided by the roadway design on 06/29/2022.

3 - Based on a stability design analysis of the hydraulic models for each crossing. At the preference of TXDOT, riprap layout will be modified to stay within existing right-of-way.

4 - At the preference of TXDOT and for economy of scale, riprap class 3 has been selected to be used for outlet protection throughout the project corridor.

5 - The outlet protection size and configuration provided for this crossing is sufficient for both this structure and the alternate structure provided in Appendix D (3-Cell 5-ft. x 4-ft. CBC).

Recommended Outlet Protection3Design Flow (50- Year, cfs)

Proposed Structure Type

Crossing Station Inlet Invert

Elevation (ft.)1

Outlet Invert Elevation (ft.)1

Projected Structure

Length (ft.)2

Structure Slope Proposed Structure Size

End Treatment

D | Appendix TX FLAP FM 709(1) – Final Hydraulics Report

Appendix D

Ditch Capacity

Appendix D - Ditch Capacity TX FLAP FM 709(1) Navarro Mills Lake Access - Hydraulics Report

Begin Condition Input STA Long. Slope (ft/ft) STA Flow (cfs) Flow Area (SF) STA Flow (cfs) Flow Area (SF)

1L 1000 0.0102 2028 23.1 6.0 3055 46.1 10.1 2L 5830 0.0135 4455 23.5 5.5 3080 48.0 9.4 3L 5830 0.0142 6305 12.9 3.4 6780 26.0 5.8 4L 8145 0.0129 7468 12.0 3.4 6790 24.4 5.7 5L 8145 0.0051 8183 0.2 0.2 8220 0.4 0.4 6L 8300 0.0099 8260 0.2 0.2 8220 0.4 0.3 7L 8300 0.0094 8993 1.6 0.8 9685 3.1 1.4 8L 9980 0.0271 9833 0.7 0.3 9685 1.3 0.5 9L 9980 0.0161 10655 2.6 1.0 11330 4.8 1.6

10L 11630 0.0180 11480 0.7 0.4 11330 1.4 0.6 11L 11630 0.0134 12698 6.8 2.2 13765 13.1 3.5 12L 14080 0.0093 13923 0.8 0.5 13765 1.5 0.8 13L 14080 0.0322 14960 3.1 0.9 15840 5.6 1.4 14L 17510 0.0210 16695 7.4 2.0 15880 14.0 3.2 15L 17510 0.0050 17570 0.3 0.3 17630 0.6 0.5 16L 20400 0.0048 19015 2.7 1.6 17630 6.3 3.0 17L 20400 0.0072 20490 0.6 0.4 20580 2.1 1.1

Begin Condition Input STA Long. Slope (ft/ft) STA Flow (cfs) Flow Area (SF) STA Flow (cfs) Flow Area (SF)

1R 1000 0.0109 2028 2.6 1.1 3055 5.2 1.9 2R 5830 0.0132 4455 6.1 2.0 3080 12.2 3.4 3R 5830 0.0132 6305 1.8 0.8 6780 3.4 1.3 4R 8130 0.0130 7460 1.8 0.8 6790 3.6 1.4 5R 8130 0.0078 8908 4.7 2.0 9685 9.7 3.5 6R 9685 0.0176 9820 0.7 0.4 9955 1.3 0.6 7R 9955 0.0153 10643 7.9 2.3 11330 16.0 3.9 8R 11535 0.0085 11433 0.5 0.4 11330 1.0 0.6 9R 11535 0.0137 12650 18.5 4.6 13765 31.7 6.8

10R 14100 0.0173 13933 0.8 0.4 13765 1.6 0.7 11R 14100 0.0339 14970 14.0 2.6 15840 27.6 4.4 12R 17630 0.0207 16755 0.9 0.4 15880 1.7 0.7 13R 19760 0.0055 18695 7.6 3.3 17630 16.0 5.8 14R 19760 0.0011 20140 3.8 3.6 20520 7.9 6.2

Left Ditch

Midpoint Area Condition End Area Condition

End Area ConditionMidpoint Area Condition Ditch Segment

Ditch Segment

Right Ditch

E | Appendix TX FLAP FM 709(1) – Final Hydraulics Report

Appendix E

HY-8 Output Reports

30+55 HY-8 Culvert Analysis Report

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 164 cfs

Design Flow: 320 cfs

Maximum Flow: 356 cfs

Table 1 - Summary of Culvert Flows at Crossing: Existing

Headwater Elevation (ft)

Total Discharge

(cfs)

30+55 Discharge

(cfs)

30+65 Discharge

(cfs)

30+70 Discharge

(cfs)

30+75 Discharge

(cfs)

Roadway Discharge

(cfs) Iterations

481.41 164.00 36.85 39.12 49.27 38.73 0.00 4

481.60 183.20 41.41 43.84 54.51 43.43 0.00 4

481.78 202.40 46.02 48.55 59.70 48.12 0.00 4

481.95 221.60 50.62 53.26 64.82 52.81 0.00 3

482.12 240.80 55.27 58.01 69.93 57.55 0.00 3

482.28 260.00 59.95 62.78 74.95 62.30 0.00 3

482.43 279.20 64.66 67.56 79.90 67.07 0.00 3

482.59 298.40 69.40 72.36 84.78 71.86 0.00 2

482.76 320.00 74.76 77.77 90.20 77.27 0.00 3

482.89 336.80 78.97 81.99 94.36 81.48 0.00 3

483.05 356.00 83.82 86.82 99.05 86.32 0.00 3

485.90 647.51 158.57 160.50 168.27 160.17 0.00 Overtopping

Rating Curve Plot for Crossing: Existing

Table 2 - Culvert Summary Table: 30+55

Straight Culvert

Inlet Elevation (invert): 479.00 ft, Outlet Elevation (invert): 478.23 ft

Culvert Length: 42.09 ft, Culvert Slope: 0.0183

Total Discharg e (cfs) Culvert

Discharg e (cfs)

Headwat er

Elevatio n (ft)

Inlet Control Depth

(ft)

Outlet Control Depth

(ft) Flow Type

Norm…