Water development and associated hydrologic changes in the Platte river,Nebraska, U.S.A

Major changes in hydrologic regime and morphology of channels of the Platte River and its major tributaries, the South Platte River and North Platte River in Colorado, Wyoming, and Nebraska have occurred since about 1860, when the water resources of the basin began to be developed for agriculture, municipal, and industrial uses. The extent of this water development, which continues to increase with growth in population and land use, has affected the timing of streamflow and transport of fluvial sediment in the Platte River through diversions, reservoir storage, and increased use of groundwater. Changes in flow regime, such as increase in low-flow magnitudes and abatement of peak-flow magnitudes, have made the riverine environment conducive to vegetative growth while reducing channel scour. These factors, in turn, contribute to morphologic changes of decreased channel width and channel area and increased island formation. This paper will focus on these trends over the last several decades in the study area on the Platte River in Nebraska.     

Application and testing of a procedure to evaluate transferability of habitat suitability criteria

A procedure designed to test the transferability of habitat suitability criteria was evaluated in the Cache la Poudre River, Colorado. Habitat suitability criteria were developed for active adult and juvenile rainbow trout in the South Platte River, Colorado. These criteria were tested by comparing microhabitat use predicted from the criteria with observed microhabitat use by adult rainbow trout in the Cache la Poudre River. A one-sided X² test, using counts of occupied and unoccupied cells in each suitability classification, was used to test for non-random selection for optimum habitat use over usable habitat and for suitable over unsuitable habitat. Criteria for adult rainbow trout were judged to be transferable to the Cache la Poudre River, but juvenile criteria (applied to adults) were not transferable. Random subsampling of occupied and unoccupied cells was conducted to determine the effect of sample size on the reliability of the test procedure. The incidence of type I and type II errors increased rapidly as the sample size was reduced below 55 occupied and 200 unoccupied cells. Recommended modifications to the procedure included the adoption of a systematic or randomized sampling design and direct measurement of microhabitat variables. With these modifications, the procedure is economical, simple and reliable. Use of the procedure as a quality assurance device in routine applications of the instream flow incremental methodology was encouraged.     

The hydroclimate niche: A tool for predicting and managing riparian plant community responses to streamflow seasonality

Habitat suitability is a consequence of interacting environmental factors. In riparian ecosystems, suitable plant habitat is influenced by interactions between stream hydrology and climate, hereafter referred to as “hydroclimate”. We tested the hypothesis that hydroclimate variables would improve the fit of ecological niche models for a suite of riparian species using occurrence data from the western United States. We focus on the climate conditions (temperature, precipitation and vapor pressure deficit) during the months of lowest and highest streamflow as integrative hydroclimate metrics of resource and stress levels. We found that the inclusion of hydroclimate variables improved model fit for all species in the western USA dataset. We then tested the utility of the improved habitat suitability models by projecting them onto a regulated segment of the Colorado River to assess potential impacts of streamflow seasonality on vegetation metrics of management concern. Species frequency derived from independent survey data in the Colorado River segment was significantly higher for species with predicted suitable habitat than for species without predicted suitable habitat. Under different simulated hydrographs for the Colorado River, overall species richness was predicted to be greatest with peak streamflows during summer, and native-to-non-native species ratios were predicted to be greatest with lowest streamflows in winter. Summer high flows were particularly associated with higher predicted habitat suitability for species that have increased in cover over recent decades (e.g., Pluchea sericea, Baccharis species). We conclude that hydroclimate covariates can be useful tools for predicting how riparian vegetation communities respond to changes in the seasonal timing of low and high streamflows.     

Equilibrium response of riparian vegetation to flow regulation in the Platte river,Nebraska

The Platte River in central Nebraska responded to water development by rapid channel narrowing and expansion of native riparian woodland. Woodland expanded most rapidly in the 1930s and 1950s; open channel and woodland area stabilized in the 1960s and have remained stable for most reaches into the mid-1990s, despite relatively low flows and infrequent peak flows in the past decade. Open channel area may have been maintained or increased under recent lower flows because of increased erodibility of the floodplain as it has aggraded, developed vertical banks and as its woodland vegetation has become older, sparser and less protective of banks. One section of the Platte River, near Grand Island, has disequilibrated in the past decade by undergoing a 10% loss of channel area. The reach occurs below an area where vegetation has been removed to increase open channel area for migrating whooping and sandhill cranes and other water birds. Vegetation clearing may have liberated excess sediment, locally aggraded the channel and stimulated tree and shrub recruitment. This management practice needs to be examined before it is used more widely in the Platte River. © 1997 John Wiley & Sons, Ltd.     

Thermal regime suitability: Assessment of upstream range restoration potential for Colorado pikeminnow,a warmwater endangered fish

Dams have reduced distribution of the endangered Colorado pikeminnow Ptychocheilus lucius in the upper Colorado River basin: low‐head diversion dams blocked upstream passage and large dams inundated free‐flowing segments and cooled downstream reaches with deep‐water releases. To date, range restoration efforts in the Colorado and Gunnison Rivers have focused on building fish ladders around diversion dams to allow recolonization of upstream reaches. Upstream thermal suitability for this warmwater cyprinid was assessed using temperature data and existing distributional information from river reaches where Colorado pikeminnow movements were unrestricted. Among‐site thermal regime comparisons were made using mean annual thermal units (ATU), derived from mean daily temperatures during 1986–2005 and the relation between temperature and Colorado pikeminnow growth. Upstream distributional limits in the Yampa and Gunnison Rivers occurred where in‐channel thermal regimes fell below a long‐term mean of 47–50 ATU, suggesting that two Colorado River fish ladders will make available an estimated 17 km of thermally suitable habitat. A Gunnison River fish ladder successfully re‐established access to 54 km of suitable habitat, but 32 km of critical habitat upstream remains unsuitable. Suitability there could be achieved by raising temperatures only 1–2°C from late May to mid‐October with installation of a temperature control device on an upstream dam. Maximum, main‐channel, summer temperatures did not limit Colorado pikeminnow distribution in downstream reaches of the upper Colorado River. Published in 2010 by John Wiley & Sons, Ltd.     

Field evaluation of a two‐dimensional hydrodynamic model near boulders for habitat calculation

Two‐dimensional hydrodynamic models are now widely used in aquatic habitat studies. To test the sensitivity of calculated habitat outcomes to limitations of such a model and of typical field data, bathymetry, depth and velocity data were collected for three discharges in the vicinity of two large boulders in the South Platte River (Colorado) and used in the River2D model. Simulated depth and velocity were compared with observed values at 204 locations and the differences in habitat numbers produced by observed and simulated conditions were calculated. The bulk of the differences between simulated and observed depth and velocity values were found to lie within the likely error of measurement. However, the effect of flow simulation outliers on potential habitat outcomes must be considered when using 2D models for habitat simulation. Furthermore, the shape of the habitat suitability relation can influence the effects of simulation errors. Habitat relations with steep slopes in the velocity ranges found in similar study areas are expected to be sensitive to the magnitude of error found here. Comparison of habitat values derived from simulated and observed depth and velocity revealed a small tendency to under‐predict habitat values. Published in 2009 by John Wiley & Sons, Ltd.     

黄河下游河道萎缩过程中输沙能力的调整

依据河床演变学原理,根据定位观测资料分析,结合河工动床模型试验,探讨了黄河下游河道萎缩过程中的输沙能力调整关系。研究表明:黄河下游河道主河槽的输沙能力调整趋势取决于河道的萎缩模式;主河槽水流挟沙力与河槽形态的关系仍然符合一般意义下的河床过程规律;河道萎缩后,河道的排沙比减小,但排沙比与河道萎缩模式无关;河道萎缩是可以逆转的。     

汶川地震对震区河流演化的影响

5.12汶川地震,不仅直接影响灾区河流的河道,并诱发了大量崩塌、滑坡、泥石流、堰塞湖等次生山地灾害,这些山地灾害的产生和发展将对震区河流的演化产生深远影响。因此,对震后山区河流河道演化规律和发展趋势进行准确的分析和预测,是震区河道修复及震后恢复重建的关键。结合野外考察资料,分别从河型、纵断面、横断面3方面分析了震区河流的演化特点。分析结果表明:河床剧烈抬升引起河型游荡分汊,两岸频发的山地灾害挤压河道;高强度山洪冲刷河床及岸滩并展宽河道,泥沙的淤积也可束窄河道;河流纵断面总体淤高,但纵断面结构渐趋稳定,大石块多且上游来水来沙丰富的河段会逐渐发育成阶梯状结构,而以淤积为主的河段,由于山洪冲刷会形成下凹型纵断面,并逐渐向直线型纵断面发展。     

Quantifying Whitewater Recreation Opportunities in Cataract Canyon of the Colorado River,Utah: Aggregating Acceptable Flows and Hydrologic Data to Identify Boatable Days

The structural norm approach was combined with the Potential for Conflict Index to define recreation streamflow needs for the Colorado River in Utah and Colorado. An online survey was completed by 128 commercial and non‐commercial boaters, who evaluated a range of flows for whitewater boating. For the Cataract Canyon reach, respondents rated the quality of their recreation experience of specific flows, describing the quality of boating opportunities across the full range of historical streamflows. Ranges for both acceptable and optimum flows were defined, as well as thresholds for unacceptable flows. These ranges were then evaluated against historical hydrologic records to quantify the timing, frequency, and duration of days when defined whitewater flows exist across different year types (i.e. average boatable days). Results indicated that on average, a total of 257 boatable days existed in dry years, and 353 total boatable days occurred in dry‐typical years. In wet and wet‐typical years, 362 and 365 total boatable days respectively, occurred on average. Results of the boatable days' analysis indicated that over the 23‐year period of record, whitewater boating opportunities occurred nearly every day of the year in all but the driest year types. Results from this study provide resource managers with information which can be used in the development of annual operating plans for the Colorado River Basin and help managers understand how changes in flow impact the quality of recreational opportunities. This application demonstrates the value of analysing boatable days on any river where recreation management is a priority. Copyright © 2016 John Wiley & Sons, Ltd.     

EFFECTS OF FLOW DYNAMICS ON THE AQUATIC‐TERRESTRIAL TRANSITION ZONE (ATTZ) OF LOWER MISSOURI RIVER SANDBARS WITH IMPLICATIONS FOR SELECTED BIOTA

Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar‐specific models of discharge‐area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing‐dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota. Published in 2011 by John Wiley & Sons, Ltd.     

Sediment transport and channel characteristics of a sand-bed portion of the green river below flaming gorge dam,Utah, USA

The Green River is a major tributary of the Colorado River with a drainage area of 115 770 km² in Colorado, Utah and Wyoming. The influence of Flaming Gorge Dam on sediment transport and the potential for future channel change were studied using comparative analysis of historical aerial photographs from 1952 to 1987 and geographical information systems, published sediment (1951-86) and discharge (1965-87) records, and sediment data collected during 1986-8. Since the closure of the dam in 1964, new equilibrium channel widths were apparently achieved by 1974 in the reach 161-279 km below Flaming Gorge Reservoir and by 1981 in the reach 465-509 km below the reservoir. Recent high flows have resulted in an increase in average channel width in both reaches as measured on aerial photographs taken in 1986 and 1987. Sediment data from US Geological Survey gauges on the Green River and its primary tributaries and three sites established on the Green River for this study suggest that bed material sediment transport in the Green River has now attained a quasi-equilibrium, with the river transporting just the load supplied to it. The potential for future channel changes exists, as evidenced by the response of the channel (i.e. channel widening) to the increased flows during 1983, 1984 and 1986. Future adjustments in channel characteristics should be limited to responses to changes in discharge and sediment supply and transport in the basin.     

河床枯萎的临界阈研究

本文首先从河流地貌临界学说的观点出发, 解释了河床枯萎的概念. 然后, 以黄河下游近期河床演变特性为例, 阐释了河床枯萎的机理以及由此带来的"小水大灾"效应, 研究了造床流量、河相关系在新的水沙条件下的变化规律, 提出了枯萎造床流量的概念. 最后, 运用河道水沙数学模型, 初步探求了黄河下游河道萎缩的外部临界阈值.     

黄河下游单向缩窄典型河道泥沙冲淤特性研究

本文选择黄河下游裴峪至官庄峪典型束窄河段为研究对象，以丁坝缩窄河道方式，通过控制水流强度、缩窄水流位置、相对缩窄尺度和边界条件等四个主要因素，进行不同缩窄尺度的动床模型试验。试验结果表明：水沙运动要素变化受相对缩窄尺度、缩窄位置和边界条件影响较大；随着相对缩窄尺度的增大，在洪水位条件下主河槽冲刷量和滩地淤积量逐渐增大，主槽范围相应扩大，其高程普遍呈下降趋势，特别是缩窄断面导流堤顶端部位出现明显的局部冲刷坑，束水冲沙、增大输沙能力的效果明显；当相对缩窄尺度B1/B大于0.50时，主流线位移、断面流速和河床冲淤的相对变化速率明显增大，这些研究成果的取得将对治黄工程具有一定的指导意义。     

Modelling changes in trout habitat following stream restoration

Stream restoration was implemented on the Upper Arkansas River near Leadville, Colorado, to improve brown trout (Salmo trutta) populations. Metals pollution and channel disturbance associated with historic mining, land use, and water development degraded aquatic and riparian habitat. Changes in instream habitat quality following restoration were investigated with a before–after–control–impact study design. Baseline, as‐built, and effectiveness surveys were conducted in 2013, 2014, and 2016, respectively. Two‐dimensional hydrodynamic modelling with River2D was used to estimate weighted usable area (WUA) for adult, juvenile, fry, and spawning brown trout across a range of flows. WUA was calculated from habitat suitability curves for velocity, depth, and channel substrate. Foraging positions (FP) and habitat heterogeneity were also evaluated as indices of habitat quality. All results were analysed with analysis of variance. At impact sites, WUA increased by 12.2% from 2013 to 2014 but decreased by 10.2% from 2014 to 2016, whereas FP increased by 24.8% from 2013 to 2014 but decreased by 26.1% from 2014 to 2016. Spawning habitat increased 53.3% from 2014 to 2016 at impact sites. The 15.4% increase in depth variability from 2013 to 2016 indicates that habitat heterogeneity was enhanced at impact sites. No changes in WUA, FP, or habitat heterogeneity were observed at control sites. Although changes in WUA and FP suggest that initial habitat improvements were not sustained, increased spawning habitat and depth heterogeneity suggest otherwise. Our results highlight the value of monitoring strategies that utilize multiple lines of evidence to evaluate restoration effectiveness, inform adaptive management, and improve restoration practices.     

Application of airborne multispectral digital imagery to quantify riverine habitats at different base flows

We employed an integrated system of airborne remote sensing and ground surveys for regional mapping of instream habitats under variable flows over a 70 km section of the Lower Yakima River in southern Washington, USA. Airborne multispectral digital imagery was obtained in conjunction with field survey measurements and used to quantify the spatial extent, condition and temporal changes of selected river habitat characteristics under two different flows (14 and 28 m³ s^?1). Under each flow, geomorphic measures were quantified (e.g. channel complexity, number and size of habitats). Water depth and velocity were also classified for instream habitats, and temperature and turbidity were recorded. Remote sensing classification accuracies for islands, exposed rocks and water surfaces were greater than 99%, while more detailed depth/flow classifications were less accurate (68% and 72%, for the high and low flows, respectively). While high turbidity (>4 Nephelometric Turbidity Units (NTU)), shadows and bidirectional reflectance factor reduced classification accuracies, the overall effect of these factors was minimal. Under the low‐flow situation, off‐channel habitats were less abundant, more isolated and had shallower depths and warmer temperatures. Our analysis suggests that airborne multispectral imagery, coupled with appropriate ground truth data, can be a viable method for regional mapping of diverse riverine habitats under variable flows. We concluded from this analysis that the higher flow situation provided substantially better habitat than currently exists in the Lower Yakima River. Copyright © 2002 John Wiley & Sons, Ltd.     

黄河下游丁坝缩窄河道泥沙冲淤特性试验研究

通过动床模型试验研究了黄河下游裴峪至官庄峪丁坝缩窄河段,在河道不同位置布设丁坝,不同情况下丁坝相对长度(丁坝长度与原河道宽度之比值)对河道泥沙冲淤变化的影响。结果表明：水沙运动要素变化受丁坝布设位置和长度等影响较大,随着丁坝相对长度的增加,汛期主河槽冲刷量和滩地淤积量逐渐增大,主槽范围相应扩大,其高程普遍呈下降趋势,特别是缩窄断面导流堤顶端部位出现明显的局部冲刷坑,束水冲沙、增大输沙能力的效果明显。当丁坝相对长度大于0.50时,主流线偏移、断面流速分布和河床冲淤的变化速率明显增大,不利于河道稳定。     

Response of sandhill crane (Grus canadensis) riverine roosting habitat to changes in stage and sandbar morphology

Over the past century, flow regulation and vegetation encroachment have reduced active channel widths along the central Platte River, Nebraska. During the last two decades, an annual program of in‐channel vegetation management has been implemented to stabilize or expand active channel widths. Vegetation management practices are intended to enhance riverine habitats which include nocturnal roosting habitat for sandhill cranes. Evaluating the success of other management treatments such as streamflow modification requires an understanding of how flow shapes the sandbars in the river and how sandbar morphology interacts with flow to create crane habitat. These linkages were investigated along a 1‐km managed river reach by comparing the spatial pattern of riverine roosts and emergent sandbars identified with aerial infrared imagery to variables computed with a two‐dimensional hydraulic model. Nocturnal observations made multiple years showed that the area and patterns of riverine roosts and emergent sandbars and the densities of cranes within roosts changed with stage. Despite sandbar vegetation management, low flows were concentrated into incised channels rather than spread out over broad sandbars. The flow model was used to compute hydraulic variables for identical streamflows through two sandbar morphologies; one following a period of relatively high flow and the other following the low‐flow period. Compared with the simulation using the morphology from the antecedent high flow, the simulation using the morphology from the antecedent low flow produced a smaller quantity of available wetted area. These remote‐sensing observations and hydraulic simulations illustrate the importance of considering flow history when designing streamflows to manage in‐channel habitat for cranes. Published in 2008 by John Wiley & Sons, Ltd.     

黄河下游宽河段漫滩洪水作用初析

通过实测资料分析,阐明黄河下游宽河道在持续萎缩的情况下漫滩洪水仍具有较强的淤滩刷槽的行洪特点,指出漫滩洪水造成的滩地淤积主要来自于滩槽水流泥沙的横向交换。通过2002年的调水调沙试验,验证了漫滩洪水可有效增加平滩流量的认识,建议在下游泥沙还没有得到有效控制的情况下允许洪水在一定范围内漫滩,这样从长远来看对防洪是有利的。     

荆江河段崩岸机理及多尺度模拟方法

三峡工程运用后,进入荆江河段的水沙条件大幅度改变,导致近期崩岸频繁发生,影响局部河段的河势稳定及河道防洪安全。荆江段河岸组成一般为上层黏性土、下层沙土的二元结构,在近岸水流冲刷及河道水位涨落过程中受多种因素作用而发生崩塌。以往崩岸模拟考虑因素少,且相关参数难以量化确定。将河流动力学与土力学结合,提出了荆江段河岸土体物理特性与抗剪、抗冲及抗拉强度三大力学特性的量化指标,建立了上、下荆江二元结构河岸稳定性的计算方法,揭示了坡脚冲刷、潜水位变化等因素对岸坡稳定性的影响;提出了河岸崩退过程的多尺度模拟方法,将崩岸力学模型与水沙数学模型耦合,不仅能模拟河道内水沙输移及床面冲淤过程,而且还能模拟不同二元结构河岸的崩退过程。将建立的模型应用于荆江河段典型断面、长河段及局部河段的崩岸过程模拟,计算结果与实测值总体符合较好。提出的多尺度模拟方法为荆江崩岸预测提供了理论与技术基础。     

An investigation of marginal habitat and macrophyte community enhancement on the River Torne,UK

During floodbank raising work as part of a major capital flood defence scheme on the River Torne between 1985 and 1990, selected reaches of the main trapezoidal channel were enhanced. By winning spoil from the channel margins and from borrow pits in the floodplain, a more varied marginal zone was created which maximised the potential habitat for wetland plant communities and their associated fauna. Enhancement comprised bank re‐profiling to create narrow wetland shelves (berms), shallow bays, channel margins of varying shape and depth and linear still ponds from the borrow pits. The 1990 planting programme comprised 11 macrophyte species and a total of 7740 individual plants. This paper reports on an initial study to evaluate the marginal habitat enhancements on the River Torne 5 years after completion of the project. Lack of pre‐scheme data necessitated a space‐time substitution; enhanced river margins were compared with neighbouring reaches that had undergone conventional floodbank repair and remained as trapezoidal channel sections planted with a standard, low maintenance seed mix. Marginal vegetation was surveyed and supported by measurements of the physical habitat at 10 enhanced and 10 conventionally‐engineered reaches. The macrophyte surveys and the results from the cluster analysis and polar ordination indicate that enhanced and conventionally‐engineered reaches are floristically distinct and that the enhanced reaches have a more varied macrophyte community. The results from the Mann–Whitney U‐tests show that enhanced reaches have significantly higher values of wetland species diversity and equitability, percentage of wetland species, bank width and soil moisture and significantly lower bank angles. However, the correlation and linear regression analyses did not show any strong associations between the physical habitat and plant parameters. Copyright © 2000 John Wiley & Sons, Ltd.