Final Environmental Assessment and
Finding of No Significant Impact
The Drain Unit 7 Extension River Maintenance Priority Site (Project) is located 500 feet upstream of San Acacia Dam, on the right bankline of the Rio Grande. The approximate River Mile is 116.3. The river is actively eroding a spoil levee embankment that protects the Drain Unit 7 Extension irrigation structure, operated by the Middle Rio Grande Conservancy District (MRGCD). The Drain Unit 7 Extension structure serves as both a drain and canal, conveying irrigation drain water to the Socorro Main Canal for downstream irrigation needs. If the river is allowed to continue erosion of the levee, the drain prism could be destroyed, and the roadway on the levee lost, which is used to access parts of the Sevilleta National Wildlife Refuge.
Erosion has been a persistent problem in recent years on approximately 350 feet of the levee that protects the drain from the river. This portion of the levee is adjacent to the active river channel. Recent bankline erosion and bend migration upstream of the site indicate that bend migration may soon begin at the site, which will expose more of the levee to active erosion. The majority of the recent bend migration upstream of the site occurred during high flows brought on by monsoon season rainstorm events during July and August of 2006.
The federal action addressed in this Environmental Assessment (EA) is the protection of the Drain Unit 7 Extension spoil levee with riprap. The project area is surrounded by a region of rural farming and ranching. Farming activities such as plowing and tilling, and ranching activities such as livestock grazing, often eliminate or reduce vegetation, even if only temporarily, and thus become a potential cause of sediment loading in the river during periods of high runoff. The purpose of this project is to prevent erosion of the existing spoil levee. The need is protection of the facility against erosion.
|Final Environmental Assessment & Finding of No Significant Impact||