Application of theoretical equations to estimate the discharge needed to maintain channel width in the Platte River from Lexington to Grand Island, Nebraska

BLM biological assessment for T and E species for the WyCoalGas project. Final technical report, November 1980-May 1982. [Proposed WyCoalGas project; Converse County, Wyoming]

“…This method is based on equations by Parker (1978) that were developed for rivers with bed and bank material consisting of non-cohesive sands. Karlinger et al (1981) show that for a hypothetical 500 foot channel near Overton that the effective discharge is about 3600 cfs. They suggest that the total volume of flow that occurs at discharges greater than 3600 cfs represents the streampower needed to maintain a 500 foot channel.…”

“…The U.S.G.S. (Karlinger et al 1981) has calibrated a method to determine the discharges (effective discharge) required to maintain the existing channel widths. This method is based on equations by Parker (1978) that were developed for rivers with bed and bank material consisting of non-cohesive sands.…”

“…They suggest that the total volume of flow that occurs at discharges greater than 3600 cfs represents the streampower needed to maintain a 500 foot channel. This theoretical reduction may have little significance for the Platte River in the critical habitat area because the method of calculation assumes u~ds and banks composed of cohesionless sands.-The method would be valid if high flows and ice scouring were sufficient to remove vegetation that becomes established, but this is apparrently not the case in most reaches of the Platte River today (Karlinger et al 1981, Aronson and Ellis 1979, Krapu 1981. Peak flows have been diminished to the point where they are no longer sufficient to remove established vegetation in a _channel of sufficient width for crane use.…”

Habitat Use by Migrant Sandhill Cranes in Nebraska

“…Designation of part of the existing unappropriated flows for channel maintenance is needed to assure a dependable source of water to scour away seeds and new seedlings of woody plants before root systems are sufficiently developed to withstand flooding. The minimum flow necessary to maintain a channel width of about 150 m at Overton has been estimated to be 108 m3/second for at least 16 days from May through August, with discharges spaced to inhibit germination of both early and late falling seeds (Karlinger et al 1981). Sufficient flows are also needed during the staging interval to inundate the channel and provide secure roost sites.…”