Effects of streamflows on stream-channel morphology in the eastern Niobrara National Scenic River, Nebraska, 1988–2010

Abstract

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Schaepe, N.J., Alexander, J.S., and Folz-Donahue, Kiernan, 2016, Effects of streamflows on stream-channel morphology in the eastern Niobrara National Scenic River, Nebraska, 1988Nebraska, -2010 A water year is the 12-month period from October 1 through September 30 of the following year and is designated by the calendar year in which it ends. DatumVertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). AbstractThe Niobrara River is an important and valuable economic and ecological resource in northern Nebraska that supports ecotourism, recreational boating, wildlife, fisheries, agriculture, and hydroelectric power. Because of its uniquely rich resources, a 122-kilometer reach of the Niobrara River was designated as a National Scenic River in 1991, which has been jointly managed by the U.S. Fish and Wildlife Service and National Park Service. To assess how the remarkable qualities of the National Scenic River may change if consumptive uses of water are increased above current levels, the U.S. Geological Survey, in cooperation with the National Park Service, initiated an investigation of how stream-channel morphology might be affected by potential decreases in summer streamflows. The study included a 65-kilometer segment in the wide, braided eastern stretch of the Niobrara National Scenic River that provides important nesting habitat for migratory bird species of concern to the Nation.The study focused on three river segments, separated at the confluences with two tributaries, Plum Creek and Long Pine Creek. With an overall temporal scope of 1988-2010 that includes a short interval preceding and a long interval following the Niobrara National Scenic River Designation Act of 1991, the study analyzed five separate time periods: 1988-93, 1994-99, 2000-3, 2004-6, and 2007-10, each of which ended with a year in which aerial photography coverage was available.Streamflow duration was analyzed for one streamgage upstream from the study area and two streamgages on tributary streams within the study area. Summer streamflows (July, August, and September) were targeted for analysis because median flows of the Niobrara River are lowest during those 3 months. In addition, peak flows during the study period were used to estimate bankfull discharge, which is one determinant of channel dimensi...

Spectrally based bathymetric mapping of a dynamic, sand‐bedded channel: Niobrara River, Nebraska, USA

“…The segment has a complex, dynamic sand‐bed braided channel, dominated by actively migrating sandbars under most flow conditions (Alexander et al, ). Mean active channel width in the study area is approximately 160 m (Schaepe et al, ), but up to half of this width can be exposed as sand bars during base‐flow conditions. The active flood plain in the study area has two primary levels: a higher level consisting of riparian woodlands dominated by cottonwood ( Populus spp.…”

“…The Niobrara gains substantial base flow as seepage from the High Plains aquifer, and much of the basin is undammed; despite some hydrologic alteration, the Niobrara maintains a relatively natural flow regime. The mean annual flow at the nearest U.S. Geological Survey gaging station (#06461500) since 1964, when a tributary was dammed, is 21 m 3 /s (Alexander et al, 2009) with a 1.5-year recurrence interval flow of 52 m 3 /s (Schaepe, Alexander, & Folz-Donahue, 2016). The river occasionally flows over bedrock, but bed material is dominated by sand originating from the surrounding Nebraska Sandhills and breakdown of the Cenozoic sedimentary bedrock underlying much of the basin (Alexander, Zelt, & Schaepe, 2010).…”