JANUARY 2013 | VOL. 12 NO. 1 | TAPPI JOURNAL 45 T he storage of logs in wet decks plays an important role in maintaining a consistent fiber supply to wood prod- ucts facilities in the southeastern United States, especially during times when weather and other seasonal difficulties slow or prevent harvesting. Wet storage involves storing logs under a system of sprinklers with the aim of achieving a very high moisture content, which allows the wood to be stored for extended periods without experiencing appre- ciable decay or damage by insects [1,2]. Water is applied to the logs continuously; however, there is a need to refine how and when water is applied owing to increased con- cerns in the southeastern U.S. regarding water use follow- ing recent drought and increasing urbanization. To better understand the effectiveness of different rates of water application to wet stored logs, it is necessary to examine how log moisture content varies throughout the period of stor- age. However, few options are available for monitoring the mois- ture content of logs stored in wet decks and, practically, access- ing logs once the deck has been built is difficult and dangerous. Hence, a moisture measurement system that can be installed as the wet deck is being built and can be used to monitor the high moisture contents that exist within logs is required. Time domain reflectometry (TDR) is one technique that might be suitable for monitoring the moisture content of wet- stored logs over an extended period. Several studies have used TDR to monitor moisture variation in standing trees [3-5], and the basic measurement principle reported in these studies can be applied to wet stored logs. A probe, which in this study consists of two 3 mm-diameter stainless steel rods brazed to a copper coaxial cable of known length and cast inside a 30 mm × 30 mm × 60 mm plastic block, is connected to a TDR instrument. A pulse of energy is transmitted through the cable to the probe where it is reflected back to the instrument. The time the pulse takes to return is influenced by the moisture content of the wood; a higher moisture content slows the pulse, and this is reported by the instrument as a change in the apparent length of the cable. The longer the apparent length, the higher the moisture content of the wood. The ap- parent length is read from a waveform trace on an oscillo- scope display [6]. Recently, Schimleck et al. [6] reported the development of a second-order linear regression model based on TDR mea- surements of apparent length for the estimation of moisture content. Calibrations were developed using rod lengths of 75 mm, 100 mm, and 125 mm; calibration accuracy improved as probe length increased. TDR readings from the 125 mm probes provided the strongest relationship (R 2 = 0.94) with moisture measurements. The authors concluded that their TDR readings were sufficiently correlated with moisture con- tent to accurately monitor moisture variation with time. As our TDR moisture content studies continued, extrapolation beyond the range of the data used for the initial model made it clear that a different calibration model might be more gen- erally appropriate. A three-parameter logistic regression, which limits moisture contents to a range between 0 and some maximum amount while maintaining a monotonic in- creasing relationship between TDR readings and moisture content, provided a more theoretically appropriate fit. A new calibration study was used to refine the calibration model. TDR presents several benefits in monitoring the moisture Examination of moisture content variation within an operational wet deck LAURENCE SCHIMLECK, KIM LOVE-MYERS, JOE SANDERS, HEATH RAYBON, RICHARD DANIELS, EDWARD ANDREWS, AND ERIK SCHILLING FIBER SUPPLY PEER-REVIEWED ABSTRACT: Many forest products companies in the southeastern United States store large volumes of round- wood under wet storage. Log quality depends on maintaining a high and constant wood moisture content; however, limited knowledge exists regarding moisture variation within individual logs, and within wet decks as a whole, mak- ing it impossible to recommend appropriate water application strategies. To better understand moisture variation within a wet deck, time domain reflectometry (TDR) was used to monitor the moisture variation of 30 southern pine logs over an 11-week period for a wet deck at the International Paper McBean woodyard. Three 125 mm long TDR probes were inserted into each log (before the deck was built) at 3, 4.5, and 7.5 m from the butt. The position of each log within the stack was also recorded. Mixed-effects analysis of variance (ANOVA) was used to examine moisture variation over the study period. Moisture content varied within the log, while position within the stack was generally not significant. The performance of the TDR probes was consistent throughout the study, indicating that they would be suitable for long term (e.g., 12 months) monitoring. Application: Moisture content variation of wet-stored logs with time can be monitored using TDR. Such infor- mation can be used to develop optimal watering strategies.