APPENDIX D 



WATERSHED AND HYDROLOGY ANALYSIS 



INTRODUCTION 



SEDIMENT DELIVERY 



Timber har-vesting and related 

 activities, such as road 

 construction and site preparation/ 

 scarification, 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, creating natural sediment 

 traps and energy dissipaters to 

 reduce the velocity and erosiveness 

 of stream flows. 



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 will be completed using a 

 sediment -source inventory. All 

 roads and stream crossings were 

 evaluated to determine sources of 

 introduced sediment and compliance 

 with applicable BMPs. The stability 

 of stream channels was assessed 

 using methods developed by Pfankuch. 

 A DNRC hydrologist conducted these 

 analyses in the fall of 2002. 



WATER YIELD 



An analysis of water-yield increases 

 will not be completed for the 

 proposed project. The project 

 proposal involves salvaging trees 

 killed by windthrow and forest 

 diseases. As a result, increases in 

 water yield have already occurred 

 through natural processes,- the 

 proposed project would not 

 contribute to the removal of live 

 vegetation or subsequent increases 

 in water yield. 



ANALYSIS AREA 



SEDIMENT DELIVERY 



The analysis will cover all stream 

 segments within the proposed project 

 area and all roads and upland sites 

 that may contribute sediment to a 

 live stream. Portions of the 

 project area are located within the 

 Soup Creek watershed; the remainder 

 of the proposal is located in small 

 unnamed, intermittent tributaries to 

 Swan River. 



Big Slowdown Salvage 



Page D-1 



