Could 2019’s flooding return for 2020 at Lake Poinsett?

KELOLAND.com Original

SIOUX FALLS, S.D. (KELO) — When Lake Poinsett is mentioned, he can’t help but think of the flooding of 2019, said Dave Schaefer, the Hamlin County Emergency Management Director.

“The potential is there for a repeat of 2019,” Schaefer said. “But that doesn’t mean it’s gonna happen.”

So far, conditions indicate a good chance for a repeat.

Water levels are high on streams and rivers that release into the lake. The region around the lake has at least a few inches of snowfall. The soil is also moist with little room to absorb more moisture. The National Weather Service in Aberdeen released its first flood outlook for the season on Thursday. The outlook said there is an above normal chance for minor, moderate or major flooding in 2020.

Aaron Dye of the NWS in Aberdeen almost audibly cringes when Lake Poinsett is mentioned.

“Let’s hope there is a slower melt this year than last year,” Dye said.

Schaefer said the 2019 flooding started with higher than normal precipitation in 2018 followed by more rain and snow in 2019. A huge rainstorm in April followed by more warm temperatures resulted in high water in the lake and the rapid break up of ice.

The National Weather Service office in Aberdeen tracks water levels on Lake Poinsett. A daily chart with updates posted throughout the day is posted on the NWS Aberdeen’s website.

This is a chart of water levels at Lake Poinsett posted on the National Weather Service Aberdeen office website. The water level is updated regularly throughout the day. To check water levels, see this link. NWS graph.

Roughly 10 days ago, the lake was 32 inches above full, Schaefer said.

Schaefer said when numbers from 2018 to 2019 are accounted for, even small amounts of snow and rain from here until April could be the tipping point for bad flooding on the lake and Hamlin County.

“Because we have been saturated for so long, it doesn’t take a big number to create a problem,” Schaefer said. “Little numbers can create a big problem.”

Lake Poinsett is a 7,903-acre lake in a watershed of 292,197 acres, according to the South Dakota Game, Fish and Parks Department

The watershed increases during flood flow conditions of the Big Sioux River Basin by about 470,000 acres because of its connection to Lake Poinsett through the Boswell diversion ditch, according to the GFP.

A map of the Lake Poinsett Watershed District from the August 2019 report on the watershed for the 2007-2014 project. The project involved Hamlin County Conservation and the South Dakota Department of Environment and Natural Resources and the United States Environmental Protection Agency.

The ice that rapidly broke apart on the lake in April 2019 was pushed up the shoreline and even into homes and buildings on the lake.

April gave way to more rain during the summer and fall, which caused more flooding on the lake.

A Sept. 23 preliminary report on damage in Hamlin County, where the lake is located, for the Federal Emergency Management Administration said 2019 flooding damage was assessed at $28.99 per capita, or effectively per person, based on the county’s population in 2010 Census. The per capita amount is the total amount of damage spread across the county’s population.

While the lake is a popular summer destination, several projects on the lake and around the lake were designed for flooding.

According to the USDA, the Boswell diversion ditch was designed to route Big Sioux River floodwaters to Lake Poinsett. A state report from August 2013 on the watershed said the gates were inoperable and closed.

The lake’s natural outlet to the Big Sioux River was modified in 1989 with the addition of a flood control structure to prevent back flow of flood waters from the river into the lake, according to the USDA.

The 2019 flooding was not the first for Lake Poinsett.

A 1971 study called the “Hydrology of Lake Poinsett” by Assad Barari for the SDGFP examined the 1969 flood as part of the study.

The 1969 spring flood was attributed to an exceptionally thick blanket of snow in the Big Sioux River Valley, according to the study. Upstream water including water from the Big Sioux entered Lake Poinsett.

If floodwaters are not controlled upstream, there is no simple way to keep the water from reaching the lakes, the 1971 study said. The study said the lakes work as a flood control system for acres downstream so if the water from the lakes was diverted that would cause downstream flooding. The study also said events such as the 1969 flood were rare.

“We’ve had so many floods on Lake Poinsett,” Schaefer said.

The NWS Aberdeen office website has a list of historic water crest levels on the lake. Thirty-three levels are listed. All are from 1983 and later. The 1969 level is not included in the top 33. The highest point was in 2011 when the water crest reached 1,657.60 feet.

The Hamlin County Conservation sponsored a Lake Poinsett Watershed Project in 2007 to 2014 in conjunction with the South Dakota Department of Environment and Natural Resources and the regional office of the Environmental Protection Agency to improve water quality and improve the performance of the watershed. A 2014 report said that while projects were completed, the 2011 record flooding stopped some work.

Successful projects included adding grassland management to the watershed, repairing stream shorelines and after 2011, repairing shoreline stabilization on Lake Poinsett. Property owners on the lake were to install rip rap at least seven feet higher than the normal water level and to plant trees and shrubs to help stabilize the shoreline.

Schaefer estimated that 60% of the properties on the lake are permanent residents with the rest being seasonal residents. The lake also includes a private campground and state park.

GFP officials said the overall camping and visitor numbers at state parks were down in 2019 in part because of flooding and other weather conditions. The state campground was open in 2019 at Lake Poinsett although the park had about 2,000 fewer campers than in 2018.

The NWS and Schaefer will be watching the weather from now until April to gauge the flooding potential.

The region needs a slow melt and little or no precipitation.

For now, Schaefer has some straight advice for property owners on Lake Poinsett

“If you have something that you cannot replace, you need to move it, not just elevate it,” Schaefer said.

The NWS has predicted higher chances of below normal precipitation, and higher chances for above normal temperatures for the next two weeks.

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