By Laura Zuckerman
SALMON, Idaho (Reuters) - Troops and residents in Pierre, South Dakota scrambled on Saturday to build earth levees to protect the capital from Missouri River flood waters, and the state's governor warned of worse to come.
Rainstorms forecast over the Memorial Day weekend are expected to swell the river and its tributaries to new highs, adding to an already grim forecast for flooding across the Northern Plains and Northern Rocky Mountains.
The regions are battling floods stemming from heavy rains, record snow melt and water releases designed to ease pressure on brimming dams and lessen the damage to communities threatened by topped-out reservoirs.
Preparations for what may prove to be historic flooding of the Missouri basin have been under way for days in South Dakota, where cities like Pierre and Fort Pierre -- which have a combined population of around 15,000 people -- are on the river corridor.
South Dakota Governor Dennis Daugaard said Saturday that forecasts by the U.S. Army Corps of Engineers showed that flooding will be more severe than anticipated as the agency is forced to release more water.
"I know this bad news will be somewhat disheartening, but I encourage South Dakotans to have heart," he said from Pierre during a news conference with reporters.
With water submerging some roads in Fort Pierre on Saturday, Daugaard stepped up the pace of efforts to protect public infrastructure, including drinking water supplies, sewage treatment plants, roads and utilities.
Daugaard urged residents of the state capital and downstream communities to be self-reliant and to prepare to evacuate based on updates from local emergency managers and maps -- posted on www.BreadySD.org -- that model areas likely to be hardest hit.
The governor warned that large-scale, multimillion-dollar projects to raise roads and build new levees might not withstand the expected onslaught by flood waters.
He said he had activated more soldiers to add to the ranks of state National Guard troops that arrived on Friday in Pierre and Fort Pierre, where they are helping exhausted residents fill sandbags.
Daugaard is the third governor in as many days to call up National Guard soldiers because of high water in the Missouri basin.
Montana Governor Brian Schweitzer on Saturday sent National Guard soldiers to the Crow Indian Reservation, to deter hundreds of displaced residents from attempting to return to their homes in inundated areas considered to be dangerous.
On Friday, Wyoming Governor Matt Mead directed the Wyoming National Guard and the state's emergency management agency to deploy teams to help counties facing floods.
In Idaho, Governor Butch Otter on Friday declared an emergency from flooding as tributaries of the Columbia River breached their banks in the eastern and northern parts of the state.
North Dakota also is bracing for flooding from the Missouri.
High water in the Columbia and Missouri follows major flooding of the Mississippi in the Midwest and South.
The Missouri is a major tributary to the Mississippi, compounding flooding fears in the downstream states of Iowa, Nebraska and Missouri.
(Editing by Tim Gaynor and Greg McCune)