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The complex interaction between flow, vegetation and sediment drives the never settled changes of riverine system. Vegetation intercepts rainfall, adds resistance to surface flow, and facilitates infiltration. The magnitude and timing of flood flow are closely related to the watershed vegetation coverage. In the meantime, flood flow can transport a large amount of sediment resulting in bank erosion, channel degradation, and channel pattern change. As climate changes, future flood frequency will change with more intense rainfalls. However, the quantitative simulation of flood flow in vegetated channel and the influence of climate change on flood frequency, especially for the arid and semi-arid Southwest, remain challenges to engineers and scientists. Therefore, this research consists of two main parts: simulate unsteady flow and sediment transport in vegetated channel network, and quantify the impacts of climate change on flood frequency. A one-dimensional model for simulating flood routing and sediment transport over mobile alluvium in a vegetated channel network was developed. The modified St. Venant equations together with the governing equations for suspended sediment and bed load transport were solved simultaneously to obtain flow properties and sediment transport rate. The Godunov-type finite volume method is employed to discretize the governing equations. Then, the Exner equation was solved for bed elevation change. Since sediment transport is non-equilibrium when bed is degrading or aggrading, a recovery coefficient for suspended sediment and an adaptation length for bed load transport were used to quantify the differences between equilibrium and non-equilibrium sediment transport rate. The influence of vegetation on floodplain and main channel was accounted for by adjusting resistance terms in the momentum equations for flow field. A procedure to separate the grain resistance from the total resistance was proposed and implemented to calculate sediment transport rate. The model was tested by a flume experiment case and an unprecedented flood event occurred in the Santa Cruz River, Tucson, Arizona, in July 2006. Simulated results of flow discharge and bed elevation changes showed satisfactory agreements with the measurements. The impacts of vegetation density on sediment transport and significance of non-equilibrium sediment transport model were accounted for by the model. The two-dimensional surface flow model, called CHRE2D, was improved by considering the vegetation influence and then applied to Santa Cruz River Watershed (SCRW) in the Southern Arizona. The parameters in the CHRE2D model were calibrated by using the rainfall event in July 15th, 1999. Hourly precipitation data from a Regional Climate Model (RCM) called Weather Research and Forecasting model (WRF), for three periods, 1990-2000, 2031-2040 and 2071-2079, were used to quantify the impact of climate change on the magnitude and frequency of flood for the Santa Cruz River Watershed (SCRW) in the Southern Arizona. Precipitation outputs from RCM-WRF model were bias-corrected using observed gridded precipitation data for three periods before directly used in the watershed model. The watershed model was calibrated using the rainfall event in July 15th, 1999. The calibrated watershed model was applied to SCRW to simulate surface flow routing for the selected three periods. Simulated annual and daily maximum discharges are analyzed to obtain future flood frequency curves. Results indicate that flood discharges for different return periods are increased: the discharges of 100-year and 200-year return period are increased by 3,000 and 5,000 cfs, respectively.
While most books only examine the classical aspects of hydrology, the three-volume set covers multiple aspects of hydrology, and includes contributions from experts from more than 30 countries. It examines new approaches, addresses growing concerns about hydrological and ecological connectivity, and considers the worldwide impact of climate change. It also provides updated material on hydrological science and engineering, discussing recent developments as well as classic approaches. Published in three books, Fundamentals and Applications; Modeling, Climate Change, and Variability; and Environmental Hydrology and Water Management, the entire set consists of 87 chapters, and contains 29 chapters in each book. The chapters in this book contain information on: Long-term generation of scheduling of hydro plants, check dam selection procedures in rainwater harvesting, and stochastic reservoir analysis Ecohydrology for engineering harmony in the changing world, concepts, and plant water use Conjunctive use of groundwater and surface water Hydrologic and hydraulic design in green infrastructure Data processing in hydrology, optimum hydrometric site selection and quality control, and homogenization of climatological series Cold region hydrology, evapotranspiration, and water consumption Modern flood prediction and warning systems, and satellite-based systems for flood monitoring and warning Catchment water yield estimation, hydrograph analysis and base flow separation, and low flow hydrology Sustainability in urban water systems and urban hydrology Students, practitioners, policy makers, consultants and researchers can benefit from the use of this text.
Climate and anthropogenic changes impact the conditions of erosion and sediment transport in rivers. Rainfall variability and, in many places, the increase of rainfall intensity have a direct impact on rainfall erosivity. Increasing changes in demography have led to the acceleration of land cover changes in natural areas, as well as in cultivated areas, and, sometimes, in degraded areas and desertified landscapes. These anthropogenized landscapes are more sensitive to erosion. On the other hand, the increase in the number of dams in watersheds traps a great portion of sediment fluxes, which do not reach the sea in the same amount, nor at the same quality, with consequences on coastal geomorphodynamics. This book is dedicated to studies on sediment fluxes from continental areas to coastal areas, as well as observation, modeling, and impact analysis at different scales from watershed slopes to the outputs of large river basins. This book is concentrated on a number of keywords: “erosion” and “sediment transport”, “model” and “practice”, and “change”. The keywords are briefly discussed with respect to the relevant literature. The contributions in this book address observations and models based on laboratory and field data, allowing researchers to make use of such resources in practice under changing conditions.
Watershed modeling is at the heart of modern hydrology, supplying rich information that is vital to addressing resource planning, environmental, and social problems. Even in light of this important role, many books relegate the subject to a single chapter while books devoted to modeling focus only on a specific area of application. Recognizing the
This report presents the development of a numerical model simulating water flow and contaminant and sediment transport in watershed systems of one-dimensional river/stream network, two-dimensional overland regime, and three-dimensional sub surface media. The model is composed of two modules: flow and transport. Three options are provided in modeling the flow module in river/stream network and overland regime: the kinematic wave approach, diffusion wave approach, and dynamic wave approach. The kinematic and diffusion wave approaches are known to be numerically robust in terms of numerical convergency and stability; i.e., they can generate convergent and stable simulations over a wide range of ground surface slopes in the entire watershed. The question is the accuracy of these simulations. The kinematic wave approach usually produces accurate solutions only over the region of steep slopes. The diffusion wave approach normally gives accurate solutions over the region of mild to steep slopes. However, neither approach has the ability to yield accurate solutions over the region of small slopes, in which the inertial forces are no longer negligible compared to the gravitational forces. The kinematic wave approach cannot address the problems of backwater effects. On the other hand, a dynamic wave approach, having included all forces, can theoretically have the potential to generate accurate simulations over all ranges of slopes in a watershed. The subsurface flow is described by Richard's equation where water flow through saturated-unsaturated porous media is accounted for.
Climate change is expected to have both direct and indirect effects on water resources. Hydrologic impacts of two indirect effects, vegetation density and stomata! conductance, are evaluated for the American River, a 200 km2 watershed in the Cascade Range of Washington state. First, a set of distributed hydrology-biogeochemistry model structures are created by coupling DHSVM (Distributed Hydrology-Soil-Vegetation Model) and Biome-BGC (BioGeochemistry Cycles). The model structures are applied to idealized hillslopes and current and future climate scenarios for the watershed. Eleven model structures, differing in vertical 1-D hydrology parameterization, lateral water routing, timestep, slope and aspect, are tested. Sensitivity of hydrology and vegetation density (as measured by leaf area index, LAI) is evaluated with respect to model structure, lapsed climate (elevation), climate change, and soil thickness and nitrogen input rate. Lapsed climate accounts for the largest range in LAI, but choice of model structure is also significant, highlighting opportunities and problems in model development. LAI is water-limited at low elevations, temperature-limited at high elevations, and solar-limited at all elevations. All model structures predict increased LAI under the future scenario that includes reduced stomatal conductancethe conifer forest grows denser. Next, climate scenarios and LAI results from the idealized hillslope simulations are input to the hydrology model DHSVM for hydrologic analysis of the full American River watershed. Basin-average annual precipitation, streamflow, and evapotranspiration all increase under the future climate scenario. The direct effect of increased temperature causes the major hydrologic impact, reduced snowpack and altered seasonal timing of streamflow and ET. Indirect effects of altered LAI and stomatal conductance on hydrology are minor in comparison to the direct effects. Future streamflow and ET are essentially the same between the simplest treatment of climate change, involving fixed LAI and physical climate change only, and the most detailed treatment, involving variable LAI and reduced stomatal conductance in addition to physical climate change.
This report presents the development of a numerical model simulating water flow, contaminant transport, and sediment transport in watershed systems. The model is composed of two modules: flow and transport. Three options are provided in modeling the flow module in river/stream network and overland regime: the kinematic wave approach, diffusion wave approach, and dynamic wave approach. The kinematic and diffusion wave approaches are known to be numerically robust in terms of numerical convergency and stability, i.e., they can generate convergent and stable simulations over a wide range of ground surface slopes in the entire watershed. The question is the accuracy of these simulations. The kinematic wave approach usually produces accurate solutions only over the region of steep slopes. The diffusion wave approach normally gives accurate solutions over the region of mild to steep slopes. However, neither approach has the ability to yield accurate solutions over the region of small slopes, in which the inertial forces are no longer negligible compared with the gravitational forces. The kinematic wave approach cannot even address the problems of backwater effects. On the other hand, a dynamic wave approach, having included all forces, can theoretically have the potential to generate accurate simulations over all ranges of slopes in a watershed. A total of eight groups of example problems were given in this report to demonstrate the capability of this model. Continuing work is underway to incorporate a three-dimensional subsurface flow and chemical transport model into this watershed model. The Richards' equation and advection-dispersion reactive chemical transport equations will form the basis to simulate the subsurface flow and chemical transport module in saturated-unsaturated media.