Newman Lake erosion study offers answers on waves, but questions remain

Newman Lake was calm and quiet on Thursday afternoon.

A light breeze rustled tree leaves and reeds on the lake’s edge. Tiny waves lapped against the shore. A lone motorboat zoomed across the shallow, green water.

It was an idyllic scene, but there’s an issue at Newman Lake on the minds of residents, public boaters, conservationists and county officials alike: erosion.

Many who live around Newman Lake’s edge say waves caused by motor boats – especially wakeboarding boats – are severely eroding parts of the shoreline. Most nonresident boaters say they don’t think there’s any issue.

In response to resident concerns, the Spokane County commissioners in 2019 asked the Spokane Conservation District to conduct a Newman Lake study.

The results of that study would help the commissioners decide whether to change existing boat wake regulations to slow or stop the possible loss of shoreline. The study findings might also help the commissioners revise wake ordinances countywide to address erosion concerns elsewhere.

On Aug. 24, the conservation district presented the first results of that study to the commissioners. One fundamental question appears to be answered: Boats, not weather, cause the biggest waves. But other questions remain.

With just one year of data, the study couldn’t offer clear answers as to the amount, and precise cause, of erosion at Newman Lake.

“I know I’m asking a lot, but I guess I was hoping there would have been maybe a stronger message on exactly how we would be able to actually prevent erosion through some type of ordinance or policy,” Spokane County Commissioner Josh Kerns said.

A boating hot spot

Newman Lake sits north of Liberty Lake near the Idaho border. It’s a beloved boating spot.

And it’s beloved by more people than it used to be. According to the Spokane Conservation District’s study, the Newman Lake watershed had 400 full-time residents and 1,800 summer residents in 1973. Today, about 17,000 people live in the watershed.

More people has meant more boats on the lake. Not only has the number of boats increased, technology has changed, too. Wakeboard boats, which create big waves, started to become more common in the 1990s.

It’s not uncommon to hear Spokane County residents tell stories about being knocked off docks by huge waves created by wakeboard boats.

Newman Lake residents say huge wakeboard boat waves are wreaking havoc on their waterfront properties. The erosion is worst on properties that have removed natural vegetation and lack bulkheads, floating logs or rip rap to block breaking waves.

Many property owners say human-caused waves have washed multiple feet of their shoreline into the lake. Erosion has toppled massive ponderosas that once stood by the water’s edge.

Boats are undoubtedly causing some erosion. The question has been, how much erosion is caused by boats and how much is natural? And if there’s hard evidence that boats are the main problem, what should the county do about it?

The conservation district’s study marks the first major effort to scientifically analyze waves and erosion at Newman Lake, and it also includes surveys of both lake residents and nonresidents.

Those surveys revealed a stark resident v. nonresident gap in erosion perception.

Among residents who responded, 49% said they had erosion issues on their property and 75% of those said boats caused the erosion.

Among public boat launch users, 70% said they believed there were no environmental issues at Newman Lake. The 30% of users who saw environmental issues said they didn’t see erosion as a problem.

In addition to surveying residents and nonresidents, the conservation district studied waves.

The district set up custom monitors that measured waves with sonar. Data included in the study was collected from May to November of last year, but the data collection is ongoing.

The wave study’s results show the vast majority of bigger waves happened on calm summer afternoons – not windy days or days with big storm events. That suggests boats, not wind or other extreme weather, cause the biggest waves.

“All signs point to it being boat-driven for the largest waves,” said Lindsay Chutas, who led the study.

Gathering useful erosion data was more difficult.

The conservation district took multiple shoreline measurements at 10 sites using a laser level. Most of the sites did not show severe erosion over a year’s worth of observation. Chutas said it’s likely that the district would have to measure erosion over a longer timeframe to draw more meaningful conclusions.

“These changes occur more slowly than we can observe in one year,” Chutas said.

No restrictions yet

It’s not illogical to assume that bigger waves breaking on shore with more energy are causing more erosion than small waves hitting the shore with much less energy. That’s the assumption that fits with the anecdotal observations of many property owners.

But the study results don’t definitively show that boat-caused waves are driving erosion more than wind-caused waves.

Kerns said he doesn’t want to restrict boat use until the study can clearly show that boats, not natural weather patterns, are responsible for the worst erosion impacts. He also said he’d like to know the specific erosion impacts of different sizes of waves. That information might allow the county to ban specific types of boats and activities that are causing the bulk of the erosion issue.

“I guess at the end I was hoping they would have had maybe a little more clear-cut answer to, ‘How much erosion is specifically caused by boats; how much is specifically caused by weather patterns?’ ” Kerns said.

Chutas said that pinpointing the erosion caused by boats – and even specific kinds of boats – as opposed to waves is “kind of next level” from a scientific study standpoint, but not impossible. She said she’d like to study it more in order to identify the differences between wind-caused and boat-caused erosion.

The Newman Lake study could still eventually help the commissioners adopt countywide boating restrictions that could protect shorelines, Kerns said. He said he just wants more information before changing county ordinances and restricting boat use.

The county commissioners said during the Aug. 24 meeting that they may ask the conservation district to continue, and even expand, the study.

“They had a lot of good data out there,” Kerns said. “We just want to make sure we’ve got all the information and all our bases covered.”