Invasion of Siberian Elm (Ulmus Pumila) Along the South Platte River: The Roles of Seed Source, Human Influence, and River Geomorphology

Riparian ecosystems in the western USA have been invaded by non-native woody species deliberately introduced for stream bank stabilization, agricultural windbreaks, and urban shade. Recent work suggests that the non-native tree Ulmus pumila (Siberian elm) is capable of significant spread in western riparian ecosystems, that range infilling is still incomplete, and that the invasion is dispersal-limited. We analyzed the interacting roles of propagule pressure from upland U. pumila, human influence based on road and farmstead density, and river geomorphology in promoting U. pumila invasion into riparian corridors along the South Platte River, Colorado, USA. U. pumila stem density increased with increasing channel and floodplain restriction and increasing human influence from both urban and rural development. Model selection indicated that local upland U. pumila seed sources were relatively unimportant to riparian U. pumila stem density, suggesting that upland propagule pressure is currently contributing less than human influences to U. pumila spread along the South Platte River. In particular, higher road density was the most important predictor for the proportional abundance of smaller U. pumila individuals (DBH < 5-cm and 5-15-cm), suggesting that human influence in densely populated areas has been the primary driver of recent U. pumila population expansion. U. pumila stem density was only weakly associated with abundance of other common riparian tree species. Land managers and other entities concerned with non-native tree invasion into important riparian habitat may be able to reduce U. pumila spread most effectively by focusing U. pumila control efforts where human influences are greatest.

Topographic Map Analysis of the North Platte River-South Platte River Drainage Divide Area, Western Larimer County, Colorado, USA Eric Clausen

The United States Supreme Court settled legal disputes concerning four different Larimer County (Colorado) locations where water is moved by gravity across the high elevation North Platte-South Platte River drainage divide, which begins as a triple drainage divide with the Colorado River at Thunder Mountain (on the east-west continental divide and near Colorado River headwaters) and proceeds in roughly a north and northeast direction across deep mountain passes and other low points (divide crossings) first as the Michigan River (in the North Platte watershed)-Cache la Poudre River (in the South Platte watershed) drainage divide and then as the Laramie River (in the North Platte watershed)-Cache la Poudre River drainage divide. The mountain passes and nearby valley and drainage route orientations and other unusual erosional features can be explained if enormous and prolonged volumes of south-oriented water moved along today&rsquo;s north-oriented North Platte and Laramie River alignments into what must have been a rising mountain region to reach south-oriented Colorado River headwaters. Mountain uplift in time forced a flow reversal in the Laramie River valley while flow continued in a south direction along the North Platte River alignment only to be forced to flow around the Medicine Bow Mountains south end and then to flow northward in the Laramie River valley and later to be captured by headward erosion of the east-oriented Cache la Poudre River-Joe Wright Creek valley (aided by a steeper gradient and less resistant bedrock). Continued uplift next reversed flow on the North Platte River alignment to create drainage routes seen today. While explaining Larimer County North Platte-South Platte drainage divide area topographic map drainage system and erosional landform evidence this interpretation requires a completely different Cenozoic history than the geologic history geologists usually describe.

Groundwater Recharge to Support Wildlife and Water Users

The Heyborne Ponds Recharge Project is a multibenefit project that simultaneously seeks to promote wildlife conservation, to address threatened and endangered species recovery, to support recreation, and to facilitate water availability for agriculture. The project delivers water from the South Platte River to recharge ponds to provide habitat for migrating birds while concurrently providing a mechanism for water to infiltrate into the alluvial aquifer and return to the river at a later time. This temporal shift in the timing of flows in the river provides several benefits. Under Colorado law, groundwater users can pump out of priority only if they augment surface water flows. Further, Colorado has interstate commitments to augmenting downstream flows in the Platte River. Multiple-benefit projects such as Heyborne Ponds represent an untapped opportunity for diverse interests to work together in implementing managed aquifer recharge.

QCam: sUAS-Based Doppler Radar for Measuring River Discharge

The U.S. Geological Survey is actively investigating remote sensing of surface velocity and river discharge (discharge) from satellite-, high altitude-, small, unmanned aircraft systems- (sUAS or drone), and permanent (fixed) deployments. This initiative is important in ungaged basins and river reaches that lack the infrastructure to deploy conventional streamgaging equipment. By coupling alternative discharge algorithms with sensors capable of measuring surface velocity, streamgage networks can be established in regions where data collection was previously impractical or impossible. To differentiate from satellite or high-altitude platforms, near-field remote sensing is conducted from sUAS or fixed platforms. QCam is a Doppler (velocity) radar mounted and integrated on a 3DR© Solo sUAS. It measures the along-track surface velocity by spot dwelling in a river cross section at a vertical where the maximum surface velocity is recorded. The surface velocity is translated to a mean-channel (mean) velocity using the probability concept (PC), and discharge is computed using the PC-derived mean velocity and cross-sectional area. Factors including surface-scatterer quality, flight altitude, propwash, wind drift, and sample duration may affect the radar-returns and the subsequent computation of mean velocity and river discharge. To evaluate the extensibility of the method, five science flights were conducted on four rivers of varying size and dynamics and included the Arkansas River, Colorado (CO), USA (two events); Salcha River near Salchaket, Alaska (AK), USA; South Platte River, CO, USA; and the Tanana River, AK, USA. QCam surface velocities and river discharges were compared to conventional streamgaging methods, which represented truth. QCam surface velocities for the Arkansas River, Salcha River, South Platte River, and Tanana River were 1.02 meters per second (m/s) and 1.43 m/s; 1.58 m/s; 0.90 m/s; and 2.17 m/s, respectively. QCam discharges (and percent differences) were 9.48 (0.3%) and 20.3 cubic meters per second (m3/s) (2.5%); 62.1 m3/s (−10.4%); 3.42 m3/s (7.3%), and 1579 m3/s (−18.8%). QCam results compare favorably with conventional streamgaging and are a viable near-field remote sensing technology that can be operationalized to deliver real-time surface velocity, mean velocity, and river discharge, if cross-sectional area is available.

North Platte River-South Platte River Confluence Area Drainage System History as Determined by Topographic Map Interpretation: Western Nebraska, USA

Detailed topographic maps of the western Nebraska North Platte River-South Platte River confluence area show a low relief and gently sloping southeast-oriented upland surface, asymmetrical drainage divides, nearly adjacent and parallel east-oriented North and South Platte River valley segments, barbed tributaries, and shallow divide crossings (low points along drainage divides) in a region south of the Nebraska Sand Hills and at the Nebraska loess region&rsquo;s western margin. Published interpretations of North and South Platte River confluence area landforms (referred to as the accepted paradigm) do not explain most drainage features and are compared with a new paradigm&rsquo;s interpretations to determine which of the two paradigms explains the regional drainage history and related surface features in a simple and consistent manner. New paradigm interpretations require large sheets of slowly-moving southeast-oriented water to have flowed toward what was probably an actively eroding Republican River valley and to have shaped the upland surface while the Platte and North and South Platte River valleys eroded headward into and across the region so as to create the asymmetric drainage divides, barbed tributaries, and shallow divide crossings. These new paradigm interpretations are consistent with each other and with recently published new paradigm interpretations of upstream North and South Platte River drainage system history. New paradigm interpretations also suggest the adjacent Nebraska Sand Hills developed on a large flood deposited delta (typical of sand dune areas on former glacial lake deltas further to the north) and the slowly-moving sheets of water may have been responsible for some or all of Nebraska&rsquo;s loess deposits, although the new paradigm leads to a fundamentally different middle and late Cenozoic regional geologic and glacial history than what workers using the accepted paradigm have described.

Topographic Map Analysis of Mountain Passes Crossing the Continental Divide Between Colorado River Headwaters and North and South Platte River Headwaters to Test a New Geomorphology Paradigm, Colorado, USA

Detailed topographic maps are used to identify and briefly describe named (and a few unnamed) mountain passes crossing high elevation east-west continental divide segments encircling south- and southwest-oriented Colorado River headwaters and linking the Colorado River drainage basin (draining to the Pacific Ocean) with the North and South Platte River drainage basins (draining to the Platte, Missouri, and Mississippi Rivers and Gulf of Mexico). Previous researchers following commonly accepted geomorphology paradigm rules have not explained how most, if any of these mountain passes originated. A recently proposed geomorphology paradigm requires all Missouri River drainage basin valleys to have eroded headward across massive south- and southeast-oriented floods, which implies south- and southeast-oriented floods flowed from what are today north-oriented North Platte River headwaters across the continental divide, the present-day south- and southwest-oriented Colorado River headwaters valley, and then across what is now the continental divide a second time to reach east- and southeast-oriented South Platte River headwaters. Paradigms are rules determining how a scientific discipline governs its research and by themselves are neither correct nor incorrect and are judged on their ability to explain observed evidence. From the new paradigm perspective, a stream eroded each of the passes into a rising mountain range until the uplift rate outpaced the erosion rate and forced a flow reversal in what would have been the upstream valley. The passes and the valleys leading in both directions from the continental divide are best explained if diverging and converging south- and southeast-oriented flood flow channels crossed rising mountain ranges. While explaining observed drainage patterns and erosional landforms such an interpretation requires a fundamentally different regional middle and late Cenozoic glacial and geologic history than what previous investigators using the accepted paradigm perspective have described.