Million-dollar mansions and houses along the zigzagging Purgatory Creek in Eden Prairie have long had a scenic view of the creek and dense woods.

But over the years, growing erosion on the 16-mile creek and other water problems along the creek’s steep bluffs have put more homeowners on alert, threatened by sinkholes and mudslides that nearly sent one house falling into the ravine last summer and pitted another homeowner against the city over costs to fix an eroded back yard.

Over the past 10 years, the city has spent $4.3 million on engineering and construction along the banks and tributaries to Purgatory Creek, such as repairing erosion and stabilizing the creek banks, according to city data. Now, the city is spending about $300,000 this year to stabilize banks on the creek, which also drains into parts of four west-metro cities.

“It’s a spectacular view,” said Wendy Gallagher, who has long lived on a slope overlooking the creek. “You can’t even believe you’re in the middle of Eden ­Prairie or a city.”

The urban creek winds through bluffs before it ends in the ­Minnesota River. Increasing runoff — more than half of the creek is on residential land, according to the Riley Purgatory Bluff Creek Watershed District — and heavier, more infrequent rainfalls have put more pressure on the creek and surrounding storm-drainage systems.

“It’s where much of Eden Prairie and parts of Minnetonka drain to, so when we get a lot of runoff, it’s all going to Purgatory Creek,” said Robert Ellis, the city’s public works director.

After last summer’s record rainfall caused flooding across Minnesota, it overwhelmed Eden Prairie’s storm-drainage system and caused a mudslide from a pipe that discharged from the neighborhood to the creek. It left one home teetering on the edge of the bluff on Burr Ridge Lane. The home was quickly demolished and the family later settled with the city.

Of the $4.3 million the city has spent over the last decade, the two most expensive projects both took place last year — repairing a road culvert on Riverview Road, which cost $707,009, and repairing the storm sewer on Burr Ridge that caused the mudslide, which cost $1.9 million for engineering and construction.

Growing erosion

Now, Ellis estimates that the city will spend $200,000 on creek bank stabilization upstream of Burr Ridge, ­putting larger boulders in place to prevent erosion at the site where the creek does a 180-degree turn.

The city plans to design the project within the next month and start construction next fall and winter.

Another project estimated at $100,000 will be done later this year south of Riverview Road to prevent erosion.

Parts of the creek watershed also fall into Shorewood, Chanhassen and Minnetonka — and a sliver of Deephaven. The Watershed District is conducting a study this year to assess all three creeks in its area to prioritize restoration efforts.

One project is already going on now in Minnetonka.

“We all have a part in the solution,” said Claire Bleser, the Watershed District’s administrator.

The Watershed District lists much of the creek as “high risk” for erosion due to the sandy soil, Bleser said.

Staff members walk the creek to assess erosion and water quality issues, and so does the city. From 2007 to 2013, erosion increased slightly, with a contractor identifying 82 erosion sites in 2007 and then 84 sites in 2013. During that time, seven sites worsened and five improved, Ellis said.

‘All of it disappeared’

In 1999, when Gallagher and her husband bought their house on the bluff some 95 feet above the creek, they knew there was minor erosion, she said. But over the years, the cliff continued to be carved away. By 2012, the whole hill collapsed, sending trees into the creek and opening up a 45-by-95-foot sinkhole.

“All of it disappeared,” ­Gallagher said.

In 2013, an engineering consultant told the city that the couple’s retaining wall and deck were at risk of collapsing off the ravine in part due to groundwater seeping out of the slope. Other homes could have been affected, so the city agreed to stabilize the slope.

A year later, the city stamped the couple with a $225,000 assessment fee — one of the largest such assessments.

The couple argued that the erosion was on city land and that the work should be paid for by the city. The city disagreed, saying the erosion was due to the water seeping below the private property.

The Gallaghers filed an appeal in Hennepin County District Court in December, but in January, the two sides reached an agreement for $197,000 over 30 years, dropping administrative costs and pre-assessment interest.

“We wanted our nightmare to end,” Gallagher said.

Now, their home and property are safe, stabilized with some 2,000 tons of rock and dirt, allowing them to enjoy the view and the sound of the creek below.

“It’s magical,” she said, adding that other homes may not be as lucky. “There are some $1 million homes here. That’s a lot of money that people are terrified they’ll lose.”