Publication

Hydrology and Geomorphology of the Rio Grande and Implications for River Rehabilitation

URL: https://webapps.usgs.gov/mrgescp/documents/Schmidt%20et%20al_2003_Hydrology%20and%20Geomorphology%20of%20the%20Rio%20Grande%20and%20Implications%20for%20River%20Rehabilitation.pdf

Date: 2003/05/12

Author(s): Schmidt J.C., Everitt B.L., Richard G.A.

Publication: in Aquatic Fauna of the Northern Chihuahuan Desert, Museum of Texas Tech University Special Publication no. 46, p. 25-45

Abstract:

The Rio Grande watershed includes a northern and southern branch that have very different hydrologic regimes. The natural flood regime of the northern branch is snowmelt driven, and that of the southern branch, the Rio Conchos, is driven by summer rainfall. Downstream from the confluence of the two branches, near Presidio, Texas, the natural pattern of high and low flow was dominated by runoff from the Conchos basin between July and the following March prior to the construction of large dams. Dams and diversions greatly altered the natural hydrologic regime of both branches. The magnitude of the 2-year recurrence flood of the Rio Grande at El Paso, on the northern branch, declined by 76% after 1915. The magnitude of the 2-year recurrence flood downstream from Presidio was reduced by 49% after 1915.

Dams and diversions have also significantly altered the natural sediment flux, and significant geomorphic adjustments of the channel have resulted. The northern branch includes reaches where degradation or aggradation has occurred during the past century. Reaches immediately downstream from dams have degraded beds and narrowed widths. Further downstream, the channel bed has aggraded, and the channel width has narrowed. Channelization and levee construction have occurred in some of these same river segments.

Restoration, defined as returning an ecosystem to a close approximation of its condition prior to disturbance, is impossible on the main stem of the Rio Grande because of current institutional demands on stream flow and the extent of alteration of the floodplain. Rehabilitation, defined as returning essential physical and ecological functions to a degraded ecosystem, is a more appropriate goal for the Rio Grande. In light of the diverse styles of twentieth-century channel adjustments that have occurred throughout the basin, different river segments must be assigned different rehabilitation goals.