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Precise estimation of flow conveyance in a two-stage open channel with vegetated floodplains is a key prerequisite to the management of the river ecosystem and the creation of flood retention space. The presence of vegetation alters the structure of water flow and affects the discharge in a two-stage channel. Nevertheless, the effect of vegetation on flow conveyance is not studied separately in the previous flow discharge research. By conducting force analysis in a control volume with considering the vegetation drag force and quantifying the energy loss caused by vegetation blocking effect and the transverse velocity gradient, this paper proposes a new method to estimate flow conveyance in compound channel covered with vegetation based on the relationship which is the total energy loss is balanced by the total energy supplied by the local flow. Experimental data series are collected to verify the new method by comparing the measured and estimated discharges and it presents a good accuracy with 2.47% relative error. The new method is also compared with the other methods, which quantify the additional resistance of vegetation by using the equivalent Manning’s roughness coefficient. The results indicate that both the vegetation drag force and the equivalent Manning’s roughness coefficient can be used in flow conveyance estimation and dominantly influence the accuracy of the predictive method so that they need to be properly quantified and calibrated. And adopting the vegetation drag force is suggested here for the simplicity of calculation.

This paper presents a study of the monitorization of the conveyance system of the collective water network in the framework of the Lis Valley Water Management Operational Group, aiming the improvement of water management by the Water Users’ Association. The methodology considered the measurement of water allocation to main canals, its distribution throughout the conveyance system, and the on-farm irrigation demand. This paper presents the results of Canal 2, for 2019 and 2020 irrigation seasons. This canal supplies an area of 410 ha, is gravity-fed from Lis river, on the Arrabalde weir, in Leiria, and has a pumping recharge during the irrigation peak period. A water balance of supply and irrigation demand was carried out at 10-day period, to evaluate the performance of the distribution water management. The analyzed system reveals the specificity of the drainage water reuse, which leads to a more flexible management of water allocated by gravity-fed, and rational of pumping supply, in order to adjust it to irrigation demand, through energy consumption. Results point to actions that prioritize consolidating the improvement management of water resources, like the implementation of optimal operational plans to adjust the water demand with distribution, accompanied with the improvement of the on-farm irrigation systems.

International audience; The drag reduction method using polymer additives is a common strategy to minimize friction losses when carrying fluids (water, oil, or slurries) in pipes over long distances. Previous studies showed that the interactions between the polymer and turbulent structures of the flow tend to modify the streamwise velocity profile close to the walls by adding a so-called elastic sublayer between the classical viscous and log layers. The gain in linear head losses can reach up to 80% depending on the roughness of the walls and the concentration of polymers. The application of this technique to sewers and the subsequent gain in discharge capacity motivated this work to quantitatively measure the drag reduction in classical open-channel flows. Three measurement campaigns were performed in a dedicated long flume for several water discharges and several polymer concentrations: backwater curves over smooth and rough channel walls (including velocity and turbulent shear-stress profiles) and flows around emerging obstacles. The addition of polymers, even in limited concentrations, allowed a high friction decrease with the typical Darcy-Weisbach coefficient reduced by factors of 2 and 1.5, respectively, in smooth and rough walls configurations without obstacles, but without strong modifications of the nondimensional velocity profiles. In contrast, when adding emerging obstacles, the flow was unaffected by the inclusion of polymers, in agreement with the prediction of the literature. The drag reduction method by addition of small concentrations of polymers thus appears to be a promising technique to increase flow conveyance in open-channel flows.

In this work, surface/interface effects for pull-in voltage and viscous fluid velocity effects on dimensionless natural frequency (DNF) of fluid-conveying multi walled piezoelectric nanoresonator (FC-MWPENS) based on cylindrical nanoshell is investigated using the Gurtin–Murdoch surface/interface theory. The nano-sensor is embedded in viscoelastic foundation, nonlinear van der Waals and electrostatic forces. Hamilton’s principle is used for deriving of the governing equations and boundary conditions and also the assumed mode method is used for changing the partial differential equations into ordinary differential equation. The influences of the surface/interface effect such as Lame’s constants, residual stress, piezoelectric constants and mass density are considered for analysis of dimensionless natural frequency respect to viscous fluid velocity and pull-in voltage of FC-MWPENS.

As it is known, vegetation is an important component of aquatic ecosystems. Because of the variety of species and, thus, of the characteristics of the vegetation elements (form, size, stiffness, etc.), it is difficult to develop a widely applicable method to predict mean flow and flow resistance. Despite the intense activity research, much work has to be done in understanding hydrodynamics in vegetated channels. This is important to analyse many physical processes involved in the ecosystem at different spatial and time scales. In this paper, attention is restricted to flexible vegetation. After a brief description of results obtained in previous experimental works conducted in a rectangular laboratory flume at the Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali – University of Palermo (Italy), the data are used to investigate how stems' concentration and flow submergence affect the mean flow and flow conveyance characteristics in vegetated channels. The results indicate that both these parameters affect the flow profile and flow conveyance characteristics, but flow submergence especially influences the dominant mechanism of momentum exchange between the vegetation layer and the layer above it.

The 1999 jokulhlaup at Solheimajokull was the first major flood to be routed through the proglacial system in over 600 years. This study reconstructed the flood using hydrodynamic, sediment transport and morphodynamic numerical modelling informed by field surveys, aerial photograph and digital elevation model analysis. Total modelled sediment transport was 469 800 m3 (+/- 20%). Maximum erosion of 8.2 m occurred along the ice margin. Modelled net landscape change was –86 400 m3 (+/- 40%) resulting from –275 400 m3 (+/- 20%) proglacial erosion and 194 400 m3 (+/- 20%) proglacial deposition. Peak erosion rate and peak deposition rate were 650 m3 s-1 (+/- 20%) and 595 m3 s-1 (+/- 20%), respectively, and coincided with peak discharge of water at 1.5 h after flood initiation. The pattern of bed elevation change during the rising limb suggested widespread activation of the bed, whereas more organisation, perhaps primitive bedform development, occurred during the falling limb. Contrary to simplistic conceptual models, deposition occurred on the rising stage and erosion occurred on the falling limb. Comparison of the morphodynamic results with a hydrodynamic simulation illustrated effects of sediment transport and bed elevation change on flow conveyance. The morphodynamic model advanced flood arrival and peak discharge timings by 100% and 19%, respectively. However, peak flow depth and peak flow velocity were not significantly affected. We suggest that morphodynamic processes not only increase flow mass and momentum but that they also introduce a feedback process whereby flood conveyance becomes more efficient via erosion of minor bed protrusions and deposition that infills or subdues minor bed hollows. A major implication of this study is that reconstructions of outburst floods that ignore sediment transport, such as those used in interpretation of long-term hydrological record and flood risk assessments, may need considerable refinement. Copyright © 2015 John Wiley & Sons, Ltd.

In-stream and riparian vegetation may significantly affect flow and sediment transport in vegetated channels. A hydraulic model has been developed in this paper to compute the flow discharge in channels with rigid and flexible vegetation under emergent and submerged conditions. An empirical formula has also been presented to determine the bed-load discharge in vegetated channels. The model has been tested against experimental and field data available in the literature. The computed flow discharge and bed-load transport rate agree well with the measured data.

Grass swales, originally used for erosion control in agricultural settings, are now widely employed in urban environments as an effective best management practice for controlling pollutants in stormwater runoff. In particular, vegetated swales are quite successful in removing heavy metal concentrations when the depth of flow is small relative to grass height. However, guidance materials currently available for design of vegetated channels focus on larger depths of flow (large flow conveyance/erosion control), and for such conditions the hydraulic resistance exerted by the vegetation can be significantly different than that observed when the depth of flow is small (remediation). Utilizing a series of laboratory channels, small-flow retardance curves have been developed in the present work for Bluegrass, Centipede, and Zoysia grass species. These “small-flow” curves extend the well-known Stillwater n versus VR diagram by approximately 1 order of magnitude, to smaller values of VR . Experimental results shou...

A low-lying part of the Croatian capital, Zagreb, is exposed to flood risk from the Sava River. The biggest flood to data, with catastrophic consequences, occurred on 26 November 1964. To protect Zagreb from the Sava River floods, a flood control system was built and set in operation at the end of 1978. The Sava River's flood response changed over time as a result of this constructed system, as well as other anthropogenic and natural influences. The series of maximum annual Sava River stages and discharges measured at the Zagreb gauging station from 1926 to 2004 were analysed. Hydrological methods were used in order to assess Zagreb safety from the Sava River floods in the new conditions. This paper detects changes in high water occurrence in the Sava River near Zagreb. Long-term stages and linear trends in discharges were examined. A simple technique for the conversion of stages to actual river channel morphology conditions was used. The technique presented in this paper enabled the recalculation of flood probabilities. It is stressed that for a complete understanding of floods, an examination should include the study of parameters of both maximum stages and maximum discharges.

최근 급속한 도시화로 인한 유역 내 불투수 면적의 증가는 자연유역에 비해 짧은 도달시간과 높은 첨두 홍수량을 유발하여 도시홍수 피해의 원인이 되고 있다. 따라서 홍수피해를 저감시키고자 구조물적 또는 비구조물적 홍수방어 대책들을 마련하여 시행하고 있다. 본 연구의 대상유역인 굴포천 유역은 유역 내의 유출 특성이 아닌 하류의 한강 외수위 조건에 의해 잦은 침수 피해가 발생하고 있으며, 이를 예방하고자 폭 20m의 임시 방수로를 폭 80m로 확장할 예정이다. 이에 따라 본 연구에서는 대표적인 도시 유출 모형의 하나인 EPA의 SWMM 모형을 근간으로 하는 XP-SWMM모형을 이용해 굴포천 방수로 확장에 따른 홍수소통능력을 분석하였다. 재현기간 100년인 설계 강우와 동일한 조위 조건 하에서 개수전과 후에 대한 수위와 유량을 비교하였으며, 분석결과 개수전 상황이 개수후에 비해 통과 유량이 1/3임에도 불구하고 비슷하거나 더 높은 수위를 나타내었다. 또한 개수후 상태에서 모의한 결과 방수로 분기점에서 자연 분류시킬 경우 최고 $300m^3/sec$ 가까운 유량이 방수로 방향으로 역류함을 확인할 수 있었다. 따라서 방수로의 안정적 운영을 위해서는 굴포천 하류로부터 방수로로의 역류를 차단하기 위한 수리 시설물의 설치가 필요함을 확인할 수 있었다. 【In recent, increasing of the impervious area gives rise to short concentration time and high peak discharge comparing with natural watershed and it is a cause of urban flood damage. Therefore, we have performed for structural and non-structural plans to reduce the damage from inundation. The Gulpo-cheon basin had been frequently inundated and damaged due to the water level of Han river. So, the Gulpo-cheon floodway was constructed with 20 meters width for flood control in the basin but it was not enough for our expectation and now we have a plan to expand the floodway to 80 meters. We use a XP-SWMM model developed based on EPA-SWMM version for analyzing the capacity of flood conveyance by the expansion of Gulpo-cheon floodway with the same 100 years return period design storm and the same tidal conditions of the Yellow sea. The flood conveyance after the expansion of floodway becomes three times comparing it with before the expansion. Also we simulate the flood discharge at the diversion point of Gulpo-cheon for the expanded condition of floodway and know that the discharge of about 300 m3/sec is flowing backward to the expanded floodway. Therefore we may need some kinds of hydraulic structures to prevent the back water.】

By using the electrical resistivity Wenner configuration, 22 sounding points were used to study the shallow subsurface geology along a proposed pass for construction of a flow convergence system in a part of Alexandria, Egypt. The study indicated that no abnormal hidden subsurface objects are present to prevent completion of the project. Lateral inhomogeneities are detected by differences in resistivity values. Some saturated limestone layers also are detected. The associated water may hinder the drilling activities. The geophysical data correlate with the results obtained from nearby boreholes.

Measurements were undertaken along a 460-m long portion of the Nashwaak River, N.B., in order to study the flow conveyance characteristics of a regional watercourse during ice-cover and open-water conditions. Elevations of the water surface under both conditions were obtained at five cross sections for varying water levels and discharges. Various difficulties experienced in defining the cross-sectional area of the flow section, determining the influence of slush and anchor ice on the slope, and the roughness characteristics of the undersurface of the ice cover are described in order to provide a perspective on some commonly encountered problems.

Macrophytes (aquatic vegetation) are known to modify river flow by reducing local velocities, increasing turbulence generation, and reducing channel conveyance capacity resulting in increased flow depth. Understanding flow response to vegetation change is imperative to inform flood mitigation strategies, however the field is nascent with much uncertainty surrounding the estimation of flow conveyance in vegetated channels and, subsequently, the best vegetation management practices and possible flood risk. Therefore, in order to develop an understanding of how macrophytes modify flow conveyance modelling techniques must be developed which can effectively represent the three-dimensional effect of natural vegetation within an open channel flow environment. This study simulated vegetation-flow interaction using a 3D finite-element modelling method to investigate the feasibility to which a vegetated natural gravel-bed river can be represented using the drag-force approach. Two methods of parameterising vegetation-induced drag were explored to investigate the effect of flow behaviour within a vegetated gravel-bed river reach.

Watershed urbanization can increase flashiness of flood peaks, increase magnitudes of floods (due to increased impervious area), and alter sediment transport dynamics in stream channels. In addition, flood control infrastructure confines increased flood peaks within artificially narrow corridors. Together, these alterations to urban and urbanizing streams have resulted in channel incision and disconnection of channels from floodplains. One form of stream restoration that has developed largely in urban watersheds has been the construction of compound channels. In the compound channel restoration approach, incised and / or confined channels are replaced with wider compound channels that have a “functional floodplain” (i.e. a flat, depositional surface that is inundated by high flows) adjacent to a “low flow channel” (i.e. an open water channel that is regularly reorganized by peak flows and is allowed to change with succession of aquatic and riparian vegetation). The primary objectives of these projects have been to maintain or improve high flow conveyance and restore floodplain functions that allow complex aquatic and riparian habitat to develop and persist, thereby improving geomorphic and ecological conditions. Recent compound channel projects on Tassajara Creek (2001), in an urbanizing area of Alameda County, CA, and lower Silver Creek (2003), in a fully urbanized area of Santa Clara County, CA illustrate successes, failures, and lessons learned from this increasingly applied approach to multi-objective stream restoration and flood management. We conducted post project appraisals (PPAs) of these two projects by analyzing design documents, design drawings, as-built surveys, available physical and ecological data from past monitoring and modeling activities, and new monitoring and modeling data conducted for this study to systematically assess performance with respect to geomorphic, ecological, and high flow conveyance objectives shared by these two projects. In 2006, both projects had successfully met high flow conveyance objectives. Both projects also improved geomorphic and ecological conditions relative to pre-project conditions. However, performance with respect to geomorphic and ecological objectives varied both within and between projects. In general, we documented better performance with respect to geomorphic and ecological objectives for the Tassajara Creek project, primarily due to greater land availability for the project than in the fully urbanized lower Silver Creek project area. We also determined that the elevation of the functional floodplain above the low flow channel bed and the width of the functional floodplain relative to the low flow channel width influenced performance of these compound channel projects with respect to geomorphic and ecological objectives.

Flooding is the deadliest and most costly natural hazard on the planet, affecting societies across the globe. Nearly one billion people are exposed to the risk of flooding in their lifetimes and around 300 million are impacted by floods in any given year. The impacts on individuals and societies are extreme: each year there are over 6,000 fatalities and economic losses exceed US$60 billion. Moreover, these problems will become much worse in the future: There is now clear consensus that climate change will, in many parts of the globe, cause substantial increases in the frequency of occurrence of extreme rainfall events, which in turn will generate increases in peak flood flows and flood increased areas of land.Faced with this pressing global challenge, reliable tools are required to predict how flood hazard and exposure will change in the future. Existing state-of-the-art Global Flood Models (GFMs) are now widely used to simulate the probability of flooding across the Earth, but in some instances the predictive ability of current models is constrained by a fundamental limitation. Specifically, current GFMs treat rivers and their floodplains essentially as 'static pipes' that remain unchanged over time. In reality, river channels evolve through processes of erosion and sedimentation, driven by the impacts of diverse environmental changes (e.g., climate and land use change, dam construction), which lead to changes in channel flow conveyance capacity and floodplain connectivity.In this paper we demonstrate the extent to which flood model predictions of flood inundation are sensitive to altered representations of channel morphology, across large spatial scales. In our GFM the channel bathymetry is inverted from bank elevation given an assumption of bankfull discharge (typically 1 in 2 year). By changing the bankfull discharge and recomputing the bathymetry it is therefore possible to simulate the impact of conveyance changes, driven by channel erosion and sedimentation, on flood hazard. Here we conducted a suite of simulations for test sites within the Mississippi River basin, at which long term change or variability in bankfull conveyance have been constrained by direct observations at gauging stations. Our results clearly indicate that in-channel changes are significant in driving altered flood hazard. It follows that until GFMs are able to fully account for morphological changes predicting the evolution of future flood hazard, understanding its underlying causes, or quantifying associated uncertainties, will remain very challenging.

The transport and accumulation of driftwood or large woody debris (LWD) in mountain streams is a natural part of catchment health and river connectivity. At hydraulic structures, the presence of LWD may impact flow efficiency and influence upstream water depth. LWD has been studied at a variety of spillways and weir types, however, little is known about its interaction at rock weirs. This study investigated factors affecting the passage of individual LWD elements and any LWD accumulations at rock weirs, as well as potential impacts upstream of LWD accumulations through field-informed scaled model testing. Observations of LWD at rock weirs located on the Blacksmith Fork River, a mountain stream located in Utah, USA, were used to replicate I- and V-shaped rock weirs in a large flume. The river response to rock weirs on the corresponding section of the Blacksmith Fork River was also investigated using historic aerial imagery and field data. Approaches to LWD management typically prioritize either natural processes or hydraulic structure safety and flow conveyance. A new hybrid approach should consider both aspects for rock weirs in mountain streams.

Flow control programs on regulated rivers can improve winter flow conveyance for hydropower operations. On the Upper Nelson River, station flows at Jenpeg Generating Station are reduced du...

In this study an urban stream network with earthen and concreted sections were studied for different seasons (wet and dry) to investigate the macroinvertebrate composition and the governing factors. The factors considered were water quality (nitrogen species, soluble reactive phosphorus etc.) and stream eco-hydraulics (velocity, wetted depth and width, vegetative indicators, number of mesoscale physical habitats, etc.). In contrast to common perception, results showed that concrete lined sites are not ecologically dead. Even though low, concrete line section had viable populations of macroinvertebrates and importantly a few native species. Interestingly, some macroinvertebrate indices of the concrete lined sites did not show a significant difference with the earthen sites. About 60% of the macroinvertebrates were grazers and filterers, and these two group populations always showed an inverse relationship. Earthen and concrete lined sites had similar diversities, but for different reasons. In general earthen sites diversity and pollution tolerance index of macroinvertebrates (PTI) was positively correlated, but no uniform correlation was observed in concrete lined sites. Some concrete lined sites with high diversity showed low PTIs (i.e. high diversity as a result of many types of pollution tolerant species) whereas in some the high diversity associated with high PTIs. Macroinvertebrate composition and the influencing factors were to a greater degree section dependent and to a lesser extent were dependent on the season. Physical heterogeneity played an important role in the macroinvertebrate responses in earthen sites. Water quality and flow rate explained comprehensively, the variations in the concrete lined sites. Results proved that nutrient levels need to be limited and instream heterogeneity needs to be improved to enhance diversity and populations of pollution intolerant species. Also, controlled vegetation harvesting is recommended in contrast to the current practice of complete removal for flow conveyance.

A high-quality parameter set is essential for reliable stormwater models. Model performance can be improved by optimizing initial parameter estimates. Parameter sensitivity analysis is a robust way to distinguish the influence of parameters on model output and efficiently target the most important parameters to modify. This study evaluates efficient construction of a sewershed model using relatively low-resolution (e.g., 30 meter DEM) data and explores model sensitivity to parameters and regional characteristics using the EPA’s Storm Water Management Model (SWMM). A SWMM model was developed for a sewershed in the City of Pittsburgh, where stormwater management is a critical concern. We assumed uniform or log-normal distributions for parameters and used Monte Carlo simulations to explore and rank the influence of parameters on predicted surface runoff, peak flow, maximum pipe flow and model performance, as measured using the Nash–Sutcliffe efficiency metric. By using the Thiessen polygon approach for sub-catchment delineations, we substantially simplified the parameterization of the areas and hydraulic parameters. Despite this simplification, our approach provided good agreement with monitored pipe flow (Nash–Sutcliffe efficiency: 0.41 – 0.85). Total runoff and peak flow were very sensitive to the model discretization. The size of the polygons (modeled subcatchment areas) and imperviousness had the most influence on both outputs. The imperviousness, infiltration and Manning’s roughness (in the pervious area) contributed strongly to the Nash-Sutcliffe efficiency (70%), as did pipe geometric parameters (92%). Parameter rank sets were compared by using kappa statistics between any two model elements to identify generalities. Within our relatively large (9.7 km^2) sewershed, optimizing parameters for the highly impervious (>50%) areas and larger pipes lower in the network contributed most to improving Nash–Sutcliffe efficiency. The geometric parameters influence the water quantity distribution and flow conveyance, while imperviousness determines the subcatchment subdivision and influences surface water generation. Application of the Thiessen polygon approach can simplify the construction of large-scale urban storm water models, but the model is sensitive to the sewer network configuration and care must be taken in parameterizing areas (polygons) with heterogenous land uses.

Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity.

Rivers are frequently relocated into new artificial channels because of mining activity. Current mine closure criteria do not adequately address river diversion practices causing an absence of guidelines and management of river diversion channels post-mining. During mine operation, river diversion channels are designed to convey large floods with an emphasis on channel stability and effective flow conveyance. After mine closure, it is now important for river diversion channels to behave more like a natural river system and imitate the characteristics of surrounding watercourses. Developing adequate closure criteria for river diversion channels is both a geomorphic and river restoration challenge. River diversion channels frequently perform poorly by creating problems during mine operation and can cause subsequent long-term legacy issues. This paper identifies the geomorphic and environmental issues of defining and implementing mine closure criteria for river diversion channels and suggests ways to improve current practices. Significant difficulties include the competing objectives of short-term channel stability and the long-term inclusion of environmentally favourable natural features, the difficulties of adequate hydrological prediction, limited understanding of regionally appropriate river characteristics and competing objectives from varied stakeholders. Effective river diversion closure criteria should include extensive hydrological, geomorphic, and ecological planning with long-term guidelines established early in the mine planning process. Lastly, river diversion closure criteria should undergo continuous revision as our understanding of river restoration develops.

Hydropower infrastructure systems are complex, high consequence structures which must be operated safely to avoid catastrophic impacts to human life, the environment and the economy. Dam safety practitioners must have an in-depth understanding of how these systems function under various operating conditions in order to ensure the appropriate measures are taken to reduce system vulnerability. Simulation of system operating conditions allows modelers to investigate system performance from the beginning of an undesirable event to full system recovery. System dynamics simulation facilitates the modelling of dynamic interactions among complex arrangements of system components, providing outputs of system performance that can be used to quantify safety. This paper presents the framework for a modelling approach that can be used to simulate a range of potential operating conditions for a hydropower infrastructure system. Details of the generic hydropower infrastructure system simulation model are provided. A case study is used to evaluate system outcomes in response to a particular earthquake scenario, with two system safety performance measures shown. Results indicate that the simulation model is able to estimate potential measures of system safety which relate to flow conveyance and flow retention. A comparison of operational and upgrade strategies is shown to demonstrate the utility of the model for comparing various operational response strategies, capital upgrade alternatives and maintenance regimes. Results show that seismic upgrades to the spillway gates provide the largest improvement in system performance for the system and scenario of interest.

Here we investigate fluid flow in 90-degree bends with and without orifice-like constrictions. The results of flow in non-constricted bends were compared with experimental results for similar Reynolds numbers and found to be in good agreement. Calculations were then carried out for various Reynolds numbers in the laminar and turbulent regimes. In addition, constrictions up to a 60% blockage were incorporated. The present study shows that the Reynolds number and the presence of an orifice-like constriction affects the velocity profile and the pressure distribution. The results indicate that if a sudden contraction is encountered, the peak velocity is larger and the flow is more predisposed to the outer wall than it otherwise would be. In addition, a sudden contraction increases the pressure loss compared to the constant-area bend and it affects the pressure distribution throughout the entire bend. This paper provides a means to predict pressure losses (similar to minor loss coefficients) in rounded bends in the presence or absence of constrictions. Such information is important to practicing engineers for designing fluid-flow conveyance systems. The behavior of the fluid is shown to be connected to the constriction and is also affected by the Reynolds number.

Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity.

Comparisons reveal that the 2.5, 10/3 and 3 order parabola-shaped channels improve flow conveyance discharges by 0.68%–7.86% and save construction costs by −0.95 to −27.99% over the common rectangular, triangular, trapezoidal sections, the extensively studied quadratic, semi-cubic and horizontal-bottom semi-cubic parabola-shaped sections. However, few researches on the critical, normal, alternate and conjugate depths, playing key roles in the design, operation and management of open channels, for these three kinds of parabola-shaped channels are available at present. Because the governing equations of normal, alternate and conjugate depths are nonlinear, so these characteristic depths cannot be solved analytically except for the critical depths. The biggest challenges in the calculation of normal depths are the nonintegrable wetted perimeters for the three kinds of parabola-shaped channels. Direct and numerical solutions for wetted perimeters are proposed based on the Gauss-Legendre six points method and the Simpson numerical integral method, respectively. Then, three direct solutions of normal depths are proposed using exact wetted perimeters based on the Simpson numerical integral method for the three kinds of channels. Subsequently, the specific energy equations are deformed into dimensionless forms. Meanwhile, analytical critical depths are skillfully utilized to obtain dimensionless specific force equations of conjugate depths. Then explicit solutions of alternate and conjugate depths have as well been proposed using iterative equations for alternate and conjugate depths based on the fixed-point iterative method by running 1stOpt software in the commonly using range of engineering. Through error analysis, the maximum relative errors of normal depths h , h ' , h ' ' ; alternate depths h c , h c ' , h c ' ' ; and conjugate (initial and sequent) depths h 1 , h 2 , h 1 ' , h 2 ' , h 1 ' ' , h 2 ' ' for 2.5, 10/3 and 3 order parabola-shaped cross-sections are only 0.34%, −0.15%, 0.001%; 0.13%, 0.12%, 0.099%; and 0.098%, −0.20%, 0.116%, −0.24%, 0.11%, 0.23% respectively. These explicit solutions of 2.5, 10/3 order parabola-shaped channels are proposed for the first time. And, explicit solutions of 3 order parabola-shaped channel have a similar range of application and higher precision than that of former studies.

Hydraulic jumps occur at the sudden transition from supercritical to subcritical flows. They are characterised by three-dimensional motions, instabilities and strong flow aeration. Due to the large energy dissipation capacity, hydraulic jumps are widely used in energy dissipators downstream of flow conveyance structures. The complexity of hydraulic jumps has fascinated researchers for centuries and numerous experimental studies provided important insights into the hydraulic jump phenomenon. However, the energy dissipation processes associated with complex three-dimensional motions and interactions of entrained air with the flow turbulence are still poorly understood due to limitations in experimental techniques. Herein, novel technologies were applied in the present study to enhance the current understanding of free-surface dynamics and three-dimensional motions inside fully aerated hydraulic jumps. Extensive experiments were conducted at the UNSW Water Research Laboratory in large-scale open channel flow facilities for fully and partially developed inflow conditions upstream of the hydraulic jumps. Distributions of air-water flow properties were measured with state-of-the-art double-tip conductivity probes identifying a strong effect of the inflow conditions on the flow aeration resulting in larger void fractions and bubble count rates for fully developed inflow conditions. World-first use of LIDAR technology in fully aerated hydraulics jumps provided the most detailed information of time-varying free-surface features and jump toe movements to date. The results highlighted the strong effect of the jump toe oscillations on the free-surface fluctuations, characteristic frequencies and turbulent scales. Unique measurements of internal three-dimensional motions in hydraulic jumps were conducted with a submerged sphere connected to a six-axis load cell. The results provided the first direct measurements of transverse and vertical motions inside hydraulic jumps highlighting the strong three-dimensionality of the internal motions and the need to consider flow processes in all directions to better understand the complex dynamics of hydraulic jumps. The combination of the new experimental results provided the most detailed picture of the dissipative flow processes inside hydraulic jumps to date. The study demonstrated that the use of advanced instrumentation can provide new insights into complex hydraulic phenomena such as hydraulic jumps.

Understanding of complex flood-riverbed interaction processes in large-scale (field) outburst floods remains incomplete, not least due to a lack of well-constrained field data on hydraulics and sediment transport, but also because consensus on an appropriate model framework has yet to be agreed. This study presents a novel full 2D hydro-morphodynamic model containing both bedload and suspended load capability. Firstly, the model design is presented with an emphasis on its design to simulate rapidly-varied sediment-laden outburst floods and also the associated geomorphological impacts. Secondly, the model is applied to a large-scale (field) glacier outburst flood or ‘jokulhlaup’ at Solheimajokull, Iceland. For this real-world event, model scenarios with only water and with inclusion of sediment with different parameter setups were performed. Results indicated that grain size specifications affected resultant geomorphological changes, but that the sensitivity of the simulated riverbed changes to the empirical bedload transport formulae were insignificant. Notably, a positive feedback occurred whereby the jokulhlaup led to significant net erosion of the riverbed, producing an increase in flow conveyance capacity of the river channel. Furthermore, bulking effects of sediment entrainment raised the peak discharge progressively downstream, as well as the flood volume. Effects of geomorphological changes on flood water level and flow velocity were significant. Overall, despite the increased computational effort required with inclusion of sediment transport processes, this study shows that river morphological changes cannot be ignored for events with significant in-channel erosion and deposition, such as during outburst floods.

The objective of this thesis is to investigate the impact of riverbank vegetation densities, which can vary greatly in natural river systems, on the flow hydrodynamics across the whole channel. A series of flume experiments are conducted with various riverbank vegetation densities and configurations. Flow velocities across the whole channel are recorded by either acoustic Doppler velocimetry (ADV) or acoustic Doppler velocimetry profiler (ADVP). Firstly, the performances of ADV and ADVP are assessed, before the impact of probe configurations on experimental results is evaluated for ADVP. The accuracy of the probe is discussed, and the best probe configurations for the given flow are suggested. The flow velocity progressively reduces at the vegetated riverbank and slightly increases at the main channel with increasing riverbank vegetation density. Turbulence intensity at the middle of the main channel and the riverbank toe increases with increasing vegetation density. However, at the riverbank region, turbulence intensity decreases due to the dramatic reduction of flow velocity. Geomorphic process feedback is given in the form of a case study, and practical recommendations for river restoration are provided. Bulk velocity, which is relevant to flow conveyance, is evaluated at each portion (main channel and riverbank) of the channel. In general, bulk velocity slightly increases at the main channel but dramatically decreases at the riverbank with increasing vegetation densities. The result of Nikuradse’s equivalent roughness also shows an increasing trend with increasing vegetation density. Bed shear stress is estimated using several methods, including the log Law of the Wall, turbulent kinetic energy and Reynolds stresses. The results obtained using all three methods show that bed shear stress considerably increases at the main channel and sharply decreases at the riverbank region for the shear stress with dense riverbank vegetation compared to the no vegetation case. Impulse is introduced as a new criterion to assess sediment transport both at the free stream portion and at the vegetated region in turbulent flow. With a range of reasonably assumed critical velocities and critical impulses, the frequency of impulse closely follows the same trend observed for shear stresses across the channel width.

To maintain a navigable channel and improve high-flow conveyance, engineers have recently proposed constructing longitudinal training walls as an alternative to the traditional transverse groynes. However, previous work has shown that the system of parallel channels created by a longitudinal training wall might be unstable in rivers with alternate bars. Many questions remain unanswered, particularly whether a stable system can be obtained by carefully designing the bifurcation point. This work analyses the stability of the bifurcating system created by a thin longitudinal wall in sand-bed rivers with alternate bars or point bars. The methodology includes performing 102 numerical tests using the Delft3D code to reproduce an idealized low-land river, either straight or meandering. The results show that the system of parallel channels separated by a training wall may indeed become unstable. An important factor is found to be the location of the bifurcation point with respect to a neighboring bar or point bar. The same trends are observed for both constant and variable discharge, in straight and meandering channels. The results suggest that cyclic growth and decline of the bifurcating channels may arise as inherent system behavior, without the need of any additional external forcing. We explain this from changes in the relationship between sediment transport ratio and discharge ratio as the bifurcation evolves. This cyclic behavior can be regarded as a form of system stability and can be obtained by carefully placing the starting point of the longitudinal training wall, and thus the bifurcation point, near the top of a bar.

Spillways are important flow conveyance structures that safely discharge flood waters to lower elevations. Spillways can be designed with various invert roughnesses ranging from smooth to macro-rough inverts and various slopes. While spillways with macro-roughness such as stepped spillways are associated with air entrainment, spillways with smooth inverts may not be naturally aerated for moderate slopes. Numerous studies have provided insights into the flow aeration and energy dissipation on spillways with macro-roughness, while there is little information on flow aeration and energy dissipation on spillways with micro-rough beds. The present study investigated air-water flow properties, energy dissipation and air-water mass transfer on an uncontrolled moderately sloped spillway (θ = 11˚) with bed micro-roughness comprising a very smooth bed and three configurations with uniformly distributed micro-roughness. The laboratory testing was conducted at the UNSW Sydney’s Water Research Laboratory on a large-scale spillway model. Visual observations of flow patterns on the smooth spillway showed no free-surface aeration along the spillway. Instead, free-surface roughness and entrapped air were observed. With increasing bed micro-roughness, the free-surface roughness increased leading to free-surface aeration further downstream. The rougher bed configurations were also characterised by an earlier onset of free-surface roughness, a faster growth rate of the turbulent boundary layer, and larger bed shear stresses indicating an increase in flow resistance. Detailed measurements of the air-water flow properties highlighted strong interactions of air and water entities downstream of the inception point of free-surface roughness. With increasing bed roughness, air-water interactions increased yielding enhanced void fraction, air-water interface count rate, turbulence intensity as well as auto- and cross-correlation timescales. With increasing bed roughness, both air-water mass transfer and energy dissipation performance rates increased, and the residual head at the toe of the spillway decreased. Empirical equations were proposed to estimate the re-aeration rate, the air-water mass transfer and the residual head at the toe of the spillway. The present study revealed strong interactions between bed micro-roughness and flow properties providing a more efficient hydraulic design of small dam spillways.

This paper reports findings from experimental studies of sediment transport and bed morphology at asymmetrical confluences with hyperconcentrated tributary flows in the upper Yellow River. The results indicate that the hyperconcentrated flow confluence can be divided into four hydraulic regions, including the backwater zone above the upstream junction corner, the maximum velocity area, the separation flow zone, and the post-confluence region downstream of the junction corner. The bed morphology also consists of four basic elements, including the sandbar in the backwater zone, the bar in the separation flow zone, the thalweg for flow conveyance and sediment transport, and bars in the reach downstream of the separation zone. The sediment load of the hyperconcentrated flow from the tributary was the most important control on fluvial processes at such confluences. The increase in deposition in the backwater zone as the sediment load increased was almost linear, and the depth of sediment deposition in the backwater zone was approximately normal in distribution. The validity of a conceptual model for discriminating the status of the backwater effect, developed earlier from field data using the relationship between the sediment load and water volume of hyperconcentrated flows, was confirmed by the experiments. Deposition in the reach downstream of the junction, sandbar height in the backwater zone, and the width and length of the separation zone bar all tended to increase as the sediment load in the tributary increased. An obvious upstream-directed density current occurred in the backwater zone when the sediment concentration of the hyperconcentrated flow exceeded a critical value. The travel distance of the density current increased as the sediment load in the tributary increased. A formula was proposed, based on sediment continuity, for estimating the deposition volume in the reach downstream of the junction. Compared with ordinary sediment-laden flow confluences, hyperconcentrated flow confluences have a sandbar in the backwater zone associated with an upstream-directed density current that may sometimes block the main channel. Hyperconcentrated flow confluences have a thalweg, and so are different from debris flow confluences, which have a fan-shaped deposit.

Recently, many channelized rivers tend to be heavily vegetated due to regime shifts in hydrological, fluvial and ecological processes. Dense vegetation in a river frequently obstructs a flood flow and reduces conveyance capacity of channels. On the other hand, river vegetation provides various ecological services such as habitats for various species and life, natural cycle of organic and inorganic substances, etc‥ It is of engineering importance to understand vegetation hydrodynamics in order to preserve vegetation nature and keep a certain level of flow conveyance capacity. In view that willows tend to be densely vegetated along the shoreline of floodplains or sandbars, a field measurement, a physical model experiment and a numerical analysis were carried out for investigating hydrodynamics in an open channel with riparian vegetation. Discussion was made focusing on flow and shear layer structures developed around the vegetation canopy.

The Upper Qu’Appelle River conveys water from Lake Diefenbaker to Buffalo Pound Lake, which is a major source of water for domestic, industrial, agricultural and recreational use in southern Saskatchewan. Water demand continues to increase with time and additional conveyance capacity may be required during the winter months. Flows in the Upper Qu’Appelle are usually below 2 m3 s–1 from December to March; however, an increase in this flow rate will be needed to meet future water demands. A numerical modelling study was carried out to simulate the degree of ice cover thickening and backwater staging during freeze-up at various discharge scenarios (up to 6 m3 s–1). The Monte Carlo framework was used to capture the variability of possible parameter ranges within various freeze-up scenarios. A bottleneck to flow conveyance is a short 4-km stretch along the river (between the Prairie Farm Rehabilitation Administration [PFRA] and Tugaske Bridges) which is infested with macrophyte growth. Results show that the pr...

Hydrograph convolution is a product of tributary inputs from across the watershed. The time-space distribution of precipitation, the biophysical processes that control the conversion of precipitation to runoff and channel flow conveyance processes, are heterogeneous and different areas respond to rainfall in different ways. We take a subwatershed approach to this and account for tributary flow magnitude, relative timing, and sequencing. We hypothesize that as the scale of the watershed increases so we may start to see systematic differences in subwatershed hydrological response. We test this hypothesis for a large flood (T > 100 years) in a large watershed in northern England. We undertake a sensitivity analysis of the effects of changing subwatershed hydrological response using a hydraulic model. Delaying upstream tributary peak flow timing to make them asynchronous from downstream subwatersheds reduced flood magnitude. However, significant hydrograph adjustment in any one subwatershed was needed for meaningful reductions in stage downstream, although smaller adjustments in multiple tributaries resulted in comparable impacts. For larger hydrograph adjustments, the effect of changing the timing of two tributaries together was lower than the effect of changing each one separately. For smaller adjustments synergy between two subwatersheds meant the effect of changing them together could be greater than the sum of the parts. Thus, this work shows that while the effects of modifying biophysical catchment properties diminishes with scale due to dilution effects, their impact on relative timing of tributaries may, if applied in the right locations, be an important element of flood management.

A baffle-drop structure is a flow conveyance structure that can be used for transport of urban storm water down to underground storage tunnels. The water cascades down the structure from baffle to baffle and plunges into a pool at the bottom from where it is conveyed to the tunnel through an adit. The structure has been used successfully in a limited number of urban drainage schemes. However, its hydraulics and air entrainment characteristics are not fully understood. Using a series of laboratory experiments, an analysis has been tested and validated that may be used for design. The analysis provides a dimensionless relationship between key variables, including design discharge, shaft diameter, baffle spacing, and position of a vertical wall dividing the shaft in a dry and a wet portion. Using this relationship the shaft can be designed to maintain atmospheric pressure throughout its height with little or no air being entrained into the tunnel.

There are many studies on the hydraulic analysis of steady uniform flows in compound open channels. Based on these studies, various methods have been developed with different assumptions. In general, these methods either have long computations or need numerical solution of differential equations. Furthermore, their accuracy for all compound channels with different geometric and hydraulic conditions may not be guaranteed. In this paper, to overcome theses limitations, two new and efficient algorithms known as linear genetic programming (LGP) and M5 tree decision model have been used. In these algorithms, only three parameters (e.g., depth ratio, coherence, and ratio of computed total flow discharge to bankfull discharge) have been used to simplify its applications by hydraulic engineers. By compiling 394 stage-discharge data from laboratories and fields of 30 compound channels, the derived equations have been applied to estimate the flow conveyance capacity. Comparison of measured and computed flow discharges from LGP and M5 revealed that although both proposed algorithms have considerable accuracy, LGP model with R 2 = 0.98 and RMSE = 0.32 has very good performance.

Natural rivers are commonly characterized by a main channel for primary flow conveyance and a floodplain, often partially covered with vegetation such as shrubs or trees, to carry extra flow during floods. The hydraulic resistance due to vegetation on the floodplain typically causes a further reduction of flow velocity and increases the velocity difference between the main channel and the floodplain. As a consequence a strong lateral shear layer leads to the exchange of mass and momentum between the main channel and floodplain, which in turn affects the overall channel conveyance and certain fluvial processes. The prediction of the lateral velocity distribution is important for many flood alleviation schemes, as well as for studies on sediment transport and dispersion in such channels. The present paper proposes a method for predicting the depth-averaged velocity in compound channels with partially vegetated floodplains, based on an analytical solution to the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term included to account for the effects of vegetation. The vegetation is modelled via an additional term in the momentum equation to account for the additional drag force. The method includes the effects of bed friction, drag force, lateral turbulence and secondary flows, via four coefficients f, CD, λ & Γ respectively. The predicted lateral distributions of depth-averaged velocity agree well with the experimental data. The analytical solutions can also be used to predict the distribution of boundary shear stresses, which adds additional weight to the method proposed.

The umbilical cord is crucially important feto-maternal unit, though very simple in structure while containing two arteries and one vein; it modulates blood flow conveyance between the fetus and placenta. Umbilical cord characteristics, such as cord length and thickness, number of vessels and their diameters, amount of Wharton's jelly, type of placental insertion, coiling and blood flow patterns are recognized contributors that may reveal increased risk for possible antenatal and perinatal complications. However, during the “routine” fetal anatomical survey, only the number of umbilical cord vessels is recorded in majority of antenatal centers. Thereafter, umbilical cord is rarely analyzed, except for umbilical artery blood flow patterns that are mainly used to further assess well-being of growth-restricted fetuses. At present time, it appears prudent to exercise more detailed umbilical cord analysis, including but not limited to vessel number, coiling patterns and cord thickness, during the fetal...

Channelization and channel incision have considerably modified channel morphology of the Czarny Dunajec River, and now it varies from a single-thread, incised or regulated channel to an unmanaged, multi-thread channel. Effects of these distinct channel morphologies on the conditions for flood flows were investigated in a study of 25 cross-sections from the middle river course. Cross-sectional morphology, channel slope and roughness were used as input data for the 1D steady-flow hydraulic modelling performed for discharges with recurrence interval between 1.5 and 50 years. Adjustment of roughness coefficients to obtain the agreement between simulated and observed peak levels of the 2014 flood allowed calibration of the model for particular cross-sections. As a result of differences in flow widths, cross-sectional flow areas and channel slope, flood flows in the three river reaches differ in unit stream power and bed shear stress, with the highest values of the parameters recorded in the incised reach, intermediate values in the channelized reach and the lowest values in the multi-thread reach. The recognised differences in the flow power and in tractive forces exerted on the flow boundary underlie and explain different evolutionary tendencies of particular river reaches during the past decades. Stabilization of river banks in channelized reaches induces a progressive increase in floodplain elevation; sedimentation in the analysed channelized cross-section of the Czarny Dunajec have reduced its initial flow conveyance by half and elevated water stages at given flood discharges by about 0.7 m during 30 years since the river channelization.

Previous investigations observed significant seepage losses from the Rio Grande to the shallow aquifer between Socorro and San Antonio, New Mexico. High-resolution telescopic modeling was used along a 10-km reach of the Rio Grande and associated drains and canals to evaluate several management alternatives aimed at improving river conveyance efficiency. Observed data consisted of ground-water and surface-water elevations, seepage rates along the Rio Grande and associated canals and drains, and borehole geology. Model calibration was achieved by adjusting hydraulic conductivity and specific storage until the output matched observed data. Sensitivity analyses indicated that the system was responsive to changes in hydrogeologic properties, especially when such alterations increased vertical connectivity between layers. The calibrated model predicted that removal of the low flow conveyance channel, a major channel draining the valley, would not only decrease river seepage by 67%, but also decrease total flow through the reach by 75%. The decreased flow through the reach would result in increased water logging and an average increase in ground-water elevations of 1.21 meter. Simulations of the system with reduced riparian evapotranspiration rates or a relocated river channel also predicted decreased river seepage, but to a much lesser degree.

An obstacle to testing human impacts on flooding is that anthropogenic and natural hydrologic changes occur simultaneously and are often indistinguishable. We attempted to isolate the impacts of overlapping mechanisms on flooding by analyzing 73-188 years of stage measurements from the Mississippi River system and the German Rhine. Although typically under-utilized in hydrologic analysis, stage data document the cumulative impacts of both upstream changes such and climate and land use as well as modifications of the river channel and floodplain. Analysis of trends in peak stages and flood frequencies shows contrasting results on the Mississippi and Rhine: increasing trends at most Mississippi stations, but no significant trends at most Rhine stations. On the Mississippi and its tributaries, statistically significant changes in peak stages and peak-stage frequencies were identified at 10 of 14 stations, with all but one exhibiting increased flooding. On the Rhine River, systematic change occurred at only 1 of 8 stations analyzed. On both river systems, channel and floodplain modifications dominated net hydrologic response, overwhelming the effects of climate change, land-use shifts, and dam construction. Specific-gage analysis, which isolates the impacts of instream river modifications, documented declining flow conveyance at all stations where flood levels and frequencies increased. Increased flooding at the Mississippi River sites appears to be driven by the history of aggressive channel engineering, in particular channel constriction to increase navigation depths. In contrast, navigation infrastructure on the Rhine has not substantially degraded the river's capacity to efficiently convey flood flows.

This study assesses historic overbank alluvial sedimentation along a low-gradient reach of West Fork Black's Fork in the northern Uinta Mountains, Utah. In this previously glaciated setting, an alluvial floodplain that is approximately 400 m wide by 1500 m long has been modified by the combined effects of valley morphometry and the recent history of clear-cut logging during the late 19th and early 20th Centuries. To quantify the effects on sedimentation and flow conveyance, three natural streambank exposures were sampled and analyzed for nuclear bomb fallout 137 Cs. The distribution of 137 Cs within the three profiles suggests that a remnant outwash terrace exerts a first-order control over the deposition of overbank alluvium. Upstream from a constriction in the floodplain caused by the terrace remnant, as much as 40 cm of overbank alluvium has been deposited since the beginning of clear-cut logging. Immediately downstream of that constriction, no evidence exists for any overbank sedimentation during that same period. Vibracore samples and Oakfield soil probe sampling throughout the study reach quantified the geographic extent and thicknesses of the historic alluvial package. Flood conveyance through the study area was modeled using the U.S. Army Corps of Engineers HEC-RAS modeling program. Model simulations were run for modern conditions (using surveyed topography) and for prehistoric conditions (using the modern topography less the historic alluvial package determined by 137 Cs analyses). Model results indicate that the floodplain constriction caused a significant impediment to flood conveyance at even modest discharges during prehistoric conditions. This promoted ponding of floodwaters upstream of the constriction and deposition of alluvium. This has increased bank heights upstream of the constriction, to the point that under modern conditions 1- to 5-year recurrence interval floods are largely confined within the channel. These results confirm the validity of this new approach of combining 137 Cs dating of alluvial sediments with HEC-RAS flow modeling to compare flood conveyance along a single stream reach prior to and since an abrupt change in alluvial sedimentation patterns.

This research detects long-term trends in flow conveyance on the Lower Missouri River, and uses equal-discharge analysis of channel-gaging time series to assess the mechanisms driving these trends. Five long-term gaging stations along the Lower Missouri were examined using specific-gage analysis, which is a technique that holds discharge constant in order to observe trends in water-surface elevation (or stage) over time. This analysis reveals that for all flood conditions on the Lower Missouri River, stages have systematically risen for equal discharge volumes over the period of record. Flows that were fully contained within the Missouri channel in the early 20th century now create floods, and extreme high flows today are associated with stages as much as 3.7 m higher than at the start of the record. Equal-discharge analysis also can be used for analyzing time series of other parameters that co-vary strongly with discharge and that change systematically over time. On the Lower Missouri, long-term records of river gaging measurements, including cross-sectional area, flow velocity, and channel width, have been collected for the past ∼70 years. Equal-discharge analysis of these parameters illustrates the mechanisms of channel change driving flood magnification. At three stations, decreased flow velocity has been the dominant mechanism driving stage changes. At two other stations, constriction in channel cross-sectional area has increased flood stages. These changes in channel geometry and flow dynamics correlate with wing-dam construction and other engineering of the Lower Missouri River, but the changes occur progressively over the duration of record as a gradual and reach-scale re-equilibration of the fluvial system. Magnification of flood stages should be recognized on the Missouri River and incorporated into current estimates of flood hazard and into strategies for river management and flood mitigation in the future.