Browsing by Author "Julien, Pierre Y., advisor"
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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 Dam overtopping and flood routing with the TREX watershed model(Colorado State University. Libraries, 2014) Steininger, Andrew, author; Julien, Pierre Y., advisor; Niemann, Jeffrey, committee member; Kampf, Stephanie, committee memberModeling dam overtopping and flood routing downstream of reservoirs can provide basic information about the magnitudes of flood events that can be beneficial in dam engineering, emergency action planning, and floodplain management. In recent years there has been considerable progress in computer model code development, computing speed and capability, and available elevation, vegetation, soil type, and land use data which has led to much interest in multi-dimensional modeling of dam failure, overtopping, and flood routing at the watershed scale. The purpose of this study is to ascertain the capability of the Two-dimensional, Runoff, Erosion and Export (TREX) model to simulate flooding from dam overtopping as the result of large scale precipitation events. The model has previously been calibrated for the California Gulch watershed near Leadville Colorado and was used for all of the simulations preformed for this study. TREX can simulate the reservoir filling and overtopping process by inserting an artificial dam into the digital elevation model (DEM) of a watershed. To test the numerical stability of the model for large precipitation events, point source hydrographs were input to the model and the Courant-Friedrichs-Lewy (CFL) condition was used to determine the maximum numerically stable time steps. Point sources as large as 50,000 m3/s were stably routed utilizing a model time step as small as 0.004 seconds. Additionally the effects of large flows on the flood plain were analyzed using point source hydrographs. The areal extent of floodplain inundation was mapped and the total areal extent of flooding was quantified. The attenuation of watershed outlet discharge due to upstream dams was analyzed. Three probable maximum precipitation (PMP) events and three estimated global maximum precipitation (GMP) events (the 1 hour, 6 hour, and 24 hour duration events), were simulated. Larger duration rainstorms had lower rainfall intensities but larger runoff volumes. A series of artificial dams ranging from 5 to 29 meters high were inserted into the DEM in sequential simulations and the attenuation of the downstream flood wave was quantified. The maximum attenuation of the peak discharge at the outlet of the watershed was 63% for an 18 meter high rectangular dam for the 1 hour PMP event, 58 % for a 20 meter high dam for the 6 hour PMP event, and 46% for a 29 meter high dam for the 24 hour duration PMP event. The same analysis was done using estimated global maximum precipitation (GMP) events. The maximum attenuation of the peak discharge at the outlet of the watershed was 59% for a 23 meter high rectangular dam for the 1 hour GMP event, 21 % for a 29 meter high dam for the 6 hour GMP event, and 9% for a 29 meter high dam for the 24 hour duration GMP event.Item Open Access Distributed runoff simulation of extreme monsoon rainstorms in Malaysia using TREX(Colorado State University. Libraries, 2013) Abdullah, Jazuri, author; Julien, Pierre Y., advisor; Bledsoe, Brian P., committee member; Venayagamoorthy, Subhas K., committee member; Wohl, Ellen E., committee memberMalaysia has a monsoon climate and most areas receive more than 2,500 mm of rainfall every year. For the past five years, the frequency and magnitude of floods in Malaysia have been relatively high. Floods have become the most significant type of natural disaster for Malaysia in terms of the population affected, financial losses and adverse socio-economic impact. This study uses the distributed two-dimensional TREX model to simulate infiltration, overland runoff and channel flow during extreme rainfall events. The main objective is to calibrate the distributed hydrological model to simulate monsoon floods. The second objective is to determine the affected flooding area under different rainfall events (i.e., large and extreme rainfall events). Large rainfall events cover return periods ranging from two to one hundred years. Extreme rainfall events include both the PMP and the world's largest rainfall events. The third objective is to examine the effect of rainfall duration on the magnitude of peak flood discharge as a function of watershed size. Finally, determine and produce graphs for the relationships between peak specific-discharge and watershed sizes. Three different sizes of watersheds are considered: Lui (small - 68 km2), Semenyih (medium - 236 km2) and Kota Tinggi (large - 1,635 km2). Generally, the topography of these watersheds is steep, except for the large watershed. The TREX model calibration and validation have been done using field measurements during several storm events. The performance of the model to find peak discharge, time to peak, and volume has been tested using three metrics: Relative Percentage Difference (RPD), Percentage Bias (PBIAS) and Nash-Sutcliffe Efficiency Coefficient (NSEC)) comparison. On average, the model performance was good for small (RPD - 7%, PBIAS - 14% and NSEC - 0.4) and medium watersheds (RPD - 14%, PBIAS - 28% and NSEC - 0.7). The RPD (4%), PBIAS (2%) and NSEC (0.8) for the large watershed shows that the model performance was very good. The spatial and temporal runoff distribution for overland and channel flows were successfully visualized in 3D. Both small and medium watersheds were not flooded by large events, except in the main channel. The flow depth reached 1.72 m in the valley of the small watershed only during extreme events. It was estimated that about 24% (±10%) and 83% (±5%) of the valley area exceed a flow depth of 1.72 m during PMP and world's largest events, respectively. For the medium watershed, the valley area was covered with water in excess of 4.49 m under the world's largest events. The visualization tool shows that the valley areas are prone to severe flooding (in excess of 4.49 m of flow depth) under this event (±5%). For the large watershed, the low land areas (i.e., along the tributaries and channels) are more likely to be flooded during large and extreme events. The water depths covered more than 2.8 m in these areas. The maximum estimated discharges (MED) for large rainfall events were highest for rainfall durations of 3 to 5 hours on small watersheds. However, the MED values for medium watersheds were obtained for rainfall durations between 5 and 12 hours. The MED values for extreme rainfall events were highest for rainfall durations between 10 and 13 hours on both watersheds. For the large watershed, the MED values of large and extreme events were obtained for a rainfall duration of 168 hour. The main conclusions of this study are: (1) rainfall intensity (i.e., hourly data) is one of the main factors that contribute to the magnitude of flooding on small and medium watersheds (watershed size less than 1,000 km2). The flooding events on large watersheds (watershed size more than 1,000 km2) result from longer rainfall durations (i.e., multi-day rainstorms), (2) for all size watersheds, the average magnitude of peak discharge for the PMP and the world's largest events are approximately 5 and 12 times larger than a 100-year rainfall event, (3) the peak specific-discharge (cms/km2) decreased as the watershed size (km2) increased, and (4) the runoff coefficient C increased significantly (i.e., a factor of three) from the 100-year rainfall event to the PMP and the world's largest events for all watersheds (CPMP,CWGR > 0.7).Item Open Access Erosion mapping and sediment yield of the Kabul River Basin, Afghanistan(Colorado State University. Libraries, 2013) Sahaar, Ahmad Shukran, author; Julien, Pierre Y., advisor; Arabi, Mazdak, committee member; Kampf, Stephanie K., committee memberSoil erosion by water is a serious issue in Afghanistan. Due to the geographic landscape, soil and climatic conditions, and the latest deforestation activities, there has been intensive soil erosion which has resulted in prolonged and great impact on social and economic development of the region. In fact, recent environmental assessment shows that decades of war and continuous drought have resulted in widespread environmental degradation throughout the country; therefore, mapping of soil erosion at the basin scale is urgently needed. The Kabul River Basin was selected for the purpose of erosion and sedimentation modeling due to its great socio-economic impact. The main objectives of this study include: (1) calculations of the annual average soil loss rates at the basin level; (2) spatial distribution of soil erosion rates at the basin level; (3) predictions of deforestation effects on sediment losses under different land cover scenarios at the watershed level; and (4) calculation of sediment delivery ratios based on soil erosion rates, and sediment yields at the sub-watershed levels in the basin. This study uses the Revised Universal Soil Loss Equation (RUSLE) model combined with Geographic Information System (GIS) techniques to analyze the gross soil loss rates and the spatial distribution of soil loss rates under different land uses. Digital elevation model (DEM), average annual precipitation data, land cover map and soil type map were used to define the parameters of the RUSLE model. The annual average soil loss rate of the Kabul River Basin was estimated to be 19 tons/acre/year (4748 tons/km2/year), and the gross mean annual soil loss rate found to be 47 million tons/year. By producing 57 % of the total annual average soil loss, rangelands were the primary contributor to the basin. In case of the spatial distribution of erosion rates at the Kabul River Basin, the relationship between probability and annual average soil loss rates were analyzed. The analysis indicated that up to sixty percent of the mean annual soil loss rates are in the range of tolerable soil loss rate (0 - 5 tons/acre/year). Moreover, northern part of the basin is prone to more extensive erosion than the southern part. The study predicted that if the forest region of the Kunar watershed is completely reduced to barren lands, the watershed will produce five times more sediment than the estimated soil loss rate from 1993's UN-FAO land cover map. The annual average soil loss rate in this watershed was about 29 tons/acre/year but it will increase to 149 tons/acre/year as deforestation continues to take place in the watershed. The range of sediment delivery ratios for the basin's rivers is 2.5 -10.8 %. Based on this evaluation, the sediment delivery ratio for the sediment gauging stations in the basin are in the similar range of predicted values by the methods of Boyce, Renfro, Williams and Maner.Item Open Access Geospatial analysis of specific degradation in South Korea(Colorado State University. Libraries, 2019) Kang, Woochul, author; Julien, Pierre Y., advisor; Grigg, Neil S., committee member; Morrison, Ryan, committee member; Kampf, Stephanie, committee memberSouth Korea experienced many local and concentrated sediment problems such as landslides, upland erosion, rills and valleys, aggradation/degradation, and flood plain sediment deposition. These problems vary in space and time, therefore a reliable and consistent approach to model sediment processes is desirable. In contrast to sediment yield at the basin scale, Specific Degradation (SD) is defined as the ratio of the sediment yield divided by the watershed area. Field measurements of discharge and sediment concentration are analyzed at 70 stations in South Korea. Half of the sampled river basins (35 stations) represent streams in mountain regions and the other half represent rivers. The Modified Einstein Procedure (MEP) was used to determine the total sediment load at all stations. The Flow Duration – Sediment Rating Curve (FD-SRC) method was used to determine the sediment yield and specific degradation for all gauging stations. The annual sediment yield of 70 rivers and streams in South Korea ranged from 10 to 1,000 tons/km2▪yr. The application of three existing models from the literature showed Root Mean Square Errors (RMSE) in excess of 1,400 tons/km2▪yr and gave negative values of the Nash-Sutcliffe Efficiency coefficient (NSE) for existing models, which indicates that the observed mean is a better predictor than the model. The main characteristics of each watershed were analyzed using GIS tools such as ArcGIS version 10.3.1. The data used for the analysis included: (1) daily precipitation data at 60 stations from the Korea Meteorological Administration (KMA); (2) a detailed soil map from the National Institute of Agriculture Sciences; (3) a 5m by 5m resolution Digital Elevation Model (DEM); and (4) land cover raster data at a 10 m resolution from the Ministry of Environment (ME). Seven regression models based on these watershed characteristics are proposed to estimate the mean annual sediment yield and specific degradation. In decreasing order of importance, the meaningful parameters are: (1) drainage area; (2) mean annual precipitation; (3) percentage of urbanized area; (4) percentage of sand of the surface soil (upper 50cm); (5) percentage of wetland and water; and (6) morphometric parameters such as watershed average slope and two parameters of the hypsometric curve. The RMSE for the newly developed models decreased to 90 tons/km2▪yr and the NSE increased from -50 to 0.5, which shows good agreement between the model and the measured sediment yield on these watersheds. The calculated specific degradation and mean annual soil loss of mountain streams were larger than alluvial rivers. Erosion loss mapping at 5m, 30m and 90m was also developed from the Revised Universal Soil Loss Equation (RUSLE). Satellite images and aerial photos were used to better represent geospatial features affecting erosion and sedimentation. Long-term reservoir sedimentation measurements were available to determine the Sediment Delivery Ratio (SDR). An important finding from this analysis is that the percentage of the area covered with wetland and water is well-correlated with the estimated sediment delivery ratios. It suggests that the transfer of sediment to the rivers is affected by wetlands located near alluvial rivers. The erosion maps at 5m resolution could clearly show unique erosion features (i.e. hill slopes, croplands, and construction sites) and locate areas for sediment deposition (i.e. wetlands and agricultural reservoirs). In comparison, the gross erosion rates at 90 m resolution were highly distorted and could not delineate the areas with high upland erosion rates. Sustainable sediment management with these methodologies could be helpful to solve various erosion and sedimentation problems.Item Open Access GIS-based soil erosion modeling and sediment yield of the N’djili River basin, Democratic Republic of Congo(Colorado State University. Libraries, 2015) Ndolo Goy, Patrick, author; Julien, Pierre Y., advisor; Fontane, Darrell G., committee member; MacDonald, Lee H., committee memberIn the Democratic Republic of Congo, the N’djili River and its tributaries are the most important potable source of water to the capital, Kinshasa, satisfying almost 70% of its demand. Due to increasing watershed degradation from agricultural practices, informal settlements and vegetation clearance, the suspended sediment load in the N’djili River has largely increased in the last three decades. With an area of 2,097 km², the N’djili River basin delivers high suspended sediment concentration, and turbidity levels that cause considerable economic losses, particularly by disrupting the operation in the N’djili and Lukaya water treatment plants, and increasing dramatically the cost of chemical water treatment. The objectives of this study are to: (1) determine the change in the land cover/use of the N’djili River basin for 1995, 2005 and 2013; (2) predict and map the annual average soil losses at the basin scale and determine the effects of land cover/use change on the soil erosion; (3) estimate the sediment yield and the sediment delivery ratio at the water intake of the N’djili water treatment plant; and (4) quantify the effects of ash concentration on water turbidity in order to understand the high turbidity observed at the beginning of the rainy season. The Revised Universal Soil Loss Equation (RUSLE) model was implemented in a Geographic Information System (GIS) to estimate the spatially distributed soil loss rates in the N’djili basin under different land uses. RUSLE model parameters were derived from digital elevation model (DEM), average annual precipitation, soil type map and land cover maps (1995, 2005, 2013) obtained from Landsat images. The land cover/use change analysis shows that bare land/burned grass/agricultural land cover represented almost 22% of the N’djili basin area in 2013 whereas it was covering only 6% of the basin area in 1995. Settlements, which covered about 8% of the basin area in 1995, represented about 18% of the N’djili Basin area in 2013. The expansion of settlements, bare land, burned areas and agricultural lands was realized at the expense of the forest, grass, and shrubs cover. The annual average soil loss rate of the N’djili River Basin is estimated to be 7 tons/acre/year for 1995, 8.7 tons/acre/year for 2005 and 16 tons/acre/year for 2013. In 2013, bare land, burned areas and rainfed crops produced about 60% of the soil loss. The analysis of the relationship between probability of soil erosion and annual average soil loss rates indicated that up to 82, 79, and 73% of the basin area are in the range of tolerable soil erosion (0 – 5 tons/acre /year) in 1995, 2005 and 2013 respectively. Based on the gross erosion and sediment yield observed in 2005 and 2013, the sediment delivery ratio of 4.6% and 4.1% were predicted in 2005 and 2013, suggesting that most of the soil eroded from upland areas of the basin is trapped on flood plains covered by grass, shrubs and trees. Regarding the effects of ash concentration on turbidity, this study found that turbidity increased as a power function of ash concentration.Item Open Access Hazard area mapping during extreme rainstorms in South Korean mountains(Colorado State University. Libraries, 2012) Kim, Jaehoon, author; Julien, Pierre Y., advisor; Watson, Chester C., committee member; Thornton, Christopher I., committee member; MacDonald, Lee H., committee memberThe concern for climate change has increased worldwide. Localized rain storms with high intensity and short duration have been observed in the United States, Europe, Australia, and China. South Korea is one of the countries that have also been impacted by extreme rainfall events during typhoons. Extreme rainstorms have caused major damage from landslides and debris flows in the South Korean mountains. The Duksan Creek watershed in South Korea was selected to simulate surface runoff using TREX during the extreme rainstorm precipitation event from July 14 to July 16, 2006. The maximum hourly rainfall was 62 mm on July 15 in 2006. The three hour rainfall from 08:00 AM to 11:00AM on this day was 168 mm. This rainstorm triggered 518 landslides and caused major infrastructure damage from debris flows. The three hour rainfall precipitation has a 100 year return period. The TREX model was calibrated in two mountainous regions of South Korea. The relative percent difference of time to peak and peak discharge on the Naerin Stream and the Naesung Stream were 6.25 %, -2.58 % and 1.90 %, -0.25 %, respectively. The TREX simulation at the Duksan Creek was performed at a 30 m resolution with distributed data on topography (DEM), soil type, and land use. The peak discharge from the TREX simulation at the Duksan Creek watershed was 452 m3/s. This value was compared to the results of several other methods and the relative percent difference was -1.1 %. The peak discharge was also compared with specific peak discharge measurements and this value corresponds to the range of values for similar watersheds. The TREX model can calculate the distribution of infiltration depth. The infiltration depth calculation typically ranged from 0.2 m to 0.3m with maximum value of 1.2 m. Based on the infinite slope analysis, such infiltration depths correspond to a critical slope angle of 25° to 29°. This range of the critical slope angle was comparable to the angle of 26° from the field investigations and from the analysis of satellite images and aerial photographs at the Duksan Creek. Several different hazard mapping methods were compared including a landslide hazard map from the Korea Forest Institute (KFRI), SINMAP, and TREX. The result of the relative predictability of TREX was slightly better an improvement of 24.6 % than the result of SINMAP. The maximum shear stress could also be calculated by the TREX model. Values of shear stress typically ranged between 0.223 kPa to 0.895 kPa in the tributaries and 1.79 kPa to 17 kPa in the main channel. Based on a critical shear stress analysis, a 1 m diameter boulder reaches incipient motion at a shear stress of 0.895 kPa.Item Open Access Interflow dynamics and three-dimensional modeling of turbid density currents in Imha Reservoir, South Korea(Colorado State University. Libraries, 2011) An, Sang Do, author; Julien, Pierre Y., advisor; Thornton, Christopher I., committee member; Venayagamoorthy, Subhas K., committee member; Wohl, Ellen E., committee memberThis study reports a detailed research identifying the turbid density flow regimes and propagation dynamics of density currents in Imha Reservoir in South Korea during Typhoon Ewiniar. We employ a high resolution 3-D numerical model (FLOW-3D), based on nonhydrostatic Navier-Stokes equations, to investigate the propagation of density flows resulting from the complicated reservoir morphometry and various mixing processes. The 3-D numerical model was modified to simulate particle-driven density currents. The particle dynamics algorithm builds upon the original FLOW-3D code in two ways: (1) improve the original buoyant flow model to compute the changes in density via particle deposition; and (2) include multiple sediment sizes in mixtures as a function of particle size. The influences of inflow characteristics and seasonal changes of thermal structure of the reservoir on the turbid density currents intruding into Imha Reservoir are studied. A series of numerical simulations of lock-exchange are validated with laboratory experiments on: (1) gravity currents propagating into a two-layered fluid; (2) gravity currents propagating into a stratified fluid; and (3) particle-driven gravity currents. The model predictions of propagation speed compared very well with laboratory experiments and analytical solutions. Two numerical approaches (Reynolds Averaged Navier-Stokes model and large-eddy simulation) are equally effective and robust in predicting propagation speed and interfacial instability compared to the laboratory experiments. The simulation of gravity currents intruding into a stratified fluid matched the theoretical solution derived from an energy model. The modified FLOW-3D model successfully captured the decreasing propagation speed due to the different deposition rates of different particle sizes, compared to experimental measurements. We extended our simulations to include the effects of particle sizes on the propagation dynamics of gravity currents. The type of gravity currents depends on particle sizes and can be subdivided into three zones: (1) When ds, is less than about 10 μm, the particle-driven gravity currents behave like IGC (Intrusive Gravity Currents) and all sediments can remain in suspension. Thus the suspended sediments can increase the density of the currents enough to travel a longer distance; (2) When ds > 40 μm, particles will rapidly settle, resulting in a decrease in excess density of the gravity currents. So, such density currents lose their momentum quickly and rapidly vanish; and (3) When 10 μm ds 40 μm, some particles will settle quickly, but others remain suspended for a long time, affecting the propagation dynamics of the currents. Modeling gravity currents in this regime particle sizes must account for particle dynamics and settling. We applied the FLOW-3D coupled with the particle dynamics algorithm to Imha Reservoir in South Korea. The model application was validated against field measurements during Typhoon Ewiniar in 2006. In the field validation, absolute mean error (AME) and root mean squared error (RMSE) for the prediction in water temperature profiles were calculated to be 1.0 oC and 1.3 oC, respectively. For turbidity predictions, AME and RMSE were 37 and 47 NTU (nephelometric turbidity units) between the simulated and the measured turbidity at stations G3, G4, and G5. We showed the influence of inflow characteristics (discharge, temperature, sediment concentration, and particle size distribution) on the fate of density currents in Imha Reservoir. Two threshold values in particle size (10 μmand 40 μm ) were identified, consistent with previous findings from the simulations of Gladstone's experiments. The simulations indicate that when the particle sizes ds are less than 10 μm, most of the sediment inflows at the inlet point (G2) will be transported to Imha Dam (G4) in suspension by interflows. When the particle sizes ds are greater than 40 μm, they will rapidly settle before reaching the dam. Therefore, highly concentrated turbid interflows could only occur when ds is less than the threshold value of 10 μm. The numerical results also present three flow regimes determining the intrusion types of density currents: (1) river inflows will form interflows when the sediment concentration Ci is less than 2000 mg/l; (2) when Ci is between 2000 mg/l and 3000 mg/l, they will form multiple intrusions (i.e., interflows and underflows); and (3) when Ci is greater than 3000 mg/l, they will plunge and propagate as underflows. These threshold values (2000 mg/l and 3000mg/l) can be used to practically predict the formation of turbid density currents, flow type, and intrusion level in Imha Reservoir.Item Open Access Mechanics of sediment plug formation in the Middle Rio Grande, NM(Colorado State University. Libraries, 2013) Park, Kiyoung, author; Julien, Pierre Y., advisor; Thornton, Christopher I., committee member; Venayagamoorthy, Subhas K., committee member; Wohl, Ellen E., committee memberThe Rio Grande is a dynamic river system which has experienced significant hydraulic and geomorphic changes through recorded history from the early 1900's to the present. These changes stem, for the most part, from natural and human interventions to the river system, which experienced channel bed elevation changes, lateral migration, straightening, channel realignment, etc. Sediment plugs have formed in the Tiffany area near San Marcial in 1991, 1995, and 2005, and in the Bosque Reach 14 miles upstream from the Tiffany plug location in 2008. Many authors have investigated the cause of sediment plugs in the Middle Rio Grande but the previous studies do not provide a complete criteria for sediment plug formation. Better understanding of the complex mechanics of plug formation on the Middle Rio Grande is therefore pursed. Based on the historic flow and geometric characteristics of plug areas, seven parameters were identified as major causing factors of sediment plug formation in the Middle Rio Grande: (1) two geometric factors: variability of channel widths and roughness; (2) two water and sediment loss factors: perching/overbanking and sediment concentration distribution profiles; and (3) three backwater effect factors: backwater effects from a reservoir, a bridge, and sharp bends. The purpose of this research is to analyze possible sediment plug parameters and to assess the primary causing factors. The specific objectives are to: (1) investigate the mechanics of sedimentation effect due to each factor; (2) simulate the historic sediment plugs using a numerical aggradation/degradation program; and (3) determine which factors contribute the most to the formation of sediment plugs. Geometric factors show that the channel has narrowed 40% between 1962 and 2002 and channel capacity has 77% decreased over time. The representative composite roughness increased 50 % between 1992 and 2002. Accordingly sediment transport capacity has decreased 45%. The narrowing (40%) with increase in roughness (50%) causes considerable loss of sediment transport capacity (45%). Therefore geometric factors induce more overbank flows and channel bed aggradation. Sedimentation factors show that the perching ratio increased from 13% to 87% between 1992 and 2002. Bank depth has decreased 51% between 1992 and 2002. The perching and lower bank depth facilitated more overbank flows and 13 ~ 20% loss of water. As particle sizes have coarsened (0.2mm in 1992 → 0.25mm in 2002) and width/depth ratios have increased (129 in 1992 → 229 in 2002), leading to higher rouse numbers and more near-bed concentration profiles. High Rouse number (Ro >1.2) and near-bed sediment concentration profile speed up the aggradation rates (4 ~ 7 times faster) than for a uniform-concentration profile. The high near-bed concentrations shorten the plug formation time from 90 to 20 days. Since snowmelt floods exceed bankfull discharges less than 2 months, the acceleration factors are essential for sediment plugs to form. Backwater effects from the Elephant Butte Reservoir influenced the upstream channel bed elevation over time. At an average flow discharge (1,550cfs), the aggradation (up to 7ft) time to fill the 25.5 mile long channel is roughly 10 years. The historic Tiffany plug area has been influenced by the reservoir levels, but with a lag time of several years. Around the San Marcial Railroad Bridge, channel bed elevation has aggraded consistently (12ft increased between 1979 and 1987). The pier contraction and congested abutments generate about a 1ft high backwater propagating to the Tiffany plug area. Sharp bends caused a 1.6ft high backwater which propagates roughly 1 mile upstream. As the beginning point of the Bosque plug is located 0.6 mile upstream of the sharp bends, backwater does influence the channel aggradation of the Bosque plug. The time to fill the main channel up to the bank crest was estimated as approximately 17 days. In terms of significance, perching/overbank flow and sediment concentration profiles can be evaluated as the primary causing factors of sediment plugs, followed by the backwater effects from bridge and sharp bends. Backwater effect from the reservoir has influenced the upstream channel elevation on a long-term basis (7 ft / 10 years). Channel narrowing and higher roughness promote overbank flows and decrease of sediment transport capacity. Owing to the increase of overbank flows, sediment concentration profiles speed up the rate of channel aggradation, causing a sediment plug within a matter of weeks, thus these two factors are the most significant factors (1.2 ft / 20 days). Two other factors, the backwater effect from the railroad bridge and sharp bends, explain why the historic sediment plugs formed at particular areas, therefore these two parameters can be classified as local triggering factors (1~1.6 ft / 20 days). On the other hand, causal factors can be divided into two groups depending on the plug location. The Tiffany plugs have been more affected by the backwater effect from the reservoir and railroad bridge. On the other hand, the Bosque plug was more influenced by the decrease of channel width/channel capacity, roughness, and sharp bends.Item Open Access Optimization of Sangju weir operations to mitigate sedimentation problems(Colorado State University. Libraries, 2016) Kim, Hwa Young, author; Julien, Pierre Y., advisor; Fontane, Darrell G., committee member; Thornton, Christopher I., committee member; Rathburn, Sara L., committee memberTo view the abstract, please see the full text of the document.Item Open Access Probability structure and return period calculations for multi-day monsoon rainfall events at Subang, Malaysia(Colorado State University. Libraries, 2013) Muhammad, Nur Shazwani, author; Julien, Pierre Y., advisor; Roesner, Larry A., committee member; Salas, Jose D., committee member; Arabi, Mazdak, committee member; Wohl, Ellen E., committee memberFlooding is the most common natural disaster in Malaysia, as a result of heavy rainfall. Malaysia is located in the equatorial zone and experiences a tropical climate with two seasons classified as the Northeast (November to May) and Southwest (May to September) monsoons. Both monsoons bring moisture, and multi-day rainfall events that cause particularly devastating floods on large watersheds. The objectives of this study are the following: (1) examine the probability structure of multi-day rainfall events; (2) determine the most suitable distribution function to represent the multi-day rainfall amounts; (3) select the most appropriate model to simulate the sequence of daily rainfall using the discrete autoregressive family models; and (4) develop and test an approach to calculate the return period of multi-day rainfall events with respect to the duration and amount. Daily monsoon rainfall data recorded at Subang Airport are gathered from the Malaysian Meteorological Department. Subang Airport is located near Kuala Lumpur (the capital city of Malaysia) and has a long and reliable daily rainfall record, with 18,993 daily measurements from 1960 to 2011. The majority of wet and dry events at Subang Airport from 1960 to 2011 are multi-days, with the fraction of 57% and 51%, respectively. The analysis of conditional probabilities for t-consecutive wet and dry days shows that the probability of occurrence for multi-day wet and dry days is increasing as the event duration increases. For example, the probability of rain on any random day is 0.53; and the conditional probability of rain the second day increases to 0.63. Also, the probability of dry on any random day is 0.47; and the probability of the second dry day increases to 0.58. The probability of rain and dry days increases gradually with rainfall duration. This finding shows that the occurrence of rain and dry is time-dependent. The autocorrelation coefficient for the daily rainfall amounts is very low at 0.0283. It is concluded that this parameter is independent from one day to another. The two parameter gamma function is most suitable to fit the daily rainfall precipitation data and the cumulative rainfall from t-consecutive rainy days up to 6 days. A graphical method, i.e. the 1:1 plot confirms the goodness-of-fit of the gamma function. Two discrete autoregressive models are tested in this study, i.e., the low order Discrete Auto Regressive [DAR(1)] and the low order Discrete Auto Regressive and Moving Average [DARMA(1,1)]. These models require data stationarity, therefore the analysis is done separately for the Northeast and Southwest monsoons. The model selection is based on the four-step process suggested by Salas and Pielke (2003). The comparisons between the observed and calculated autocorrelation coefficient and the low sum of squared errors for the probability distributions confirm that DARMA(1,1) is most suitable to simulate daily rainfall sequences at Subang Airport for both monsoons. The return period for 1-day and multi-day rainfall events is defined as a function of wet run length and rainfall amount. A test of return period calculations up to 20 years based on the mean wet and dry run lengths shows good agreement between calculation and observations of multi-day rainfall amounts up to 150 mm. A very long sequence of daily rainfall (1,000,000 days) is generated to extend the analysis of multi-day events with cumulative rainfall up to 350 mm, which gives an estimated return period of more than 2,000 years. The mean, standard deviation, maximum daily rainfall, lag-1 ACF coefficient and maximum wet and dry run lengths of the generated daily rainfall sequence using DARMA(1,1) are also comparable with the observed data. The December 2006 rainstorm event at Kota Tinggi, Johor is used as an example of the application of the algorithms developed in this study. This multi-day rainstorm totaling 350 mm caused devastating floods in the area. The December 2006 rainstorm is extremely rare because the cumulative rainfall amount from the multi-day event gives an estimated return period of greater than 2,000 years. The method proposed in this study is helpful for the design of levees on large watersheds (size of more than 1,000 km2) because multi-day rainstorms are the main cause of flooding to the area. For example, the return period to overtop the current levee at Kota Tinggi is 220 years when considering a 1-day rainstorm, but this period of return decreases to 24 years when considering 4-day rainstorms.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 Series expansion of the Modified Einstein Procedure(Colorado State University. Libraries, 2009) Shah-Fairbank, Seema Chandrakant, author; Julien, Pierre Y., advisorThis study examines calculating total sediment discharge based on the Modified Einstein Procedure (MEP). A new procedure based on the Series Expansion of the Modified Einstein Procedure (SEMEP) has been developed. This procedure contains four main modifications to MEP. First, SEMEP solves the Einstein integrals quickly and accurately based on a series expansion. Next, instead of dividing the suspended sediment and bed material samples into particle size classes, the total sediment discharge calculation is based on a median grain size in suspension (d50ss). Thirdly, for depth-integrated samples the Rouse number (Ro) is determined directly by calculating the fall velocity (ω) based on dsoss, the shear velocity (u. = -√ghS) and assuming the value of the von Karman constant (κ) is 0.4. For point concentration measurements, the Ro is calculated by fitting the concentration profile to the measured points. Lastly, SEMEP uses the measured unit sediment discharge and Ro to determine the unit bed discharge directly. Thus, SEMEP can determine the unit bed discharge (qb), unit suspended sediment discharge (qs), unit total sediment discharge (qt), ratio of measured to total sediment discharge (qm/qt) and ratio of suspended to total sediment discharge (qs/qt).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 TREX-SMA: a multi-event hybrid hydrologic model applied at California Gulch, Colorado(Colorado State University. Libraries, 2012) Halgren, James, author; Julien, Pierre Y., advisor; Kampf, Stephanie K., committee member; Gates, Timothy K., committee member; Venayagamoorthy, S. Karan, committee memberThis dissertation describes a hydrologic model, Two-Dimensional Runoff Erosion and Export (TREX) Soil Moisture Accounting (SMA), created from adding the Sacramento Soil Moisture Accounting model (SAC-SMA) to the TREX surface hydrology model. TREX-SMA combines the capabilities of TREX as a distributed physical surface hydrology model with a conceptual rendering of infiltration and return flow as found in SAC-SMA. In order to form the hybrid, infiltrated water (computed as a distributed function on the surface) is aggregated as an input to a system of soil moisture accounting zones, underlying the entire watershed. In each model time step, TREX SMA releases baseflow from the accumulated infiltrated water according to simple transfer functions. Evapotranspiration (ET) losses from the soil moisture zones are computed based on potential ET demand and available water. As baseflow and ET are released between precipitation events, TREX SMA recovers capacity in the soil moisture zones. Based on the simulated recovery, the model then re-initializes the infiltration parameters of the surface model to prepare for the next event, allowing continuous simulation of multiple events. The capabilities of the TREX SMA model to continuously simulate soil moisture, infiltration, and rainfall-runoff are demonstrated with an application to multi-event modeling on the 30 km2 California Gulch watershed, near Leadville, Colorado, United States. Precipitation inputs are derived from measurements at a system of six precipitation and stream flow gauges providing ten-minute data for the summer of 2006. Eight major events were recorded during this time with runoff produced at all gauges. One additional event with partial watershed response was also evaluated for a total of 54 event hydrographs in the 50-day simulated series. Time steps in the simulation ranged between 2.0 and 4.0 seconds. Parameters for the surface hydrology were obtained from a prior calibration of TREX and were distributed across 34,000 grid cells based on the 30-meter United States Geological Survey (USGS) Digital Elevation Model (DEM). Parameters for the soil moisture zones were obtained from a-priori estimates used by the Arkansas Basin River Forecast Center of the National Weather Service (NWS) of the National Oceanographic and Atmospheric Administration (NOAA) in their real-time operational flood forecasting model for the Arkansas River. Using conceptual soil moisture states to re-initialize distributed infiltration parameters, the simulation results with TREX SMA improved relative to results from the unmodified TREX model with constant infiltration parameters. Model results are processed using gnuplot to create real-time hydrograph plots as the simulation progresses. Gnu R scripts produce real-time plots of simulated minus observed residual and statistical analyses as the simulation progresses. Statistics generated for each gauge include Nash-Sutcliffe, percent bias, absolute percent bias, Pearson correlation and modified Pearson correlation, and mean-squared error. These statistics were generated both for the entire simulation series and for each individual storm event. The gnuplot and R plots are produced using web-based technology for instantaneous sharing via the Internet. Model results such as surface and channel water depth are processed with GRASS GIS and KML scripts to create 2.5 dimensional, browseable animations overlaid on a Google Earth terrain. Statistical measures of the improvement of TREX SMA over TREX are presented in this dissertation. The overall accuracy, measured by the Nash-Sutcliffe coefficient, improved in four out of six gauges. Peak over-estimation was corrected in a majority of the 54 peaks evaluated. Implementation of the TREX SMA soil moisture accounting algorithm to re-initialize the infiltration parameters reduces the total absolute peak error from 180% to 135% of the observed peak flow rates. The Nash-Sutcliffe model efficiency improved over standard TREX simulations by 43%, 11%, 5%, and 10% at CG-1, CG-4, CG-6, and SHG09A.