Hydraulics_Report.pdf

Subject: CA ERFO DEVA 11(1) – Boulder Weir Flow Training Structures

From: Laura Girard, PE & Megan Frye, PE Hydraulic Engineer

FHWA-Central Federal Lands Lakewood, CO

To: Brent Nagen, PE Project Manager

This memorandum presents the design analyses and recommendations for the proposed channel training structure at the boulder weir upstream of the stream restoration site. Prior to the flood, the main channel flow followed the north canyon wall. The flow path dispersed into an existing wetland. A low flow spring channel also followed a flow path along the northern edge of the main channel and fed into the existing wetland.

The pre- and post-flood flow paths are shown in the Google Earth image below.

Figure 1. Google Earth image

Memorandum

Date: September 13, 2017

Pre-flood flow path

Post-flood flow path

Water intake building

N

During the flood, the main flow path migrated to the south along the roadway embankment abandoning the channel along the northern wall. Due to degradation, the pre-flood channel is now abandoned and perched approximately 3 feet above the post-flood main flow path. The current post-flood flow path falls within the proposed roadway embankment and needs to be redirected towards the north canyon wall to avoid damage to the proposed roadway. The migration of the channel away from the wetlands towards the road has also cut off the surface water source for the wetlands. Redirecting the main flow path back to the wetlands will help reestablish the lost riparian vegetation.

Figures 2 and 3 illustrate the pre- and post-flood conditions at the boulder weir location. The vegetation along the roadway and in the wetland is evident in Figure 2. Figure 3 demonstrates the degraded main flow channel adjacent to the roadway and the lack of vegetation throughout the floodplain.

Figure 2. Pre-flood condition at proposed boulder weir location

Figure 3. Post-flood condition at proposed boulder weir location

The extreme channel grading and restoration required to return the channel to its pre-flood path is impractical and beyond the scope of this project. The intent of the design at this site is to train the main flow back towards the wetlands and away from the roadway embankment with a boulder weir. The weir

Perched channel

Spring flow channel will direct flows away from the roadway embankment and into the wetlands reestablishing the hydrologic connection in the wetlands encouraging reestablishment of the wetland vegetation.

Hydraulic analysis at this site included a hydrologic assessment to determine design discharges and hydraulic modeling to determine hydraulic conditions.

HYDROLOGY

Design discharges for the basin encompassing Bonnie Clare Road were estimated using the 2007 Caltrans Regional Regression Study. It was determined that the Caltrans study better represents the unique properties of desert storms than the USGS regional regression equations. The design discharges at the boulder weir are represented in the following table.

Main Channel Flow (cfs)

Q5 917 Q10 1690 Table 1: Design Discharge

HYDRAULICS

The proposed design at this location includes a 50-foot boulder weir, relocation of the spring flow channel, and willow plantings along the spring flow channel and along the boulder weir. The combination of design elements will redirect flow towards the abandoned wetland and away from the roadway embankment.

Post-flood, the spring flow channel has reestablished a flow path along the roadway embankment and is no longer feeding into the wetlands to the north. Figure 4 shows the existing flow path of the spring flow channel.

Figure 4. Spring flow channel along roadway embankment

The relocation of the spring flow channel will redirect the flow into the wetland to support the re-establishment of riparian vegetation. Given the channel bed characteristics and the dynamic nature of spring flow, it is expected that the channel will migrate throughout the floodplain. The migrating channel is expected to widen the riparian corridor and further re-establish floodplain vegetation. Figure 5 illustrates the existing and approximate alignment of the proposed spring flow channel.

Figure 5. Spring flow channel along roadway embankment

A boulder weir is proposed along the roadway embankment on the south side of the canyon (See Figure 5). The weir will re-direct channel forming flows, 5-year flow events and less, away from the roadway embankment and into the wetland adjacent to the abandoned channel to the north. The design intent is to push channel forming flows back to the north and distribute flow into the riparian area, like pre-flood channel morphology. The area between the roadway and the boulder weir will be filled and willows stakes planted (See Figure 5). A small seep exists under the roadway at this location and the hope is the seep will feed the willow plantings behind the boulder weir. The willows will help to hide the boulder weir from view and will be used in the permitting as credit for riparian revegetation.

The conditions for the 5-year design event were analyzed during the development of the recommendations at the boulder weir. The 5-yr design event was considered to represent the channel forming flow during which sediment deposition and channel migration are most common. The intent of the boulder weir is to redirect the higher velocities towards the northern bank and into the wetland. The higher velocities should erode the northern bank and help establish the main flow path directing into the wetland along the bank of the abandoned channel.

Figure 6 demonstrates the decrease in velocities from the existing conditions to the proposed condition for the 5-year event. The red areas represent the greatest reduction in velocity while the blue areas represent little reduction in velocity. The greatest reduction in velocity occurs directly downstream of the boulder weir along the proposed roadway embankment. This reduction should help protect the

Current spring flow path

Proposed spring flow path (approx.)

Boulder weir

Willow planting roadway embankment while encouraging sediment deposition in the floodplain adjacent to the roadway.

Figure 7 demonstrates the increase in velocities from the existing conditions to the proposed condition for the 5-year event. The red areas represent the greatest increase in velocity while the blue areas represent a small increase in velocity. The greatest increase in velocity occurs along the northern bank of the wetland area. This increase will help reestablish the main flow around the northern bank dispersing flow throughout the wetland.

Figure 6. Reductions in Velocity – Heat Map

Figure 7. Increase in Velocity – Heat Map

Figures 8 and 9 illustrate the existing and proposed conditions of the flow depth for the 5-year design event. The red and yellow areas indicate deeper flow while the green and blue areas indicate shallow flow. The existing depth heat map shows a relatively channelized system flowing along the southern border of the wetland adjacent to the roadway embankment. With the addition of the boulder weir, it is evident from the proposed depth heat map that the flow is dispersed through the wetland up to the northern bank along the abandoned channel.

The group of design elements at the boulder weir will promote channel migration away from the roadway and back into the wetland area. This will increase the resiliency of the roadway and will help re-establish vegetation throughout the floodplain downstream.

Figure 8. Existing Condition – Depth Heat Map

Figure 9. Proposed Condition – Depth Heat Map

REFERENCES

Caltrans. “Improved Highway Design Methods for Desert Storms.” August 2007.

Aquaveo Surface Water Modeling System 12.2.7 (www.aquaveo.com).

http://www.aquaveo.com/

Subject: CA ERFO DEVA 11(1) – Cottonwood Corner

From: Laura Girard, PE Megan Frye, PE Hydraulic Engineer

This memorandum presents the design recommendations for the proposed grading and site work at Cottonwood Corner. Prior to the flood, the tributary flowing south to north and across the road followed the northeast canyon wall and crossed the road just south of the existing wetland. During the flood, a significant amount of material from the tributary flow was deposited just south of the roadway. This deposition has created a new preferential tributary flow path along the southwest face of the canyon.

The tributary flow now continues along the roadway to the west rather than crossing and joining the main channel.

The pre- and post-flood flow paths are shown in the Google Earth image in Figure 1.

Date: October 16, 2017

Pre-flood flow path

Post-flood flow path

Existing wetland

Main channel

Figures 2 through 4 illustrate the pre- and post-flood conditions at Cottonwood Corner. The rills and gulls from the tributary flow along the northeast canyon wall pre-flood are demonstrated in Figure 2 while the wide, flat flow path established along the southwest wall post-flood is shown in Figures 3 and 4.

Figure 2. Pre-flood condition at tributary crossing

Figure 3. Post-flood condition at tributary crossing, looking south.

Pre-flood flow path

Post-flood flow path

Material deposition post- flood

Figure 4. Post-flood condition at tributary crossing, looking southeast.

The area just south of the roadway has been identified for potential use during construction and will require re-grading during the final clean up near completion of the project. The re-grading in this area will be completed to mimic the pre-flood condition of the tributary flow path as shown in Figure 5.

Figure 5. Approximate extents of grading south of road

The wetland area just northeast of the proposed flow path shown in Figure 5 has been identified by the Timbisha Shoshone as a spring site and should be preserved as a natural and cultural resource. The work proposed north of the road will avoid impacting the wetland vegetation.

Post-flood flow path

Pre-flood flow path

Regrade area to establish flow path shown

Approx. location of proposed flow path

Figure 6. Post-flood condition north of road

As part of a previous construction project, a concrete barrier and 12-inch gabion revet mattress was installed along the north side of the road. The southern end of this protection is shown in Figure 6.

Additional concrete barrier and revet mattress is proposed along the north side of the road. This protection will tie into the southern end of the existing protection and will extend 100 feet to the southeast along the shoulder as demonstrated in Figure 7.

Figure 7. Proposed extents of protection at Cottonwood Corner

The channel north of the road has degraded approximately 3 feet as shown in Figure 8. To address this degradation and provide protection against future degradation effecting the roadway, the proposed gabion revet mattress will extend 3 feet below the existing channel elevation at a 3 (horizontal) to 1 (vertical) slope. The channel material removed to place the revet mattress will be replaced over the mattress to restore the existing ground elevation.

Existing concrete barrier

Figure 8. Existing channel degradation

The buried revet mattress will protect the roadway from future degradation of the channel to the south of the wetland vegetation. To mitigate erosion from tributary flow along the south side of the wetland vegetation, several boulders will be placed (at the direction of the Project Engineer) along the southeast end of the wetland vegetation as shown in Figure 8.

Figure 8. Approximate location of boulders

This work proposed at Cottonwood Corner will re-establish the tributary flow across the roadway just south of the wetland vegetation. This will address the erosion concerns along the ditch along the south side of the road where the post-flood tributary path has been re-directed. The proposed concrete

Existing degradation.

Bank is approx. 3 feet high.

Approx. location of placed boulders barrier and revet mattress along the north side of the road will protect the roadway from future degradation in the channel.

Subject: CA ERFO DEVA 11(1) – Drop Structure at 168+00

From: Laura Girard, PE Megan Frye, PE Hydraulic Engineer

FHWA‐Central Federal Lands

This memorandum presents the design analyses and recommendations for the proposed drop structure upstream of the water intake berm. Figure 1 provides an aerial of the area for reference.

Flood flows in the main channel resulted in approximately 8 feet of degradation in the main channel just north of the roadway.

Date: December 8, 2017

Tributary flow

Water intake berm

Main channel flow

Figures 2 and 3 illustrate the pre‐ and post‐flood conditions at the boulder weir location. The vegetation along the roadway and in the wetland is evident in Figure 2. Figure 3 shows the degraded main flow channel adjacent to the roadway and the lack of vegetation throughout the floodplain.

Figure 2. Pre‐flood condition at proposed drop structure

Figure 3. Post‐flood condition at proposed boulder weir location

The intent of the design at this site is to lower the road grade to create a low water crossing for the main channel, to reinforce the roadway embankment to the north, and to provide a rockery drop structure that addresses the remaining elevation difference between the roadway and the main channel to the north.

Approx. 8’ degradation at roadway

Hydraulic analysis at this site included a hydrologic assessment to determine design discharges and hydraulic modeling to determine hydraulic conditions.

HYDROLOGY

Design discharges for the basin encompassing Bonnie Clare Road were estimated using the 2007 Caltrans Regional Regression Study. It was determined that the Caltrans study better represents the unique properties of desert storms than the USGS regional regression equations. The design discharges at the drop structure at 168+00 are represented in the following table.

Q5 917

Q10 1690

The proposed design at this location includes lowering the roadway profile to create a low water crossing, armoring the northern roadway embankment, and constructing a rockery drop structure just north of the roadway in the main channel. Figure 4 shows to location of the proposed design elements.

The combination of elements will address the 8 feet of degradation and will help to armor the new roadway during future flow events.

Figure 4. Proposed design elements at 168+00

From 165+00 to 168+50, the road profile was lowered approximately four feet to create a low water crossing for the main channel. This low water crossing provides a flow path across the roadway from south to north stopping the preferential flow path down the roadway. Lowering the road profile also addresses a portion of the 8 feet of main channel degradation to the north of the roadway.

Rock bank protection

Main channel flow

Low water crossing

N

Revet mattress and buried concrete barrier

Rockery drop structure

Figure 5 shows the flow depth for the 10‐year event with the drop structure in place. The main channel flow path is shown between 165+00 and 168+50 where the low water crossing is proposed. Some additional flow runs down the ditch to the west and intersects with the tributary flow at 170+00 and crosses the road.

Along with the revet mattress and buried concrete barrier armoring along the north shoulder of the roadway, additional rock will be placed along the embankment remaining around the power pole at 169+00 shown in Figure 6. The bank armoring will be constructed with boulders on‐site. It will tie into the revet mattress around 169+00 and will extend 40 feet along the south bank as shown.

Figure 6. Existing and proposed conditions at 169+00

Figure 5. Water depth with flow vectors for the 10‐yr event

Roadway embankment and revet mattress

Bank armoring flow

To address the remaining channel degradation to the north of the road, a rockery drop structure will be constructed using larger boulders on site (min. 3’ diameter). The location of the drop is show in Figure 7.

Figure 7. Location of proposed drop structure

The drop structure will be 20 feet wide (across the channel) and will have a vertical drop of 1 foot. To mitigate for scour at the base of the vertical drop, the rockery will extend 4 feet below the channel bed elevation. In total, the rockery will be 5 feet high.

Figure 8 shows the channel profile from the edge of roadway downstream along the main channel. The existing water surface elevation is shown in red while the proposed is shown in blue. The edge of roadway and location of the vertical drop is sketched in for reference. While the water surface elevation increases upstream of the drop, the depth of flow upstream of the drop is actually lower taking into account the increase in bed elevation from existing to proposed. For example, at distance 180 feet, the existing water surface elevation and flow depth are 3356.65 feet and 2.3 feet respectively. The proposed water surface elevation and flow depth at this point are 3357.10 feet and 1.9 feet.

Rockery drop structure Rockery drop structure flow

The increase in the bed elevation upstream of the drop provides a more uniform channel slope upstream and downstream of the drop which will promote channel stability. Figure 9 shows the increases in water depth between the existing and proposed conditions. The increase in bed elevation upstream of the proposed drop results in some localized increases in water depth across the roadway in the low water crossing. The maximum increase in depth on the roadway is 0.5 feet. The largest increase in depth is immediately downstream of the drop where the depth of flow increases by a maximum of

1.9 feet.

The group of design elements between 165+00 and 170+00 will address the 8 feet of degradation in the main channel. This will increase the resiliency of the roadway during future flow events.

Figure 8. Water surface elevations for the 10‐yr event

Figure 9. Increase in flow depth from existing and proposed for the 10‐yr event

Rockery drop structure

Edge of roadway

Rockery drop structure

D ro p St ru ct ur e

Ed ge o f r oa dw ay

Subject: CA ERFO DEVA 11(1) – Scotty’s Castle Scour Protection

From: Megan Frye, PE Laura Girard, PE Hydraulic Engineers

This memorandum presents the design analyses and recommendations for the scour protection and grade control at the Scotty’s Castle bridge. Scour and degradation has removed 4‐6 feet of material from the bridge section, exposing a footing, undermining the right abutment on the downstream end of the bridge, leaving the bridge in a scour critical condition. A 5‐foot headcut is located about 80‐100 feet upstream of the bridge. Another 2‐foot headcut exists at the downstream end of the bridge.

Maintenance efforts to arrest both headcuts with rocks are failing. Long‐term degradation and scour will continue to lower the channel bed through the bridge section further undermining the structure footings unless countermeasures are installed.

Figures 1 and 2 illustrate the post‐flood channel conditions from February 2016. The headcut and armoring at the downstream end of the bridge is shown in Figure 1 and the headcut immediately upstream of the bridge is shown in Figure 2. During the May 2017 site visit, the headcut upstream of the bridge has moved approximately 50 feet upstream of the location shown in Figure 2. The upstream headcut is continuing to progress upstream and the actual location at the time of construction will most likely be different than the location represented in the survey. Some flexibility in the project funding should be built into the estimate to account for this difference.

Date: October 24, 2017

Figure 1. At the downstream face of right abutment, looking upstream through bridge

Figure 2. At the upstream face of right abutment, looking across channel observations downstream of the site suggest an additional 6 feet of degradation could move through the bridge section. Two, 2‐foot headcuts were observed between Scotty’s Castle and the confluence with Tie Canyon and an additional 2 feet of degradation is anticipated between the confluence with Tie Canyon and the outlet of the canyon approximately 1 mile downstream of the confluence. The

Existing 5‐foot headcut upstream of bridge

2‐foot headcut arrested with boulders

Right abutment undermining countermeasure design at the bridge needs to address local scour at the abutments as well as the long‐ term degradation anticipated.

Hydraulic analysis at this site included a hydrologic assessment to determine design discharges and hydraulic modeling to determine hydraulic conditions.

HYDROLOGY

Design discharges for the basin encompassing Bonnie Clare Road were estimated using the 2007 Caltrans Regional Regression Study. It was determined that the Caltrans study better represents the unique properties of desert storms than the USGS regional regression equations. The 10‐ and 50‐year design discharges at Scotty’s Castle is represented in the following table.

Q10 1689

Q50 5073

The 10‐year design discharge is the hydraulic design discharge used for Scotty’s Castle bridge. The hydraulic design discharge is selected based on the level of risk acceptable at the structure. For the proposed work at this location, the 10‐year design discharge was used to determine the capacity of the bridge under the existing and proposed conditions to ensure the capacity is not reduced with the proposed design. The depth of flow and velocities were also used to determine the size of articulating concrete blocks (ACBs) used in the design and the final elevation where the ACBs tie into the banks along the channel.

The 50‐year design discharge was used to determine the scour depth at the abutments. For shallow foundation bridges, the scour design flood is equal to the scour check flood. Based on the risk‐based approach presented in HEC‐18 (2013) Chapter 2, the 50‐year design event is the equivalent check flood frequency for a bridge with a 10‐year hydraulic design discharge.

Long‐term degradation and scour during the 2014 flood event high flow resulted in exposed footings on the right abutment. Observed undermining of the footing at Scotty’s Castle bridge qualifies the bridge as scour critical. Because the footings of the existing structure are exposed and undermined, scour countermeasures are required at the bridge.

The total scour depth at the abutments is a combination of anticipated long‐term degradation, contraction scour, and local scour at the abutment. The scour depth at the abutment was calculated using the NCHRP Method outlined in HEC‐18 (2013). The NCHRP Method combines contraction scour calculations with an amplification factor based on the abutment configuration and scour condition to determine the local scour depth at the abutment. Using the 50‐year design flow, live‐bed scour conditions, and an amplification factor representative of vertical wall abutments, the local scour depth at the abutments is 9 feet. As previously stated, an additional 6 feet of long‐term degradation is expected to move through the bridge section. Therefore, the total anticipated scour depth at the abutments is 15 feet, which corresponds to an elevation of 2964 feet. Ideally, the top of the footing would be set at an elevation at or below the elevation that represents the total scour depth for the scour check flood. This is not the case with the bridge at Scotty’s Castle where the top of the footing is at approximately 2978 feet.

To protect the bridge foundations, a combination of design elements is proposed. Grade control structures in the form of sloped drop structures will be used to mitigate channel bed instability and scour countermeasures will be used to protect the bed and banks at the bridge. Both will be constructed with articulating concrete blocks (ACBs). The extent of the ACBs will link the upstream grade control, the scour countermeasure through the bridge section, and the downstream grade control.

The upstream armoring will begin above the existing headcut (approximately 50 feet upstream of the bridge in current survey). Through the section upstream of the bridge, a 10‐foot wide by 1‐foot deep low flow channel to concentrate the low flows into a defined channel through the section lined with ACBs. The low flow channel in planform will be straight with no meanders essentially in the middle of the channel cross section. The width and depth of this channel was set based on pre‐flood aerial photos and site observations. The banks will be armored with ACBs with side slopes not to exceed a 1 (horizontal) to 2 (vertical). Figure 3 demonstrates the cross section of the channel upstream of the bridge.

Figure 3. Upstream Channel Cross Section

Through the bridge section, the ACBs will extend from abutment wall to abutment wall covering the full channel width. Figure 4 shows the typical cross section through the bridge.

Figure 4. Bridge Channel Cross Section

Downstream of the bridge, the ACB armoring will extend across the full channel, including flow channel, and along the banks with side slopes not to exceed a 1 (horizontal) to 2 (vertical). Figure 5 demonstrates the cross section downstream of the bridge.

Figure 5. Downstream Channel Cross Section

The location and elevation of the sloped drops stabilizes the existing headcuts upstream of the bridge and at the downstream end of the bridge. The sloped drops downstream of the bridge will relocate the existing headcut at the end of the bridge downstream providing a 4% channel slope through the bridge section consistent with the natural channel slope upstream and downstream of the bridge. The vertical drop associated with the existing headcut in the bridge will be redistributed over two sloped drops: one 10 feet downstream of the bridge with a 2‐foot vertical drop over 8 feet horizontal, and one 40 feet downstream of the bridge with a 1.5‐foot vertical drop over 3 feet horizontal. To mitigate future degradation at this sloped drop, the ACBs will be embedded 6 feet below the channel bed at 1 (horizontal) to 2 (vertical) slope. To help identify the progression of the downstream headcut moving towards the bridge, the embedded blocks will have a series of visual indicators, such as every other row of blocks painted to monitor degradation. Figure 6 demonstrates the vertical profile of the proposed channel bed elevation of the ACBs.

Figure 6. Vertical Profile of ACB Channel

If the design included only the scour countermeasures at the bridge for abutment scour protection, the extents of the armoring would reach 22 feet upstream and downstream of the bridge and 25 feet from the face of the abutment along the approach embankment. The addition of grade control upstream and downstream adds 33 linear feet of armoring upstream and 50 linear feet of armoring downstream.

Figures 7 demonstrates the increases in water depth between the existing and proposed conditions. The increases in water depth are generally localized within the floodplain immediately upstream of the bridge with some small increases in depth through the bridge section. The increases in water depth upstream of the bridge do not impact any of the existing facilities around Scotty’s Castle.

Figure 7. Increase in Water Depth for the 10‐yr event

Figure 8 shows the channel profile through the section to be armored. The existing water surface elevation is shown in red while the proposed is shown in blue. The bridge is sketched in for reference.

The more gradual sloped drop at the upstream headcut results in the increase in water depth shown in plan view in Figure 7 and in profile view in Figure 8 between 50 and 75 feet on the channel profile. The existing conditions demonstrated in Figure 8 are representative of the post‐flood conditions. In pre‐ flood conditions, the channel bed elevation was approximately 5 feet higher than the post‐flood elevation. Though the proposed condition raises the channel elevation above the post‐flood elevation, the capacity of the bridge is still more than it was in pre‐flood conditions.

Figure 8. Water surface elevations for the 10‐yr event

Existing ground profile

Proposed ground profile

Bridge

Figures 9 shows the velocity and depth for the proposed condition along the channel. The velocity is shown in red while the depth is shown in blue. The extents of the bridge are shown for reference.

Figure 9: Depth and Velocity along Channel

The greatest depths coincide with the lowest velocities which occur between the first drop upstream of the bridge and the bridge. The lower depths coincide with the highest velocities downstream of the bridge. The increase in water depth upstream of the bridge is the result of backwater from the channel constriction through the bridge. The channel geometry upstream of the bridge is characterized by a wide, flat floodplain while the channel geometry through the bridge is confined with no floodplain access. The channel downstream of the bridge is less confined than the channel through the bridge which results in lower water depths. The contraction of flow through the bridge is shown in Figure 10.

Figure 10:Water Depth for 10‐yr Event

Bridge

Depth

Velocity

Once the ACBs are installed, a minimum of 6 inches of conserved channel bed material will be placed on top of the blocks in the channel. The ACBs must be open celled blocks, similar to those shown in Figure

11. The open celled blocks will promote vegetation growth in the blocks.

Figure 11. Example of Articulating Concrete Blocks (Photo from Contech®)

A factor of safety of 1.3 was used to determine an adequate block size for the design. The typical range of factors of safety at a bridge are between 1.5 and 1.7. With the high velocities and shear stresses immediately downstream of the bridge reaching a factor of safety acceptable for bridge protection was not possible with the material available. Some risk of failure is assumed using a factor of safety of 1.3.

The greatest risk to failure exists downstream of the bridge. In this section, the maximum velocity is 21 feet per second with a water depth of 2.8 feet. These conditions result in a factor of safety of 1.3 for a 9‐inch thick block that is 23.9 feet wide and 17.4 feet long. Safety factor, or protection from failure, could be increase by selecting a thicker block.

The group of ACB design elements at Scotty’s Castle will provide scour protection through the bridge section while stabilizing the channel bed upstream and downstream of the bridge. The armoring across the channel and onto the banks around the bridge will serve as scour countermeasures mitigating future undermining of the bridge foundation. The sloped drops downstream of the bridge will redistribute the existing vertical drop at the bridge over several structures downstream of the bridge providing energy dissipation through the bridge section and immediately downstream of the bridge.

FHWA. “Hydraulic Engineering Circular No. 18 – Evaluating Scour at Bridges.” April 2013

NAME: Scotty's Castle Bridge RG#:

PROJECT: CA ERFO DEVA 11(1) Bonnie Clare Road DATE:

ENGINEER'S ESTIMATE (30%)

EE EE

ITEM NO. ITEM DESCRIPTION UNIT QUANTITY UNIT PRICE ITEM COST

15101-0000 Mobilization LPSM 1 $18,000 $18,000 20304-1000 Removal of Structures and Obstructions LPSM 1 $1,500 $1,500 20420-0000 Embankment Construction CUYD 350 $50 $17,500 20820-0000 Dewatering LPSM 1 $20,000 $20,000 25306-1000 Revetment Mat, Articulated Concrete Block SQYD 1000 $150 $150,000 61401-0000 Lean Concrete Backfill CUYD 5 $500 $2,500

Total = $209,500 20% contingency Total = $251,400

Notes Removal of structures and obstructions covers removal of gabion baskets placed as part of leach field contract Embankment construction includes 6" channel material (~250 cy) and fill needed under ACBs (~350 cy) ACB quantity accounts for full-channel ACBs from headcut US of bridge, through bridge to ~50 ft downstream of bridge (including toe down) Lean concrete backfill at scour holes beneath structure footings

PRE

LIM

INARY

NOT

FOR

CO

NST

RUCTI

ON

SHEET

NO.

PROJECTSTATE

CA

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

DEATH VALLEY NATIONAL PARK

INYO COUNTY, CALIFORNIA

DRAWING NO.DATEBRIDGE DRAWING

KARL EIKERMANN

PROJECT TEAM LEADERSCALE

CHECKED BY

DRAWN BY

R.WEHNER

DESIGNED BY

REVISIONS

BY

DATENO.

N

C A e r f o (1

B r id g e R

G C

A

F il e s D

G N

F il e s r g s it e .d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

NPS PMIS NO.: 224986 NPS DRWG. NO.: 143/140011

C BridgeL

N

Wall A

Wall B

Wall C

Wall D

PLAN

S2

To Bonnie Clare Road

To Scotty's Castle

1" = 20'-0"

A

B

C

D D

C

B

A

F lo w

F lo w

C Bridge SpanL

Upstream face of bridge deck

NOTE:

B

SCOUR MITIGATION SITE PLAN

K. EIKERMANNM. FRYE

10'-0"

2'-0"

5'-0"5'-0"

2'-0"

10'-0"

14'-0" 14'-0"

Construct Embankment to El. 2986.5

10'-0"

2'-0"

5'-0"5'-0"

2'-0"

10'-0"

Limits of articulated concrete block revetment mat proposed revetment mat.

Remove portion within

Existing gabion basket berm.

Location of footing scour to be filled with lean concrete backfill. See RG3033-G & H.

See RG3033-C & D for Sections A-A thru D-D.

50 40 30 20 10 0 10 20 30

C Bridge SpanL

C Bridge SpanL

SECTION A-A

SECTION B-B

" = 1'-0"8

40 30 20 10 0 10 20 30 40

REVETMENT SECTIONS (1 OF 2)

El. 2987

Approximate existing ground max.

max.

Embankment Construction

El. 2987

K. EIKERMANNM. FRYE

Existing Bridge Abutment Wall

Existing Bridge Abutment Wall

Approximate existing ground

Embankment Construction

3 C

S3

NOTES:

Revetment Mat.

Articulated Concrete Block

Finished grade revetment mat.

Place 6" (min.) conserved bed material over articulated concrete block

See RG3033-B for location of sections.

10'-0"2'-0"5'-0" 5'-0"2'-0"10'-0"

2'-0" 2'-0"5'-0"5'-0"

Block Revetment Mat.

Articulated Concrete

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g x s e c .d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

NPS PMIS NO.: 224986 NPS DRWG. NO.: 143/140011

C Bridge SpanL

C Bridge SpanL

SECTION C-C

SECTION D-D

" = 1'-0"8

40 30 20 10 0 10 20 30 40 50

40 30 20 10 0 10 20 30 40 50

REVETMENT SECTIONS (2 OF 2)

2'-0"10'-0" 5'-0"5'-0" 2'-0" 10'-0"

El. 2986 El. 2986 max.1 max.1

Approximate existing ground

Embankment Construction

Approximate existing ground max. 1 max.

El. 2982El. 2982

2'-0"14'-0" 5'-0"5'-0" 2'-0" 14'-0"

M. FRYE K. EIKERMANN

S4

D4

Mat.

Block Revetment

Articulated Concrete

Finished grade

Finished grade

Embankment Construction

Revetment Mat.

Articulated Concrete Block

See RG3033-F for Top of Slope Detail (typ.)

NOTES:

revetment mat.

Place 6" (min.) conserved bed material over articulated concrete block

See RG3033-B for location of sections.

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g x s e c .d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

REVETMENT MAT ELEVATION

" = 1'-0"32

REVETMENT MAT ELEVATION @ C BRIDGE SPANL

El. 2986.8

El. 2982.3

El. 2979.6

El. 2977.6 El. 2976.8

El. 2969.2

Approx. Existing Ground @ C Bridge SpanL

Revetment Mat Articulated Concrete Block o f b r id g e d e c k

U p s tr e a m f a c e

-4% o f b r id g e d e c k d o w n s tr e a m f a c e

Embankment construction (typ.)

20'-4"

Bridge Deck

K. EIKERMANNM. FRYE 5 E

S5

NOTES:

revetment mat.

Place 6" (min.) conserved bed material over articulated concrete block

See RG3033-F for Top of Slope Detail.

15'-0"20'-0"8'-0"30'-0"37'-0"18'-0"

-4%

1:4

1:4

1:2

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g r e v e tm e n t.

d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

Articulated concrete blocks

PLAN VIEW

TYPICAL MAT

17.4"

23.6"

8.5"

8.5"

TOP VIEW END VIEW

SIDE VIEW

Note:

2.

1.

Existing streambed

Existing ground

NONE

3 u nit s

TOP OF SLOPE DETAIL

1(max.)

TYPICAL UNIT

CHANNEL SECTION

714.01(a).

Furnish geotextile conforming to subsection submitted to the CO for approval.

Alternate concrete block designs may be

Geotextile

6 F

REVETMENT MAT DETAILS

'-0

R

Existing Subgrade

1:2 (m ax.)

Backfill

S6

K. EIKERMANNM. FRYE

Existing Ground

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g r e v e tm e n t.

d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

-4%

1:3

-4%

1:3

Articulated Block Revetment Mat.

Articulated Block Revetment Mat.

Flow

Flow

ABUTMENT 1

ABUTMENT 2

" = 1'-0"16 3 G

ABUTMENTS

6" x 2'-6" delamination construction joint construction joint

4 8" to 3 " wide crack

2'-0" x 2'-0" delamination

4" wide crack

Approx. existing ground

Approx. existing ground

S7

"2 11'-9

"2 11'-9

38'-5"

1'-9"1'-9"

" 5

38'-4"

"2

4" crack

Existing riprap wier

1'-2"

Existing riprap wier

1'-2"Blockout

K. EIKERMANN

concrete backfill.

Fill with lean

6" scour depth.

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g a b u t.

d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

WALLS

H

WALL B WALL D

WALL A

WALL C

22'-4" ground

Approx. existing lagging wall

Concrete post ground

Approx. existing ground

Approx. existing ground

Approx. existing

K. EIKERMANN 8

S8

8"

18'-1"

20'-6"

9'-0"

3'-6"

6" Ø drain

Existing riprap wier

20'-6"

Eixisting riprap wier

18'-1"

" = 1'-0"8

Articulated concrete block revetment mat.

mat.

revetment block concrete

Articulated

Articulated concrete block revetment mat.

22'-4" backfill.

Fill with lean concrete x 6' deep scour hole.

Approx. 1'-6" high

PRE

LIM

INARY

NOT

FOR

CO

NST

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

SCOTTY'S CASTLE BRIDGE

N

C A e r f o (1

B r id g e R

G C

A e s D

G N

F il e s r g w a ll e le v .d g n

RG3033-

BONNIE CLARE ROAD

ERFO DEVA 11(1)

of OCTOBER 2017

OPTION X

Subject: CA ERFO DEVA 11(1) – Ubehebe Flow Training Structures

From: Laura Girard, PE & Megan Frye, PE Hydraulic Engineer

This memorandum presents the design analyses and recommendations for the proposed channel training structures at the tributary crossing on Bonnie Clare Road just upstream of Ubehebe Crater Road.

Prior to the flood, the main channel flow path was approximately 80 feet from the edge of the roadway.

The tributary upstream of Ubehebe Crater Road crossed Bonnie Clare Road and join the main channel flow approximately 1200 feet upstream of the low water crossing on Ubehebe Crater Road. The combined flow, main channel and tributary, passed over the low water crossing on Ubehebe Crater Road.

Figure 1. Google Earth image showing pre-flood flow paths

Post flood, the main channel has moved close to Bonnie Clare Road causing the road to overtop during high flow events. Flood flows also cut an 8-foot-wide path downstream of the tributary crossing along

Memorandum

Date: September 12, 2017

Main channel flow, pre-flood

Tributary flow, pre-flood

Main channel flow, post-flood

Tributary flow, post-flood the south side of the road creating a preferential flow path for the tributary along the south side. This new tributary flow path was exacerbated by the removal of a rock outcropping along the south side of the confluence of Bonnie Clare Road and the tributary. Rather than joining in the main channel and continuing to the low water crossing at Ubehebe Crater Road, the tributary flow and overtopping flow from the main channel continue west and south into the facilities at Grapevine.

The intent of the design at this location is to train the main flow back to the pre-flood flow path along the northern bank and across the low water crossing on the Ubehebe Crater Road away from the infrastructure at Grapevine. Hydraulic analysis at this site included a hydrologic assessment to determine design discharges and hydraulic modeling to determine hydraulic conditions.

HYDROLOGY

Design discharges for the basin encompassing Bonnie Clare Road were estimated using the 2007 Caltrans Regional Regression Study. It was determined that the Caltrans study better represents the unique properties of desert storms than the USGS regional regression equations. The design discharges at this location are represented in the following table.

Tributary Flow (cfs)

Q5 1,469 64 Q10 2,715 116

Table 1: Design Discharge

HYDRAULICS

The proposed design includes four spurs in the main channel along on existing berm, reestablishing the rock wall at the confluence of the tributary and Bonnie Clare Road, and constructing a roadside berm along the north side of Bonnie Clare Road. The combination of design elements will work together to redirect the main flow into the pre-flood alignment to the low water crossing at Ubehebe Crater Road.

During the flood event, a section of the rock wall at the confluence of the tributary and Bonnie Clare Road was removed allowing a preferential flow path to establish from the tributary down the south ditch. Figures 2 and 3 show the pre- and post-flood conditions at this site.

Figure 2. Google Earth Street View from 2012

Figure 3. Photo from site visit in 2016

The intent of the proposed reestablished rock wall is to cut off the post-flood flow path along the south ditch and to restore the pre-flood conditions at the confluence of the tributary and Bonnie Clare Road.

The combination of reestablishing the rock wall and lowering of the road profile to create a low water crossing at this location will direct the tributary flow across the road and into the main channel.

To mitigate the main channel migration, a series of four spurs are proposed along the berm just upstream of the tributary crossing along the south bank.

Rock feature post-flood

Rock feature prior to flood

Tributary flow path

Preferential flow path along south ditch

Pre-flood tributary flow path across road

Figure 4. Site Plan for Spur Design

The function of the spurs is to maintain the main channel flow in the pre-flood location along the northern bank. The most upstream spur is angled in the downstream direction to transition the flow lines away from the banks and towards the tip of the remaining spurs. The downstream spurs will be perpendicular to the bank. This orientation will direct the main flow towards the northern bank reducing the velocity along the southern bank which will allow for sediment deposition between the spurs. Sediment deposition will continue in future events which will continue to push the main flow path towards the north bank away from Bonnie Clare Road. The preferred material for the spurs is angular riprap. Each spur is between 20-30 feet long and 4-6 feet high. The height of the spur was set such that the berms do not overtop for the 10-year design event.

To mitigate the potential for overtopping downstream of the tributary crossing, an earthen berm is proposed along the north side of Bonnie Clare Road. The berm will be 2 feet high and will keep the 10-year design flow in the main channel.

Figures 5 and 6 are heat maps illustrating the existing and proposed conditions of the velocity for the 10-year design event. The heat maps demonstrate the redirection of the main flow from the southern bank towards the northern bank. The red and yellow areas shown indicate higher velocities while the blue and green areas indicate lower velocities. The high velocities shift from along the southern bank towards the middle of the main channel with the spurs installed.

Existing berm

Tributary crossing

Proposed spurs

Figures 7 and 8 are heat maps illustrating the existing and proposed conditions of the water depth for the 10-year design event. The heat maps demonstrate the redirection of the main flow into the main channel and towards the northern bank with the spurs installed. Downstream of the confluence with the tributary, the flow along the southern bank is contained in the channel and is no longer overtopping Bonnie Clare Road. Areas of red and yellow indicate deeper flow depths while areas of blue and green indicate shallow flow depths.

Figure 5. Existing Condition – Velocity Heat Map

Figure 6. Proposed Condition – Velocity Heat Map

Figure 7. Existing Condition – Water Depth Heat Map

Figure 8. Proposed Condition – Water Depth Heat Map

The group of design elements at this site will direct the tributary flow across the road and into the main channel. The combined flow is contained within the main channel and no longer overtops the roadway.

The combined flow will ultimately cross the Ubehebe Crater Road low water crossing rather than continuing south and west toward the Grapevine facilities.

http://www.aquaveo.com/

Subject: CA ERFO DEVA 11(1) – Water System Intake Berm Design

From: Megan Frye, PE Hydraulic Engineer

This memorandum presents the design analyses and recommendations for the proposed work at the water intake berm on Bonnie Clare Road. During the flood event, the existing berm protecting the water system intake was overtopped and the spring house inundated. During discussions with the Park, it was proposed that the berm crest elevation be raised 4 feet to prevent overtopping in future events.

Hydraulic analysis at this site included a hydrologic assessment to determine design discharges and hydraulic modeling to determine hydraulic conditions.

HYDROLOGY

Design discharges for the basin encompassing Bonnie Clare Road were estimated using the 2007 Caltrans Regional Regression Study. It was determined that the Caltrans study better represents the unique properties of desert storms than the USGS regional regression equations. The design discharges at the water intake berm are represented in the following table.

Flow (cfs) Q10 1689 Q50 5073

Q100 7570

The proposed modifications to the existing berm included a 4-foot increase in crest elevation and an additional 30 feet at the southwest end of the berm. The additional length at the south end of the berm was included to prevent water from flanking the berm and reaching the intake system.

The proposed rise in crest elevation was checked with the 10-yr, 50-yr, and 100-yr water surface elevations from the 2-dimensional hydraulic model along the berm. The requested 4-foot increase in crest elevation provides between 1.5 and 1.8 feet of freeboard over the 50-year water surface elevation.

The following table represents the water surface elevation at each station for the 10-, 50-, and 100-year events.

Date: August 10, 2017

Station Berm Crest

Elev. (ft)

10-yr WSEL (ft)

10-yr Freeboard (ft)

50-yr WSEL (ft)

50-yr Freeboard (ft)

100-yr WSEL (ft)

100-yr Freeboard (ft)

2+00 3239.23 Dry n/a 3237.77 1.46 3240.03 Overtopping 3+00 3235.31 3231.20 4.11 3233.74 1.57 3234.40 0.91 4+00 3230.57 3226.14 4.43 3228.79 1.78 3229.32 1.25

Table 2: Water Surface Elevation along Proposed Berm

The following heat map images for velocity and depth for the 50-yr design event are shown below for reference.

Figure 1: Velocity Heat Map

Figure 2: Water Depth Heat Map

Aquaveo Surface Water Modeling System 12.2.7 (www.aquaveo.com).

http://www.aquaveo.com/