Three watersheds located in Westmoreland County, Virginia were monitored to
evaluate effectiveness of forestry best management practices (BMPs) for minimizing
hydrologic and water quality impacts associated with timber harvesting. One watershed
was clear-cut without implementation of BMPs, one watershed was clear-cut with the
implementation of BMPs and the third watershed was left undisturbed as a control. The
27 months of pre-harvest monitoring data and 17 months of post-harvest monitoring data
were compared using the paired watershed regression analysis and the minimum detectable
change (MDC) statistic.
Analysis of the hydrologic data showed that peak discharge rates were not
impacted by harvesting, regardless of whether BMPs were implemented. Harvesting with
or without the implementation of BMPs resulted in no statistically significant change in
stormflow volume.
BMP implementation was found to be effective in minimizing harvesting impacts
on stormflow total suspended solids (TSS), ammonia, total Kjeldahl nitrogen (TKN), total
nitrogen (TN), sediment-bound nitrogen and total phosphorous (TP) concentrations and
total flow TSS and TP concentrations. BMP implementation was also effective in
minimizing harvesting impacts on stormflow TSS, TKN, sediment-bound nitrogen, TP and
sediment-bound phosphorous loadings and total ammonia loading. The BMPs were not
effective in reducing nitrate concentrations and loadings.
The BROOK90 forest hydrology model was used to predict the site hydrology.
Model predictions compared favorably with streamflow measurements from watersheds
QN3 and QN4 until the time of harvest, but did not predict streamflows as accurately for
the control watershed, QN5.
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