The water balance equation is one of the most fundamental concepts in hydrology. How much precipitation a river basin receives, and where that water goes, defines what flora, fauna, and industry the basin can support. Models for solving this equation originally relied only on precipitation, air temperature, and day length, but have adapted as new data becomes available. Recent advances in technology, especially remote sensing and web services, make it cheaper and easier than ever to obtain hydrological data, including many variables that were previously impossible to measure. This thesis will examine the water balance of the San Marcos River Basin and demonstrate how remote sensing and web services can improve our understanding of the basin's hydrology. It was found that 72% of precipitation in the San Marcos Basin is lost to evapotranspiration. This percentage varies from year to year as a function of precipitation, but the annual volume of evapotranspiration stays almost constant. It was only during the second consecutive year of drought that there was an appreciable change in evapotranspiration. This suggests that annual evapotranspiration can be thought of as a property inherent to a watershed's hydrology, and so long as there is enough stored water in the soil, that demand will be met. The water left over after ET takes its share can either flow out of the basin through a river channel or stay within the basin as storage. After examining methods for partitioning the available water between outflow and storage, it was found that lumped water balance models cannot be used in the San Marcos River Basin because of its complex interactions with the Edwards Aquifer. In order to better model soil moisture dynamics and groundwater infiltration, a distributed model will have to be developed that accounts for flow in and out of the aquifer. / text

Meteorological and environmental (i.e. soil water content) data measured from semiarid watersheds (Lucky Hills and Kendall) during the summer rainy and winter periods were used to study the interrelationships between variables, and to evaluate the effects of variables on the daily estimation of actual evapotranspiration (AET). The relationship between AET and potential evapotranspiration (PET) as a function of an environmental factor was the major consideration of this research. The relationship between AET and PET as a function of soil water content as suggested by Thornthwaite-Mather, Morton and Priestley-Taylor was studied to determine its applicability to the study area. Furthermore, multiple linear regression (MLR) analysis was employed to evaluate the order of importance of the meteorological and soil water factors involved. Finally, the information gained was used for MLR model development. The results of MLR analysis showed that the combined effects of available energy, soil water content and wind speed were responsible for 77 % of the observed variations in AET at Lucky Hills watershed and 70 % at Kendall watershed during the summer rainy period. The analyses also indicated that the combined effects of available energy, vapor pressure deficit and wind speed were responsible for 70 % of the observed variations in AET at Lucky Hills watershed and 72 % at Kendall watershed during the winter period. However, the test results of three different approaches, using the relationships between AET and PET as a function of soil water content indicated some inadequacy. The low correlation between PET, AET, and soil moisture conditions raised some doubt concerning the validity of methods developed elsewhere, and indicated the effects of energy availability on the relationship between PET, AET, and soil water content regardless of the soil water condition. In contrast, agreement between observed AET and estimated AET from MLR models during the summer rainy and winter periods at both watersheds indicated that MLR models can give reasonable estimates of AET, at least under the climatic conditions in which the formulae were developed.

Bank storage is defined as a volume of water that periodically infiltrates a river's banks during increases in stream stage. It is a potentially critical variable for accurately modeling the water budget in semi-arid riparian systems, but is particularly difficult to assess and quantify. It is especially essential for understanding ground-water/surface-water interactions. In collaboration with other projects, a field-scale vadose monitoring effort took place in the San Pedro Riparian National Conservation Area (SPRNCA), Arizona. The San Pedro River flows north from Mexico into the United States, and SPRNCA is a 60 km stretch of U.S.-protected ecosystem north of the border. In addition to a progressive climate of ecological conservation, hydrological research that leads to an improved understanding of the water budget will ultimately improve the prospects for improved water policy decisions. Soil moisture, stream stage, and soil tension data were collected for over 8 consecutive months in both 1997 and 1998, and the data were used as input into a software program called HYDRUS-2D (§imiinek et al. 1996), which models two-dimensional, variably saturated flow. Field-collected data and subsequent modeling efforts suggest that the effects of bank storage were estimated to contribute approximately 8.5% of the river's total flow for 147 days in 1997. Accordingly, bank storage and its effects should be considered in future water-balance simulations of stream-aquifer interaction, and of the San Pedro River in particular. In addition, model estimates of root water uptake match favorably with other estimates of evapotranspiration in the cottonwood-willow forest gallery of the SPRNCA.

Project Report / September 1981

The boreal forest forms a band that stretches across the continents of the northern hemisphere. Wildfire disturbances have helped transform this forest into stands of varying ages with varying soil drainage. It is well known that the boreal forest contributes greatly to the global water cycle, but less is known as to how variable these water fluxes are throughout the forest mosaic. Throughout the growing seasons of 2006 and 2007, meteorological measurements were taken during the growing season from three different aged black spruce stands near Thompson, MB. The stands that were burned in 1930 and 1964 each included upland and lowland sites with independent measurements. The stand burned in 1850 had measurements taken only from an upland site. Evapotranspiration (ET) was calculated from the residual energy after net radiation (Rn), sensible heat flux (H) and ground heat flux were measured. We sought to investigate whether ET varied with stand age and topographic location. Results indicate that there is a significant increase in Rn, H, and ET as forests age. ET levels range from being 4% to 19% lower for younger stands. It is assumed that the depth of the organic layer at older sites allows for mosses to more effectively wick up available moisture through capillary rise, and have higher transpiration levels. The larger tree density at the 1964 sites compared to the 1930 sites may account for a portion of the observed increase in ET for these ages. Differences in drainage between the 1930 and 1850 sites may also account for a portion of the increase in ET observed between these two ages. Wetland sites had H and ET that were significantly less than for the upland sites. ET rates were 11 to 20% higher at the upland sites than the wetland sites; part of this difference is thought to be due to the presence of larger trees, with an increased capacity to transpire water at upland sites. As the number of forest fires has been predicted to increase substantially in the future, the prospect of the boreal forest average stand age being younger would affect the boreal’s water and energy budgets. Our data helps to describe water and energy budgets for forest stands with different drainage capabilities, for stands between the ages of 45 and 160 years. This knowledge will be used to help predict the degree and speed of climate change that will be experienced in the boreal forest.

The boreal forest forms a band that stretches across the continents of the northern hemisphere. Wildfire disturbances have helped transform this forest into stands of varying ages with varying soil drainage. It is well known that the boreal forest contributes greatly to the global water cycle, but less is known as to how variable these water fluxes are throughout the forest mosaic. Throughout the growing seasons of 2006 and 2007, meteorological measurements were taken during the growing season from three different aged black spruce stands near Thompson, MB. The stands that were burned in 1930 and 1964 each included upland and lowland sites with independent measurements. The stand burned in 1850 had measurements taken only from an upland site. Evapotranspiration (ET) was calculated from the residual energy after net radiation (Rn), sensible heat flux (H) and ground heat flux were measured. We sought to investigate whether ET varied with stand age and topographic location. Results indicate that there is a significant increase in Rn, H, and ET as forests age. ET levels range from being 4% to 19% lower for younger stands. It is assumed that the depth of the organic layer at older sites allows for mosses to more effectively wick up available moisture through capillary rise, and have higher transpiration levels. The larger tree density at the 1964 sites compared to the 1930 sites may account for a portion of the observed increase in ET for these ages. Differences in drainage between the 1930 and 1850 sites may also account for a portion of the increase in ET observed between these two ages. Wetland sites had H and ET that were significantly less than for the upland sites. ET rates were 11 to 20% higher at the upland sites than the wetland sites; part of this difference is thought to be due to the presence of larger trees, with an increased capacity to transpire water at upland sites. As the number of forest fires has been predicted to increase substantially in the future, the prospect of the boreal forest average stand age being younger would affect the boreal’s water and energy budgets. Our data helps to describe water and energy budgets for forest stands with different drainage capabilities, for stands between the ages of 45 and 160 years. This knowledge will be used to help predict the degree and speed of climate change that will be experienced in the boreal forest.

The measurement of water in soil on a potential, gravimetric or volumetric basis is considered, with studies concentrating on the measurement of water by dielectric and neutron moderation methods. The ability of the time-domain reflectometry technique to measure water content simultaneously at different spatial locations is an important advantage of the technique. The reported apparent dielectric by the TRASE� time-domain reflectometer and Pyelab time-domain reflectometry systems is sensitive to change in extension cable length. In some soil, e.g. a commercial sand, the response to increasing extension length of extension cable is linear. For other soil a linear response occurs for certain lengths of cable at different moisture contents. A single model accounting for clay content, extension cable length, time-domain reflectometry system, probe type and inherent moisture conditions explained 62.2 % of variation from the control (0 m extension) cable. The extension cable causes a decrease in the returning electromagnetic-wave energy; leading to a decline in the slope used in automatic end-point determination. Calibration for each probe installation when the soil is saturated, and at small water contents is recommended. The ability of time-domain reflectometry, frequency-domain and neutron moderation techniques in measuring soil water content in a Brown Chromosol is examined. An in situ calibration, across a limited range of water contents, for the neutron moderation method is more sensitive to changing soil water content than the factory supplied 'universal' calibration. Comparison of the EnviroSCAN� frequency-domain system and the NMM count ratio indicates the frequency-domain technique is more sensitive to change in soil water conditions. The EnviroSCAN� system is well suited to continuous profile-based measurement of soil water content. Results with the time-domain reflectometry technique were disappointing, indicating the limited applicability of time-domain reflectometry in profile based soil water content measurement in heavy-textured soil, or soil with a large electrical conductivity. The method of auguring to a known depth and placement of the time-domain reflectometry probe into undisturbed soil is not recommended. A time-domain reflectometry system is adapted for in situ measurement of water in an iron ore stockpile. The laboratory calibration for water content of the processed iron ore compares favourably to a field calibration. In the field study, the 28 m extension cable used to connect the probes to the time-domain reflectometry affected the end-point determination of the time-domain reflectometry system. To account for this, 0.197 should be subtracted from the reported apparent dielectric before calculation of volumetric moisture content.

Thesis (M.S. - Hydrology and Water Resources) - University of Arizona. / Includes bibliographical references (leaves 116-119).

Thesis (M.S.)--Ohio University, June, 2008. / Title from PDF t.p. Includes bibliographical references.

Orientador: José Eduardo Pitelli Turco / Banca: Renato Farias do Valle Junior / Banca: José Carlos Sartori / Banca: Luiz Carlos Pavani / Banca: Adhemar Pitelli Milani / Resumo: A evapotranspiração de referência (ETo) é mais frequentemente obtida em diferentes situações e locais por meio de métodos de estimativa. A não verificação do erro da ETo, devido ao uso de instrumentos de medidas, pode conduzir os trabalhos de pesquisa a resultados não confiáveis e inconsistentes. Utilizando os Métodos de Hargreaves; Radiação Solar e Penman-Monteith, com os erros da ETo fixados em 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% e 10%, determinou-se as acurácias dos instrumentos de medidas necessárias para obter a estimativa da ETo, com os erros citados. Os dados foram coletados em uma Estação Meteorológica Automatizada, modelo Vaisala, da Usina Hidroelétrica de Nova Ponte, de propriedade da CEMIG, localizada no Rio Araguari. Estes valores foram registrados por meio da média diária de cada informação. A obtenção da ETo com erros propostos neste trabalho requer instrumentos de medidas com acurácias para os Métodos: de Hargreaves com temperatura do ar de 0,2645% a 2,6335% e radiação líquida de 0,0331% a 0,3315%; de radiação solar com temperatura do ar de 0,15% a 1,47%, velocidade do vento de 0,01% a 0,04%, umidade relativa do ar de 0,14% a 0,1,43% e radiação líquida de 0,02% a 0,23% e o de Penman-Monteith com Temperatura do ar de 0,33% a 3,2%, Velocidade do vento de 0,10% a 1,00%, de Umidade Relativa do ar de 0,06% a 0,58% e de Radiação Líquida entre 0,02% a 0,17%. As acurácias obtidas permitirão selecionar instrumentos de medidas para determinação da ETo, pelos métodos de Penman-Monteith, Hargreaves e Radiação Solar com erros máximos pré-estabelecidos. O método da Radiação Solar apresentou uma maior acurácia dos equipamentos meteorológicos utilizados em relação aos métodos PM (FAO 56) e Hargreaves / Abstract: The reference evapotranspiration (ETo) is most often obtained in different situations and locations through estimation methods. The failure to find the error of ETo, due to the use of measuring instruments, can conduct research work to unreliable and inconsistent results. Using Hargreaves, Solar Radiation and Penman-Monteith methods, with ETo errors fixed in 1%, 2%, 3%, 4% ,5%, 6%, 7%, 8%, 9% and 10%, determined the accuracy of the instruments necessary to acquire the estimated ETo with the errors cited. The data were obtained in an Automated Weather Station, Vaisala model, of Nova Ponte Hydroelectric Plant, owned by Cemig, located in Araguari River. These values were recorded by the daily-average of each information. The attainment of ETo with errors proposed in this work requires measurement instruments with accuracies for the methods: Hargreaves with air temperature  0.2645% to  2.6335% and Net Radiation  0.0331% to  0, 3315% of solar radiation in air temperature  0.15% to 1.47%, wind speed  0.01% to 0.04%, Relative Humidity  0.14% of the  0,1,43% and Net Radiation  0.02% to  0.23% and the Penman-Monteith with air temperature  0.33% to 3.2%, wind speed  0 ,  10% to 1.00% RH air  0.06% to 0.58% and net radiation between  0.02% to 0.17%. The accuracy obtained will allow the selection of measurement instruments to determine the ETo by the Penman-Monteith, Hargreaves and Solar Radiation methods with pre-established maximum errors. The solar radiation method showned a greater accuracy of meteorological equipment used in the methods PM (FAO 56) and Hargreaves / Doutor