The Missouri River has flooded the Morehead Island Campground in Plattsmouth, Nebraska.

In March, Gavins Point Dam on the Missouri River was put to one of its greatest tests in its 64-year-history: Record-breaking runoff in the dam’s watershed, primarily from the Niobrara River, exceeded its capacity.

That prompted the second-highest discharge from the dam since it started operating in 1955.

Simultaneously, about 180 miles downstream, flooding on the Platte River sent record amounts of water into the Missouri River. From Plattsmouth south, the Missouri River reached record levels. Levees broke, towns flooded, farmland was inundated, and livestock, crops and equipment were lost.

Here, U.S. Army Corps of Engineers officials address questions The World-Herald has been hearing about management of Gavins Point Dam during the flooding.

Talk, for a minute, about some of the actions taken by the corps that succeeded in lessening flooding along the Missouri River.

First, the corps shut down releases from Fort Randall Dam, which is immediately upstream of Gavins Point, on March 13, during the time that the Niobrara River Basin was peaking. The surge in releases from Gavins Point Dam came from the unregulated Niobrara River and the smaller watersheds immediately around the dam. None of it came from that portion of the Missouri River impounded by the five upstream dams.

Second, the corps operated the Gavins Point spillway gates to raise the pool behind the dam — peaking 1.6 feet higher than its previous peak of 1210.7 feet in 1960.

How did inflows into Gavins Point compare to its flood storage capacity?

On March 13, the Gavins Point pool had 107,000 acre-feet of flood control space available. If no releases had been made from Gavins Point, the March 14 inflow of 250,000 acre-feet would have filled the available space in about 10 hours. If all of the flood control storage space were available, it would have been about 13 hours.

Could Gavins Point’s base elevation be lowered so that it holds back more floodwater in addition to re-regulating Fort Randall’s discharges?

Gavins Point Dam is one of six Missouri River dams. To set aside more space behind Gavins Point Dam would affect all six dams and require an examination of the potential effects to each of the authorized purposes throughout the system and along the full length of the Missouri River.

Even with Fort Randall releases of zero cubic feet per second and the Gavins Point reservoir empty, significant releases from Gavins Point would have been necessary.

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How did flows coming out of Gavins Point compare to the flows entering the Missouri from the Platte River?

The Platte River contributed significantly more flow to the Missouri River than Gavins Point or any of the other tributaries between Gavins Point and Plattsmouth. At its peak on March 16, the U.S. Geological Survey estimated that the Platte River contributed more than 190,000 cubic feet per second into the Missouri River.

When did the surge in releases from Gavins Point start reaching Plattsmouth and when did it subside (in other words, how long did it last)?

The travel time for water between Gavins Point and Plattsmouth is three to four days. The large increases at Gavins Point began early March 14, starting at 33,000 cubic feet per second, peaked temporarily in the early hours of March 15, at 100,000 cubic feet per second and were stepped down from there. By March 20 releases were back to 24,000 cubic feet per second.

During February and early March, as snowpack built up in the Gavins Point Dam watershed, how come the corps didn’t start boosting releases from the dam to make room for additional runoff?

The corps was making above-average winter releases of about 20,000 cubic feet per second (normal range is 12,000 to 17,000 cubic feet per second) throughout winter to finish evacuating all of the 2018 stored floodwaters. This was accomplished in late January.

We monitor basin conditions on an ongoing basis, including mountain and plains snowpack. Our March 1 upper basin runoff forecast indicated that runoff would likely be slightly above normal and that we might need to start initiating flood storage evacuation measures once the river ice conditions between the reservoirs no longer presented a risk for ice jams from increased releases (typically in mid- to late March).

In mid-March, when the “bomb cyclone” was forecast — rain on top of the snowpack — how come the corps didn’t, at that point, ratchet up releases from Gavins Point to adjust for the impending glut of runoff?

The National Weather Service is the agency that forecasts precipitation and river levels. In the final days before the storm hit, forecasts changed, with the heaviest rains falling farther north than originally expected.

The record runoff came from a combination of three things: 1) moderate to heavy rainfall, 2) on top of a heavy plains snowpack, 3) on top of frozen soils. The soil normally absorbs some of the rainfall and snowmelt. During this event, it’s estimated that the top 1 to 2 feet of soil was frozen, and nearly all of the rain and snowmelt became direct runoff.

Assessing the volume of runoff that was going into Gavins Point reservoir was extremely challenging, both for the National Weather Service and the corps.

“At the end of the day, it was an event that, every time we got the new forecast and expectation of what was going to happen on the river, it kept going up,” said Col. John Hudson, Omaha District commander. “There was very little time to react.”

As early as March 7, the National Weather Service in Valley was warning of major flooding, and by March 15, it was warning that people shouldn’t assume levees on the Platte, Loup and Elkhorn would hold. Why didn’t the corps have similar concerns about the Missouri River levees in the flood-prone stretch of river between Plattsmouth, Nebraska, and St. Joseph, Missouri?

In its response, the Corps underscored that emergency managers were warned of overall flood risks and kept apprised of issues with levees. On Feb. 22 and March 7, the National Weather Service (the agency that issues forecasts for river levels) briefed state and county emergency managers on the "strong possibility of major flooding in this area," the Corps said. 

Additionally, the Corps adheres to a chain of command in emergency communication — with communication flowing from the Corps to the state to the county and below, and vice versa. If the Corps usurps that chain of command, it sets up a potential for conflicting messages among various governmental agencies. Advising residents on local conditions is a fundamental responsibility of mayors and the local community.

“If there are questions about whether farmers should move their equipment or anything out of a field, if the water is going to be up on a levee, we’re talking to state emergency officials and they’re talking to their county emergency managers, who are pushing that down to the local level where decisions are made,” said Matt Matthew Krajewski, readiness branch chief.

The L-575 levee near Hamburg, Iowa, was overtopped about midnight March 14, less than a day after the storm hit the area. At that time, the Missouri River in this stretch was carrying 214,000 cubic feet per second. The Gavins Point contribution, based on releases March 10 and a four-day travel time, would have been about 20,000 cubic feet per second.

Regarding the overall management of the river: When was the last time the corps adjusted flows out of its dams to provide for endangered and threatened species?

In spring 2017, we performed two three-day cycles from Gavins Point Dam. A “cycle” lowers and then increases releases so that downstream river fluctuations discourage threatened and endangered birds from nesting in the lower portions of sandbars.

The Gavins Point spring pulse, which was only conducted in 2006, 2008 and 2009, was removed from the corps’ 2018 Master Manual.

Floods devastate Nebraska, Iowa in March 2019

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People who populate the towns and small lake communities along the Platte River west and south of Omaha were taking stock of their homes and futures this week. Some of the properties are second homes or summer getaways, but just as many are full-time residences, from small mobile homes to comfortable villas.

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After drenching rains Tuesday and heavy snow on Wednesday, Gibbon’s low spots became apparent, first as water filled streets to the curb, and later on Thursday and Friday as the water spilled into lawns and driveways before lapping at foundations. “I’ve never seen so much water, or the force and damage it can do in a short time,” firefighter Jamey Rome said.

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Thirty buildings, including the 55th Wing headquarters and the two major aircraft maintenance facilities, had been flooded with up to 8 feet of water, and 30 more structures damaged. About 3,000 feet of the base’s 11,700-foot runway was submerged. No one, though, had been injured.

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Nancy Gaarder helps cover public safety and weather events as an editor on The World-Herald's breaking news desk. Follow her on Twitter @gaarder. Phone: 402-444-1102.

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