Cottonwood Creek: “It Will Cost a Pretty Penny”

It must have been a dry July when the City of Boise founders platted the first streets in 1863. They established the city in the channel of Cottonwood Creek. Although Cottonwood Creek is a large tributary to the lower Boise River, it can dry up for months between rain storms and snow melt. The natural course of Cottonwood Creek was down what became 5th Street, across Main, Grove, and Front streets and then across Tom Davis’ orchard, (now Julia Davis Park), to the Boise River. It wasn’t long before city residents learned what it meant to live in the path of Cottonwood Creek. See part 1 of this series.

In 1881, after years of repeated flooding, the Boise City Council paid for construction of a flume to route Cottonwood Creek through Fort Boise to the Boise River. The route of the flume is shown below on the excerpt of an 1885 map.  A section at Fort Boise was built in stone and remains standing today. According to the Idaho Tri-Weekly Statesman, the “flume seems to answer all purposes.” But this wasn’t to be the case. 

A map of the Cottonwood Ck flume today

A River of Sand

Cottonwood Creek carried more than water from the foothills to the valley – tremendous quantities of sand and gravel also were swept downstream with summer thunderstorms and spring freshets. The sand rapidly filled the flume causing the water to overflow and take out the flume walls. Crews of men were tasked with regularly digging out the sand. Sand also filled irrigation ditches that had been built across the creek’s path causing much complaint from the owners.

Flume “Wiped Away”

On May 23, 1891 a massive flash flood poured out of Cottonwood Creek canyon. The Idaho Tri-Weekly Statesman reported eye-witnesses saw a wall of water ten feet high emerge from the mouth of the canyon. The reporter dramatically described the scene: “As though nature was determined to avenge the affront of man in attempting to divert the natural course of one of her streams, the water in its mad rush could not be stopped by the frail wooden barrier that stood in its path, but wiped away at its first onslaught the flume and swept triumphantly along the old bed of the stream…Nearly every street in the northeast part of the city soon became the scene of a raging torrent of muddy water which tore along unchecked carrying great masses of broken limbs and other debris.”  He concluded, “Thousands of dollars have already been spent upon the Cottonwood Creek flume which was knocked ‘galley-west’ yesterday, and it will cost a pretty penny to rebuild the work on a proper scale.”

After more flooding in May 1892, the Boise City Council voted in September of that year to replace the primarily wooden flume with a stone aqueduct. The new flume was built with sandstone blocks from the foothills quarry. It was built in a V-shape and back-filled with sand at a cost of $9,000.

A section of the flume

The V-shape can be seen today in this section of the flume at Flume Ct.

“The Most Inexcusable Botch”

The first break in the new aqueduct occurred on March 29, 1893, just months after it was constructed. The sand back fill gave away about 100 yards below Main St. In a scathing editorial, the Idaho Daily Statesman wrote, “The flume was the most inexcusable botch that could be conceived of…Long sections of the flume were built on top of the ground, with nothing but a narrow bank of sand on either side to support the loose stone work.” The flume continued to give way requiring city crews to continuously patrol and repair it. The expensive problems with the flume didn’t win four-term mayor James Pinney any friends at the Idaho Daily Statesman.  The editors called Mayor Pinney foolish to have “built the Cottonwood aqueduct upon the sand.”

Mayor Supervises Flume Repair

A new mayor, Peter Sonna, was sworn in on July 15, 1893. According to the Idaho Daily Statesman, Mayor Sonna personally supervised repair work on the flume in October of that year.  A new rock wall was built, and concrete was poured into the gap between the flume and the wall. The outside of the flume may have been more secure, but the inside of the flume still filled with sand, and, as a consequence, Cottonwood Creek overtopped and broke the flume and flooded the new East Side Addition neighborhood in March 1894.  Mayor Sonna, relieved the water was flowing east and not west down Main St., delayed repair work until the high flows had ended. The flume was filled with three feet of sand, and yards throughout the neighborhoods were “washed full of sand,” according to the Idaho Daily Statesman.

Emergency repairs were made to the Cottonwood flume year after year after year. The city continued to develop and more houses were built in the East Side Addition and in the Central Addition. The population grew to 5,957 by 1900.  Then came March of 1904, when 2.46 inches of rain fell in 24 hours.

Part 2 of a blog series exploring the history of Cottonwood Creek. Made possible by the Idaho Fish and Wildlife Foundation and the Boise River Enhancement Network.

The Cottonwood Creek Daylighting Project

The Boise River Enhancement Network is a partner in a cooperative project to daylight Cottonwood Creek where it flows through Julia Davis Park and enters the Boise River. The creek currently runs through a stone flume under the park. A new natural creek channel will be constructed benefiting fish and wildlife, water quality and park visitors. The project leads are City of Boise and Trout Unlimited and partners include the Intermountain Bird Observatory, Ada County Highway District, Golden Eagle Audubon Society, and Land Trust of the Treasure Valley. The project is funded, in part, by the US Bureau of Reclamation, the City of Boise Open Space and Clean Water Fund and the Idaho Foundation for Fish and Wildlife.