The Catholic Church did not discard immersion, it was and still in practice. Pouring of water, however, is a practical alternative as suggested by Didache — an ancient Church document dating between the late 1st century and early 2nd century:
“And concerning baptism, baptize this way: Having first said all these things, baptize into the name of the Father, and of the Son, and of the Holy Spirit, in living water. But if you have no living water, baptize into other water; and if you cannot do so in cold water, do so in warm. But if you have neither, pour out water three times upon the head into the name of Father and Son and Holy Spirit. But before the baptism let the baptizer fast, and the baptized, and whoever else can; but you shall order the baptized to fast one or two days before.” (Didache 7)
“Those who have had a bath need only to wash their feet; their whole body is clean.”
However, despite the validity of “pouring”, this video shows a proof of the Catholic practice of “baptismal immersion” wherever it is applicable and practical.