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<p> At the rate the population is growing it is important to find ways to be more efficient with the energy and water we use. The increase in population increases the need for electricity and water, but the way we are using our sources will not leave us with enough for future generations. The constant use of &ldquo;dirty energy&rdquo;, energy that emits CO2 and other chemicals into the atmosphere, will continue to harm our environment. A new system is needed to help preserve water and produce green energy that will not harm the only earth we have.</p>

<p> The traditional paradigm of baseflow generation assumes a uniform water table contributes baseflow evenly across a watershed. This thesis considers an alternate paradigm in which baseflow originates from a mix of localized sources that drain at different rates. Four forested headwater catchments across the United States were examined for spatial variability in baseflow sources by analyzing fractional baseflow contribution from each subcatchment relative to the catchment outlet. This revealed that subcatchment flow contributions changed dynamically through time, supporting the idea of different drainage rates in different places. A parallel linear reservoir model, which is predicated on heterogeneity in flow sources and not groundwater hydraulics, was used to simulate results consistent with observations in some of the study catchments. These results support the idea that in some locations baseflow recession may be better explained by landscape spatial heterogeneity than by aquifer hydraulics. </p>

<p> Groundwater plays an important role in runoff generation in the humid tropics, both as subsurface stormflow during rain events and sustaining baseflow during dry periods. Yet groundwater fluxes in tropical areas, particularly groundwater/surface-water (GW-SW) interactions, are not very well characterized at regional scales, thus preventing us from estimating how climate change and anthropogenic activities will affect future groundwater availability. In the case of Panama, abundance of water resources has caused its misuse and thus groundwater is exploited without previous knowledge of its distribution and availability. However, regions of the country such as the Central Pacific Region suffer from water scarcity during periods of extended drought, when streamflow reduces significantly and shallow wells get dry. Understanding groundwater dynamics, especially GW-SW interactions, is crucial for government authorities to make informed decisions in order to secure water availability for current and future generations. This thesis presents advances on the characterization of the La Villa groundwater basin, located in the Central Pacific Region of Panama. By building a groundwater conceptual and numerical model, and a surface water model, potential recharge areas and groundwater flow patterns were identified. Also, the model reveals that groundwater feeds the rivers, not only during dry periods, but throughout the year. Although this preliminary model is not yet capable of predicting the total amount of groundwater stored, and neither can be used to inform management decision, it can inform us of which features have the greatest influence on groundwater flow and it can tell us what types of data are necessary to improve the results of the simulation. The development of these models is the first step towards the development of an integrated hydrologic simulation that can be used to test different climate change and/or management scenarios.</p><p>

<p> Streamflow information is essential for many important uses across a broad range of scales, including global water balances, engineering design, flood forecasting, reservoir operations, navigation, water supply, recreation, and environmental management. </p><p> Natural streams are characterized by changes in cross-section geometry, slope, and geophysical properties (bed-roughness, channel slope, etc.) along their reaches. Variations in the shape and size of the channel bed geometry result from several interacting features of the river system including the effect of different flow regimes, slope, sediment load, etc. Simplifying the river bed geometries could reduce the burden of assembling the required data, so implementing less detailed routing procedures could lower the computational burden. &ldquo;At-a-station&rdquo; hydraulic geometry (AHG) relationships are power-law functions which relate river discharge to key the hydraulics (i.e., velocity, depth, width, and flow area). The AHG relations have been introduced and discussed among researchers, engineers, and geomorphologist since the '50s based upon a limited number of observations made over few flow monitoring stations across the United States. </p><p> This doctoral thesis starts with an introduction to statistical data filtering procedures that are being trained and tested over both synthetic and realistic data followed by being applied over ~4000 U.S. Geological Survey&rsquo;s river monitoring stations to compute AHG parameters based upon robust discharge-hydraulic measures. Given &ldquo;refined&rdquo; dataset, estimated AHG parameters are combined with morphological (channel pattern, channel slope, etc.) and geophysical features at a site. Doing so, potential interrelation among independent and dependent variables will be highlighted. Accordingly, given some assumptions, it is verified how well channel morphology and hydraulic components are intertwined and combined with AHG parameters and how categorizing river monitoring stations according to these characteristics will be practical and useful for further studies. For instance, the application of AHG parameters in modifying numerical hydraulic routing coefficients will result in an improvement in predictability of flood routing schemes (here, Muskingum-Cunge). The thesis will be concluded by the analysis of trade-off between computation time and accuracy or complexity vs. simplicity among advanced, hydrodynamic (HEC-RAS 2D) vs. low-complexity (AutoRoute and HAND) models that is also an alternative way to affirm the advantage of idealizing or simplifying a hydraulic system over-relying on time- and energy-costly approaches.</p><p>

In recent years, physically-based hydrological models provided a robust approach to better understand the cause-effect relationships of effective hydraulic properties in soil hydrology. These have increased the flexibility of studying the behavior of a soil system under various environmental conditions. One disadvantage of physical models is their inability to model the vertical and horizontal heterogeneity of hydraulic properties in a soil system at the regional scale. In order to overcome this limitation, inverse modeling may be used. Near surface soil moisture, which has been collected routinely by remote sensing (RS) platforms, and evapotranspiration, that is also a pivotal key for water balance near the land surface can be used as alternatives for quantifying the effective soil hydraulic parameters through inverse modeling. However, the new approach suffers from not only the scale discrepancy between RS pixel resolution and model grid resolution, but also its application in complex terrains. Furthermore, hydrological models require a number of required input parameters. Hence, this dissertation focuses on developing a methodology for addressing these problems. The field-scale Soil-Water-Atmosphere-Plant model (SWAP) was extended to regional application, and then coupled with a Genetic Algorithm (GA), to operate as the core of the developed decision support system at the regional level. Also, various stochastic processes were developed and applied to the GA for improving the searching ability of optimization algorithms. The computational simulation-optimization approach was tested and evaluated under various synthetic and field validation experiments demonstrating that the methodology provided satisfactory results. In this dissertation, the proposed methodologies analyzed the spatio-temporal root zone soil moisture with RS and in-situ soil moisture data at the multiple scales. Also, these approaches could provide better input parameters for hydro-climatic models, resulting in better understanding of the hydrologic cycle. Thus, a better understanding of water cycle would help us to be better prepared for efficient water resources management, agriculture, and devastating natural disasters in the real world.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 140-144). Available also in a digital version from Dissertation Abstracts.

Water resources information in Albania is very scarce. The country does not have a consolidated monitoring network to collect hydrological and other related data and the quantity and quality of the carried out measurements carried out is limited. The water institutions are very fragmented and the monitored and collected data are being stored in different databases, and non-standardized formats, making it hard for the data to be easily retrieved and exchanged. This thesis explores the available water resources and related data that there is in Albania, and also in the European and Global level. The thesis provides some recommendations as to a way of establishing a water resources geodatabase for Albania focusing on some relevant guidelines from the European Commission and the World Meteorological Organization. In the second part of the thesis, a mean annual precipitation map is compiled as a demonstration of one of the uses of a geodatabase. / text

<p> Almond water use was investigated at the leaf, plant and canopy level under a range of irrigation conditions in commercial orchards in California. Understanding plant response to water stress, specifically the behavior of plant transpiration and water use during periods of water stress, has important implications for irrigation scheduling in agriculture but also for water resources management and policy making. </p><p> Leaf gas exchange measurements of stomatal conductance and photosynthetic rate were performed at midday on shaded and on sunlit leaves, with midday stem water potential used to assess plant water stress. An essentially linear decline in both photosynthetic rate (from 25 to 5 &mu;mol m^-2 s^-1) and stomatal conductance (from 400 to 50 mmol m^-2 s^-1) as stem water potential declined over the range of -0.5 to -3 MPa was observed in sunlit leaves. These data indicated a strong sensitivity of leaf-level physiological processes to water stress. However, evapotranspiration at the canopy level, measured using Eddy Covariance, did not show a reduction relative to atmospheric demand during periods of water stress. The apparent disconnect observed between leaf conductance, responsive to water stress and canopy evapotranspiration, insensitive to water stress, is the central problem investigated in this study.</p><p> When the transpiration data was analyzed in the framework of a "Big Leaf" model, decoupled conditions (i.e. a limited stomatal control of transpiration) were shown to prevail at the experimental site, contrary to previous findings reported in the literature for tall crops such as almond orchards. Low coupling implies only a moderate sensitivity of transpiration to stomatal closure. Measured coupling increased substantially with wind speed but showed a wide range of values at the low wind speeds (&lt;1m s^-1) that were observed at the site. At any wind speed however, higher canopy resistance resulted in higher coupling. The high leaf area index observed in the orchard may have been responsible for causing decoupled conditions, because when leaf area decreased as a result of harvesting operations, canopy transpiration appeared to become more sensitive to water stress. </p><p> Cumulative daily sap velocity was used as an estimate of plant transpiration. At the plant level, contrasting behaviors were observed in plant transpiration in the presence of water stress, depending on the duration and intensity of the stress. During long soil dry-down periods encompassing several weeks, plant transpiration relative to the evaporative demand of the atmosphere showed a statistically significant decline associated with a decrease in stem water potential and in stomatal closure. However, when the cycle of water stress was short (days), reductions in stem water potential seemed to be associated with an increase in cumulative sapflow velocity. The analysis of these results led to the development of a simple model that describes the theoretical interactions between three dependent variables, namely stem water potential, stomatal conductance and transpiration. The model output suggested that in wet soil, an increase in transpiration may be caused by increasing evaporative demand even if stem water potential and stomatal conductance decrease.</p>

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