What Went Wrong at Cochiti Dam

Numerous studies have been conducted on the Cochiti Dam in New Mexico in order to quantify the changes in stream geomorphology following dam construction in 1973. The dam, one of the largest in the United States, was constructed primarily for sediment and flood control of the Rio Grande River and is a good example of what happens when Lane's diagram (one of my key principles) is not followed.

Following construction, there was little effort to restore natural flows and sediment was trapped upstream of the dam. Consequently, the once braided stream channel transformed into a single channel system with an increasing depth, decreasing width, and islands eroded away. Average sediment size has increased from fine sands to gravels.

The above graph (Richard and Julien 2003) shows peak flows (purple bars), sediment flowing into the study reach (dotted line), and sediment flowing out of the study reach (solid line) following dam construction.

Cross-sectional profiles from 1971-1998 as taken by Richard and Julien (2003).

Aerial photos depicting changes in stream channel morphology after dam construction (Richard et al. 2005)

Ecologically, these changes have been problematic for the Rio Grande silvery minnow because habitat has been heavily degraded. In addition, because the river is no longer connected to the floodplain, lack of regular inundation has decreased the population of cottonwood while increasing the invasion of nonnative species such as saltcedar and Russian olive.




Richard, G. A., and P. Y. Julien. 2003. Dam impacts and restoration of an alluvial river- Rio Grande, New Mexico. International Journal of Sediment Research 18: 89-96.
Richard, G. A., P. Y. Julien, and D. C. Baird. 2005. Case study: modeling the later mobility of the Rio Grande beow Cochiti Dam, New Mexico. Journal of Hydraulic Engineering 131: 931-941.