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The Crayfish of Nebraska

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4 numerous wind-excavated depressions which filled with rainwater, creating thousands of acres of marshes and wetlands that were a major waterfowl production and stopover area, hence the name "Rainwater Basin". Now most of the wetlands have been drained and the region is almost completely converted to irrigated cropland. Perennial streams are found on the southern and eastern edges of this region which include the Little Blue and the Big Blue River watersheds. To the southwest are the Rolling Plains and Breaks. This is also a loess covered region whose dissected topography is similar to the Dissected Loess Plains except the loess is not as thick. The land has been converted to a mix of rangeland and cropland. There is extensive irrigation development which has markedly changed the hydrology. Several large reservoirs have been built for the dual purpose of irrigation and flood control including Harlan County, Swanson, Enders, Red Willow and Medicine Creek Reservoirs as well as several low-head irrigation diversions. Groundwater pumping has reduced flows or dried several streams such as the upper reaches of the Frenchman and the Republican. The Republican below Harlan County Reservoir functions as an canal with high flows during the irrigation season and low flow at other times. In the center of the region is the Platte River Valley, a wide, flat valley composed of alluvial silt, sand and gravel deposits. This was the travel corridor for the Oregon Trail so there are numerous historical diary descriptions of the landscape. This area was originally a lowland tallgrass prairie with marshes and wet meadows. Trees were almost totally absent except on the islands. The Platte River was historically wide, shallow and braided. It is now periodically intermittent due to irrigation withdrawals. In the western part, due to the loss of the spring floods which scoured the channel, the channel is now heavily forested and the river has been reduced to small meandering channels. One of the unique features of the Platte River is the nature of its valley. Most rivers erode their own valleys through increasingly older strata. With the Platte River, the valley walls are younger than the river itself. That is because the Platte was a The Rainwater Basin near Aurora, Nebraska

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