FINAL_UT_Straw_Hydraulic_Recommendations.pdf

Subject: Strawberry Sheep Creek Hydraulic Recommendations

Date: May 24, 2019

Project Number: UT FLAP 70131(1) Strawberry Sheep Creek

From: Brian Campbell, P.E.

Hydraulics Engineer FHWA Central Federal Lands Lakewood, CO

To: Braden Peters, P.E.

Project Manager

Summary The following summarizes the hydraulic recommendations for UT FLAP 70131(1) Strawberry Sheep Creek. The project includes a hydraulic investigation of 6 existing culvert drainage crossings. During the 70% design review, two options were proposed for culverts at site 866+59 (Indian Creek) and 995+30 (Crooked Creek). Alternatives selected at that time with the Partners are included here for final design. The options memo is included in the Appendix.

A summary of the hydraulic recommendations is included in Table 1:

Table 1: Summary of Hydraulic Recommendations

Station Q25 (cfs)

Existing Size Length (ft) Condition Proposed Recommendation

825+71 60 48”CMP 92 Fair - Replace with 48”

- Headwall at inlet

- Outlet armor

855+00 13 36” CMP 72 Fair - Replace with 36”

- Flared End Section at Inlet

- Grade inlet

- Outlet armor

866+59 (Indian Creek)

200 8’ 7” X 5’ 11” Structure Plate

71 Fair/ Undersized

- Replace with suppressed 12’10” x 8’4” structure plate

- Add headwall, wingwall, and cutoff wall at inlet and outlet

- Stream restoration at inlet

880+00 22 24” CMP 101 Good - Clean pipe

- Add FES to inlet

- Outlet armor

952+00 (Streeper Creek)

160 9’4” X 6’3” Structure Plate

54 Good - Leave as is, monitor outlet after large storms

995+30 (Crooked Creek)

130 48” CMP 53 Fair/ Undersized

- Replace with suppressed 8’7” x 5’11” structure plate

- Add headwall, wingwall, and cutoff wall at inlet and outlet

Project Location and Description The project is located in Wasatch County, south of Strawberry Reservoir, on FR 042. Approximate coordinates of the starting location are (LAT 40.118703°, LONG -111.175398°). The project consists of reconstruction, pavement widening, and improvements to drainage and safety. The proposed hydraulics analysis is for existing crossings at station 825+71, 855+00, 866+45 (Indian Creek), 881+1, 952+00 (Streeper Creek), and 995+00 (Crooked Creek).

Figure 1: Location Map (Image from Google Earth)

Hydraulic Design Standards Roadway Classifications The roadway is designated as a low standard road with a design ADT of 600.

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:

- 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

- Select Environmental Permitting Requirements Specific to the Culverts o Applications that propose installation of a culvert or other similar structure will be subject to the following conditions and requirements:

The grade and elevation of the bottom (or floor) of the culvert shall not change the profile from that of the original undisturbed streambed, unless the culvert is intended to be used as a fish barrier.

The bottom of the culvert should contain natural streambed material if the natural stream contains a fishery. This may require installing the culvert flowline below the bed of the channel or installation of an open bottom culvert.

The culvert shall be sized to allow passage of flood flows and in some cases wildlife migration.

The culvert design should include energy dissipation structures or devices when necessary.

o Select items from the joint Utah/Corps permit for streams:

Strawberry Reservoir

North

Work in waters of the U.S. shall only be conducted during periods of low or no flow, unless the applicant demonstrates the proposed work during higher flows is necessary and would not result in more than minimal impacts, or that this condition is otherwise not appropriate or practicable.

Culverts placed in streams must be installed in a manner that maintains flows during low flow periods, and in a manner that maintains fish passage in locations where periodic flows provide stream connectivity and allow fish movement above and below the installed structure.

Hydrologic Analysis and Peak Flow Estimates The Watershed Modeling System (WMS vs 10.1) was used to delineate drainage areas from the tributaries. Delineated basins can be seen in Figure 2.

Peak runoff from the basins in this area are dominated by snow melt. Four of the 6 basins of interest had drainage areas below the minimum area of 2.95 mi² to use regional regression equations for the area. None of the basins within the project footprint are gaged.

A USGS gage station within the Strawberry Reservoir Basin, Hobble Creek (USGS 09280400), is located approximately 14 miles north west of the project site. The Hobble Creek location, in reference to the project basins, can be seen in Figure

3. The Hobble Creek drainage basin has similar conditions to the sites of interest. Peak annual flow rates recorded from this site are a good approximate model of the snow melt runoff response of the sites of interest within the project footprint. The gage has 21 years of annual peak flows documented. A Log Pearson III analysis of these flows as documented in USGS Investigation Report 2007-5158 was used to conduct an Area Ratio Method analysis of the basins of interest.

Area Ratio Method. If a nearby basin with similar physical and hydrologic characteristics has gage data, the Log Pearson Type III analysis of this gage is completed. Then, an area ratio factor may be applied to determine peak flows for the design basin when the two areas are within 25 percent of each other. In this case, not all the basins for comparison were within 25 percent of the control basin, Hobble Creek. However, of the available methods to estimate the peak flows due to snow melt, this method had the most reasonable data for analysis. The calculated values for areas outside the applicable range may be more conservative. A difference in the results do not vary the hydraulic recommendations as discussed in the hydraulics section. The Area Ration Method equation is:

QD = QG (AD /AG )

c where QD is the peak flow at the design point; QG is the peak flow at the gage; AD is the drainage area at the design point; AG is the drainage area at the gage; and c is drainage area exponent from the applicable regression equation.

Table 2: Area Ration Method Results

Drainage Basin Area mi² Q25* (cfs)

Hobble Creek 2.89 149

826+70 0.90 60

855+00 0.13 13

866+45 (Indian Creek) 4.16 200

880+00 0.26 22

952+00 (Streeper Creek) 3.15 160

995+00 (Crooked Creek) 2.44 130

* Drainage area exponent from the applicable regression equation = 0.804

Figure 2: Drainage Basins (Image from Google Earth)

Strawberry

Figure 3: Basin used for Area Ratio Method

Strawberry Reservoir

North

Project Sites

Hobble Creek

Site Analysis for Minor Structures

Station 826+70 and Station 855+00 The 48” CMP at station 825+71 and the 36” CMP at station 855+00 are in Fair condition. Flow marks could be seen approximately at the spring line of the pipe suggesting the size is adequate for annual flows. During the field inspection, material was deposited on the invert along the length of the pipe.

Warping can be seen and some separation at the segments was noted. Fill material could be seen through the joints, see Figure 4. At station 855+00, some minor joint separation could be seen.

Figure 4: 48” CMP at station 825+71. Segment separation can be seen on the left. Warped alignment can be seen on the right.

Figure 5: 36" CMP at station 855+00. Minor joint separation can be seen halfway through the pipe.

Recommendation To improve the longevity of each of these culverts, two options were considered:

1. Retrofit the existing pipe with a grouted slipline

2. Replace existing pipe.

The grouted slipline retrofit example can be seen in Figure 6. The new liner pipe can be HDPE or a smaller CMP.

Figure 6: Grouted slipline

Conversations during the design process identified it would be less expensive and more efficient to replace the pipes.

The ability to close the road during this replacement is a benefit and will expedite the process over a slipline operation.

It is recommended to include an FES on the inlet and armor the outlet.

Station 880+00 The 24” CMP at station 880+00 is in good condition. Flow marks could be seen approximately at the spring line of the pipe suggesting the size is adequate for annual flows. Some material deposition could be seen in the invert.

Figure 7: The image on the left shows larger material deposited in the pipe. The image on the right shows flow lines at a depth slightly greater than spring line suggesting the size is adequate for annual flows.

Recommendations In the existing configuration, the hydraulic capacity is not sufficient to pass the 25-year design event without exceeding the headwater to depth ratio criteria of 1.5. Although installing an improved inlet will not meet the criteria, it does improve the culvert efficiency and will improve the longevity of the existing system. It is recommended to clean the pipe, install an FES on the inlet, and armor the outlet.

Site Analysis for Major Structures

Station 866+45 (Indian Creek) The Indian Creek structure plate crossing was partially embedded during the site visit. The embedment depth was estimated at 1 foot. From measurements taken in the field, the conduit size was estimated at 8’ 7”W X 5’ 11”H. Water and silt lines along the top of the conduit suggest this pipe does run full for annual flows. Minor rusting could be seen on the walls. In few areas, wall deformations were noticed however penetrations were not visible. The condition was estimated as Good/Fair, see Figure 7.

Figure 8: Structure Plate at station 866+45. Wall deformations can be seen. Silt on the crown suggest this pipe runs full during annual flows.

The existing embedment depth was estimated at ≈ 1 foot.

The inlet is depressed approximately 3 feet, however, the slope of the pipe matches the slope of the downstream channel. After further analysis, it is likely the upstream grade was not originally 3 feet higher than the inside of the pipe, rather, the 3 feet is a result of aggradation upstream. There are no other material marks throughout the culvert that would suggest this abrupt change in channel thalweg elevation is the result of a headcut. During a peak flow event, a constrictive inlet will cause backwater upstream. The backwater is a zone of lower velocity and shear stresses. This zone results in material settling out of the flow that is normally mobilized. After many storm events, aggradation as seen at station 866+45 can occur.

Figure 9: The image on the left is from the upstream side, looking downstream, at the inlet. The image on the right is from within the pipe looking upstream at the inlet. It is likely the change is a result of aggradation upstream.

Hydraulic modeling of the existing condition suggests the road is overtopped to the north at approximately the 5-year return interval. The existing condition does not meet the 25-year capacity requirement.

During the 70% design review, two options were proposed to address this conduit:

1. Retrofit the Existing Pipe

2. Replace the Existing Pipe

After conversations with the Partners, it was selected to replace the structure.

Replace Due to the cover requirements and sensible constructability methods, replacement includes:

- Arch Plate o Span = 12’-10” o Rise = 8’ 4”

- The structure requires a headwall, wingwall, and cutoff wall at the inlet and outlet.

- Embed the structure with 2 feet of stream material excavated from the upstream aggradation zone.

- Place Class 2 riprap along the walls, mixed with the stream material.

It is anticipated the stream will adjust to the natural equilibrium slope after a number of storm events. See Outlet Protection and AOP Consideration for discussion.

Station 952+00 (Streeper Creek) The Streeper Creek crossing is a structure plate conduit estimated 9’4”H X 6’3”V. Water and silt lines along the sides, as well as hydraulic modeling results, suggest the conduit is sufficiently sized for events up to and exceeding the design event. The structure is in Good condition.

A headcut in the channel is migrating towards the outlet. This headcut is likely controlled by the water surface elevation of Strawberry Creek Reservoir approximately 2 miles downstream. At this time, the headcut is being arrested by a hardpoint just downstream of the inlet. The hardpoint appears to be a rock outcrop, however, it is unclear the extent or footprint of the hardpoint, see Figure 11.

Figure 7: A headcut in the channel is migrating towards the outlet. This headcut is likely controlled by the water surface elevation of Strawberry Creek Reservoir. At this time, the headcut is being arrested by a hardpoint just downstream of the inlet. The hardpoint appears to be a rock outcrop, however, it is unclear the extent or footprint of the hardpoint.

Rock outcrop

Recommendation It is recommended to monitor this structure after large runoff events.

a. It is unclear how long the existing condition has been exposed to the headcut. It is possible that as the water elevation in Strawberry Reservoir fluctuates, the stream bed adjusts accordingly with aggradation and degradation cycles.

b. It is unclear the extent of the rock outcrop. It is possible this rock outcrop is sufficient to protect the structure from a headcut migrating under the conduit.

c. Monitoring the structure after large events may be sufficient. If a problem manifests, action can be taken at that time to protect the structure.

995+00 (Crooked Creek) The Crooked Creek structure is a 48-inch CMP without headwall infrastructure. Hydraulic modeling of the existing condition suggests the road is overtopped at approximately the 5-year return interval. The existing condition does not meet the 25-year capacity requirement. Additionally, evidence of piping and minor segment separation was seen during the field visit.

A minor headcut can be seen in the channel downstream of the culvert migrating towards the outlet. This headcut is likely controlled by the water surface elevation of Strawberry Creek Reservoir approximately 1 mile downstream. The lack of embedment of the current configuration limits the flexibility for the culvert invert to adjust to any changes in stream thalweg elevation. This could become a barrier in the future.

Figure 11: The image on the left shows evidence of piping along the culvert from the inlet side. The image on the right shows a minor headcut being arrested at the culvert exit.

Recommendations Based on the results of the analysis, it is recommended to replace this pipe. Due to the cover requirements and sensible constructability methods, replacement includes:

- Arch Plate; 90-inch equivalent

- The structure requires a headwall, wingwall, and cutoff wall at the inlet and outlet.

- Embed the structure with 2 feet of material that matches the gradation of in-situ stream material at the proposed location.

- Place Class 2 riprap along the walls, mixed with the stream material.

See Outlet Protection and AOP Consideration for discussion.

Outlet Protection and AOP consideration Methods outlined in FHWA Hydraulic Engineering Circular 14 (HEC 14) were used to determine the need and size for outlet protection for the two proposed culverts at Indian Creek and Crooked Creek. 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 4.

Table 3: Outlet Velocity Comparison

Culvert Location

At Culvert Outlet Shear Stress lb/ft² Difference at Culvert Outlet from Channel Condition (%) 25-Year Return

Proposed Condition (ft/s)

25-Year Return Channel Condition (ft/s)

25-year Return Shear Stress (lb/ft²)

Indian Creek 3.96 2.24 1.10 48%

Crooked Creek

5.81 4.94 2.60 18%

Indian Creek The outlet velocities for the design event exceed the 30% threshold as described in HEC-14. However, because the magnitude of the velocity and shear stress is low, energy dissipation is not considered necessary. Additionally, the current condition of the pipe does not show that outlet scour is a threat. Rather, the current condition shows inlet aggradation is a threat. A small natural scour hole may form at the outlet during a peak event. If this occurs, it is anticipated the hole will fill in with material on the tailing end of the event. Scour holes are caused by high outlet velocities and concentrated flows. Aside from aesthetics, scour holes are not necessarily detrimental unless structural damage due to undermining occurs. Scour holes at culvert outlets provide efficient energy dissipators.

A concrete headwall, wingwall, and cutoff wall system is recommended on both the upstream and downstream side.

The cutoff wall is to be 4 feet below the existing channel elevation. On the upstream side, this system will enable a shorter pipe length, protect the pipe from failure due to buoyancy, and protect the pipe from piping action. On the downstream side, this system will enable a shorter pipe length, protect from buoyancy, and protect from outlet scour.

It is recommended the pipe be inspected after major storm events to ensure adequate performance is met and outlet scour is not encroaching on the structure.

Crooked Creek The outlet velocities exceed the minimum 10% threshold as described in HEC-14. However, because the magnitude of the velocity and shear stress is low, energy dissipation is not considered necessary. Additionally, the current condition of the pipe does not show that outlet scour is a threat. As described above, a small scour hole may manifest during a peak event. Similar to Indian Creek, a concrete headwall, wingwall, and cutoff wall system is recommended on both the upstream and downstream side. The cutoff wall is to be 4 feet below the existing channel elevation.

Other minor culverts within the project limits Riprap is the most common, economical, and available material used for erosion and scour protection for culverts 48 inches in diameter and smaller. Riprap aprons, per Central Federal Lands detail C251-50, are recommended for outlet protection for each identified site.

Figure 12:CFL C251-50: Placed Riprap at Culvert Outlets

Aquatic Organism Passage (AOP) Consideration

The following is documented in HEC-26, Culvert Design for Aquatic Organism Passage

Embedment is intended to encourage AOP and to allow for downward adjustment in the bed within the culvert while still maintaining a natural bed. Conversely, the initial embedment level should allow for an upward adjustment to the bed while maintaining sufficient conveyance. Embedment provides the following benefits:

1. Flexibility to provide for vertical adjustments in the profile over the life of the culvert.

2. Sufficient bed thickness to allow for natural bed transformation processes, such as armoring.

3. Adequate wetted perimeter with increased bed roughness to mitigate acceleration of flows in the culvert.

For each of these benefits, increasing the depth of embedment enhances the ability of the culvert to provide the stated characteristics. However, once the desired function is obtained further increasing embedment may have undesirable consequences such as increasing the potential for subsurface flows and reducing the hydraulic capacity of the culvert such that QP requirements cannot be met. An embedment depth of 2-feet is appropriate for Indian Creek and Crooked Creek.

The bed gradation within the culvert should match the bed gradation within the streambed as closely as possible. To insure the long-term performance of the embedded material within the culvert, the stability of the bed material is assessed to determine if it is stable at peak flows. In many situations, the streambed material in the culvert and the upstream and downstream channel will be mobile when subjected to significant flow rates such as the design flood peak. Depending on the capacity of the stream for replenishment, streambed material may be redeposited within the culvert on the receding limb of the flood hydrograph or during subsequent smaller runoff events resulting in a sustainable bed within the culvert.

However, to be able to demonstrate that replenishment at a given site is likely requires significant sediment transport analyses that are beyond the scope of this design procedure. Therefore, this procedure relies on a worst-case assumption of no replenishment and the stability of a designed sublayer, if needed, to enhance the re-establishment of the natural channel substrate.

If the streambed material within the culvert is unstable at peak flows, a stable sublayer is recommended to maintain the bed profile in the culvert during the peak design flow, maintain roughness in the bottom of the culvert barrel, and promote deposition of native material. This recommendation presumes that at flood flows the shear stresses within the culvert will be greater than those in the upstream and downstream channels because the width in the culvert is limited and there may be no floodplain relief access.

In some channel systems, the bed within the culvert may be naturally replenished. If the designer has performed a site-specific sediment transport analysis documenting this to be the case, a stable sublayer may not be needed.

An oversized sublayer beneath the native streambed material is the primary tool currently available to achieve a stable bed within the culvert. The layer of native streambed material will overlay the oversized sublayer and will continue to provide the desired substrate and the potential for vertical adjustment.

Class 2 riprap is specified as the stable sublayer for both Indian Creek and Crooked Creek.

Proposed Hydraulic Recommendations The following table summarizes the existing and proposed conditions at each site.

Table 5: Summary of Hydraulic Recommendations

Station Q25 (cfs)

Existing Size Length (ft) Condition Proposed Recommendation HW/D ratio

825+71 60 48”CMP 92 Fair - Replace with 48”

- Headwall at inlet

- Outlet armor

0.86

855+00 13 36” CMP 72 Fair - Replace with 36”

- Flared End Section at Inlet

- Grade inlet

- Outlet armor

0.23

866+59 (Indian Creek)

200 8’ 7” X 5’ 11” Structure Plate

71 Good/Fair - Replace with suppressed 12’10” x 8’4” structure plate

- Add headwall, wingwall, and cutoff wall at inlet and outlet

- Stream restoration at inlet

0.79

880+00 22 24” CMP 101 Good - Clean pipe

- Add FES to inlet

- Outlet armor

1.89*

952+00 (Streeper Creek)

160 9’4” X 6’3” Structure Plate

54 Good - Leave as is, monitor outlet after large storms

0.76

995+30 (Crooked Creek)

130 48” CMP 53 Fair/ Undersized

- Replace with suppressed 8’7” x 5’11” structure plate

- Add headwall, wingwall, and cutoff wall at inlet and outlet

1.10

*See discussion below.

Variance in Design Criteria, * In 1 case, the HW/D ratio of 1.5 was exceeded. The FHWA HW/D criterial for culverts 48 inches and smaller is 1.5. Some risk considered when evaluating increasing the structure size to meet the 1.5 criteria includes: buoyancy potential, piping potential through the upstream face, magnitude of variance, and cost to increase structure size. For the 1 case, buoyancy is not a concern because the pipe is under approximately 13 feet of fill and the ends are not projecting. The inlets are proposed to be encased in a flared end section for station 880+00. Piping potential will be minimized with the flared end section at the inlet. The magnitude of the variance is small, 0.39 at the greatest.

Additionally, the site has a significant amount of storage upstream which may attenuate the peak flow to the site. The cost to increase the structure size will be realized in pipe material costs, user costs due to road closures, excavation, and is considered large.

The improvement for this case is still a significant betterment to the existing condition.

Because of the above reasons, the costs to increase the structure size to meet a 1.5 HW/D ratio is considered greater than the risk reduction realized by increasing the conduit sizes.

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 (2012) “Hydraulic Design of Highway Culverts” Hydraulic Design Series No. 5. US Dept. of Transportation, Federal Highway Administration.

Federal Highway Administration (2002) “Highway Hydrology” Hydraulic Design Series No. 2. US Dept. of Transportation, Federal Highway Administration.

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.

Kenney, TA, et. Al. 2008, Methods for Estimating Magnitude and Frequency of Peak Flows for Natural Streams in Utah:

U.S. Geological Survey Scientific Investigations Report 2007–5158

United States Department of Agriculture (2007) “Grade Stabilization Techniques”

Appendix A: 70% Hydraulic Memo

Subject: Strawberry Sheep Creek Hydraulic

Date: January 4, 2019

Project Number: UT FLAP 70131(1) Strawberry Sheep Creek

From: Brian Campbell, P.E.

Hydraulics Engineer

To: Braden Peters, P.E.

Project Manager

The following is a summary of the recommendations for the UT FLAP 70131(1) Strawberry Sheep Creek project corridor.

A detailed discussion is included for the crossings located at Crooked and Indian Creek. Input from the project Partners is requested, specifically for the crossings located at Crooked and Indian Creek. A detailed hydraulics report will be submitted at the 70% milestone.

Summary of Recommendations:

The hydraulic scope includes investigations of 6 existing culvert drainage crossings.

A summary of the hydraulic recommendations is included in Table 1:

Table 1: Summary of Hydraulic Recommendations

Station Q25 (cfs)

Existing Size Length (ft) Condition Proposed Recommendation

825+71 60 48”CMP 92 Fair - Replace with 48”

- Headwall at inlet

- Outlet armor

855+00 13 36” CMP 72 Fair - Replace with 36”

- Flared End Section at Inlet

- Grade inlet

- Outlet armor

866+45 (Indian Creek)

200 8’ 7” X 5’ 11” Structure Plate

71 Good/Fair - See Discussion Section

880+00 22 24” CMP 101 Good - Clean pipe

- Add FES to inlet

- Outlet armor

952+00 (Streeper Creek)

160 9’4” X 6’3” Structure Plate

54 Good - Leave as is, monitor outlet after large storms

995+00 (Crooked Creek)

130 48” CMP 53 Fair/ Undersized

- See Discussion Section

Project Location and Description The project is located in Wasatch County, south of Strawberry Reservoir, on FR 042. Approximate coordinates of the starting location are (LAT 40.118703°, LONG -111.175398°). The project consists of reconstruction, pavement widening, and improvements to drainage and safety. The proposed hydraulics analysis is for existing crossings at station 825+71, 855+00, 866+45 (Indian Creek), 881+1, 952+00 (Streeper Creek), and 995+00 (Crooked Creek).

Figure 1: Location Map (Image from Google Earth)

Select Environmental Permitting Requirements Specific to the Discussion Section Select items from the State code relating to stream alteration permits:

Applications that propose installation of a culvert or other similar structure will be subject to the following conditions and requirements:

- The grade and elevation of the bottom (or floor) of the culvert shall not change the profile from that of the original undisturbed streambed, unless the culvert is intended to be used as a fish barrier.

- The bottom of the culvert should contain natural streambed material if the natural stream contains a fishery. This may require installing the culvert flowline below the bed of the channel or installation of an open bottom culvert.

- The culvert shall be sized to allow passage of flood flows and in some cases wildlife migration.

- The culvert design should include energy dissipation structures or devices when necessary.

Select items from the joint Utah/Corps permit for streams:

- Work in waters of the U.S. shall only be conducted during periods of low or no flow, unless the applicant demonstrates the proposed work during higher flows is necessary and would not result in more than minimal impacts, or that this condition is otherwise not appropriate or practicable.

- Culverts placed in streams must be installed in a manner that maintains flows during low flow periods, and in a manner that maintains fish passage in locations where periodic flows provide stream connectivity and allow fish movement above and below the installed structure.

Strawberry

Hydraulic Design Standards Roadway Classifications The roadway is designated as a low standard road with a design ADT of 600.

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:

- 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

Discussion

Station 866+45 (Indian Creek) The Indian Creek structure plate crossing was partially embedded during the site visit. The embedment depth was estimated at 1 foot. From measurements taken in the field, the conduit size was estimated at 8’ 7”W X 5’ 11”H. Water and silt lines along the top of the conduit suggest this pipe does run full for annual flows. Minor rusting could be seen on the walls. In few areas, wall deformations were noticed however penetrations were not visible. The condition was estimated as Good/Fair, see Figure 2.

Figure 2: Structure Plate at station 866+45. Wall deformations can be seen. Silt on the crown suggest this pipe runs full during annual flows.

The existing embedment depth was estimated at ≈ 1 foot.

The inlet is depressed approximately 3 feet. This configuration appears to be part of the initial design intent. There are no other material marks throughout the culvert that would suggest this abrupt change in channel thalweg elevation is the result of a headcut. However, the depression does not appear to have a designed geometric configuration per depression standards, see Figure 3.

Figure 3: The image on the left is from the upstream side, looking downstream, at the inlet. The image on the right is from within the pipe looking upstream at the inlet. It is assumed the depressed inlet is part of the initial design intent.

Hydraulic modeling of the existing condition suggests the road is overtopped to the north at approximately the 5-year return interval. The existing condition does not meet the 25-year capacity requirement.

The existing hydraulic condition within the culvert is similar to the hydraulic condition of the channel outside the influence of the culvert for normal (average annual) flow conditions where fish would likely be migrating. The conditions within the culvert are not a fish barrier for normal flow conditions.

However, the 3-foot depression with a near vertical face at the culvert entrance is an area with a rapidly varied flow condition. These conditions are a challenge to model using numerical modeling methods. There is likely turbulence at this transition that could be a barrier to juvenile fish. Adult fish can likely pass the transition by jumping or sprinting upstream.

Options and Recommendations Two options are proposed to address this conduit:

1. Retrofit the Existing Pipe

2. Replace the Existing Pipe

Retrofit The existing pipe is in Good condition. Constructing a retrofit which consists of a depressed concrete inlet and headwall and wingwalls will make the conduit more efficient. Hydraulic modeling shows these improvements can meet the 25-year peak runoff event. Additional improvements include a headwall at the outlet and armor.

Inlet Depression An inlet depression is created by constructing the entrance inlet below the streambed. The amount of inlet depression is defined as the depth from the natural streambed at the face to the inlet invert. The inlet control equations or nomographs provide the depth of headwater above the inlet invert required to convey a given discharge through the inlet. This relationship remains constant regardless of the elevation of the inlet invert. If the entrance end of the culvert is constructed below the streambed, more head can be exerted on the inlet for the same headwater elevation.

Inlet depressions are constructed at the entrance end of a culvert as shown in Figure 4. Figure 4 depicts the use of an approach apron with the fill retained by wingwalls. The apron will be armored. The maximum slope of the apron shown at depth “T” is 3H : 1V. The width “W” is 15 feet.

This configuration does not change the rapidly varied flow condition of the inlet transition. The existing fish passage condition would continue.

Figure 4: Culvert with inlet depression and with apron and wingwalls.

Replace Due to the cover requirements and sensible constructability methods, replacement would include:

- Arch Plate o Span = 167.2” (13.9’) o Rise = 103” (8.6’)

- The structure would have a headwall and toewall at the inlet and outlet.

- The structure would be partially buried with material to simulate a natural bottom.

Further hydraulic analysis is required to identify the embedment depth to achieve the channel’s equilibrium slope through the reach to remove the inlet depression. It is likely the embedment depth will be no greater than 2 feet.

995+00 (Crooked Creek) The Crooked Creek structure is a 48-inch CMP without headwall infrastructure. Hydraulic modeling of the existing condition suggests the road is overtopped at approximately the 5-year return interval. The existing condition does not meet the 25-year capacity requirement. Additionally, evidence of piping and minor segment separation was seen during the field visit.

W

The existing hydraulic condition within the culvert is similar to the hydraulic condition of the channel outside the influence of the culvert for normal (average annual) flow conditions where fish would likely be migrating. The conditions within the culvert are not a fish barrier for normal flow conditions.

A minor headcut can be seen in the channel downstream of the culvert migrating towards the outlet. This headcut is likely controlled by the water surface elevation of Strawberry Creek Reservoir approximately 1 mile downstream. The lack of embedment of the current configuration limits the flexibility for the culvert invert to adjust to any changes in stream thalweg elevation. This could become a barrier in the future.

Figure 5: The image on the left shows evidence of piping along the culvert from the inlet side. The image on the right shows a minor headcut being arrested at the culvert exit.

Recommendations Based on the results of the analysis, it is recommended to replace this pipe. Requirements considered during the structure selection process included:

- From the section “Select Environmental Permitting Requirements Specific to the Discussion Section”:

o The grade and elevation of the bottom (or floor) of the culvert shall not change the profile from that of the original undisturbed streambed, unless the culvert is intended to be used as a fish barrier.

o The bottom of the culvert should contain natural streambed material if the natural stream contains a fishery. This may require installing the culvert flowline below the bed of the channel or installation of an open bottom culvert.

- Cover requirements

- Sensible constructability methods

Structures considered for the replacement include:

- Metal Box o Span = 126” (10.5’) o Rise = 66” (5.5’)

- Arch Plate o Span = 95” (7.9’) o Rise = 67” (5.6’)

- Both structures would have a headwall and toewall at the inlet and outlet.

- Both structures would be partially buried with material to simulate a natural bottom.

The difference in the structure selection is due to the constructability methods for placing the material in the bottom of the conduit. Further investigation into these methods will guide the structure selection.

Further hydraulic analysis is required to identify the embedment depth to achieve the channel’s equilibrium slope through the reach to remove the inlet depression. It is likely the embedment depth will be no greater than 2 feet.