Allen C Gellis, Ph.D. (Former Employee)

Areas of the Petroglyph National Monument, specifically those located along the West Mesa escarpment, are being affected by erosion and gullying. A reconnaissance along the 17-mile-long escarpment identified 50 gullies. The gullies were given a qualitative ranking of Class I, least erosion, to Class IV, highest erosion. Of the 50 gullies identified, 21 were assigned Class I, 22 to Class...

During the latter part of the 19th century and the early part of the 20th century, a major cycle of erosion, arroyo cutting, and gullying occurred in the southwestern United States. Since this erosion cycle began, many projects to control erosion, such as the Civilian Conservation Corps projects in the 1930s, were initiated. However, in the Southwestern United States few studies have...

In the two main tributaries that enter Lago Loiza, Rio Grande de Loiza and Rio Gurabo, 99 600 tonnes of suspended sediment was transported by 58.2??106 m3 of runoff in a 48 h period. The storm-average suspended-sediment concentration in the Rio Grande de Loiza for Hurricane Hugo was 2290 mgl-1, the second lowest for the 12 storms that have been monitored at this site. In Rio Gurabo the...

No abstract available.

Suspended-sediment and dissolved-solid (salt) loads decreased after the early 1940s in the Colorado Plateau portion of the Colorado River basin, although discharge of major rivers - the Colorado, Green and San Juan - did not change significantly. This decline followed a period of high sediment yield caused by arroyo cutting. Reduced sediment loads have previously been explained by a...

No abstract available.