Page:United States Statutes at Large Volume 48 Part 2.djvu/368

 1640 RECTIFICATION OF THE RIO GRAND-MEXICO. :FEB. 1, Ina:3. Minute No. 1290f In· 1 -DESCRIPTION. ternational Boundary. Commission-Contd. (a) The Rio Grande is a sedi- ment bearing stream and as such is constantly building up its bed, and would from this cause, in time of flood, change its channel to a lower location wher) it would again start building up its bed and repeat. the cycle at some future flood stage. This phase of changing channel has been largely prevented thru El Paso-Juarez Valley by the construction of artificial works, such as railroad and road grades, canal and drain banks, and in late years, levees. Under these conditions the river bed has been continuously ele- vated. The Elephant Butte Dam was completed in the year 1916, and as a result of its function of providing an irrigation supply during years of low run-off, It stores the floods, which previous to its construction had passed on down the river. The action of these floods was to scour out the river channel, partly by carrying deposits on thru the valleys and partly by making deposits upon the valley floor whenever bank overflow stage was reached. The absence, since the completion of Elephant Butte Dam, of large scouring floods has changed the characteristics of the river chan- nel thru the EI Paso-Juarez Valley. Although large floods have been controlled behind the Elephant Butte Dam, smaller floods from the run-off area lying between Elephant Butte and EI Paso-Juarez are of annual occur- rence. These usually occur dur- ing the rainy season, that is, in August and September, and are generally flashy in character, the peak lasting only a few hours, and would pass harmlessly thru the valley were it not for the ele- vated bed. l. -D ESCRIPCION. (a) El Rio Bravo (Grande), es una corriente de caracter sedi- mentario y por 10 tanto sobre- eleva continuamente su lecho, 10 que do. lugar a que en epocas de credentes cambie de cauce pasan- do a localizaciones mas bajas, donde vuelve a sobre-elevar su lecho, repitiendose indefmida- mente este proceso. Esta fase de cambios de cauce, ha sido en gran parte prevenida, a trav-es del Valle de Juarez-EI Paso, por 10. construcci6n de obras artificiales como terraplenes de ferrocarriles y de caminos, bordos de canales de riego y drenaje y, en los ultimos anos, diques de protec- ci6n contra inundaciones. En estas circunstancias el lecho del Rio ha continuado sobre-elevan- dose. La Presa del Elefante ter- minada el ano de 1916, 0.1 llenar su objeto, <J.ue consiste en asegurar una dotaclon permanente para el riego de terrenos durante los anos de poco. J?recipitaci6n, al- macena las creClentes que, antes de su construcci6n, pasaban Rio abajo. El efecto de estas cre- cientes era socavar el cauce del Rio, arrastrando parte de los azolves y depositando otra parte sobre los terrenos adyacentes al desbordarse 10. corriente. La ca- rencia de fuertes crecientes ero- sivas despues de 10. terminaci6n de 10. Presa del Elefante, marco el cambio del regimen de 10. corriente en el Val1e de Juarez- El Paso. A pesar de que las grandes avenidas se almacenan en el vaso del Elefante, anual- mente ocurren crecientes mas pequenas que provienen de 180 cuenca tributaria del Rio entre el Elefante y Juarez-El Paso. Estas ultimas crecientes se presentan durante 10. estaci6n de lluvias, generalmente en los meses de agosto y septiembrej son repen- tinas y de poco. duraci6n y pasa- rian a traves del Valle sin causar danos si no fuese por 180 posici6n elevada del cauce del Rio con respecto a los terrenos adya- centes.