Browsing by Author "Ettema, Robert, committee member"
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Item Open Access A framework for the analysis of coastal infrastructure vulnerability under global sea level rise(Colorado State University. Libraries, 2017) O'Brien, Patrick S., author; Julien, Pierre Y., advisor; Watson, Chester C., committee member; Ettema, Robert, committee member; Rathburn, Sara L., committee memberThe assumption of hydrologic stationarity has formed the basis of coastal design to date. At the beginning of the 21st century, the impact of climate variability and future climate change on coastal water levels has become apparent through long term tide gauge records, and anecdotal evidence of increased nuisance tidal flooding in coastal areas. Recorded impacts of global sea rise on coastal water levels have been documented over the past 100 to 150 years, and future water levels will continue to change at increasing, unknown rates, resulting in the need to consider the impacts of these changes on past coastal design assumptions. New coastal infrastructure plans, and designs should recognize the paradigm shift in assumptions from hydrologic stationarity to non-stationarity in coastal water levels. As we transition into the new paradigm, there is a significant knowledge gap which must address built coastal infrastructure vulnerability based on the realization that the underlying design assumptions may be invalid. A framework for the evaluation of existing coastal infrastructure is proposed to effectively assess vulnerability. The framework, called the Climate Preparedness and Resilience Register (CPRR) provides the technical basis for assessing existing and future performance. The CPRR framework consists of four major elements: (1) datum adjustment, (2) coastal water levels, (3) scenario projections and (4) performance thresholds. The CPRR framework defines methodologies which: (1) adjust for non-stationarity in coastal water levels and correctly make projections under multiple scenarios; (2) account for past and future tidal to geodetic datum adjustments; and (3) evaluate past and future design performance by applying performance models to determine the performance thresholds. The framework results are reproducible and applicable to a wide range of coastal infrastructure types in diverse geographic areas. The framework was applied in two case studies of coastal infrastructure on the east and west coasts of the United States. The east coast case study on the Stamford Hurricane Barrier (SHB) at Stamford CT, investigated the navigation gate closures of the SHB project. The framework was successfully applied using two performance models based on function and reliability to determine the future time frame at which relative sea level rise (RSLR) would cause Navigation Gate closures to occur once per week on average or 52 per year. The closure time analysis also showed the impact of closing the gate earlier to manage internal drainage to the Harbor area behind the Stamford Hurricane Barrier. These analyses were made for three future sea level change (SLC) scenarios. The west coast case study evaluated four infrastructure elements at the San Francisco Waterfront, one building and three transportation elements. The CPRR framework applied two performance models based on elevation and reliability to assess the vulnerability to flooding under four SLC scenarios. An elevation-based performance model determined a time horizon for flood impacts for king tides, 10 and 100-year annual exceedance events. The reliability-based performance model provided a refinement of results obtained in the elevation-based model due to the addition of uncertainty to the four infrastructure elements. The CPRR framework and associated methodologies were successfully applied to assess the vulnerability of two coastal infrastructure types and functions in geographically diverse areas on the east and west coasts of the United States.Item Open Access Floodwave and sediment transport assessment along the Doce River after the Fundão Tailings Dam collapse (Brazil)(Colorado State University. Libraries, 2019) Palu, Marcos Cristiano, author; Julien, Pierre, advisor; Thornton, Christopher, committee member; Ettema, Robert, committee member; Rathburn, Sara, committee memberThe collapse of the Fundão Tailings Dam in November 2015 spilled 32 Mm3 of mine waste, causing a substantial socio-economic and environmental damage within the Doce River basin in Brazil. Approximately 90% of the spilled volume deposited over 118 km downstream of Fundão Dam on floodplains. Nevertheless, high concentration of suspended sediment (≈ 400,000 mg/l) reached the Doce River, where the floodwave and sediment wave traveled at different velocities over 550 km to the Atlantic Ocean. The one-dimensional advection-dispersion equation with sediment settling was solved to determine, for tailing sediment, the longitudinal dispersion coefficient and the settling rate along the river and in the reservoirs (Baguari, Aimorés and Mascarenhas). The values found for the longitudinal dispersion coefficient ranged from 30 to 120 m2/s, which are consistent with those in the literature. Moreover, the sediment settling rate along the whole extension of the river corresponds to the deposition of finer material stored in Fundão Dam, which particle size ranged from 1.1 to 2 μm. The simulation of the flashy hydrographs on the Doce River after the dam collapse was initially carried out with several widespread one-dimensional flood routing methods, including the Modified Puls, Muskingum-Cunge, Preissmann, Crank Nicolson and QUICKEST. All of these methods presented unsatisfactory results, with prediction errors in peak discharge up to 44%, and differences in timing to peak up to 5 hours. A new and more accurate one-dimensional flood routing approach was then used, solving the full dynamic equation into an equivalent diffusive wave format and reformulating the hydraulic diffusion coefficient in terms of the Froude number and floodwave celerity. The numerical solution to this new approach was implemented using Crank Nicolson and QUICKEST schemes. The error in predicted peak discharge along the Doce River was reduced to 2%, and the maximum difference found in time to peak was about 1 hour. Regarding sediment transport, a comprehensive one-dimensional numerical model is developed, coupling the new floodwave propagation algorithm with the numerical solution for advective sediment transport and settling. One of the main features of this model is the ability to simulate the propagation of the floodwave and sediment through the entire Doce River extension with or without reservoirs. A sensitivity analysis showed that a hypothetical decrease in water temperature from 30°C to 5°C would have resulted in a concentration 13 times higher at the outlet. In addition, without the presence of hydropower reservoirs on the Doce River, the sediment concentration at the basin outlet would have been 70,000 mg/l instead of the observed 1,600 mg/l. Finally, a simplified numerical model based on the Doce River measurements can simulate the hypothetical collapse of 56 tailings dams in the Doce River basin to estimate the potential impact on the water supply for the towns along the river. Those simulation results show that tailings dams located in the Piracicaba basin, a Doce River sub-basin, have the highest potential to adversely impact the water supply of the downstream towns due the volume stored and proximity with populated towns. Ultimately, the collapse of the biggest dams in this sub-basin could affect approximately 1,000,000 people for several days.Item Open Access Flow resistance corrections for physical models using unit flowrates(Colorado State University. Libraries, 2024) Cote, Cassidy B., author; Thornton, Christopher, advisor; Ettema, Robert, committee member; Rathburn, Sara, committee memberFlow resistance is an essential aspect of evaluating flow behavior in open-channel hydraulic models. Flow resistance in open channels is commonly characterized by Manning's resistance equation, where a value of Manning's roughness coefficient n, indicates the magnitude of flow resistance. Physical hydraulic models are one method to estimate Manning's n values for prototype channel reaches. A physical hydraulic model evaluates prototype channel characteristics at the model scale. The scale for a given physical model may be characterized by length-scale factor, given by the relationship of prototype to model geometry. Models that have a large length-scale factor are known to introduce errors associated with instrumentation, measurement, and scale effects, therefore minimization of the length-scale factor is an important consideration in the development of hydraulic models. Evaluating physical models using a scaled unit flowrate provides a method by which the length-scale factor may be minimized. In this way, a scaled design discharge per unit width of channel is applied to a channel that is less wide than the prototype design. Using this approach greatly improves the ability of laboratories to utilize available facilities, without being constrained by prototype design width, which can otherwise be a driving factor increasing the length-scale factor for a given model. This thesis documents the construction and analysis of two physical models of a proposed rectangular canal along Rio Puerto Nuevo in San Juan, Puerto Rico. One model used a scaled unit flowrate and a reduced channel width at a lesser length-scale factor, and the other model accommodated the total scaled design flowrate and design channel width at a larger-scale factor. Tests were conducted for three sidewall conditions to identify the impact associated with applying a unit flowrate physical modeling approach for models with different Manning's n values specific to the sidewalls. The unit flowrate approach was found to result in larger estimates of flow depth and composite Manning's n compared to the model that accommodated the full prototype channel width. Insights regarding the variability of Manning's n as a function of channel width for each sidewall condition were identified by comparing results from the two models. A correction method was proposed for improving estimates of Manning's n derived from scaled unit flowrate models. Correction factors were identified as a function of two dimensionless parameters, relative prototype channel width (defined as the ratio of the width evaluated using a unit flowrate model to the design width of the channel), and relative flow resistance exerted by the individual boundary elements as determined from the unit flow rate model (defined as the ratio of Manning's n values between the sidewall and channel bed boundary elements). Findings indicate that it becomes increasingly important to apply correction factors to flow resistance estimates on unit flowrate models when wall boundary elements exert a larger contribution to flow resistance than that of the channel bed (large relative roughness), and when the scaled unit flowrate approach results in a prototype channel width that is significantly smaller than the proposed design channel width (small relative channel width). Correction factors were developed for a range of relative channel width values from approximately 0.4 to 1.0, and a range of relative roughness values from approximately 0.5 to 3.0. Future physical models using unit flowrates with relative channel widths and relative flow resistance within the range evaluated may use the presented correction methods to improve estimates of flow resistance.Item Open Access Hydrologic alteration under hydropower dam operations and climate change: a case study in the Sesan River Basin, Lower Mekong Region(Colorado State University. Libraries, 2023) Ghalley, Wangmo, author; Niemann, Jeffrey D., advisor; Shrestha, Sangam, advisor; Ettema, Robert, committee member; Poff, N. LeRoy, committee memberHydropower dam developments exacerbated by climate change can significantly disrupt the natural flow regimes, leading to adverse effects on river ecosystems. The Sesan River, a major tributary of the Lower Mekong Basin, is renowned for its diverse biomes and is an important resource for nearby inhabitants. Rapid expansion of hydropower dams has occurred in recent years, but the hydrologic impacts remain poorly understood, particularly when combined with the effects of climate change. This study assessed the hydrologic alterations in Sesan River streamflow due to hydropower dams and potential climate change. Daily streamflow in the Sesan River was simulated using the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), which was calibrated and evaluated based on streamflow observations. Climate change projections were based on daily precipitation and temperature, which were estimated using an ensemble of three Earth system models from the Coupled Model Intercomparison Project Phase-6 under two Socioeconomic Pathways: SSP2-4.5 (Middle of the road) and SSP5-8.5 (Fossil-fueled development). Future projections spanned 2025 to 2100, which was divided into three 25-year periods called the Near Future (NF), Mid-Future (MF), and Far Future (FF). The projections were compared to a 30-year baseline (BL) period from 1984 to 2014. Results show a consistent rise in both precipitation and temperature for the Sesan basin across all future periods and SSP scenarios. Precipitation is projected to increase by 4% to 13% for SSP2-4.5 and 7% to 29% for SSP5-8.5. Minimum temperature is projected to increase by 8% to 16% for SSP2-4.5 and 10% to 26% for SSP5-8.5, and maximum temperature is projected to increase by 3% to 7% for SSP2-4.5 and 3% to 12% for SSP5-8.5. Hydrologic alterations were assessed using the Range of Variability Approach (RVA) within the Indicators of Hydrologic Alteration (IHA). The impact of dams was assessed by comparing streamflow with dams and without dams during the BL period. The dams significantly altered the hydrograph characteristics by decreasing the high flows and increasing the low flows. The overall alteration due to dams fell within the "moderate" category. The impact of climate change was assessed by comparing streamflow without dams between the BL and the future periods. Climate change increased the high flow rates, with the impact limited to September in the NF but impacting much of the year in the MF and FF periods. Another notable change was the shift in the timing of peak flow from August in the BL to September in the future periods. The hydrologic alteration due to climate change fell within the "low" category. Finally, the combined impact of dams and climate change was assessed by comparing the BL streamflow without dams to future streamflow with dams. Dams were found to mitigate some impacts of climate change by smoothing extreme high flows, especially in the FF period. Overall, the combined impact showed greater alteration than the individual scenarios but fell within the "moderate" category.Item Open Access Nonstationary flood risk assessment in coastal regions under climate change(Colorado State University. Libraries, 2021) Ghanbari, Mahshid, author; Arabi, Mazdak, advisor; Ettema, Robert, committee member; Schumacher, Russ, committee member; Bhaskar, Aditi, committee memberCoastal cities are exposed to multiple flood drivers including high tide, storm surge, extreme rainfall, and high river flows. The occurrence of these flood drivers, either in isolation or in combination, can cause significant risk to property and human life. Climate change is placing greater pressure on coastal communities by increasing frequency and intensity of flood events through sea level rise (SLR) and more extreme rainfall and storm events. Therefore, effective adaptation strategies are essential to reduce future flood risk in exposed communities. The planning and implementation of effective adaptation strategies require a comprehensive understanding of future flood hazards and risks under future climate conditions and adaptation options. The overarching goal of this dissertation is to improve the capacity to understand, estimate and mitigate future flood hazards and risks in coastal areas under uncertain climate change. To achieve this goal, first, a nonstationary mixture probability model was developed that enables simultaneous characterization of minor and major flood events under future sea level conditions. The probability model was used to estimate minor and major flooding frequency at 68 locations along the coasts of the Contiguous United States (CONUS). The results showed a significant increase in frequency of both minor and major flood events under future sea level conditions. However, the frequency amplification of minor and major flooding varied by coastal regions. While regions in the Pacific and southeast Atlantic coast are likely to be exposed to higher frequency amplification in major flooding, the Gulf and northeast Atlantic coastal regions should expect the highest minor flood frequency amplification. Second, the proposed mixture probability model was employed in a flood risk assessment framework to enable assessing future acute and chronic coastal flood risks under different SLR and adaptation levels. The HAZUS-MH flood loss estimation tool was used to estimate property damage. The application of the framework in Miami-Dade County revealed that as sea level rises, chronic risks from repetitive nonextreme flooding may exceed acute risks from extreme floods. Third, a nonstationary bivariate flood hazard assessment method was developed that enables estimation of future frequency of compound coastal-riverine flooding with consideration of impacts of climate change including SLR and variations in extreme river flows. The proposed method was employed at 26 paired tidal-riverine stations along the CONUS coast. Specifically, the joint return period of compound major coastal-riverine flooding, defined based on flood impact thresholds, was explored by mid-century. The results showed that under current climate conditions the northeast Atlantic and western part of the Gulf coasts are exposed to the highest compound major coastal-riverine flood probability. However, considering future SLR, emerging high compound major flooding probability was evident in the southeast Atlantic coast. The impact of changes in extreme river flows was found to be negligible in most of the locations. Finally, four stormwater intervention scenarios including gray (i.e., conventional centralized conveyance systems and water treatment plants) and green (i.e., decentralized infiltration measures) infrastructure systems, were assessed in New York City (NYC). The results revealed that in developed and urbanized cities like NYC, green systems should not be considered as a substitute for gray systems. Complementary benefits on flood and combined sewer outflow (CSO) reduction can be gained through integration of green and gray systems.Item Open Access Numerical simulations on patterns of alluviation in mixed bedrock-alluvial channels(Colorado State University. Libraries, 2023) Cho, Jongseok, author; Nelson, Peter A., advisor; Julien, Pierre Y., committee member; Ettema, Robert, committee member; Wohl, Ellen E., committee memberMixed bedrock-alluvial rivers can exhibit partial alluvial cover, which may play an important role in controlling bedrock erosion rates and landscape evolution. However, numerical morphodynamic models generally are unable to predict the pattern of alluviation in these channels. Hence we present a new two-dimensional depth-averaged morphodynamic model that can be applied to both fully alluvial and mixed bedrock-alluvial channels, and we use the model to gain insight into the mechanisms responsible for the development of sediment patches and patterns of bedrock alluviation. The model computes hydrodynamics, sediment transport, and bed evolution, using a roughness partitioning that accounts for differential roughness of sediment and bedrock, roughness due to sediment transport, and form drag. The model successfully replicates observations of bar development and migration from a fully alluvial flume experiment, and it models persistent sediment patches observed in a mixed bedrock-alluvial flume experiment. Numerical experiments in which the form drag, sediment transport roughness, and ripple factor were neglected did not successfully reproduce the observed persistent sediment cover in the mixed bedrock-alluvial case, suggesting that accounting for these different roughness components is critical to successfully model sediment dynamics in bedrock channels. Understanding the development and spatial distribution of alluvial patches in mixed bedrock-alluvial rivers is necessary to predict the mechanisms of the interactions between sediment transport, alluvial cover, and bedrock erosion. This study aims to analyze patterns of bedrock alluviation using a 2D morphodynamic model, and to use the model results to better understand the mechanisms responsible for alluvial patterns that have been observed experimentally. A series of simulations are conducted to explore how alluvial patterns in mixed bedrock-alluvial channels form and evolve for different channel slopes and antecedent sediment layer thicknesses. In initially bare bedrock low-slope channels, the model predicts a linear relationship between sediment cover and sediment supply because areas of subcritical flow enable sediment deposition, while in steep-slope channels the flow remains fully supercritical and the model predicts so-called runaway alluviation in which the bedrock remains fully exposed at all sediment supplies below a threshold. For channels that are initially covered with sediment, the model predicts a slope-dependent sediment supply threshold above which a linear relationship between bedrock expo-sure and sediment supply develops, and below which the bedrock becomes fully exposed. For a given sediment supply, the fraction of bedrock exposure and average alluvial thickness converge toward the equilibrium value regardless of the initial cover thickness so long as it exceeds a minimum threshold. Steep channels are able to maintain a continuous strip of sediment under sub-capacity sediment supply conditions by achieving the balance between increased form drag as bedforms develop and reduced surface roughness as the portion of alluvial cover decreases. In lower-slope channels, alluvial patches are distributed sporadically in regions of the subcritical flow.Item Open Access Propagation of the Sidoardjo mud in the Porong River, East Java, Indonesia(Colorado State University. Libraries, 2021) Andika, Neil, author; Julien, Pierre Y., advisor; Grigg, Neil S., committee member; Ettema, Robert, committee member; Rathburn, Sara, committee memberThe Sidoarjo Mud Volcano in East Java, Indonesia erupted on May 29, 2006. It caused controversy because of the impact of the mud volcano had on communities around it. The discharge of the mud volcano was 50,000 m3/d (Harnanto, 2011) which comprised a 35% concentration of silt and clay. To mitigate the damage to surrounding regions, the Government of Indonesia diverted the mud to Madura Strait through the Porong River in 2016 (Hadimuljono, 2008). The objectives of this thesis are to: (1) understand the physical properties of mud from the mud volcano and its interaction with the water in the river; (2) carry out field measurements of sediment concentration along the Porong River for a model validation; (3) determine how the concentration of mud from the mud volcano varies along the river; (4) create a framework or guideline for the mitigation of a mud volcano disaster in the future. Laboratory experiments were used to test the sediment properties. The experiments of turbidity and sediment concentration, C, concluded that the linear regression, C=5.297×Turbidity+24, was the best fitted regression. Flocculation tests in 2019 showed that the recorded deflocculated settling velocity for the sample of the Ginonjo Outlet was 0.013 mm/s which was approximately 2 times slower than the natural settling velocity of 0.028 mm/s. This value was one order slower than the general settling velocity for flocculated particles. Two field measurement programs were completed, in July 2018 and in September 2019. The field programs in 2018 observed the sediment concentration along the Porong River at 106 cross-sections and the point source sediment concentration at Ginonjo Outlet was 57,000 mg/l. It was found that the observed maximum sediment concentration ranged between 691 mg/l and 4,198 mg/l. The average sediment concentration at the downstream end of the Porong River on the other hand was 90 mg/l. The field program in 2019 captured the vertical sediment concentration profiles of the first 4 km of the Porong River. The highest near-bed sediment concentration was 1,500 mg/l at Line C cross-section 9. This was followed by 1,450 mg/l at Line C cross-section 6. These measurements showed that the sediment concentration are uniform along the Porong River except for the first 4 km where the bottom sediment concentration are higher. There are three flow conditions based on the hydrograph of the Porong River: low flow with 45 m3/s, medium flow with 250 m3/s, and high flow with 2500 m3/s. For low flow, the average flow velocity was 0.12 m/s and the shear velocity was 0.01 m/s. Results from the two-dimensional mixing model without settling was the fully-mixed concentration for low flow condition achieved at 4 km downstream from the outlet with a concentration of 470 mg/l. There was 380 mg/l difference between the model's result and the observed concentration. The two-dimensional mixing and setting model without flocculation produced a result of sediment concentration of 195 mg/l at the downstream end of the Porong River. This came from the clay fraction which was about 48% of the total sediment. The sediment concentration difference between this model and the observed data was 105 mg/l. The two-dimensional mixing and setting model with flocculation was then used. The sediment concentration at the left bank side of the Porong River was about 90 mg/l, which matched the observed data. The gravel, sand and coarser silt fractions settled at the first 4 km of the study reach was also captured by the model. This result proved that the two-dimensional mixing and settling model with flocculation was a suitable model for the sediment propagation in Porong River.Item Open Access The effect of resins on the aggregation behavior of asphaltenes(Colorado State University. Libraries, 2020) Derakhshani Molayousefi, Mortaza, author; McCullagh, Martin, advisor; Szamel, Grzegorz, committee member; Van Orden, Alan, committee member; Ettema, Robert, committee memberMillions of barrels of crude oil are extracted on a daily basis. Crude oil has four main components separated by the SARA fractionation method.1 Asphaltenes are the heaviest component of the cured oil. They are known to be responsible for clogging oil wellbores and pipelines, which bedevils the oil industry financially. Additionally, the cleaning chemicals and the clogging waste has a huge negative impact on our environment. The majority of the research on understanding the clogging problem is focused on the asphaltenes as a fraction of crude oil without much consideration for the effects of specific chemical structure. Moreover, the role of other components of the crude oil such as resins is not clear. Here, we have performed structure specific studies of asphaltenes by performing all-atom molecular dynamics (MD) simulations to quantify the aggregation behavior of asphaltenes in the absence and presence of resins. In this research, we have studied the aggregation tendency of asphaltenes in connection with their molecular properties. Systems with 20 counts of model asphaltene molecules were studied for nanoaggregation behavior of eight model asphaltenes in their neat state. We have quantified the aggregation tendency of asphaltene molecules in n-heptane with isodesmic free energy of aggregation, ∆Giso, as well as a quantity called aggregation propensity (AP). Using ∆Giso and AP value, we have classified model asphaltene molecules to three main category of non-aggregating, mildly-aggregating, and readily-aggregating asphaltenes. Each category of asphaltene have different aggregation behavior. They differ in their molecular features that ultimately is related to their aggregation propensity. Subsequently, we have studied the aggregation tendency of asphaltene in the presence of resin with total of 48 systems comprising 8 model asphaltene molecules in the presence of 6 model resins. We wanted to determine the role of resins in the aggregation behavior of asphaltenes by observing the effect of presence of resin on the ∆Giso and AP values. Additional to ∆Giso, we have defined a normalized quantity called aggregation propensity ratio (APR) to compare the effect of resin on the aggregation of asphaltenes. Resins studied in this work had no promoting effect on the aggregation tendency of asphaltenes. In general, both ∆Giso and APR metrics suggest that aggregation of asphaltene in presence of resin is either not affected or is prevented to different degrees. We have studied the aggregation behavior of asphaltenes in nanoaggregation, clustering and flocculation stages proposed by Yen-Mullins model. Resins have from minimal disruptive to highly disruptive effect on the nanoaggregation of asphaltenes. We investigated the further aggregation of stable nanoaggregates into clustering and flocculation with 500 counts of mildly-aggregating and readily-aggregating asphaltene molecules. We found that both clustering and flocculation stages occur for the readily-aggregating asphaltenes and do not occur for the mildly-aggregating asphaltenes. Readily-aggregating asphaltene molecules with large negative ∆Giso and large AP values lead to clustering and flocculation whereas the mildly-aggregating asphaltenes stay in the form of nanoaggregates. Our results show that in order for asphaltenes to flocculate, there is a threshold for existence of adequate favorable molecular features. Asphaltenes containing large enough aromatic cores and/or heteroatom reach clustering and flocculation stages. Furthermore, we found that in the presence of a highly disruptive resin, clustering and flocculation does not occur. For the readily-aggregating asphaltenes the aggregation stops in the nanoaggregation stage and for the mildly-aggregating asphaltenes the size of the nanoaggregates decreases. Our results explain what kind of resins are capable of potentially solving the deposition problem with providing insight on the molecular features of both asphaltene and resin molecules. Such molecular insights paves the road to explore more natural based solutions in preventing the clogging problem in the oil industry by informed characterization of each oil reservoir and its capability to form aggregate or prevent aggregates within itself and in another reservoir.Item Open Access The sediment yield of South Korean rivers(Colorado State University. Libraries, 2019) Yang, Chun-Yao, author; Julien, Pierre Y., advisor; Ettema, Robert, committee member; Nelson, Peter, committee member; Rathburn, Sara L., committee memberSouth Korea is experiencing increasing river sedimentation problems, which requires a reliable method to predict the sediment yield. With the recent field measurements at 35 gaging stations in South Korea provided by K-water, we quantified the sediment yield by using the flow duration curve and sediment rating curve. The current sediment yield models have large discrepancies between the predictions and measurements. The goal of this dissertation is to provide better understanding to the following questions: (1) How much of the total sediment load can be measured by the depth-integrated samplers? (2) Can we predict the sediment yield based only on watershed area? (3) Is there a parametric approach to estimate the mean annual sediment yield based on the flow duration curve and sediment rating curve? With 1,962 sediment discharge measurements from the US D-74 sampler, the total sediment discharge is calculated by both the Modified Einstein Procedure (MEP) and the Series Expansion of the Modified Einstein Procedure (SEMEP). It is concluded that the SEMEP is more accurate because MEP occasionally computes suspended loads larger than total loads. In addition, SEMEP was able to calculate all samples while MEP could only compute 1,808 samples. According to SEMEP, the ratio Qm/Qt of measured sediment discharge Qm to total sediment discharge Qt is a function of the Rouse number Ro, flow depth h, and the median grain size of the bed material d50. In Korean sand and gravel bed rivers, the materials in suspension are fine (silt or clay) and Ro ≈ 0. The ratio Qm/Qt reduces to a function of flow depth h, and at least 90% of the total sediment load is measured when h > 1 m. More than 80% of the sediment load is measured when the discharge Q is larger than four times mean annual discharge ¯Q(Q/¯Q > 4). The ratio Qs/Qt of suspended sediment discharge Qs to total sediment discharge can be also analyzed with SEMEP and the result shows that Qs/Qt is a function of h/d50 and Ro. When Ro ≈ 0, the ratio Qs/Qt increases with h/d50. The suspended load is more than 80% of the total sediment load when h/d50 > 18. The relationship between specific sediment yield, SSY, and watershed area, A, is SSY = 300A-0.24 with an average error of 75%. Besides the specific sediment yield, the mean annual discharge, the normalized flow duration curve, the sediment rating curve, the normalized cumulative distribution curve, and the half yield discharge vary with watershed area. From the normalized flow duration curve at an exceedance probability of 0.1%, small watersheds (A<500 km2) have 425000 km2) which have 14 < Q/¯Q < 33. In terms of sediment rating curves, at a given discharge, the sediment load of small watersheds is one order of magnitude higher than for large watersheds. From the normalized cumulative distribution curves, the half yield (50% of the sediment transported) occurs when the discharge is at least 15 times the mean discharge. In comparison, the half yield for large watersheds corresponds to Q/¯Q < 15. The flow duration curve can be parameterized with â and ˆb by using a double logarithmic fit to the flow duration curve. This parametric approach is tested with 35 Korean watersheds and 716 US watersheds. The value of â generally increases with watershed area. The values of ˆb are consistently between 0.5 and 2.5 east of the Mississippi River and the Pacific Northwest. Large variability in ˆb is found in the High Plains and in Southern California, which is attributed to the high flashiness index in these regions. A four-parameter model is defined when combining with the sediment rating curve. The four parameters are: â and ˆb for the flow duration curve, and ā and ¯b for the sediment rating curve. The mean annual discharge ¯Qs is calculated by ¯Qs = āâ¯bΓ(1+ ˆb¯b). The model results are compared to the flow-duration/sediment-rating curve method. The average error of this four-parameter model is only 8.6%. The parameters can also be used to calculate the cumulative distribution curves for discharge and sediment load.
Item Open Access Water resources on outer-lying islands in Micronesia(Colorado State University. Libraries, 2016) Beikmann, Alise Marie, author; Bailey, Ryan, advisor; Ettema, Robert, committee member; Grigg, Neil, committee member; Ronayne, Michael, committee memberTo view the abstract, please see the full text of the document.