A collaboration of management agencies is closely monitoring the situation as reservoirs on the North Platte River in Wyoming fill and water is released. Flooding is likely in an area along the river in western Nebraska for several weeks to several months.
Multiple Agencies Monitor River Flows
Early last week there was a conference call with representatives of the US Army Corps of Engineers (USACE), US Bureau of Reclamation, the National Weather Service, Basin Electric Power Coop (Grayrocks Reservoir), Nebraska Emergency Management Agency, Wyoming State Parks, and local Emergency Managers in Wyoming and Nebraska. Recent and continued precipitation events in the Upper North Platte River Basin prompted this meeting to address the expected increased releases from the reservoirs in Wyoming along the North Platte River.
On May 10 Glendo Reservoir went into the “flood pool” http://www.usbr.gov/gp/aop/resaloc/glendo.pdf ). This means the water level at Glendo Reservoir had exceeded its “normal” storage capacity and the excess water now entering was going into the storage capacity designated for flood control/management. This amount is approximately 270,000 acre-feet of “normal” flood control capacity with a surcharge of an additional 330,000 acre-feet. Any surcharge water would flow through the uncontrolled spillway at Glendo dam. When Glendo goes into the flood pool, the USACE takes over management of water releases from the US Bureau of Reclamation. At this time the USACE plans to use 50% of the normal flood pool to prevent major flooding downriver. Forecasted runoff in the Upper North Platte River Basin may exceed 850,000 acre-feet of water.
Current Reservoir Water Levels
At this week’s meeting on Tuesday (May 17) the National Weather Service 30-day outlook for the region indicated below normal temperatures and slightly above precipitation. Grayrocks Reservoir (Laramie River) is releasing more water than they are taking in and are trying to maintain a release rate of 4,500 – 4,700 cfs for the next one to three weeks. The flow rate coming out of Guernsey Reservoir is 5,000 cfs into the North Platte River. The Interstate/Pathfinder Canal is taking 1,100 cfs of this amount and the Tri-State Canal is expected to start taking about 640 cfs. When all is said and done, the expected flow rate at (South) Mitchell bridge is 7960 cfs this Wednesday.
Runoff in the Lower North Platte River Basin, below Alcova Reservoir to Glendo Reservoir, started about May 1 and is continuing at a steady rate. Runoff in the Upper North Platte River Basin also started about May 1, but then went back up and has now started to come off again. Most of this snow melt comes from the Sierra Madre and Snowy Range mountains. To view this data, go to http://www.usbr.gov/gp/lakes_reservoirs/wareprts/wygraph1.html and view the Glendo and Seminoe Reservoir graphs.
Water Measures
1 cfs (one cubic foot per second) of water equals 449 gallons of water per minute, which equals 1.98 acre-feet of water per 24 hours.
The reservoirs in Wyoming are near filling to capacity. There is a total of 261,000 acre-feet of combined storage remaining in Seminoe and Pathfinder reservoirs. Pathfinder has only 62,000 acre-feet of storage remaining. At the current inflows, Pathfinder would fill in less than six days and spill. To view this data go to http://www.usbr.gov/gp/hydromet/teacup_form.html and in the drop-down box click on NP – North Platte Basin. Then click on Submit. You will be shown a “Teacup” model of the reservoirs in Wyoming along the North Platte River. It will show inflows, outflows, capacities, etc.
Lake McConaughy is approximately 90% full. Current inflows into Lake McConaughy are 7,200 cfs and outflows are 3,600 cfs. Lake McConaughy has approximately 275,000 acre-feet of storage remaining before it is considered full. Central Nebraska Public Power and Irrigation District Lake McConaughy Reservoir information can be found at http://www.cnppid.com/wp-content/uploads/2016/05/WPelevation_flows.html .
Minor to moderate lowland flooding is occurring along the North Platte River from Lewellen west into southeastern Wyoming and will continue for several weeks or months. The areas affected are primarily the river bottom, mostly pasture but some cropland and homes. River levels are expected to remain high for the foreseeable future. With more than 90% of the snowmelt to come off above Seminoe Reservoir in Wyoming, there will be a lot of water to move through the system into the Central Platte River and east. The reservoirs in Colorado which feed into the South Platte River are also near capacity and a lot of snowmelt still needs to come out to those basins that feed the South Platte drainage.
For more information on the North Platte River Surface Irrigation Projects and Power Generation, view the slideshare presentation found on the UNL Panhandle Research and Extension web page at http://panhandle.unl.edu/. Bureau of Reclamation water operations information can be found at their web site http://www.usbr.gov/gp/wyao/index.html and snow water content and precipitation can be found at http://www.wrds.uwyo.edu/wrds/nrcs/snowprec/snowprec.html . This web link includes the North and South Platte River drainages.
