Effects Of Hydraulics Research Articles

Coupled hydraulics and carbon economy underlie age-related growth decline and revitalisation of sand-fixing shrubs after crown removal.

Crown removal revitalises sand-fixing shrubs that show declining vigour with age in drought-prone environments; however, the underlying mechanisms are poorly understood. Here, we addressed this knowledge gap by comparing the growth performance, xylem hydraulics and plant carbon economy across different plant ages (10, 21 and 33 years) and treatments (control and crown removal) using a representative sand-fixing shrub (Caragana microphylla Lam.) in northern China. We found that growth decline with plant age was accompanied by simultaneous decreases in soil moisture, plant hydraulic efficiency and photosynthetic capacity, suggesting that these interconnected changes in plant water relations and carbon economy were responsible for this decline. Following crown removal, quick resprouting, involving remobilisation of root nonstructural carbohydrate reserves, contributed to the reconstruction of an efficient hydraulic system and improved plant carbon status, but this became less effective in older shrubs. These age-dependent effects of carbon economy and hydraulics on plant growth vigour provide a mechanistic explanation for the age-related decline and revitalisation of sand-fixing shrubs. This understanding is crucial for the development of suitable management strategies for shrub plantations constructed with species having the resprouting ability and contributes to the sustainability of ecological restoration projects in water-limited sandy lands.

Swimming behaviour of Atlantic salmon kelts migrating past a hydropower plant dam: Effects of hydraulics and dam operations

Hydropower plants commonly impede the downstream migration of Atlantic salmon (Salmo salar) kelts. Thus, understanding the effects of hydraulic conditions on kelt behaviour and passage performance at dams is crucial for developing effective mitigation measures. In this study, we investigated the influence of hydraulic conditions on kelt passage performance and swimming behaviour at a Norwegian hydropower plant. We combined biological data from 48 kelts collected via acoustic telemetry with hydraulic data modelled using computational fluid dynamics. We assessed kelt passage performance using metrics such as time-to-pass, total number of detections, and total number of detections per day. Additionally, we analysed swimming depths and speeds in relation to the hydraulic conditions created by different dam operating conditions. We found that the dam operation schedule impacted the kelts' ability to find a route past the dam. Though kelts could have passed the dam throughout the study period via a submerged pipe at the dam (which had seemingly sufficient discharge for the kelts to find), 98 % of the kelts instead waited for a spill gate to open partway through the study period. The swimming depth analysis indicated diel variation, with kelts swimming nearer to the water surface during the night. We found that swimming speed increased with increasing kelt body length, particularly under high turbulence kinetic energy and during the day. Furthermore, kelts swam faster as water velocity increased, but slowed down again as turbulence intensity increased. Our findings reveal the effects of hydraulic conditions and dam operations on the migration behaviour of Atlantic salmon kelts. This provides valuable insights for developing strategies to optimise dam operations and improve fish passage performance, including the need to spill enough water to increase passage success and will contribute to sustainable management of Atlantic salmon populations in regulated rivers.

Effects of boundary hydraulics, dissolved oxygen, and dissolved organic carbon on growth and death dynamics of aerobic microbes in riverbed dune-induced hyporheic zones

Surface and groundwater interact in the hyporheic zone beneath and adjacent to rivers in the presence of a diverse microbial community. Heterotrophic bacteria mediate a range of environmentally important reactions, yet few studies have quantified bacterial growth and death dynamics in the hyporheic zone, and none have systematically analyzed their response to variations in hydraulic or chemical conditions. We used MODFLOW and SEAM3D to simulate hydraulics; dissolved oxygen (DO) and dissolved organic carbon (DOC) transport; and aerobic microbial metabolism, growth, and death in hyporheic zones induced by riverbed dunes. We ran simulations both with and without growth/death processes, and varied hydraulic parameters and DO/DOC boundary concentrations. Microbial biomass reached steady state (t = 3 days) in every simulation, at which time there was greater biomass and DOC biodegradation rates in the hyporheic flowcell (300 % and 85 % higher for the base case, respectively) when accounting for microbial growth dynamics. This occurred as microbial biomass tailored its spatial distribution to the availability of DO and DOC, demonstrating the importance of simulating growth/death processes. Biomass generally increased with hyporheic flow cell area as upwelling groundwater decreased. When varying surface water DO and DOC source concentrations relative to the base case, the greatest effect on biomass occurred when increasing DOC and decreasing DO. We determined minimum DO and DOC steady-state concentrations required for microbial growth, but the minimums were not absolute or related by stoichiometry. Increasing DOC created a smaller area of microbes with higher concentrations relative to the base case. Increasing DO slightly increased the area occupied by microbes while keeping the total biomass nearly constant. Overall, microbial growth and death dynamics depend on DO and DOC availability in the hyporheic zone, which is dependent on DOC/DO boundary concentrations and hyporheic flow paths, and in turn the hydraulic interaction between surface water and groundwater.

Research on the method of responsibility division of transboundary water pollution

With the rapid development of China’s economy and society, there has been a serious crisis in the field of water environment safety. Due to the mobility of water and the spatial distribution of water in the basin and other reasons, cross-border water pollution has become a major issue of general concern to the state and the whole society. In this paper, the scope of responsibility of pollutants is generated using the one-dimensional steady-state water quality dynamics based on the basic data of the target area, the corresponding basic data of water quality, water quantity, administrative scope and responsible person so on, so as to realize the comprehensive responsibility division of water quality of cross-border water bodies. The pollutant attenuation coefficient was used to calculate the pollution concentration of pollutants from the initial section of the upstream of the responsibility jurisdiction to the section of the river section at the end of the jurisdiction, which can avoid the calculation error caused by the concentration changes of the pollutants under the comprehensive effects of hydrology, hydraulics, chemistry, physics, geography, biochemistry, climate, location and meteorology in the process of transportation, and improve the accuracy of pollution liability definition of each administrative area.

Effects of benthic hydraulics on sediment oxygen demand in a canyon-shaped deep drinking water reservoir: Experimental and modeling study

Sediment oxygen demand (SOD) is a major contributor to hypolimnetic oxygen depletion and the release of internal nutrient loading. By measuring the SOD in experimental chambers using in both dissolved oxygen (DO) depletion and diffusional oxygen transfer methods, a model of SOD for a sediment bed with water current-induced turbulence was presented. An experimental study was also performed using near-sediment vertical DO profiles and correlated hydraulic parameters stimulated using a computational fluid dynamics model to determine how turbulences and DO concentrations in the overlying water affects SOD and diffusive boundary layer thickness. The dependence of the oxygen transfer coefficient and diffusive boundary layer on hydraulic parameters was quantified, and the SOD was expressed as a function of the shear velocity and the bulk DO concentrations. Theoretical predictions were validated using microelectrode measurements in a series of laboratory experiments. This study found that flow over the sediment surface caused an increase in SOD, attributed to enhanced sediment oxygen uptake and reduced substances fluxes, i.e., for a constant maximum biological oxygen consumption rate, an increased current over the sediment could increase the SOD by 4.5 times compared to stagnant water. These results highlight the importance of considering current-induced SOD increases when designing and implementing aeration/artificial mixing strategies.

Effects of Flow Hydraulics, Pipe Structure and Submerged Jet on Leak Behaviour

The aim of this paper is numerical and experimental study of the effects of flow hydraulics, pipe structure (particularly elastic behaviour) and submerged jet on leak behaviour. In this regard, experimental tests were performed on a high-pressure circulation set up. Experiments were performed on an old steel pipe and a High Density Polyethylene (HDPE) pipe discharged to the atmosphere in a wide range of pressures up to 50 m. To analyze the leak behaviour, the effect of the surrounding environment and the pressure on leak area, the experimental setup was modeled by ANSYS software. Then, the numerical model was validated using experimental results and used to analyze and generalize leakage results in other situations. The results indicated that: 1) Standard k-e turbulence model showed a better performance and relatively better results in modelling leakage in comparison with the other turbulence models, 2) Combining the Finite Volume and Finite Element methods for taking into account the impact of pressure allowed simultaneous examination of the pipe hydraulics and the structure of the leak area to obtain more reasonable results from hydraulic analysis of the flow and pipe structure, 3) Pressure fluctuations in the submerged jet affect the leakage discharge so that it is reduced compared to discharging to the atmosphere, 4) it was observed that the leakage exponent is close to the theoretical value of 0.5, considering the effect of pressure head on leak area behaviour. Furthermore, there is a linear relationship between pressure head and leak area for elastic pipes.

Solar-ice systems for multi-family buildings: hydraulics and weather data analysis

Dynamic simulations using the TRNSYS environment were used to assess the potentials of solar-ice systems for multi-family buildings in Switzerland. The goals of this paper were: i) to analyze and quantify the effects of different hydraulics in the primary loop (solar collectors, ice storage and heat pump), ii) to determine the energetic performance of solar-ice systems for multi-family buildings and iii) to assess the influence of the chosen weather data on the system performance. Simulations were carried out for a range of collector areas of 1.5 m2/MWh to 2.5 m2/MWh and for ice storage volumes of 0.4 m3/MWh to 0.6 m3/MWh being MWh the total yearly heat demand. An averaged increase of the ΔSPF of 26% was obtained by using direct solar heat in the warm storage. Adding the possibility to use solar heat for heat pump evaporator, increased the SPFSHP+ by 31 %. Simulations of eight cities in Switzerland using cold, warm and normal weather data sets from SIA were carried out. Results for Davos and Locarno achieved the best results with averaged SPFSHP+ of 7.4 and 6.3 respectively. Simulations for the rest of the cities achieved averaged SPFSHP+ in the range of 3.8 to 4.5. The use a cold weather data respect to the normal one defined by the SIA standard led to an average decrease of the SPFSHP+ of 25 %. The use of a warm weather data led to an increase of the SPFSHP+ of 5 %.

Multiphase-Flow Simulation Helps Find Optimal Lateral Length for Best Production

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 187502, “Production Optimization in the Midland Basin Through Lateral Multiphase-Flow Simulation,” by Yogashri Pradhan, SPE, and Hongjie Xiong, SPE, Texas Oil and Gas Institute, prepared for the 2017 SPE Liquids-Rich Basins Conference—North America, Midland, Texas, USA, 13–14 September. The paper has not been peer reviewed. Wellbore lateral lengths and uniformity are important for production optimization, affecting liquid holdup and productivity throughout well production life. However, wellbore construction designed for holding leases and completed under time constraints could negatively affect production and limit operators’ potential for their acreage. This paper demonstrates a work flow to determine optimal lateral lengths and trajectories in the Midland Basin by studying the effect of the lateral length and trajectory on well production. Introduction Operators often use a scalar to determine wellbore contributions for wells with an atypical lateral length on their leases. The work flow presented here provides realizations to justify use of this scalar, evaluating whether lateral lengths proportionally increase production, whether wellbore contributions are uniform throughout the lateral length of the wells, and whether various wellbore deviations and tortuosities should have the same scalar applied for estimating well production. A team investigated the effect of lateral length on well estimated ultimate recovery (EUR). The EURs were calculated from daily production data from 15 operators and then normalized by well lateral length from the top perforation to the bottom perforation. The modified hyperbolic method was used to perform the decline-curve analysis. Simply applying a scalar for the lateral length among the wells would not yield proportionate EURs. When drilled and completed in unconventional reservoirs with multiple-stage hydraulic fracturing, horizontal wells experience a decline in productivity with time because the conductivity of those manmade fractures deteriorates with production and time. Therefore, in order to understand the effect of wellbore trajectory and lateral length on production fully, the team developed a work flow to incorporate an in-depth analysis on transient effects of wellbore hydraulics combined with unconventional reservoir performance over time. Methodology To develop an understanding of reservoir performance over time, numerical models are developed on the basis of previous knowledge, geology, and reservoir data. With respect to the Lower Spraberry and Wolfcamp B wells considered in this study, case studies for which are presented in the complete paper, the numerical models were first calibrated with historical pressure and production data. Fig. 1 displays the work flow that the team developed to combine long-term reservoir performance with wellbore hydraulics. The team used several production metrics to compare wellbore contributions throughout the lateral affected by the trajectory with respect to different times throughout the well life, including drawdown pressure, pressure decline throughout the lateral, and liquid-holdup results.

Indicators for contaminant transport in a three-layer wetland with wind

Abstract The effect of global climate change is increasing and it can influence agriculture in many ways, especially in that it makes great threaten on agricultural water resources. Since agricultural water supply is a key issue for agricultural production, indicators for contaminant transport in wetlands should be considered in order to solve agricultural water pollution and promote water protection. In this paper, we analyze the environmental dispersion in a typical three-layer wetland flows with the effect of wind taken into account. The analytical solution for velocity distribution is rigorously derived and the dependence of characteristic parameters on averaged dimensionless velocity is recorded. The asymptotic analysis theory of Gill is employed to measure dispersivity for natural wetland flows with a commonly high Peclet number. Both velocity and environmental dispersion are significantly influenced by wind, in terms of its direction and the magnitude of force. The effects of hydraulics and ecological degradation are considered to obtain the analytical solution for the mean concentration and maximal critical length of the region influenced by the process of contaminant transport.

Effects of flow hydraulics on total nitrogen loss on steep slopes under simulated rainfall conditions

Abstract Flow hydraulics play important roles in soil erosion and loss of soil nutrients. A better understanding of the relationship between flow hydraulics and nutrient losses will improve chemical transport modeling. The laboratory experiment was conducted to determine flow hydraulics' effects on total nitrogen (TN) loss. The impacts of rainfall intensities (0.6, 1.1, 1.61, 2.12, and 2.54 mm·min−1) and slope gradients (10°, 15°, and 20°) on TN loss were also studied. Selected soils were derived from purple sandy shales, which are the main parent materials in Wangjiaqiao watershed, southern China. Results show that negative linear relationships (R2 = 0.71) were observed between the rate of Manning roughness coefficient to average flow depth and the unit area runoff-associated TN transport rate. There was a good linear relationship between the unit area sediment-associated TN transport rate and Reynolds numbers (R2 = 0.90), flow velocity (R2 = 0.87), and stream power (R2 = 0.73), while Froude numbers, Darcy–Weisbach and Manning friction coefficients were not good hydraulic indicators of the sediment-associated TN loss of purple soil. The equation including stream power and flow velocity may have a better correlation coefficient (R2 = 0.94).

The impact of well-field configuration and permeability heterogeneity on contaminant mass removal and plume persistence

The purpose of this study is to investigate the effects of well-field hydraulics and permeability heterogeneity on mass-removal efficiency for systems comprising large groundwater contaminant plumes. A three-dimensional (3D) numerical model was used to simulate the impact of different well-field configurations on pump-and-treat mass removal for heterogeneous domains. The relationship between reduction in contaminant mass discharge (CMDR) and mass removal (MR) was used as the metric to examine remediation efficiency. The impacts of well-field configuration on mass removal behavior are attributed to mass-transfer constraints related to regions of low flow associated with the well field, which can be muted by the influence of permeability heterogeneity. These impacts are reflected in the associated CMDR-MR profiles. Systems whose CDMR-MR profiles are below the 1:1 relationship line are associated with more efficient well-field configurations. The impact of domain heterogeneity on mass-removal effectiveness was investigated in terms of both variance and correlation scale of the random permeability distributions and indexed by the CMDR-MR relationship. Data collected from pump-and-treat operations conducted in a section of the Tucson International Airport Area (TIAA) federal Superfund site were used as a case study. The comparison between simulated and measured site data supports the general validity of the numerical model, and results from the case study are consistent with the conclusions of the theoretical study. These results illustrate that the CMDR-MR relationship can be an effective way to quantify the impacts of different factors on mass-removal efficiency.

Performance of multiple fractured horizontal wells with consideration of pressure drop within wellbore

In this paper, we proposed a novel model for multiple fractured horizontal wells (MFHW) with consideration of pressure drop in the wellbore. To begin with, we proposed an analytical model incorporating with turbulent flow in wellbore, Darcy's flow in reservoir and hydraulic fractures, and effect of stress-sensitivity of permeability. Then, the model was solved by used mathematical methods of line source function, Pedrosa's substitution, and Newton-Raphson algorithm. After that, based on the solution, pressure transient behavior of the MFHW was obtained. Finally, model validation and sensitivity analysis were conducted.Results of validations show that there are good matches among our results, analytical results and numerical results. According to results of sensitivity analysis, we find that the pressure depletion decreases as fracture volume increases, and their effect on pressure depletion becomes weaker when increasing the pressure drops within wellbore. The pressure depletion increases with the increase of Reynolds number and relative pipe roughness; it decreases with the increase of reservoir-wellbore constant. The effects of Reynolds number, reservoir-wellbore constant, and relative pipe roughness on pressure behavior become stronger as fracture parameters increase, especially for fracture number. It is also found that the relative pipe roughness mainly affects the flow regimes at the early time, including bilinear flow and formation linear flow, while Reynolds number and reservoir-wellbore constant can influence all the flow regimes.This work provides some guidelines on understanding the effects of wellbore hydraulics on well performance in the tight gas reservoirs.

Experimental Testing of Water Disinfection Models under Varying Hydraulic and Kinetic Conditions.

The concomitant effects of hydraulics and reaction kinetics on the disinfection efficiency (DE) of Chlorine Contact Tank (CCT) setups were experimentally assessed, to test the predictive-ability of first order kinetics models: Chick-Watson (C-W), C-t rule and Wehner-Wilhelm (W-W). Prototype tests were conducted using river water characterised for quality parameters, chlorine demand and inactivation rates of total and thermotolerant coliform. Poor, average and superior CCT baffling conditions were assessed by tracer experimentation and for their DE under three chlorine dosages. The models' DE predictive-ability was comparable and high for superior baffling, but decreased differently with the hydraulic efficiency (maximum errors of +15.3% with W-W, +26.0% with C-W and -36.6% with C-t). The positive bias shown by W-W renders it unsafe for CCT design, so the results favoured the C-t rule as the preferred analytical tool of comparable complexity. Potential refinements to these models that could lead to operational savings are identified.

<B>Performance Evaluation and Modeling of Synthetic-Fiber Barrier in the Treatment of Turbid Water</B>

A synthetic-fiber barrier for the removal of turbidity in water was developed and tested using a laboratory scale channel. The effects of hydraulics (flow rate and exchange rate); density current caused by temperature and turbidity difference; barrier conditions (thickness, number and shape); and particle size were analyzed. The experimental results indicated that removal efficiency was positively related to barrier thickness and number, was inversely related to the strength of the density current, and was also negatively affected by the flow rate and exchange rate. A wedged barrier was found to work better than a rectangular one when the same amount of fiber was used. Based on the experimental work, empirical models for the removal efficiency and barrier design were established using dimensionless groups. The modeling results indicated that the predicted values were consistent with the experimental work and the increases and decreases in the performance were suitably simulated.

Aquatic ecosystem functions of an isolated floodplain and their implications for flood retention and management

Summary We used an isolated floodplain of the river Danube as a model system to gain an understanding on the functioning of retention areas to predict future developments and to sustain their ecological services. We applied correlation analysis and spline regression models to assess the effects of geomorphology, hydraulics, and seasonality on sediment characteristics, suspended solids, hydrochemistry and primary producers. The spatio‐temporal connection to the river is the primary factor influencing the hydrochemical characteristics and sediments. Allochthonous processes such as nutrient and sediment input during high waters dominate in connected parts of the floodplain, whereas autochthonous processes, for example, the release of phosphorus from the sediments and internally driven eutrophication, dominate in isolated parts. These conditions also affect the dominating primary producers, biodiversity, the degree of floodplain aggradation and thus the potential life span of aquatic habitats. Measures to improve the functional basis for ecological services may use both allochthonous and autochthonous processes as a starting point, that is, minimizing sediment storage and nutrient input and improving the water balance to prolong the life span of isolated waters, and thus maximizing water body diversity and associated biodiversity. Based on the results of our analysis and literature, eight alternative management measures have been evaluated. As a result, we propose a stepwise adaptive approach beginning with a controlled water supply with low sediments and nutrient loads. If these measures prove insufficient to sustain ecological functions and conservation value, more radical steps must be considered. Synthesis and applications The increasing problems with catastrophic flooding have forced decision makers to seek basin‐wide solutions with focus on ‘more room for the river’ and the reintegration of former floodplains as retention basins. Such reintegrations also represent opportunities to improve the ecological conditions for nature development in addition to their principal function, that is, the storage of water during floods. The results of our study can serve as an effective tool to predict the effects of alternative management options and to establish and define the design criteria of water retention areas with regard to their ecological functions, life spans and biodiversity.

Comparative Study of Digital Hydraulics and Digital Electronics

Digital fluid power has gained substantial attention in the last decade and recently has been the focus of several fluid power conferences. Recognizing that digital hydraulics is an enabling technology for many new high-efficiency and novel hydraulic systems, this paper demonstrates that digital fluid power cannot simply be treated as an extension of the well-accepted digital technology in the electronics domain due to some key differences between the hydraulic and electrical systems. Digital hydraulics incorporates similar ideas as those from digital electronics with a goal of reducing the energy losses caused by the throttling of the fluid in typical hydraulic systems. A good understanding of the differences between hydraulic and electronic systems is needed because fluid and electrical properties are different. The compressibility and inertia effects of hydraulics are compared to the capacitance and inductance of electrical systems. The different actuation efforts of hydraulics and electronics are shown. Also, some of the different ideas for achieving hydraulic transformers are discussed. By understanding and accounting for the differences and similarities during the design process, novel digital hydraulic systems can be more efficient and effective while minimizing noise and vibration due to switching techniques.

Theoretical development on the effects of changing flow hydraulics on incipient bed load motion

Several decades of flume and field measurements have indicated that in rough turbulent flows the critical Shields stress increases with increasing slope and associated decreasing relative depth. This result contradicts the usual consideration of a decreased critical Shields value on very steep slopes because of increased gravitational effects. However, recent studies have demonstrated that these experimental results could be reproduced with a force balance model if the classical logarithmic velocity profile was replaced with a velocity profile that was more compatible with available velocity measurements over gravel beds. These measurements indicate the existence of a roughness layer that is a zone of almost constant velocity close to the bed, whose properties (mean velocity and turbulence) depended on the flow's relative depth. Unfortunately, velocity profile measurements for low relative depth associated with steep slopes are scarce, and it is still difficult to include such flow properties in a force balance model. Flow resistance data (on the basis of depth average velocity measurements) are very common and cover a wide range of slopes and relative depths. In this paper these data are used to fit a velocity profile including a roughness layer. When used in a force balance model for incipient motion, it adequately reproduced a data set composed of 270 critical Shields values measured in a flume with near‐uniform sediments. The relevance of this research to field problems is discussed using a data set composed of 92 critical Shields stresses obtained from field measurements. Finally, a model is proposed for field applications taking into account the slope effect.

Interactive effects of cover and hydraulics on brown trout habitat selection patterns

AbstractHabitat modelling results are extremely sensitive to the habitat suitability criteria (HSC) used in the simulations. HSCs are usually expressed as univariate habitat suitability curves, although such univariate approach has been long questioned, since overlooking interactions between hydraulic variables may misrepresent the complexity of fish behaviour in habitat selection. It could lead to adopt erroneous flow management decisions based on misleading results. Furthermore, the interactive effects of hydraulic variables on habitat selection may be driven by the structural features of the channel, which determine cover availability. Therefore, we compared brown trout habitat selection patterns through multivariate resource selection functions (RSFs) in structurally contrasting rivers to unveil the interactive effects of hydraulics and cover elements and their consequences in univariate HSC results. Microhabitat preferences of young‐of‐the‐year (0+) trout were similar across fast and slow waters, meanwhile juvenile (1+) and adult (>1+) preferences significantly changed. RSFs for young‐of‐the‐year trout were consistent with univariate results and did not differ among water types. However, RSFs for older trout varied among water types and revealed complex interactions among hydraulic variables and between hydraulics and structural elements, which were not described accurately by univariate curves. Therefore, results suggest that interactions between water depth and current velocity have a significant effect on habitat selection patterns in juvenile and adult brown trout, this effect being controlled by cover availability. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of stream hydraulics and other environmental variables on density of Narapa bonettoi (Oligochaeta) in the Paraná River system

AbstractHydraulic and substratum conditions have been identified as two stream features which affect the benthic community composition, abundance and distribution. However, little attention has been given to the influence of hydraulic variables in large river beds. The aim of this study was to analyse the incidence of the near‐bottom hydraulic conditions and other environmental variables on the density of Narapa bonettoi (Oligochaeta, Narapidae), a typical and dominant species found in sandy bed rivers of diverse hierarchy of the Paraná River basin. A large amount of existing and available benthic data were used. The highest correlations among N. bonettoi densities and environmental variables were obtained with the hydraulic variables of friction Reynolds number (R*) and shear stress (τ0); the substratum type (sand, silt and clay) and organic matter content. The results show that N. bonettoi density would be related with the hydraulic variables following a ‘bell‐shaped’ tendency, e.g. with the friction Reynolds number, N. bonettoi would have a preference for transition values of turbulence (∼40 < R* < ∼50), which is equivalent to τ0 between ∼0.6 and ∼0.8 kg −2. Densities show a slight decreasing tendency toward the maximum R* values, suggesting that the species does not support a completely developed turbulence (R* > ∼70). Significant but negative correlations were reported in the literature between benthic macroinvertebrates typical of smaller and steeper streams and R* values far beyond the threshold 70 value. N. bonettoi shows a clear preference for a completely sandy substratum and for sand particles sizes around 300 µm. Finally, considering the important role played by the hydraulic variables on the benthic community studied herein, the contagious distribution pattern of N. bonettoi, reported by other authors, would be principally linked with the interactions between current and sediment near the bottom rather than with the mobility of these organisms. Copyright © 2008 John Wiley & Sons, Ltd.

Case Study in Cost-Based Risk Assessment for Selecting a Stream Restoration Design Method for a Channel Relocation Project

A low-risk, stream restoration design includes methods that validate design assumptions, incorporate uncertainty in the decision-making process during the project design phase, and reduce uncertainty by checking the final design. A two-step method of incorporating uncertainty and risk in stream restoration design has been developed as a combination of design failure modes and effects analysis (DFMEA) and risk quantification. As a first step, DFMEA is applied to identify risk in terms of ratings with respect to consequence of failure, the likelihood of occurrence of a failure, and the ability to detect a failure. Due to its evolutionary nature, the DFMEA can be revised to account for design modifications and relative ratings are reevaluated to examine reductions in uncertainty, and thereby, risk. The second step of the method is quantifying risk using initial and expected failure costs. The two-step, risk-based method is illustrated through application to a stream relocation project in Pennsylvania. Both sediment transport capacity and supply analysis and alluvial channel modeling design methods were shown to reduce uncertainty and risk by detecting design deficiencies that the initial design using incipient motion tests overlooked. However, the alluvial channel model method was favored due to its ability to simulate the combined effects of flow hydraulics, sediment transport, and river channel adjustment.