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HORSESHOE DAM ()

Ash Meadows National Wildlife Refuge

Inspection Date: 11/13/2018

TABLE OF CONTENTS

CHAPTER Page

1. Current Conclusions 1

2. Current Recommendations and Cost Summary 3

3. Status of Previous Recommendations 7

4. Screening Level Risk Assessment 8

5. Pertinent Data 11

6. Inspection Checklist 18

7. Inspection and Project History 24

APPENDICES

A. Photos B. Figures, Maps and Plans C. Current Recommendations and Detailed Cost Data D. Supporting Documentation 2014 Seismic Hazard Map E. References

1. CURRENT CONCLUSIONS

A.

B.

C.

1. Current Conclusions

Overall Safety Classification The overall safety classification of the dam is POOR.

POOR is defined by FWS as follows: A potential dam safety deficiency is recognized for unusual loading conditions that may realistically occur during the expected life of the structure. This term may also be used when uncertainties exist as to critical analysis parameters that identify a potential dam safety deficiency, i.e., further investigations and studies are necessary.

The reason for this rating is: Deficiency Recognized.

Horseshoe Lake Dam was in POOR condition due to the dense vegetation in the emergency spillway, the combined service spillway/outlet works, and the discharge structure approach and discharge channels which will likely limit discharge capacities; dense vegetation on the upstream and downstream slopes; erosion occurring downstream of the combined service spillway/outlet works structure intake (on the upstream slope); and inadequate slope protection on the downstream slope.

Screening Level Risk Assessment The Screening Level Risk Assessment (SLRA) system for evaluating dams used by the FWS is a modification of the Bureau of Reclamation's SLRA method. The numeric total from the semi-quantitative method is used to rank a given dam with respect to the dam's downstream consequences and potential failure modes (normal, hydrologic, and seismic). The ranking factor total is unlimited based on the number of potential failure modes, with higher numbers being a worse condition. The

SLRA factors are assigned by the SEED inspector according to his or her evaluation at the time of the current inspection. The numeric total is used by the FWS to set priorities for repairs, studies, analyses, construction, and other dam safety activities.

The total SLRA value for this dam assigned during the current inspection is 26.

This is the initial SLRA score for Horseshoe Dam. The score is based on the following key driving factors:

-The dam is located in an active seismic area (PGA>0.2g) and a liquefaction evaluation has not been performed.

-The potential for seepage into or along conduits was assigned a very high likelihood.

-The potential for internal erosion was assigned a very high likelihood.

Hazard Classification The dam is classified as a LOW HAZARD dam.

/ HORSESHOE DAM 1

D.

E.

F.

G.

If Horseshoe Dam failed, the dam-failure flood wave would flow into Lower Crystal Dam. From

Lower Crystal Dam, the flood water would cross Stateline Road and continue into California. A hazard classification was performed and recommended that Horseshoe Dam be classified as a Low

Hazard Dam (Wheeler, 2019).

Hydrology and Hydraulics Review Horseshoe Dam is an small sized, Low Hazard Dam which requires the dam to safely pass the 100-year flood. The 100-year flood was developed for the 0.26 square mile drainage basin by W. W.

Wheeler and Associates, Inc. for the 2019 Hazard Classification Evaluation (Wheeler, 2019). The 100-year precipitation was developed based on the depths and temporal distributions from NOAA Atlas 14 for a 24-hour storm, resulting in a 2.75-inch depth. The drainage basin consists of hydrologic soil type

"C" soils. The peak inflow into Horseshoe Dam was 54 cubic feet per second (cfs) with a storm volume of 22 acre-feet. The reservoir routing of this storm event results in a maximum water surface

Elevation of 2152.7 feet, which provides about 5.3 feet of freeboard to the dam crest.

The drainage basin for Horseshoe Dam has a non-inventory dam upstream, Upper Horseshoe Dam.

Upper Horseshoe Dam and its water control structure were not considered in the hydrology and reservoir routing thus the results are considered to be conservative.

According to the Refuge Manager, a 500-year flood event occurred on Ash Meadows National

Wildlife Refuge in October 2015. Erosion was not observed in the spillway channels as a result of this event; however, the Refuge did not provide documentation of the water level or spillway discharges as a result of this event.

Seismicity Review The 2014 USGS update of the United States National Seismic Hazard Map, provided in the

Supporting Documentation, indicates that the peak ground acceleration associated with a 2-percent probability of exceedance in 50 years is 0.3 to 0.4 g at the dam site.

Geologic and Geotechnical Review There is no known design information to perform a geologic and geotechnical review.

Civil and Structural Review There is no known design information to perform a civil and structural review.

/ HORSESHOE DAM 2

2. CURRENT RECOMMENDATIONS AND COST

SUMMARY

2. Current Recommendations and Cost Summary

Year of Estimate: 2018

A. Emergency Situation

B. Maintenance

C. Operations and Monitoring

Recommendation(s) Cost None

Total Emergency Situation Recommendations 0 Total Emergency Situation Costs $0.00

Priority 1 Recommendation(s) Cost

1. (2018-1MA-01) Remove vegetation from the upstream slope and the downstream slope of the embankment for a distance of 20 feet downstream of the downstream toe. Also, remove vegetation from the approach and discharge channels for the emergency spillway, combined outlet works/service spillway structure, and discharge structure at Station 0+20. Upstream slope:

trees with trunks less than 2 inches in diameter cut and treat with sealant; trees with trunks greater than 2 inches in diameter remove tree, root mass, and roots greater than one half inch in diameter and backfill with appropriate on-site soil and compact as needed. Spillways and downstream slope: trees with trunks less than 6 inches in diameter cut and treat with sealant; trees with trunks greater than 6 inches in diameter remove tree, root mass, and roots greater than one half inch in diameter and backfill with appropriate on-site soil and compact as needed.

$15,403.46

P1 Maintenance Recommendations 1 P1 Maintenance Costs $15,403.46

Priority 2 Recommendation(s) Cost None

P2 Maintenance Recommendations 0 P2 Maintenance Costs $0.00

Total Maintenance Costs $15,403.46

Priority 1 Recommendation(s) Cost None

P1 Operations and Monitoring Recommendations 0 P1 Operations and Monitoring Costs $0.00

Priority 2 Recommendation(s) Cost

1. (2018-2OM-01) On a monthly basis and during significant flood events, visually monitor seepage areas on the toe and around the conduit for signs of changing seepage patterns and flow including boils, increased flow, or cloudy discharge. Contact the Regional Dam Safety Officer if any of these conditions are observed.

$0.00

P2 Operations and Monitoring Recommendations 1

/ HORSESHOE DAM 3

D. Construction

E. Additional Studies or Analyses

F. Future Inspections

P2 Operations and Monitoring Costs $0.00 Total Operations and Monitoring Costs $0.00

Priority 1 Recommendation(s) Cost None

P1 Construction Recommendations 0 P1 Construction Costs $0.00

Priority 2 Recommendation(s) Cost

1. (2018-2CO-01) Regrade dam crest to drain to the upstream embankment slope, repair cracks on the dam crest, repair erosion gullies along the downstream embankment slope, and repair the upstream slope in the area of the combined service spillway/outlet works intake riser. This activity should be coordinated with the Regional Dam Safety Officer to determine appropriate engineering supervision requirements.

$6,436.99

2. (2018-2CO-02) Consider breaching the dam to remove it from the US Fish & Wildlife Service Inventory. Consultation with the Regional Dam Safety Engineer is required to ensure that the dam is removed in accordance with the US Fish & Wildlife Service Standards. If this recommendation is implemented, the other recommendations will not be required.

$151,543.42

P2 Construction Recommendations 2 P2 Construction Costs $157,980.41

Total Construction Costs $157,980.41

Priority 1 Recommendation(s) Cost None

P1 Additional Studies or Analyses Recommendations 0 P1 Additional Studies or Analyses Costs $0.00

Priority 2 Recommendation(s) Cost

1. (2018-2SA-01) Evaluate the dam decommissioning requirements and design the potential dam modifications needed to breach the dam consistent with FWS dam safety policy.

$111,564.00

2. (2018-2SA-02) Consider performing a field survey or drone survey of the State Line Road to validate the hazard classification and the assumptions from the December 2019 Hydrology and Hazard Classification Evaluation.

$6,655.77

P2 Additional Studies or Analyses Recommendations 2 P2 Additional Studies or Analyses Costs $118,219.77

Total Additional Studies or Analyses Costs $118,219.77

Recommendation(s) Cost None

Total Future Inspections Recommendations 0 Total Future Inspections Costs $0.00

/ HORSESHOE DAM 4

Definitions

The U.S. Fish and Wildlife Service (FWS) has established the following categories to determine a priority ranking system for which work must be completed in order to maintain the integrity and operation adequacy of dam structures:

Emergency Situation - Structure is in danger of imminent failure and action must be taken immediately to alleviate the emergency.

Priority 1 (P1) - Normal condition of the structure is impaired and the safety of the structure is in jeopardy.

Priority 2 (P2) - Conditions do not currently appear to threaten the safety of the dam. Continued deterioration and/or unusual loading may threaten the safety of the dam.

Total Emergency Recommendations 0 Total Emergency Costs $0.00

Total P1 Recommendations 1 Total P1 Costs $15,403.46

Total P2 Recommendations 5 Total P2 Costs $276,200.19

Total Future Inspection Recommendations 0 Total Future Inspection Costs $0.00

Total Recommendations 6 Total Costs $291,603.66

/ HORSESHOE DAM 5

Table 4-1 Operations Schedule

Horseshoe Dam

W ee kl y

M on th ly

Q ua rt er ly

Se m i-A nn lly

A nn lly

E ve ry

Y ea rs

E ve ry y ea rs

O cc as io na l

O cc ur re nc e

Responsible Entity

R ef ug e

M an ag er

R D

SO

SD

SO

STANDING OPERATION

Operations Dam Visit B(1)

Transmit Log & Forms Flood Operations B B Instrumentation Reservoir Staff Gage B,A Inspection Station Inspection(2) B,C SEED Inspection (3) B Special Inspection(4) B,C

Interior Pipe Inspections (5)

Maintenance Control Vegetation (6) B

Maintain Stoplogs & Hoist Per Manufacturer’s Recommendation B

General Maintenance B Unusual or Emergency Event Emergency Action B

Shading indicates responsible entity.

(1) Letters indicate forms used for respective activity. Forms can be found in the Low Hazard SOP:

A Form 2a B Form 1a - Operations Log C Form 1b – Intermediate Inspection Checklist for Low Hazard Dams

(2) Items to look for during monthly inspections are outlined in Chapter 2 of the Low Hazard SOP and should be documented on Form 1b. Items to pay special attention to during monthly inspections include monitoring for erosion on the embankment slopes; seepage, particularly near the right abutment; and sediment deposits at the downstream toe.

(3) Alternate Formal SEED Inspection and Intermediate SEED Inspection every 5 years.

(4) Items to look for during special inspections are outlined in Chapter 2 of the Low Hazard SOP and should be documented on Form 1b. Special inspections should be performed after a significant flood or an earthquake.

(5) The interior of the discharge pipes for the combined service spillway/outlet works and the discharge structure at Station 0+20 should have an interior pipe inspection performed as needed.

(6) At least twice during growing seasons.

3. STATUS OF PREVIOUS

RECOMMENDATIONS

3. Status of Previous Recommendations

There are no previous recommendations for this dam.

/ HORSESHOE DAM 7

4. SCREENING LEVEL RISK ASSESSMENT

Dam Name: Horseshoe Dam NID No.: NV10340 Station: Ash Meadows National Wildlife Refuge Region: 8 Hazard Classification: Low (pending 2019 Hazard Classification) Dam Type: Earthfill Dam Height: 9 feet Maximum Storage: 77.5 acre-feet

Low Hazard Screening Level Risk Matrix

Extremely High (greater than 1E-02 or less than 100yr)

Very High (1E-03 to 1E-02 or 1,000yr to 100yr)

High (1E-04 to 1E-03)

Moderate (1E-05 to 1E-04)

Low (1E-06 to 1E-05)

Consequence Level

Total SLRA Risk Score: 26

Static - Stoplog failure

Static - Seepage in

Embankment/Foundation Static - Seepage at Conduit

10 30 100

Static - Stability 5 10 30

0 1 3 5 10

Hydrologic - Operations

Hydrologic - Overtopping 1 3 5

Li ke lih oo d

Seismic - Liquefaction 30 100

0 1 2 3 4

/ HORSESHOE DAM 8

Consequences: Level 0

Level 1

Failure Modes:

Likelihood Consequences Score

High 1 3

Very High 1 5

Very High 1 5

Very High 0 3

Low 1 0

Low 0 0

Extremely High 1 10

Static Potential Failure Modes Structure instability (static), resulting in failure of the dam. Slopes between 2H:1V and 3H:1V and no known adverse conditions. FS unknown.

Construction materials are unknown, soils appear to be comprised of erodible materials.

Damage to the structure and the resource it provides (pool/habitat) and/or FWS property that would not impact the mission of the Station/Service and would not require repair.

In the case of a dam failure associated with the potential failure modes, expected consequences include moderate damage to the structure and the resource it provides (pool/habitat); however, the Refuge intends to remove the dam in the future because it does not provide value to their habitat mission;

inundation of the Refuge property including Lower Crystal Springs Dam.

Description Reason

Gate deterioration/failure and/or misoperation, resulting in uncontrolled releases (ie, pin friction, lack of maintenance).

Stoplog structure with restricted access during flooding conditions. Infrequent or inconsistent maintenance and operation.

Seepage along/into conduits/drains, resulting in internal erosion/piping.

No observed piping or seepage along or into conduit/drain. Construction methods unknown. The downstream discharge was not accessible or able to be observed for the discharge structure near Sta. 0+20. Erosion observed at the upstream slope for the combined service spillway/outlet that could provide shortened seepage path. Scour was observed underneath the combined service spillway/outlet structure outfall.

Seepage through the embankment/foundation, resulting in internal erosion/piping.

Due to the grass vegetation near the right abutment, it appears there is a history of seepage. Could not observe for seepage/piping due to no storage in the reservoir during 2018 inspection and heavy vegetation preventing access to the dam toe.

Discharge/release capacity is reduced or inoperability / misoperation of gates, resulting in premature overtopping(ie, debris, high tailwater, high reservoir levels, fish screens, loss of power / access / communication, ASR, mechanical failure).

Normal operating pool/stoplogs is maintained with recommended minimum freeboard. Multiple spillways allow for redundancy in capacity.

Hydrologic Potential Failure Modes Erosion of embankment dam due to overtopping, resulting in breach of the reservoir.

Dam can pass the 100-yr flood with 5.3 feet of freeboard. According to Refuge Staff, a 500-year flood occurred on the Refuge in 2015 and no erosion of the service or emergency spillways was observed.

Seismic Potential Failure Modes Liquefaction of embankment/foundation materials, resulting in deformation, loss of freeboard, cracking/separation, or structural failure.

Located in active seismic area (PGA > 0.2g) and unknown embankment or foundation materials. Not designed for EQ loading.

/ HORSESHOE DAM 9

/ HORSESHOE DAM 10

5. PERTINENT DATA

A.

B.

5. Pertinent Data General

Dam Section(s)

1. Dam Name *: HORSESHOE DAM

2. NID Number *:

3. Other Dam Name(s) *: LAKE NUMBER 6

4. Dam Former Name(s) *:

5. Dam State *: NV

6. Dam County *: NYE

7. Dam Latitude *: 36.4

8. Dam Longtitude *: -116.34

9. Legal Description (Section, Township, Range Location) *:

S9,T18S,R50E

10. River or Stream Name *: CARSON SLOUGH - TR

11. Basin: AMARGOSA RIVER

12. Reservoir Name: LAKE NUMBER 6

13. Year Constructed *: 1960

14. Year and Reason Dam Modified *:

15. Downstream Hazard Potential Classification *: LOW

16. Resource Value: Secondary Resource

17. Inventory Status: Inventory

18. Size Classification: SMALL OR MINOR

19. SAMMS#:

20. Confined Space: yes

21. Estimated Economic Losses Downstream: < $ 1 million

Notes:

Item No. 2: NID number is NV10340 per the NID database. Nevada has the NID as

NV00190.

Item No. 5: State ID for this dam is J-093.

Item No. 13: Information from the National Inventory of Dams (NID) Database.

Item No. 14: Construction information is not available beyond the NID information.

Item No. 15: Dam being evaluated in 2019 hazard classification (Wheeler, 2019).

Embankment Dam Section 1: MAIN EMBANKMENT

1. Dam Type *: EARTH

2. Crest Elevation: 2,158 Ft.

3. Dam (Crest) Length *: 1,385 Ft.

4. Crest Width: 18 Ft.

5. Dam Height *: 9 Ft.

6. Structural Height *: 9 Ft.

7. Hydraulic Height *: 3.7 Ft.

8. Upstream Slope: 4 H:1V to 4.7 H:1V

9. Downstream Slope: 2.4 H:1V to 3.4 H:1V

/ HORSESHOE DAM 11

C.

D.

Saddle Dike(s)

Discharge Structure(s)

10. Core Position *: UNLISTED/UNKNOWN Type *: UNLISTED/UNKNOWN Certainty *:

11. Foundation *: UNLISTED/UNKNOWN Certainty *:

Karst: unknown

12. Volume of Dam *: 21,883 CY

Notes:

Dimensions updated based on 2007 LiDAR data (FWS, 2007) and measurements collected in the field during the 2018 SEED Inspection.

Item 2: Dam crest varies in elevation form 2158 - 2160.

Item 4: The dam crest width varies from 13 to 18 feet.

Item 5: The dam height is based on the vertical distance between the lowest point on the dam crest and the lowest point in the original streambed; El. 2158.0 - El. 2149.0 = 9.0 feet. The lowest point in the original streambed was based on the LiDAR elevation data at the downstream toe.

Item 6: The structural height is based on the vertical distance between the lowest point on the dam crest and the lowest point of the excavated foundation; El. 2158.0 - El. 2149.0 = 9.0 feet.

The lowest point of the excavated foundation was based on the LiDAR elevation data at the downstream toe.

Item 7: The hydraulic height is based on the vertical distance between the maximum design water level and the lowest point in the original streambed; El. 2152.7 - El. 2149.0 = 3.7 feet.

The lowest point in the original streambed was determined using the LiDAR data. The hydrologic analysis concluded that the 100-year event would result in a water surface elevation of 2152.7 (Wheeler, 2019).

Item No. 12: The volume of the dam was estimated assuming a consistent section extends from the left abutment to the right abutment. Using a cross sectional area of 426.6 SF (assuming height = 9 feet, crest width = 15 feet, upstream slope = 4.3H:1V, downstream slope = 2.9H:1V). Volume of dam = 426.6 SF * 1,385 feet = 21,883 CY.

There are no saddle dikes currently associated with this structure.

Discharge Structure 1: Discharge Structure at Dam Station 0+20

1. Discharge Structure Type: Service Spillway

2. Description: Half-round CMP riser

3. Location: Station 0+20

4. Approach Channel: Reservoir

5. Intake Structure: Half-round CMP riser with stoplog control

a. Crest Elevation: Ft.

b. Invert Elevation: 2,153.9 Ft.

c. Size: 3-foot-diameter CMP

d. Material: CMP

e. Width: 3 Ft.

6. Control Structure: Stoplog control

a. Type *: CONTROLLED

OTHER CONTROLLED

/ HORSESHOE DAM 12

b. Min Control Elevation: 2,153.9 Ft.

c. Max Elevation of Gate Opening: Ft.

d. Max Control Elevation: 2,156.9 Ft.

e. Size: 3-foot-wide stoplogs slots

f. Material: Unknown

7. Conveyance Structure: 24-inch-diameter CMP conduit

a. Length: 25 Ft.

b. Size: 24-inch-diameter

c. Inlet Invert Elevation: 2,153.9 Ft.

d. Outlet Invert Elevation: Ft.

e. Year of Conduit Installation:

8. Outlet Structure: Unknown

a. Energy Dissipation: Unknown

9. Discharge Channel: Earth channel

10. Discharge Capacity with Water Surface at *: Top of Dam : 23.5 cfs and is based on the following formula: Culvert Master Calculation

Notes:

Item No. 5, 6, 7c: The difference in elevation between the dam crest and upstream invert was

6.1 feet, measured in the field using a hand level during 2018 field visit. LiDAR data indicates that the dam crest elevation in this particular location is 2160 feet, so the upstream invert was calculated based on Elevation 2160 - 6.1 feet = Elevation 2153.9 feet. The CMP riser was 3 feet high; maximum control elevation was 2156.9 feet.

Item No. 6f: Stoplogs were not on-site. Material is unknown.

Item No. 7d, 8: Downstream discharge of the outlet pipe was not accessible or observable during 2018 SEED inspection.

Item No. 10: Discharge is controlled by the 2-foot-diameter CMP discharge conduit.

Calculations provided in Wheeler, 2019.

Discharge Structure 2: Combined Service Spillway/Outlet Works at Dam Station 7+75

1. Discharge Structure Type: Combined Service Spillway and Outlet

Works

2. Description: Steel riser with stoplog slots

3. Location: Station 7+75

4. Approach Channel: Reservoir

5. Intake Structure: Steel riser with stoplog slots

a. Crest Elevation: Ft.

b. Invert Elevation: 2,150.3 Ft.

c. Size: 4-foot by 4-foot square riser

d. Material: Steel

e. Width: 4 Ft.

6. Control Structure: Stoplogs

a. Type *: CONTROLLED

OTHER CONTROLLED

b. Min Control Elevation: 2,150.3 Ft.

c. Max Elevation of Gate Opening: Ft.

d. Max Control Elevation: 2,157.6 Ft.

/ HORSESHOE DAM 13

e. Size: 2.5-foot-wide

f. Material: Wood

7. Conveyance Structure: 24-inch-diameter CMP conduit

a. Length: 45 Ft.

b. Size: 24-inch-diameter CMP

c. Inlet Invert Elevation: 2,150.3 Ft.

d. Outlet Invert Elevation: 2,150.3 Ft.

e. Year of Conduit Installation:

8. Outlet Structure: None

a. Energy Dissipation: None

9. Discharge Channel: Earth channel

10. Service Spillway Discharge Capacity with Water Surface at *: Top of Dam : 32.7 cfs and is based on the following formula: Culvert Master Calculation Outlet Works Discharge Capacity with Water Surface at: Top of Dam : 32.7 cfs and is based on the following formula: Culvert Master Calculation

Notes:

Item No. 5, 6, 7c, 7d: The difference in elevation between the dam crest and upstream invert was 8.7 feet, measured in the field using a hand level during 2018 SEED inspection. LiDAR data indicates that the dam crest elevation in this particular location is 2159 feet, so the upstream invert was calculated based on Elevation 2159 - 8.7 feet = Elevation 2150.3 feet.

The steel riser was 7.3 feet high; maximum control elevation was 2157.6 feet.

Item No. 10: Discharge is controlled by the 2-foot-diameter CMP discharge conduit.

Calculations provided in Wheeler, 2019.

Discharge Structure 3: Emergency Spillway at Dam Station 12+65

1. Discharge Structure Type: Emergency Spillway

2. Description: Trapezoidal earth channel

3. Location: Station 12+65

4. Approach Channel: Unlined Earth Channel

5. Intake Structure: Riprap Lined Trapezoidal Channel

a. Crest Elevation: 2,152 Ft.

b. Invert Elevation: Ft.

c. Size: Bottom width of 20 feet and 4H:1V side slopes

d. Material: Riprap Lined

e. Width: 20 Ft.

6. Control Structure: None

a. Type *: UNCONTROLLED

b. Min Control Elevation: Ft.

c. Max Elevation of Gate Opening: Ft.

d. Max Control Elevation: Ft.

e. Size:

f. Material:

7. Conveyance Structure: Earthen Trapezoidal Channel

/ HORSESHOE DAM 14

E. Reservoir / Flood Hydrology

a. Length: Ft.

b. Size: 20-foot-wide

c. Inlet Invert Elevation: Ft.

d. Outlet Invert Elevation: Ft.

e. Year of Conduit Installation:

8. Outlet Structure: None.

a. Energy Dissipation: None.

9. Discharge Channel: Earth Channel

10. Discharge Capacity with Water Surface at *: Top of Dam : 794 cfs and is based on the following formula: Q = C*L*H^1.5

Notes:

Item No. 5, 7: Dimensions and elevations from the LiDAR data (FWS, 2007).

Item No. 10: The discharge of the emergency spillway can be estimated using the following formula: Q = C*L*H^1.5, where C = 2.7, L = 20 feet, H = water surface elevation - spillway crest = 2158 - 2152 = 6.0 feet Q = 2.7 x 20 feet x (6 feet)^1.5 = 794 cfs

Reservoir Storage Level Elevation (feet) Surface Area

(acres) Capacity (acre-feet)

Maximum Normal Pool * 2,151 3.9 9.7 Discharge Structure 1:

Discharge Structure at Dam Station 0+20

2,153.9 9 34.5

Discharge Structure 2:

Combined Service Spillway/Outlet Works at Dam Station 7+75

2,150.3 3.2 7.9

Discharge Structure 3:

Emergency Spillway at Dam Station 12+65

2,152 5.8 14.6

Top of Dam * 2,158 15.9 77.5

Flood Hydrology

1. Inflow design flood: 100-year storm

2. Storm Duration: 24 hours

3. Total Rainfall: 2.75 inches

4. IDF Peak Inflow: 54 cfs

5. Storm Volume: 22 acre-feet

6. Max. reservoir water surface elevation during the IDF:

2,152.7 Ft.

7. IDF Freeboard: 5.3 Ft.

8. Depth of Overtopping:

0 Ft.

9. Duration of Overtopping:

0 hours.

10. IDF Peak Outflow: 45 cfs

11. Drainage Area: 0.26 square miles

12. Drainage Basin Description *:

Armagosa Valley closed basin

Notes:

Maximum normal pool set at 1-foot below the emergency spillway crest elevation.

Surface area, capacity table and flood hydrology information updated as documented in Wheeler, 2019. The flood hydrology did not consider routing through Upper Horseshoe

/ HORSESHOE DAM 15

F.

G.

H.

Management

EAP / SOP

Inspection Details

Dam, which is a non-inventory dam with a water control structure in the drainage basin upstream from Horseshoe Dam. As a result, the hydrology values are considered to be conservative.

1. Owner Name *: US FISH AND WILDLIFE SERVICE

2. Owner Type *: FEDERAL

3. Dam Designer *: Chuck Armuth

4. Private Dam on Federal Property *: no

5. Field Station: Ash Meadows National Wildlife Refuge

6. Dam Purposes *: FISH AND WILDLIFE POND

7. Field Station Contact Information:

Name: Corey Lee Address1: 610 E. SPRING MEADOWS ROAD Address2: AMARGOSA VALLEY, NV 89020 Phone: (775) 372-5435

8. Dam Safety Program Contact:

Name: Zach Spruell

Regional Dam Safety Officer, Region 8 Address: Region 1 7 8 Division of Engineering

911 NE 11th Avenue (3W) Portland, OR 97232

Phone: (503) 231-2396

9. Organization Code: 84554

10. Region: 8

11. Ecosystem:

12. Federal Agency Involvement in Design *:

13. Federal Agency Involvement in Construction *:

14. Federal Agency Involvement in Regulatory *: U.S. Fish and Wildlife Service

15. Federal Agency Involvement in Inspection *: U.S. Fish and Wildlife Service

16. Federal Agency Involvement in Operation *: U.S. Fish and Wildlife Service

17. Federal Agency Owner *: U.S. Fish and Wildlife Service

18. Federal Agency Involvement - Other *:

Notes:

Item No. 3: Information from the NID Database.

Item No. 14: The NID database indicates that the dam was initially privately owned by Nye County Land Company.

1. Emergency Action Plan (EAP): * not required

Notes:

Not required.

1. Date of Previous Inspection:

/ HORSESHOE DAM 16

I. Pertinent Data Notes The elevations are based on the LiDAR data (FWS, 2007), NAVD88.

* denotes data submitted to the NID.

Inspection Type:

2. Date of Most Recent Inspection *: 11/13/2018 Inspection Type: Formal

3. Inspection Frequency *: 5 Est. Date of Next Inspection: 11/13/2024

4. Inspected By (Primary): Danielle Tripp Hannes, P.E., Associate

Engineer, W. W. Wheeler and Associates, Inc.

Inspected By (Secondary): Andrea Fasen, P.E., Water Resource Engineer, W. W. Wheeler and Assoicates

5. Reviewed By: Ying-Kit Choi, P.E., Technical Reviewer, W. W. Wheeler and Assoicates, Inc.

6. Prepared By: W.W. Wheeler and Associates, Inc.

7. Date of Most Recent Internal Inspection:

None

Notes:

Item No. 2: The 2018 SEED Inspection is the initial inspection of Horseshoe Dam.

Item No. 7: It is unknown if an internal inspection has ever been performed for the combined service spillway/outlet works or discharge structure outlet pipes.

/ HORSESHOE DAM 17

6. INSPECTION CHECKLIST

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 1

INSPECTION CHECKLIST FOR LOW HAZARD DAMS

DAM NAME: Horseshoe Dam (Lake No. 6) DATE INSPECTED: November 13, 2018

NID NO.: NV10340; Nevada inspection report: NV00190 DATE OF PREVIOUS INSPECTION: N/A

STATION: Ash Meadows National Wildlife Refuge WEATHER/TEMP.: Sunny, 60F

COUNTY/STATE: Nye County, Nevada POOL ELEVATION: No water impounded

HAZARD CLASSIFICATION: LOW TAILWATER ELEVATION: No tailwater.

INSPECTED BY: Danielle Hannes P.E. and Andrea Fasen E.I, W. W. Wheeler and Associates, Inc.

CHANGE IN INVENTORY STATUS: Inventory Non-inventory No Change

UPSTREAM SLOPE – EMBANKMENT

PROBLEMS NOTED: (1) None (2) Excessive vegetation (3) Animal burrows

(4) Wave erosion; with scarps (5) Appears too steep (6) Depressions or bulges

(7) Sinkholes (8) Cracks; with displacement (9) Slides (10) Concrete facing:

holes; cracks; displacement; undermined (11) Slope protection: missing; sparse; displaced;

weathered (12) Other

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(2) Excessive vegetation was observed from approximate Sta. 5+00 to 13+00. Vegetation included a mixture of tall and thick grass, shrubs, and bushes (refer to Photo Nos. 1 through 6) to trees that had trunks that were up to 6 inches in diameter (refer to Photo Nos. 2 and 5).

(11) A majority of the upstream slope did not have any slope protection. A few areas were noted to have some intermittent rock that could provide some slope protection. See Photo Nos. 1 through 4.

(12) Due to vegetation, access and visual observation was difficult from approximate Sta. 5+00 to 13+00.

PHOTOS: Upstream slope shown on Photo Nos. 1 through 6.

CREST – EMBANKMENT

PROBLEMS NOTED: (1) None (2) Excessive vegetation (3) Animal burrows

(4) Erosion (5) Sinkholes (6) Cracks; with displacement (7) Ruts or puddles

(8) Inadequate surface drainage (9) Not wide enough (10) Misalignment

(11) Low areas (12) Other

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(4) Erosion was observed on the downstream side of the dam crest that extends from the dam crest to the downstream toe in several areas. Erosion was up to about 1.8 feet wide and 1.2 feet deep. See Photo Nos. 13, 14, 23, and 36.

(6) Shallow longitudinal cracks were observed near Station 9+75, extending for approximately 20 feet. See Photo No. 16.

(7) Vehicle ruts were observed on the entire dam crest. The largest vehicle rut was from Station 5+30 to 5+80 measuring 32 inches wide and 4 inches deep. See Photo No. 15.

(8) Inadequate surface drainage was noted in areas on the crest where large vehicle ruts are present. See Photo No. 15.

(11) The dam crest elevation varies based on field observations and LiDAR data resulting in several low areas on the dam crest.

Low areas were observed near approximately Stations 8+75 and 11+75. See Photo No. 12.

PHOTOS: Dam crest shown on Photo Nos. 7 through 16, 23, 36.

/ HORSESHOE DAM 18

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 2

DOWNSTREAM SLOPE – EMBANKMENT

PROBLEMS NOTED: (1) None (2) Excessive vegetation (3) Animal burrows

(4) Erosion or gullies (5) Appears too steep (6) Depressions or bulges

(7) Sinkholes (8) Cracks; with displacement (9) Slides (10) Slope protection:

missing; sparse; displaced; weathered (11) Soft areas (12) Livestock damage

(13) Other

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(2) Excessive vegetation was observed on the downstream slope from about Station 11+00 to 12+00 and from Station 6+50 to 8+25 making the inspection of the downstream slope difficult in these areas. Vegetation was observed on the remainder of the downstream slope; however, to a lesser extent. Vegetation was generally a mix of shrubs and bushes, with trunk diameters that are about 1-inch. See Photo Nos. 17 through 24.

(4) Erosion was observed on the downstream side of the dam crest that extends from the dam crest to the downstream toe in several areas. Erosion was up to about 10 feet wide and 1 foot deep on the downstream slope. See Photo Nos. 23 and 36.

(10) No slope protection was observed on the downstream slope. See Photo Nos. 17 through 24.

(11) Several piles of soft soils were observed at the downstream toe and appear to have been eroded from the downstream slope near Sta 5+40. See Photo No. 24.

PHOTOS: Downstream slope shown on Photo Nos. 17 through 24, 36.

SEEPAGE

PROBLEMS NOTED: (1) None (2) Flow adjacent to outlet (3) Saturated embankment areas (4) Seepage area at toe (5) Seepage exists at point source

(6) Seepage exists on embankment (7) Seepage increased/muddy (8) Other

DRAIN OUTFALLS SEEN? yes no N/A (9) Flow increased/muddy (10) Drain dry/obstructed (11) Pipe deteriorated (12) Animal guard (13) Other

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(1) Water was not impounded by the dam during the inspection so no seepage was observed.

(2) Grass vegetation was observed downstream of the right abutment, which could be indicative of seepage occurring in this area of the embankment. See Photo No. 25.

PHOTOS: Potential area of seepage shown on Photo No. 25.

DISCHARGE STRUCTURE: Discharge Structure at Station 0+20

PROBLEMS NOTED: (1) None (2) Inadequate freeboard (3) Erosion; with backcutting (4) Flow obstructed (5) Upstream/downstream structure deteriorated/undermined (6) Cracks; with displacement (7) Restricted by vegetation

(8) Scour protection: missing; sparse; displaced; weathered (9) Other

INTERIOR INSPECTED? yes no N/A (10) Conduit deteriorated or collapsed

(11) Joints displaced (12) Valve leakage (13) Other

CONTROLS (gates/valves/stoplogs) INSPECTED? yes no N/A (14) Controls not operated during inspection (15) Controls inoperable (16) Poor operating access

(17) Other (including configuration of controls at time of inspection)

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(7) Heavy vegetation made access and observations of the upstream inlet difficult, see Photo No. 28. Heavy vegetation made the access to the structure outfall impossible, Photo No. 30.

(13) Approximately 4 inches of sediment was deposited in the upstream inlet, see Photo No. 29.

(16) Heavy vegetation around the inlet made access very difficult to install stoplogs. See Photo No. 28.

(14 & 17) No stoplogs were installed at the time of the inspection. Stoplogs were not operated during inspection.

PHOTOS: Discharge structure at Station 0+20 shown on Photo Nos. 26 through 30.

/ HORSESHOE DAM 19

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 3

DISCHARGE STRUCTURE: Combined Service Spillway/Outlet Works at Station 7+75

PROBLEMS NOTED: (1) None (2) Inadequate freeboard (3) Erosion; with backcutting (4) Flow obstructed (5) Upstream/downstream structure deteriorated/undermined (6) Cracks; with displacement (7) Restricted by vegetation

(8) Scour protection: missing; sparse; displaced; weathered (9) Other

INTERIOR INSPECTED? yes no N/A (10) Conduit deteriorated or collapsed

(11) Joints displaced (12) Valve leakage (13) Other

CONTROLS (gates/valves/stoplogs) INSPECTED? yes no N/A (14) Controls not operated during inspection (15) Controls inoperable (16) Poor operating access

(17) Other (including configuration of controls at time of inspection)

OBSERVED CONDITIONS

GOOD

FAIR

POOR

(7) Heavy grass vegetation was observed in the reservoir that would prevent flow into the intake structure (see Photo Nos. 31 and 33).

(9) Erosion of the upstream slope was observed between the upstream embankment and the riser structure (see Photo No. 34).

Erosion was also observed on the downstream slope extending from the dam crest to the downstream toe, measuring about 4 inches wide and 4 inches deep (see Photo No. 36).

(10) The CMP outlet pipe was deformed near the outfall, see Photo No. 35.

(16) Heavy vegetation around the inlet made access very difficult to inspect stoplogs, see Photo Nos. 31 and 33. Due to the configuration of the inlet riser and stoplogs, it will be impossible to control water levels during a flood event, see Photo No. 34.

(14 & 17) 5 stoplogs (estimated to be about 20 inches in height) were installed in the intake structure at the time of the inspection. Due to the vegetation around the inlet, direct access was not possible to confirm the height of the stoplogs (see Photo No. 33).

PHOTOS: Combined service spillway/outlet works shown on Photo Nos. 31 through 36.

DISCHARGE STRUCTURE: Emergency Spillway at Station 12+65

PROBLEMS NOTED: (1) None (2) Inadequate freeboard (3) Erosion; with backcutting (4) Flow obstructed (5) Upstream/downstream structure deteriorated/undermined (6) Cracks; with displacement (7) Restricted by vegetation

(8) Scour protection: missing; sparse; displaced; weathered (9) Other

INTERIOR INSPECTED? yes no N/A (10) Conduit deteriorated or collapsed

(11) Joints displaced (12) Valve leakage (13) Other

CONTROLS (gates/valves/stoplogs) INSPECTED? yes no N/A (14) Controls not operated during inspection (15) Controls inoperable (16) Poor operating access

(17) Other (including configuration of controls at time of inspection)

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS:

(7) Vegetation restricted both the upstream approach channel (tall grass, see Photo No. 37) and the downstream discharge channel (shrubs and trees with trunks up to 1-foot in diameter, see Photo No. 39).

(8) Scour protection was only installed on the control crest, see Photo Nos 37 through 40. No slope protection was observed upstream or downstream of the control section.

PHOTOS: Emergency spillway shown on Photo Nos. 37 through 40.

/ HORSESHOE DAM 20

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 4

MONITORING

EXISITING INSTRUMENTATION FOUND: (1) None (2) Gage rod (3) Seepage weirs/flumes (4) Piezometers (5) Survey monuments (6) Other

MONITORING OF INSTRUMENTATION? yes no N/A

OBSERVED CONDITIONS

GOOD

FAIR

POOR

COMMENTS: Staff gage located immediately upstream of the combined service spillway/outlet works inlet riser.

(2) Staff gage extends one-foot above the maximum anticipated water surface elevation resulting from the 100-year storm. The staff gage does not reference the same datum as the pertinent data in the SEED Report.

PHOTOS: The reservoir staff gage is shown on Photo No. 41.

HAZARD CLASSIFICATION

HAZARD CLASSIFICATION VERIFIED? yes no

CHANGE IN DOWNSTREAM CONDITIONS? yes no

The U.S. Fish and Wildlife Service authorized W. W. Wheeler and Associates, Inc. to perform a hazard classification evaluation which was completed December 2019. The Hazard Classification Evaluation recommended that Horseshoe Dam be classified as a low hazard-potential dam.

OVERALL CONDITIONS

Based on this Safety Inspection, the overall condition is determined to be:

SATISFACTORY – No existing or potential dam safety deficiencies (P1) are recognized. Safe performance is expected under all anticipated loading conditions, including such events as the spillway design flood (SDF).

FAIR – No existing dam safety deficiencies (P1) are recognized for normal loading conditions. Infrequent hydrologic and/or seismic events would probably result in a dam safety deficiency.

POOR – A potential dam safety deficiency is recognized for unusual loading conditions that may realistically occur during the expected life of the structure. This term may also be used when uncertainties exist as to critical analysis parameters that identify a potential dam safety deficiency, i.e., further investigations and studies are necessary.

UNSATISFACTORY – A dam safety deficiency exists for normal conditions. Immediate remedial action is required.

REASONS: Horseshoe Dam was in POOR condition due to the dense vegetation that will restrict flows from the emergency spillway, combined service spillway/outlet works, and discharge structure; vegetation on the upstream and downstream slopes;

erosion occurring downstream of the combined service spillway/outlet works intake structure (on the upstream slope); and erosion gullies on the downstream slope.

/ HORSESHOE DAM 21

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 5

DEFINITIONS

DAM – An artificial barrier, including appurtenant works, constructed for the purpose of storage, control, or diversion of water.

DAM HEIGHT – The vertical distance between the lowest point on the dam crest and the lowest point in the original streambed.

HYDRAULIC HEIGHT – The vertical distance between the maximum design water level and the lowest point in the original streambed.

STRUCTURAL HEIGHT – The vertical distance between the lowest point on the dam crest and the lowest point of the excavated foundation.

MAXIMUM WATER STORAGE ELEVATION – The elevation commensurate with the maximum impounding capacity of the dam, including temporary storage of flood water.

MAXIMUM DESIGN WATER LEVEL – The elevation commensurate with the maximum water surface elevation as a result of safely passing the Inflow Design Flood (IDF).

HAZARD CLASSIFICATION – Hazard Classification is a rating based on the potential loss of life (as defined below) or property damage downstream of a dam caused by failure or misoperation. Hazard Classification is not determined by the existing condition of a dam and its appurtenant structures or the anticipated performance or operation of a dam.

(1) Low – No persons at risk.

(2) Significant – 1 to 6 persons at risk.

(3) High – More then 6 persons at risk.

SIZE CLASSIFICATION – The structural height or the water storage capacity at maximum water storage elevation, whichever yields the larger size classification, is used to determine the size of a dam. Size classification categories are as follows.

(1) Small dams are structures that are less than 40 feet high or that impound less than 1,000 acre-feet of water.

(2) Intermediate dams are structures that are 40 to 100 feet high or that impound 1,000 to 50,000 acre-feet of water.

(3) Large dams are structures that are more than 100 feet high or that impound more than 50,000 acre-feet of water.

INVENTORY DAM – A dam is included in the Service Inventory of Dams and the National Inventory of Dams if it meets any of the following three criteria.

(1) It exceeds 25 feet in height from the natural bed of the stream (or a watercourse) measured at the downstream toe of the dam, or if it is not across a stream channel or watercourse, measured from the lowest elevation of the outside limit of the dam, to the maximum water storage elevation, and has a storage capacity at maximum water storage elevation in excess of 15 acre-feet.

(2) It exceeds an impounding capacity at maximum water storage elevation of 50 acre-feet and a height, measured as in (1) above, of at least 6 feet.

(3) It has a high or significant hazard classification regardless of height or storage capacity.

NON-INVENTORY DAM – Non-inventory dams are defined as follows.

(1) A low hazard dam that does not satisfy the criteria as set forth in the Inventory Dams.

(2) An interior dike or cross dike located within an impoundment or levee.

OBSERVED CONDITIONS – Observed conditions can generally be defined as,

(1) Good – In general, this part of the structure has a good appearance and conditions observed in this area do not appear to threaten the safety of the dam. No existing dam safety deficiencies are recognized for normal loading conditions.

(2) Fair – Although this part of the structure is maintained, minor deficiencies are noted. A potential dam safety deficiency is recognized for unusual loading conditions that may realistically occur during the expected life of the structure.

(3) Poor – Conditions observed in this area appear to threaten the safety of the dam. Conditions observed in this area are unacceptable. A potential dam safety deficiency is clearly recognized for normal loading conditions. Immediate actions to resolve the deficiency are recommended.

OVERALL CONDITIONS – Overall conditions are defined as,

(1) Satisfactory – No existing or potential dam safety deficiencies (P1) are recognized. Safe performance is expected under all anticipated loading conditions, including such events as the spillway design flood (SDF).

(2) Fair – No existing dam safety deficiencies (P1) are recognized for normal loading conditions. Infrequent hydrologic and/or seismic events would probably result in a dam safety deficiency.

(3) Conditionally Poor – A potential dam safety deficiency is recognized for unusual loading conditions that may realistically occur during the expected life of the structure. This term may also be used when uncertainties exist as to critical analysis parameters that identify a potential dam safety deficiency, i.e., further investigations and studies are necessary.

/ HORSESHOE DAM 22

[Horseshoe Dam, (Lake No. 6), Ash Meadows NWR] Page 6

(4) Poor - A potential dam safety deficiency is clearly recognized for normal loading conditions. Immediate actions to resolve the deficiency are recommended. (Reservoir restrictions may be considered until the problem is fixed.)

(5) Unsatisfactory – A dam safety deficiency exists for normal conditions. Immediate remedial action is required.

PRIORITY RATINGS – Priority ratings are assigned to recommendations as follows,

(1) Emergency Situation – An emergency situation exists when the structure is in danger of imminent failure and action must be taken immediately to alleviate the emergency.

(2) Priority 1 (P1) – A P1 recommendation indicates that the normal condition of the structure is impaired and the safety of the structure is in jeopardy.

(3) Priority 2 (P2) – A P2 recommendation indicates that conditions do not currently appear to threaten the safety of the dam. Continued deterioration and/or unusual loading may threaten the safety of the dam.

/ HORSESHOE DAM 23

7. INSPECTION AND PROJECT HISTORY

7. Inspection and Project History

Inspection History The following is the history of the SEED inspections and SEED inspection reports for HORSESHOE

DAM:This is the initial inspection report for HORSESHOE DAM.

Project History There is very little documented project history available for Horseshoe Dam. According to the NID data, the dam was constructed in 1960 by the Nye County Land Company. The property was subsequently purchased by The Nature Conservancy and then acquired by the U.S. Fish and Wildlife Service and established as part of the Ash Meadows National Wildlife refuge in June of 1984 (FWS, 1985).

/ HORSESHOE DAM 24

A. PHOTOS

1. View of the upstream slope looking left from Station 3+00. Note the missing slope protection.

2. View of the upstream slope looking right from Station 3+00.

/ HORSESHOE DAM A-1

3. View of the upstream slope looking left from Station 5+40. Note excessive vegetation on the slope that made the inspection difficult.

4. View of the upstream slope looking right from Station 5+40. Note excessive

/ HORSESHOE DAM A-2

5. View of the upstream slope looking right from Station 9+65. Note tree on slope with a 6 inch diameter trunk.

6. View of the upstream slope looking left from Station 12+00. Note excessive

/ HORSESHOE DAM A-3

7. View of the dam crest looking left from Station 3+00.

8. View of the dam crest looking right from Station 3+00. Note vehicle ruts on the dam crest.

/ HORSESHOE DAM A-4

9. View of the dam crest looking left from Station 5+40.

10. View of the dam crest looking right from Station 5+40.

/ HORSESHOE DAM A-5

11. View of the dam crest looking right from Station 9+65.

12. View of the dam crest looking left from Station 12+00. Note low area observed in the dam crest near Station 11+75.

/ HORSESHOE DAM A-6

13. View of typical erosion observed on the downstream side of the dam crest near Station 5+00. The erosion was about 8 inches deep and 16 inches in diameter .

14. View looking upstream at erosion observed at the dam crest and downstream slope contact near Station 11+50. Erosion was about 1.2 feet deep and 1.8 feet in diameter.

/ HORSESHOE DAM A-7

15. View of a vehicle rut on the dam crest extending from Station 5+30 to 5+80.

Rut was 4 inches deep and 32 inches wide.

16. View of longitudinal cracks on the dam crest near Station 9+75. Cracks are about 20 feet long.

/ HORSESHOE DAM A-8

17. View of the downstream slope looking left from Station 3+00.

18. View of the downstream slope looking right from Station 3+00.

/ HORSESHOE DAM A-9

19. View of the downstream slope looking left from Station 5+40.

20. View of the downstream slope looking right from Station 5+40.

/ HORSESHOE DAM A-10

21. View of the downstream slope looking right from Station 9+65.

22. View of the downstream slope looking left from Station 12+00. Note heavy vegetation on the downstream slope and tall grasses on the downstream toe.

/ HORSESHOE DAM A-11

23. View looking upstream at erosion on the downstream slope near Station 10+20. The erosion was about 10 feet wide and was 1-foot deep.

24. View of soft soil mounds observed at the downstream toe of the embankment near Station 5+40.

/ HORSESHOE DAM A-12

25. View looking upstream at the downstream slope from the right downstream abutment.

26. View of the approach channel looking upstream from the discharge structure inlet at Station 0+20.

/ HORSESHOE DAM A-13

27. View looking downstream from the dam crest at the channel downstream of the discharge structure discharge at Station 0+20.

28. View looking downstream from the approach channel at the discharge structure 3-foot-diameter half round inlet riser. Note, stoplog slots were present but stoplogs were not installed.

/ HORSESHOE DAM A-14

29. View looking downstream through the 2-foot-diameter CMP discharge structure conduit from the inlet near Station 0+20.

30. View looking upstream at the outlet of the discharge structure at Station 0+20.

Note that the outlet was blocked by vegetation and access was not possible.

/ HORSESHOE DAM A-15

31. View of the combined service spillway/outlet works approach channel and inlet looking upstream from the dam crest near Station 7+75.