Condition Assessment of a 

Historic Trout Rearing Station 

in Upper Michigan

Frederico J. N. França

Tâmara S. F. Amorim França

Lon A. Yeary 

Christopher Hohnholt

John W. Forsman

Robert J. Ross

Research Note

FPL–RN–0334

United States Department of Agriculture

Forest 

Service

Forest Products

Laboratory

June

2015
June 2015

França, Frederico J. N.; França, Tâmara S. F. Amorim; Yeary, Lon A.; 

Hohnholt, Christopher; Forsman, John W.; Ross, Robert J. 2015. Condition 

assessment of a historic trout rearing station in upper Michigan. Research 

Note FPL-RN-0334. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 5 p.

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Abstract

Michigan Technological University’s (Michigan Tech) 

School of Forest Resources and Environmental Science 

maintains a log cabin on the north branch of the Otter River 

in southern Houghton County (Portage Township), Michigan. The cabin was built in 1934–1935 and measures 

150 m2. The cabin’s location is less than 10 m from the 

river, and when combined with the region’s high snowfall 

(5+ m per year) and subsequent spring melting, is highly 

susceptible to occasional flooding and subsequent water 

damage and decay. 

The history and use of the cabin dates back to the mid1930s. The Michigan Conservation Department (predecessor of the Michigan Department of Natural Resources) 

and the Civilian Conservation Corps built the cabin in 

1934–1935 to house workers who used the site as a trout 

hatchery.

Since 1998 Michigan Tech, in cooperation with the USDA 

Forest Products Laboratory (FPL), has conducted periodic 

inspections of the cabin. This report summarizes results 

obtained from the inspection conducted in 2013. It includes 

a brief summary of the nondestructive testing techniques 

used, observations, and data from tests conducted on the 

cabin.

Keywords: Nondestructive assessment, decay, moisture 

content

Contents

Introduction.....................................................................1

Methods...........................................................................1

Results.............................................................................3

Summary.........................................................................4

Recommendation ............................................................4

Literature Cited ...............................................................4

Other Sources..................................................................5
Condition Assessment of a Historic Trout 

Rearing Station in Upper Michigan

Frederico J. N. França, PhD Student

Tâmara S. F. Amorim França, PhD Student

Department of Sustainable Bioproducts

Mississippi State University, Starkville, Mississippi

Lon A. Yeary, Engineering Intern

Forest Products Laboratory, Madison, Wisconsin

Christopher Hohnholt, Director of Development & Outreach

John W. Forsman, Assistant Research Scientist

School of Forest Resources and Environmental Science

Michigan Technological University, Houghton, Michigan

Robert J. Ross, Supervisory Research General Engineer

Forest Products Laboratory, Madison, Wisconsin

Introduction

Michigan Technological University’s (Michigan Tech) 

School of Forest Resources and Environmental Science 

maintains a log cabin on the north branch of the Otter River 

in southern Houghton County (Portage Township), Michigan, USA. The cabin was built in 1934–1935 and measures 

150 m2. Untreated red pine (Pinus resinosa) logs were used 

as the primary construction material. The cabin’s location is 

less than 10 m from the river, and when combined with the 

region’s high snowfall (5+ m/year) and subsequent spring 

melting, results in it being highly susceptible to occasional 

flooding and subsequent water damage and decay. 

The history and use of the cabin dates back to the mid1930s. The Michigan Conservation Department (predecessor of the Michigan Department of Natural Resources) and 

the Civilian Conservation Corps built the cabin in 1934–

1935 to house workers who used the site as a trout hatchery. 

Grayling (Thymallus arcticus), rainbow (Oncorhynchus 

mykiss) and German brown (Salmo trutta) trout were propagated at the site. The cabin was transferred to Michigan 

Tech in 1955 with the reservation that public rights of hunting, fishing, and trapping would be maintained. The cabin 

has been used regularly by students of Michigan Tech’s 

School of Forest Resources and Environmental Science. Access to the cabin is also granted to a variety of user groups 

within the local community. 

Ongoing maintenance of the cabin is required because of its 

proximity to the river and the region’s heavy annual snow 

fall. Excessive water exposure as a consequence of flooding of the nearby river has resulted in the deterioration of 

several of the logs of the cabin during its service life. For 

example, in 1959, deteriorated logs were removed and replaced with a ventilated crawl space using a red sandstone 

foundation. Several attempts to mitigate the effects of snow 

on the roof have been undertaken. Asphalt shingles replaced 

the original cedar shake roof in 1956, and in 1990 a metal 

roof was installed. 

Since 1998, Michigan Tech has conducted periodic inspections of the cabin in cooperation with the USDA Forest 

Products Laboratory (FPL). This research note summarizes 

results obtained from the inspection conducted in 2013. It 

includes a brief summary of the techniques we used and observations and data from tests conducted on the cabin.

Methods

We inspected the cabin on July 30, 2013. Figure 1 is the 

cabin, and Figure 2 illustrates the location of the cabin relative to the Otter River. 

Similar inspections of the cabin were completed in 1998 

and 2008. In these inspections, we used accepted inspection 

techniques to assess the condition of the timbers that comprise the cabin. These techniques are discussed in detail in 

Figure 1—Otter River cabin, 2013.
Research Note FPL–RN–0334

2

Wood and Timber Condition Assessment Manual, Second 

Edition (White and Ross 2014). A brief description of the 

techniques we used follows. 

Visual Inspection

The simplest method for locating deterioration in wood 

members is visual inspection. An inspector observes the 

structure for signs of actual or potential deterioration, noting 

areas that require further investigation. Visual inspection is 

useful for detecting intermediate or advanced surface decay, 

water damage, mechanical damage, or failed members. 

Visual inspection cannot detect early stage decay or deterioration. Several key indicators are looked for in visual 

inspections: fruiting bodies (evidence of advanced decay), 

staining or discoloration of members (indicators of water 

damage), evidence of insect activity (holes, frass, and 

powder posting), plant or moss growth in a member, deep 

checks or splits, and failed or missing members. 

In our inspection of the cabin, we specifically looked for the 

following: 1. Evidence of water intrusion and subsequent 

damage, especially near its foundation, and 2. Evidence of 

structural failure of the timbers and noting collapsed timbers 

near the foundation and at hips and valleys of the roof.

Sound Transmission

A significant volume of research has been devoted to the use 

of sound waves for locating areas of deterioration in timber 

structures, and a practical set of guidelines for their use has 

been prepared by FPL (Ross and others 1999). In summary, 

the transmission of sound in wood is affected significantly 

by the presence of deterioration. Consequently, ultrasound 

and stress-wave based technologies have been developed 

and are widely used to inspect wood structures (Allison and 

others 2008; Brashaw and others 2005; Clausen and others 

2001; Emerson and others 2002; Ross and others 1999; Ross 

and others 2001; Ross and Wang 2005; Ross and others 

2006) and have been used for the assessment of culturally 

significant historic ships and artifacts (Ross and others 

1998; Wang and others 2008; Dundar and Ross 2012).

We used a simple, inexpensive stress-wave timer in our inspection (Fig. 3). Sensors were placed on opposite sides of 

a timber. The timber was then struck, generating a stress 

wave. The time it took for the wave to travel between the 

sensors was measured by the timer and recorded. Transmission times for wood from several species are known and 

were used as a baseline. Transmission times significantly 

longer than baseline values indicated the presence of deteriorated wood.

Micro-Drilling Resistance 

Simple mechanical tests are frequently used for in-service 

inspection of wood members in structures. Drilling and 

coring are the most common, simple tests used to detect 

internal deterioration. Both are used to detect the presence 

C

A

B

Otter River

N

S

W E

Figure 2—Orientation of the cabin relative to the Otter River. 

Note the location of walls A, B, and C.

Figure 3—Testing of wall timbers using a stress-wave 

timing device.

Figure 4—Micro-drilling resistance of wall timber in 

Otter River cabin.
Condition Assessment of a Historic Trout Rearing Station in Upper Michigan

3

of voids and to determine the thickness of the residual shell 

when voids are present. 

Micro-drilling resistance is a commercially developed technique originally developed for use by arborists and tree care 

professionals to evaluate the condition of urban trees and 

locate voids and decay. It is now being used to identify and 

quantify decay, voids, and termite galleries in wood beams, 

columns, poles and piles (Fig. 4) (Brashaw and others 

2005). The underlying premise for this technique is that degraded wood is relatively soft and will have low resistance 

to drill penetration. 

Our tests were conducted using a micro-drilling resistance 

device manufactured by IML, Inc. (Instrument Mechanic 

Labor, Inc., Kennesaw, Georgia). We conducted micro-drilling resistance tests in areas of the timbers that we believed 

contained deteriorated wood, based on results from our 

visual assessments and stress-wave testing. 

Results

Visual Inspection

Figures 5 and 6 illustrate examples of the types of deterioration we found in our visual inspection. Note that the logs 

used in the construction of the cabin were not treated with 

a wood preservative; hence they are highly prone to deterioration from decay fungi. Many of the logs that are in 

direct contact with the sandstone foundation showed signs 

of significant deterioration. The log shown in Figure 5 is an 

excellent example of the type of deterioration we observed. 

It contained significant splits and cracks, and upon probing 

with a pocket knife was found to be soft, both indicators of 

advanced deterioration. 

Many of the logs showed signs of severe deterioration, as 

shown in Figure 6, with the ends of several having been 

entirely destroyed. Several showed signs of mechanical 

failure.

Sound Transmission

Table 1 summarizes results from sound transmission tests 

for logs from several locations of the camp. Note that a 

baseline reading of approximately 200 micro-seconds or 

smaller indicates solid wood. Transmission times greater 

than 200 micro-seconds indicate deteriorated wood, and values greater than 250 indicate severe deterioration. Note that 

an electrical resistance moisture meter was used to determine their moisture content. Moisture content of the cabin’s 

timbers ranged from 8.0% to 20.4%.

Micro-Drilling Testing

Tests results from logs that compromised Wall Section A 

confirmed that many were deteriorated. Most had an outer 

shell of solid material, whereas their core was severely 

Figure 5—Visual evidence of deterioration of wall timbers. Figure 6—Visual evidence of severe deterioration of 

wall timbers.
Research Note FPL–RN–0334

4

deteriorated. Similarly, micro-drilling testing of several timbers in Wall Section C confirmed that they were significantly compromised (Fig. 7). 

Summary

An inspection Michigan Technological University’s Otter 

River Camp was conducted in August 2013. Several widely 

used techniques were used in the inspection. Because of its 

close proximity to the Otter River, the Camp’s cabin has 

significant water damage. Several areas of the cabin have 

significantly deteriorated timbers. Amplitude (%)

4 6 8

Drilling depth (cm)

0 2

20

30

10

0

Wall A is directly underneath a valley in the cabin’s roof. 

Prior inspections revealed significant water damage. The 

roof was repaired subsequent to the 1998 inspection. The 

logs that comprise this wall section have been water damaged because of flooding from the river and water entering 

through the roof. All of the logs in this section are deteriorated, some severely. The logs in Wall B of the cabin 

showed no signs of deterioration. Several of the logs in 

Wall C were deteriorated. 

Recommendation 

We strongly recommend that the cabin be dismantled, salvaging the historic materials (hardware and any timber that 

is sound) and that a smaller structure be built on the site using the salvaged materials where appropriate. 

Literature Cited

Allison, R.B.; Wang, X.; Ross, R.J. 2008. Visual and nondestructive evaluation of red pines supporting a ropes course 

in the USFS Nesbit Lake Camp, Sidnaw, MI. Proceedings, 

15th Nondestructive Testing of Wood Symposium, September 10–12, 2007, Duluth, MN. Forest Products Society: 

43–48. 

Brashaw, B.K.; Vatalaro, R.J.; Wang, X.; Ross, R. J.; Wacker, J.P. 2005. Condition assessment of timber bridges. 2. 

Evaluation of several stress wave tools. General Technical 

Report FPL–GTR–160. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

11 p. 

Clausen, C.A.; Ross, R.J.; Forsman, J.W.; Balachowski, J.D. 

2001. Condition assessment of roof trusses of Quincy mine 

blacksmith shop in Keweenaw National Historical Park. Research Note FPL–RN–0281. Madison, WI: U.S. Department 

of Agriculture, Forest Service, Forest Products Laboratory. 

4 p. 

Dundar, T.; Ross, R.J. 2012. Condition assessment of 2500 

year old wood coffin. Research Note FPL–RN–0327. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 3 p. 

Emerson, R.; Pollock, D.; McLean, D.; Fridley, K.; Pellerin, 

R.; Ross, R.J. 2002. Ultrasonic inspection of large timber 

bridge members. Forest Products Journal. 52(9): 88–95. 

Ross; R.J.; Soltis, L.A.; Otton, P. 1998. Assessing wood 

members in the USS Constitution using nondestructive evaluation methods. APT Bulletin. 29(2): 21–25.

Ross, R.J.; Volny, N.; Pellerin, R.F.; Salsig, W.W.; Falk, 

R.H. 1999. Inspection of timber bridges with stress wave 

nondestructive evaluation tools. A guide for use and interpretation. General Technical Report FPL–GTR–114. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 

Figure 7—Typical results obtained from a micro-drilling 

resistance test of a deteriorated timber from the Otter 

River cabin.

Table 1—Results from stress wave tests of timbers 

in the Otter River cabin 

Wall 

Timber 

position in 

the wall 

Stress wave 

transmission 

time 

(μs) Comments 

A 1 250 Deteriorated 

2 241 

3 289 Deteriorated 

4 262 Deteriorated 

5 246 

6 319 Deteriorated 

7 248 Deteriorated 

8 526 Severe 

deterioration 

B 1 135 

2 130 

3 145 

4 153 

5 145 

6 235 Deteriorated 

C 1 174 

2 232 

3 187 

4 207 

5 250 Deteriorated 

6 256 Deteriorated 
Condition Assessment of a Historic Trout Rearing Station in Upper Michigan

5

Ross, R.J.; Brashaw, B.K.; Wang, X. 2006. Structural condition assessment of in-service wood. Forest Products Journal. 

56(6): 4–8.

Wang X.; Wacker, J.P.; Ross, R.J.; Brashaw, B.K. 2008. 

Condition assessment of the main structural members of 

historic steam schooner Wapama. Research Paper FPL–RP–

649. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 

White, R.H.; Ross, R.J. 2014. Wood and timber condition 

assessment manual. Second Edition. General Technical Report FPL–GTR–324. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 102 p. 

Other Sources

Brashaw, B.K.; Vatalaro, R.J.; Wacker, J.P.; Ross, R.J. 2005. 

Condition assessment of timber bridges. Evaluation of a 

micro-drilling resistance tool. General Technical Report 

FPL–GTR–159. Madison, WI:U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 8 p. [Not 

called out in text]

Ross, R.J.; Pellerin, R.F.; Forsman, J.W.; Erickson, J.R.; 

Lavinder, J.A. 2001. Relationship between stress wave 

transmission time and compressive properties of timbers 

removed from service. Research Note FPL–RN–0280. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 4 p. [Not called out in text]

Ross, R.J.; Wang, X. 2005. Quincy Mine Blacksmith Shopcondition assessment of timbers. Structure Magazine. September 2005: 32–34. [Not called out in text]