Pinenut Creek is down to a trickle below Jo Lane on Thursday. Typically fed by snowmelt in the Pine Nut Mountains the creek bed is usually dry by late summer.
A feasibility study for flood control on Pine Nut Creek carries a $78 million price tag, including a dam and at least a half-dozen basins.
Completed in July, the study was posted to Douglas County Engineering’s web site on Thursday.
A dam near the end of Jacobsen Lane would reduce flooding through most of Fish Springs but would cost around $24.1 million all by itself.
Fish Springs resident Mark Dieter said after reading the study he still believes the best solution is a dam.
“It will control the water before it potentially floods the housing below and would ease the demand on lower basins,” he said. “The annual cost of flood repairs by the county, plus federal government support will hopefully justify these improvements.”
Dieter pointed out that the dam would not form a permanent reservoir.
“People should understand that the dam is a detention structure that will actively control flow during a flood event and subsequently drain within a day or two,” he said.
Basins along the stream are estimated to cost from $7.6 million to $13.9 million, according to a preliminary cost estimate included with the study conducted by consultant Kimley Horn.
The goal of all that work was to reduce Pine Nut Creek to the capacity of the Upper and Lower Allerman Canals and eliminate runoff west of the lower canal.
One of the things that puzzled consultants was that despite having a smaller drainage shed, Pine Nut Creek has a higher peak discharge and runoff.
They attribute that to a difference in methodology, though Pine Nut Creek was still running in late June.
According to a chart included in the study, Buckeye Creek has 74 square miles of drainage with a 100-year discharge of 3,940 cubic feet per second, while Pine Nut Creek has 55.5 square miles and a discharge of 5,150 cubic feet per second.
Even adjusting the flow to one similar to Buckeye Creek, consultants concluded that the work wouldn’t reduce the flows to the study goals.
“The proposed basins did reduce runoff downstream, but flow was still overtopping the Allerman Canal,” consultant said. “Additional storage would be necessary such that identifying additional potential open space to construct a basin would likely not be feasible.”
That means the dam would have to be included if the project were to reach the desired flows. It would be located on private land not far from City of Refuge.
An alternative location further upstream would require a much wider dam and would have a lower capacity.
In addition to the ownership, there were several factors that would have to be considered before a dam was determined.
Estimates are that 2,200 acre feet could be stored behind a dam 110 feet tall. That would result in the ability to make the basins smaller than the proposed 15 feet deep.
Before this winter, the last big flood on Pine Nut Creek was Aug. 6, 2014, when a thunderstorm struck dumping an inch or more of rain over the mountains in 45 minutes that night.
Not a single drop of rain fell in lower Fish Springs from that storm, and residents were alerted to the danger until they heard roaring coming down the canyon.
