4_c__-_AMNWR__Crystal_Springs_Dam_Report.pdf

$VK�0HDGRZV�1DWLRQDO�:LOGOLIH�5HIXJH

1<(�&2817<��19

&5<67$/�635,1*6�'$0

/2:�+$=$5'�327(17,$/�'$0

1$7,21$/�,19(1725<�2)�'$06�12��19�����

)250$/�6(('�,163(&7,21�5(3257

,163(&7,21�'$7(������������

6XEPLWWHG�7R� 3UHSDUHG�%\�

8�6��)LVK� �:LOGOLIH�6HUYLFH :�:��:KHHOHU�DQG�$VVRFLDWHV��,QF�

'LYLVLRQ�RI�(QJLQHHULQJ �����6RXWK�,QFD�6WUHHW

�����1RUWK�)DLUID[�'ULYH��6XLWH����� (QJOHZRRG��&2������

$UOLQJWRQ��9$������ 7HO��������������

7HO�������������� )D[��������������

)D[��������������

,QVSHFWHG�%\��1DPH�7LWOH��

'DQLHOOH�7ULSS�+DQQHV��3�(���$VVRFLDWH�(QJLQHHU��:��:��:KHHOHU�DQG�$VVRFLDWHV��,QF�

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB�����BBBBBBBBBBBBBBBBBBBBB

6LJQDWXUH�����������������������������������������������������������������������'DWH

5HYLHZHG�%\��1DPH�7LWOH��

<LQJ�.LW�&KRL��3�(���7HFKQLFDO�5HYLHZHU��:��:��:KHHOHU�DQG�$VVRLFDWHV��,QF�

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB�����BBBBBBBBBBBBBBBBBBBBB

6LJQDWXUH�����������������������������������������������������������������������'DWH

CRYSTAL SPRINGS DAM (NV00189)

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 4

3. Status of Previous Recommendations 8

4. Screening Level Risk Assessment 11

5. Pertinent Data 13

6. Inspection Checklist 19

7. Inspection and Project History 26

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.

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.

Crystal Lake Dam was in POOR condition due to the erosion undermining the outlet works siphon on the downstream slope; lack of supports for the outlet works siphon pipe; erosion gullies on the downstream slope; heavy vegetation in the emergency spillway and service spillway approach and discharge channels likely to limit spillway discharge capacity; and historical seepage that has been observed with a lack of available geotechnical data to evaluate the adequacy of the embankment and foundation materials of the dam.

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 101.

This is the initial SLRA score for Crystal Springs Dam 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.

- Concerns have been documented on the structural stability of the embankment with no geologic information available to evaluate the stability.

NV00189 / CRYSTAL SPRINGS DAM 1

C.

D.

E.

F.

- Misoperation of the siphon resulting in joint leakage, erosion of the downstream slope, and undermining of the siphon pipe.

- History of seepage.

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

If Crystal Springs 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 Crystal Springs Dam be classified as a

Low Hazard Dam (Wheeler, 2019).

Hydrology and Hydraulics Review Crystal Springs Dam is an intermediate sized, Low Hazard Dam which requires the dam to safely pass the 100-year flood. The 100-year flood was developed for the 5.3 square mile drainage basin by W.

W. Wheeler and Associates, Inc. for the 2019 Hazard Classification Evaluation. 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 for Crystal Springs Dam predominately consists of hydrologic soil type "C", with some type "B" and "D" soils present. The peak inflow into Crystal Lake Dam was 987 cubic feet per second (cfs) with a storm volume of 400 acre-feet. The reservoir routing of this storm event results in a maximum water surface Elevation of

2183.3 feet, which provides about 2.7 feet of freeboard to the dam crest.

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 service spillway or emergency spillway channels 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.

It is recommended that geotechnical explorations be performed to have the information available to perform a liquefaction and deformation analysis.

Geologic and Geotechnical Review There is no known information on the geology or geotechnical information available.

A memorandum in the 2005 SEED report documented that the dam that was originally constructed for

NV00189 / CRYSTAL SPRINGS DAM 2

G.

agricultural purposes without engineered materials and the native soil material may have high concentrations of salts and clays that could dissolve. It is recommended that geotechnical explorations be performed to evaluate the adequacy of the embankment and foundation.

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

NV00189 / CRYSTAL SPRINGS DAM 3

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. (1997-1MA-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 emergency spillway and service spillway approach and discharge channels. Upstream slope: trees less than 2 inches in diameter cut and treat with sealant; trees 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 less than 6 inches in diameter cut and treat with sealant; trees 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.

$51,809.70

P1 Maintenance Recommendations 1 P1 Maintenance Costs $51,809.70

Priority 2 Recommendation(s) Cost None

P2 Maintenance Recommendations 0 P2 Maintenance Costs $0.00

Total Maintenance Costs $51,809.70

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. (2002-2OM-02) On a monthly basis, visually monitor the upstream slope, crest, and downstream slope for animal burrows. Backfill observed animal burrows with appropriate on-site soil and compact as needed. See U.S. Fish and Wildlife Service Standard Operating Procedures (SOP) for additional guidance. Contact the Regional Dam Safety Officer if conditions become worse or if animal burrows persist.

$5,474.49

NV00189 / CRYSTAL SPRINGS DAM 4

D. Construction

E. Additional Studies or Analyses

2. (2002-2OM-04) Install a reservoir staff gage that extends at least one foot above the top of the dam so that accurate reservoir readings are possible under all anticipated reservoir levels. The reservoir staff gage should reference the same datum as the Pertinent Data in the SEED report.

$3,458.19

P2 Operations and Monitoring Recommendations 2 P2 Operations and Monitoring Costs $8,932.68

Total Operations and Monitoring Costs $8,932.68

Priority 1 Recommendation(s) Cost

1. (2018-1CO-01) Support siphon outlet pipe every 10 feet with concrete support cradle. Repair the siphon pipes where joint separation has occurred and repair damage to the embankment where siphon leakage has eroded under the siphon pipe on the downstream slope. This activity should be coordinated with the Regional Dam Safety Officer to determine appropriate engineering supervision requirements.

$44,436.87

2. (2018-1CO-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.

$259,513.36

P1 Construction Recommendations 2 P1 Construction Costs $303,950.22

Priority 2 Recommendation(s) Cost

1. (2005-2CO-01) Regrade dam crest to drain to the upstream embankment slope and repair erosion gullies along the downstream embankment slope.

This activity should be coordinated with the Regional Dam Safety Officer to determine appropriate engineering supervision requirements.

$6,436.99

P2 Construction Recommendations 1 P2 Construction Costs $6,436.99

Total Construction Costs $310,387.22

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. (2005-2SA-03) Perform SEED geotechnical field data collection to:

1) Collect subsurface soil samples to perform index and shear strength laboratory tests.

2) Install piezometers to identify seepage and groundwater conditions.

3) Prepare a field data collection report.

$139,455.00

2. (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

3. (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

NV00189 / CRYSTAL SPRINGS DAM 5

F. Future Inspections

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.

P2 Additional Studies or Analyses Recommendations 3 P2 Additional Studies or Analyses Costs $257,674.77

Total Additional Studies or Analyses Costs $257,674.77

Recommendation(s) Cost None

Total Future Inspections Recommendations 0 Total Future Inspections Costs $0.00

Total Emergency Recommendations 0 Total Emergency Costs $0.00

Total P1 Recommendations 3 Total P1 Costs $355,759.91

Total P2 Recommendations 6 Total P2 Costs $273,044.44

Total Future Inspection Recommendations 0 Total Future Inspection Costs $0.00

Total Recommendations 9 Total Costs $628,804.38

NV00189 / CRYSTAL SPRINGS DAM 6

Table 4-1 Operations Schedule Crystal Springs 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 (2) B,A Inspection Station Inspection (3) B,C SEED Inspection (4) B Special Inspection(5) B,C Diversion Structure Per RDSO B

Maintenance Maintain Siphon Equipment (pump) Per Manufacturer’s Recommendation B

Control Vegetation (6) B General Maintenance B Fill Rodent Holes 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) The reservoir staff gage observed during the 2018 SEED inspection was not of sufficient height to monitor the reservoir under all anticipated water levels. An Operations and Monitoring Recommendation was added in the 2018 SEED Report to replace the staff gage.

(3) 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 the seepage that has historically been observed downstream of the dam from about dam Station 10+00 to 25+00, animal burrows, and significant downstream slope erosion. Any changes in condition should be reported to the Regional Dam Safety Officer.

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

(5) 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.

(6) At least twice during growing seasons.

3. STATUS OF PREVIOUS

RECOMMENDATIONS

1.

C.

1.

2.

3.

3. Status of Previous Recommendations

Year of Estimate: 2019

Emergency Situation

None

Maintenance

PRIORITY 1 Recommendation(s) Recommendation (1997-1MA-01): Remove all vegetation from the upstream slope, downstream slope, approach and discharge channel within 100 feet of the emergency spillways control section (dam crest) as well as the left abutment of the dam. Backfill and compact soil in holes remaining from removal of roots along embankment slopes and spillways.

Total Cost:$51,521.40 Response: This recommendation has been partially completed and has been renewed. The trees generally larger than 12-inch-diameter trunks were removed from the embankment; however, significant woody vegetation is still present on the upstream and downstream slopes.

PRIORITY 2 Recommendation(s)

Operations and Monitoring

PRIORITY 1 Recommendation(s)

None

PRIORITY 2 Recommendation(s) Recommendation (2002-2OM-01): Continue to monitor the dam at least quarterly to assess seepage conditions at the toe of the dam between Station 10+00 and Station 25+00.

Total Cost:$0.00 Response: This recommendation has not been renewed. This is an on-going activity that is addressed in the Operations Schedule.

Recommendation (2002-2OM-02): Several animal burrows were observed during this inspection, and have been observed in the previous inspections. Continue to monitor (and backfill) upstream and downstream embankment slopes and dam crest for occurrence of animal burrows.

Total Cost:$1,581.25 Response: This recommendation has not been completed and has been renewed. This is also an on-going activity that is included in the Operations Schedule.

Recommendation (1997-2OM-03): Perform an internal video inspection of the older 6 inch diameter steel siphon conduit.

Total Cost:$7,041.56

NV00189 / CRYSTAL SPRINGS DAM 8

4.

1.

1.

E.

1.

1.

Response: This recommendation has not been renewed. The 6-inch-diameter steel siphon was removed in 2013 and replaced with a 12-inch-diameter HDPE siphon.

Recommendation (2002-2OM-04): Replace reservoir staff gage.

Total Cost:$1,918.35 Response: This recommendation has been partially completed and has been renewed. A new staff gage was installed after the 2011 SEED inspection; however, the staff gage does not extend to the dam crest.

Construction

PRIORITY 1 Recommendation(s) Recommendation (1997-1CO-01): Support siphon outlet pipes every 10 feet with concrete support cradle. Repair siphon pipes where joint separation and damage due to corrosion has occurred. Replace upstream valves with flap gate or back flow prevention valves to aid in priming siphon(s). Coordinate construction project with RDSO.

Total Cost:$43,848.00 Response: This recommendation has not been renewed. The siphon has been replaced since this recommendation was made.

Recommendation (2005-2CO-01): Regrade dam crest to drain to the upstream embankment slope and repair erosion gullies along the downstream embankment slope. Coordinate construction project with RDSO.

Total Cost:$5,618.02 Response: This recommendation has not been completed and has been renewed.

Additional Studies or Analyses

PRIORITY 1 Recommendation(s) Recommendation (2005-1SA-01): Revise the inflow hydrology and review hazard classification.

The updated hydrology should evaluate revised infiltration rates based on more impervious soils.

The hazard classification review should include impacts on Lower Crystal Dam and Stateline Road.

Total Cost:$37,500.00 Response: This recommendation has been completed. The inflow hydrology was updated and the hazard classification evaluated by Wheeler, 2019.

Recommendation (2002-2SA-01): Perform an analysis to determine if erosion protection is needed for the emergency spillway. If necessary, evaluate the size and extent of armoring needed in the emergency spillway where the spillway channel crosses the dam embankment.

Total Cost:$15,000.00 Response: This recommendation has not been renewed. Based on Wheeler, 2019, the 100-year

NV00189 / CRYSTAL SPRINGS DAM 9

2.

3.

F.

storm is passed by the service spillway and no flows are discharged through the emergency spillway.

Recommendation (2005-2SA-02): Perform a jurisdictional survey on the seven dams (including Crystal Springs Dam) on the Refuge, which are identified in the August 22, 2005 Memorandum from W.W. Wheeler and Associates, Inc. and included in the General Appendix.

Total Cost:$22,500.00 Response: This recommendation has been completed. A dam inventory assessment was performed for Ash Meadows National Wildlife Refuge by Wheeler in November 2018, concurrently with this SEED inspection work.

Recommendation (2005-2SA-03): Perform SEED geotechnical field data collection to: 1)Collect subsurface soil samples to perform index and shear strength laboratory tests. 2)Install piezometers to identify seepage and groundwater conditions. 3)Prepare a field data collection report. This recommendation is based on the August 22, 2005 Memorandum from W.W. Wheeler and Associates, Inc. and included in the General Appendix.

Total Cost:$156,000.00 Response: This recommendation has not been completed and has been renewed.

Future Inspections

NV00189 / CRYSTAL SPRINGS DAM 10

4. SCREENING LEVEL RISK ASSESSMENT

Dam Name: Crystal Lake Dam NID No.: NV00189 Station: Ash Meadows National Wildlife Refuge Region: 8 Hazard Classification: Low (pending 2019 Hazard Classification) Dam Type:

Dam Height: feet Maximum Storage: 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: 101

Earthfill

0 1 2 3 4

Hydraulic - Operations

Hydraulic - Overtopping 3 5

0 1 3 5 10

Li ke lih oo d

Static-Instability

Static-siphon Misoperation Seismic - Liquefaction

1 3 5 10

3 5

Static-Seepage 30 100

NV00189 / CRYSTAL SPRINGS DAM 11

Consequences: Level 0

Level 2

Failure Modes:

Likelihood Consequences Score

Extremely High 2 30

High 2 10

N/A N/A N/A

Extremely High 2 30

Low 2 1

Low 0 0

Extremely High 2 30

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; and inundation of State Line Road located downstream with a traffic count in excess of 400 vehicles per day and is paved. A hazard classification was authorized in 2019 to evaluate the consequences of a dam failure.

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 or foundation materials. Not designed for EQ loading.

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).

Siphon does not operate under all reservoir levels; however, the spillways can pass the inflow not resulting in consequences.

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

Dam can pass the 100-yr flood. 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.

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

Misoperation or failure of siphon pipe has discharged water onto the downstream slope resulting in significant embankment erosion.

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

No conduits exist through the embankment.

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

History of seepage; past inspections indicate observed seepage from a point source although not observed in 2018 inspection.

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.

Some over-steepened sections of the embankment, unknown and erodible embankment materials, with concerns of structural stability (documented in Supporting Documentation in 2005 SEED Report).

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.

Description Reason

NV00189 / CRYSTAL SPRINGS DAM 12

5. PERTINENT DATA

5. Pertinent Data General

Dam Section(s)

1. Dam Name *: CRYSTAL SPRINGS DAM

2. NID Number *: NV00189

3. Other Dam Name(s) *:

4. Dam Former Name(s) *:

5. Dam State *: NV

6. Dam County *: NYE

7. Dam Latitude *: 36.41

8. Dam Longtitude *: -116.32

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

S3,10 & 11,T18S,R50E

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

11. Basin: AMARGOSA RIVER

12. Reservoir Name: CRYSTAL

13. Year Constructed *: 1970

14. Year and Reason Dam Modified *: 2013H. (See Notes below).

15. Downstream Hazard Potential Classification *: LOW

16. Resource Value: Secondary Resource

17. Inventory Status: Inventory

18. Size Classification: INTERMEDIATE

19. SAMMS#: 10005161

20. Confined Space: no

21. Estimated Economic Losses Downstream: < $ 1 million

Notes:

Item 14: A 12-inch-diameter siphon was constructed around 2013, according to Refuge staff.

This siphon replaced the 6-inch-diameter siphon that was constructed in 2010.

Embankment Dam Section 1: CRYSTAL SPRINGS DAM

1. Dam Type *: EARTH

2. Crest Elevation: 2,186 Ft.

3. Dam (Crest) Length *: 4,350 Ft.

4. Crest Width: 20 Ft.

5. Dam Height *: 30 Ft.

6. Structural Height *: 30 Ft.

7. Hydraulic Height *: 27.2 Ft.

8. Upstream Slope: 2.7 H:1V to 3.3 H:1V

9. Downstream Slope: 2.7 H:1V to 3 H:1V

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

NV00189 / CRYSTAL SPRINGS DAM 13

C.

Saddle Dike(s)

Discharge Structure(s)

11. Foundation *: UNLISTED/UNKNOWN Certainty *:

Karst:

12. Volume of Dam *: 190,000 CY

Notes:

Dimensions updated based on 2007 LiDAR data (FWS, 2007).

Item 4: The dam crest width varies from 17 to 22 feet.

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. 2183.2 - El. 2156.0 = 27.2 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 2183.2 (Wheeler, 2019).

Item 12: The volume of the dam was reported to be 190,000 cubic yards in the 1985 Initial SEED inspection report.

There are no saddle dikes currently associated with this structure.

Discharge Structure 1: Emergency Spillway

1. Discharge Structure Type: Emergency Spillway

2. Description: EARTH CUT CHANNEL

3. Location: STATION 1+50 TO STATION 8+00

4. Approach Channel: RESERVOIR

5. Intake Structure: BROAD-CRESTED WEIR SECTION

a. Crest Elevation: 2,185 Ft.

b. Invert Elevation: Ft.

c. Size:

d. Material: EARTH

e. Width: 650 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: NO DEFINED CHANNEL

a. Length: Ft.

b. Size:

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: NO DEFINED CHANNEL

NV00189 / CRYSTAL SPRINGS DAM 14

10. Discharge Capacity with Water Surface at *: Top of Dam : 1,690 cfs and is based on the following formula: Q=C*L*H^1.5

Notes:

Dimensions updated based on LiDAR data (FWS, 2007).

Item 10: The discharge capacity of the emergency spillway can be estimated using the following formula; Q=C*L*H^1.5, where H = water surface elevation - spillway crest elevation, C = 2.6, L=650 feet. At the dam crest (EL 2186), discharge = 2.6*650*(2186- 2185)^1.5 = 1690 cfs.

Discharge Structure 2: SERVICE SPILLWAY

1. Discharge Structure Type: Service Spillway

2. Description: UNLINED EARTH CHANNEL

3. Location: APPROXIMATELY 200 ft LEFT OF

EMERGENCY SPILLWAY

4. Approach Channel: UNGATED APPROACH CHANNEL

5. Intake Structure: UNLINED EARTH CHANNEL

a. Crest Elevation: 2,181 Ft.

b. Invert Elevation: Ft.

c. Size:

d. Material:

e. Width: 15 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 TRAPEZODIAL

CHANNEL

a. Length: Ft.

b. Size: 15-FOOT-WIDE

c. Inlet Invert Elevation: Ft.

d. Outlet Invert Elevation: Ft.

e. Year of Conduit Installation:

8. Outlet Structure: NONE.

a. Energy Dissipation:

9. Discharge Channel: UPPER SPRINGS DIVERSION

DITCH

10. Discharge Capacity with Water Surface at *: Top of Dam : 436 cfs and is based on the following formula: Q=CLH^1.5

Notes:

Dimensions verified from 2011 SEED Inspection Report with LiDAR data (FWS, 2007).

Item 10: The discharge capacity of the service spillway can be estimated using the following formula; Q=C*L*H^1.5, where H = water surface elevation - spillway crest elevation, C = 2.6, L=15 feet. At the dam crest (EL 2186), discharge = 2.6*15*(2186-2181)^1.5 = 436 cfs.

NV00189 / CRYSTAL SPRINGS DAM 15

E. Reservoir / Flood Hydrology

Discharge Structure 3: Outlet Works

1. Discharge Structure Type: Outlet Works

2. Description: 12-inch-diameter siphon

3. Location: Approximately Station 33+40

4. Approach Channel: Reservoir

5. Intake Structure: Unknown

a. Crest Elevation: Ft.

b. Invert Elevation: Ft.

c. Size: 12-inch diameter

d. Material: HDPE

e. Width: Ft.

6. Control Structure: Siphon Pump to Initiate Siphon

a. Type *: CONTROLLED

OTHER CONTROLLED

b. Min Control Elevation: Ft.

c. Max Elevation of Gate Opening: Ft.

d. Max Control Elevation: Ft.

e. Size:

f. Material:

7. Conveyance Structure: 12-inch-diameter siphon pipe

a. Length: 140 Ft.

b. Size: 12-inch-diameter pipe

c. Inlet Invert Elevation: 2,175.5 Ft.

d. Outlet Invert Elevation: 2,168.5 Ft.

e. Year of Conduit Installation: 2013

8. Outlet Structure: None

a. Energy Dissipation: Fish screen/ plunge pool

9. Discharge Channel: Unlined earthen channel

10. Discharge Capacity with Water Surface at *: Top of Dam : 16.3 cfs and is based on the following formula: CA(2gH)^0.5

Notes:

The outlet works siphon was replaced in 2013 according to Refuge staff. The dimensions were updated based on the LiDAR data (FWS, 2007) and measurements taken in the field using a hand level and measuring tape.

Item 5 and Item 7c: The siphon intake was submerged at the time of the inspection. Intake elevation and dimensions could not be measured. According to the Refuge staff, the siphon is only able to operate with a reservoir water level above about Elevation 2175.5 (staff gage height of 3.0). The pump will not prime the siphon at lower reservoir elevations.

Item 7a: Measurement from the dam crest to the downstream fish screen using a hand level.

Item 10: The discharge for the 12-inch-diameter siphon is calculated using the conduit equation: Q=CA(2gH)^0.5 where H = water surface elevation - discharge elevation (2186 - 2168.5) = 17.5 feet), C = coefficient = 0.62, A = pipe area = 0.785 feet^2, g = 32.2 feet per second^2.

NV00189 / CRYSTAL SPRINGS DAM 16

F. Management

Reservoir Storage Level Elevation (feet) Surface Area

(acres) Capacity (acre-feet)

Maximum Normal Pool * 2,181 128 1,102 Discharge Structure 1:

Emergency Spillway

2,185 177 1,738

Discharge Structure 2:

SERVICE SPILLWAY

2,181 128 1,102

Top of Dam * 2,186 188 1,926

Flood Hydrology

1. Inflow design flood: 100-year storm

2. Storm Duration: 24 hours

3. Total Rainfall: 2.75 inches

4. IDF Peak Inflow: 987 cfs

5. Storm Volume: 400 acre-feet

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

2,183.3 Ft.

7. IDF Freeboard: 2.7 Ft.

8. Depth of Overtopping:

0 Ft.

9. Duration of Overtopping:

0 hours.

10. IDF Peak Outflow: 132 cfs

11. Drainage Area: 5.27 square miles

12. Drainage Basin Description *:

Armagosa Valley closed basin

Notes:

Storage/Capacity Table and Flood Hydrology information updated as documented in Wheeler, 2019.

1. Owner Name *: US FISH AND WILDLIFE SERVICE

2. Owner Type *: FEDERAL

3. Dam Designer *: Spring Meadows, Inc.

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: 06

NV00189 / CRYSTAL SPRINGS DAM 17

G.

H.

I.

EAP / SOP

Inspection Details

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

* denotes data submitted to the NID.

12. Federal Agency Involvement in Design *: U.S. Fish and Wildlife Service

13. Federal Agency Involvement in Construction *: U.S. Fish and Wildlife Service

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 *:

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

Notes:

Not required.

1. Date of Previous Inspection: 03/22/2011 Inspection Type: Intermediate

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:

Discharge Structure 3: Outlet Works

Notes:

Item 7: The outlet works siphon was constructed in 2013. It is unknown if the pipe interior was inspected during this construction.

NV00189 / CRYSTAL SPRINGS DAM 18

6. INSPECTION CHECKLIST

Crystal Springs Dam, Ash Meadows NWR Page 1

INSPECTION CHECKLIST FOR LOW HAZARD DAMS

DAM NAME: Crystal Springs Dam DATE INSPECTED: November 13, 2018

NID NO.: NV00189 DATE OF PREVIOUS INSPECTION: March 23, 2011

STATION: Ash Meadows National Wildlife Refuge WEATHER/TEMP.: Sunny, 68F

COUNTY/STATE: Nye County, Nevada POOL ELEVATION: 2173.3 (12.7 feet below dam crest, staff gage = 0.75-foot)

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:

(3) Animal burrows observed at the top of the upstream slope. Typical animal burrows were about 12 inches deep and 7 inches in diameter, see Photo No. 8 for view of animal burrow near Sta. 19+00.

(5) The upstream slope was over-steepened near the top of the slope, above the normal high water line, near Sta 34+00. See Photo No. 6.

(11) Slope protection was sparse in areas of the upstream slope. The size of the riprap slope protection was variable on the entire slope. See Photo No. 6.

(12) A majority of the trees that had a trunk diameter in excess of about 12 inches were cut down on the upstream slope, but the tree stumps and root systems were not removed. Vegetation was observed on most of the upstream slope including bushes and small trees with trunks that were approximately 2 inches in diameter, see Photo No. 4. A tree with a trunk diameter that was about 12 inches was observed on the upstream slope near Sta 23+00, see Photo No. 7.

(12) Erosion was observed on the upstream slope above the normal high water line near Sta. 48+50, see Photo No. 9.

PHOTOS: Upstream slope shown on Photo Nos. 1 through 9.

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:

(3) Animal burrows were observed throughout the dam crest. Typical animal burrows were about 7 inches deep and 2 inches in diameter. See Photo No. 15 for typical burrow near Sta 44+00.

(4) Erosion was observed on the downstream side of the dam crest that extends from the crest to the downstream toe along the entire dam crest. Erosion was up to about 1.4 feet wide and 0.5 feet deep, see Photo No. 16.

(7) Typical minor ruts were observed on the dam crest that were approximately 1-foot-wide and 2 inches deep. See Photo No.

17.

PHOTOS: Dam crest shown on Photo Nos. 10 through 17.

NV00189 / CRYSTAL SPRINGS DAM 19

Crystal Springs Dam, 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:

(4) Erosion gullies were observed on the downstream slope throughout. Erosion gullies begin at the crest and extend along the downstream slope to the dam toe. The erosion gullies were up to 1.4 feet wide and 0.5-foot deep at Sta 33+00, see Photo No.

16. Other erosion gullies were observed to be up to one-foot deep, see typical erosion in Photo Nos. 25 and 26.

(5) Several areas along the downstream slope were observed to be over-steepened, primarily due to surface erosion washing materials down the downstream slope. See Photo No. 37.

(10) The downstream slope did not have slope protection. See Photo Nos. 20, 25, and 26.

(11) Several piles of soft soils were observed along the downstream toe and appear to have been eroded from the downstream slope. See Photo Nos. 20 and 27.

(13) Minor trees and large bushes were observed on the downstream slope that were generally less than 2 inches in diameter.

See Photo No. 20, which includes a tree with a 2-inch diameter trunk near approximate Sta. 18+50.

(13) Slope materials are sandy/silty and erodible.

PHOTOS: Downstream slope shown on Photo Nos. 18 through 27 and 37.

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:

(4) Standing water, saturated soils, and green vegetation were observed downstream of the downstream toe from about Sta.

9+00 to 30+00, see Photo Nos. 28 and 29. The observations are consistent with historic documentation of the seepage areas.

However, past inspections indicated discharge points approximately 50 feet downstream of the toe. Flowing water or discharge points were not observed during this inspection.

PHOTOS: Seepage shown on Photo Nos. 28 and 29.

NV00189 / CRYSTAL SPRINGS DAM 20

Crystal Springs Dam, Ash Meadows NWR Page 3

DISCHARGE STRUCTURE: Outlet Works - Siphon

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

(3) Erosion of the downstream slope was observed on the side of the siphon pipe that rests on the downstream slope. Erosion was observed from the downstream side of the dam crest to the dam toe, generally starting in the location of the joints that appear to have an additional external seal applied. Erosion was up to 10 inches deep and 2 feet wide. See Photo Nos. 36 - 38.

(5) Erosion alongside the siphon pipe on the downstream slope is starting to undermine the pipe since the downstream slope is the only support for the siphon pipe. See Photo Nos. 36 - 38. The siphon on the upstream slope is unsupported, see Photo No.

32.

(8) Scour protection was not observed on the downstream slope where joint leakage is likely causing erosion, see Photo No. 36.

A riprap plunge pool is located at the outfall, see Photo No. 41.

(13) Evidence of erosion and an additional seal applied to the HDPE joints indicates that joint leakage may be occurring during siphon operation. See Photo Nos. 36 and 37.

(14, 15) The siphon was not operated during the 2018 inspection because the reservoir was too low to prime the siphon using the pump, see Photo No. 33. The Refuge staff indicated that they can start the siphon if the reservoir is above about Elevation

2175.5 (staff gage reading 3.0-foot). The Refuge staff indicated that the siphon was operational the prior week.

(17) According to the Refuge staff, the siphon was replaced in 2013.

PHOTOS: Outlet works siphon shown on Photo Nos. 30 through 41.

DISCHARGE STRUCTURE: Emergency Spillway

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) Significant vegetation was observed upstream and downstream of the emergency spillway control crest. See Photo Nos. 42- 45.

(8) No scour protection was observed in the emergency spillway.

(17) The Refuge Manager indicated a large flood occurred on the Refuge in 2015 that was approximated at the 500-year flood event. No erosion was observed in the emergency spillway as a result of this event; however, the Refuge did not confirm if they observed discharges in the emergency spillway during or following this event.

PHOTOS: Emergency spillway shown on Photo Nos. 42 through 45.

NV00189 / CRYSTAL SPRINGS DAM 21

Crystal Springs Dam, Ash Meadows NWR Page 4

DISCHARGE STRUCTURE: Service Spillway

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) Significant vegetation in approach and discharge areas. See Photo Nos. 46-50.

(8) No scour protection was observed in the service spillway.

(17) The Refuge Manager indicated a large flood occurred on the Refuge in 2015 that was approximated at the 500-year flood event. No erosion was observed in the service spillway as a result of this event; however, the Refuge did not confirm if they observed discharges in the service spillway during or following this event.

PHOTOS: Service spillway shown on Photo Nos. 46 through 50.

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:

(2) Staff gage in the reservoir does not extend to the maximum water surface elevation or dam crest. The staff gage is monitored by Refuge staff; however, no formal record keeping of the water level recordings was indicated aside from photographs. See Photo No. 51.

(3) Deteriorated survey monuments were located downstream of the downstream toe at approximately 100-foot intervals, comprised of wood. Monitoring records were not available. Monitoring of these monuments would be of limited value considering their compromised condition. See Photo No. 52.

PHOTOS: The instrumentation is shown on Photo Nos. 51 and 52.

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 Crystal Springs 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.

NV00189 / CRYSTAL SPRINGS DAM 22

Crystal Springs Dam, Ash Meadows NWR Page 5

REASONS: Crystal Lake Dam was in POOR condition due to the erosion undermining the outlet works siphon on the downstream slope; lack of supports for the outlet works siphon pipe; erosion gullies on the downstream slope; heavy vegetation in the emergency spillway and service spillway approach and discharge channels likely to limit spillway discharge capacity; and historical seepage that has been observed with a lack of available geotechnical data to evaluate the adequacy of the embankment and foundation materials of the dam.

NV00189 / CRYSTAL SPRINGS DAM 23

Crystal Springs Dam, Ash Meadows NWR Page 6

DEFINTIONS

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…