Comparison of Alternatives 



The risk of detrimental levels of water yield increase due to timber harvest and new road 

 construction is low for all affected watersheds under each of the proposed action 

 alternatives. Predicted cumulative water yield increases for the entire Upper Willow Creek 

 watershed are < 1 % for all of the proposed action alternatives. Water yield increases for the 

 tributary analysis area's range from 1.9% to 7.7% above natural conditions. These levels of 

 water yield increase are below those levels normally associated with increased magnitude or 

 duration of peak flows that would cause or contribute to detrimental channel impacts. 



The predicted levels of water yield increase under all of the action alternatives are well 

 below thresholds set for each watershed analysis area. Thresholds were specifically 

 established for each watershed analysis area by a DNRC hydrologist using a risk matrix. 

 Under this process thresholds are determined by considering acceptable levels of risk, 

 watershed sensitivity (flow regime and channel conditions) and downstream resource values 

 (beneficial uses). Thresholds for allowable increases in water yield were set at 8% for Upper 

 Willow Creek, Bear Creek and Beaver Creek, and 12 % for all of the other watershed 

 analysis areas. 



Proposed action Alternatives B and C include watershed restoration activities designed to 

 address all identified sources of erosion and potential sediment delivery to streams or 

 ephemeral draw features. The proposed installation of a headgate structure and stabilization 

 of the eroding irrigation ditch is expected to substantially reduce impacts caused by flow 

 alteration, increased peak flows and increased sediment yields in lower Bear Creek. The 

 irrigation ditch gully has been identified as the single largest existing source of sediment 

 within the proposed sale area. 



These restoration measures are expected to result in substantial long-term reduction in existing 

 levels of sediment yield in Bear Creek and Upper Willow Creek. The risk of water quality 

 impacts that are associated with the proposed action alternatives due to new road construction, 

 temporary stream crossings, permanent culvert installations and timber harvest units are low. 

 Some short-term increases in sediment delivery to Bear Creek and Upper Willow may result 

 from installation of the headgate and stabilization of the irrigation ditch gully. However, the 

 overall long-term effects of implementation of any of the proposed action alternatives would be 

 reduced risk of cumulative impacts to water quality, cold water fisheries and other downstream 

 beneficial uses when compared to the current existing conditions. Improved watershed 

 conditions are also anticipated in Arbuckle and Slusser Gulch under any of the action alternatives 

 due to the planned improvements to existing roads and stream crossings. 



Action Alternative D includes some restoration activities including road reconstruction and 

 abandonment, but does not address the gully erosion from the existing irrigation ditch. This 

 area has been identified as an existing condition that contributes elevated levels of sediment 



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