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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Sensitivity of water and sediment yield to parameter values and their spatial aggregation using SWAT watershed simulation model

Jasso-Ibarra, Rodolfo, 1959- January 1998 (has links)
The USDA-ARS and SARH-INIFAP conduct a binational project entitled "Developing New Conservation Management Systems" which objective is to provide agricultural production strategies that preserve natural resources and the environment. Watershed simulation models play an important role in this project because watershed response can be predicted as a function of management decisions in different scenarios. Current modeling technology requires development of large databases to parameterize watershed simulation models. Simplification of this process will contribute significantly in accomplishing the general objective on both sides of the border. The SWAT model--Soil and Water Assessment Tool--was selected for this project since it allows for long term spatially distributed watershed response simulation. Available records on daily rainfall, surface runoff, and soil erosion from subwatersheds at the Walnut Gulch Experimental Watershed were used to study the effect of parameter value variation and its spatial aggregation on model output accuracy. The methodology included the integration of input databases with information from previous studies and field surveys. Statistical analysis of measured data included the double mass technique, model calibration, sensitivity analysis both the univariate and the multivariate approaches. The effect of aggregating spatially input data on model output accuracy was evaluated to determine the size of subwatershed for which databases must be developed in semiarid environments using the SWAT model. Results of this research showed that Curve Number is the most influencing parameter for both water and sediment yield. Other parameters that were important include hillslope steepness and those related to channel dimensions and hydraulic properties of channel alluvium. Regarding their spatial aggregation, it was observed that model accuracy is proportional to the number of subwatersheds in a nonlinear manner. Non significant increase in model accuracy was observed when watershed discretization yields mean subwatershed size lower than 1.2 square kilometers. This value is consistent with other studies and it represents the level of spatial aggregation of the input data for which model accuracy reaches its maximum.
2

The use of multispectral video remote sensing to monitor suspended sediment concentrations.

Lee, Christopher Tom. January 1990 (has links)
Detailed knowledge of suspended sediment concentration and sediment transport rates is one of the most important and, most elusive goals of data collection for studies involving stream channel morphology and water quality monitoring. Reliable, continuous data on the suspended sediment load of streams are virtually nonexistent. Although it is relatively easy to obtain information on the water discharge through an open channel, it is far more difficult to sample the sediment load of a stream. Suspended sediment concentration is highly variable with time, cumbersome and costly to sample even for short duration periods, and largely independent of other stream flow characteristics such as discharge. This study explored the potential of using ground-based multispectral video remote sensing to monitor suspended sediment concentrations. Data were collected during seven sampling episodes at two test sites in northern Arizona. Two different video systems were employed. The Xybion system recorded reflectance data in four bandwidths for three dates while the Bi-spectral system recorded data in two spectral bands for the remaining four episodes. Video imagery was acquired simultaneously with water samples containing suspended sediment. Digital numbers (DNs) for the two and four band imagery were extracted from 5 by 5 pixel arrays and the average value computed. Water samples were analyzed to determine sediment concentration. Relationships between DNs and reflectance were explored through the use of simple and multiple linear and non-linear regression. Models were generated for the best single and multiple band combinations for both the single date and multidate data sets. Correlation coefficients for the models were comparable or superior to similar models generated from orbital and airborne data. The results of the study indicate that the ground-based technique has great promise for providing suspended sediment data of high spatial and temporal resolution to supplement existing measurement techniques. Recommendations for future work to help improve the basic technique are included.
3

Use of inverse methods for estimating unsaturated flow parameters.

Toorman, Alexander Frederik. January 1990 (has links)
Transient laboratory experiments are evaluated for their use in inverse methods to estimate soil-water parameters for unsaturated flow. The experiments are upward infiltration, One-Step outflow, stepwise inflow and evaporation. The experiments are simulated numerically for three inch standard size cores. A theoretical sandy and a clayey soil are used and are described by the closed-form van Genuchten soil-water relations. During each numerical experiment, for each soil, measurements of different auxiliary variables are simulated. These auxiliary variables are the inflow or outflow at the boundary, and the water content and matric potential within the soil core at three different locations. For each auxiliary variable the sensitivity to estimate the parameters α, n and the saturated hydraulic conductivity is studied by plotting the objective function surface in the parameter planes defined by these parameters. The objective function is calculated for 900 points in each parameter plane and describes the error between the measured and generated auxiliary variable. The shape of these surfaces indicates how well an inverse procedure can find a unique and accurate solution. From these surfaces auxiliary variables, or combinations thereof, are selected which provide sensitive parameter estimates. The surfaces indicate that the contours are nonconvex and that confidence regions for parameters are not symmetric. The hydraulic conductivity is the least sensitive parameter to estimate. For a wetting experiment the parameter sensitivity will increase when the measurement of the auxiliary variable is taken further away from the inflow boundary. To obtain sensitive parameter estimates the auxiliary variable used in the inverse procedure needs to be least similar to the known and changed boundary variable. The shape of the objective function surface for the degenerate case, where an auxiliary variable would be measured at the changed boundary, can provide prior information regarding the sensitivity of estimating parameters from an auxiliary variable and regarding the start values of the parameters for the parameter search. The difference in parameter sensitivity between the sandy and clayey soil is small.
4

The Salt River Project of Arizona: its organization and integration with the community.

Smith, Courtland L. January 1968 (has links)
The Salt River Project is a large Southwestern water and power project created under the National Irrigation Act of 1902, This is a study of the adaptation of the Salt River Project to rapid urbanization. The population within the Salt River Reservoir District, which includes most of Phoenix, Arizona and eight other municipalities, has increased from 175,000 in 1940 to over 800,000 in 1967. This report discusses the laws and conventions embodied in the reclamation principle, which provides for the allocation of power revenues to reduce the cost of water to landowners. The magnithde of this transfer has been increasing with increased numbers of electric customers, increased electric customer usage and improved operating efficiency of the power system. For the water system the revenues from the power system have been adequate to make up for the increased cost of producing surface and ground water so that the water charges to water users have not followed the postwar price spiral, but have decreased. The changes which have occurred in the transfer of water from farm to urban uses are enumerated. This transfer has meant less use of Project water per acre and a lesser percentage of total potential water users using irrigation water in the urban situation, However, farm water use per acre has been increasing arid the net effect has been no change in the total Project water requirement. The Project has tended to accept the requirements of water users while adjusting its technical, economic, legal and social ability in order to continue the distribution of an adequate supply of low cost water, With the impact of increased numbers of urban residents since World War II, the Project has developed programs to educate and inform the urban public about its activities and objectives. The Project is faced with the decision as to what role the urban public is to take in the decision making process. A linked set of hypotheses has been developed to explain the Projects adaptation to urbanization. These hypotheses relate the variables distribution, need and position; advantage and technical, economic, legal and social ability; the change in position with increased numbers of participants in a social organization and homogeneity, personalization, disorganization, secularization and individualization. These hypotheses have been derived from Lenskits Power and Privilege, Weberts The Theory of Social and Economic Organization and "Class, Status and Party" in From Max Weber: Essays in Sociology, Wirth's "Urbanism as a Way of Life" and Redfield's The Folk Culture of Yucatan. From this linked set of hypotheses the effect of different degrees of disorganization, secularization and inclividualization can be assessed in relation to the change in the distribution of water with respect to position and the change in position in a social orgaiization with increased numbers of participants. The methods for the study derive from the suggestions of Redfield in The Little Community and the systems concept. A social system is delineated by components which are statuses, aggregates or groups, and their relation to one another. The effects of elements external to the system being analyzed must be recognized and the functioning to the system indicated. The data to describe a social system are: the technological, demographic and ecological situation; the relation between and within organizations; the relations of organizations to individuals, and individuals to organizations; the ideology; and changes which have occurred through time. These methods and hypotheses do not reveal all which is known about the Salt River Project. However, they are designed to reveal the nature of the Project's adaptation to a rapidly urbanizing cornmunity.
5

Using Airborne Lidar to Differentiate Cottonwood Trees in a Riparian Area and Refine Riparian Water Use Estimates

Faridhosseini, Alireza January 2006 (has links)
Airborne lidar (light detecting and ranging) is a useful tool for probing the structure of forest canopies. Such information is not readily available from other remote sensing methods and is essential for modern forest inventories. In this study, small-footprint lidar data were used to estimate biophysical properties of young, mature, and old cottonwood trees in the Upper San Pedro River Basin, Arizona, USA. The lidar data were acquired in June 2003 and 2004, using Optech's 1233 ALTM (Optech Incorporated, Toronto, Canada). Canopy height, crown diameter, stem diameter at breast height (dbh), canopy cover, and mean intensity of return laser pulses from the canopy surface are estimated for the cottonwood trees from lidar data. The lidar estimates show a good degree of correlation with ground-based measurements. This study also demonstrates that other parameters of young, mature, and old cottonwood trees such as height and canopy cover, when derived from lidar, are significantly different (p < 0.05). These lidar-derived canopy metrics provided the basis for a supervised image classification of cottonwood age categories, using a maximum likelihood algorithm. The results of classification illustrate the potential of airborne lidar data to differentiate age classes of cottonwood trees for riparian areas quickly and quantitatively.In addition, four metrics (tree height, height of median energy, ground return ratio, and canopy return ratio) were derived by synthetically constructing a large footprint lidar waveform from small-footprint lidar data (we summed up a series of Gaussian pulses that vertically stacked at the elevations produced by the small-footprint elevation data to create a modeled large-footprint return waveform and compared the synthetic waveforms with ground-based Intelligent Laser Ranging and Imaging System (ILRIS) scanner images in cottonwood trees). These four metrics were incorporated into a stepwise regression procedure to predict field-derived LAI for different age classes of cottonwoods.Additionally, this study applied the Penman-Monteith model to estimate transpiration of the cottonwood clusters using lidar-derived canopy metrics, such as height and LAI, and compared it with transpiration measured by sap flow, so that improved riparian water use estimates could be made.
6

A Study of Groundwater Transport in the Effluent-Dominated Reach of the Santa Cruz River, Arizona

McAndrew, Rose M. January 2011 (has links)
The Upper Santa Cruz Basin has experienced population growth and industrial development resulting in increased water demand and greater risk of groundwater contamination. Contaminant occurrence and transport in the subsurface were examined in the Upper Santa Cruz Basin by creating conceptual models and using a groundwater flow model coupled with a contaminant transport model to determine the movement of contaminants. Water–quality data from numerous sources were collected and compiled into a database for the area, which was aggregated to identify major contaminants and their distribution. Using this data and a numerical model (MT3DMS, Zheng and Wang, 1999), simulations have been conducted for nitrate to evaluate its movement in the aquifer and to determine if this is an appropriate tool to use in the Santa Cruz Basin. Results show that the model was not able to capture the nitrate movement and that additional sources need to be considered.
7

Accounting for Stream Bank Storage for a Seasonal Groundwater Model

Mallakpour, Iman E. January 2011 (has links)
In recent research on groundwater and surfacewater interaction, attention has focused on the study of water exchanges between the near-stream aquifer and stream. One of the important near stream processes is bank storage. The aim of this thesis is to document the procedure required to develop a bank storage model that can be linked into a MODFLOW groundwater model. For this purpose, a groundwater model and a MATLAB code that can simulate bank storage process was developed. These two models were linked through the well package of MODFLOW. Result indicated that the number of stage rise and shape of stage hydrograph entering to stream system, when they have the same average stream stage, produced similar net flux of water between surface water and groundwater. In addition, the results show that reaches, which were gaining during normal flow of the stream network, can become a losing stream during high flow periods.
8

Combined Impact of Spatial Scale, Land Use, and Climate on Streamflow and Nitrogen: A Comparative Analysis

Al-Lafta, Hadi January 2011 (has links)
Catchments of different spatial scale, land use, and climate are characterized by highly variable N fluxes. In order to understand these controls on nitrogen flux, Total Dissolved Nitrogen (TDN) budgets were quantified and analyzed for fifty seven different catchments around the world. These catchments have a wide range of spatial scales, land uses, and climates. Results demonstrate that each variable in our analysis (i.e. spatial scale, land use, and climate) imposes a specific impact on TDN yield though their impact is not similar. For example, climate is the strongest and most significant driver for TDN yield followed by catchment area and land use. Importantly, based on current study analysis, degree of perturbation of a catchment can be determined on the basis of only a few measurements of discharge and corresponding TDN concentration at a certain point (e.g. outlet of a catchment).
9

Analysis of data from tracer injection experiments at Stanton Artificial Recharge Facility, Stanton, Texas

Broermann, James, 1962- January 1991 (has links)
Concentration breakthrough data collected by the USGS at Stanton, Texas during tracer injection tests of the Ogallala aquifer are simulated using an approximate and an exact analytical solution of conservative solute transport in a radial flow field from an injection well. Data were collected at selected depths in the aquifer and at fully screened observation wells. The concentration breakthrough data were simulated with the analytical solutions by finding the values of hydraulic conductivity and dispersivity which provided the best fit of the data. The exact analytical solution is the appropriate solution for analyzing data collected at the Stanton site. Both dispersivity and hydraulic conductivity vary greatly at the site. Bromide is considered to be conservative. Boron distribution coefficients are determined by using hydraulic conductivities estimated by simulation of boron and bromide breakthrough curves. Additional tracers used in the experiments at the Stanton site include aniline, phenolphthalein and benzoate.
10

A regression model for mineral solubility as a function of ionic strength and temperature

Shaikh, Muhammad Javed, 1955- January 1991 (has links)
An algorithm is developed to predict the solubility of gypsum and anhydrite as a function of ionic strength and temperature. Critically evaluated experimental data were used for fitting of an eight parameter equation using multiple regression analysis. The model was also used to fit the simulated solubility data for anhydrite and gypsum, generated by program PHRQPITZ. The correlation between the observed and fitted values was very high. The errors between experimental model and PHRQPITZ simulation were computed with the variation of temperature and ionic strength. A significant improvement in the errors was noticed by replacing the values of equilibrium constants in PHRQPITZ. Modifications have been made in the FORTRAN code of PHRQPITZ to convert the program for VAX and PC computers. Additional modifications were made in PHRQPITZ to convert the index numbering of elements/species compatible to another geochemical model PHREEQE. (Abstract shortened with permission of author.)

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