CUMITLATIVE EFFECTS TO SEDIMENT 

 DELIVERY 



• Owmulative F^ffectg qfthe JVo^cHon 

 .Alternative to Sediment Delivery 



Sediment delivery would be very 

 similar to those described in the 

 EXISTING CONDITIONS portion of 

 this analysis. All existing 

 sources of sediment would 

 continue to recover or degrade as 

 dictated by natural and 

 preexisting conditions until a 

 source of funding became 

 available to repair them. 

 Sediment loads would remain at or 

 near present levels. 



• Cunmlative E^ffects qfthe Action Alternative 

 to Sediment Delivery 



Cumulative effects to sediment 

 delivery would be primarily 

 related to roadwork, culvert 

 replacements, and the proposed 

 removal and rehabilitation of the 

 bridge over Soup Creek. The 

 sediment generated by the 

 proposed replacement of existing 

 culverts would increase the total 

 sediment load in the wetland- 

 dominated watersheds in the 

 project area for the duration of 

 activity. Sediment levels in 

 Soup Creek would be elevated in 

 the short-term during the period 

 of bridge removal and reshaping 

 of fill slopes. In the long 

 term, the cumulative effects to 

 sediment delivery in all proposed 

 watersheds would be a decrease 

 from existing levels. As the 

 sites stabilize and revegetate, 

 sediment levels resulting from 

 these culvert replacements and 

 installation would return to or 

 drop below preactivity levels. 

 Over the long term, cumulative 

 sediment loads may be reduced due 

 to better designed crossings. 

 Improved design would reduce the 

 risk of failure of the 

 structures, which would reduce 

 the risk of sediment delivery to 

 downstream waters . 



The installation and improvement 

 of erosion-control and surface- 

 drainage features on existing 

 roads would also affect the 

 cumulative sediment delivery in 

 the unnamed watersheds in the 

 proposed project area. In the 

 short term, the exposure of bare 

 soil would increase the risk of 

 sediment delivery to live 

 streams. The utilization of all 

 applicable BMPs during this work 

 would make increased sediment 

 loads unlikely. Over the long 

 term, installation of more 

 effective surface-drainage and 

 erosion- control features on the 

 existing road system would likely 

 decrease cumulative sediment 

 delivery to downstream waters. 



Page D-4 



Watershed and Hydrology Analysis 



