7 - 2024 Hancock Creek Dam Safety Inspection Report.pdf

DAM SAFETY INSPECTION REPORT

Hancock Creek Dam – Dam ID No. 88

Hancock Creek Dickinson County – Section 25, T 41N, R 28W

OWNER(S)/OPERATOR(S): MDNR Wildlife Division - UP Region 1985 US 42 Hwy West Ishpeming, MI 49849

(906) 485-1031311

HAZARD POTENTIAL

CLASSIFICATION: Low

INSPECTION DATE: August 5, 2024

REPORT DATE: February 10, 2025

PREPARED AND INSPECTED BY:

Micheal Size, E.I.T. Lucas A. Trumble, P.E.

Dam Safety Unit Dam Safety Unit Water Resources Division Water Resources Division Dept. of Environment, Great Lakes, and Energy Dept. of Environment, Great Lakes, and Energy 2100 West M-32 P.O. Box 30458 Gaylord, Michigan 49735 Lansing, Michigan 48909 989-619-4295 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 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 Hancock Creek Dam is in Fair condition. No existing dam safety deficiencies are recognized for normal loading conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. The following recommended actions are listed by priority:

Upstream Slope Depression Action: Fill in depressions with compatible material and compact by December 31, 2026.

Upstream Slope Rodent Burrow Action: Fill in burrows with compatible material and compact by December 31, 2026.

Vegetation Action: Maintain vegetation annually by December 31, 2025.

Seepage Action: Remove excess vegetation on annual basis. Monitor seepage for embankment material movement as necessary December 31, 2026.

Principal Spillway Concrete Component Action: Monitor crack for growth and patch if gap widens as necessary by December 31, 2026.

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 earthen embankment with a structural 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 roc 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 hydraulic height of the dam, as defined by Part 315, is the difference in elevation from the design flood (100-year event) elevation to the invert of the outlet stream. The hydraulic 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, 2014, and 2019. A copy of the 2019 inspection report is on file with the Dam Safety Program. The 2019 inspection report prepared by EGLE Dam Safety was used as a reference for this report.

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 uprooted 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.

Upstream Slope

Pool elevation at time of inspection (ft) At crest of concrete inlet

Upstream slope ground cover Vegetation

What issues are present on the upstream slope? Depressions, Rodent Burrows

Slope Protection

What types of slope protection are used? Vegetation

Condition of vegetation Too Tall

Action required for vegetation Maintenance

Describe action required Maintain vegetation annually

Depressions / Uneven Surface

What is the width of the depressed area? Varies

What is the depth of the depressed area? Varies

Location of depressed area Entire Surface, Upstream Slope

Action required for depressions Maintenance

Describe action required Fill in depressions with compatible material and compact.

Animal Burrows

Approximate number of rodent burrows <10

Location of rodent burrows Upstream Slope

Action required for rodent burrows Maintenance

Describe action required Fill in burrows with compatible material and compact.

Crest

Approximate width of crest (ft) 10

Approximate freeboard (ft) 2

Crest ground cover Grass, Gravel

What issues are present on the crest? None

Downstream Slope

Downstream slope ground cover Vegetation

What issues are present on the downstream slope?

Other Vegetation, Seepage

Ground Cover / Vegetation Issues

Describe the vegetation Weeds

Location of vegetation Entire Surface, Downstream Slope

Quantity of other vegetation Dense

Seepage

What type of seepage is present Wet Area

Location of seepage Downstream toe

Issues present in seepage area Aquatic Vegetation

Action required for seepage Monitor, Maintenance

Describe action required Remove excess vegetation on annual basis.

Monitor seepage for embankment material movement

Principal Spillway

What type of spillway is present? Weir Wall

What is the primary material used in the spillway? Concrete, Wooden Stoplogs

Which components are present? Stoplog

What issues are present with the primary spillway?

Deteriorating Materials

Material Deterioration

What materials are deteriorating in the spillway? Concrete

What issues are noted with the concrete components?

Isolated Crack

How large is the impacted area (in)? 48

Where are the issues located? Endwall / Headwall

Action required for concrete components of the spillway

Monitor

Describe action required Monitor crack for growth and patch if gap widens

Erosion Control / Energy Dissipation

What type of erosion control structure is in place? Rock-Lined Channel

Are there any issues with the outlet erosion control structure?

None

Does the outlet erosion control structure include any drains?

No

Gates / Valves

Does the spillway include a gate? No

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, 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, inspection photographs, and 2024 EGLE estimated flood flows are attached.

Approximate Dam Location (1:70,000 Scale):

Approximate Dam Location (1:40,000 Scale):

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

Figure 1: Impoundment upstream of dam.

Figure 2: Impoundment upstream of dam

Figure 3: Embankment upstream slope looking right from left abutment area.

Figure 4: Upstream slope looking right from left abutment. Deficiency: Brush.

Figure 5: Typical embankment upstream slope. Deficiency: Animal burrow.

Figure 6: Typical embankment upstream slope. Deficiency: Animal burrow.

Figure 7: Embankment upstream slope. Deficiency: Depression.

Figure 8: Embankment crest looking right from left abutment area.

Figure 9: Embankment downstream slope looking left from right abutment area. Deficiency: Brush.

Figure 10: Embankment downstream slope looking right from left abutment area. Deficiency: Brush.

Figure 11: Downstream area looking left and downstream from right abutment area. Deficiency: Brush.

Figure 12: Embankment downstream slope. Deficiency: Seepage.

Figure 13: Principal Spillway and Outlet Overview looking down from drone.

Figure 14: Principal spillway inlet. Right weir wall looking down from platform.

Figure 15: Right concrete wingwall looking downstream and right from platform.

Figure 16: Right concrete wingwall downstream and right from platform. Deficiency: Deteriorating Material

Figure 17: Principal spillway inlet. Left weir wall looking down from platform.

Figure 18: Left concrete wingwall looking downstream and left from platform.

Figure 19: Left concrete wingwall looking downstream and left from platform. Deficiency: Deteriorating Material.

Figure 20: Principal spillway concrete inlet looking down from platform. Wooden stoplogs.

Figure 21: Principal spillway concrete inlet looking down from platform.

Figure 22: Principal spillway concrete inlet looking down from platform.

Figure 23: Principal spillway. 60-inch corrugated metal pipe looking upstream from outlet. Deficiency: corrosion.

Figure 24: Downstream rock channel looking downstream.

Hancock Creek Dam Dickinson County

DAM ID NO. 88

HYDROLOGIC DATA

From: EGLE-wrd-qreq <EGLE-wrd-qreq@michigan.gov> Sent: Thursday, April 25, 2024 8:38 PM To: Size, Michael (EGLE) <SizeM@michigan.gov> Subject: RE: Flood or Low Flow Discharge Request

We have processed the discharge request submitted by email on April 5, 2024 (Process No.

20240243), 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)).

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: Friday, April 5, 2024 1:46 PM To: EGLE-wrd-qreq <EGLE-wrd-qreq@michigan.gov> Subject: Flood or Low Flow Discharge Request

Requestor: Mike Size Company: EGLE Address: Gaylord DO City/State: Gaylord, MI ZIP Code: 00000 Phone: 9896194295 Date: 04/05/2024 1 percent Flood Discharge Request Type: Dam Other Description (if request type "Other" selected):

Dam Hazard Potential (if request type "Dam" selected): Low Dam ID (if request type "Dam" selected): 88 Low Flow Project Description:

Contact Person:

Watercourse: Hancock Creek Local Name:

County: Dickinson City/Township: ?

Section: 25 Town: 41N Range: 28W Location: Hancock Creek Dam Email: SizeM@michigan.gov