“I terminated one of the most ridiculous regulations of all: the last administration’s disastrous Waters of the United States rule,” Mr. Trump told the American Farm Bureau Federation’s annual convention in Texas on Sunday, to rousing applause. He added, “That was a rule that basically took your property away from you.”

His administration had completed the first step of its demise in September with the rule’s repeal.

His replacement on Thursday will complete the process, not only rolling back 2015 rules that guaranteed protections under the 1972 Clean Water Act to certain wetlands and streams that run intermittently or run temporarily underground, but also relieves landowners of the need to seek permits that the Environmental Protection Agency had considered on a case-by-case basis before the Obama rule.

It also gives President Trump a major policy achievement to bring to his political base while his impeachment trial continues.

“Farmers coalesced against the E.P.A. being able to come onto their land, and he’s delivering,” said Jessica Flanagain, a Republican strategist in Lincoln, Neb. “This is bigger news for agricultural producers than whatever is happening with the sideshow in D.C.,” she added,

The new water rule will remove federal protections from more than half the nation’s wetlands, and hundreds of thousands of small waterways. That would for the first time in decades allow landowners and property developers to dump pollutants such as pesticides and fertilizers directly into many of those waterways, and to destroy or fill in wetlands for construction projects.