This thesis investigates the potential application of a two-dimensional depth-averaged sediment transport and morphological model on a large braided river system and examines its capability to build a computational gravel budget and predict the morphological changes. The Lower Fraser River gravel reach is characterized by an irregularly sinuous single-thread channel split around large gravel bars and vegetated islands, and riverbed aggradation because of gradual gravel deposition over the years, bank hardening and channel confinement. Gravel removal from selected locations is considered as one of the viable management options to maintain the safety and integrity of the existing flood protection system along the reach. Therefore, any gravel removal plan in this reach requires a reliable sediment budget estimation and identification of deposition zones. It is also required to examine the possible future morphological changes with and without gravel removal and to assess its impact on design flood level. The main objective of this study is to build a computational sediment (gravel) budget for the 33 km long gravel reach that extends from Agassiz-Rosedale Bridge to Sumas Mountain near Chilliwack. In this study, a two-dimensional depth-averaged curvilinear mathematical model MIKE 21C was modified and applied to predict the gravel bedload transport and detect the change of morphology for the next 10 years period. A gravel transport formula was coded and added into the MIKE 21C model. Sediment transport code modification and application has been done side by side in a trial and error fashion. This is the first use of a conventional two-dimensional depth-averaged model for the entire gravel reach of the Lower Fraser River within affordable computational effort. The model application was successful in term of gravel budgeting, aggradation and degradation zones identification and long-term morphological change prediction, with some limitations and drawbacks. Further modification and model testing with recent bedload data is recommended.

No description available.

No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on May 7, 2009) Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [136]-147).

Master of Science / Department of Civil Engineering / Sunanda Dissanayake / In the United States, the mileage of unpaved roads is about 1.6 million miles. Total length of unpaved roads in Kansas is about 98,000 miles, of which about 78,000 miles are gravel roads. Most of the gravel roads are not posted with speed limit signs but regulated with a 55 mph blanket speed limit established by the Kansas Statutes. Surface conditions of gravel roads are very likely to change with time, space, and quality of maintenance work, making it even more necessary to have proper control of speeds on gravel roads. Normally used speed regulations and rules for freeways or other types of paved roadways might not be appropriate for gravel roads, especially for those local gravel roads which usually carry very low traffic in rural areas. Based on an extensive literature search, there was no specific rule or references to provide guidelines on how speed limits on gravel roads could be set. Therefore, an effort was made in this study to evaluate the effects of currently posted lower speed limits in some counties in Kansas, based on traffic characteristics and safety on gravel roads, with the intention of providing proper guidelines for setting speed limits on gravel roads in Kansas. In order to study traffic characteristics on gravel roads, field speed studies were conducted with automatic traffic counters on more than forty gravel road sections in seven counties in Kansas. Important speed measures, such as 85th-percentile speed and mean speed, were obtained from the raw data. A group of other related road characteristics were also recorded at the time of field data collection. Crash data on gravel roads were extracted from the Kansas Accident Recording System (KARS) database. Speed analysis on a number of gravel roads where the statutory imposed, unposted speed limit of 55 mph was utilized indicated that they are functioning at a reasonably acceptable level in terms of actual speeds. In order to evaluate whether there were differences in traffic speeds between two counties or groups which have different speed limit settings on gravel roads, t-test was used. The analysis found that there was no significant difference between the mean speeds in two counties, one of which has 35 mph posted speed limit on gravel roads while the other does not post any speed limits. Moreover, the mean speed on the sections with 35 mph posted speed was a little higher than that on gravel roads without any speed limits. Linear models to predict 85th-percentile speed and mean speed on gravel roads were developed based on speed data. Both models indicated that traffic speeds are not significantly affected by the speed limit, but are related with 90% confidence to road width, surface classification and percentage of large vehicles in traffic. Chi-square tests were conducted with the crash data, and the results indicated that the posted 35 mph speed limit on gravel roads had not resulted in either smaller total number of crashes or decreased proportion of severe crashes, compared to gravel roads where no speed limits were posted. Logistic regression models were also developed on four levels of crash severity, which indicated that gravel roads with higher speed limits are likely to experience higher probability of having injury crashes. Two mail-back surveys were also conducted to gather the opinions of county engineers and road users on the subject of suitable speed limits on gravel roads. The majority of county engineers believed that blanket speed limit should be used for gravel roads and does not need to be posted. Three restrictions: changeful road conditions, unpractical law enforcement, and limited funds, are basic reasons why they do not think that gravel roads should be posted. Besides that, a few respondents said 55 mph is too high for gravel roads and needs to be lowered. Majority of the road users suggested that all gravel roads be posted with lower speed limit signs. However, they were more concerned about law enforcement since they believe that posted speeds won't bring any benefits if no law enforcement patrol gravel roads. Based on all aspects looked into in this study, it does not appear that reducing the speed limits and posting it with signs, is going to improve either traffic operational or safety characteristics on gravel roads in Kansas, and therefore is not recommended for new situations.

This thesis investigates the potential application of a two-dimensional depth-averaged sediment transport and morphological model on a large braided river system and examines its capability to build a computational gravel budget and predict the morphological changes. The Lower Fraser River gravel reach is characterized by an irregularly sinuous single-thread channel split around large gravel bars and vegetated islands, and riverbed aggradation because of gradual gravel deposition over the years, bank hardening and channel confinement. Gravel removal from selected locations is considered as one of the viable management options to maintain the safety and integrity of the existing flood protection system along the reach. Therefore, any gravel removal plan in this reach requires a reliable sediment budget estimation and identification of deposition zones. It is also required to examine the possible future morphological changes with and without gravel removal and to assess its impact on design flood level. The main objective of this study is to build a computational sediment (gravel) budget for the 33 km long gravel reach that extends from Agassiz-Rosedale Bridge to Sumas Mountain near Chilliwack. In this study, a two-dimensional depth-averaged curvilinear mathematical model MIKE 21C was modified and applied to predict the gravel bedload transport and detect the change of morphology for the next 10 years period. A gravel transport formula was coded and added into the MIKE 21C model. Sediment transport code modification and application has been done side by side in a trial and error fashion. This is the first use of a conventional two-dimensional depth-averaged model for the entire gravel reach of the Lower Fraser River within affordable computational effort. The model application was successful in term of gravel budgeting, aggradation and degradation zones identification and long-term morphological change prediction, with some limitations and drawbacks. Further modification and model testing with recent bedload data is recommended. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This study investigates channel bed scour and fill as a result of individual flood events in a gravel-bed channel. Given the complexity of interactions between hydraulic force, the texture and arrangement of bed material, and input of sediment to a particular point of the channel bed, study objectives were pursued with the view that bed material movement is a stochastic phenomenon. A two-year field program was conducted in Carnation Creek, a small gravel-bed stream draining 11 km2 on the west coast of Vancouver Island, British Columbia. In the 900 m study reach, an array of measurement techniques, including scour indicators, magnetically-tagged stones, and conventional survey, yielded information about the fluctuations of the channel bed elevation and movement of scoured material for individual flooding periods. Frequency distributions of scour and fill depths associated with individual flooding periods are adequately modeled by negative exponential functions over the range of flood peak magnitudes observed in Carnation Creek. Analysis of scour depths measured in streams on the Queen Charlotte Islands demonstrates the applicability of the exponential model to flooding periods and flood seasons. Further, exploratory analysis suggests that a regional scour depth model is possible. Power functions relating mean depths of scour and fill to flood peak discharge show that depth increases with an increase in peak magnitude. Observed maximum scour depths in flooding periods are linked, in general, to streambed conditions influenced by antecedent flow conditions. These patterns in scour and fill exist within an overall pattern of increasing variability in depths of scour and fill as peak discharge increases. Evaluation of a heuristic model for mean travel distance as a function of particle size proposed by Church and Hassan (1992) provides convincing evidence for its general merit. Mean travel distance decreases inversely with particle size as size increases beyond the median diameter of subsurface sediment. This trend is consistent in both individual flooding periods as well as flood seasons. The majority of material finer than the median diameter of surface sediment is supplied from subsurface material, which influences the travel distances of these finer fractions because of burial. Computation of volumetric transport rates of bed material, based on the active scour depth and width of the channel bed, the virtual velocity of particle movement, and sediment porosity, suggests the potential for building scale correlations with streamflow, which have usually been defined by bedload sampling during floods. Error analysis indicates that determination of active width contributes most significantly to the imprecision of transport rate estimates. Results underscore the stochastic nature of sediment transport in gravel-bed channels. / Arts, Faculty of / Geography, Department of / Graduate

Unpaved roads comprise about 72 percent of the national and provincial road network in South Africa and substantially more of the total southern African road network. Significant costs are incurred annually by the authorities on the maintenance of these roads and enormous sums are associated with the cost of using these roads. Specifications for the use of materials for unpaved roads in southern Africa abound, the origin of most of these, however being rather obscure. It would appear that many of them have been transferred from other countries, mostly in the northern hemisphere. The geological materials used for construction in southern Africa, having been subjected to aeons of weathering and minimal major periods of recent glaciation, differ greatly from those in the northern hemisphere. One of the main objectives of this research was to investigate the performance of local geological materials used in wearing courses for unpaved roads and relate this to their geotechnical properties. This involved the sampling, testing and monitoring of 110 sections of unpaved road in the Transvaal and South West Africa over a period of more than three years. A large data base of gravel height, roughness, rut and corrugation measurements and the severity and extent of dustiness, stoniness, potholes, cracks, loose material, slipperiness and trafficability was compiled. The material and performance data were then used to develop performance related specifications and prediction models for roughness progression and gravel loss with the aim of providing improved unpaved roads and consequently reducing the road user and maintenance costs, in the national interest. Some of the savings will obviously be off-set to some extent by slightly increased materials location and construction costs. These costs are, however, shown to be minimal in comparison with the potential savings to the road user, the national economy and the generally improved quality of life of many road users in southern Africa. A good knowledge of the geotechnical properties of potential wearing course materials (which are significantly dependent on the geological origin) is necessary to differentiate good gravels from poor ones. / Ongeplaveide paaie maak ongeveer 72 persent uit van die nasionale en provinsiale padnetwerk in Suid Afrika en heelwat meer van die totale padnetwerk van suidelike Afrika. Groot kostes word jaarliks aangegaan deur die owerhede vir die instandhouding van hierdie paaie, asook enorme kosts wat in verband gebring kan word met die gebruik van hierdie paaie. Materiaalspesifikasies vir ongeplaveide paaie in suidelike Afrika is volop. Die oorsprong van die meeste hiervan is egter twyfelagtig en dit wil voorkom of dit uit ander lande, hoofsaaklik in die noordelike halfrond, afkomstig is. Die geologiese materiale gebruik vir padkonstruksie in suidelike Afrika verskil grootliks van die in die noordelike halfrond. Dit was onderwerp aan eeue se verwering en minimale groot-skaalse onlangse glasiale werking verskil grootliks van die. Een van die hoof doelwitte van hierdie navorsing was om ondersoek in te stel na die werkverrigting van plaaslike geologiese materiale wat gebruik word vir die slytlaag van ongeplaveide paaie en om dit in verband te bring met hul Geotegniese eienskappe. Dit het behels monsterneming en toets van materiale, asook monitering van 110 seksies ongeplaveide pad in Transvaal en Suid-Wes Afrika oor 'n tydperk van drie jaar. 'n Groot databasis bestaande uit inligting oor metings van gruishoogte, ongelykheid, spoor en sinkplaat asook inligting van graad en omvang van stof, klipperigheid, slaggate, krake, los materiaal, glibberigheid en rybaarheid is saamgestel. Die materiaal- en werkverrigtingsdata is toe gebruik om werkverrigtingsverwante spesifikasies op te stel, asook om modelle daar te stel om verswakking in gelykheid, en gruisverlies te voorspel. Die doel is om beter ongeplaveide paaie te voorsien en gevolglik die padverbruikers- en onderhoudskoste in nasionale belang te verminder. 'n Gedeelte van die besparing sal onvermydelik deur effens duurder konatruksiekoste en moontlike langer vervoerafstande van materiaal gekanselleer word. Hiedie koste is egter minimaal in verhouding tot die potensiele besparing vir die padgebruiker, die nasionale ekonomie en die algemene verbetering in lewenskwaliteit van baie padgebruikers in suidelike Afrika. 'n Goeie kennis van die geotegniese eienskappe van potensiele slytlaagmateriale (wat grootliks afhanklik is van geologiese oorsprong) is noodsaaklik om te differensieer tussen goeie an swak gruise. / Thesis (PhD)--University of Pretoria, 1989. / Civil Engineering / Thesis (PhD)--University of Pretoria, 1989. / Unrestricted

Traditional culvert designs, in many cases, have become habitat barriers to aquatic animal species. In response, environmentally sensitive culvert designs have been developed to function as ecological bridges. Bottomless and buried invert culverts are examples of such designs and are commonly used for fish passage. Additional design guidance specific to streambed stability in buried-invert or bottomless culverts under high flow events is needed. This study investigated incipient motion conditions for four substrate materials in a 2-ft (0.61-m) diameter circular bottomless arch culvert and in a 1-ft (0.30-m) wide rectangular flume in a laboratory setting. General scour of the streambed within the bottomless arch culvert was also investigated under partially pressurized and non-pressurized flow conditions. This thesis discusses the experimental methods used to determine incipient motion conditions and analyses of incipient motion prediction methods. This thesis also presents the experimental results obtained from both test facilities with the results of other published incipient motion studies on gravel streambeds. Finally, the prediction efficiency of eight stone sizing methods (open channel and culvert application) applied to the experimental results was analyzed, which may be useful for determining stable stone diameters to be used as riprap in simulated streambeds through bottomless culverts.