Stream Surface Research Articles

Environmental factors controlling stream water temperature in a forest catchment

Heat budget of a stream, the Putoisaroma Stream, Hokkaido, Japan, in a forest catchment was estimated in order to investigate environmental factors controlling stream water temperature. In August 2008–October 2009, water temperature was measured at six sites along the stream channels, and the streambed temperature was measured at depths of 5 cm and 30 cm at one of the sites. In order to quantify incoming and outgoing radiations at the stream surface, hemispherical photographs were taken and the shading factors (ratio of the shade to the whole sky) were calculated at the observation sites over the summer. The shading factors, exhibiting seasonal and spatial variations, produced seasonal and spatial changes of shortwave and longwave radiations. The wind speed above stream surface was much smaller than in an open field, which produced turbulent heat fluxes one third as large as that in the open field. The shortwave and longwave radiations and the advective heat flux from upstream showed the major contribution to the stream heat budget, while the streambed heat conduction was secondary. The time series of stream water temperature were simulated well (RMSE = 0.771 ℃, NASH = 0.888) by applying the estimated heat budget. This evidences that the quantification of the shade above stream surface and the calculation of the heat budget are both reasonable. The sensitivity analysis for the simulation indicates that the shading factors along the stream channels control the stream water temperature.

Microbial mats as shelter microhabitat for amphipods in an intermittent karstic spring

Microbial mats represent complex communities where cyanobacteria and diatoms as key organisms provide shelter for diverse assemblages of aquatic invertebrates, like the small stygophilous amphipodSynurella ambulans. Studies addressing such communities in the karst springs have rarely examined springheads, and have ignored intermittent springs. During high flow conditions the stygophilic crustaceans are flushed to the surface of a temporary stream Krčić where microbial mats prevent their drift and enables their successful retreat into underground in the periods of drought. The objective of this study was to characterize the microbial mat community of the Krčić Spring as a shelter forS.ambulansduring strong current and high water level. Representative samples for diatom and cyanobacterial species identification and composition, as well as the fresh mat material for potential animal activity and cyanobacterial phylogenetic analysis were collected. The most dominant diatom wasAchnanthidiumminutissimum, whilstFragilariacapucina,Meridioncirculare,NaviculacryptocephalaandNitzschiapaleahad abundance greater than 0.5%. Morphological observations of cyanobacteria revealed thatPhormidiumfavosumwas the most dominant, withHydrocoleummuscicolaas a subdominant. Cyanobacterial phylogenetic relationship revealed two distinct clusters: (i) "Phormidiumcluster", confirming morphological observations in both winter and spring samples, and (ii) "Wilmottiacluster", a first report for Croatia and found exclusively in the winter sample. Laboratory observations revealed a small stygophilic amphipodS.ambulans, hiding and feeding inside the pockets of fresh microbial mat. The intermittent Krčić Spring as a predator-free and competitor-free ecosystem provides a spatiotemporal conformity between microbial mat and stygophilous amphipod.

人工遮光和营养添加对河流反硝化活性和反硝化细菌群落结构的影响

River ecosystems have been disturbed and aggravated by increasing human activities including those activities wherein forest area is changed to agricultural area in riparian zones and intensive fertilizer usage in agriculture. These anthropogenic activities lead to an increase in the light received by the surface of the river and nutrient (nitrogen and phosphorus) enrichment in the river. Denitrification driven by microorganisms in sediments is the most important path for the removal of nitrogen from aquatic ecosystems. The alteration of light intensity influences the denitrification process owing to the change in the amount of available organic carbon produced via the metabolism of algae and photosynthetic bacteria. We added slow-releasing fertilizer into the river to simulate nutrient enrichment similar to the effect of fertilization from the agricultural industry. We also covered a part of the stream surface to achieve conditions similar to those of rivers in headwaters with thick forest coverage. We selected six streams to conduct manipulated experiments at the core area in the natural reserve in the upper Jinshui River, Hanjiang, to assess the responses of denitrification to the different treatments-nutrient addition and coverage. We also analyzed subsequent changes in community structure and diversity of bacteria using the encoding nirS gene by MiSeq high-throughput sequencing technology. The results showed that artificial shading above streams can reduce the denitrification activity of sediments, relative abundances of dominant bacteria (Dechloromonas) and the diversity of bacteria as indicated by the encoding nirS gene. Furthermore, nutrient addition into the stream increased the denitrification activity of sediments, whereas there was a decrease in relative abundance of dominant bacteria and the diversity of bacteria. The preliminary results confirmed the increase in denitrification activity of stream sediments as a result of increasing light intensity and nutrient content. This study has allowed us to understand the denitrifying capacity of rivers and provides scientific primary data for river management.

Fissure structure analysis to unravel groundwater inflow problem in gold mining site of Pongkor area, West Java, Indonesia

Hydrogeology of Pongkor area, West Java, Indonesia is characterised by fractured aquifer system. The aquifer consists of volcanic rocks of tertiary period, namely Cimapag formation. It is fractured with orientations axis of the fracture patterns are northwest - southeast and northeast - southwest. Pongkor area is drained by two main surface streams, called River Cikaniki and river Cimaja, normally flowing northward direction. In the study area, there is such a vein structure known as Vein Ciurug containing gold ore deposits. The vein is exploited by subsurface tunnelling system. During expansion of the mining activity, some ramps were needed to be constructed. When a ramp at the altitude of +484 m above sea level was expanded, before reaching the vein, the drilling penetrated a saturated zone, causing groundwater inflow with a relatively massive rate. Further, static groundwater flow flooded the opening ramp down with water level of +499 m above sea level, resulted in disruption of mining activities at the ramps under the elevation 500 m above sea level. This study is to analyse the source of groundwater inflow and set a recommendation to solve the problem.

Geochemistry of Croatian superhigh-organic-sulphur Raa coal, imported low-S coal, and bottom ash: their Se and trace metal fingerprints in seawater, clover, foliage, and mushroom specimens

The Labin city area has represented the major Croatian coal mining, metal industry, and coal- fired electricity centre for more than two centuries. The domestic superhigh-organic- sulphur (SHOS) Rasa coal is a unique variety compared to other coal types worldwide, based on its highest organic sulphur values, up to 11%. It was utilized in the Plomin coal-fired power plant during the period 1970-2000, and was replaced by an imported low-S coal afterwards. This paper presents the levels of S, Se, V, U, Hg, Sr, Cd, Cr, Pb, Cu, and Zn in the two coal types, their bottom ash, seawater, and plant (clover, mushroom, and foliage) specimens collected from the Labin city area, while the sulphate was measured in surface stream water. Their levels were compared with relevant legislative as well as the published data from different world localities. Data analysis was interpreted in the context of past and recent coal combustion activities.

Heat transfer enhancement using U-shaped flow routing plates in cooling printed circuit boards

This study presents a numerical investigation on the effect of the U-shaped flow routing plate to laminar mixed convection heat transfer from protruded heat sources at the side walls of a horizontal channel. The air was used as a cooling fluid and protruded heat sources were equipped as 4 × 8 rows into the rectangular channel with insulated walls. Numerical investigations are carried out for the plate width/channel width ratio (LP/W) of 3/20, 1/10, 1/20 and plate angles (α) of 0°, 30°, 60° at different Reynolds (Re), modified Grashof (Gr*) and Richardson (Ri) numbers. In the study, periodic plate placement was analyzed numerically and the effects of a plate placement array on heat transfer enhancement were investigated. The highest heat transfer enhancement (180%) was observed for the values of α = 30° LP/W = 3/20 at all the Re, Gr* and Ri number values. The predominance of natural convection increases the use of the flow routing plate effectiveness but causes a decrease in the heat transfer enhancement after a certain number of Ri. Therefore, the increase in natural convection needs to be controlled. Theoretical fan power (Nfan) requirements due to pressure loss are also investigated. Depending on the parameters used in the numerical study, as a result of the plate usage, the pressure losses increased according to the case without a plate. It is observed that the most important factor affecting the pressure loss was the Re number and this case indicated that the plate placement was more appropriate for low values of Re. The findings obtained during the numerical studies were presented in detail as graphics of the row averaged Nusselt number (Nurow ave.) and the heater temperatures, surface stream lines, and temperature contours.

Modeling habitat requirements of riverine stone loach, Paracobitis hircanica (Teleostei: Nemacheilidae) in the Zarin-Gol River, Caspian Sea basin, Iran

For sustainable exploitation and conservation of biodiversity in riverine ecosystems which have been exposed to considerable modifications by human activities, it is necessary to understand the habitat requirements of the species inhabiting these ecosystems. The Zarin-Gol River in the east of Alborz Mountains, Golestan province, is one of the environments inhabited by the native Hircanian stone loach, Paracobitis hircanica . This stream has been exposed to human activities such as rural discharges, agriculture, fish farm effluents and ecotourism. Habitat requirements of this species and the impacts of human activities were determined in 17 stations along the Zarin-Gol River. Binary Logistic Regression was implemented to develop the distribution model of P. hircanica according to habitat variables. Finally, according to the best model selected by the Akaike Information Criterion (AIC), stream surface width, depth, vegetation cover, altitude and discharge were determined as the most significant parameters for the presence of P. hircanica. Also, other suitable models according to AIC values showed that the stream surface width and depth are the most important independent variables affecting the presence of this loach. Therefore, it was concluded that most significant factors affecting the presence and distribution of P. hircanica are stream surface width, depth, substrate and flow rate.

Exploring dissolved organic carbon cycling at the stream–groundwater interface across a third-order, lowland stream network

The stream–groundwater interface (SGI) is thought to be an important location within stream networks for dissolved organic carbon (DOC) processing (e.g., degradation, removal), since it is considered a hotspot for microbial activity and biogeochemical reactions. This research is one of the first attempts to collect and assess DOC conditions at the SGI across a stream network—an entire third-order, lowland watershed in Michigan, USA. We present an initial exploration of this unique data set and highlight some of the challenges when working at these scales. Overall, our results show that SGI DOC conditions are complex at the network scale and do not conform to predictions based upon previous point- and small-scale studies. We found no strong pattern of DOC removal within the SGI at the network scale even after using chloride and temperature as natural tracers to differentiate between hydrological processes and biogeochemical reactions influencing DOC cycling. Instead, trends in DOC quantity and molecular qualities suggest that potential biotic reactions, including aerobic microbial respiration, had an influence on DOC concentrations at only some of the sites, while physical mixing of ground and stream surface waters appears to explain the majority of the observed changes in DOC concentrations at other sites. In addition, results show that neither SGI sites indicating DOC removal nor DOC molecular quality shifts measured correlated with stream order. It did reveal that DOC variability across surface water, groundwater, and the SGI locations was consistently greatest in the shallow sediments of the SGI, demonstrating that the SGI is a systematically distinct location for DOC conditions in the watershed. Our empirical stream network-scale SGI data are some of the first that are compatible with recently developed process-based, network-scale, SGI models. Our results indicate that these process-based models may not accurately represent SGI exchange of lowland, groundwater discharge-dominated streams like the one in this study. Lastly, this study shows that new methods are needed to achieve the goal of making and linking SGI observations to network-scale biogeochemical processes and theory. To help develop these methods we provide a discussion of the approach we used (i.e., “lessons-learned”) that might become the basis for systematic data analysis of SGI porewaters in future, network-wide biogeochemical studies of the SGI.

Geometrical characteristic-based stream surface of 3D flow field

This paper addressed a novel stream surface generation method to represent the structure of flow field smoother, feature more prominently and better visual clarity than the conventional triangulate method. To have a nice expressive force in the visualization of 3D flow field, first a strategy for adaptive streamline based on geometrical characteristic in 3D flow field space is presented to show a clear flow field pattern and the important flow features in our algorithm. Characteristics such as Euclidean distance between adjacent streamlines, curvature and torsion of each individual streamline are considered as influence factors to determine the number of seed points in the focused regions. Then, in the process of stream surface generation, an adaptive triangulation technique based on geometrical characteristic of streamlines is adopted to keep the structural continuity, smoothness, concavity and convexity of stream surface. At last, the whole algorithm is implemented using CUDA, and it can effectively shorten the lag phase appeared in the process of interaction with the control line and parameter modification. Compared with conventional triangulate method, comprehensive experiments conducted on dataset of delta-wing show that the proposed algorithm can better reflect the underlying properties of the flow field and greatly improve the readability of 3D flow field dataset.

Review of water and soil contamination in and around Salihli geothermal field (Manisa, Turkey)

The town of Salihli is situated in Gediz Graben in the western Anatolia. This region is important in terms of industry, mining, geothermal energy, water sources, and agricultural production. Geothermal flow and anthropogenic activities in Salihli threaten the surrounding environment due to the contamination of cold groundwater, surface water, and soil. The goal of the present study is to determine the environmental effects of the geothermal and anthropogenic activities in Salihli on soil, stream sediments, and water. Stream sediments and farm soil have been contaminated by substances derived from geothermal and industrial effluents. To this end, the quality review of the water was completed and the heavy metal levels in stream sediment samples were measured to determine the extent of contamination. The elements As, B, Br, Fe, and Ni are the major contaminants present in surface water and groundwater in the study area. The concentrations of these elements excess tolerance limits of international water standards. Gibbsite, K-mica, kaolinite, sepiolite, halite, sulfur, willemite, and Pb(OH)2 might be precipitated as scales at low temperatures on the soil; this could be interpreted as a resultant from soil contamination. The concentrations of 17 elements (As, Ba, B, Cd, Co, Cr, Cu, Fe, Hg, Li, Mo, Mn, Ni, Pb, Sb, Sr, and Zn) were measured in samples from stream sediments and surface soils. In the study area, especially geothermal and anthropogenic activities give rise to environmental pollution.

Aerodynamic design of a multi-stage industrial axial compressor

Axial compressors are widely used in industrial applications; high efficiencies and large operating ranges are main performance requirements for their aerodynamic designs. In this study, an aerodynamic design method for multi-stage axial compressors is proposed. The design of the first stage is based on the S1/S2 stream surface theory, and a repeated stage design method is proposed for subsequent stage designs. And in the first stage design, a multi-point optimization design is used to design the rotor and stator blade profiles for both high efficiencies and large operating ranges. A five repeated stage axial compressor with a large mass flow rate has been designed by this design method. Analysis results of the rotor and stator three-dimensional flow fields indicate that the flow is primarily limited to the S1 stream surface and the two-dimensional design method is applicable; the flow in subsequent stages possesses similar characteristics as the flow in first stage. In addition, the designed five-stage axial compressor has a total pressure ratio that approaches the design goal and a stability margin that exceeds the design goal. The novelty of this study includes two parts, one is the usage of multi-point optimization method for rotor and stator blade design, and the other is the repeated stage design method.

Influence of a rock glacier spring on the stream energy budget and cold‐water refuge in an alpine stream

AbstractThe thermal regimes of alpine streams remain understudied and have important implications for cold‐water fish habitat, which is expected to decline due to climatic warming. Previous research has focused on the effects of distributed energy fluxes and meltwater from snowpacks and glaciers on the temperature of mountain streams. This study presents the effects of the groundwater spring discharge from an inactive rock glacier containing little ground ice on the temperature of an alpine stream. Rock glaciers are coarse blocky landforms that are ubiquitous in alpine environments and typically exhibit low groundwater discharge temperatures and resilience to climatic warming. Water temperature data indicate that the rock glacier spring cools the stream by an average of 3 °C during July and August and reduces maximum daily temperatures by an average of 5 °C during the peak temperature period of the first two weeks in August, producing a cold‐water refuge downstream of the spring. The distributed stream surface and streambed energy fluxes are calculated for the reach along the toe of the rock glacier, and solar radiation dominates the distributed stream energy budget. The lateral advective heat flux generated by the rock glacier spring is compared to the distributed energy fluxes over the study reach, and the spring advective heat flux is the dominant control on stream temperature at the reach scale. This study highlights the potential for coarse blocky landforms to generate climatically resilient cold‐water refuges in alpine streams.

How landscape organization and scale shape catchment hydrology and biogeochemistry: insights from a long‐term catchment study

Catchment science plays a critical role in the protection of water resources in the face of ongoing changes in climate, long‐range transport of air pollutants, and land use. Addressing these challenges, however, requires improved understanding of how, when, and where changes in water quantity and quality occur within river networks. To reach these goals, we must recognize how different catchment features are organized to regulate surface chemistry at multiple scales, from processes controlling headwaters, to the downstream mixing of water from multiple landscape sources and deep aquifers. Here we synthesize 30‐years of hydrological and biogeochemical research from the Krycklan catchment study (KCS) in northern Sweden to demonstrate the benefits of coupling long‐term monitoring with multi‐scale research to advance our understanding of catchment functioning across space and time. We show that the regulation of hydrological and biogeochemical patterns in the KCS can be decomposed into four, hierarchically structured landscape features that include: (1) transmissivity and reactivity of dominant source layers within riparian soils, (2) spatial arrangement of groundwater input zones that govern water and solute fluxes at reach‐ to segment‐scales, (3) landscape scale heterogeneity (forests, mires, and lakes) that generates unique biogeochemical signals downstream, and (4) broad‐scale mixing of surface streams with deep groundwater contributions. While this set of features are perhaps specific to the study region, analogous hierarchical controls are likely to be widespread. Resolving these scale dependent processes is important for predicting how, when, and where different environmental changes may influence patterns of surface water chemistry within river networks. WIREs Water 2018, 5:e1265. doi: 10.1002/wat2.1265This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water and Environmental Change Science of Water > Methods

Influence of turbidity and aeration on the albedo of mountain streams

AbstractStream surface albedo plays a key role in the energy balance of rivers and streams that are exposed to direct solar radiation. Most physically based analyses and models have incorporated a constant stream albedo between 0.03 and 0.10, based primarily on measurements from low‐gradient streams with low suspended sediment concentrations. However, albedo should vary with solar elevation angle, suspended sediment concentration, aeration, and fraction of direct versus diffuse radiation. The objective of this study was to quantify the dependence of albedo of mountain streams on the controlling factors and to develop a predictive model for use in physically based analysis and modelling of stream temperature, especially for future climate and land‐use scenarios. Stream surface albedo was measured at nine sites with a variety of gradients and suspended sediment characteristics in the southern Coast Mountains of British Columbia, Canada. As expected, albedo of low‐gradient, non‐white water (flatwater) streams increased with solar elevation angle, suspended sediment concentration, and proportion of diffuse to direct solar radiation, ranging between 0.025 during cloudy periods over clear water to 0.25 for turbid water at elevation angles of less than 20°. Albedo was enhanced in steep reaches or at channel steps and cascades where flow was visibly aerated, with a range of 0.09 to 0.33. In clear weather, albedo exhibited notable diurnal variability at flatwater sampling sites. For example, during late summer, surface albedo typically fluctuated between 0.08 and 0.15 on a daily basis at a flatwater site on the highly turbid, glacier‐fed Lillooet River. Multiple regression models explained approximately 60% and 40% of the variance under cross validation for flatwater and white water data subsets, respectively, with corresponding root mean square errors of approximately 0.02 and 0.06.

Modelling surface geomorphic processes using the RUSLE and specific stream power in a GIS framework, NE Peloponnese, Greece

Mediterranean regions, with climate variability and long histories of human disturbance, are particularly vulnerable to soil erosion and sediment redistribution. This study examines surface soil stability and stream energy of the 243 km2 Inachos River watershed in the northeast Peloponnese, Greece. This mountainous, semi-arid Mediterranean region has an extensive history of human activity. Soil loss and stream energy are each quantified by applying the Revised Universal Soil Loss Equation (RUSLE) using the Unit Stream Power Erosion Deposition (USPED) method and the specific stream power approach to the main river channels. These models are used to indicate the spatial variability in geomorphic activity. Results show an average soil loss for the Inachos River catchment of 15.0 t ha−1 a−1, exceeding the rate of soil formation. Values range from nil in low gradient environments to 4287 t ha−1 a−1 in steep, mountainous regions. Gradient and rainfall erosivity are the primary factors. High specific stream power in the upper watershed exceeds 17,100 W m−2, resulting in the mobilization of sediment into channelized debris flows that transport sediment from the steep hillslopes. Episodic high-magnitude precipitation events promote the longitudinal connectivity of the catchment. The long occupation and agricultural history, extending as far back as Neolithic time, has accelerated downslope sediment transport.

Regional-scale lateral carbon transport and CO<sub>2</sub> evasion in temperate stream catchments

Abstract. Inland waters play an important role in regional to global-scale carbon cycling by transporting, processing and emitting substantial amounts of carbon, which originate mainly from their catchments. In this study, we analyzed the relationship between terrestrial net primary production (NPP) and the rate at which carbon is exported from the catchments in a temperate stream network. The analysis included more than 200 catchment areas in southwest Germany, ranging in size from 0.8 to 889 km2 for which CO2 evasion from stream surfaces and downstream transport with stream discharge were estimated from water quality monitoring data, while NPP in the catchments was obtained from a global data set based on remote sensing. We found that on average 13.9 g C m−2 yr−1 (corresponding to 2.7 % of terrestrial NPP) are exported from the catchments by streams and rivers, in which both CO2 evasion and downstream transport contributed about equally to this flux. The average carbon fluxes in the catchments of the study area resembled global and large-scale zonal mean values in many respects, including NPP, stream evasion and the carbon export per catchment area in the fluvial network. A review of existing studies on aquatic–terrestrial coupling in the carbon cycle suggests that the carbon export per catchment area varies in a relatively narrow range, despite a broad range of different spatial scales and hydrological characteristics of the study regions.

Quantifying shortwave and longwave radiation inputs to headwater streams under differing canopy structures

Abstract The extent to which riparian understory vegetation in harvested areas can partially or fully negate changes in incoming shortwave and longwave radiation was investigated along 1st-order headwater streams. Despite similarities in shade provisioning, others have noted increased stream temperatures in post-harvest understory-only canopies, relative to mature forest canopies. To advance the process understanding of how management of riparian vegetation affects stream energetics, incoming shortwave and longwave radiation was measured directly at the stream surface for 6 stream reaches in a mid-latitude, temperate, montane, forested watershed with strongly contrasting riparian canopies. Radiometer arrays were installed during mid-summer, clear-sky conditions underneath combined tree and understory vegetation canopies within non-impacted forested reaches (references), a partial-cut reach (∼50% overstory canopy removal), and two recently (∼5 year.) clear-cut reaches with contrasting densities of understory vegetation. Results indicate that incoming all-wave radiation was 37–39% less in the three undisturbed reference reaches, compared to an open area reference. The radiative regimes in the partial-cut and dense-understory clear-cut reaches were similar to the intact forested reaches, with 37% and 39% less all-wave radiation, respectively, in comparison to the open reference location. The sparse-understory clear-cut exhibited a 16% reduction in all-wave radiation. Findings from this study indicate that some recently clear-cut and partial-cut headwater riparian ecosystems can rapidly recover (

Quantification and characterization of the dynamics of spring and stream water systems in the Berchtesgaden Alps with a long-term stable isotope dataset

The understanding of alpine groundwater dynamics and the interactions with surface stream water is crucial for water resources research and management in mountain regions. In order to characterize local spring and stream water systems, samples at 8 springs, 5 stream gauges and bulk samples of precipitation at 4 sites were regularly collected between January 2012 and January 2016 in the Berchtesgaden Alps for stable water isotope analysis. The sampled hydro-systems are characterized by very different dynamics of the stable isotope signatures. To quantify those differences, we analyzed the stable isotope time series and calculated mean transit times (MTT) and young water fractions (YWF) of the sampled systems. Based on the data analysis, two groups of spring systems could be identified: one group with relatively short MTT (and high YWF) and another group with long MTT (and low YWF). The MTT and the YWF of the sampled streams were intermediate, respectively. The reaction of the sampled spring and stream systems to precipitation input was studied by lag time analysis. The average lag times revealed the influence of snow and ice melt for the hydrology in the study region. It was not possible to determine the recharge elevation of the spring and stream systems due to a lack of altitude effect in the precipitation data. For two catchments, the influence of the spring water stable isotopic composition on the streamflow was shown, highlighting the importance of the spring water for the river network in the study area.

The devil is in the tails: the role of globular cluster mass evolution on stream properties

We present a study of the effects of collisional dynamics on the formation and detectability of cold tidal streams. A semi-analytical model for the evolution of the stellar mass function was implemented and coupled to a fast stellar stream simulation code, as well as the synthetic cluster evolution code EMACSS for the mass evolution as a function of a globular cluster orbit. We find that the increase in the average mass of the escaping stars for clusters close to dissolution has a major effect on the observable stream surface density. As an example, we show that Palomar 5 would have undetectable streams (in an SDSS-like survey) if it was currently three times more massive, despite the fact that a more massive cluster loses stars at a higher rate. This bias due to the preferential escape of low-mass stars is an alternative explanation for the absence of tails near massive clusters, than a dark matter halo associated with the cluster. We explore the orbits of a large sample of Milky Way globular clusters and derive their initial masses and remaining mass fraction. Using properties of known tidal tails we explore regions of parameter space that favour the detectability of a stream. A list of high probability candidates is discussed

Probabilistic safety evaluation of a river bridge substructure against floods

Many factors affect the safety of a reinforced concrete river bridge, and some of these factors might have significant uncertainty that should be evaluated. This study focuses on a system reliability analysis of a reinforced concrete bridge, which is the most common type of river bridge in Taiwan. Specifically, non-linear behaviours of core/cover concrete and steel reinforcement in the substructure of a bridge are considered. Uncertainties of stream surface elevation, water velocity, local scour depth, soil property and record-to-record variations are included in the probabilistic model. The aforementioned parameters of six river geometries are incorporated into a Hydrologic Engineering Center-river analysis system (HEC-RAS) model to assess their impacts on the bridge safety. The effect of river geometry has not been studied thoroughly. Results shown here indicate that it plays an important role. Adopting Bayesian theory to consider the record-to-record uncertainty by combining historic and HEC simulation data is another innovative aspect of this study. Monte Carlo simulation is used to conduct the reliability analysis. The results obtained indicate that the proposed procedure for the bridge reliability analysis is consistent with expert engineering judgement and that the variation in scouring depth and river geometry are pertinent to bridge safety.