Importantly the United States and Mexico needed an agreement on the appropriation of waters in the lower Rio Grande. This was wrought in a mutually ratified treaty that stated that Texas would have all the rights from its own tributaries and that Mexico would assure 350,000 acre-feet annually to Texas from Mexican tributaries.
The treaties also anticipated the construction of two major reservoirs on the river.
These were to be Falcon Dam, completed in October 1953, and Amistad Dam, completed in 1969. Also established by the treaty was the International Boundary and Water Commission charged with coordinating the work between the two countries.
The ability of the flood control system to operate successfully was put to the test on September 20, 1967 and the days to follow as Category 3 Hurricane Beulah made landfall just north of the mouth of the river.
It was a slow moving system that dumped massive amounts of rain over the Valley and points west in the river’s watershed over a three day period. Heavy storms in August has previously saturated much of the LRGV.
At Rio Grande City the peak discharge occurred on September 22 at 210,00 cubic feet per second and 10 feet above flood stage. On the 25th, Mission experienced 206,000 and also 10 feet while on the 26th Hidalgo had 81,000 cfs and 6 feet. On the 29th San Benito registered 25,00 cfs and 6 feet above flood stage. The following day Brownsville registered 16,000 and 1 foot respectively.
The floodway was soon inundated with overflow waters from the rivers as well as runoff from the cities.
The airport of the City of McAllen was flooded on September 26 by waters from the Mission floodway that overpoured high ground about three miles west of the airport.
As floodway waters reached the division point near Progreso the majority of the flow diverted into the Arroyo Colorado.
This soon resulted in urban areas along the Arroyo in Harlingen being submerged by the flooded stream.
The crest was ten feet higher than that occurring in 1958 when in October-November spills at Falcon Dam and flood inflows from the San Juan River were the culprits.
An estimated 8,000 people, about 20 percent of the city’s population, required evacuation…
While it didn’t pass the House, it may have laid the groundwork for later appropriations, for in February 1971 Congress appropriated $29 million for the first phase of Valley flood control.