A04 Attachment 3 Big Bonito Design Report Final_20200527.pdf

Design Report Final

Big Bonito Creek Fish Barrier US Fish and Wildlife Service

Arizona Fisheries Resource Office

Natural Channel Design, Inc.

2900 N. West St., Suite 5 Flagstaff, AZ 86004

May 2020

Design Report

Big Bonito Fish Barrier

United States Fish and Wildlife Service

Submitted to:

US Fish and Wildlife Service

Arizona Fish and Wildlife Conservation Office

Point of Contact:

Zachary Jackson zachary_jackson@fws.gov

May 2020

Prepared by:

Natural Channel Design, Inc.

2900 N. West St., Suite 5 Flagstaff, AZ 86004

Big Bonito Creek Fish Barrier Design Report

Natural Channel Design, Inc. ii May 2020 Flagstaff, Arizona

TABLE OF CONTENTS

Table of Contents .......................................................................................................................................... ii

List of Figures ........................................................................................................................................... ii List of Tables ............................................................................................................................................ ii Attachments .............................................................................................................................................. ii

Project Description Design Approach

Fish Jumping Ability Watershed and Hydrology Barrier Geometry and Flow Characteristics HEC-RAS Analysis Barrier Design Data Construction Considerations Bid Tab

References

LIST OF FIGURES

Figure 1. Site Map of Big Bonito Creek Fish Barrier Figure 2. Jump trajectory at 13.5 feet per second Figure 3. Jump height vs. tailwater velocity Figure 4. Big Bonito Watershed Figure 5. Flow geometry for a straight drop spillway structure (FHA 2006) Figure 6. Key elevations in tail water at design discharge Figure 7. HEC-RAS Profile of design discharge over the barrier Figure 8. HEC-RAS model of Velocities on tailwater apron Figure 9. Barrier Cross-Section Geometry Figure 10. Rock Outlet Structure Plan and Profile Figure 11. Construction Access and Impoundment Figure 12. Big Bonito Fish Barrier potential material borrow pits Figure 13. Big Bonito Fish Barrier construction limits

LIST OF TABLES

Table 1. Barrier Geometry and Flow Characteristics Table 2. Bid Tab

ATTACHMENTS

Attachment 1. Big Bonito Creek Fish Barrier, Geotechnical Evaluation Report, Western Technologies Attachment 2. Big Bonito Creek Fish Barrier, Final Plans Attachment 3. Big Bonito Creek Fish Barrier, HEC-RAS Analysis Q50, Q100 and Existing Condition

Natural Channel Design, Inc. 1 May 2020

PROJECT DESCRIPTION

This design report provides a brief description of the project need, proposed solution, and methodology used to design a fish barrier on Big Bonito Creek on White Mountain Apache tribal lands. The conservation of native fish species and their habitat is a top priority for the Arizona Fish & Wildlife Conservation Office (AZFWCO). Objectives for Apache Trout recovery include the establishment and maintenance of 30 self-sustaining populations. The AZFWCO conducted a fish count recently and found Brown trout upstream of the Big Bonito Fish Barrier, indicating the existing fish barrier on Big Bonito Creek provides inadequate protection for Apache trout (Oncorhynchus apache) from invasive Brown trout (Salmo trutta) and Rainbow trout (Oncorhynchus mykiss).

In 2010, Natural Channel Design (NCD) assessed efficacy of several barriers for the White Mountain Apache Tribe. The Big Bonito Creek barrier was reviewed at that time. NCD found that the structure, grout capped gabion baskets, is an ineffective jump height barrier. In addition, the gabion basket construction allowed fish passage when the internal rock was not stacked properly, allowing gaps between the rocks.

Second, there was no adequate footing, allowing the basket structure to slump on what appeared to be relatively fine-grained wetland soils, causing leakage under the structure and likely allowing fish passage.

At the time NCD recommended removal of the failing apron, increasing the height by at least 2 ft and installing a new 30-foot apron. The site of the existing barrier is a wide plane, not ideal to place a high barrier structure, as the valley side slopes are over 150-feet apart. The barrier ends were tied to the existing road prism, which would lead to water backing against the prism during periods when the stream flow exceeded barrier capacity.

During a previous site visit with USFWS personnel, the proposed fish barrier site was found approximately 300 yards downstream of the road crossing in a relatively narrow section of stream valley, pinched off by basalt bedrock on either side of the stream and in the stream bottom.

A site visit was made on October 28, 2019 to survey the proposed barrier site and perform geotechnical testing (see attachment 1: Geotechnical Report).

Figure 1. Site Map of Big Bonito Creek Fish Barrier

Natural Channel Design, Inc. 2 May 2020

DESIGN APPROACH

At AZFWCO direction the fish barrier design is based on a 50-year design storm, with an expected design life of 50 years. An effective fish barrier must either provide a velocity barrier, or a jump height barrier. At the project location, a jump height barrier was chosen as the stream width is naturally pinched by the basalt bedrock, and provides a site where barrier height up toa 50-year storm event can keep invasive species from jumping upstream. The design height is based on maintaining a minimum jump height of 4.2 feet (2.8 of assumed jumping ability plus 1.4 feet of fish length, or a safety factor of 1.5) even when downstream conditions during high flows increase tailwater pool height (below the weir). The jump height is measured from the top of the downstream surface of the tailwater to the bottom of flows over the barrier. A factor of safety is also calculated to judge barrier height efficacy (actual jump height / 2.8). This factor of safety is incorporated to account for environmental and biologic variation (fish length, etc.) Previous studies in Arizona have indicate that the minimum factor of safety of 1.3 is required. The rationale for these parameters has been provided in previous barrier assessment studies (NCD 2009, NCD 2010) and are highlighted in the next sections. These parameters are based on the hypothesis that fish jumping ability is based on ballistics and swimming speed, while jump height changes with tailwater stage at various stream flows. Consequently, stream hydrology, barrier hydraulics and jumping ability are modeled simultaneously. While jump height calculations are based on assumption of near zero velocity somewhere in the tailwater, the barrier design also includes a ramped tail water design to ensure that tailwater velocities are uniformly high and help to prevent efficient jumping. This tailwater velocity barrier will provide an additional measure of safety to prevent fish passage.

FISH JUMPING ABILITY

Fish jumping ability was estimated using a ballistic equation after Bell (1991). Jump height varies as a function of relative velocity at the time the fish leaves the water and angle of attack. Relative velocity is based on maximum burst swim velocity minus the water velocity. Adequate depth for jumping is also required but is often not limiting (>0.5 ft). For the purposes of this design it is assumed that fish will always have a suitable depth to jump from. Bell (1991) suggests adding the length of the fish to the jump height to accommodate continued propulsion until the fish’s tail has left the water. While adding the length of fish to estimate jump height is recommended, it is problematic to estimate fish length over the many different populations. Instead, focus was on estimating maximum burst velocity for the largest fish in the population, and then calculating a factor of safety which can incorporate fish body length.

Maximum velocity for burst speed used in this report is 13.5 feet per second (fps) for full-sized adult Rainbow trout; Brown trout is slightly less (13 fps). Estimating reasonable burst speeds is critical to the calculation of barrier height, but problematic. Several authors have compiled information on trout swimming performance and many references are available in the literature dealing with fish passage.

However, many of these estimates come from laboratory experiments, utilizing caged fish. Estimates of burst swimming or jump height for wild, motivated trout are not available. The approach utilized herein is a consensus of literature and experts to come up with a narrower range of values that was compared to known successful jumps over barriers. Swimming performance was back-calculated using trajectory formulas, size of fish, and barrier conditions at the time of the barrier attainment.

Field calibration of the minimum swimming ability for local salmonids came from analysis of barrier breaches at Conklin Creek. The Conklin Creek Fish Barrier project is a retrofitted barrier off the FR 25 on the Apache-Sitgreaves National Forest. The old barrier consisted of a long culvert, concrete pad with a 4 ft long perforated grate at the end and a 2 foot jump (at base flow) onto the supposedly dry grating. Analysis of fish passage required several steps throughout the range of expected hydrology that examined both burst speed and sustained swimming speeds for jumping and swimming through long tailwaters and culverts.

The analysis indicated that given the assumptions of swimming ability the barrier would not be effective

Natural Channel Design, Inc. 3 May 2020 during relatively frequently available range of discharges. This analysis fit the known breach history of the barrier.

Angle of attack is an important aspect of jumping height with angles close to 90° providing maximum height but less forward motion. Some barrier geometries may force very low angles of attack and limit jump height; however, a maximum angle of attack of 80° which maximizes height while ensuring forward motion to propel fish over the barrier was used.

Using the ballistics equation, 𝑦 = 𝑐 + 𝑉 × 𝑡 − 𝑔 × 𝑡 , where cy is the length of the fish, Vy is the burst speed 13.5fps times the sin of the angle of attack, g is gravitational acceleration, and t is the time in seconds, we get a jump height of 2.8 ft (Figure 2) for an 80° angle of attack (when cy is 0). This does not take into account the length of the fish, however to account for the fish length we use a Factor of Safety multiplier of 1.5, we get a jump height of 4.2 feet. Accordingly, the relative height of the barrier at any flow would need to be greater than 4.2 feet. Minimum barrier height is defined as the height between the surface of the tailwater pool and the top of the barrier. This distance diminishes as flows increase. For a conservative estimate of jump height, it is assumed that fish can find enough zero velocity water at the base of the falls to jump from. Thus, tailwater velocity is not considered for barrier effectiveness in this design. However, the design has a concrete apron with steep slopes expected to maintain higher velocities that will limit relative swim velocity. While tailwater velocity can provide a significant reduction in jump height (Figure 3), leaving tailwater velocity out of the jump height calculations provides another layer of safety to prevent passage.

Figure 2. Jump trajectory at 13.5 feet per second

Jump trajectories were calculated from the ballistic equation utilized by Bell (1991) using a range of trajectory angles.

Trajectories are based on burst velocity of 13.5 fps. No correction for fish length was made.

Natural Channel Design, Inc. 4 May 2020

Figure 3. Jump height vs. tailwater velocity

Figure shows the reduction in jump height due to increasing tailwater velocities.

WATERSHED AND HYDROLOGY

The Big Bonito Creek watershed above the project site (Figure 4) encompasses a total of 11,123 acres, or

17.38 square miles. The watershed has an average slope 23%, and is nearly 96% forest coverage. The most recent NSS software was used to determine the design storm flows in the watershed. Using the NSS software, the 50-year design storm is 757 cfs, see Table 1. The watershed was determined using topographic maps from, CALTOPO and QGIS.

Natural Channel Design, Inc. 5 May 2020

Figure 4. Big Bonito Watershed.

BARRIER GEOMETRY AND FLOW CHARACTERISTICS

The design of the barrier will be of a retaining wall constructed of cast-in-place concrete with a broad central weir notch. Hydraulic analysis using the principles of weir hydraulics and flow geometries estimate discharges for varying flow depths. The physical geometry of the barrier is constrained to the outcropping of bedrock surveyed in the field. Local channel slopes were measured at some sites; others used the average slope of the watershed.

Flow geometry of a straight drop spillway is shown in Figure 5. Flows through the straight drop structure are figured using the weir formula, Q = C·L·H3/2 for a broad-crested rectangular weir (C=3.1). The barrier acts as compound weir (geometry includes a low-flow weir notch with higher discharges using all of the remaining dam crest length). Hydraulics to evaluate the effective fish jumping height utilized the weir hydraulics of the notch section only. The corresponding hydraulic depths and velocities were determined (FHA 2006, Saila 2005, and NRCS 2008). Through an iterative process a design drop height of 10’-9” was determined to provide the lowest weir height and a minimum jump height of 4.2 feet.

Weir hydraulic parameters are as follows:

Q = Discharge (cfs) L = Weir Length

Natural Channel Design, Inc. 6 May 2020

H = Stage or Flow Depth (ft) Geometric parameters are as follows:

Ln and Lc = Weir Notch Length and Crest Length (Compound Weir) Hn = Weir Notch Height ho = Drop Height W = Stream or Channel Width S = Average Channel Slope

Hydraulic parameters were determined as follows:

yc = Depth of the Dam Crest (ft) Ln = Length of Weir Notch (ft) An = yc Ln Flow Area of Weir Notch for a Given Depth (ft2) qn = Q/Ln Unit Discharge through the Weir Notch (cfs/ft) Nd = qn

2/gho 3 Drop Number Gives a Quantitative Number for Drop y1 = 1.0hoNd

0.22 Pool Depth under the Nappe (ft)

y2 = 0.54hoNd

0.425 Depth at Toe of Nappe or Beginning of the Hydraulic Jump (ft) y3 = 1.66hoNd

0.27 Tailwater Depth Below the Drop (ft)

HJ = ho-y1 Fish Jump Height is the Difference between Drop Height and Pool Depth (ft) Vn= Q/An Average Velocity through the Weir for a Given Depth (ft/s) HD = (ho+yc)-y2 Head Differential between the Reservoir Surface Elevation and the Depth of

Flow at the Beginning of the Hydraulic Jump (ft) VF = (2gHD)1/2 Velocity of the Falling Water as it Enters the Plunge Pool (ft/s) VT = Q/Wy3 Tailwater Velocity (ft/s)

Figure 5. Flow geometry for a straight drop spillway structure (FHA 2006)

Analysis of barrier hydraulics allows the estimation of two important functions of fish jumping ability.

Primarily, the difference between the barrier drop height and pool depth (ho - y1) provides an estimation of the relative jump height required to attain the barrier. As discharge varies y1 depths vary while the barrier n

Natural Channel Design, Inc. 7 May 2020 drop height remains constant. As discharges increase, the difference between y1 and barrier drop height (relative jump height) becomes less, increasing the chances that the barrier will be attained.

The analysis of weir hydraulics utilizes formulas that are functions of unit discharge. Unit discharge is the discharge through the weir notch at a particular stage divided by the length of the weir. As unit discharge increases, the pool depth (y1) at the base of the drop structure increases disproportionally to changes in discharge, decreasing relative jump height. This relationship indicates that a barrier with relatively low unit discharge (relatively longer weir length) should be more effective than one with shorter weir length and higher unit discharge.

Table 1. Barrier Geometry and Flow Characteristics

Weir Inputs C

Top Height 10.75 Q = CLH3/2 3.1

Top Length 36.8 H_0n 9.92

Notch Depth 0.83 L_t 16.8

Notch Length 20

Flood Freq. Q2 Q5 Q10 Q25 Q50 Q100

Floow Flows 113 251 377 579 757 958

*NSS, Region 1 High Elev, Contributing Drainage Area = 17.4 mi², Crippen & Bue Region 16 yc Total Q Area Velocity Nappe Depth

Flow Depth

Tailwater Depth

Jump Height

Factor of Safety

Drop Length

Apron Length

Vyc y1 y2 y3 ho-y1 L1 L2

ft. cfs ft² ft/s ft ft ft ft ft ft

0.10 1.96 2.00 0.98 1.67 0.17 1.85 8.24 2.94 4.80 14.40

0.50 21.92 10.00 2.19 2.85 0.48 3.56 7.07 2.53 9.21 27.64

1.00 65.54 22.80 2.87 3.58 0.75 4.71 6.34 2.26 12.20 36.60

1.25 100.65 32.00 3.15 3.85 0.86 5.16 6.07 2.17 13.35 40.06

Q2 1.33 113.33 34.94 3.24 3.93 0.90 5.29 5.99 2.14 13.69 41.08

1.50 142.25 41.20 3.45 4.09 0.97 5.55 5.83 2.08 14.38 43.13

2.00 240.99 59.60 4.04 4.50 1.16 6.24 5.42 1.94 16.15 48.46

Q5 2.05 251.87 61.44 4.10 4.53 1.18 6.30 5.38 1.92 16.32 48.95

2.25 297.07 68.80 4.32 4.67 1.25 6.54 5.24 1.87 16.94 50.83

2.50 357.13 78.00 4.58 4.84 1.34 6.83 5.08 1.81 17.68 53.05

Q10 2.58 377.16 80.94 4.66 4.89 1.37 6.91 5.03 1.79 17.91 53.73

2.75 420.94 87.20 4.83 4.99 1.42 7.09 4.92 1.76 18.38 55.13

3.00 488.26 96.40 5.06 5.14 1.50 7.35 4.78 1.71 19.04 57.11

3.25 558.92 105.60 5.29 5.28 1.58 7.59 4.64 1.66 19.66 58.99

Q25 3.32 579.28 108.18 5.35 5.32 1.61 7.66 4.60 1.64 19.83 59.50

3.50 632.76 114.80 5.51 5.41 1.66 7.82 4.51 1.61 20.26 60.79

3.75 709.65 124.00 5.72 5.53 1.73 8.04 4.38 1.57 20.84 62.51

Q50 3.90 757.20 129.52 5.85 5.61 1.78 8.17 4.31 1.54 21.17 63.51

4.00 789.48 133.20 5.93 5.65 1.81 8.26 4.26 1.52 21.39 64.17

4.25 872.13 142.40 6.12 5.77 1.88 8.46 4.15 1.48 21.92 65.76

Q100 4.50 957.51 151.60 6.32 5.88 1.95 8.66 4.04 1.44 22.43 67.30

Flood Frequency

Red < 1.5 < Green

Additionally, the velocity of the tailwater increases as discharge increases. High velocities can thwart jumping fish by reducing effective burst velocity (flow velocity minus fish swimming speed). Significant reductions in burst velocity can reduce jump height; however, most stream conditions provide areas of effectively “zero” velocities that fish can work from. Boundary layer velocities and eddy velocities will be much lower than mean velocities modeled from hydraulic analysis. As such, tailwater velocity will help to limit jump height but is not considered in calculation of jump height effectiveness. The addition of a steep tailwater apron to this barrier design is meant to help ensure that velocities remain as high as possible and tail water pooling is moved as far as possible from the base of the jump barrier., The sloping tailwater will also improve stability of the structure by widening the base and provide a more stable transition to the native stream channel downstream of the barrier.

Natural Channel Design, Inc. 8 May 2020

HEC-RAS ANALYSIS

While jump height efficacy was relatively easy to determine, the effects of the sloped tailwater on tailwater velocity and tailwater elevation requires additional analysis methods. Several methods were utilized to provide independent estimates of specific dimensions and help verify estimates from other analysis.

To determine the distance flow would travel from over the fish barrier to the concrete pad, an iterative process utilizing the average speed of the water, the vertical travel height, the time and corresponding distance traveled can be calculated where:

𝑥 = 𝑉 𝑡 + 𝑔 𝑡 + 𝑐 and ℎ = 𝑉 𝑡 + 𝑔 𝑡 + 𝑐 and 𝑔 = 𝑐 = 𝑉 = 𝑐 = 0 h = ½ so 𝑡 = 2ℎ 𝑔 𝑥 = 𝑉 𝑡 gy = gravity (32.2 ft/s²) Vx = The average velocity of flow in feet per second h = height from the top of weir to the top of the concrete pad in feet t = time in seconds x = the distance from the face of the fish barrier in feet

The analysis indicates that at the design discharge flows land on the sloped tailwater approximately 5.7 feet horizontally and 7.2 feet vertically below the Low Weir. Combined with a HEC RAS analysis of the tailwater depth (1.07 feet), a fish would have to ascend 4.93 feet to achieve the weir elevation. The factor of safety in this instance would be 1.76 (Error! Reference source not found.).

g 32.2 ft/s² 5.7 Vx 8.46 ft/s * High Weir Elev 7935.58 elev weir 7934.75 ft Low Weir Elev 7934.75 Elev pad begin 7928.75 ft Elev pad end 7925 ft 7.195 Length of pad 17.75 ft 6.000 4.930 Slope 0.211268 ft/ft h1 6.000 ft t1 0.610 s 1.07** x1 5.165 ft 7928.75 h2 7.091 ft t2 0.664 s x2 5.615 ft 7925.00 h3 7.186 ft t3 0.668 s x3 5.652 ft h4 7.194 ft t4 0.668 s Jump height of 4.93 17.75 x4 5.655 ft determined by adding water height h5 7.195 ft to concrete pad elevation and Not to scale t5 0.668 s subtracting from low weir elev * From HEC-RAS Q50 output @ RS 98.8 x5 5.655 ft **From HEC-RAS Q50 output @ RS 98.7

Figure 6. Key elevations in tail water at design discharge.

Natural Channel Design, Inc. 9 May 2020

HEC-RAS was used to model the flow of water over the weir, the velocity and scour downstream of the fish barrier, and to verify the impoundment conditions. The HEC-RAS analysis shows 1.07 feet for the depth of flow at 0.10 feet from the face of the fish barrier (Figure 8). This analysis provides confirmation that the height and slope of the concrete pad will to prevent a condition where fish will have an ability to jump over the barrier. Additionally, the flow at this location is 22.78 ft/sec, higher that the maximum burst speed of 13.5 ft/sec of an adult Rainbow Trout. We still assume there will be some area(s) of low velocity and with water depth at 1 foot at the base of the Weir, still there is a 4.93 foot jump height, providing a factor of safety over 1.7.

Figure 7. HEC-RAS Profile of design discharge over the barrier

Natural Channel Design, Inc. 10 May 2020

Figure 8. HEC-RAS model of Velocities on tailwater apron

Tailwater Velocities

HEC-RAS modeling provides estimates of tail water velocities on the apron (Figure 8). Flow on the concrete apron are supercritical with velocities in the mid-section of the apron (~10 feet downstream of the barrier face) in excess of 20 feet per second and outside the burst speeds considered in this study. The apron will provide additional assurance that fish cannot achieve high exit velocities required to power a jump to clear the barrier. As such, the apron will provide additional assurance that fish cannot clear the barrier.

BARRIER DESIGN DATA

In previous studies, data collected suggests that barriers with longer weir lengths and width to depth ratios nearer to those found in the natural channel have a higher factor of safety and are less likely to pass fish than those with shorter weir lengths and lower width to depth ratios.

The results of that study directly implicate the design and enhancement of the Big Bonito Creek fish barrier.

These are:

Weir notch width 20’-0” is based on the surveyed bankfull width Weir depth is 10”, and is based on the measured bankfull area Elevation of high weir 7935.58 feet Elevation of Low Weir 7934.75 feet Elevation of concrete apron at weir is 7928.75 feet Elevation of the top of concrete footing is 7924.83 feet The jump height from the resulting pool during the Q50 event is 4.93 ft (FOS 1.76).

Jump height of 4.63 ft (FOS 1.65) is maintained during Q100 Simple ballistics using the average velocity of the flow over the weir indicates the flow traveling 5.66 ft from the downstream face to the concrete apron during Q50 event.

Concrete apron beginning elevation 7928.75, with slope of 4.7:1, is 17’-9” long Rock Outlet Structure was determined based on a combination of the HEC-RAS models.

The fish barrier is designed as a cantilevered retaining wall, with the wall acting as a single notch weir.

The retaining wall geometry, heel length, toe length, key height and wall thickness were determined

Natural Channel Design, Inc. 11 May 2020 through an iterative process to minimize the amount of concrete and rock excavation. See Figure 9 for the barrier cross section geometry.

Factor of Safety against Sliding is 2.2 Factor of Safety against Overturning is 2.6 Building Code Requirements for Structural Concrete (ACI 318-19) was used to design the barrier Ultimate Load using ACI 318-19 eq 5.3.1a where U = 1.4*(Dead Load + Fluid Load)

It is assumed that the existing grade is also the elevation of bedrock. If, however, during construction bedrock is not found at the base of the foundation, alternate 1 will be required. Alternate 1 has similar geometry to the Barrier shown in Figure 10, the only differences are a thickened footing (3’-0”) and the addition of a Key directly below the stem wall and also (3’-0”) below the bottom of footing.

Concrete Requirements

Since the fish barrier will be exposed to freezing and thawing, and exposed to water, and not deicing materials, the minimum compressive strength of the concrete (f’c) is 5,000 pounds per square inch (psi).

The maximum water-cementitious ratio is 0.40. The nominal maximum aggregate size is 1”. The target air entrainment is 7.0 percent. A six inch by 3 inch (6”x3”) keyway shall be constructed in the footing to wall interface. Concrete will conform to FP-14 Section 552, Class D Concrete

Figure 9. Barrier Cross-Section Geometry

Natural Channel Design, Inc. 12 May 2020

Reinforcing Steel

All reinforcing steel shall be Grade 40, with a minimum Tensile strength of 40,000 psi. Concrete cover shall be 3” for all foundation concrete, and 2½” for the wall reinforcement. Reinforcing steel will conform to FP-14 Section 554.

Rock Outlet Structure

The sloped spillway creates high velocity flows and a slightly overwidened flowpath compared to the native channel. The depth to bedrock below the natural bed material at the downstream limit of the concrete apron is unknown. Thus, the ability to rely upon a bedrock foundation to limit scour depth is unknown as well.

As a result, the design includes the use of a rock outlet structure, made up of large feature rock, sized to resist movement under the higher shear stresses. In order to reduce energy and help to ease the active flow path back to native channel dimensions, a rock, cross vane weir is to be built at the base of the sloped concrete apron. The configuration of the weir is designed to narrow the flow path back to the width of the native channel by concentrating shear stress towards the center of the stream and away from the channel margins. The weir creates stable scour pools for release of energy and the heavy rocks are designed to resist shear stresses developed by the design discharge. Installation of the weir will reduce the potential for undercutting of the concrete apron.

Based upon a HEC-RAS model of the pre-project condition, the shear stresses downstream of the proposed fish barrier location range from approximately 2 lb/ft2 to 4 lb/ft2. These shear stresses are capable of initiating movement of 10 to 16 inch rock (River Stability Field Guide, Figure 3-11, Dave Rosgen, 2008).

This generally correlates with the upper limit of the bed material that as observed to be at this location. The post-project HEC-RAS model predicts significantly higher shear stresses immediately downstream of the fish barrier where the steeply sloping concrete apron ends and the stream bed begins. At this location, the high velocity flows on the concrete apron meeting the lesser sloped natural channel grade produces a hydraulic jump with turbulent flow conditions and high shear stresses that dissipate the energy until a normal flow conditional resumes at a location approximately 50 feet downstream of the barrier. The rock outlet structure was designed taking into consideration the shear stresses as determined from the HEC-RAS analysis and with the intent to extend far enough downstream to a point where the pre- to post-project shear stresses approximately match.

The rock outlet structure and cross vane weir is to be installed below the concrete apron using 36 inch feature rocks inset into a matrix of D50= 16-24 inch riprap as depicted in Figure 10. The 36 inch feature rocks should resist the design shear stresses, calculated in HEC-RAS to be as high as 20 to 50 lbs/ft2 through the hydraulic jump during the 50 year event and checked against the 100 year flow event to ensure stability.

The 36 inch minimum rock size (0.91 m) can be expected to resist shear stresses up to 120 lb/ft2 (5 kg/m2), providing a factor of safety of 2 during the 100 year flow condition. The D50= 16-24 inch riprap will provide an interlocking matrix of rock between the larger feature rocks with the intent of providing a stable, composite size rock apron. Below the rock outlet structure, shear stresses from the 50 and 100 year flows approximately match the pre-project conditions.

Natural Channel Design, Inc. 13 May 2020

More detailed results of the HEC-RAS modeling are provided in Attachment 3 of this report.

CONSTRUCTION CONSIDERATIONS

The plans call for the construction on an access and staging area departing from Y-55, just west of the existing fish barrier, and heading down to the proposed barrier site, approximately 900-feet (Figure 11).

The contractor is then expected to install a dewatering system, to use tarping, framing and sandbags to dam the flow of Big Bonito Creek, and utilizing a flexible pipe, send the flows downstream, along the east bank of the Creek, over and around the future fish barrier. It is expected that subsurface flows exist, and are brought to the surface at bedrock, these flows will be contained in a sump hole and pumped over and around the future barrier. This plan will prevent the need to place a pipe within the retaining wall system, however a design consideration will be made to ensure that if sending the water through the fish barrier is necessary, it can be incorporated. The contractor will need to create access to the creek below the staging area, a small excavator for placing materials over the retaining wall toe, placing rip rap and fitted with a hydraulic hammer for rock excavation is anticipated in the construction costs. It is expected that all borrow materials for the access road and staging area, and all rock excavation will be placed upstream of the fish barrier, although compaction or careful placement of materials is not expected or needed. The completed barrier is expected to impound 36,059 cubic feet, or 0.83 Acre-Feet of water, see Figure 11. The expected spoils material, will fill approximately 6,400 cubic feet, reducing the immediate impoundment to just over 0.68 Acre-Feet of water. The volume of water retained upstream from the barrier remains 29,659 (0.68 ac-ft).

Figure 10. Rock Outlet Structure Plan and Profile

See also Sheet 8 of the plans in Attachment 2

Natural Channel Design, Inc. 14 May 2020

This volume will diminish over time to near zero as the stream deposits sediment upstream of the barrier.

In many streams this process occurs rapidly, especially if a large runoff event occurs. However, the upstream reach of Big Bonito Creek is already impounded by a barrier and associated wetland. These features will slow sediment transport to the downstream reach considerably.

The construction period is expected to be several months from the time of initial clearing and cleaning of the bedrock through completion and filling of the structure.

Construction should occur during a period of stable, low flows when the road into the site will be easily passable by large trucks. (generally, April through July). During this period, road traffic on the low traffic Y55 will likely increase due to workers and materials transport on a daily basis. There may be a need to provide road maintenance at the end of the construction period.

The site is small and limits the size of construction crew. The crew size will ultimately be determined by the contractor. However, we anticipate that a crew of 10 or less will be utilized to prepare the site and accomplish the construction. The area is remote, but within reasonable daily travel distance from White River or

Pinetop/Lakeside. Crews will not likely need to camp on site, except for a fire guard/night watchman to secure materials and equipment at the site.

The plans call for roadbed material, aggregate base for a concrete apron, and rip rap to armor the creek, it is expected that the borrow materials for these items will be mined from one of two materials pits as noted in Figure 12. Borrow pit number one is approximately one-half mile from the project, and borrow pit number two is approximately 6.9 miles from the project.

Figure 11. Construction Access and Impoundment

Natural Channel Design, Inc. 15 May 2020

Figure 12. Big Bonito Fish Barrier potential material borrow pits.

When dewatering is stopped after construction of the barrier, we estimate that the impoundment will take approximately 24 hours to fill. Dewatering will continue at a minimum of fifty percent (50%) of low flow being maintained in the creek until flow overtops the fish barrier. At that point the dewater system(s) shall be completely removed.

After construction, it is recommended that the haul road and staging areas be regraded and replanted, using native and weed free vegetation, to match preconstruction conditions to limit access to the barrier site.

Natural Channel Design, Inc. 16 May 2020

Figure 13. Big Bonito Fish Barrier construction limits.

BID TAB

The assumption is that during construction bedrock will be found within six inches of the creek bed surface.

In this case the barrier geometry shown in Figure 8, will be adequate. However, should the contractor not find bedrock for several feet, than an alternative barrier geometry will be required. The alternative barrier geometry described in the Barrier Geometry section, differs only in the footing thickness increased to 3-feet, and a key added to the bottom of the footing, 2-feet thick by 3-feet deep.

Limits of Construction

Natural Channel Design, Inc. 17 May 2020

Table 2. Bid Tab

Big Bonito Fish Barrier: Footing Embedded in Bedrock Category Line Item Quantity Unit Unit Cost Cost Fish Barrier: Footing Embedded in Bedrock

Fish Barrier 56 CY

Apron & Stream Hardening Concrete Apron & Sill 15 CY Rock Outlet Structure 1 LS

Mobilization Mobilization 1 LS Dewatering 1 LS

Demobilization Demobilization 1 LS Reseed 0.25 Acre

Construction Management Layout and Survey Control 1 LS Testing 1 LS

Total

REFERENCES

ACI 318-19 Building Code Requirements for Structural Concrete, June 2019, American Concrete Institute, Farmington Hills, MI

U.S. Army Corps of Engineers, 2016. HEC-RAS River Analysis System Hydraulic Reference Manual, Version

5.0. US Army Corps of Engineers, Institute for Water Resources, Hydrologic Engineering Center, Davis, CA

Gordian RSMeans Data, Site Work & Landscape Costs, 2017, Construction Publishers & Consultants, Rockland, MA

NRCS, Cross -Section Hydraulic Analyzer, Uniform flow hydraulic parameters, Version xsecAnalyzerVer18.xlsm, United States Department of Agriculture, Natural Resources Conservation Service