Platte River Channel Becomes a Focus for Platte River Cooperative Program Studies2001

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3. Reduction in the supply of sand and coarsening of the river bed: The construction of large dams on the North Platte .River reduced the annual flood peaks and trapped the entire sand load in the reservoirs. Therefore, the South Platte River, with coarser sand, is now the major sand source to the Central Platte River. Consequently, the sand bed of the Central Platte River has been coarsening, which leads to downcutting and narrowing of the channel. This process started at North Platte, Nebraska, has been progressing downstream, and is still continuing today. 4. Erosion by clear water: The final cause of channel narrowing is the erosion of the river bed caused by clear water flows into the river. The water released from Kingsley Dam and the water returned to the Central Platte from canals is clear ( "sediment- hungry") water that tends to erode the river bed, causing the bed to lower and the channel to narrow. The effects are mostly local: the scouring and lowering of the riverbed below the Keystone Dam and below the J -2 return canal is moving downstream at a very slow rate. Possible Solutions. The report offers possible approaches to offsetting the continued narrowing of the river and loss of habitat. 1. Clearing and leveling some of the wooded islands within the existing channel: This would allow for a wider and slower river flow, with less erosion of banks and the river bed; more open channel and shallow sand bars, providing better roost and nest sites for cranes, terns and plovers. Returning some of the river sand that is perched on the islands back into the deeper channels will also help reduce erosion rates. As with all aspects of the cooperative program, such actions would only be undertaken with willing landowners. 2. Augmenting flows in the Central Platte to attain roughly 8,000 cfs in the reach from Lexington to Grand Island, for 1 -3 days each spring, by matching releases from Lake McConaughy with natural South Platte flows: While these flows would be below the river's bank -full capacity, they would be higher than the current average high flow. The short pulse flow would scour new vegetation from the channel, preventing further encroachment of trees into the channel. The pulse flow would also help build higher elevation sand bars for tern and plover nesting, preventing loss of nests from summer thunderstorm flows. Any such program would be implemented in a phased, incremental manner. It would be accompanied by continuous monitoring of the river to track its effects and avoid any negative consequences. Based on monitoring results, the next increment would be modified as necessary. The technical report is still considered a draft, as it awaits review and comment from the states and their consultants. As the states proceed with their own independent review of the channel stability issues, discussions among the Cooperative Agreement parties will continue. Any plans that emerge from those discussions will be analyzed in a draft environmental impact statement (EIS) scheduled for publication and public review next January.