Made available in DSpace on 2014-10-09T12:54:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:59Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

O adequado projeto de obras fluviais requer o conhecimento das condições sob as quais um curso d\'água natural atinge seu estado de equilíbrio. Para que este estado de equilíbrio seja determinado analiticamente é necessário utilizar um número de equações compatível com a quantidade de incógnitas do sistema, denominadas de graus de liberdade. Em um curso d\'água escoando sobre leito aluvionar não coesivo é possível admitir até quatro graus de liberdade, que são: a largura, a profundidade, a declividade e o traçado em planta do canal. Neste trabalho são apresentados alguns métodos que permitem avaliar as condições de estabilidade de um canal através do uso de relações puramente empíricas, ou através da aplicação de equações derivadas dos princípios físicos que regem a Hidráulica Fluvial, sendo possível ainda combinar o uso das duas abordagens no mesmo método. / The properly design of river improvements depends on the knowledge of the conditions under which a natural river becomes stable. This state of equilibrium is determined analytically if the number of equations is enough to describe the unknown system factors, called degrees of freedom. In an alluvial stream, it\'s possible to consider four degrees of freedom, they are: width, depth, channel slope and the variations in plan-form stream. This text presents some methods to evaluate the stability condition of a channel using empirical relationships, equations based on theoretical principles of Fluvial Hydraulics or both of these approaches in the same method.

Orientador: Ana Inés Borri Genovez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Civil, Arquitetura e Urbanismo / Made available in DSpace on 2018-08-17T09:38:36Z (GMT). No. of bitstreams: 1 Silva_LucianaVasquesCorreiada_M.pdf: 4691353 bytes, checksum: 05ef8f206bb1957c550c8b6cee57b065 (MD5) Previous issue date: 2007 / Resumo: A preocupação com o aprimoramento das técnicas de segurança de barragens tem sido cada vez mais discutida, devido ao aumento de incidentes ocorridos com estas estruturas situadas em locais densamente habitados. O objetivo deste trabalho é determinar a viabilidade técnica de uso do vertedor de emergência de vegetação em pequenas barragens de material solto. Para atingir este objetivo o dimensionamento foi realizado através do equacionamento básico e usando um modelo numérico, para dois tipos diferentes de cobertura vegetal. O uso de grama Bermuda com maior uniformidade, resultou numa menor descontinuidade na superfície de contato com o escoamento e menor probabilidade de erosão no canal. Este fato combinado com as dimensões resultantes para o canal permitem sugerir o uso deste tipo de cobertura vegetal. Os resultados indicaram que o vertedor de emergência de vegetação mostrou-se viável e uma alternativa eficiente para aumentar a segurança de barragens de material solto, apresentando construção simples e baixo custo, além de causar baixo impacto ao ambiente, sendo esteticamente melhor e adaptando-se às condições naturais da região de implantação da obra. A manutenção e diretrizes de inspeção devem proporcionar o bom funcionamento do vertedor de vegetação / Abstract: The concern about an enhancement of safety techniques for dams has been discussed more and more, due to an increase of the number of incidents that happened with structures located in places densely inhabited. The objective of this work is to establish the technical viability of using a vegetated emergency spillway in small embankment dams. To achieve such objective the design was done using a basic set of equations and a numerical model, for two different kinds of vegetation. The use of Cynodon dactylon grass with a bigger uniformity, resulted in a smaller discontinuity of the surface in touch with the flow and a smaller probability of having an erosion of the channel. Such factors, and the channel resulting dimensions, allow us to suggest the use of such vegetation cover. The results showed the viability of the emergency spillway with vegetation and also an efficient alternative to increase the safety of embankment dams, with inexpensive and easy construction, besides of causing a low environmental impact, also being esthetically best and adapting to the surrounding natural conditions. The maintenance and directions of inspection must provide a good operation of the vegetated spillway / Mestrado / Recursos Hidricos, Energeticos e Ambientais / Mestre em Engenharia Civil

Made available in DSpace on 2014-10-09T12:54:44Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:07:59Z (GMT). No. of bitstreams: 0 / Este trabalho descreve o estudo e testes de um sistema capaz de identificar e classificar os transientes, ou estados transitórios, de sistemas termo-hidráulicos, utilizando a técnica de redes neurais artificiais do tipo mapas de características auto-organizáveis, com o objetivo de sua implantação nas novas gerações de reatores nucleares. A técnica desenvolvida neste trabalho consiste no uso de múltiplas redes para fazer a classificação e identificação dos estados transitórios, sendo cada uma especialista em um respectivo transitório do sistema, que competem entre si por meio do erro de quantização, que é uma medida gerada por estas redes neurais. Esta técnica se mostrou eficiente, apresentando características muito promissoras no que diz respeito ao desenvolvimento de novas funcionalidades em futuros projetos. Uma dessas características consiste no potencial de que a rede, além de responder qual estado transitório está em curso, também pode oferecer informações adicionais sobre esse transitório. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

In this study, a comprehensive approach including mathematical, numerical and experimental study has been taken in order to develop new models for describing free surface flow behavior in porous media. The study suggested that modeling free-surface flow in porous media is possible using a single equation capable of showing proper transition between inertial and classical Darcian flow, based on the similarity distribution functions of depth and velocity. The developed integral model inherits both the flow regimes as depicted in the analysis. For both laminar and turbulent flows through porous media, the integral models give satisfactory results. Also the proposed algorithm for numerical simulation is capable of solving various problems of free-surface flow through porous media. This study adds a new dimension to fluid flow in porous media by replacing Darcy's equation with new models that are capable of representing both Darcy and non-Darcy flow behaviors. These are new nonlinear ordinary differential equations inherited both the flow regimes investigated. Integral formulations for unsteady depth distribution, velocity and front speed under constant water level and constant flux discharge inlet conditions have been developed based on similarity law. The formulations presented provide additional analytical insight about the intrusion dynamics. It is pointed out that, based on the self-similarity analysis, the temporal intrusion processes can be categorized into the inertia-pressure (IP) and the pressure-drag (PD) regimes. The early inertia-pressure regime is followed by the pressure-drag regime. In addition, the integral models proposed can be successfully used for the solution of a host of other nonlinear problems that admit self-similarity. The analytical and numerical solutions for constant inlet water level condition are verified with experimental observations. The unsteady distributions of flow depth, inflow velocity and front speeds are compared for various porous media characterized by its corresponding porosity and permeability. Analyses indicate that the integral models clearly represent the nonlinear flow behavior in porous media both in laminar and turbulent flow conditions. The integral model results are in agreement with those obtained by similarity solution for the temporal change of velocity, depth at inlet and front positions. The thesis also presents a computational fluid dynamics (CFD) model developed for the analysis of unsteady free-surface flows through porous media. Vertical two-dimensional numerical simulations are carried out for the free-surface flow inside the porous media governed by a set of Navier-Stokes equations extended for porous media flow. This model includes the convective and local inertia terms along with viscous diffusion term and resistance term comprising Darcy's linear resistance and Forchheimer's inertial resistance terms. The Finite volume method is applied using constrained interpolated propagation (CIP) method and highly simplified marker and cell (HSMAC) type pressure solver for the numerical solution. The evolution of moving free surface is governed by volume of fluid (VOF) method, adapted for the flow through porous media. To prevent the spurious oscillation and generate diffusion-free sharp interface, a third order monotone upstream-centered schemes for conservation laws (MUSCL) type total variation diminishing (TVD) schemes is used to solve the VOF convection equation. The power law derivation and validation for the general flux inflow condition are made for a channel having a backward facing step. The result of theoretical analysis is compared with that of the numerical simulation and it shows a good agreement. The model can be a tool for the proposition of some empirical flow relationships using multivariate correlation. In the case of rapid vertical infiltration of water through a vertical column filled with porous media, a number of experiments and analytical investigations are carried out to see the effect of acceleration in the intrusion process. It is concluded that the conventional infiltration models like Green-Ampts infiltration model cannot account for the acceleration effect in the case of high velocity flow. It is revealed that it takes certain time for intruding water to be accelerated to its peak velocity before decreasing to almost constant velocity. The investigations are made for two different cases: constant water level and variable water level above the porous media. For porous media having low permeability, the effect of acceleration was not so significant. In the case of dam break flow over horizontal porous strata, the model is applied to a complicated domain regarding both geometry and flow boundary conditions. Single set of governing equation is implemented to simulate the complex phenomenon. The model shows its capability in simulating the flow where interface between pressurized and open channel flow moves forward. The vertical acceleration has a significant effect on the rapid vertical infiltration which the shallow water equations cannot account for. In particular, it is shown that vertical two dimensional numerical solution that couples the fluid and solid systems simultaneously at macroscopic scale are feasible and extremely beneficial, shedding a new light into the phenomena unavailable otherwise. It is also found that the proposed numerical model can be used for the determination of storm water storage in porous sub-base in a typical road section. The capability of the model is assessed by using the unsteady inflow condition so as to simulate the condition during high precipitation. The model could be a promising tool for planners and decision makers for effective drainage calculations to mitigate urban flood. The model successfully simulates the free surface flow in the bulk fluid as well as in the porous region. The velocities and stresses are assumed to be continuous at the interface of free and porous media so that a single set of governing equations could be solved. The robustness of the model is demonstrated by the capability of the numerical approach proposed in this thesis. / Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14916号 / 工博第3143号 / 新制||工||1471(附属図書館) / 27354 / UT51-2009-M830 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 細田 尚, 教授 戸田 圭一, 准教授 岸田 潔 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15344号 / 工博第3223号 / 新制||工||1485(附属図書館) / 27822 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 細田 尚, 教授 後藤 仁志, 准教授 米山 望 / 学位規則第4条第1項該当

Stormwater ponds (SWPs) are becoming increasingly important due to the negative impacts on flood mitigation and water quality control that results from rapid urbanization. These ponds are not only designed to control the discharge of large precipitation and snow melt events, but also to mitigate the water quality of the retained stormwater. Consequently, improper design and maintenance may lead to hypoxic conditions in SWPs, which result in poor water quality and generation of noxious gases. Riverside South Stormwater Pond II (RSPII) in Ottawa periodically experiences low dissolved oxygen (DO) concentrations and subsequently hypoxic conditions at depth in the pond, especially during summer days with less precipitation and winter ice covered periods. Hydrogen sulfide gas (H2S) has been generated and released into the ambient atmosphere during these periods of lesser water quality. Hence, there is a need to understand how DO spatial distribution and seasonal change trigger and affect H2S production. The conventional shallow design criteria of SWPs likely cause these systems to be susceptible to wind conditions. Very few research has demonstrated the correlation between wind-driven hydraulic performance and detained stormwater quality. Hence an understanding of pond-scale mixing generated by wind-induced flow and the subsequent correlation to DO concentrations and stratification in SWPs are important to understanding the water quality and performance of these systems, especially in a wind-induced flow dominated SWPs. The overall research objective is to develop a comprehensive understanding of hypoxic conditions of SWPs and to investigate the impact of wind induced hydraulics on DO seasonal characteristics and the subsequent production of H2S. RSPII was shown to experience lower DO and longer hypoxic conditions than an adjacent reference pond (RSPI) at both non-ice covered and ice covered months. In addition, hypoxia was shown to be initiated at the outlet of RSPII where the depth of the pond was a maximum. Interestingly, chlorophyll-α blooms were observed during ice covered conditions in the study, with synurids, tabellaria, and asterionella being identified as the dominant species. A bottom-mount acoustic Doppler current profiler (aDcp) was used to collect small wind-generated currents in RSPII. The three-dimensional current and DO model produced by MIKE 3 (DHI software) suggests a conclusive result of pond scale mixing produced by wind-driven flow as well as countercurrents near the bed opposite to wind direction. A wind dominated circulation was shown to be generated even with moderate wind speed, and with a higher wind condition pond-scale complete DO mixing was created. The MIKE 3 simulation further provided a comprehensive understanding of the correlation between wind-induced hydraulics and DO concentrations distribution in a shallow stormwater pond. Therefore, this research demonstrates that wind is an essential hydraulic driver in shallow ponds, which also likely affects water quality by initiating pond mixing.

In connection with the government’s approval on the proposed national plan (NAP) in 2019, it has become highly topical to find solutions problems regarding fish migration in Swedish watercourses. At Finsjö Övre hydropower plant in Emån, a new type of fishway is planned to be installed and evaluated starting at the end of 2022. The fishway is a double Archimedes screw turbine that has never been assessed in a Nordic country. The energy company Fortum is operating the power plant. Fortum’s main purpose with the installation is to evaluate the double-screw turbine to gain knowledge about how it performs in Nordic conditions and with Swedish fish species. The evaluation of the fishway will focus on why fish choose to use it or not. It will then be advantageous to have knowledge of velocities in the area below the fishway since fish´s choice of route is affected by that.   The goal of this project was to investigate flow velocities below the intended fishway through hydraulic simulations. Then by the results produce a basis that can be helpful in future evaluations of the fishway’s function for upstream fish migration. In addition to this, to also link the results to previous studies on upstream fish migration to be able to detect shortcomings. In that case to give suggestions for improvement measures.   Field measurements were conducted to collect data on the environment at the hydropower plant. The environment was then recreated in the simulation software HEC-RAS and the planned fishway was added to the model. Three different flow scenarios were assessed and information on flow velocities was obtained.   The simulations showed that the velocity distribution below the fishway probably is suitable for most fish species due to both fast and calm water near the fishway’s opening. No obvious shortcomings emerged. However, the volume flow rate from the fishway is low and is below the recommended guide values. Upstream fish migration will probably work best at low volume flow rates in the river since the velocity of the attraction flow then is relatively high compared to the currents from the hydropower plant. The higher flows from the hydropower plant and the spillway, the less attractive the flow from the fishway becomes. / I samband med att regeringen fattade beslut den nationella planen (NAP) år 2019 har det blivit högaktuellt att hitta lösningar på problematiken kring fiskvandring i svenska vattendrag. Vid Finsjö Övre vattenkraftverk i Emån är en ny sorts fiskväg planerad att installeras och utvärderas med början i slutet av 2022. Fiskvägen är en dubbel Arkimedesskruv som aldrig tidigare har testats i ett nordiskt land. Energiföretaget Fortum, som ansvarar för driften av kraftverket, har som huvudsyfte med installationen att utvärdera skruven för att få kunskap om hur den presterar i nordiska förhållanden och med svenska fiskarter. Vid utvärdering av fiskvägen är det fördelaktigt att ha kunskap om hydrauliska förhållanden i området nedanför fiskvägen, då det bland annat ska undersökas varför fiskar väljer att använda den eller inte.   Målet med detta projekt var att genom hydrauliska simuleringar undersöka flödeshastigheter nedanför den tilltänkta fiskvägen. På så vis sedan ta fram ett underlag som ska kunna användas vid framtida utvärderingar av fiskvägens funktion gällande uppströmsvandring. Utöver detta att också koppla resultaten till tidigare studier kring fiskvandring för att kunna upptäcka eventuella brister och i så fall ge förslag på förbättringsåtgärder.   Fältmätningar genomfördes för att samla in data om miljön vid vattenkraftverket. Därefter återskapades miljön i simuleringsprogrammet HEC-RAS och den planerade fiskvägen adderades till modellen. Tre olika flödesscenarior testades och information om flödeshastigheter erhölls.   Simuleringarna visade att hastighetsfördelningen nedanför fiskvägen troligtvis lämpar sig för flertalet fiskarter på grund av både snabbt och lugnt vatten i nära anslutning till fiskvägens öppning. Inga uppenbara brister visade sig. Dock är flödeshastigheten från fiskvägen låg och ligger under rekommenderade riktvärden. Troligtvis kommer uppströmsvandring fungera bäst vid låga volymflöden i ån eftersom hastigheten på lockvattnet då är relativt hög. För ju högre flöden från kraftverket och spillfåran, desto mindre attraktivt blir flödet från fiskvägen.

Ice regime plays a significant role in River hydraulics and morphology in Northern hemisphere countries such as Canada. The formation, propagation and recession of ice cover introduce a dynamic boundary layer to the top of the stream. Ice cover affects the water velocity magnitude and distribution, water level and consequently conveyance capacity. A stable ice cover also tends to reduce bed shear and associated sediment transport, but bank scour and ice jamming events can increase sediment entrainment. These effects are even more intense during the ice cover break-up period when extreme conditions such as ice-jamming and release and mechanical ice cover break-up can locally accelerate the flow, and ice can mechanically scour the river bed and banks. The presence of ice has some important implications for hydro-electrical power generation operations too. The ice cover changes the channel conveyance capacity (and therefore increases the flood risk), may increase sediment transport and causes scouring, and is likely to block water intakes and turbines. The rate of water release should, therefore, be adjusted in the presence of the ice cover to avoid unwanted consequences on the dam structure and equipments as well as on the downstream channel and the environment. Even though the influence of ice cover on rivers is widely recognized, large gaps still exist in our understanding of ice cover processes in rivers. Two main reasons for such a shortage are the difficulty and danger involved in collecting hydraulic and sediment transport data under ice cover, especially during the unstable periods of freeze-up and break-up. In the absence of sufficient data, the applicability of available formulae and theories on hydraulic processes in ice-covered rivers cannot be extensively tested and improved. The purpose of this research mainly is a) to perform a continuous, in-situ monitoring of water velocity profiles, sediment loads and ice-cover condition during several years through winter field campaigns at a section of the Lower Nelson River, Manitoba, Canada.The Lower Nelson River is a regulated river (Manitoba Hydro). It receives augmented flow from the Churchill River Diversion, and is subject to operation of many hydro-electricity facilities, one of which is currently under construction, while others are planned to be constructed in the future. Due to the geographical location of the study reach, it is covered by ice and experiences severe ice condition for several months during the year. b) Analysis of the collected data in order to study the impact of ice cover on the hydraulic properties and sediment conveyance capacity at the study reach and c) using the insight gained from the field data analysis to improve a river ice simulation model to apply in the study of Lower Nelson River ice regime. The selection of the Lower Nelson river is motivated by intention of Manitoba Hydro (MH) ,as the industrial partner in this research, to study the winter flow regime at the Lower Nelson River. Manitoba Hydro operates several dams on the Lower Nelson River and is considering more hydropower developments in the future. This study is composed of six steps as are described in the following main steps. Step 1: Selection of potential study sites and data collection techniques: The particular study site for this research is located immediately upstream of Jackfish Island, between Limestone generating station and Gillam Island in Lower Nelson River, Manitoba, Canada. River width at the study site location is about 1km. Water depth at the deployment site varies between 10-12 meters depending on both the time of year and the time of day due to hydropeaking fluctuations. Given the low accessibility to the field during winter time and considering the type of the required data, acoustic techniques were selected as the main approach for the field measurements. Two types of acoustic instruments, Acoustic Doppler Current Profiler (ADCP) and Shallow Water Ice Profiling Sonar (SWIPS) are selected for field investigations in this study. Both of them were planned to be deployed in the river for an extended period of time in order to record necessary data during the ice cover and open water periods. Step 2: Data acquisition. After the site selection and defining the appropriate techniques, data acquisition has been started through a series of annual field measurement campaigns starting from winter 2012. Measured data mainly consist of water velocity and sediment suspension during various ice cover stages, including river ice break-up. The velocity profiles are analyzed to determine dynamic changes in boundary shear stress and hydraulic resistance and stresses in the flow during the both open water and ice cover periods. Step 3: Data analysis and development/testing of roughness and sediment transport formulas. Several aspects of river-ice interactions are covered in the recorded data including ice cover condition and cover thickness variation, river hydraulic characteristics such as depth and velocity and finally information about the concentration of suspended particles. These data are analyzed to define the behavior of the ice cover and river during different ice stages. Ice effect on river conveyance capacity is also evaluated . The accuracy of common assumptions in composite roughness calculations in rivers is estimated and a new approach is developed and validated using the field observations and measurements. Ice cover influence on suspended sediment concentration is also studied as the other part of this research. Considering the type of the river sediment load (mostly bed load) available methods for sediment transport simulation are studied and applied for estimation of the sediment transport under ice cover condition. According to the results, the most suitable methods were planned to be a part of the river ice numerical simulation model, developed in this study. Turbulent characteristics in ice covered flows are also studied through two years of data recordings. Acoustic Doppler Current Profiler employed in this study is programmed for appropriate recording of the water velocity for this purpose. Results are analyzed and turbulent structures in the river are studied in this research as well. Step 4: Testing of Hatch-MH’s river ice simulation model. A numerical model has been selected in order to simulate the river ice process at the study site (LNR). ICESIM, a steady state, one-dimensional river ice process model originally developed in 1973 by Acres International Limited (now Hatch), is selected for this study.ICESIM is originally developed in FORTRAN and is capable of predicting the progression and stabilization of river ice cover. Step 5: Improvement of Hatch-MH’s river ice simulation model: ICESIM model is converted to Matlab as the first step of the model improvements. A Graphical User Interface (GUI) is designed for the program which facilitates the assessment of model performance during the simulation leads to a more user-friendly model to operate. The new model, ICESIMAT is calibrated and evaluated based on the conducted field studies. Simulation capabilities of ICESIMAT are improved in the form of extended or additional subroutines to enhance its capabilities in the simulation of river ice processes and sediment transport. The current version of ICESIMAT is a steady state model, capable of simulating river ice , river hydrodynamic characteristics and sediment transport along the study reach. Though the model is restricted in the terms of the dimensions of the simulation (only one dimensional) its lower computational cost, permits a longer study reach to be simulated (in the scale of hundred kilometers instead of couple hundred meters in three dimensional simulation). ICESIM model is unable to simulate the break-up period which reduces the model capability in the simulation of the complete cycle of river ice. New subroutines are designed and added to extend the model capability to include simulation of ice processes during the ice cover break-up and finally to calculate the sediment transport under the ice cover. Step 6: As the final step, the new subroutines are adjusted and linked to the main improved code, providing a new framework for dynamic ice cover simulation, more prepared for further future improvements both in terms of conceptual and programming aspects of the river ice modeling . The new Matlab basis of the code facilitates upgrading the model to include more complicated processes like river ice jam simulations. As the general result of this thesis, we have a better understanding of hydraulics and sediment transport processes in ice covered rivers ( direct and indirect measurements of river hydraulics characteristics), improved formulas for these processes (including more involving parameters) and a better version of the river ice simulation model (capable of simulating the complete river ice processes) for the contributors to this study in the industry.

Culverts can increase stream velocities as a result of reduced waterway areas and prevent upstream passage of small non-salmonid fish such as the Native Utah Leatherside chub (Gila copei) and Longnose dace (Rhinichthyscataractae). To mitigate this problem, current culvert design standards for fish passage match sustained fish swim speeds with average cross sectional velocity through the culvert. Such policies dictate relatively large barrels and do not recognize the role of reduced velocity zones near culvert boundaries. Obstacles and streambed substrate create turbulent regions with lower velocity zones that can increase upstream fish passage. A comparison of upstream passage success using native Utah fish in an experimental flume was conducted with three different conditions: (1) a smooth boundary, (2) a smooth boundary with strategically placed cylinders, and (3) a boundary consisting of natural substrate. The refuge provided by the cylinders and substrate allowed fish to expend less energy as they swam upstream. Energy expenditure was compared between the conditions by mapping the velocity field near the boundary and tracing fish swim paths. Substrate provided sufficient refuge for the fish to behave in a manner similar to their behavior in a natural environment and with significantly reduced energy expenditure. Cylinders provided limited refuge that allowed fish to rest periodically as they navigated the flume. The smooth boundary case required the highest energy expenditure as there was no refuge provided. Fish swimming capabilities in the form of prolonged and burst velocities have been recorded for most species. Streamwise velocity near the boundary can be compared to the prolonged and burst swim speeds to predict passage rates. Further field testing is necessary to fully substantiate the effectiveness of utilizing reduced velocity zones in non-salmonid fish passage prediction. If such a design approach can be used instead of using the conservative but overly simplistic average velocity to evaluate the retrofit of existing culverts and to design new culverts it will help minimize costs and result in fewer culvert replacements and smaller and simpler new designs. Other implications such as downstream effects on stream bed stability and scour remain an issue.