DAKOTA DUNES -- As the Missouri River continued to swell Wednesday, residents of Dakota Dunes braced for more flooding that authorities said would rival the high water that briefly forced the evacuation of hundreds of residents in March.
A notice from the planned community posted Tuesday night suggested more evacuations are not out of the question this week.
"With these elevations being so close to the top of our protection, low lying property owners would be wise to prepare your property so you can evacuate on short notice," the notice read.
Dunes residents have also been asked to minimize water and sanitary sewer use during this period to help "preserve water and sewer utility."
The rising fears came as the U.S. Army Corps of Engineers released more water from Gavins Point Dam near Yankton, South Dakota, due to heavy rainfall upstream in recent days. The corps raised releases at Gavins Point by 5,000 cubic feet per second, to 70,000 cfs on Wednesday, and said a further increase to 75,000 cfs was likely by Saturday morning.
"We will reassess that later today to see if that is necessary, but we probably will, in all likelihood," John Remus, chief of the Missouri River Basin Water Management Division, said in a conference call Wednesday with media and government officials.
Remus said releases would remain at 75,000 cfs for the foreseeable future, and the corps would continue to monitor the situation and make any necessary adjustments in releases from Gavins Point, the Missouri River dam closest to Sioux City.
"I don't think it will be less. I hope it won't be significantly more," he said.
The Missouri River is forecast to rise as high as 29.4 feet by Friday afternoon, according to the National Weather Service, just shy of the roughly 30-foot crest in March.
The March flooding forced the overnight evacuation of 260 households in Dakota Dunes, an upscale community in extreme southeast South Dakota. The residents were allowed to return home the same day.
Dakota Dunes Community Improvement District Manager Jeff Dooley told the Journal Wednesday the community is watching the latest river forecast closely and preparing for flooding in low-lying areas.
"We would expect a situation that we had in March, and we have protective measures in place to try to manage that," Dooley said. There is a sandbag structure in one of the town's low-lying areas, storm sewers have been plugged, and pumps are set up.
In South Sioux City, the riverfront Scenic Park Campground is facing flooding, particularly in the lower-lying, east portion of the campgrounds. Parks Director Gene Maffit said 44 of the campground's 135 campsites are flooded, while the other 91 spots remained open.
Some of the soccer fields in South Sioux City's soccer complex could also be under water.
"Other than that it's not really going to affect us a lot," Maffit said.
In Sioux City, fire department officials warned Hamilton Boulevard soon could be inundated with water at the Interstate 29 interchange. A detour would be posted in such an event. The low-lying intersection is the only place in Sioux City currently expected to be impacted by the flooding.
Corps officials said rainfall in parts of Nebraska and South Dakota that normally see 1 to 1.5 inches of rain in late May have received 6 to 8 inches in the past two weeks. With soil in those areas already saturated from a wet March and April, most of the rain is running into Missouri River tributaries and making its way to reservoirs like Gavins Point rather than soaking in.
Runoff in the Missouri River basin above Sioux City during the three-month period of March through May has reached 26.3 million acre-feet, the highest total for that period since record keeping began in the late 1800s. May runoff is currently at 7.2 MAF, second only to 9.2 MAF in 2011. Normal runoff for a year is 25 MAF.
"There's just a tremendous amount of rain that has fallen and run off," said Kevin Grode, team leader of the corps' Reservoir Regulation Division.
In March, the corps increased releases from Gavins Point as high as 90,000 per cubic feet to free up space in the adjacent Lewis and Clark Reservoir, which had filled due to snow melt and heavy rains on frozen, wet soils, and unanticipated runoff from uncontrolled tributaries. It was believed to be the second-highest daily releases on record, behind only the months-long Missouri River flooding in 2011, when releases peaked at 160,200 cfs.
Other parts of the tri-state region faced growing flooding threats Wednesday as heavy rains swelled nearby rivers and creeks. Here is a roundup based on data from the National Weather Service in Sioux Falls:
Big Sioux River
Near Hawarden, Iowa, the Big Sioux crested at 30.83 feet early Wednesday morning. The river is in major flood stage and will remain there until Saturday, when it is expected to drop to moderate flood stage.
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At the current river depth, Iowa Highway 10 is expected to begin flooding, some farm houses on the South Dakota side of the river could be isolated by high water, and South Dakota Highway 46 could flood, as well as agricultural flooding on the South Dakota side. Some other roads leading into the western Sioux County city were closed Wednesday due to water running over the payment.
Downstream, at Akron, Iowa, the Big Sioux is expected to crest at 21.8 feet deep early Thursday morning. The river depth was 21.33 feet Wednesday morning. At that level, flooding may occur on Highway 48, as well as rural roads in the area, farm houses and thousands of acres of farmland. Farm levees will likely be over-topped in some areas.
The Big Sioux at Sioux City is expected to crest at 30.6 feet early Friday morning. Measured at 29.09 feet Wednesday morning, the level is not expected to reach flood stage.
Floyd River, Alton
At Alton, Iowa, the Floyd River crested at 12.89 feet Tuesday night. The river is expected to drop below flood stage by Wednesday night.
With this level of river depth, flooding could begin to affect lower lying farmland along the river.
At Rock Rapids, Iowa, the Rock crested at 17.68 feet deep Monday night, and dropped to 14.94 feet Wednesday morning. Currently the river is in minor flood stage and is expected to drop below flood stage by Thursday night.
At current river levels, the lower banks on the left side of the river are expected to begin flooding.
At Rock Valley, Iowa, the Rock crested at 17.94 feet Tuesday morning before declining to 16.14 feet as of Wednesday morning. The river is expected to drop below flood stage Wednesday evening.
At current river depth, significant amounts of agricultural lands are expected to flood, and some rural roads are threatened by high water.
Ocheyedan River, Spencer
The Ocheyedan River at Spencer, Iowa, has been hovering around the level of major flood stage since Tuesday morning. Major flood stage begins at 10.5 feet, and the river hit that level Wednesday. It is expected to decline from there, dropping below flood stage by Saturday.
At the current level, major agricultural flooding begins and some county roads are expected to be flooded.
Little Sioux River
The Little Sioux at Spencer crested at 13.85 feet Tuesday night, and river levels have begun to fall. Currently the river is in minor flood stage, just below moderate flood stage.
At current river levels, minor flooding of the Spencer city park and some rural agricultural land is anticipated.
Near Milford, Iowa, the Little Sioux is in moderate flood stage. As of Wednesday morning, the river was hovering just below 15.3 feet.
The river is expected to drop back below flood stage by Monday morning.
At current river levels, significant areas of pasture and other farm lands could begin flooding.
At Cherokee, Iowa, the Little Sioux River has been in minor flood stage since Monday and is expected to remain for the next several days. The river was 18.66 feet deep as of Wednesday morning.
At that river depth, the city park is expected to begin flooding on the south bank of the river and lowland flooding could begin.
Journal reporter Nick Hytrek contributed to this report.