Stage Fluctuations Research Articles

Nitrate Sink Function of Riparian Zones Induced by River Stage Fluctuations

Nitrate Sink Function of Riparian Zones Induced by River Stage Fluctuations

Aerobic respiration in riparian exchange zones of regulated river corridors

AbstractRiver stage fluctuations drive surface water‐groundwater exchanges within river corridors. This study evaluates how repeated daily stage fluctuations, representative of hydropeaking conditions, influence aerobic respiration of river‐sourced dissolved organic carbon (DOC) in the riparian exchange zone using reactive flow and transport simulations. Over 50 hypothetical scenarios were modelled to evaluate how the duration of the daily flood signal, river DOC concentration, aquifer hydraulic conductivity and ambient groundwater flow condition affect the fate and transport of DOC and DO in the riparian aquifer. Time series subsurface snapshots highlight how the various factors influence the subsurface distribution of DOC and DO. The total mass of DOC respired per meter of river had a wide range depending on the parameters, spanning from 1.4 to 71 g over 24‐h, with high hydraulic conductivity and losing ambient groundwater flow conditions favouring the largest amount of DOC respired. The ratio of DOC mass entering the riparian zone with the mass returning to the river showed that as little as 5% to as much as 76% of the DOC that enters the bank during stage fluctuations returns to the river. This return ratio is dependent on river DOC concentration, hydraulic conductivity and ambient groundwater flow. The results illustrate that stage variations due to river regulation can be a significant control on aerobic respiration in riparian exchange zones.

On River‐Aquifer Exchange Flow With Irregular and Semipervious Bank

AbstractRiver water flowing into and out of riparian aquifers driven by stage fluctuations during floods is critical for streamflow and biogeochemical cycling of hyporheic zones. Previous studies paid limited attention to the complex exchange flow between rivers and the adjacent unconfined aquifers through irregular and semipervious banks which are commonly seen in nature. This study proposed a new semi‐analytical solution for describing the river‐aquifer exchange flow by incorporating river stage hydrograph, and semipervious banks with irregular geometries. The solution was verified by comparing with the numerical solutions of the one‐dimensional Boussinesq equation and two‐dimensional variably saturated flow models. The comparisons indicated that the semi‐analytical solution was robust to closely approximate the bank storage exchange flow through an irregular and semipervious bank. Moreover, an innovative dimensionless river bank index (BI) was proposed to quantitively identify the importance of riverbank geometry irregularity. BI = 0.4 and BI = 0.76 are the critical threshold values to determine whether realistic bank geometry should be incorporated or not. Specifically, when BI is less than 0.4, the conventionally vertical bank can be applied to substitute realistic irregular riverbanks; When BI is greater than 0.76, however, realistic bank geometries should be included and otherwise significant errors may occur, especially when BI is much greater than 0.76. The semi‐analytical solution and BI have been successfully applied to the Hanford Reach of Columbia River, Washington, USA. The proposed solution and BI are useful for conceptual and diagnostic analysis of bank storage exchange flow and for understanding which factors and responses are important.

Experimental analysis of infiltration process and hydraulic properties in soil and rock profile in the Taihang Mountains, North China

Abstract In this research, an experiment was conducted in the Taihang Mountains in China with a self-designed automatic soil and rock water infiltration monitoring system and a time domain reflectometry (TDR) device to analyze the infiltration process of disturbed soil and rock profile under constant head, unsaturated seepage properties and permeability coefficient of discontinuous rock masses. It was found that the infiltration process curve has an obvious fluctuation in the late stage of unsaturated seepage (after 18:00 p.m. on March 20th) which not only reflects the temporal variation of infiltration rate, but the spatial variation of rock structure. The lateral soil water of soil and rock dual-texture mainly flows in the interface of soil and rock. The infiltration rate of soil water can be as high as 2.42 × 10−4 cm/s, accounting for about 20% of the stable infiltration rate. After the water infiltrated in the lower rock layers, the water was mainly stored and flowed in the fissure network in the rocks, but did not completely fill the whole fissure network. Firstly, the local priority channel is adopted to infiltrate. With the increasing of rock saturation, the local priority channel will also expand and finally extend to the whole fissure network. The permeability coefficient of the soil and rock dual-texture in the study area is 1.26 × 10−3 cm/s.

Geophysical mapping of hyporheic processes controlled by sedimentary architecture within compound bar deposits

AbstractHyporheic exchange influences water quality and controls numerous physical, chemical, and biological processes. Despite its importance, hyporheic exchange and the associated dynamics of solute mixing are often difficult to characterize due to spatial (e.g., sedimentary heterogeneity) and temporal (e.g., river stage fluctuation) variabilities. This study coupled geophysical techniques with physical and chemical sediment analyses to map sedimentary architecture and quantify its influence on hyporheic exchange dynamics within a compound bar deposit in a gravel‐dominated river system in southwestern Ohio. Electromagnetic induction (EMI) was used to quantify variability in electrical conductivity within the compound bar. EMI informed locations of electrode placement for time‐lapse electrical resistivity imaging (ERI) surveys, which were used to examine changes in electrical resistivity driven by hyporheic exchange. Both geophysical methods revealed a zone of high electrical conductivity in the center of the bar, identified as a fine‐grained cross‐bar channel fill. The zone acts as a baffle to flow, evidenced by stable electrical conditions measured by time‐lapse ERI over the study period. Large changes in electrical resistivity throughout the survey period indicate preferential flowpaths through higher permeability sands and gravels. Grain size analyses confirmed sedimentological interpretations of geophysical data. Loss on ignition and x‐ray fluorescence identified zones with higher organic matter content that are locations for potentially enhanced geochemical activity within the cross‐bar channel fill. Differences in the physical and geochemical characteristics of cross‐bar channel fills play an important role in hyporheic flow dynamics and nutrient processing within riverbed sediments. These findings enhance our understanding of the applications of geophysical methods in mapping riverbed heterogeneity and highlight the importance of accurately representing geomorphologic features and heterogeneity when studying hyporheic exchange processes.

Evolution of initial stage fluctuations in the glasma

We perform a calculation of the one- and two-point correlation functions of energy density and axial charge deposited in the glasma in the initial stage of a heavy ion collision at finite proper time. We do this by describing the initial stage of heavy ion collisions in terms of freely evolving classical fields whose dynamics obey the linearized Yang-Mills equations. Our approach allows us to systematically resum the contributions of high momentum modes that would make a power series expansion in proper time divergent. We evaluate the field correlators in the McLerran-Venugopalan model using the glasma graph approximation, but our approach for the time dependence can be applied to a general four-point function of the initial color fields. Our results provide analytical insight into the preequilibrium phase of heavy ion collisions without requiring a numerical solution to the Yang-Mills equations.

A Substitute Technology for the Currently Applied Bridge-Like Water Intake along the River Nile in Egypt

Bridge-like intakes are structures extended into open channels carrying suction pipes to reach out to sufficient water depths that can secure permanent abstraction. Such intakes have been found to suffer problems that threaten their performances. The present study aims to highlight these problems and introduce a new technology as a substitute solution. Three problems could be identified by continuous field surveys and monitoring. First, the sediment accumulation at the suction pipe inlet clogs the strainer holes and obstructs water abstraction. Second, the offshore water surface recession due to water stage fluctuation or sediment accumulation causes water surface to be inaccessible to the pipe inlet. Third, the stationary inlet position aggravates the other two problems. A case study of a bridge-like intake at El Koraymat area, south of Cairo, along the Nile eastern bank was introduced to clarify these problems. The intake was found to suffer annual sediment accumulations of about 14000 m3 which resulted in water recession and abstraction interruption. An alternative solution was proposed. The solution concept depends on making the pipe inlet position moveable so that it can mitigate and reduce the occurrence of sediment accumulation and water recession. The tower crane technology was proposed to accomplish this concept.

Study of Electric Field Impact on Crystallization in Tunnel Drainage Pipes in Hard Water Area

To solve the problem of blockage of crystallization in tunnel drainage pipes in hard water area, electric field devices are designed and applied in the transversal tunnel drainage pipe according to the fundamental law of crystallization. Laboratory tests were carried out to test the crystallizing tunnel drainage pipe under the effect of electric field in order to study the law of electric field impact on crystallization in tunnel drainage pipes in hard water area. The test results indicate that the arranged circumferential and parallel plate electric field devices can form an electrical field within a narrow and small space inside the pipe and influence the ion movement in water and adsorption performance between crystals and the pipe. Under the condition of full flow, the amount of crystals in the ordinary pipe without electric field treatment increases progressively along water flow direction and remains relatively uniform later. The amount of crystals along the water flow direction of the pipe treated with circumferential and parallel plate electric fields presents signs of fluctuation in the early stage and then stableness later. The amount of crystals in the fluctuating section is higher and lower in the uniform section, and its uniform section length is longer than that in ordinary pipes. Under the condition of full current, crystallizing speed declines with elapse of running time. After the electric field is imposed, crystallizing acceleration progressively decreased to a relatively lower level. Comparing three voltages of 5 V, 12 V, and 24 V, the effect of scale inhibition under 5 V is superior. When water amount in the pipe varies, the effects of scale inhibition under different electric field modes are different. The electric field effect causes the changes of the external form of calcium carbonate crystal and its surface abrasion, porous crystal, and structural looseness.

Understanding Contaminant Migration Within a Dynamic River Corridor Through Field Experiments and Reactive Transport Modeling

The behavior of a persistent uranium plume within an extended river corridor at the DOE Hanford site is dominantly controlled by river stage fluctuations in the adjacent Columbia River. The plume behavior is further complicated by substantial heterogeneity in physical and geochemical properties of the host aquifer sediments. Multi-scale field and laboratory experiments and reactive transport modeling were integrated to understand the complex plume behavior influenced by highly variable hydrologic and geochemical conditions in time and space. In this paper, we (1) describe multiple data sets from field-scale uranium adsorption and desorption experiments performed at our experimental well-field, (2) develop a reactive transport model that incorporates hydrologic and geochemical heterogeneities characterized from multi-scale and multi-type datasets and a surface complexation reaction network based on laboratory studies, and (3) compare the modeling and observation results to provide insights on how to refine the conceptual model and reduce prediction uncertainties. The experimental results revealed significant spatial variability in uranium adsorption/desorption behavior, while modeling demonstrated that ambient hydrologic and geochemical conditions and heterogeneities in sediment physical and chemical properties both contributed to complex plume behavior and its persistence. This research underscores the great challenges in adequately characterizing this type of site to model the reactive transport processes over scales of 10 m or more. Our analysis provides important insights into the characterization, understanding, modeling, and remediation of groundwater contaminant plumes influenced by dynamic surface water and groundwater interactions.

Hyporheic exchange mechanism driven by flood wave

AbstractTo study the hyporheic exchange driven by a single peak flood‐induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real‐time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine‐type) and its change rate v (cosine‐type), and was proportional to the polynomial of them q ∝ (ω∙h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.

River Dynamics Control Transit Time Distributions and Biogeochemical Reactions in a Dam‐Regulated River Corridor

AbstractTransit time distributions (TTDs) exert important controls on biogeochemical processes in watershed systems. TTDs are often assumed to follow time‐invariant exponential, lognormal, or heavy‐tailed power law distributions in headwater or low‐order streams. However, under dynamic hydrological forcing, transit time could exhibit more complex distribution patterns with strong spatial and temporal variability. In this study, we used a numerical particle tracking approach to characterize TTDs along the Hanford Reach of the Columbia River under the influences of river stage fluctuations and evaluate the associated effects on biogeochemical reaction potentials within the river corridor. Particle tracking was conducted using velocity fields simulated by high‐resolution three‐dimensional groundwater flow models that capture both the river stage fluctuations and physical heterogeneity. Our results revealed that multifrequency flow variations led to multimodal TTDs that varied in time and space. Such characteristics can only be captured by multiyear numerical simulations supported by multiyear field monitoring. Dam‐induced high‐frequency (subweekly) flow variations increased additional hydrologic exchange flows with short (subweekly) transit times, which accounted for up to 44% of reactant consumption in the river corridor along the Hanford Reach. The dam‐induced river stage fluctuations have more significant impacts on faster biogeochemical reactions because they cause a larger fraction of shorter transit times. Numerical particle tracking provides an efficient alternative for characterizing TTDs for large complex systems where in situ field experiments are not feasible. Such a numerical approach is thus essential for improving large‐scale biogeochemical modeling from watersheds to basins.

Local relative density fluctuation in the early stage of a sintered glass sphere compact determined by X-ray computed tomography

The relative density of a sintered glass-powder compact varies at the local level due to its heterogeneous nature, which makes its characterization essential. In this work, high-resolution X-ray computed tomography (XCT) was used to quantitatively characterize the local relative density fluctuation of a sintered glass compact in its initial stage. The degree of heterogeneity of the microstructure was calculated taking into account the coarseness parameter. With a basis of 23,500 particles scanned in the representative volume element (RVE), the local environment was subdivided into three different groups of particles, represented by a cubic cell with a volume equivalent to that of approximately 600, 80 and 10 spherical particles with a diameter of 80 μm. Independent of the particle group analysed, we found that the maximum of the local relative density distributions, which could be described by a normal distribution function, always occurs around the relative density of the RVE. However, the fluctuation of the data showed a considerable change regarding the width, which increases as the volume of the analysed group of particles decreases, suggesting that particle packing is more heterogeneous on a small scale. In particular, we observed that the heterogeneity of the microstructure for the RVE under consideration becomes pronounced for groups of approximately 10 to 80 particles.

The spatial-temporal evolution and spatial convergence of ecological total factor productivity in china

Based on the theory of strong sustainability, this paper evaluates the ecological environment from two aspects of ecological environment construction and ecological environment damage, and incorporates the ecological environment into the research framework of total factor productivity (TFP), and proposes a new ecological total factor productivity (ETFP) index, and studies the source of factors, spatial-temporal evolution and spatial convergence of the ETFP in China from 2001 to 2018. The results show the following: ETFP is driven by technological efficiency, and the stage fluctuation differentiation is obvious; the growth rate of the sub-factors of the “labor —energy — ecological environment construction — capital” decreases in sequence, and the contribution degree of the factors of “labor — ecological environment construction — energy — capital” keep decreasing in turn; the distribution pattern evolves from unipolar to bimodal. The path dependence of TFP on capital, labor and energy is relatively strong; There was a spatial convergence in china's provincial ETFP, and convergence speed was accelerated of 4.07% under Geo-economic weight matrix. Considering the influence of institutional factors, environmental decentralization and fiscal decentralization can put off the ETFP’s increasing speed, but the interaction between them can drive the ETFP’s growth.

Analysis of groundwater and river stage fluctuations and their relationship with water use and climate variation effects on Alto Grande watershed, Northeastern Brazil

Sustainable use of water resources on the behavior of groundwater table and surface water level variations, especially in phreatic sedimentary aquifers, where a strong interaction between stream flow and groundwater normally takes place. In the present study, precipitation, water level fluctuation, river flow and pivot installation data from an important agricultural frontier with an increasing water use for irrigated agriculture and a downward precipitation trend were compared with surface and water level fluctuation monitoring data. The main purpose was to assess possible impacts on the aquifers and to analyze the variation in groundwater table and surface water levels due to long-term downward precipitation trend (climate variation effects) and increasing water demand (irrigation). A growing number of central pivots installed for irrigation are withdrawing water from the Urucuia Aquifer System (UAS) in western Bahia State, Northeastern Brazil, one of the leading agricultural frontiers of the world. Field surveys provided hydrogeological aspects that led to the construction of a hydrogeological conceptual model. Monitoring groundwater and surface water through Brazilian Geological Survey's Integrated Groundwater Monitoring Network (RIMAS-CPRM), satellite images and Hydrological Information System (HidroWeb-ANA) network formed the databases for the study. This data was compared with rainfall data and evolution of irrigated areas captured by satellite image analysis. Results indicate that reduction of rainfall volumes from 1990 to 2018 in the headwaters of Alto Grande basin, due to cyclic droughts, and an increase in surface and groundwater exploitation due to flourishing agribusiness activity has caused a considerable groundwater level drawdown. The drawdown of up to 6.63 m points to the need of strong management actions, which should provide a long-term sustainable use of water resources (superficial and underground) within Alto Grande watershed. This study is part of the actions undertaken to provide the scientific and technical basis to secure the availability of water and a sustainable agricultural activity, since an important part of the Cerrado, the Brazilian savanna ecosystem, and considerable proportion of São Francisco river flow, lies in the study area.

Regionalization of stage-discharge rating curves for hydrodynamic modeling in ungauged basins

Stage-discharge rating curves are empirical power functions that represent river dynamics by explaining the temporal variations of river discharge with respect to stage fluctuations. The widespread access to measured river discharge and stage at gauging stations in the United States provides a valuable opportunity to perform regionalization techniques and transfer this information to ungauged areas. In this study, a recently proposed regionalization framework that integrates the behavioral-based hierarchical clustering (BHC) with classification and aggregation, namely BHC-CA, is applied to 128 rating curves in the Arkansas-White-Red region to detect homogeneous river reach catchments with similar river dynamics. Additionally, the performance of the BHC, compared to commonly used attribute-based hierarchical clustering (AHC) algorithms, is tested. The BHC-CA framework divides the entire study area into three homogeneous clusters, creates three regional rating curves and finds a logistic regression with 7 physical/climatic attributes as the best classifier for transferring regional rating curves to ungauged catchments. Results also demonstrate the effectiveness of the BHC and its usefulness as an alternative clustering algorithm for the regionalization of environmental model problems.

An Assessment of Hydropeaking Metrics of a Large-Sized Hydropower Plant Operating in a Lowland River, Lithuania

This paper discusses rapid flow and stage fluctuations in a large lowland river downstream from a large hydropower plant (HPP) in Lithuania. The main problem arises when the HPP is operating in peak mode. Such operation of HPP causes rapid flow and stage fluctuations, which can have a certain impact on river ecosystems. The study analyzes general abiotic indicators such as upramping and downramping rates and stage fluctuations downstream of the HPP. The main idea was to assess recorded stage upramping and downramping rates along the river downstream of large HPP. To assess stage fluctuation statistics, COSH software was used. A maximum upramping rate of 1.04 m/h and maximum downramping rate of 0.88 m/h were identified using data from temporary and permanent gauging stations. Obtained results revealed that stage fluctuations exceed ecologically acceptable rates up to 20 km downstream of HPP. The effect of hydropeaking fades out only at a chainage of 45 km downstream of HPP. In mountainous regions, ecologically acceptable rates are reached at much smaller distances. The study shows that the traditional coefficient of variation of stage fluctuation data can be used to describe hydropeaking indicators. The main results of this study can be used for environmental impact assessment downstream from HPPs.

Fluctuations, criticality and nonequilibrium effect of the QCD matter

The multiplicity distributions of net-baryon number fluctuation in the first-order chiral phase transition associated with the nonequlibrium effect are investigated within the improved Polyakov–Nambu–Jona–Lasinio model. Compared with the idealized first-order transition in equilibrium, the calculation indicates that the density fluctuations in the metastable and unstable regions are more violent, which possibly affects the statistical distributions of density fluctuation in later stage of an expanding system. Signals induced by the first-order phase transition and those from the nonequilibrium effect are discussed in detail, which could be exploited to identify the first-order phase transition. Besides, the critical exponents of the thermodynamic quantities at both the critical end point and spinodal boundary are investigated.

Defining a Riverine Tidal Freshwater Zone and Its Spatiotemporal Dynamics

AbstractTidal freshwater zones (TFZs) are transitional environments between terrestrial and coastal waters. TFZs have freshwater chemistry and tidal physics, and yet are neither river nor estuary based on classic definitions. Such zones have been occasionally discussed in the literature but lack a consistent nomenclature and framework for study. This work proposes a measurable definition for TFZs based on three longitudinal points of interest: (1) the upstream limit of brackish water, (2) the upstream limit of bidirectional tidal velocities, and (3) the upstream limit of tidal stage fluctuations. The resulting size and position of a TFZ is transient and depends on the balance of tidal and riverine forces that evolves over event, tidal, seasonal, and annual (or longer) timescales. The concept, definition, and transient analysis of TFZ position are illustrated using field observations from the Aransas River (Texas, USA) from July 2015 to July 2016. The median Aransas TFZ length was 59.9 km, with a late summer maximum of 66.0 km and a winter minimum of 53.6 km. The TFZ typically (annual median) began 11.8 km upstream from the river mouth (15.4 km winter/11.2 km summer medians) and ended 71.7 km upstream (69.0 km/77.2 km). Seasonally low baseflow in the Aransas River promoted gradual coastal salt encroachment upstream, which shortened the TFZ. However, sporadic large rainfall/runoff events rapidly elongated the TFZ. The TFZ definition establishes a quantifiable framework for analyzing these critical freshwater systems that reside at the nexus of natural and human‐influenced hydrology, tides, and climate.

Evaluation of Water Transport Energy Efficiency in Jiangsu Province Based on Unexpected Output

In this study, the non-expected output SBM - undependable model was introduced to evaluate the efficiency of waterway transportation in Jiangsu province from 2007 to 2015. The results show that: (1) The evolution of water transport efficiency during the study period is characterized by a small fluctuation in the early stage and a large change in the late stage. Between 2007 and 2012, efficiency values ranged from 0.4 to 0.6, and were at an inefficient and stable stage; Between 2013 and 2015, efficiency values ranged from 0.6 to 1.0 and were in a medium - to high-efficiency fluctuation phase. (2) Through the analysis of the reasons of inefficient transportation in the study period, we can find that there are some phenomena in Jiangsu province, such as redundant input factors, low energy utilization rate and more unexpected output. The efficiency of water transport in Jiangsu province can be improved by optimizing the transport capacity structure, improving energy efficiency and reducing environmental pollution.

Filling the Void: The Effect of Stream Bank Soil Pipes on Transient Hyporheic Exchange During a Peak Flow Event

AbstractThe hyporheic zone is the ecotone between stream and river channel flow and groundwater that can process nutrients and improve water quality. Transient hyporheic zones occur in the riparian zone (bank storage or “lung model” exchange) during channel stage fluctuations. Recent studies show that soil pipes are widespread in stream banks and beneath floodplains, creating highly preferential flow between channel and riparian groundwater such that the traditional Darcy model of flow does not apply. We used MODFLOW with the conduit flow package to model a series of stream bank soil pipes and examined soil pipe density (number per m), length, diameter, height above baseflow water surface, connectivity, and matrix hydraulic conductivity on transient particle flow paths and total hyporheic exchange volume (i.e., bank storage) over the course of a peak flow (e.g., storm) event. We found that adding five soil pipes per meter more than doubled hyporheic volume. Soil pipe length was the most important control; adding one 1.5‐m‐long soil pipe caused a 73.4% increase in hyporheic volume. The effect of increasing soil pipe diameter on hyporheic volume leveled off at ~1 cm, as flow limitation switched from pipe flow to pipe‐matrix exchange. To validate our approach, we used the model to successfully reproduce trends from field studies. Our results highlight the need to consider soil pipes when modeling, monitoring, or managing bank storage, floodplain connectivity, or hyporheic exchange.