6 - 2019 Hancock Creek Dam Safety Inspection Report.pdf

DAM SAFETY INSPECTION REPORT

HANCOCK CREEK DAM – DAM ID NO. 88

HANCOCK CREEK

DICKINSON COUNTY – SECTION 25, T41N, R28W

OWNER/OPERATOR: Michigan Department of Natural Resources Wildlife Division

1420 Highway US-2 West Crystal Falls, MI 49920 906-875-6622

HAZARD POTENTIAL

CLASSIFICATION: Low

INSPECTION DATE: June 25, 2019

REPORT DATE: November 25, 2019

INSPECTED AND PREPARED BY:

Lucas A. Trumble, P.E.

Hydrologic Studies and Dam Safety Unit Water Resources Division Department of Environment, Great Lakes, and Energy P.O. Box 30458 Lansing, Michigan 48909 517-420-8923

INTRODUCTION

The purpose of this inspection was to evaluate the structural condition and hydraulic capacity of the Hancock Creek Dam, as required by Part 315, Dam Safety (Part 315), 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 provisions of its Memorandum of Understanding with the Department of Natural Resources (DNR), the owner of the dam. 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 was not based on 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 Hancock Creek Dam is in satisfactory condition overall. There were no deficiencies observed during the inspection that would lead to the dam’s failure. The dam has adequate spillway capacity to safely convey the design flood. The following recommended actions are listed by priority:

1. Monitor the depression adjacent to the principal spillway outlet on a quarterly basis. Report any additional settlement, expansion, or new depressions to the Dam Safety Program.

2. Continue to monitor cracks in the principal spillway concrete inlet riser on a quarterly basis. Report any significant movement or deterioration to the Dam Safety Program.

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

PROJECT INFORMATION

Hancock Creek Dam was constructed in 1951 to control a wildlife flooding originally created by a beaver dam. Reduced copies of construction plans are available in the Dam Safety Program files.

The dam consists of a 338-foot long earth embankment with a height of 12 feet, as measured from the top of the embankment to the invert of the outlet channel. The principal spillway is a concrete drop box spillway with a single 7-foot wide stoplog section. The spillway has a total weir length of 21 feet. The concrete inlet structure is founded on eight-gauge steel sheet pilings. The inlet structure is connected to a 40-foot long, 60-inch diameter corrugated metal pipe (CMP) outlet pipe. A plank walkway with a pipe handrail provides access to the stoplogs.

The embankment consists of unspecified earth fill with an upstream slope of 3 horizontal to 1 vertical (3H:1V), downstream slope of 2.5h:1V, and a top width of 10 feet. The embankment foundation consists of rock overlain by sand and gravel up to five feet thick and covered with topsoil or muck varying up to two feet thick. Drawing notes indicate that unsuitable foundation material was to be excavated prior to placing embankment fill.

The height of the dam, as defined by Part 315, is the difference in elevation from the design flood elevation to the invert of the outlet stream. That height for the Hancock Creek Dam is approximately 11 feet. The head, or difference in upstream and downstream water elevations, was approximately six feet on the date of the inspection.

Normal freeboard is approximately four feet. The impoundment created by the dam has a surface area of approximately 70 acres under normal conditions.

Previous inspection reports were completed in 1978, 1979, 1988, 1991, 1995, 1999, 2004, 2009, and 2014.

SITE INVESTIGATION

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

The dam’s earthen embankment, shown in Photographs 1 through 4 and 20 through 22, is in satisfactory condition. The DNR has done an excellent job maintaining the embankment free of trees and brush. These maintenance practices should continue.

The entire embankment is covered in dense, well-maintained grass. No significant slumps, slides, cracks, or settlement were observed during the inspection. There was a small slough observed on the downstream slope to the right of the outlet pipe, as shown in Photograph 15. This area should be monitored quarterly for changes. Any additional settlement, expansion, or new depressions should be reported to the Dam Safety Program.

The principal spillway structure, shown in Photographs 5, 6, 8 through 14, and 17 through 19, is in satisfactory condition. Two cracks and slight displacement of the concrete inlet riser, adjacent to the outlet pipe, and several cracks along the concrete head walls have been reported in previous inspection reports. These cracks do not appear to have worsened since previous inspections. No remedial action is required at this time. However, monitoring of the cracks on a quarterly basis should continue. Any significant movement or deterioration should be reported to the Dam Safety Program.

The principal spillway safety fencing, catwalk platform, and stoplogs appear to have been replaced since the 2014 inspection of the dam. These improvements have eliminated previous concerns with leaking stoplogs. No further remediation is required at this time.

Given its size and confined space entry restrictions, a thorough inspection of the interior of the CMP outlet pipe was not completed as part of this inspection. The age of the pipe is unknown; however, the dam was constructed in 1951. The interior of the pipe appears to be in satisfactory condition, with only minor signs of corrosion and loss of bituminous coating, as shown in Photograph 17, indicating that the pipe may have been replaced since the dam was constructed. Given the excellent condition of the pipe, immediate inspection of the interior is not warranted at this time. However, a televised camera inspection of the interior of the pipe will need to be completed sometime in the future as the pipe gets older or shows sign of deterioration. Such inspections are generally completed by a contractor utilizing specialized mobile camera equipment capable of providing a 360-degree view of the pipe’s interior along the entire length.

STRUCTURAL STABILITY

Based upon observations during the inspection, there were no indicators of any conditions that represent an immediate threat to the dam’s stability.

HYDROLOGY AND HYDRAULICS

The contributing drainage area to the Hancock Creek at the Hancock Creek Dam is approximately 6.9 square miles. The design discharge for this low hazard potential dam is the 1-percent annual chance (100-year) flood discharge, which is estimated to be 360 cubic feet per second (cfs). The dam has a maximum spillway capacity of approximately 230 cfs, with no freeboard at the earthen embankment.

Given this apparent lack of spillway capacity, the design flood was routed through the system using the U.S. Army Corps of Engineers, Hydrologic Modeling Center’s Hydrologic Modeling Software (HEC-HMS). Flood routing takes into account available storage and attenuation of peak flows provided by the impoundment and dam. The HEC-HMS model predicts that the dam can pass the design flood with a maximum discharge of approximately 190 cfs, resulting in 1.0 feet of freeboard. Therefore, the dam is considered to have adequate storage and spillway capacity to safely convey the design flood.

Copies of the hydraulic calculations and HEC-HMS model outputs are on file with the Dam Safety Program.

OPERATION AND MAINTENANCE

Operation of the dam is the responsibility of the owner or their designee. A written Operations and Maintenance Plan is on file and should be periodically reviewed and updated as necessary.

EMERGENCY ACTION PLAN

An Emergency Action Plan (EAP) does not exist for this dam. Due to the low hazard potential rating for this dam, an EAP is not required.

APPENDICES

A location map and inspection photographs are attached.

HANCOCK CREEK DAM

Hancock Creek Dam Dam ID No. 88 Section 25, T 41N, R 28W Dickinson County

DICKINSON COUNTY

DAM ID NO. 88

Photograph 1 – Hancock Creek Dam impoundment

Photograph 2 – Upstream slope of right embankment

Photograph 3 – Crest of right embankment

Photograph 4 – Downstream slope of right embankment

Photograph 5 – Intake structure viewed from right embankment

Photograph 6 – Intake structure from right embankment

Photograph 7 – View of impoundment from intake structure

Photograph 8 – Left wingwall of spillway

Photograph 9 – Right wingwall of spillway

Photograph 10 – Left side of stoplogs and guides

Photograph 11 – Right side of stoplogs and guides

Photograph 12 – Right side of intake structure headwall

Photograph 13 – Left side of intake structure headwall

Photograph 14 – intake structure gate entrance and work platform

Photograph 15 – Minor slough observed on downstream slope to right of outlet

Photograph 16 – Channel downstream of outlet

Photograph 17 – Interior of outlet culvert, viewed from downstream

Photograph 18 – Looking downstream at culvert outlet

Photograph 19 – Looking downstream at culvert outlet

Photograph 20 – Upstream slope of left embankment

Photograph 21 – Crest of left embankment

Photograph 22 – Downstream slope of left embankment

From: deq-wrd-qreq <deq-wrd-qreq@michigan.gov> Sent: Thursday, February 14, 2019 5:42 PM To: Pawloski, Jim (DEQ) <PAWLOSKIJ@michigan.gov> Cc: Trumble, Luke (DEQ) <TrumbleL@michigan.gov> Subject: RE: flood or low flow discharge request (ContentID - 168812)

We have estimated the flood frequency discharges requested in your email of February 11, 2019 (Process No. 20190091), as follows:

Hancock Creek at Hancock Creek Dam, Dam ID 88, Section 25, T41N, R28W, Breen Township, Dickinson County, has a drainage area of 6.9 square miles. The design discharge for this dam is the 1% chance (100-year) flood. The 1% chance peak outflow is estimated to be 190 cubic feet per second. The 1% chance flood volume is estimated to be 600 acre-feet. (Watershed Basin No. 50E Sturgeon (Dickinson)).

Please include a copy of this letter with your inspection report or any subsequent application for permit.

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 Dam Safety Unit, at 517-284-5579, or by email at: GreinerS@michigan.gov.

-----Original Message----- From: PAWLOSKIJ@michigan.gov <PAWLOSKIJ@michigan.gov> Sent: Monday, February 11, 2019 2:16 PM To: deq-wrd-qreq <deq-wrd-qreq@michigan.gov> Subject: flood or low flow discharge request (ContentID - 168812)

Requestor: Jim Pawloski Company: DEQ Address: 2100 West M-32 City: Gaylord, MI Zip: 49735 Phone: 989-370-1528 Date: 2019-02-11 F1percent: Yes ContactAgency: None Selected ContactPerson:

Watercourse: Hancock Creek LocalName:

CountyLocation: Dickinson CityorTownship: ?

Section: 25 Town: 41N Range: 28W Location: Hancock Creek Dam #88 FFR1: Dam mailto:deq-wrd-qreq@michigan.gov mailto:PAWLOSKIJ@michigan.gov mailto:TrumbleL@michigan.gov mailto:GreinerS@michigan.gov mailto:PAWLOSKIJ@michigan.gov mailto:PAWLOSKIJ@michigan.gov mailto:deq-wrd-qreq@michigan.gov