Kara J. Carr

Scaling and Self-Similarity of One-Dimensional Unsteady Suspended Sediment Transport with Emphasis on Unscaled Sediment Material Properties

AbstractCurrent methods utilized in scaling sediment transport in unsteady open-channel flow result in a number of model and scale effects, decreasing the accuracy and applicability of scale models. Identifying the conditions under which the governing equations of sediment transport are self-similar, and require no sediment diameter or density scaling, can reduce scale effects and increase model applicability. Conditions for self-similarity of one-dimensional unsteady suspended sediment transport are identified by applying the one-parameter Lie group of point scaling transformations, both for the general case and with unscaled sediment diameters. Under the scaling ratio relations found when holding sediment diameter to be unscaled, sediment diameter, density, critical and total shear, porosity, kinematic viscosity, and particle Reynolds number are all unscaled. It is shown that under Lie group scaling, the unsteady one-dimensional suspended sediment transport process as an initial-boundary value problem i...

Assessment of 21st century drought conditions at Shasta Dam based on dynamically projected water supply conditions by a regional climate model coupled with a physically-based hydrology model

Along with socioeconomic developments, and population increase, natural disasters around the world have recently increased the awareness of harmful impacts they cause. Among natural disasters, drought is of great interest to scientists due to the extraordinary diversity of their severity and duration. Motivated by the development of a potential approach to investigate future possible droughts in a probabilistic framework based on climate change projections, a methodology to consider thirteen future climate projections based on four emission scenarios to characterize droughts is presented. The proposed approach uses a regional climate model coupled with a physically-based hydrology model (Watershed Environmental Hydrology Hydro-Climate Model; WEHY-HCM) to generate thirteen equally likely future water supply projections. The water supply projections were compared to the current water demand for the detection of drought events and estimation of drought properties. The procedure was applied to Shasta Dam watershed to analyze drought conditions at the watershed outlet, Shasta Dam. The results suggest an increasing water scarcity at Shasta Dam with more severe and longer future drought events in some future scenarios. An important advantage of the proposed approach to the probabilistic analysis of future droughts is that it provides the drought properties of the 100-year and 200-year return periods without resorting to any extrapolation of the frequency curve.

Assessment of the effects of multiple extreme floods on flow and transport processes under competing flood protection and environmental management strategies

Extreme floods are regarded as one of the most catastrophic natural hazards and can result in significant morphological changes induced by pronounced sediment erosion and deposition processes over the landscape. However, the effects of extreme floods of different return intervals on the floodplain and river channel morphological evolution with the associated sediment transport processes are not well explored. Furthermore, different basin management action plans, such as engineering structure modifications, may also greatly affect the flood inundation, sediment transport, solute transport and morphological processes within extreme flood events. In this study, a coupled two-dimensional hydrodynamic, sediment transport and morphological model is applied to evaluate the impact of different river and basin management strategies on the flood inundation, sediment transport dynamics and morphological changes within extreme flood events of different magnitudes. The 10-year, 50-year, 100-year and 200-year floods are evaluated for the Lower Cache Creek system in California under existing condition and a potential future modification scenario. Modeling results showed that select locations of flood inundation within the study area tend to experience larger inundation depth and more sediment is likely to be trapped in the study area under potential modification scenario. The proposed two dimensional flow and sediment transport modeling approach implemented with a variety of inflow conditions can provide guidance to decision-makers when considering implementation of potential modification plans, especially as they relate to competing management strategies of large water bodies, such as the modeling area in this study.

Projected 21st century climate change on snow conditions over Shasta Dam watershed by means of dynamical downscaling

Abstract Snow is an important component of the Earths climate system and is particularly vulnerable to global warming. It has been suggested that warmer temperatures may cause significant declines in snow water content and snow cover duration. In this study, snowfall and snowmelt were projected by means of a regional climate model that was coupled to a physically based snow model over Shasta Dam watershed to assess changes in snow water content and snow cover duration during the 21st century. This physically based snow model requires both physical data and future climate projections. These physical data include topography, soils, vegetation, and land use/land cover, which were collected from associated organizations. The future climate projections were dynamically downscaled by means of the regional climate model under 4 emission scenarios simulated by 2 general circulation models (fifth‐generation of the ECHAM general circulation model and the third‐generation atmospheric general circulation model). The downscaled future projections were bias corrected before projecting snowfall and snowmelt processes over Shasta Dam watershed during 2010–2099. This studys results agree with those of previous studies that projected snow water equivalent is decreasing by 50–80% whereas the fraction of precipitation falling as snowfall is decreasing by 15% to 20%. The obtained projection results show that future snow water content will change in both time and space. Furthermore, the results confirm that physical data such as topography, land cover, and atmospheric–hydrologic data are instrumental in the studies on the impact of climate change on the water resources of a region.

Analysis of future climate change impacts on snow distribution over mountainous watersheds in Northern California by means of a physically-based snow distribution model

The impacts of climate change on snow distribution through the 21st century were investigated over three mountainous watersheds in Northern California by means of a physically-based snow distribution model. The future climate conditions during a 90-year future period from water year 2010 to 2100 were obtained from 13 future climate projection realizations from two GCMs (ECHAM5 and CCSM3) based on four SRES scenarios (A1B, A1FI, A2, and B1). The 13 future climate projection realizations were dynamically downscaled at 9 km resolution by a regional climate model. Using the downscaled variables based on the 13 future climate projection realizations, snow distribution over the Feather, Yuba, and American River watersheds (FRW, YRW, and ARW) was projected by means of the physically-based snow model. FRW and YRW watersheds cover the main source areas of the California State Water Project (SWP), and ARW is one of the key watersheds in the California Central Valley Project (CVP). SWP and CVP are of great importance as they provide and regulate much of the Californias water for drinking, irrigation, flood control, environmental, and hydro-power generation purposes. Ensemble average snow distribution over the study watersheds was calculated over the 13 realizations and for each scenario, revealing differences among the scenarios. While the snow reduction through the 21st century was similar between A1B and A2, the snow reduction was milder for B1, and more severe for A1FI. A significant downward trend was detected in the snowpack over nearly the entire watershed areas for all the ensemble average results.

Scaling and Self-Similarity of One-dimensional Suspended Sediment Transport Equations

The governing physical process of sediment transport can be represented in a scale model without the simplifying assumptions required in numerical modeling, making scale modeling a considerable complement to numerical simulations. However, the current methods utilized in scaling sediment transport in unsteady openchannel flow result in a number of model and scale effects, which decrease the accuracy and applicability of scale models. These model and scale effects may be reduced, and model applicability may be increased, by determining the conditions under which the governing equation for non-equilibrium sediment transport in unsteady flows are self-similar and require no scaling of sediment diameter and density. Conditions for self-similarity and unscaled sediment properties, for nonequilibrium sediment transport could be identified by applying the one-parameter Lie group of point scaling transformations. When coupled with one-parameter Lie group scaling of the Saint Venant equations for unsteady open channel flow, the scale effects of physical models could be reduced further. This article describes briefly the methodology of Lie-group scaling transformations and leaves the derivation of the self-similarity conditions of one-dimensional suspended sediment transport equations to later studies.

Hydraulic and Sediment Transport Modeling for Cache Creek Settling Basin, Woodland California

The Cache Creek Settling Basin is located two miles east of Woodland, California and was constructed to preserve the floodway capacity of the Yolo Bypass by entrapping sediment. Cache Creek is the main source of mercury entering the San Francisco Bay-Delta. Entrapping sediment helps to entrap mercury thus acting to protect the aquatic life of the San Francisco Bay-Delta. A 2-dimensional hydraulic and sediment transport model is under development. The model modules for sediment transport and hydrodynamic modeling will be coupled under historical flow conditions. Preliminary results are presented herein.