A bipartisan water transportation bill that would allow Maryland to unload tons of dredging material on Chesapeake Bay islands — an effort that officials say is critical for the port of Baltimore — won broad support in the House of Representatives on Tuesday and is poised for final approval in the Senate.

Despite concerns raised by budget watchdog groups and some environmentalists, the $12 billion measure sailed through the politically rancorous House on a 412-4 vote, all but assuring passage in the Senate this week. President Barack Obama is expected to sign the legislation.

If the measure is approved, it would mark the first time in seven years that Congress has authorized spending on dams, harbors and other maritime projects.

In Maryland, the bill would allow officials to continue dumping muck dredged from bay shipping channels onto Poplar Island, which supporters say benefits the ecosystem while allowing the port to prepare for an increase in trade expected from the widening of the Panama Canal. Without the legislation, funding would run out in about two years.

"This bill takes care of the dredging needs of the port, one of the great economic drivers of Maryland," said Sen. Ben Cardin, a Maryland Democrat, one of eight senators who negotiated the final compromise between the House and Senate. "It is very important for us."

More than 5 million cubic yards of silt are dredged from the Chesapeake annually, about 2 million cubic yards of it from bay channels in Maryland.

Much of that sediment has been used to build up Poplar Island off Talbot County into a bird sanctuary — a project that has been praised by state officials as model. The state needs approval to continue using the island.

The legislation would also clear the way for the creation of new disposal sites on James and Barren islands, off Dorchester County, once Poplar runs out of space.

"Keeping our channels properly and safely dredged in order to accommodate some of the largest vessels in the world ... is a necessary year-round process," James J. White, executive director of the Maryland Port Administration, said in a statement. "Finding beneficial ways to reuse that dredged material such as rebuilding long-eroded islands is something in which we have become a national leader."

The bill would authorize 34 water projects around the country. They include the deepening of a channel between Louisiana and Texas through which a significant portion of the nation's imported crude oil travels, and flood protection efforts in California, North Dakota and Kentucky.

It would also speed the review of maritime projects and require that the Harbor Maintenance Trust Fund — paid for by shipping companies — is actually used for the nation's ports. Some have complained that that money was being siphoned off for other expenses. Companies that work at the port of Baltimore contributed roughly $40 million in fees to that fund in 2012.

Taxpayers for Common Sense, a Washington-based budget watchdog, said lawmakers fell short in their efforts to overhaul the way Army Corps of Engineers projects are chosen and prioritized. And the group criticized the reauthorization of decades-old projects to replenish stretches of shoreline, describing them as "beaches on Medicare."

The National Wildlife Federation and other groups said the legislation would short-circuit the environmental review process for some projects by making it more difficult to raise objections.

"At the end of the day, its new restrictions on public participation and expert input into environmental reviews will lead to even more damage to our nation's waters," said Adam Kolton, who heads the group's advocacy efforts.

Debra A. Colbert, senior vice president of the Waterways Council, a group supported by shipping companies, port operators and others from industry, said the legislation would enable the federal government to begin addressing long-delayed construction projects.

"The locks and dams are way beyond their 50-year design life," she said. "Everyone recognizes that we have kicked the infrastructure can down the road for far too long."

The legislation would reauthorize the 18-year-old Chesapeake Bay Environmental Restoration Program, in which the Army Corps of Engineers works to restore bay ecosystems. Ultimately, the amount of federal money dedicated to that and other programs in the legislation is to be set by lawmakers during the annual appropriations process.

The dredging issue was the top priority for Maryland lawmakers.

The question of where to dispose of dredged material has been controversial for decades. In the 1970s, Baltimore County officials fought a $300 million state plan to use dredge spoil to restore two tiny islands at the mouth of Middle River. A compromise that turned Hart-Miller Island into a state park is now hailed by the state as a model.

State law imposes limits on where material dredged from Baltimore's harbor can be dumped. That sediment is stored in containment ponds in Masonville Cove in South Baltimore, and none of it would be used on the bay islands, port officials have said.