By Gary Stone, Jessica Groskopf and David Ostdiek
The Goshen Irrigation District (GID) and the Gering-Fort Laramie Irrigation District (GFD) are reviewing repair and upgrade options for tunnels on their main delivery canal.
The main canal begins at the Whalen Diversion Dam near Guernsey, Wyo., where water is diverted from the North Platte River to run 129 miles through Goshen County, Wyo., and Scotts Bluff County, Neb.
The canal delivers water to about 107,000 acres of cropland in the two irrigation districts. A collapse in one of three tunnels along the canal disrupted water deliveries for about six weeks in July, August and September until temporary repairs could be made.
Of the seven repair and upgrade options being considered, only two are relatively feasible. One of those two options is to pump a special cement mixture into the space between the existing concrete tunnel wall and surrounding geologic material. The second option is to excavate an aboveground canal to replace the tunnels.
But the location of the tunnels and the surrounding historic artifacts limit the irrigation districts' options.
Repair options for individual tunnels
Tunnels 1 and 2 are located in Goshen County, Wyo.
Since Tunnel 1 is located near historic Fort Laramie, the Oregon Trail and a pioneer gravesite, the only probable option for this tunnel is to have the special concrete pumped into the void. Tunnel 1 is about 0.52 miles long and is in the Arikaree (geologic) formation, which consists mainly of gray, fine, loose-to-compact sand with layers of hard, fine-grained, dark-gray concretions that vary from a few inches to 15 inches and often have tabular form. It also includes a large amount of volcanic ash mixed in with the sand.
Tunnel 2, which collapsed in July, is about 0.40 miles long and also is in the Arikaree formation. This is the tunnel that has been "patched" to allow irrigation water deliveries, but this is not a permanent repair. This tunnel also has nearby historic artifacts that will have to be addressed. Both of the two repair and upgrade options are being considered for this tunnel.
SAK, the contractor for the temporary repairs to Tunnel 2, will be removing the trench boxes to facilitate repairs to the main tunnel collapse site. Working from the outlet end of Tunnel 2, the contractors will be installing more "ribs" inside the tunnel per U.S. Bureau of Reclamation recommendations.
GID and GFD personnel are installing fabric mat to stabilize the excavated soil from the collapse site to prevent wind erosion and sloughing. Final touch-up work was completed on the canal breach area.
Tunnel 3 is located near Rifle Sight Pass in Scotts Bluff County, Neb. The tunnel is about 1.23 miles long and is in the Brule formation, which consists mainly of a hard, sandy clay of pale-pink color. Because of the length of the tunnel and its location in the Brule formation, pumping the special cement into the void may be the only upgrade option.
Moving forward with planning, repairs
The irrigation districts are getting cost estimates from contractors. Both irrigation districts will have to agree to the permanent repairs and upgrades that will be made on Tunnels 1 and 2, as they share operation and maintenance costs for these two structures. Decisions regarding repair and upgrades for Tunnel 3 will be made by the Gering-Fort Laramie Irrigation District.
All three tunnels will have to have an environmental assessment and other permitting processes completed before any work can be started. Funding for the repairs and upgrades still is in question. The start and completion dates for the repairs and upgrades will depend on how fast the permitting process is completed and the source of funding.
The Fort Laramie National Historic Site is about 51 miles west of Scotts Bluff National Monument and 71 miles west of Chimney Rock National Historic Site, all along the North Platte River Valley.
Nearby Oregon Trail artifacts
Historic artifacts of the great migration along the Oregon Trail (Oregon-California Trail) today affect decision-making for land use along its path.
The Oregon Trail started in Independence, Mo., and then later in Council Bluffs, Iowa, and ends near Oregon City, Ore. It is about 2,000 miles long and crosses six states: Missouri, Kansas, Nebraska, Wyoming, Idaho and Oregon.
The Mormon Trail, which starts in Nauvoo, Ill., follows the same basic route, most of which was on the north side of the Platte River Valley, until the trails merged near Casper, Wyo. The Mormon Trail diverges from the Oregon Trail at Fort Bridger, Wyo. The routes basically "followed the water" across the "Great American Desert." For the Oregon Trail, this included the Kansas, Little Blue, Platte, North Platte, Sweetwater, Green, Snake, Columbia and other rivers.
The largest numbers of pioneers, estimated to be more than 400,000, crossed the "Great American Desert" from the 1840s through the 1860s. Some of the key points along the trails in Nebraska are Fort Kearney, Ash Hollow, Chimney Rock and Scotts Bluff.
Key points in Wyoming are Fort Laramie, Register Cliff, Independence Rock, Devils Gate and South Pass. South Pass is where the trail crosses the Continental Divide and is located in the high prairie, not the mountains.
Many hardships followed the pioneers across the trails, including overturned wagons, sickness, bad weather and death. Some were buried in the trail to hide the grave so that it would not be disturbed by humans or animals.
Others were marked at the time, and some of those remain today. The grave of Rebecca Winters is just east of Scottsbluff along Highway 26. Other graves, such as that of Mary Elizabeth Holmsley, are out on the open prairie along the Oregon Trail. Such sites are our history and legacy.
Nebraska Extension and the University of Wyoming Extension are working together and hosting a joint website to share information about this situation.
For information on the North Platte River and the irrigation projects in Nebraska and Wyoming, visit the slideshare presentation on the University of Nebraska Panhandle Research and Extension Center website.
See related CropWatch stories on the canal tunnel collapse and repair.
Stone is a Nebraska Extension educator. Groskopf is a Nebraska Extension educator for agricultural economics. Ostdiek is a communications specialist at the Panhandle Research and Extension Center.