The waterfall that was the birthplace of Minneapolis is suddenly a hot spot for plans to generate hydroelectricity, with three groups vying to join longtime generator Xcel Energy for rights to share in the flow of St. Anthony Falls.

The proliferation of proposals is raising new questions about how much flow can be diverted for hydro power, an issue that federal regulators have ordered Xcel to study before they decide.

Riverfront advocates already fear that diverting too much water will undercut the appeal of the falls as a magnet for tourists and area residents.

Xcel has generated power at the falls through as many as three hydro plants since 1882, and runs the only current hydro plant at the upper falls.

But now a developer is trying to fast-track the lengthy federal approval process to put its hydro power in place by the end of this year, when tax credits expire that the developer says makes the project feasible.

That company, Dominium, wants to insert large pipes and new turbine-generators in historic water power canals in the bowels of the Pillsbury A Mill. The plant would power more than half of the needs of the 251 units of artist loft housing it is developing in the East Bank mill complex. The Marcy-Holmes Neighborhood Association has endorsed it, but the proposal still must satisfy federal power regulators and preservation officials.

Meanwhile, there's another proposal on the other end of the upper falls, where Symphony Hydro wants federal approval to install twin turbine-generators in the lock that will close to navigation by June 1. Congress ordered the lock closed to halt the spread of invasive carp.

Symphony wants to install the compact lightweight turbines on the upper end of the lock, using a mechanism similar to a garage door to hoist them out of the way when the lock is needed for flood control. The U.S. Army Corps of Engineers want assurances that it will still be able to open the locks when floodwaters rage, and that the turbines won't be damaged by ice or floating debris.

The third proposal comes from Crown Hydro, already well-known for ill-fated proposals for hydro generation near Portland Avenue and West River Parkway by the lock. It's fighting to keep the license that the Federal Energy Regulatory Commission (FERC) granted in 1999. It wants to amend that permit to install generators in tunnels just outside the lock on Corps of Engineers property.

Symphony and Crown each seek about 1,000 cubic feet per second of flow, or roughly five times the maximum that the A Mill proposal needs. Concern over how dry the plants might leave the falls during low flows has driven much of the public outcry about Crown's previous attempts.

Richard Savelkoul, an attorney representing Crown, said the firm is doing the studies needed to satisfy FERC. He said the firm is benefiting from the corps' mission to develop hydro power and increased demand for green power.

The study that FERC ordered Xcel to perform by the end of next year will be key to the new applicants, especially Crown and Hydro. The falls will be photographed at various flow rates, from 100 cubic feet per second to 20 times that, then researchers will use the images to see what's acceptable to the public. However, determining how much water is flowing over the dam has slowed that process.

The average flow at the falls is about 7,500 cubic feet per second, with Xcel typically drawing about 4,300 for its Hennepin Island powerhouse. It's rare to get down to the 100 cubic foot per second flow FERC set as a minimum threshold, according to Matt Miller, an Xcel hydro licensing specialist.

The Park Board wants a minimum flow of 2,000 feet per second.

The look of the falls is important to David Tinjum, chair of the Mill District Neighborhood Association.

"A cement wall is not going to attract tourists," he said.

John Anfinson, superintendent of the National Park Service unit covering the Twin Cities area waterfront, said one possible solution is to embed small ridges across the face of the falls to create the illusion of more water.

While the debate rages at the upper falls, a hydro project began in late 2011 at the lower falls, which is much less visible to the public, with little ado. The same operator also has taken over hydrogeneration at the Ford Dam downstream.

Steve Brandt • 612-673-4438

Twitter: @brandtstrib