Spelling suggestions: "subject:"meander"" "subject:"leander""
1 |
Channel planform dynamics of an alluvial tropical riverAlvarez, Aldo 29 August 2005 (has links)
The meandering stream has been well studied in temperate environments but the
same level of research has not been achieved for meandering streams in tropical areas.
The overall objective of this research was to gain an increased understanding of
meandering planform dynamics in humid tropical rivers. The objective was pursued by
examining the rate of change of channel pattern and results indicate that migration rate
and the range of radius of curvature to width ratio where maximum migration occurs is
similar to those reported for humid temperate rivers. In summary, as regards to these
aspects, the results suggest that the representative humid tropical river is no more
dynamic than its temperate counterparts.
A second objective was to document the response and recovery of a humid
tropical river system to an extreme flood event. As a result, the trend of shorter recovery
times following a major perturbation was demonstrated, and suggests that in the long
term, a large flood such as a 100-year event apparently plays a relatively minor role as a
formative event in shaping the overall humid tropical landscape.
A third objective was to develop an empirical model for predicting bend
migration rates in humid tropical rivers, resulting in empirical relationships that indicate
that meander migration has a high degree of correlation with the number of bankfull
discharge events under all scenarios, and that model correlation can be enhanced when
the silt-clay composition of the banks, and the radius of curvature to width ratio are
included as independent variables. The resulting equations were tested to predict
maximum meander migration distance, and predictions produced very satisfactory
results.
In addition to increasing basic understanding of meander processes in tropical
areas and for developing fluvial geomorphological theory, the results of this research
have potentially important benefits to society. Because property and structures are often
threatened by channel movement, there is a need for improved predictive capability of
deformation of stream channels, and the results can therefore be useful to engineers and
other professionals in delineating channel hazard zones.
|
2 |
Channel Meander Migration in Large-Scale Physical Model StudyYeh, Po Hung 2009 August 1900 (has links)
A set of large-scale laboratory experiments were conducted to study channel meander migration. Factors affecting the migration of banklines, including the ratio of curvature to channel width, bend angle, and the Froude number were tested in the experiments. The effect of each factor on the evolution of channel plan form was evaluated and quantified. The channel bankline displacement was modeled by a hyperbolic function with the inclusion of an initial migration rate and a maximum migration distance. It is found that both the initial migration rate and maximum migration distance exhibit a Gaussian distribution along a channel bend. Correlations between the distributions and the controlling parameters were then studied. Two sets of equations were developed for predicting the initial migration rate and the maximum migration distance. With the initial migration rate and maximum migration distance being developed as a function of geometric and flow parameters, a hyperbolic-function model can be applied to estimate the bankline migration distance.
The prediction of channel centerline migration was also developed in this study. The channel centerline was represented with a combination of several circular curves and straight lines. Each curve with the radius of curvature and bend angle was used to describe the channel bend geometry. HEC-RAS was applied to estimate the flow hydraulic properties along the channel by adjusting the channel bed slope. The intersections of two consecutive centerlines were found to be the inflection points of the centerline migration rate. Phase lag to the bend entrance was measured and correlated with the bend length and water depth. The migration rate between two successive inflection points demonstrated a growth and decay cycle. A sine function was used to model the centerline migration rate with regression analysis of the measurement data. The method was applied to four sites of four natural rivers in Texas. The results showed that the prediction equation provides agreeable results to the centerline migration of natural rivers.
|
3 |
Conveyance capacity of meandering compound channelsWilson, Catherine Anna Margaret Elizabeth January 1998 (has links)
No description available.
|
4 |
Dispersion of solutes in sinuous open channel flowsBoxall, Joseph B. January 2000 (has links)
The research undertaken for this Ph.D. thesis concerns the dispersion of solutes in sinuous open channel flows. The aim of the work is to address the void in knowledge and understanding of mixing and transport processes in natural watercourses. The influences of plan form curvature and non-uniform cross sectional shape on transverse and longitudinal mixing are specifically addressed. Experimental work was undertaken on the Flood Channel Facility at HR Wallingford Ltd. This involved creating a pseudo natural sand channel within the concrete meander plan form of the facility, and then stabilising the form. Tracer studies using instantaneous injection to investigate longitudinal mixing and continuous point source release to study transverse mixing were performed. Fluorescent tracer was used. Measurement was by six Turner Design Field Fluorometers in pump through mode and these were digitally logged. Detailed hydrodynamic measurements were made using a two-dimensional Laser Doppler Anemometer (LDA) fitted with a 14mm fibre-flow probe. The resulting data has undergone robust analysis and detailed interpretation. The conclusions are that the dominant processes in mixing, in the natural channel form studied, are shear effects. Simple equations for the prediction of flow fields have been investigated and validated against LDA measurements. It has been possible to make accurate predictions of the transverse and longitudinal mixing coefficients from the predicted flow fields. These predictions have been shown valid for the variations in mixing coefficients over the meander cycle and with discharge.
|
5 |
A hydrograph-based prediction of meander migrationWang, Wei 16 August 2006 (has links)
Meander migration is a process in which water flow erodes soil on one bank and
deposits it on the opposite bank creating a gradual shift of the bank line over time. For
bridges crossing such a river, the soil foundation of the abutments may be eroded away
before the designed lifetime is reached. For highways parallel to and close to such a
river, the whole road may be eaten away. This problem is costing millions of dollars to
TxDOT in protection of affected bridges and highway embankments. This research is
aimed at developing a methodology which will predict the possible migration of a
meander considering the design life of bridges crossing it and highways parallel to it.
The approaches we use are experimental tests, numerical simulation, modeling of
migration, risk analysis, and development of a computer program.
Experimental tests can simulate river flow in a controlled environment.
Influential parameters can be chosen, adjusted, and varied systematically to quantify
their influence on the problem. The role of numerical simulation is to model the flow
field and the stress field at the soil-water interface. Migration modeling is intended to
integrate the results of experimental tests and numerical simulations and to develop a
model which can make predictions. The Hyperbolic Model is used and its two major
components Mmax equation and τmax equation are developed. Uncertainties in the
parameters used for prediction make deterministic prediction less meaningful. Risk
analysis is used to make the prediction based on a probabilistic approach. Hand
calculation is too laborious to apply these procedures. Thus the development of a user
friendly computer program is needed to automate the calculations.
Experiments performed show that the Hyperbolic Model matches the test data
well and is suitable for the prediction of meander migration. Based on analysis of shear stress data from numerical simulation, the τmax equation was derived for the Hyperbolic
Model. Extensive work on the simplification of river geometry produced a working
solution. The geometry of river channels can be automatically simplified into arcs and
straight lines. Future hydrograph is critical to risk analysis. Tens of thousands of
hydrographs bearing the same statistical characteristics as in history can be generated.
The final product that can be directly used, the MEANDER program, consists of 11,600
lines of code in C++ and 2,500 lines of code in Matlab, not including the part of risk
analysis. The computer program is ready for practice engineers to make predictions
based on the findings of this research.
|
6 |
Efectos de la represa Casa de Piedra en la variación témporo espacial de las características hidrológicas y del diseño de drenaje del Río ColoradoCazenave, Héctor Walter 12 December 2011 (has links)
El río Colorado se ubica en la parte Norte de la Patagonia argentina y atraviesa con dirección Oestenoroeste - Sur-sureste un sector del país de condición árida y semiárida ubicado entre la Cordillera de los Andes y el océano Atlántico, con un recorrido cercano a los 1.000 km. Esta tesis doctoral aborda el estudio de las características hidrológicas y el estudio específico de las variaciones en el diseño de drenaje de un tramo testigo ubicado en un área predeterminada por su cartografía secuencial y fiable en relación con las posibles variaciones hidrogeomorfológicas. Dentro de la problemática general que presenta el río Colorado, se tuvo en cuenta la función del río Curacó, último tramo de la gran cuenca Desa-guadero Salado Chadileuvú, a la que le da carácter de exorreica. Las periódicas activaciones del Curacó crean serios problemas de salinidad en las cuencas media y baja del Colora-do, parcialmente mitigados en la actualidad por la represa Casa de Piedra. El levantamiento del dique Casa de Piedra, sobre la parte final del alto valle, alteró drásticamente el comportamiento del río en cuanto al arrastre de sólidos. Por acción de su gran embalse se produce la deposición del mate-rial trasportado en suspensión, dándole una nueva condición física -y en parte también química- a las aguas emergentes del dique, que han dejado en el lago las arcillas y el limo que trasportaban. Esos materiales, antes de existir el dique, se depositaban aguas abajo e impermeabilizaban naturalmente los canales en las áreas de regadío de los valles medio e infe-rior. El agua que vierte Casa de Piedra, casi carente de sedi-mento, tiene una capacidad erosiva mayor que la que fluye antes del embalse; esa condición permite reducir el tiempo de formación de meandros con respecto a sectores de aguas arriba de la presa. Esas condiciones han generado también el fenómeno conocido como aguas claras. El estudio ordena en el tiempo y el espacio las variaciones de curvas y meandros del tramo testigo, cuantificándolas. Aunque también se han visto alteradas las curvas de caudal y salinidad es en el gasto sólido donde el dique Casa de Piedra ha provocado los cambios más visibles y fundamentales en el ser y quehacer del río. La curva resultante de los nuevos valores refleja la situa-ción con respecto a la anterior y marca una fuerte disminu-ción en el acarreo. Esta tesis es además un aporte a poste-riores investigaciones interdisciplinarias, especialmente en el campo de la hidráulica y la geomorfología fluvial, dos disci-plinas bajo las cuales el río Colorado ofrece un amplio campo de estudios. El trabajo detecta, determina y cuantifica los cambios físicos y humanos generados por la presencia del dique, algunos ya evidentes y otros en trance de serlo. / The construction of Casa de Piedra dam, in the final stretch of Colorado river high valley, radically modified down waters the hydrologic river course, specially as regards sediment transport, the majority of which settles in the lake. Conse-quently, waters the dam distributes, contain a remarkable erosive capacity, and accelerate down waters hydrographic processes, increasing river meandering and bringing about what is known as the clear waters phenomenon causing adverse effects on watering zones. With the purpose of checking the fact in a quantitative way, cartographies from a certain stretch were taken, being this stretch considered a witness one in periods around 25 years, assessing meanders appearance and disappearance, and comparing these quantities with the variation -in the same sense-, that took place since Casa de Piedra start up. The quantities were sig-nificant considering the relatively short time gone by. The fact was checked in a new aero - photographic flight, according to which, in a shorter lapse, meanders number increased again in the witness stretch.
|
7 |
An Analogical Garden of MemoryVermillion, Emma Flower 14 August 2022 (has links)
An architect draws from a deep
repository of past memories
made durable in the act of architecture.
This thesis is a study of
the analogous relationship between
a childhood memory of a
garden and a set of architectural
acts giving form to this memory.
The ideas of threshold, meander,
focus, and framing are the basic
conditions of the project. Perspectives
and montages are the
primary methods of study. The
project is a garden placed within
the context of an imagined city
setting up the interplay of silence
amidst the cacophony of the city.
It centers around a singular tree,
informed by a specific childhood
memory. The single tree in concert
with the architectural conditions
allows one to resist the inexorable
rush of urban time. / Master of Architecture / An architect draws from memories
of the past to inform the
future. This thesis is a study that
pulls from memories of a childhood
garden and compares them
to a set of basic architectural elements.
The ideas of threshold,
meander, focus, and framing are
explored.
|
8 |
River Hydro- and Morphodynamics: Restoration, Modeling, and UncertaintyPosner, Ari Joseph January 2011 (has links)
The study of fluvial geomorphology is one of the critical sciences in the 21st Century. The previous century witnessed a virtual disregard of the hydro and morphodynamic processes occurring in rivers when it came to design of transportation, flood control, and water resources infrastructure. This disregard, along with urbanization, industrialization, and other land uses has imperiled many waterways. New technologies including geospatially referenced data collection, laser-based measurement tools, and increasing computational powers by personal computers are significantly improving our ability to represent these complex and diverse systems. We can accomplish this through both the building of more sophisticated models and our ability to calibrate those models with more detailed data sets. The effort put forth in this dissertation is to first introduce the accomplishments and challenges in fluvial geomorphology and then to illustrate two specific efforts to add to the growing body of knowledge in this exciting field.First, we explore a dramatic phenomenon occurring in the Middle Rio Grande River. The San Marcial Reach of the Rio Grande River has experienced four events that completely filled the main channel with sediment over the past 20 years. This sediment plug has cost the nation millions of dollars in both costs to dredge and rebuild main channels and levees, along with detailed studies by engineering consultants. Previous efforts focused on empirical relations developed with historical data and very simple one dimensional representation of river hydrodynamics. This effort uses the state-of-the-art three-dimensional hydro and morphodynamic model Delft3D. We were able to use this model8to test those hypotheses put forth in previous empirical studies. We were also able to use this model to test theories associated with channel avulsion. Testing found that channel avulsions thresholds do exist and can be predicted based on channel bathymetric changes.The second effort included is a simple yet sophisticated model of river meander evolution. Prediction of river meandering planform evolution has proven to be one of the most difficult problems in all of geosciences. The limitations of using detailed three dimensional hydro and morphodynamic models is that the computational intensity precludes the modeling of large spatial or temporal scale phenomenon. Therefore, analytical solutions to the standard Navier-Stokes equations with simplifications made for hydrostatic pressure among others, along with sediment transport functions still have a place in our toolbox to understand and predict this phenomenon. One of the most widely used models of meander propagation is the Linear Bend Model that employs a bank erosion coefficient. Due to the various simplifications required to find analytical solutions to these sets of equations, efforts to build the stochasticity seen in nature into the models have proven useful and successful. This effort builds upon this commonly used meander propogation model by introducing stochasticity to the known variability in outer bank erodibility, resulting in a more realistic representation of model results.
|
9 |
The underpinnings for successful route tourism development in South AfricaLourens, Marlien 26 May 2008 (has links)
This study examines the critical success factors of route tourism development.
The aim is to provide a set to practical planning guidelines to assist the
successful implementation of routes on a local level. Lessons are drawn from
case studies of the Camino de Santiago in Spain, the heritage trails in
Queensland, Australia, Hadrian’s Wall in the United Kingdom and of the Midlands
Meander in South Africa. Routes are considered important because it
demonstrated to be an effective vehicle for local economic development. The
evidence of their positive impact on rural economies is confirmed throughout the
case studies. It is argued that the successful development of tourism routes is
not an exact science and emerging destinations often have many hurdles to
overcome. Through an analysis of these four case studies, the study explores the
elements of themed routes that constitute successful destinations and highlights
the importance of planning, promotion and institutional development.
|
10 |
A prediction of meander migration based on large-scale flume tests in clayPark, Namgyu 15 May 2009 (has links)
Meander migration is a complex and dynamic process of the lateral movement of
a river due to erosion on one bank and deposition on the opposite bank. As a result, the
channel migrates in a lateral direction, which might be a major concern for the safety of
bridges during their life span of 75 years. Although there are several existing models for
predicting meander migration of a river, none of them are based on the physical model
tests on a specific type of soil.
A total of eight flume tests are conducted to develop a prediction equation of
meander migration in clay. The test results of migration rate follow a hyperbolic
function, and spatial distribution of the maximum migration distance is fitted with the
Pearson IV function. The proposed equations of the initial migration rate and the
maximum migration distance, obtained by a multiple regression technique, are validated
with the laboratory data.
A new methodology for risk analysis is developed to process a number of
predicted channel locations based on each future hydrograph generated in such a way that all the hydrographs have the same probability of occurrence. As the output from risk
analysis, a CDF map is created for a whole river representing a general trend of
migration movement along with the probability associated with new location of the river.
In addition, a separate screen is generated with a CDF plot for a given bridge direction
so that bridge engineers can read a specific migration distance along the bridge
corresponding to the target risk level (e.g. 1 %).
The newly developed components through this research are incorporated with the
other components in the MEANDER program which is a stand-alone program and the
final outcome of the research team. Verification study of the MEANDER program is
conducted with full-scale field data at the Brazos River at SH 105, Texas. The prediction
results matched quite well with the measured field data. However, a more extensive
verification study for other sites is highly recommended.
|
Page generated in 0.0499 seconds