The effect of silt‐removal and flow‐regulation on the regimen of Rio Grande and Colorado Rivers

Abstract

The completion of Elephant Butte Dam on Rio Grande in 1915 inaugurated a new regimen of flow‐characteristics for that Stream and the closing of the tunnels at Boulder Dam on February 1, 1935, will cause Colorado River to turn over a new leaf and begin a better regulated life. The changes in regimen are far reaching and of great importance to the developmental program below these structures. Two factors are mainly responsible for the changes: (a) Floods originating on the main river above these reservoirs are largely absorbed and the outflow is almost wholly under control; (b) instead of the silt‐laden water that formerly passed into these reaches there now issues from the control‐gates at the dams, rivers of bluish green clearness with hardly a vestige of silt—an absolutely novel experience in the life‐history of these streams.

The role of feedback mechanisms in historic channel changes of the lower Rio Grande in the Big Bend region

“…Stream flow was further impacted by Francesco I. Madera (completed in 1947) and Luis L. Leon Dams (1967) in the Rio Conchos basin and Caballo Dam (1938), immediately downstream from Elephant Butte Dam (Stevens, 1938;Schmidt et al, 2003). Operations of Elephant Butte and Caballo Dams, and irrigation diversions in the El Paso-Juarez valley completely eliminated the natural spring snowmelt flood of the upper Rio Grande (Schmidt et al, 2003).…”

“…Stream flow was profoundly changed by La Boquilla Dam, completed in 1915 on the Rio Conchos, and by Elephant Butte Dam in southern New Mexico, completed in 1916(Stevens, 1938Everitt, 1998, Schmidt et al, 2003. Stream flow was further impacted by Francesco I. Madera (completed in 1947) and Luis L. Leon Dams (1967) in the Rio Conchos basin and Caballo Dam (1938), immediately downstream from Elephant Butte Dam (Stevens, 1938;Schmidt et al, 2003).…”

Sedimentation Engineering

“…Stevens (1936) states that after closure, degradation began downstream from the dam and by 1925 extended for about 100 miles downstream; at El Paso about 127 highway miles below Elephant Butte Dam and farther downstream, the bed of the channel began to aggrade because floods originating above the reservoir were eliminated and no longer moved the deposits of coarse material brought in by tributaries (Stevens, 1938). The problems caused by channel instability of the Rio Grande resulted in a "canalization project" between Caballo Dam about 23 miles below Elephant Butte Dam and El Paso and the "rectification project" between El Paso and Fort Quitman, Texas originally about 150 river miles downstream.…”

The rate and pattern of bed incision and bank adjustment on the Colorado River in Glen Canyon downstream from Glen Canyon Dam, 1956-2000

“…Large dams, which are defi ned as those that impound more than 10 7 m 3 of water (Graf, 2005), cause changes to downstream fl ow and sediment supply that lead to changes in downstream channel form (e.g., Lawson, 1925;Stevens, 1938;Stanley, 1951;Borland and Miller, 1960;Petts, 1979;Lagasse, 1981;Galay, 1983;Williams and Wolman, 1984;Brandt, 2000aBrandt, , 2000bSimon et al, 2002;Hazel et al, 2006). Because large dams typically trap all sediment delivered from the upstream watershed, supply to the channel segment immediately downstream is virtually eliminated.…”

“…Thus, erosion of material from channel margins or pools between riffl es that does not change the large-scale gradient is considered sediment evacuation, not incision. Incision has also been referred to as degradation (Pemberton, 1976) and retrogression (Stevens, 1938). Evacuation processes result in changes to the channel cross section, bed-material grain size, channel planform, and rates of channel migration.…”