Assessing the impacts of log extraction by typical small shovel logging system on soil physical and hydrological properties in the Republic of Korea.

Typical small shovel logging system, using manual felling and extraction by small crawler excavator with grapple and crawler carriers, is the predominant logging method in the Republic of Korea, due to the associated high productivity. The trails with ground pressure and one more passes of the shovel and carriers may lead to soil compaction. However, impacts of these bunching-extraction technologies on physical and hydrological properties of soils are not well known. The main objectives of this study were to: (1) determine the bulk density, porosity, and saturated hydraulic conductivity of soils in logging operation areas with three different disturbance types (i.e., undisturbed areas [UAs], bladed trails [BTs], and skid trails [STs]), and (2) compare soil compaction between these disturbance types. The most intense compaction occurred within BTs and STs, with increased bulk density and reduced porosity and hydraulic conductivity. Soil bulk density increased by 27-53% at all depths in BTs and STs compared to UAs, while porosity decreased by 23-49%. On average, saturated hydraulic conductivity at depths of 0-20 cm decreased from 337.5 mm h-1 to 30.5 mm h-1 in the most compacted sections of BTs and STs. Skid trails, which are characterized by trail construction and frequent vehicle movement, also caused greater impacts on soil compaction than BTs. This study provides useful insights to aid forest consultants and field managers in planning more environmentally sound mechanized logging operations.

Comparison of HSPF and SWAT models performance for runoff and sediment yield prediction.

A watershed model can be used to better understand the relationship between land use activities and hydrologic/water quality processes that occur within a watershed. The physically based, distributed parameter model (SWAT) and a conceptual, lumped parameter model (HSPF), were selected and their performance were compared in simulating runoff and sediment yields from the Polecat Creek watershed in Virginia, which is 12,048 ha in size. A monitoring project was conducted in Polecat Creek watershed during the period of October 1994 to June 2000. The observed data (stream flow and sediment yield) from the monitoring project was used in the calibration/validations of the models. The period of September 1996 to June 2000 was used for the calibration and October 1994 to December 1995 was used for the validation of the models. The outputs from the models were compared to the observed data at several sub-watershed outlets and at the watershed outlet of the Polecat Creek watershed. The results indicated that both models were generally able to simulate stream flow and sediment yields well during both the calibration/validation periods. For annual and monthly loads, HSPF simulated hydrologic and sediment yield more accurately than SWAT at all monitoring sites within the watershed. The results of this study indicate that both the SWAT and HSPF watershed models performed sufficiently well in the simulation of stream flow and sediment yield with HSPF performing moderately better than SWAT for simulation time-steps greater than a month.

Simulating fecal coliform bacteria loading from an urbanizing watershed.

The fate and transport of fecal coliform bacteria in the urbanizing Polecat Creek watershed, located in Virginia, was simulated using the Hydrological Simulation Program-FORTRAN (HSPF). Both point and nonpoint sources of fecal coliform were included in the simulation. Hydrologic and water quality parameters of HSPF were calibrated and validated using observed data collected from October 1994 to June 2000 at three monitoring stations. The percent errors in total runoff volumes between observed and simulated values ranged from 0.4 to 4.2% for the calibration period, and 0.4 to 6.7% for the validation period. The geometric mean of simulated fecal coliform concentrations at the outlet of the watershed was 10% lower than that of observed values for the calibration period. HSPF moderately under-predicted the geometric mean concentration by 16.4% for one sub-watershed and slightly over-predicted by 7.3% for another. Observed fecal coliform concentrations were compared with the range defined by the minimum and maximum simulated concentrations occurring within a 3-day window centered on the day the water sample was collected. Over 42% of grab sample data collected at the three monitoring sites in the watershed fell within the max min range of simulated concentrations over the 3-days window for the calibration period. For all monitoring sites, 39.5% of the total samples taken during the validation period fell in the range of simulated concentrations over the 3-day window period. Results presented in this study demonstrate that HSPF reasonably represents the hydrology and water quality of an urbanizin watershed and that it could be utilized as a planning tool for future assessment of land use impacts on fecal coliform on in-stream concentrations.