Using an acoustic Doppler current profiler in a small river

Some practical and theoretical concepts related to the use of an acoustic Doppler current profiler (ADCP) in a small river are examined. The importance of understating the limitations of the measurement equipment and a system for locating the exact position of the ADCP are discussed. Details of a new measurement protocol which is suitable for small rivers are presented. Small samples of data measured in the River Blackwater are used to illustrate the concepts outlined in the paper. It is concluded that ADCPs can be successfully used in small rivers provided sufficient care is taken over their deployment and subsequent data analysis. However, in some cases it is acknowledged that additional modifications to the ADCP may need to be undertaken as illustrated in the paper.     

GPS与声学多普勒流速剖面仪在"动底"测流中的应用研究

在高水期和含沙量较大的情况下,用声学多普勒流速剖面仪ADCP(Acoustic Dopppler Current Profilers)在进行底跟踪测量时会发生偏差.本文引入全球定位系统的定位技术,将两者有机地结合起来,并进行GPS跟踪方式的方向改正,用于"动底"长江流量测验,降低ADCP的底跟踪模式下的测量偏差.     

Reduction of fecal indicator bacteria (FIB) in the Ballona Wetlands saltwater marsh (Los Angeles County, California, USA) with implications for restoration actions

A benefit of wetland preservation and restoration is the ecosystem service of improving water quality, typically assessed based on bacterial loading. The Ballona Wetlands, a degraded salt marsh of approximately 100 ac located on the southern border of Marina Del Rey (Los Angeles County, California, USA) are currently the focus of publicly funded restoration planning. The wetlands receive tidal water, usually contaminated with fecal indicator bacteria (FIB: total and fecal coliforms, Escherichia coli, enterococci) from the adjacent Ballona Creek and Estuary. During the summer of 2007, two 24-h studies were conducted to determine FIB tidal dynamics within the wetland. Measurements of water flow and mean FIB concentrations (n = 3) were measured every 1.5 h to determine total FIB load estimates. FIB loading rates (MPN/s) were greatest during flood tides as water entered the wetlands, and then again during spring tide conditions when sediments were resuspended during swifter spring ebb flows. During daylight hours, the wetland acted as a sink for these bacteria as loads diminished, presumably by sunlight and other processes. Conversely, during late afternoon and night, the wetlands shifted to being a source as excess FIB departed on ebb flows. Therefore, the wetlands act as both a source and sink for FIB depending on tidal conditions and exposure to sunlight. Future restoration actions would result in a tradeoff - increased tidal channels offer a greater surface area for FIB inactivation, but also would result in a greater volume of FIB-contaminated resuspended sediments carried out of the wetlands on stronger ebb flows. As levels of FIB in Ballona Creek and Estuary diminish through recently established regulatory actions, the wetlands could shift into a greater sink for FIB.     

Stratification and fine sediment transport mechanisms in a semi-enclosed tidal lagoon (Pagham Harbour, West Sussex)

Preliminary analysis of data collected at a macrotidal semi‐enclosed lagoon (Pagham Harbour, UK) has revealed useful information about long‐term patterns of siltation and some of the related mechanisms. Sediment surface‐level measurements made over 2 years at different sites within Pagham Harbour have shown a steady siltation, in common with earlier measurements, which is moderated by seasonal effects due to erosion by locally generated waves. Furthermore, inspection of vertical profiles of salinity and turbidity over individual tidal cycles has revealed that the degree of sediment transport on the flood tide is related to the vertical salinity gradient. Thus, at the Ferry Pool site, which is characterised by episodic pumped discharges from a nearby sewage treatment plant, landward sediment transport is enhanced by the high degree of salinity stratification observed during the flood tide. The mobility of the sediment, and the greater distribution of softer, less well‐consolidated sediment deposits, is greater here than at the other significant freshwater inflow at the Salthouse site, where the fresh water flow is instead moderated by a tidal flap gate. Preliminary analyses suggest that the higher the salinity stratification, the greater the landward sediment transport during the flood tide. Such analyses could help inform future policy on the methods of land drainage to macrotidal lagoons, and on the potential for managed realignment at such sites.     

Application of surrogate artificial intelligent models for real‐time flood routing

Developing a robust flood forecasting and warning system (FFWS) is essential in flood‐prone areas. Hydrodynamic models, which are a major part of such systems, usually suffer from computational instabilities and long runtime problems, which are particularly important in real‐time applications. In this study, two artificial intelligence models, namely artificial neural network (ANN) and adaptive neuro‐fuzzy inference system (ANFIS), were used for flood routing in an FFWS in Madarsoo river basin, Iran. For this purpose, different rainfall patterns were transformed to run‐off hydrographs using the Hydrologic Engineering Center (HEC)‐1 hydrological model and routed along the river using HEC river analysis system RAS hydrodynamic model. Then, the simulated hydrographs with different lag times were used as inputs for training of ANN and ANFIS models to simulate flood hydrograph at the basin outlet. Results showed that the simulations obtained from ANN and ANFIS coincided with the results simulated by the HEC‐RAS, and application of such models is strongly suggested as a backup tool for flood routing in FFWSs.     

Messung der Infiltrationsgeschwindigkeit von Oberflächenwasser mit Hilfe des natürlichen Isotops Radon-222

Owing to its different concentrations in groundwater and river water, the naturally occuring isotope radon-222 can be used as a natural tacer to determine the residence time of freshly infiltrated water and the infiltration velocity. In the study area, predominant correlation was found between the radon activity concentration of groundwater and the lithologic structure of the aquifer. Misinterpretation of low radon activity concentration measured near surface waters due to geological inhomogeneities can result in false assumptions about groundwater flow paths. The infiltration of river water into the adjacent aquifer during a flood wave was also ascertained by measuring radon activity concentration. Further the residence time of infiltrated water was determined at a sampling point installed beneath the river Elbe and infiltration velocity was calculated.     

Observations of turbidity in the Thames Estuary,United Kingdom

Two years of data of water level, salinity and turbidity have been analysed to understand the response of the estuarine turbidity maximum in the Thames to variations in tidal range and freshwater flow. We show the increase in turbidity in spring, together with a sudden decrease in autumn after fluvial flooding. In order to try to understand the mechanisms, we also present data from individual tides. During dry periods, there is a period of slack water around high tide when settling occurs. There is little equivalent settling at low tide, nor is there any significant settling during wet weather periods, pointing to the importance of tidal asymmetry at certain times of year. We also present an empirical relationship between peak tidal water level and turbidity during flood tides, which clearly shows the greater landward transport of sediment under spring tides, although this is moderated by the availability of erodible material.     

The impacts of ‘run‐of‐river’ hydropower on the physical and ecological condition of rivers

This paper synthesises published literature on run‐of‐river hydropower, highlighting its potential to affect both the physical and ecological conditions of river systems. The paper considers the limited number of direct studies and reviews a wider literature on the two principal impacts of such schemes on river systems: the introduction or maintenance of in‐channel barriers and water abstraction/flow regime alteration. We outline how river systems are likely to be impacted by such schemes and identify the key issues arising from their continued development. Potential mitigation approaches are highlighted and the areas of future research required to adequately address current knowledge gaps are identified.     

Density currents in the Chicago River: characterization, effects on water quality, and potential sources

Bidirectional flows in a river system can occur under stratified flow conditions and in addition to creating significant errors in discharge estimates, the upstream propagating currents are capable of transporting contaminants and affecting water quality. Detailed field observations of bidirectional flows were made in the Chicago River in Chicago, Illinois in the winter of 2005-06. Using multiple acoustic Doppler current profilers simultaneously with a water-quality profiler, the formation of upstream propagating density currents within the Chicago River both as an underflow and an overflow was observed on three occasions. Density differences driving the flow primarily arise from salinity differences between intersecting branches of the Chicago River, whereas water temperature is secondary in the creation of these currents. Deicing salts appear to be the primary source of salinity in the North Branch of the Chicago River, entering the waterway through direct runoff and effluent from a wastewater-treatment plant in a large metropolitan area primarily served by combined sewers. Water-quality assessments of the Chicago River may underestimate (or overestimate) the impairment of the river because standard water-quality monitoring practices do not account for density-driven underflows (or overflows). Chloride concentrations near the riverbed can significantly exceed concentrations at the river surface during underflows indicating that full-depth parameter profiles are necessary for accurate water-quality assessments in urban environments where application of deicing salt is common.     

Evaluation of the water quality in the Guadarrama river at the section of Las Rozas‐Madrid,Spain

The variation of the water quality of the Guadarrama river and its tributaries in a section of Las Rozas‐Madrid, Spain, was studied during the time period between January 2003 and January 2008. The parameter water quality index (WQI) was used to determine the water quality based on the conventional parameters of pollution. It was found that the WQI was slightly affected in the section evaluated. The value of the WQI was in the range of 56–64, which corresponded to the classification of ‘good quality’. It was determined that 64.3% of the organic matter present in the river was removed in the section of Las Rozas‐Madrid. The river acted as a plug flow reactor and a first‐order kinetics governed the ultimate biological oxygen demand (BOD₅) (BOD_U) decay. The value of the first‐order constant demonstrated the river's high self‐purification capacity. In addition, a high linear relationship was found between the WQI and the dissolved oxygen deficit (D). Therefore, a quick determination of WQI may be carried out if the values of D are known. These are easily obtainable by field measurements.     

EFFECT ON ESTUARINE FINE-SEDIMENT TRANSPORT OF INTERMITTENT PUMP DISCHARGE AT PAGHAM HARBOUR, WEST SUSSEX

Field investigations were undertaken to identify the mechanisms of fine-sediment transport at a landward limit of Pagham Harbour. Which is a semi-enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near-bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near-bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh-water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2-D depth-averaged predictive numerical models.     

基于河流动态自然过程的生境修复策略

全球气候变化和土地利用方式的改变对河流的动态自然过程带来不利影响。而目前人们对河流的修复重治理效果而轻自然过程,特别是风景园林与相关学科的交叉与融合研究较少,缺乏聚焦中、微尺度基于河流动态自然过程的生境恢复方法指导。基于此,从雨洪淹没、潮汐消落的河流动态自然过程规律着眼,提出对应的生境修复策略：1)恢复水陆边界的自然属性,重建泛洪区和河岸的联系;2)梯度式快速恢复近自然河岸带生境植被;3)连通感潮河涌湿地和营建关键生物生境,实现多种共生生物栖息地的再生。该方法有助于恢复河流长期、稳定的自由流动,生境在河流动态潮汐作用下异质性不断提高,从而提高河流湿地的生物多样性,还能为城市中心的居民提供亲近自然的休闲空间,以期在河流生境修复实践方面为风景园林和多学科融合提供新思路。     

Die Sturzflut von Braunsbach – Ingenieuranalyse der Gebäudeschäden

The flash flood of Braunsbach – engineering analysis of the building damage At the end of May to the beginning of June, a series of extreme rainfall events occurred in the southern part of Germany, which triggered some severe flash floods with significant building damage in the affected municipalities. The devastating flash flood of May 29, 2016 in Braunsbach in the district Schwäbisch Hall in Baden‐Württemberg caused heavy structural damage to some of the approximately 130 affected buildings. The paper gives an overview of the building damages documented immediately after the event. The damages cases were classified and assessed using the evaluation system of the EDAC‐flood damage model developed at the Earthquake Damage Analysis Center (EDAC) of the Bauhaus‐Universität Weimar. The analysis illustrates the particularities of the damage patterns due to flash floods compared to conventional river floods.     

The Lower River Roding Regeneration

The Lower River Roding Regeneration (LRRR) project was funded by the Office of the Deputy Prime Minister (ODPM) with a contribution from the Environment Agency and was charged with achieving environmental and social gains along the highly urbanised lower 4.4 km of the River Roding. The funding allowed £1.5 million for all elements of work within a 2‐year‐period. Of the four sites constructed, two allowed significant river restoration to be achieved: Creekmouth Open Space and Frogmore Frontage. In the former, an existing flood defence was set back to create a tidal backwater. In the latter, a concrete river wall was demolished and a graded riverbank was created. A total of 1 ha of new saltmarsh was created on these two sites. The project demonstrates how multiple objectives of river restoration, flood defence, habitat creation, improved public amenity and urban regeneration can be achieved in an industrial urban area.     

A mixing‐length‐scale‐based analytical model for predicting velocity profiles of open‐channel flows with submerged rigid vegetation

In open‐channel flows with submerged vegetation, the vertical velocity profile can often be described by two layers: the vegetation layer in the lower region and the surface layer in the upper non‐vegetated region. In this paper, a new mixing‐length scale of eddy is proposed for predicting the vertical velocity profile of flow in an open‐channel with submerged rigid vegetation. The analytical model of velocity profile is based on the momentum equation of flow where the turbulent eddy viscosity is assumed to have a linear relationship with the local velocity. The proposed model was tested against different datasets from the literature. The 22 datasets used cover a range of submergence [flow depth (H)/vegetation height (h) = 1.25 ~ 3.38], different vegetation densities of ah = 0.11 ~ 1.85 (a defined as the frontal area of the vegetation per unit volume) and bed slopes (S_o = 1.8 × 10^?6 ~4.0 × 10^?3). This study showed that the proposed model can predict the velocity profiles well against all datasets, and that the mixing length scale of eddies (λ) is well related with both vegetation height (h) and flow depth of surface layer (i.e. the height of non‐vegetation layer, H–h). Close examination of λ in the proposed model showed that when λ = 0.03, the model predicts vertical velocity profiles well for all datasets used except for very shallow submergence (i.e. H/h < 1.5).     

Berücksichtigung der Fließgeschwindigkeit bei Hochwasser‐Schadensmodellen

Die Quantifizierung der Schadenspotentiale infolge Hochwasser setzt realistische Zusammenhänge zwischen Einwirkungs‐ und Verlustkenngrößen voraus. Da sich herkömmliche Schadensfunktionen auf den Zusammenhag zwischen Fluthöhe und den versicherungsseitig nachvollziehbaren Kosten für eine bestimmte Nutzungsklasse (wie. z. B. private Wohngebäude) beschränken, fehlt zum einen die notwendige Differenzierung nach den für die Widerstandsseite relevanten Merkmalen, zum anderen bleiben weitere Einwirkungsgrößen wie die Fließgeschwindigkeit unberücksichtigt. Auf der Grundlage einer einheitlichen Datenerhebung wurde ein System entwickelt, mit dem die strukturelle Schädigung eines Bauwerks oder eines betroffenen Bauwerksbestands für konkrete Hochwasserszenarien bestimmt werden kann. Dieses Instrumentarium wird erweitert, so dass der Zusammenhang zwischen den Einwirkungskenngrößen Überflutungshöhe und Fließgeschwindigkeit und dem strukturellen Schaden hergestellt werden kann. Die Studie stützt sich auf dabei zwei Datensätze, die nach dem Hochwasser 2002 erhoben wurden: – Datensatz 1 bezieht sich auf eine schriftliche Befragung, welche zwischen 2002 und 2004 in Sachsen durchgeführt wurde. – Datensatz 2 stellt dabei das Ergebnis einer Auswertung von Schadensgutachten im Auftrag der Landestalsperrenverwaltung Sachsen dar. Im Ergebnis kann ein neuartiger Typ von Verletzbarkeitsfunktionen bereitgestellt werden, der den Zusammenhang zwischen Überflutungshöhe, Fließgeschwindigkeit und den Schadensgraden D_i in Abhängigkeit von der konkreten Bauwerksverletzbarkeit beschreibt. Mit Hilfe ebenfalls neu entwickelter Schadensfunktionen werden die so berechneten Schadensgrade in konkrete Verlustaussagen überführt. Wie an drei Testgebieten im Freistaat Sachsen nachgewiesen werden kann, gelingt es mit diesen Funktionen, die gemeldeten Verluste infolge des Hochwassers 2002 in guter Übereinstimmung nachzuvollziehen. Im Weiteren werden erste Untersuchungen zum Einfluss der städtebaulichen Einbindung und der Anströmrichtung auf die strukturellen Schäden vorgestellt. Consideration of flow velocity in flood damage models. Reliable prognoses of building damage caused by flood impact require realistic relationships between action and damage or loss describing parameters. Due to the fact that commonly applied damage functions are related to the different usage classes (i.e. private housing), the required differentiation according to the parameters on the resistance side is still missing and further impact parameters like flow velocity remain unconsidered. On the basis of the August 2002 Saxony flood data base, a method to determine the structural damage for any given flood scenario was developed. This method is improved to consider the correlation between inundation level and flow velocity and structural damage. The study is based on two different datasets collected after the flood 2002 in Saxony: – Dataset 1 is related to the outcome of a questionnaire survey performed by the authors between 2002 and 2004. – Dataset 2 is the outcome of an evaluation of damage expertises by order of the “Landestalsperrenverwaltung Sachsen”. A set of new Specific Vulnerability Functions (SVF) for calculation of damage grades is derived considering the inundation level and the flow velocity depending on the vulnerability of the predominant building types. Based on new developed Specific Damage Functions (SDF) the calculated damage grades are transferred into loss estimates. The developed tools are applied to the reinterpretation of the August 2002 flood damage. Results of the approach are presented for three different study areas in the free state of Saxony. In all cases a remarkable good agreement between the predicted and the reported loss can be stated. First investigations with respect to the location of buildings, the direction of inflow and the structural damage are represented.     

Comparative experimental study of full‐scale H‐subframe using a new industrialized building system and monolithic reinforced concrete beam‐to‐column connection

Industrialized building system (IBS) is a construction process that uses techniques, products, components or building systems that involve prefabricated components and on‐site installation. The structural behaviour of a prefabricated frame structure is widely affected by the specifications of the beam‐to‐column connection. The understanding on the real behaviour of a connection can be assessed by conducting full‐scale experimental tests. In this study, a new IBS hybrid steel–concrete connection in a full‐scale H‐subframe under monotonic loading is investigated. This innovative connection system, consists of precast concrete beam‐and‐column elements with embedded steel end connectors, is patented as Smart IBS. This paper reports the testing procedures and results of this semi‐rigid IBS beam‐to‐column connection to obtain the important attributes of the connection as well as its comparison with monolithic cast‐in‐place reinforced concrete model. The height of both H‐subframes is 3.3 m while the free length of the beam is 3.2 m. The incremental loads were applied as two point loads in one‐third and two‐third of the beam length. The characteristic relationships of the connection such as load to mid‐span deflection, strength, stiffness, ductility, failure modes and crack patterns are studied and compared between both structural systems. Copyright © 2012 John Wiley & Sons, Ltd.     

地下水渗流与地电场参数响应的定量研究

 开展均匀介质稳态渗流模拟试验、非均匀介质稳态渗流模拟试验和采动应力影响下的非均匀介质渗流模拟试验,运用回归分析方法讨论室内试验中一次场电流(激励电流)I与试验模型进水量Qi之间的相关关系;深入矿井开展为期一个多月的地下水渗流地电场动态监测试验,在试验期间发生了矿井突水事故,及时进行了突水水量Qo的测试工作,并讨论一次场电流I与突水水量Qo之间的相关关系。均匀介质稳态渗流模拟试验和非均匀介质稳态渗流模拟试验都表明,固水二相介质中,水未达饱和时,一次场电流I与模型进水量Qi呈线性相关关系。非均匀介质采动条件下的渗流模拟试验表明,在水文条件稳定(水源充足、流速稳定)的情况下,一次场电流I仍然呈现稳态渗流特征,即I与Qi呈线性相关关系,由此认为,在该种条件下,一次场电流主要响应于渗流场的演变和渗流过程的发展,而对岩体的破断与裂隙发育过程响应相对不明显。结合室内试验结论,运用相关分析方法分析井下探测数据,发现在矿井突水过程中,一次场电流I与探测区域出水量Qo呈正相关关系,基于相关分析方法,可以利用电流I的变化趋势实现对探测区域出水量Qo的变化趋势的预测。同时一次场电流与出水量相关度较高的电极,对渗流通道的位置具有指示作用,有助于视电阻率探测成果的分析与解释。     

Experimental study on flow behavior at open channel confluences

Channel confluences are common in natural rivers and hydraulic engineering, and the flow behavior at confluences becomes very complex because of the interaction between the tributary and the main river. In this study, the experiments were performed in a combined flume with a 30° angle between the main and tributary flume located at Sichuan University. The velocity was measured by using a three-component acoustic Doppler velocimeter (ADV) over a grid defined throughout the junction region. Based on the analysis of the velocity at the confluence, the distinctive characteristics of a channel confluence flow may be divided into several zones including a zone of separation immediately downstream of the junction branch channel, the maximum and minimum velocity regions at the upstream and downstream in the confluent channel, and a shear plane developed between the two combining flows downstream of the confluent channel. In addition, secondary circulations in different directions at the higher and lower velocity zones are observed as well. Translated from Journal of Sichuan University (Engineering Science Edition), 2006, 38(2): 1–5 [译自: 四川大学学报 (工程科学版)]     

The influence of drought-induced low freshwater flow on an upper-estuarine macroinvertebrate community

Severe drought in the Thames catchment during 1989 and 1990 resulted in increased water abstraction from the river Thames, reducing the amount of freshwater flowing into the Thames estuary over Teddington weir. Increased salinity levels were recorded in the upper estuary, related to the decrease in flow, which in turn affected the community of freshwater invertebrates inhabiting a site below Teddington weir. A large decrease in BMWP score was recorded following increased abstraction in both 1989 and 1990. However, the disappearance of taxa was not directly related to their perceived sensitivity to organic pollution, with Asellidae, Caenidae and Unionidae being amongst the first families to be affected. Multidimensional scaling ordination indicated that the community demonstrated a cyclical pattern of disturbance and recovery related to variations in salinity and flow-dependent influx of organisms via invertebrate drift. The study indicates that reducing freshwater flow below a critical level can have detrimental effects on the diversity of macroinvertebrate communities in certain sections of tidal rivers.