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APPENDIX D 

 HYDROLOGY ANALYSIS 



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INTRODUCTION 



This analysis is designed to address 

 the public concerns particular to 

 hydrology, as listed in TABLE I-l- 

 SUMMARY AND TRACKING OF ISSUES AND 

 CONCERNS FROM PUBLIC COMMENTS of the 

 EA, and analysis elements considered 

 necessary by the ID Team. 



SEDIMENT DELIVERY 



Timber harvesting and related 

 activities, such as road 

 construction, can lead to water- 

 quality impacts by increasing the 

 production and delivery of fine 

 sediment to streams. Construction 

 of roads, skid trails, and landings 

 can generate and transfer 

 substantial amounts of sediment 

 through the removal of vegetation 

 and exposure of bare soil. In 

 addition, removal of vegetation near 

 stream channels reduces the 

 sediment-filtering capacity and may 

 reduce channel stability and the 

 amounts of large woody material. 

 Large woody debris is a very 

 important component of stream 

 dynamics and creating natural 

 sediment traps and energy 

 dissipaters to reduce the velocity 

 and erosiveness of streamflows. 



WATER YIELD 



Timber harvesting and associated 

 activities can affect the timing, 

 distribution, and amount of water 

 yield in a harvested watershed. 

 Water yields increase 

 proportionately to the percentage of 

 canopy removal, because removal of 

 live trees reduces the amount of 



water transpired, leaving more water 

 available for soil saturation and 

 runoff. Canopy removal also 

 decreases interception of rain and 

 snow and alters snowpack 

 distribution and snowmelt, which 

 lead to further water-yield 

 increases. Higher water yields may 

 lead to increases in peak flows and 

 peak-flow duration, which can result 

 in accelerated streambank erosion 

 and sediment deposition. 



ANALYSIS METHODS 



SEDIMENT DELIVERY 



Methodology for analyzing sediment 

 delivery was completed using a 

 sediment -source inventory. All 

 roads and stream crossings were 

 evaluated to determine the sources 

 of introduced sediment. In 

 addition, in-channel sources of 

 sediment were identified using 

 channel-stability rating methods 

 developed by Pfankuch, and through 

 the conversion of stability rating 

 to reach condition by stream type 

 developed by Rosgen (1990) . These 

 analyses were conducted in 2000 and 

 2002 by a DNRC hydrologist. 



WATER YIELD 



The water yield increase for the 

 watershed in the project area was 

 determined using the ECA method, as 

 outlined in Forest Hydrology Part II 

 (1976) . ECA is a function of total 

 area roaded and harvested, percent 

 of crown removal in harvesting, and 

 amount of vegetative recovery that 

 has occurred in harvest areas. This 

 method equates area harvested and 



