AMID ALL the angry rhetoric about granting amnesty to 11 million undocumented workers — the centerpiece of the immigration overhaul passed last month by the Senate — a far more tangible and immediate impact of the bill has gone mostly unnoticed. Years before any illegal immigrants would qualify for citizenship, the Senate bill would open the doors to a major surge in legal immigration that would be seen and felt in communities across the nation.

That surge could compress almost 25 years of “normal” legal immigration — potentially as many as 4 million or more newcomers — into a decade or less starting in 2015. It would clear a backlog of visa seekers who are entitled to become legal permanent residents of the United States under current law, but who have been forced to wait years for green cards because of annual limits that are out of sync with demand.

That backlog is the notorious “line” of legal immigrants — the one that lawmakers insist cannot be cut by unauthorized immigrants already in the country. The trouble is that some categories of green card petitioners — for instance, Filipino brothers and sisters and married sons and daughters of adult U.S. citizens — have been waiting in this line for more than 20 years. Some may have lost interest in becoming Americans; others have died.

Consequently, no one can say with certainty how large a surge in legal immigration will be triggered by immigration reform or predict the short-term effects on the job market and unemployment. But whatever its dimensions, the Senate bill does an important thing in reunifying families and clearing an absurdly long backlog.

The bill also aims to avoid the formation of new backlogs. It does so partly by abolishing visa preferences in the future for siblings of U.S. citizens (who now constitute the largest single component of the backlog, with nearly 2.5 million on the green card waiting list) and married children over age 31 of U.S. citizens. Together, those two groups account for nearly 90,000 legal immigrants annually.

That provision, pushed mainly by Republicans who dislike what they call “family chain migration,” will harm many foreign-born U.S. citizens who depend on family support networks — to help care for children, start businesses and negotiate the language and customs of their adopted country. But the Senate opted to create more opportunities for highly qualified workers and a merit-based system that assigns points to visa seekers with advanced education, fluency in English and other attributes that are critical to sharpening America’s competitive edge in the global economy. Those are sensible steps, but they needn’t have come at the expense of family-based visas.

America’s percentage of foreign-born residents is already hovering near its historic high. By clearing the backlog of green card petitioners, the Senate bill is likely to drive that proportion higher still. In the short term, that may lead to social tensions of the sort that have attended spikes in immigration throughout American history. In the long run, it will contribute to the nation’s vibrancy and wealth.