AURORA, Colo. -- The cities of Aurora and Thornton reached a $51 million deal Monday that will provide Aurora with additional water for its reservoirs and help Thornton improve its water supply system.

The plan will give Aurora an average of 7,000 acre-feet of water per year from ranches in South Park southwest of Denver, Aurora utilities director Peter Binney said. It will also give the city 4,000 acre-feet of storage capacity in Spinney Mountain Reservoir that belonged to Thornton.

In exchange, Aurora will pay Thornton $51 million to finance water projects and 7,883 acre-feet of water each year from various sources. Binney said the money will come from 20-year revenue bonds to be issued in the fall and paid by water sales and tap fees in Aurora.

"This was an opportunity for Aurora and Thornton to put together an arrangement that meets their needs and meets ours," Binney said. "The city will continue to grow, we will have to continue to acquire additional water resources, and this gives us a little more breathing room than we had a year ago."

Aurora Mayor Paul Tauer and Thornton Mayor Noel Busck are scheduled to sign the agreement Thursday morning.

Two years ago, Aurora had tried unsuccessfully earlier to obtain South Park water through a South Park Conjunctive Use Project. The project would have pumped water from South Park aquifers and replenished it during wet years.

A water court judge dismissed the application saying the augmentation modeling showed insufficient water available.