TABLE OF CONTENTS CONCLUSIONS AND RECOMMENDATIONS ....................................................................... 3 BACKGROUND INFORMATION ............................................................................................ 3 FIELD INSPECTION ............................................................................................................... 6 SPILLWAYS ............................................................................................................... 7 STRUCTURAL STABILITY ......................................................................................... 7 HYDROLOGY AND HYDRAULICS......................................................................................... 8 OPERATION AND MAINTENANCE ....................................................................................... 8 APPENDIX A: PHOTOGRAPHS ........................................................................................... 10 APPENDIX B: LOCATION MAPS ......................................................................................... 20 APPENDIX C: FIELD REPORT ............................................................................................ 22 APPENDIX D: ENGINEERING DATA ................................................................................... 29 APPENDIX E: TECUMSEH DAM REPAIR PERMIT DRAWINGS ........................................ 32 APPENDIX F: RED MILL POND LEGAL LAKE LEVEL STUDY, JULY 18, 2012, FTC&H .... 37 APPENDIX G: TECUMSEH DAM EMERGENCY ACTION PLAN ........................................ 59 The purpose of this dam safety inspection report and Michigan’s Dam Safety Law is to evaluate the existing condition of the dam. The report is limited to a visual investigation, review of previous inspection reports, plans and data (when available) at the time of the inspection. The contents of the report should not be treated as an in-depth engineering evaluation. Such evaluations or detailed investigations may be recommended based on the findings of this report. 2 CONCLUSIONS AND RECOMMENDATIONS • The Dam is structurally sound, but does show the results of age. • Repairs to the auxiliary spillway that were recommended in 2012 should be addressed immediately, including: − Spillway gates and concrete − Apron concrete • Three areas of reported seepage should be addressed. • Safety items that do not affect the structural stability of the dam should be addressed, for the operation and maintenance of the dam, including: − Fall protection and written procedures − Floatation devices and written procedures − Hand rails − Regrading stairway access − Night time lighting − Follow up of MiOSHA final report • Repairs to the south retaining wall noted in the 2012 report should be completed. BACKGROUND INFORMATION The Tecumseh Dam and its impoundment, referred to as the Red Mill Pond, are the furthest upstream of three impoundments on the River Raisin in the City of Tecumseh, Michigan. (Refer to Appendix B for a general & detailed location map.) The Tecumseh Dam consists of two separated areas for impoundment flow. The southern and larger of the two is described as the main spillway. The northern, smaller area is the auxiliary spillway. The main spillway and the auxiliary spillway are located near the south and north ends of the dam, respectively. Drawings from the most recent dam improvement work approved in 2013 & repairs performed in 2014, can be seen in Appendix E. The main spillway has a 14-foot wide by 9-foot high manually operated vertical steel gate located in the center bay. Flanking the lift gate are two 24-foot wide bays containing timber stop planks. Each row of stop planks contains two wood planks that may be installed and removed with poles by two individuals. The spillway is constructed of reinforced concrete and masonry retaining walls on the north and south ends, and pier/counterfort walls on 3 each side of the lift gate. The walls have been partially overlaid with shotcrete. The apron is composed of reinforced concrete. The toe of the apron is protected by steel sheet piling and riprap. The auxiliary spillway was formally used as a raceway for flow through an old hydroelectric power plant. There are seven metal sluice gates. The center five gates have manual operators. The southern and northern sluice gates have vertical channels in lieu of operators. It is presumed that these gates are intended to be operated by a vehicle or equipment parked on the bridge above. The main and auxiliary spillways are separated by earth fill. A concrete retaining wall adjoins the impoundment and structurally connects the main and auxiliary spillway retaining walls. Another concrete retaining wall extends along the impoundment for 60 feet south of the main spillway. A two-lane, four-span bridge with a walkway on the east side is adjacent to the dam and spans over the spillways. The bridge is owned by the City of Tecumseh and was built after the dam was constructed. At least a third of this bridge appears to be on this site. The auxiliary spillway, north retaining wall was a bridge abutment at the time of the dam construction. The north retaining wall on the main spillway was a bridge abutment for an earlier bridge that spanned the river. The current bridge is structurally independent. The dam was originally constructed for the Tecumseh Electric Company for electricity generation purposes. The power plant was removed in 1968. The dam now serves to provide impoundment and level control for the Red Mill Pond. The pond is mostly surrounded by large residential properties. Below is a chronological list of the owners of the dam. Prior to 1928, information on ownership could not be confirmed. − October 1928 George Smith to Tecumseh Electric Company. − November 1928 Tecumseh Electric Company to Lenawee County Light & Power Company. − June 1933 Lenawee County Light & Power Company to Quirk Farms. − July 1944 Quirk Farms to Ford Motor Company. 4 − April 1948 Ford Motor Company to Tecumseh Products Company. − April 2011 Tecumseh Products Company to Red Mill Pond LLC. − October 2012 Red Mill Pond LLC to Lenawee County On March 2, 2012 a petition by landowners abutting Red Mill Pond was submitted to establish a legal lake level according to Part 307, Public Act 451, 1994 – Inland Lake Levels for Lenawee County to own the dam and maintain a legal lake level. The County Board of Commissioners appointed the Lenawee County Drain Commissioner as the delegated authority to perform the operation and maintenance of the dam and instructed the Lenawee County Prosecuting Attorney to proceed with establishing a legal lake level in Circuit Court. On February 14, 2013 the Honorable Circuit Court Judge Margaret M. S. Noe ordered a legal level to be 777.6 feet NAVD 88 from April to November and 776.6 feet NAVD 88 from November to April of each year. On March 18, 2013 the Honorable Circuit Court Judge Margaret M. S. Noe ordered a special assessment district be established. Repairs to the dam that occurred in 2014 are listed below. Construction Drawings are on file at the Lenawee County Drain Commissioner’s office. Main and Auxiliary Spillway Bridge Rehabilitation - Demolish and replace auxiliary spillway footbridge metal components. - Install chain link fencing along main spillway footbridge. - Repair spalls on main spillway concrete deck. - Install locked fence gates on ends of footbridges. - Rehabilitate auxiliary gate floor stands, cranks, and gate stem covers. Main Spillway - Removed and rebuilt sluice gate. - Replaced seals & sills. - Repair eroded concrete adjacent to gate. - Repaired spalled concrete on pier nosings on each side of gate. - Repaired spalled concrete on south guide wall upstream of spillway. - Reconditioned operating mechanism. 5 South Retaining Wall - Installed hydrophilic sealant into joint at main spillway south abutment wall. Auxiliary Spillway - Remove and repair deteriorated concrete on counterfort walls. - Installed hydrophilic sealant into north abutment wall joint. - Repaired deteriorated concrete at west end of south abutment wall. Intermediate Retaining Wall - Repaired spalled concrete along waterline. The above repairs were recommended by FTC&H in the Legal Lake Level Study of July 18, 2012, included here as Appendix F. On page 3 of that study, the work completed has been highlighted. Repairs to the south retaining wall that were recommended in the 3- to 6-year range have not been completed, and should be completed soon. The repairs to the auxiliary spillway recommended in the 6- to 9-year timeframe should be completed soon, with an emphasis on the spillway apron concrete. Photographs taken during the field investigation and inspection are attached in Appendix A. Location, plan, and elevation drawings of the dam are located in the Lenawee County Drain Office. Portions of those maps are provided in Appendix B. Appendix C contains the 6/21/2018 and 2/25/2020 Dam Safety Inspection field reports. Appendix D contains the Michigan Department of Environment, Great Lakes and Energy (EGLE)’s flood discharge engineering data as of January 10, 2019, used in this report. Permit drawings for the Tecumseh Dam Repair are filed with the EGLE Dam Safety Program. Portions of those drawings are provided in Appendix E. FIELD INSPECTION This section summarizes the observations during the dam inspections and provides background to the recommendations. Directional orientation referring to left or right in the 6 following text is based on standing on top of the dam or earth embankment and looking downstream.