STATE OF MICHIGAN

DEPARTMENT OF

ENVIRONMENT, GREAT LAKES, AND ENERGY

LANSING

CONSTITUTION HALL • 525 WEST ALLEGAN STREET • P.O. BOX 30473 • LANSING, MICHIGAN 48909-7973

Michigan.gov/EGLE • 800-662-9278

GRETCHEN WHITMER

GOVERNOR

PHILLIP ROOS

DIRECTOR

VIA EMAIL

TO: Sara Thompson, Acting Chief Wildlife Division Department of Natural Resources

FROM: Mitchel Thelen, P.E., Regional Engineer Dam Safety Unit Water Resources Division

DATE: January 31, 2024

SUBJECT: Shiawassee Flats Dam, Dam ID No. 1819; Saginaw County

Attached is a copy of our Dam Safety Inspection Report and recommendations for the Shiawassee Flats Dam, Dam ID No. 1819, located in Saginaw County. This inspection was conducted by the Department of Environment, Great Lakes, and Energy (EGLE) per the Memorandum of Understanding between the Michigan Department of Natural Resources (MDNR) and the Michigan Department of Environment, Great Lakes, and Energy [EGLE, formerly Michigan Department of Environmental Quality (MDEQ)], entitled “Inspection of MDNR-Owned Dams and Funding of MDEQ's Dam Safety Program.”

The purpose of this inspection was to evaluate the structural condition and hydraulic capacity of this dam, as required by Part 315 (Dam Safety), of the Natural Resources and Environmental Protection Act, 1994 PA 451, as amended.

The Shiawassee Flats Dam is in poor condition overall. The inspection report contains several recommended actions for monitoring and maintenance of deficiencies that should be addressed in the timeframes provided in the report. Specifically, the report recommends the following:

1. Sink Hole (Action: Engineer): Hire an Engineer to evaluate the conduit condition and the cause of the sink hole. The sink hole should be monitored weekly and after any rain events, until the maintenance is completed. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit and/or embankment. When a sink hole is observed above a conduit there is concern that a piping failure is already initiated in the embankment. Complete action by December 31, 2024.

a. Outlet 2: Conduit

b. Outlet 3: Conduit

Sara Thompson, DNR January 31, 2024

2. Depression (Action: Engineer): Hire an Engineer to evaluate the conduit condition and the cause of depression. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit and/or embankment. When a depression is observed above a conduit there is concern that a piping failure could or already is initiated in the embankment. Complete action by December 31, 2024.

a. Outlet 2: Conduit

3. Deteriorating Material (Action: Engineer, Material: Metal): Hire and Engineer to repair and/or replace conduit. The metal deterioration has progressed enough to where routine maintenance cannot recover the service life of the conduit. The Engineer must determine the next steps to ensure the structural and hydraulic integrity of the dam. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit. Complete action by December 31, 2024.

a. Outlet 3: Conduit – Outlet

4. Erosion (Action: Maintenance): Reshape and stabilize area damaged by erosion. Regrade the area to original condition with suitable fill material. Install concrete, appropriate size riprap on filter fabric, and/or vegetation with 4-inches of topsoil to provide adequate protection against erosion. Erosion issues will continue to get worse and more expensive to repair if not addressed. Complete action by December 31, 2024.

a. Embankment - Upstream Slope

b. Auxiliary Spillway: Downstream

5. Steep Slope (Action: Engineer, Severity: Low): Regrade embankment slope to achieve a minimum of 1:2 (V:H) slope. Hire Engineer for permitting and design. Complete action by December 31, 2024.

a. Embankment - Downstream Slope

6. Seepage (Action: Monitor, Type: Wet Area): Inspect twice a year for an increase in water flow from seepage area. All dams have seepage. However, any changes in the seepage flow or color are a concern and should be addressed by an Engineer.

a. Principal Spillway: Abutment - Right Wall

7. Gates should be operated through their entire range of motion a minimum of once a year to ensure they are working properly.

8. Review and update the Operation and Maintenance Plan (O&M Plan) regularly.

Provide any updates to the Dam Safety Program.

Sara Thompson, DNR January 31, 2024

Please contact Mitchel Thelen, P.E, Dam Safety Program, at 517-230-5866 or ThelenM21@Michigan.gov, if you have any questions or concerns regarding the inspection report or the recommendations.

Attachment cc: Cameron Dole, DNR

John Niewoonder, DNR File

DAM SAFETY INSPECTION REPORT

SHIAWASSEE FLATS DAM – DAM ID NO. 1819

SHIAWASSEE RIVER

SAGINAW COUNTY – SW 1/4 SECTION 34, T 11N, R 03E

OWNER(S)/OPERATOR(S): Department of Natural Resources Wildlife Division Lower Peninsula Southwestern Region 225 E Spruce St Saint Charles, MI 48655

HAZARD POTENTIAL

CLASSIFICATION: Low

INSPECTION DATE: September 27, 2023

REPORT DATE: January 31, 2024

PREPARED AND INSPECTED BY:

Mitchel K. Thelen, P.E.

Registration Number: 09306 Dam Safety Unit Water Resources Division Department of Environment, Great Lakes, and Energy P.O. Box 30458 Lansing, Michigan 48909 517-280-5866

INTRODUCTION

The purpose of this inspection was to evaluate the structural condition and hydraulic capacity of the Shiawassee Flats Dam, as required by Part 315 (Dam Safety), of the Natural Resources and Environmental Protection Act, 1994 PA 451, as amended. This inspection was conducted by the Department of Environment, Great Lakes, and Energy (EGLE) per the Memorandum of Understanding between the Michigan Department of Natural Resources (MDNR) and the Michigan Department of Environment, Great Lakes, and Energy (EGLE, formerly Michigan Department of Environmental Quality (MDEQ)), entitled “Inspection of MDNR-Owned Dams and Funding of MDEQ's Dam Safety Program.”

The report is limited to a discussion of observations based on a visual investigation and review of any available previous inspection reports, plans, and data. This report should not be considered an in-depth engineering investigation. All references to “right” and “left” in this report are based on the observer facing downstream.

CONCLUSIONS AND RECOMMENDATIONS

The Shiawassee Flats Dam is in poor condition. Dam safety deficiency is recognized for loading conditions which may realistically occur. Remedial action is necessary. Poor rating may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Further investigations and studies are necessary.

The following recommended actions are listed by priority:

1. Sink Hole (Action: Engineer): Hire an Engineer to evaluate the conduit condition and the cause of the sink hole. The sink hole should be monitored weekly and after any rain events, until the maintenance is completed. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit and/or embankment. When a sink hole is observed above a conduit there is concern that a piping failure is already initiated in the embankment. Complete action by December 31, 2024.

a. Outlet 2: Conduit

b. Outlet 3: Conduit

2. Depression (Action: Engineer): Hire an Engineer to evaluate the conduit condition and the cause of depression. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit and/or embankment. When a depression is observed above a conduit there is concern that a piping failure could or already is initiated in the embankment. Complete action by December 31, 2024.

a. Outlet 2: Conduit

3. Deteriorating Material (Action: Engineer, Material: Metal): Hire and Engineer to repair and/or replace conduit. The metal deterioration has progressed enough to where routine maintenance cannot recover the service life of the conduit. The Engineer must determine the next steps to ensure the structural and hydraulic integrity of the dam. The Engineer must apply for an EGLE permit for the repair or reconstruct of the conduit. Complete action by December 31, 2024.

a. Outlet 3: Conduit - Outlet

4. Erosion (Action: Maintenance): Reshape and stabilize area damaged by erosion. Regrade the area to original condition with suitable fill material. Install concrete, appropriate size riprap on filter fabric, and/or vegetation with 4-inches of topsoil to provide adequate protection against erosion. Erosion issues will continue to get worse and more expensive to repair if not addressed. Complete action by December 31, 2024.

a. Embankment - Upstream Slope

b. Auxiliary Spillway: Downstream

5. Steep Slope (Action: Engineer, Severity: Low): Regrade embankment slope to achieve a minimum of 1:2 (V:H) slope. Hire Engineer for permitting and design. Complete action by December 31, 2024.

a. Embankment - Downstream Slope

6. Seepage (Action: Monitor, Type: Wet Area): Inspect twice a year for an increase in water flow from seepage area. All dams have seepage. However, any changes in the seepage flow or color are a concern and should be addressed by an Engineer.

a. Principal Spillway: Abutment - Right Wall

7. Gates should be operated through their entire range of motion a minimum of once a year to ensure they are working properly.

8. Review and update the Operation and Maintenance Plan (O&M Plan) regularly.

Provide any updates to the Dam Safety Program.

The dam’s current low hazard potential rating remains appropriate.

PROJECT INFORMATION

The original construction date of the dikes at the Shiawassee Flats Dam is not known.

Improvements, including the installation of the Seven Tubes Structure, were completed based upon plans prepared in 1963. The dual radial gates were installed in 1977. The dam is located in the Shiawassee River State Game Area and maintained by Wildlife Division personnel.

The Dam consists of the following parts:

Principal Spillway

Spillway Type: Tainter Gate Primary Material: Metal/Concrete

Gate 1 and 2

Gate Type: Tainter Gate Material: Metal

Bay Material: Concrete Width: 20'

Operation: Manual

Abutment

Material: Concrete Thickness: 18

Bridge

Material: Wood Width: 16'

Auxiliary Spillway

Spillway Type: Tainter Gate Primary Material: Metal/Concrete

Gate

Gate Type: Tainter Gate Material: Metal

Bay Material: Concrete Width: 9’

Operation: Manual Height: 10'

Abutment

Material: Concrete Thickness: 18”

Height: 15'

Bridge

Material: Concrete Width: 16'

Emergency Spillway

Spillway Type: Weir Wall Primary Material:

Weir Wall

Material: Earth Crest Width: 16'

Crest Length: 80'

Outlet 1, 2, and 3

Spillway Type: Sluice Gate/Conduit Primary Material: Metal/Concrete

Conduit

Gate

Gate Type: Sluice Operation: Manual

Bay Material: Concrete Gate Material: Metal

Deck

Material: Metal Width: 2'

Embankment

Material: Earth Crest Width: 16’

Length: 20,300' Crest Cover: Vegetation

Upstream Slope (V1toH_): 2 Downstream Slope (V1toH_): 2

Upstream Slope Cover: Vegetation Downstream Slope Cover: Vegetation

The Dam has the following measurements:

Structural Height (ft): 12 Normal Freeboard (ft): 4

Normal Head (ft): 8 Flood Freeboard (ft): 0

Hydraulic Height (ft): 12 Normal Impoundment (acre): 1600

Major repairs to the gate structure and erosion protection just downstream from the radial gate structure were completed in 2011-12 in response to the previous inspection report. Impoundment levels were formerly controlled by a stop log-controlled overflow weir structure connected to seven 36-inch corrugated metal pipes (CMP) (Seven Tubes Structure). The overflow weir was removed and the CMPs filled with flowable fill in 2001, based upon concerns over the condition of the riser frame support and the corrugated metal outlet pipes.

SITE INVESTIGATION

The following discussion of the dam’s physical condition and appurtenances is based on observations and photographs obtained on the inspection date.

In addition to the specific findings listed below, it is important to continue good maintenance practices. These practices include regular inspection of the dam embankments and hydraulic structures for any deficiencies. Some of the more common issues that are found include growth of trees and brush, development of erosion areas, and animal burrows.

If woody vegetation is allowed to mature, it could develop an extensive root system.

These root systems can lead to piping failure or if the brush and trees are uprooting in a storm, can cause extensive deterioration of the embankment. Embankments should be clear of woody vegetation and mowed 10 feet past the toe of the embankment.

Similarly, animal burrows and surface erosion, can propagate into increased seepage and potentially piping failure, as well as lead to slope stability issues.

The following data was collected on the date of the inspection and includes deficiencies observed during the inspection and necessary actions for remediation of the observed deficiencies.

Embankment Upstream Slope

What issues are present: Erosion Erosion

Photo: 41 Type: Gully

Action Required: Maintenance Describe action required: Reshape and stabilize area damaged by erosion.

Crest What issues are present: None

Downstream Slope What issues are present: Steep Slope

Steep Slope Photo: 83

Severity: Low Action Required: Engineer

Describe action required:

Regrade embankment slope to achieve a minimum of 1:2 (V:H) slope.

Spillways Principal Spillway

What issues are present: Seepage Seepage

Component: Abutment Part: Right Wall

Photo: 10 Type: Wet Area

Action Required: Monitor

Describe action required:

Inspect twice a year for an increase in water flow from seepage area.

Auxiliary Spillway What issues are present: Erosion

Erosion Part: Downstream

Photo: 15,16 Type: Bank

Action Required: Maintenance Describe action required: Reshape and stabilize area damaged by erosion.

Emergency Spillway What issues are present: None

Outlet 1 What issues are present: None

Outlet 2 What issues are present: Sink Hole, Depression

Sink Hole Component: Conduit

Photo: 29 Action Required: Engineer

Describe action required:

Hire an Engineer to evaluate the conduit condition and the cause of depression.

Depression Component: Conduit

Photo: 28 Action Required: Engineer

Describe action required:

Hire an Engineer to evaluate the conduit condition and the cause of depression.

Outlet 3 What issues are present: Sink Hole, Deteriorating Material

Sink Hole Component: Conduit

Photo: 34 Action Required: Engineer

Describe action required:

Hire an Engineer to evaluate the conduit condition and the cause of depression.

Deteriorating Material Component: Conduit

Part: Outlet Photo: 33

Material: Metal Action Required: Engineer

Describe action required: Hire and Engineer to repair and/or replace conduit.

The above monitoring and maintenance items should be addressed in accordance with the Conclusions and Recommendations section of this report.

STRUCTURAL STABILITY

Based upon observations during the inspection, the conduits for outlets 2 and 3 appear to be in poor condition. Piping failure in the embankment may have already started or will likely start due to the poor condition of the conduits. The recommendations stated above should be completed to ensure the structural stability of the embankment.

HYDROLOGY AND HYDRAULICS

The contributing drainage area to the Shiawassee River at the dam is approximately 626 square miles. The design discharge for this dam is the 1 percent chance (100-year) flood discharge of 8,300 cubic feet per second (cfs). The actual spillway capacity of the dam is highly dependent upon tailwater conditions. As shown on the Saginaw County Flood Insurance Study, the 100-year floodplain elevation in the vicinity of the dam is 593.9 feet, which would result in at least 1.5 feet of embankment submergence.

Given the long crest width being overtopped and minimal head differential between the headwater and tailwater, the overtopping velocity is not expected to become severe enough to cause failure of the dam. Additional spillway capacity is not required.

OPERATION AND MAINTENANCE

Operation and maintenance (O&M) of the dam is performed by Department of Natural Resources, Wildlife Division, Lower Peninsula Southwestern Region. A written O&M Plan was developed for this dam and is on record with the Dam Safety Program. The O&M Plan should be reviewed periodically and updated as necessary. Updated copies should be provided to the Dam Safety Program.

EMERGENCY ACTION PLAN

An Emergency Action Plan (EAP) is not required under Part 315 for a low hazard potential dam. Our records indicate that an EAP has not been developed for the dam.

APPENDICES

Appendix A - Location map, Appendix B - Inspection photographs Appendix C - Hydrologic Data

SHIAWASSEE FLATS DAM - SAGINAW COUNTY - DAM ID NO. 1819

Appendix A – Location Map

Appendix B – Inspection Photos

Photo #1: Principal Spillway Impoundment.

Photo #2: Principal Spillway Impoundment.

Photo #3: Principal Spillway Downstream.

Photo #4: Principal Spillway. Water Level.

Photo #5: Principal Spillway Gate 1.

Photo #6: Principal Spillway Gate 2.

Photo #7: Principal Spillway Abutment Left Wall.

Photo #8: Principal Spillway Abutment Left Wall.

Photo #9: Principal Spillway Abutment Left Wall.

Photo #10: Principal Spillway Abutment Right Wall. Seepage is coming out high on the wall..

Issue: Seepage, Action: Monitor.

Type: Wet Area.

Photo #11: Principal Spillway Abutment Right Wall.

Photo #12: Principal Spillway Abutment Right Wall.

Photo #13: Principal Spillway Bridge.

Photo #14: Principal Spillway Bridge.

Photo #15: Auxiliary Spillway Downstream.

Issue: Erosion, Action: Maintenance.

Type: Bank.

Photo #16: Auxiliary Spillway Downstream.

Issue: Erosion, Action: Maintenance.

Type: Bank.

Photo #17: Auxiliary Spillway Downstream.

Photo #18: Auxiliary Spillway. Water Level.

Photo #19: Auxiliary Spillway Abutment Left Wall.

Photo #20: Auxiliary Spillway Abutment Right Wall.

Photo #21: Auxiliary Spillway Bridge.

Photo #22: Emergency Spillway Weir Wall.

Photo #23: Outlet 1 Conduit Inlet.

Photo #24: Outlet 1 Gate.

Photo #25: Outlet 1 Deck.

Photo #26: Outlet 2 Conduit Inlet. Could not visually inspect.

Photo #27: Outlet 2 Conduit Outlet.

Photo #28: Outlet 2 Conduit.

Issue: Depression, Action: Engineer.

Photo #29: Outlet 2 Conduit.

Issue: Sink Hole, Action: Engineer.

Height: 20, Depth: 32.

Photo #30: Outlet 2 Gate.

Photo #31: Outlet 2 Deck.

Photo #32: Outlet 3 Conduit Inlet.

Photo #33: Outlet 3 Conduit Outlet.

Issue: Deteriorating Material, Action: Engineer.

Material: Metal.

Photo #34: Outlet 3 Conduit. Downstream bank has severe sink hole.

Issue: Sink Hole, Action: Engineer.

Height: 3.5', Depth: 2'.

Photo #35: Outlet 3 Gate.

Photo #36: Outlet 3 Deck.

Overview Map

Photo #37: Embankment Upstream Slope.

Photo #38: Embankment Upstream Slope.

Photo #39: Embankment Upstream Slope.

Photo #40: Embankment Upstream Slope.

Photo #41: Embankment Upstream Slope.

Issue: Erosion, Action: Maintenance.

Type: Gully.

Photo #42: Embankment Upstream Slope.

Photo #43: Embankment Upstream Slope.

Photo #44: Embankment Upstream Slope.

Photo #45: Embankment Upstream Slope.

Photo #46: Embankment Upstream Slope.

Photo #47: Embankment Upstream Slope.

Photo #48: Embankment Upstream Slope.

Photo #49: Embankment Upstream Slope.

Photo #50: Embankment Upstream Slope.

Photo #51: Embankment Upstream Slope.

Photo #52: Embankment Upstream Slope.

Photo #53: Embankment Upstream Slope.

Photo #54: Embankment Upstream Slope.

Photo #55: Embankment Upstream Slope.

Photo #56: Embankment Upstream Slope.

Photo #57: Embankment Crest.

Photo #58: Embankment Crest.

Photo #59: Embankment Crest.

Photo #60: Embankment Crest.

Photo #61: Embankment Crest.

Photo #62: Embankment Crest.

Photo #63: Embankment Crest.

Photo #64: Embankment Crest.

Photo #65: Embankment Crest.

Photo #66: Embankment Crest.

Photo #67: Embankment Crest.

Photo #68: Embankment Crest.

Photo #69: Embankment Crest.

Photo #70: Embankment Crest.

Photo #71: Embankment Crest.

Photo #72: Embankment Crest.

Photo #73: Embankment Crest.

Photo #74: Embankment Crest.

Photo #75: Embankment Crest.

Photo #76: Embankment Downstream Slope.

Photo #77: Embankment Downstream Slope.

Photo #78: Embankment Downstream Slope.

Photo #79: Embankment Downstream Slope.

Photo #80: Embankment Downstream Slope.

Photo #81: Embankment Downstream Slope.

Photo #82: Embankment Downstream Slope.

Photo #83: Embankment Downstream Slope.

Issue: Steep Slope, Action: Engineer.

Slope V1: H_:0.25, Severity: Low.

Photo #84: Embankment Downstream Slope.

Photo #85: Embankment Downstream Slope.

Photo #86: Embankment Downstream Slope.

Photo #87: Embankment Downstream Slope.

Photo #88: Embankment Downstream Slope.

Photo #89: Embankment Downstream Slope.

Photo #90: Embankment Downstream Slope.

Photo #91: Embankment Downstream Slope.

Photo #92: Embankment Downstream Slope.

Photo #93: Embankment Downstream Slope.

Photo #94: Embankment Downstream Slope.

Photo #95: Embankment Downstream Slope.

SHIAWASSEE FLATS DAM

SAGINAW COUNTY

DAM ID NO. 1819

Appendix C – Hydrologic Data

We have processed the discharge request submitted by email on January 11, 2023 (Process No. 20230035), as follows:

Shiawassee River at Shiawassee Flats Dam, Dam ID 1819, Section 34, T11N, R3E, Swan Creek Township, Saginaw County, has a total drainage area of 623 square miles and a contributing drainage area of 614 square miles. The design discharge for this dam is the 1% chance (100-year) flood. The 1% chance peak flow is estimated to be 8300 cubic feet per second. (Watershed Basin No. 32C Shiawassee).

These estimates should be confirmed by our office if an application is not submitted within one year. If you have any questions concerning the discharge estimates, please contact Ms. Susan Greiner, Hydrologic Studies and Floodplain Management Unit, at 517-927-3838, or by email at: GreinerS@michigan.gov.

-----Original Message----- From: EGLE-Automated <EGLE-Automated@michigan.gov> Sent: Wednesday, January 11, 2023 11:29 AM To: EGLE-wrd-qreq <EGLE-wrd-qreq@michigan.gov> Subject: Flood or Low Flow Discharge Request

Requestor: Mitchel Thelen Company: EGLE Address: 525 W. Allegan City/State: Lansing ZIP Code: 48933 Phone: 5172305866 Date: 01/11/2023 1 percent Contact Agency:

Contact Person:

Watercourse: Shiawassee River Local Name:

County: Saginaw City/Township: ? (requestor did not provide) Section: 34 Town: 11N Range: 03E Location: Shiawassee Flats Dam #1819 FFR1: Dam Email: ThelenM21@michigan.gov