PORTLAND DISTRICT

The Corps of Engineers developed the SEIS alternatives through a multi-step process to identify, screen, and refine a broad range of potential measures capable of addressing identified sediment issues. Based on data analysis and research, the Corps developed four alternatives. A brief summary is included here; for more information about the alternatives and how they were developed, please review the Alternatives section in the SEIS.

"No Action" alternative

Under the No Action alternative, the Corps would take no further action to manage sediment in the Toutle/Cowlitz River system. No changes to the SRS would be made and no dredging in the lower Cowlitz River would be undertaken to manage levels of protection for the lower Cowlitz River communities.

 

"Dredging Only" alternative

The Dredging Only alternative would rely solely on dredging to address sediment accumulation in the lower Cowlitz River and manage levels of protection to maintain authorized levels. Components of this alternative would be: dredging, dredged material placement and storage, and monitoring.

 

"SRS Raise" alternative

This alternative involves raising the SRS as the primary sediment management measure. It would raise the SRS spillway by 43 feet and would raise the top of the SRS dam by 30 feet. It would also involve constructing new outlet works consisting of four rows of eight 4-foot diameter pipes in each row (32 pipes total), allowing the modified SRS to function as it did when originally constructed. Construction of this alternative would take about 2 years.

 

"Phased Construction" alternative (preferred alternative)

The Phased Construction alternative involves up to two incremental raises, not to exceed 23 feet, of the SRS spillway crest elevation without raising the elevation of the top of dam; constructing grade-building structures in the sediment plain upstream of the SRS; and as-needed dredging in the lower Cowlitz River. Each phase of this alternative would be implemented only if and when needed. To determine whether a next phase would need to be constructed, the Corps would monitor hydrologic and sediment conditions in both the sediment plain and the lower Cowlitz River and decide whether conditions trigger the need for action. The three phases of the Phased Construction Alternative are sequential and are listed below in order of implementation:

• Phase 1: First SRS spillway crest raise

• Phase 2: Second/final SRS spillway crest raise

• Phase 3: Grade building structures

For more information about the alternatives and how they were developed, please review the Alternatives section in the SEIS.

The Corps wants individuals, organizations and federal, local and tribal agencies to review these alternatives and provide comments. It encourages comments relating to actions which may not have been discussed, or impacts not yet reviewed.