HYD"RDLOGY 



INTRODUCTION 



This analysis is designed to 

 disclose the existing condition of 

 the hydrologic resources, display 

 the anticipated effects that may 

 result from each alternative, and 

 address the following issues and 

 concerns : 



• Timber-harvesting activities may 

 increase the amount of sediment 

 flowing into the streams . 



• The removal of vegetation near 

 streams reduces its sediment- 

 filtering capacity and channel 

 stability. 



• Harvesting may reduce future 

 amounts of large woody material in 

 streams; the material is used as 

 natural sediment traps and energy 

 dissipaters to reduce the velocity 

 and erosiveness of streamflows. 



• Removing tree canopies would 

 decrease rain and snow 

 interception and alter the 

 distribution of snowpack and 

 snowmelt, which would lead to 

 water yield increases. This may 

 result in more streambank erosion 

 and sediment deposits. 



ANALYSIS METHODS 



A DNRC hydrologist evaluated roads 

 and stream crossings to determine 

 the location of sediment sources and 

 identify in-channel sources of 

 sediment. The increase in water 

 yield for the Dog Creek watershed 

 was also determined using the 

 equivalent-clearcut-acre (EGA) 

 method. This method equates the 

 area harvested and percent of crown 

 removed with an equal amount of 

 clearcut area. This method also 

 calculates the recovery of these 

 increases as new trees grow on the 

 site and move toward preharvest 

 water use . 



ANALYSIS AREA 



The analysis area for sediment 

 delivery is the Dog Meadow Timber 

 Sale Project area and the proposed 



haul routes. Dog Creek, a 9,4 59- 

 acre watershed that includes Dog 

 Lake, is a perennial third-order 

 tributary to Stillwater River. The 

 sediment delivery analysis will 

 cover all stream segments within the 

 watershed and all roads and upland 

 sites that may contribute sediment 

 to Dog Creek. 



The analysis area for water yield is 

 the 9,459-acre, third-order Dog 

 Creek watershed. Dog Lake covers 99 

 acres and is fed and drained by Dog 

 Creek. The Dog Creek watershed also 

 contains dozens of wetlands and 

 beaver dam complexes. These all 

 serve to dampen the effect of water 

 yield by releasing water more slowly 

 and evenly than incoming flows. 



EXISTING CONDITIONS 



The Montana Surface Water Quality 

 Standards classifies the Stillwater 

 River drainage, including Dog Creek, 

 as B-1, which does not allow 

 increases in sediment above 

 naturally occurring levels and 

 allows only minimal increases over 

 natural turbidity. 



Bull trout or migratory cutthroat 

 trout do not inhabit streams in the 

 project area. Eastern brook trout, 

 an exotic species, are present in 

 the streams. 



The SMZ Law defines Dog Creek as a 

 Class 1 stream; Dog Creek and many 

 of its tributaries flow for more 

 than 6 months of the year. Many of 

 these tributaries also support fish. 

 Some of the smaller first-order 

 tributaries may be Class 2 or 3, 

 depending on the site-specific 

 conditions . 



Stream channels in the Dog Creek 

 watershed are mostly in good 

 condition. Though some sediment 

 deposits exist, no areas of in- 

 channel erosion were found during 

 reconnaissance. Stream crossings in 

 the project area and on the haul 

 route are in good condition 

 generally and are not contributing 

 sediment to streams. Some stream 



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Page III -10 



Dog/Meadow Timber Sale Project Draft EA 



