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Rising water ushers irrigation

Jun 2, 2014 - By Eric Blom, Staff Writer

System managers 'charge' ditches first, then fill agriculture requests

With snow melting fast and water streaming off mountains encircling Fremont County, irrigation districts were ready. Local officials are keeping an eye on the weather and streamflows to watch for floods developing.

As the runoff flows down the Wind River, it encounters Diversion Dam 34 miles northwest of Riverton on the river's east bank, where the Midvale Irrigation District can draw up to 2,200 cubic feet per second into its system anchored by the Wyoming Canal.

Dams, reservoirs, ditches

Below Diversion Dam, smaller systems also divert water, including the Riverton Valley Irrigation District, the LeClair Irrigation District and Lefthand Ditch.

Snowmelt from the lower Wind River Mountains flows into the three forks of the Popo Agie River and several ditches around Lander before joining up with the Little Wind River southwest of Riverton.

Charge it

Those waters combine with the Wind River at Riverton, which then turns north and goes into Boysen Reservoir, from after which it flows north into Big Horn Lake and into Montana.

In late April and early May, Midvale Irrigation District began filling its canals with water, a process called charging, so it would be ready to deliver water. District manager Jon Howell said the process to takes about three weeks.

Charging is necessary because there has to be water in a ditch before a user can draw water out of it.

"We have to use water we have to keep a minimum amount of water in all the canals and all the laterals at any point in time," Howell said. "Until we get them charged up we can't deliver water."

To start the process, the district's ditch riders first open Diversion Dam. Water flows into the Wyoming Canal, which extends 62.4 miles southeast to rejoin the Wind River.

About 10 miles down the Wyoming Canal from Diversion Dam, smaller canals branch off, leading to Pilot Butte Reservoir, which can hold about 32,000 acre feet of water.

The reservoir's outlet works lead to the Pilot Butte Canal, a 38-mile-long waterway.

To the fields

Once the Wyoming Canal and Pilot Butte canals have water in them, the ditch riders open headgates to laterals, which are ditches branching off the canals and connecting to fields.

They first fill the laterals at the downstream end of the system and work their way upstream.

As soon as a ditch is full, users along it can order water. When the district gets an order, a ditch rider goes and turns on the headgate for that user's property.

Early allotment

The Midvale District board in April set the water allotment for users at 1.5 acre feet, but they can change the number at future meetings. Last year, the final figure was 3 acre feet.

Howell is optimistic about the amount of water that will be available this summer.

"We're not expecting any shortage of water in the Wind River this year," he said.

Midvale operates another reservoir, Bull Lake, upstream from the rest of the district's system and on the west side of the Wind River. Bull Lake Reservoir was created by an 81-foot-tall dam on Bull Lake Creek south of Crowheart, and it holds 152,000 acre feet of water.

When Midvale draws water out of the reservoir, the water flows back into Bull Lake Creek before joining the Wind River's main channel and being drawn back out at Diversion Dam.

When charging began Bull Lake was about two-thirds full at 102,000 acre feet and filling steadily.

As runoff picked up in May, more water was flowing in that out, allowing it to retain about 14 cubic feet per second.

Jim Fahey, National Weather Service hydrologist based in Riverton, tries to forecast the runoff and watch out for floods. He saw this weekend's near-flood runoff coming.

"I think the peak's going to be late May into early June this year," he said earlier in May.

Spring weather was cool until recently, delaying the big melt, Fahey said.

Forecasting floods

In his forecasts, Fahey knows to expect a large runoff or even a flood if he sees the snowpack drop sharply in a short period of time. He looks for at least a 1-inch drop in snow water equivalent, the amount of liquid water snow would melt into, in 24-hour period.

Predicted temperatures also tip him off.

"Usually we need three days of 75 (degrees) plus," he said.

Those are the conditions that arrived last week.

Along with those indicators, Fahey can monitor high water moving through the county by watching data from water stream flow gauges. Starting at Dubois, a string of five gauges tests the depth and flow of the Wind River above Riverton. They send signals via satellite back to computers that then post the information online in real time.

If hydrologists see a deluge coming, they can forecast how high the water will get and can warn residents and other agencies ahead of time.

Water passing Dubois takes about 24 hours to reach Riverton, Fahey said, and having the forewarning helps officials forecast flows at the larger city.

Through Saturday, the Wind River and tributaries in the Riverton area were running at or near capacity, but no significant flooding was recorded. Upstream, isolated flooding took place.

Summer-level temperatures are expected to cool significantly Sunday and hold closer to seasonal norms through this week, easing flood risk considerably.

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