"Floods Were Annual Events to Eagle Island Old Timers" read a headline in the Idaho Statesman on Sept. 24, 1940. Vivian Prestwich was the Statesman's local reporter in Eagle at the time, who not only reported on all that was going on in the little town of 500 people, but talked to pioneers of the area and recorded their memories in feature stories.
"Old man Boise River was a 'she' in the old days, inhabitants of Eagle Island claimed, for only a member of the female sex could change her course so frequently," Prestwich wrote. "Floods usually started in February and lasted on two occasions to July 4. Residents either traveled in boats or swam a team of horses across to the mainland, where they kept a wagon. T.C. Catlin kept a boat moored to the porch pillars of his house to travel [to his barn]. Severe as [floods] were the inhabitants were made of stern stuff and stuck it out — mud and all."
Old timers the reporter talked in 1940 to thought the two branches of Boise River that surrounded the island were usually about equal in size, but that could change every season. Sometimes 70 percent went into the south channel, and in another year 70 percent could go into the north channel. Like the Mississippi, "Old Man Boise" just kept rolling along, with little regard for the convenience or safety of those along its banks.
The earliest recorded flooding of Eagle Island was in 1862. Watermaster William E Welsh who had studied the river for a long time wrote in 1944: "Indications from old-timers' stories are that the flow in 1862 probably exceeded the high water on any year since that time. I. N. Coston, who homesteaded on a ranch near the present site of Barber ... stated that all the land in the river bottoms extending from bluff to bluff and from the present site of Boise westward to the canyon near the present site of Caldwell was completely under water on the 4th of July that year." In the fall of 1862 an emigrant party rested their animals and camped for three weeks on Dry Creek against the hills north of present Eagle. They found lots of driftwood to burn that had been deposited by the river far from its banks near Eagle Island.
The Grimes party of prospectors came down from the Owyhee Mountains that summer on their way to Boise Basin, where their discovery of gold on Aug. 6 would lead to a stampede to southern Idaho the following year. They followed Snake River to the mouth of the Boise, where the Hudson's Bay Company's abandoned fur trade post stood, but found the torrent so fierce that they had to spend three weeks building a boat before they could get across.
Severe flooding in the area of Eagle was recorded in 1862, 1871, 1896, 1936, 1938, 1943, 1955, 1963, 1971, and 1982. This year's flooding is considered by experts to be the worst since 1943.
Three dams on the Boise River upstream from the valley, built primarily to conserve water for irrigation, have helped control the annual spring runoff from the mountains, but the capacity of their reservoirs has to be carefully monitored and enough water released to allow room for more. When Arrowrock dam was finished in 1916, it was the tallest dam in the world. Anderson Ranch dam was finished in 1950, and Lucky Peak dam, a few miles above Boise, was finished in 1955. Without them, spring flooding would be much worse, but Mother Nature reminds us regularly that we aren't yet in total control, and probably never will be.