The new design is expected to boost the cost of the bridge about $600,000 from the original $1 million.
The bridge in question, called the "north pedestrian bridge," is part of the city's ongoing efforts to enhance pedestrian and bicycle access from downtown to its parks, trails and cultural resources.
But the location of the bridge in a flood zone and near unexcavated, underground archaeological sites on the north side of the river has created problems for the project.
Originally designed to be a cost-efficient, single-span bridge, the city paid nearly $200,000 for engineering designs, environmental studies, and other necessities.
After ruins Superintendent Larry Turk raised concerns over the potential for damage to the archeological materials, he asked the engineering firm and city commissioners to guarantee the underground site would not be at risk.
"We worked closely with our archeologists to identify the all-Pueblo archeological material," said Lauren Blacik, an Aztec Ruins ranger. "We don't know exactly what's down there, but we want to ensure that every archeology (asset) is protected."
And the original bridge design called for an earthen berm to support and level both landings for the bridge.
But in the event of a flood, it was determined that the berm would cause a "damming effect" that could back up water and cause flooding in upstream areas.
Ed Kotyk, city projects manager, provided an update on the project at a recent Aztec Trails and Open Space meeting.
"I told them that a redesign was necessary and that last month the commission had approved spending roughly an additional $50,000 for engineers to make the bridge a multi-span design," Kotyk said. "Due around July, the projected re-design will add two more spans and use pylons to support the bridge."
HDR Engineering, of Albuquerque, is in charge of both phases of the bridge design.
The engineering firm had assured the city and the Ruins that a multi-span design would lessen the potential impact to flooding and archeology, Kotyk said.
"You just can't predict mother nature," Kotyk said. "But some environmental impacts can be mitigated based on modeling."
Originally designed to be just over 200 feet long, the new design will extend the bridge's length and price tag.
The cost is expected to increase to about $1.6 million.
"A project like this one takes quite a bit of time during the design and engineering phase," said Kathy Lamb, finance director for the city. "And this one will take a little bit longer because of the flooding and archeological concerns."
The final design will have to be approved by various government agencies, including the Federal Highway Administration, Lamb said.
"It's all part of the process, but it will be worth it in the end," she said.
James Fenton may be contacted at email@example.com; 564-4621. Follow him on Twitter @fentondt.