Hydraulics_NM_FTFS_107(1)_Mingus_Mountain.pdf

Subject: Lincoln National Forest, Hydraulics Recommendations

Date: September 28, 2018

Project Number: NM FTFS 107(1) Mingus Mountain

From: Brian Campbell, P.E.

Hydraulics Engineer FHWA Central Federal Lands Lakewood, CO

To: Justin Henwood

Project Manager FHWA Central Federal Lands Lakewood, CO

Summary The following report summarizes hydraulic recommendations for NM FTFS 107(1) Mingus Mountain. The project includes hydraulic investigation for the inclusion of 3 drainage crossings over the Bonito Creek.

Project Location and Description The project is located in Lincoln County near Ruidoso, New Mexico. The purpose of the project is to realign NFSR 107 onto Forest Service Land to permanently bypass Runnels Ranch property. Currently, the Forest Service has an easement through Runnels Ranch, but continued issues with access through Runnels property have necessitated the consideration of other options. The proposed project would realign NFSR 107 across Bonito Creek approximately 0.5 miles east of Runnels Ranch. Approximately 0.5 miles of at‐grade, access road would be upgraded to design standards, while an additional 0.25 miles of new alignment would be constructed. Another crossing of Bonito Creek, approximately 0.25 miles west of Runnels Ranch, would realign the proposed route with the existing alignment of NFSR 107. Additionally, the Big Bear Creek tributary just south of Runnels Ranch would require a water crossing.

Figure 1: Location Map

Project Location

Figure 2: Location Map. The proposed roadway alignment is shown.

Runnels Ranch

Big Bear Crossing

Upper Crossing

Runnels Ranch

Lower Crossing

Proposed Alignment

Proposed Alignment

Hydraulic Design Standards Roadway Classifications The roadway is designated as a low standard road with a design ADT of 350.

Chapter 7 of the Project Development and Design Manual (PDDM) published by the FHWA (2012) provides guidance for sizing drainage facilities on low standard road. The following standards are applied to this project:

- FEMA

o Two of the culverts on the project are in a FEMA Zone A. Area Zone A does not have a detailed study associated with it to identify the base flood elevation. Any improvements in the project within the FEMA Zone A limits will not exceed a 1-foot rise in the 100-year flood elevation. This is based on existing and proposed project water surface models.

- Culverts o Culverts will convey runoff from the 25-year flood o The maximum Headwater to Diameter Ratio (HW/D) is 1.5 for culverts equal to or less than 48 inches and 1.2 for culverts greater than 48 inches o The minimum culvert diameter is 24 inches

- Environmental o Culverts will meet criteria for fish passage design as outlined in FHWA HEC 26 Culvert Design for Aquatic

Organism Passage

Hydrologic Analysis and Peak Flow Estimates In June of 2012, the Little Bear Fire burned approximately 35,300 acres of the Lincoln National Forest. Although post fire hydrology can be much larger than pre fire hydrology, the majority of the drainage basins contributing to the project area are in a “Low Severity” burn zone as outlined in BAER, 2012, see Figure 3. The duration the burned area will be impacted by post fire hydrology has not been quantified. However, low severity areas are anticipated to recover more quickly. By the time this project is complete (anticipated 2019) the area will have been recovering for 7 years.

For the reasons listed above, as well as low ADT and low standard road designation, pre fire hydrology was used to size the crossing structures.

Figure 3: Burn Severity Map, BAER 2012

The Watershed Modeling System (WMS vs 10.1) was used to delineate drainage areas from the tributaries. Drainage areas are shown in Figure 4. The Bonito Creek is un-gaged in the project limits. The nearest gage is located approximately 2.5 miles downstream at the outlet of the Bonito Lake Reservoir. The reservoir is operated by the City of Alamogordo, NM. However, the values reflected in the gage data are a function of the reservoir release operations and are not directly representative of flood flow events. Traditional statistical flood flow frequency analysis (Log Pearson III) cannot be performed to calculated design storm runoff values using this gage. Per Bulletin 17B, “The procedures do not cover watersheds where flood flows are appreciably altered by reservoir regulation… The guide was specifically developed for the treatment of annual flood peak discharge.”

The most recent New Mexico regional regression equations for the Southeast Mountain Flood Region (3) from USGS 2008 were used to calculate peak flood-frequency values for tributary areas. The regional regression equations for storm return periods are listed in Table 1. A summary of the computed flows in Table 2.

AOP Hydrology Fish passage hydrology can be defined as High and Low flows. High flows (QH), represents the upper bound of discharge at which fish are believed to be moving within the stream, while Low flows (QL) is the lowest discharge for which fish passage is required. QH and QL are not defined in the same manner throughout the country. The New Mexico region guidelines in Table 5.1 of HEC 26, outlines the for identifying fish passage high flows (QH) to analyze fish passage. Per Table 5.1, QH can be estimated as either 1% of the annual exceedance flow or 50% of the 2-year return flow. The QH was based on 50% of the 2-year return flow since gage data does not exist to prepare an exceedance curve.

The culverts will be designed to maintain similar hydraulic parameters associated with the QH fish passage hydrology in the stream.

Project Area: Majority in Low Severity Region

Table 1: Regional Regression Equations for Southeast Mountain Flood Region (3), USGS 2008

Figure 4: Drainage Areas

Table 2: Summary of Peak Flow Estimates

Area (mi²)

QH Fish Passage (cfs)

Q2 (cfs)

Q5 (cfs)

Q10 (cfs)

Q25 (cfs)

Q50 (cfs)

Q100 (cfs)

Downstream Bonito Creek

15.72 61 122 246 353 526 683 865

Upstream Bonito Creek 7.86 38 77 149 208 300 380 470

Bear Creek 3.06 22 44 82 111 154 189 227

Downstream Bonito Creek

Upstream Bonito Creek

Big Bear Creek

North

Hydraulic Analysis

Model Development The proposed condition contains unique split-flow runoff patterns where the new alignment crosses Bonito Creek to the west. In this particular case, portions of the flow went through the culvert and portions of flow went to the east down a roadside ditch to another crossing, and portions of flow overtopped the roadway, see Figure 6. This type of split-flow condition at a hydraulic structure is challenging to model in a 1 dimensional (1D) hydraulic model and introduces uncertainty.

A 2 dimensional (2D) hydraulic model was determined to be a more appropriate method to model the project limits.

The existing and proposed condition models were created using SRH-2D and Aquaveo’s SMS vs 12.2.12 2D software.

The 2D model was able to capture and quantify the split flow condition of the area of interest and remove the uncertainty associated with a 1D model with the site.

The surveying and mapping data used for the hydraulic analyses are based on LIDAR data collected by the Forest in 2013. The LIDAR data was provided in UTM Zone 13, NAD 83, and meters. SMS was used to re-project the surface to State Plane New Mexico Central, NAD 83, and feet. The re-projected system was checked with field survey data collected in 2017.

Manning’s n-values for the main channel, vegetated overbank, and grass overbank were 0.07, 0.08, and 0.043 respectively. These values represent the predominately gravel and cobble main channel with vegetated banks, heavily vegetated overbank in areas, and the relatively wide open floodplain grass overbank in areas. The values are consistent with stream headwaters in steep mountain streams and slightly larger than the 2009 FEMA effective Flood Insurance Study (FIS) of the Bonito Creek much further downstream where it becomes the Rio Bonito.

Culvert Hydraulics The hydraulic design standards pertaining to the 25-year design capacity and the FEMA floodplain requirements controlled the selection of culvert type, size, and placement of the culvert structures.

Culvert types reviewed included arch CMP and concrete box culverts structures. Early during the modeling process, it was clear the structures needed to operate under weir flow conditions (roadway overtopping) during the 100-year event to meet the FEMA Zone A criteria and minimize structure costs. To value engineer the most cost efficient solution, multiple model iterations were calculated to maximize the efficiency of the weir action over the structure to meet FEMA Zona A criterial and minimize the size of the structure to meet the 25-year capacity criteria. The solution required the structure be built with the top of structure acting as the driving surface. This approach led the design team to select reinforce concrete box structures as the culvert type.

Table 3 is a summary of the culvert hydraulic analysis. The selected structures meet all hydraulic design standards for the project. Figure 5 and figure 6 are an output from the 2D hydraulic model for the 25-year event. All three culvert crossings convey the flow from the 25-year event without overtopping the roadway.

Table 3: Summary of Culvert Hydraulic Analysis

Structure Location Concrete Box Structure Dimensions (ft)

*Inlet Invert Elevation (ft)

*Outlet Invert Elevation (ft)

25-year Design Capacity (cfs)

**HW/D ratio (25-year Design)

Upper Bonito Creek

12H x 6V 7711.4 7710.8 300 1.00

Big Bear Creek 10H x 6V 7699.6 7698.9 154 0.75

Lower Bonito Creek

12H x 8V 7638.4 7638.1 526 1.04

*2-foot embedment of the culvert invert is needed to meet AOP requirements.

**The low HW/D ratio for the 25-year design is due to meeting the FEMA Zone A requirements for the 100-year design. The HW/D ratio meets the design standard.

Figure 5: Output from the 2D hydraulic model for the 25-year event for the Lower crossing. The crossing passes flow from the 25-year event without overtopping the roadway.

Figure 6: Output from the 2D hydraulic model for the 25-year event for the Upper and Big Bear crossings. The crossings pass flow from the 25-year event without overtopping the roadway.

Floodplain Analysis FEMA FIRM Panel 35027C1875D issued November 16,2011 illustrates two of the proposed crossings within the project limits (Upper and Lower Crossings) are within a Zone A. FEMA Zone A floodplains include approximate floodplain footprints where a previous base flood elevation has not been established. No depths or base flood elevations are shown within these zones because no detailed analysis has been performed. Figure 7 shows the FIRM obtained from the FEMA website.

A FEMA Zone A floodplain requires any development in the floodplain to be designed so the resulting rise in the 100-year water surface elevation is limited to 1 foot or less. Because an existing hydraulic model of the project limits did not exist, an existing condition and proposed condition hydraulic model needed to be created to verify the requirements are met.

Multiple cross sections were analyzed upstream and downstream of the Upper and Lower Crossings for both the existing and proposed condition. For both structures, the difference in water surface elevation is less than 1 ft, see Table 4 and Table 5.

Split Flow Condition

Figure 7: FEMA FIRM Panel 35027C1875D showing proposed location in Zone A Floodplain

Lower Crossing Discussion The comparison of the existing and proposed condition is shown between Figure 8 and Figure 9 in plan view. A minor culvert structure (24” CMP) not modeled is shown in Figure 9 and is included in the design. This minor structure provides relief to the north west corner of the proposed alignment during the 100-year return period as the proposed alignment departs from the existing roadway.

The comparison of the existing and proposed condition is shown in Figure 10 in profile view. Note: Figure 10 is an exaggerated vertical scale for visual comparison. Table 4 shows the calculated difference in water surface elevation.

Lower Crossing

Upper Crossing

Figure 8: Lower Crossing 100-year return floodplain footprint for the existing condition.

Figure 9: Lower Crossing 100-year return floodplain footprint for the proposed condition. A minor culvert structure (24” CMP), not shown, is included in the design. This minor structure provides relief to the north west corner of the proposed alignment.

Minor (24” CMP) not shown in model

Figure 10: Lower Crossing 100-year return water surface elevation profile comparison for the existing and proposed condition. Note: The scale is exaggerated vertical scale for visual comparison.

Table 4: Lower Crossing 100-year return existing and proposed condition water surface elevation comparison

X section Station Proposed WSE (ft) Existing WSE (ft) Difference < 1.00'

79 7647.93 7647.31 0.63

90 7647.84 7647.06 0.78

98 7647.51 7646.83 0.69

108 7646.09 7646.59 -0.50

Upper Crossing Discussion The comparison of the existing and proposed condition is shown between Figure 10 and Figure 11 in plan view. A minor culvert structure (24” CMP) not modeled is shown in Figure 11 and is included in the design. This minor structure provides relief to the south corner of the proposed alignment during the 100-year return period.

The comparison of the existing and proposed condition is shown in Figure 12 in profile view. Note: Figure 12 is an exaggerated vertical scale for visual comparison. Table 5 shows the calculated difference in water surface elevation.

Proposed 100-year return WSE

Existing 100-year return

WSE

Figure 11: Upper Crossing 100-year return floodplain footprint for the existing condition.

Figure 12: Upper Crossing 100-year return floodplain footprint for the proposed condition. A minor culvert structure (24” CMP), not shown, is included in the design. This minor structure provides relief to the south of the proposed alignment.

Minor (24” CMP) not shown in model

Figure 13: Upper Crossing 100-year return water surface elevation profile comparison for the existing and proposed condition. Note: The scale is exaggerated vertical scale for visual comparison.

Table 5: Upper Crossing 100-year return existing and proposed condition water surface elevation comparison

X section Station Proposed WSE (ft) Existing WSE (ft) Difference < 1.00'

53 7718.79 7718.22 0.57

63 7718.71 7718.04 0.67

70 7718.64 7717.91 0.73

79 7718.52 7717.75 0.78

87 7718.34 7717.61 0.74

90 7718.23 7717.52 0.71

102 7717.49 7717.17 0.32

Culvert Outlet Protection

Methods outlined in FHWA Hydraulic Engineering Circular 14 (HEC 14) were used to determine the need and size for outlet protection for all 3 proposed culverts. Per HEC 14, “If the outlet velocity is substantially higher from the downstream condition, the designer should evaluate energy dissipators. Definition of the terms “approximately equal,” “moderately higher,” and “substantially higher” is relative to site-specific concerns such as sensitivity of the site and the consequences of failure. However, as rough guidelines that should be re-evaluated on a site-specific basis, the ranges of less than 10 percent, between 10 and 30 percent, and greater than 30 percent, respectively, may be used.”

An analysis of the outlet velocity for each site for the 25-year return period is shown in Table 6.

Proposed 100-year return WSE

Existing 100-year return

WSE

Table 6: Culvert Outlet Armor

Culvert Location

At Culvert Outlet Difference at Culvert Outlet (%)

Downstream Distance Downstream Distance (ft)

D50 Fletcher and Grace (Equation D.5) (ft)

D50

Proposed Condition (ft/s)

Existing Condition (ft/s)

Proposed Condition (ft/s)

Existing Condition (ft/s)

Upper Crossing

7.3 4.2 75 4.7 5.1 30 0.72 Class 3

Big Bear 6.2 4.9 30 4.3 4.7 15 0.87 Class 3

Lower

9.4 6.7 40 7.4 6.7 10 0.44 Class 3

The difference in the culvert outlet velocity and the natural channel condition suggests armoring is needed.

However, a hydraulic jump is present from the culvert outlet to varying distances downstream. The hydraulic jump effectively dissipates energy within the jump envelope. A comparison of velocities at the listed distances show the proposed condition and existing condition are nearly the same. A riprap apron is suggested to be installed to protect the outlet bed material within the limits of the hydraulic jump for each condition.

Using Equation D.5 in HEC 14 (Fletcher and Grace 1972), and approximate D50 was calculated for each site.

The value was rounded up to a D50 of 1.00 ft for each site which is consistent with a Class 3.

AOP Hydraulic Analysis Figure 14 summarizes the design process for the HEC-26 AOP procedure.

Figure 14: Design flow chart for HEC-26 AOP procedure

Table 7 summarizes the existing and proposed condition velocity upstream of the culvert, within the culvert envelope, and downstream of the culvert for the QH return period.

Table 7: Velocity comparisons for key locations for all 3 proposed locations for QH return period

Culvert Location

Upstream Cross Section Culvert Cross Section Downstream Cross Section

Existing Condition (ft/s)

Proposed Condition (ft/s)

Existing Condition (ft/s)

Proposed Condition (ft/s)

Existing Condition (ft/s)

Proposed Condition (ft/s)

Upper Crossing

3.6 3.6 3.6 3.4 3.7 3.4

Big Bear 2.9 3.0 3.3 3.1 3.3 2.8

Lower

3.3 3.5 3.7 3.4 3.5 2.9

Upstream of Big Bear and the Upstream Crossing, the proposed condition produces slightly larger velocities in the channel. This slight increase is not cross section wide and is isolated to areas near the culvert ends where accelerated flow is anticipated. These values are within the limits of the maximum natural velocity in the channel in areas downstream. This slight increase is not considered a barrier and will not impede fish passage.

The calculated velocity values for the proposed area within the culvert envelope and downstream of the culvert are less than the calculated velocity values for the existing condition. This is likely due to an increased roughness section within the box due to the design of stable bed material within the structure for the 25-year return event.

The proposed culverts are not a barrier for the QH flow condition.

The computed stable bed material size for the 25-year return event within the culvert was similar to the D50 size in column 8 of Table 6. Similar to the outlet protection, the values were rounded up to meet the specification of a Class 3 riprap.

References Aquaveo (2016) “Watershed Modeling System (WMS)” Software version 10.1.11

Federal Highway Administration (FHWA)(2016) “Hydraulic Toolbox” Software Version 4.3

Federal Highway Administration (FHWA)(2016) “HY-8” Software Version 7.4

Federal Highway Administration HEC-26, Culvert Design for Aquatic Organism Passage, October 2010

Federal Highway Administration HEC-14, Hydraulic Design of Energy Dissipators for Culverts and Channels, July 2006

Federal Highway Administration (FHWA)(2012) “Project Development and Design Manual” Chp. 7.

Hydrology and Hydraulics. Federal Lands Highway Division. Federal Highway Administration. Dept. of Transportation. Washington, DC.

US Forest Service (USFS)(2012) “Little Bear Fire BAER Resource Report”

Waltemeyer, S.D., 2008, Analysis of the magnitude and frequency of peak discharge and maximum observed peak discharge in New Mexico and surrounding areas: U.S. Geological Survey Scientific Investigations Report 2008–5119, 105 p.