Water BudgetThis chapter documents the hydrologic analysis of a watershed within the Windy Ridge mega-landslide of Central Utah to (1) create a water budget and (2) place a quantitative limit on the magnitude of climatic changes documented by Shurtliff et al. (2017) and Hudson et al. (2019). (1) A water budget was calculated over the last four years using instrumentation and weather stations both within and surrounding the watershed, In terms of precipitation input, 85% is released by the evapotranspiration of the Pinyon-Juniper forest, 4% discharges as surface water from the base of the watershed, and 11 % infiltrates the groundwater system. This infiltration rate is slightly lower than the 15% suggested by Maxey-Eakin method (Maxey and Eakin, 1949), likely due to the less permeable, clay-rich sediment. (2) Previous studies performed on Garden Basin Cattail (GBC) Fen at the base of its watershed suggest swings from pond-like to wetland environments (Shurtliff et al, 2017; Hudson et al, 2019). This study estimated precipitation values necessary to create standing water (pond) environments. Changes in annual precipitation, as well as input from North American monsoon (NAM), may cause these environmental changes. Each of these cases were examined. Trends in piezometer measurements compared to mean annual precipitation indicated that ‰¥ 644 mm of annual precipitation are required to sustain a wet (perennial standing water) environment. The change from wetland to pond conditions may depend on seasonal trends in precipitation. This study suggests an increase of 150-300 mm of precipitation in late summer (NAM) may be connected to perennially wet conditions. The higher annual precipitation values, largely accomplished by NAM fluctuations, caused a transition from wetland to pond (Hudson et al., 2019; Shurtliff et al., 2017). Chapter 2: Core AnalysisChapter 2 further documents the watershed's historical environmental and climate record by analyzing sediment and topography surrounding GBC fen, adding to the works of Shurtliff et al. (2019) and Hudson et al. (2019). A core was extracted from GBC fen at the base of the watershed and the sediment analyzed in terms of color, texture, environmental scanning electron microscope (ESEM) imaging, RockEval pyrolysis, and 14C ages. These results were then compared to pre-existing pollen and diatom proxies completed on a previous core by Shurtliff et al. (2019). This study suggests climatic variation, along with basin fill processes, was the driver of environmental change in GBC fen (Garden Basin watershed). Climate proxies show the basic trend from a particularly wet period (12-9 ka BP) of more stagnant or deeper water, to a much dryer period of much shallower water levels (9-3 ka BP), followed by a rebound in moisture levels, especially in the past few hundred years. Although climate was the driver of transitions within GBC2 core, a pollen record of sustained shallow water plants and MASW (Park et al., 1999) survey may suggest beaver activity.

This report deals with rainfall-runoff modeling and small water reservoir projection with usage of modern software equipments (GIS, HEC-HMS), using maximum number of available data sources (BPEJ, LPIS, N-year rainfall gages, 3D contours …). The advantage of this method is that it is possible to predict the shape of hydrograph and flood wave volume as well. Other methods cannot offer judgment of flood wave volume and hydrograph shape as this method does. The most important thing in small water reservoir projection is the flood wave volume value, which is undervalued nowadays using wrong evaluation. This method’s advantage is variability of scenarios depending on soil surface, used agricultures, hydraulic and hydrologic parameters etc.

Indiana University-Purdue University Indianapolis (IUPUI) / This study investigates the hydrological functioning of a riparian zone in central Indiana in a glaciated valley with concave topography (16% slope gradient) and ground water seeps on the valley walls. Unlike sites found in most riparian zone studies with lateral ground water inputs (Clement et al., 2003; Jordan et al., 1993; Blicher-Mathiesen and Hoffman, 1999; Hoffman et al., 2000), the site in this study is connected to thin, permeable upland sediments (≈2 m). The objectives of this research include: 1) understanding the influence of the hydrogeomorphic (HGM) setting on riparian hydrology (including determining the sources of water to the site), 2) determining how the HGM setting influences riparian zone water quality functioning, and 3) comparing the results from this site with conceptual models of riparian zone hydrologic functioning. Water chemistry and hydrometric data were collected over a 16-month period. Three factors influence riparian zone hydrological functioning at the site: 1) the nature of water contributions from upland sources, 2) riparian zone soil texture, and 3) the location of a preWisconsinan till unit. When the uplands are contributing water to the riparian zone a shallow water table is found near the hillslope and ground water flows from the hillslope to the stream. Conversely, when upland contributions cease a large water table drop occurs and ground water flows in a downvalley direction. Fine textured soils near the hillslope result in shallow water tables and small ground water fluxes. Hydrometric data, water chemistry, and statistical analyses suggest water from an intertill layer adjacent to the site is the primary source of water to the site. NO3- concentrations decreased in ground water flow in the riparian zone suggesting the site is removing nutrients. A preWisconsinan glacial till deposit at shallow depths in the riparian zone limits ground water flow to horizontal flow paths. Overall, the hydrologic functioning of the site agrees well with riparian zone conceptual models (Vidon and Hill, 2004a; Vidon and Hill, 2004b; Devito et al., 1996; Hill, 2000; Baker et al., 2001; Burt et al., 2002). The results of this study are important additions towards conceptualizing riparian zone hydrologic functioning.

Prior to using hydraulic and spatially distributed modelling softwares, the theory of the unit hydrograph was a commonly used tool for modelling of surface and runoff water. While distributed models often provide detailed results from extensive calculation durations, the unit hydrograph have been questioned for simplifying the physical characteristics of the watershed modelled. Typically, the unit hydrograph theory does not explicitly take the flow paths of the watershed in consideration during calculation. With the rise of geographical information systems, methods of deriving spatially distributed unit hydrographs have been developed. The aim of these have commonly been to find a spatially varied form of hydrological modelling, while still keeping the computation times low. The method is commonly built by calculating the travel time to the watershed outlet along the flow path. In this study, spatially distributed unit hydrographs are derived separately for the watershed’s pervious and impervious surfaces in a Python script using map algebra and the Esri’s Python wrapper module Arcpy. The travel times are generated from a velocity field calculated using Maidment and Olivera’s velocity equation. The velocity equation contains three unknown parameters; one for an average velocity and two calibration parameters. The excess precipitation is calculated of a 100 year return period Chicago Design Storm hyetograph using the SCS-CN method. The direct runoff hydrographs are calculated over three semi-urban watersheds in Smedby in southern Sweden, and the results are compared to MIKE 21 hydrograph data of each corresponding watershed and rain input. The result obtained showed to replicate the hydrograph response quite well, but only if the unknown parameters in the velocity equation were calibrated to match the MIKE 21 data. The unknown parameters of the velocity equations produces uncertainties of using the method without calibration data, which implies that the script is not well adapted to use for modelling predictions. It may be of interest to calculate the travel times of the locations within the watershed using a different formula. The script tool could be tested using different design storms as input, and areas of different characteristics compared to Smedby could be tested. / Innan det blev vanligt att använda hydrauliska och rumsliga modellerings- mjukvaror användes ofta teorin bakom enhetshydrografen för modellering av avrinning. Medan de rumsliga mjukvarorna ofta erbjuder detaljerade resultat till priset av långa beräkningstider, har enhetshydrografen ifrågasatts för att förenkla den fysiska karaktären av avrinningsområdet. Typiskt sett tar inte enhetshydrografen avrinningsområdets flödesvägar direkt i hänseende vid beräkning. Utveckling och ökad tillgänglighet av geografiska informations- system förenklade möjligheterna att utveckla beräkning av enhetshydrografer som tar hänsyn till avrinningsområdets karaktär, typiskt sett genom att beräkna rinntiden från varje läge i avrinningsområdet, längs rinnvägarna och till utloppet. I den här studien beräknas spatiala enhetshydrografer separat för avrinningsområdets hårdgjorda och icke hårdgjorda ytor, genom att utveckla ett Python skript med hjälp av karalgebra och Esri’s wrapper modul ArcPy. Rinntiderna från olika lägen i avrinningsområdet beräknas med Maidments och Oliveras formel för hastighet, vilken innehåller okända parametrar för en uppskattad medelhastighet samt två kalibreringsparametrar. Effektivt regn från ett Chicago Design Storm regn med en återkomsttid på 100 år beräknas med hjälp av SCS-CN metoden. Hydrograferna för direkt avrinning faltas för tre semi-urbana avrinningsområden i Smedby i södra Sverige för att sedan jämföras mot MIKE 21 genererad hydrograf data för respektive motsvarade avrinningsområde. Hydrografdata producerat av MIKE 21 har tagits fram med lika CDS-regn data som input. Resultatet visar att hydrografer snarlika MIKE 21 hydrograferna kan tas fram med Maidments spatialt fördelade enhetshydrograf, om de okända parametrarna i Maidments formel kalibrerades mot MIKE 21 data. Utan kalibreringsdata för att bestämma de okända parametrarna kan resultatet anses vara mycket osäkert, vilket antyder att Python skriptet ej bör användas för använda metoden för att förutspå responser av regnevent. Andra beräkningar än Maidments ekvation kan vara av intresse att implementera. Olika typer av regninput samt spatial data över andra platser än Smedby kan vara av intresse att testa Python skriptet för.

The hydrograph at the watershed outlet was simulated using the time-area curve concept implemented in a geographic information system (GIS). The goal of this study was to determine if hydrograph prediction accuracy would be improved by accounting for spatial and temporal variation of excess rainfall. Three models with different methods of estimating excess rainfall were developed: the Distributed Curve Number (DCN) model uses a CN for each cell, generating spatially distributed excess rainfall using the Soil Conservation Services curve number method (SCS, 1972); the Uniform Curve Number (UCN) model uses a single "average" CN for the whole watershed, thus generating a uniform excess rainfall; the Phi index model which uses the Phi-index method to generate uniform excess rainfall. With the aid of a GIS, the cumulative flow time to the watershed outlet is estimated for each cell in the watershed and the isochrones of equal travel time are developed. The time-area curve is developed in the form of an S curve. The spatially distributed 1-hr unit hydrograph is derived from the S curve as the difference between the S curve and its value lagged by 1-hr. The models used in this study describe the physical processes and flow mechanisms. They also reflect effects of watershed characteristics (slope, landuse, soil drainage potential) and excess rainfall intensity on the resulting hydrograph at the watershed outlet. Surface flow is divided into channel flow and overland flow based on the upstream drainage area. Flow is routed to the watershed outlet through a channel network derived from the watershed Digital Elevation Model (DEM). The models developed were tested against observed rainfall-runoff data from the 1153-ha Virginia Piedmont watershed (Owl Run). A total of 30 storms were simulated, with statistical comparison of peak flow rate, time to peak flow rate, and the hydrograph shape. The hydrograph shape was compared both visually and statistically. Results indicated that the two models which account for temporal variation in excess rainfall (DCN and UCN) predicted the output hydrograph much more accurately than the Phi model which lacks the ability to capture the temporal variation of excess rainfall. For this watershed, results showed that the spatial variability in excess rainfall which was accounted for by the DCN model did not improve the prediction accuracy over the UCN model which lacks that ability. However, a sensitivity analysis for the effect of the spatial distribution of the excess rainfall indicated that can be a significant effect of spatial distribution on the predicted hydrograph. / Master of Science

Ce travail de thèse porte sur l’étude des mécanismes et des bilans de transfert des pesticides vers les cours d’eau sur deux bassins versants agricoles emboités, de tailles différentes en Gascogne (Sud Ouest de la France) : la Save à Larra (1110 km2).et le Montoussé (3,28 km2) à Auradé. Dans cette région, les pratiques d’une agriculture intensive conduisent à des risques importants pour les ressources en eau, notamment pendant les périodes de crue. C’est pour cela que nous avons porté une attention particulière dans cette étude à ces événements au cours desquels une grande quantité de contaminants sont transportés par les cours d’eau. Quatorze molécules de pesticides (herbicides et fongicides) largement utilisées sur ces bassins versants ont été étudiées grâce à un échantillonnage intensif, notamment en périodes de crue, durant deux années hydrologiques (2007/2008 et 2008/2009). La majorité des molécules étudiées présentent des concentrations qui dépassent les limites autorisées par l’Union Européenne pour l’eau potable (0.1 μg.L-1 pour chaque molécule et 0.5 μg.L-1 pour l’ensemble des molécules), notamment en périodes de crue. L’analyse des hystérésis mises en évidence sur les relations entre les concentrations (pesticides, MES, COD, POC) et les débits du cours d’eau permet de mieux comprendre les mécanismes de transfert des pesticides et de leurs paramètres de contrôle. Ces hystérésis montrent pour un même débit des concentrations différentes en montée et en descente de crue ; elles peuvent être dextres (sens des aiguilles d’une montre) ou senestres (sens inverse) suivant l’origine des molécules et l’écoulement responsable de leur transfert des sols vers les eaux. C’est pourquoi nous avons procédé dans cette étude à une séparation des différentes composantes (ruissellement superficiel, écoulement hypodermique, écoulement de nappe) de l’écoulement fluvial pour mieux comprendre la dynamique de transferts des pesticides et de leurs paramètres de contrôle. On peut ainsi mettre en évidence des relations positives entre MES, COD, COP ou certaines molécules de pesticides et les débits des écoulements de surface (ruissellement superficiel ou écoulement hypodermique suivant les caractéristiques physico-chimiques des molécules). Les calculs de flux des différents pesticides exportés par les cours d’eau montrent que 60 à 90% (suivant les molécules) des transports annuels se font durant les épisodes de crue. Les flux spécifiques (masse exportée par unité de surface) calculés sont plus importants sur le bassin versant de la Save que sur celui du Montoussé et les relations flux spécifiques-débits mettent en évidence des concentrations plus élévées sur la Save où l’utilisation des pesticides est globalement plus importante que sur le Montoussé où les pratiques sont raisonnées. L’analyse des pesticides dans l’eau filtrée et non filtrée nous a permis d’estimer la distribution de chaque molécule entre les phases particulaires et dissoutes (Kd). De plus, les valeurs de flux calculés pour chaque crue nous ont permis d’estimer un Kd moyen pour chaque molécule. Ces valeurs de Kd présentent une très bonne relation avec les valeurs de Kow (coefficient de partage octanol-eau) extraites de la littérature. De même, les pourcentages calculés de chaque pesticide exporté sous forme particulaire sont aussi très bien corrélés au Kow de chaque molécule. / The mechanisms of pesticides transport to stream flow were studied in two agricultural nested catchments of different size in Gascogne region (South West of France): the Save river basin at Larra (1110 km2) and the Montoussé experimental watershed at Auradé (3.28 km2). The intensive agricultural practices used in this region lead to an important risk for water resources by pesticides, especially during storm events. This is why we have paid special attention on storm events when a large quantity of contaminant was transported during hydrological periods. Fourteen molecules of pesticides (herbicides and fungicides) were investigated during the study period. Both of these groups are widely used for agricultural purposed in these catchments. The results achieved over the two years monitoring (2007-2009) enable us to emphasize the principal processes, implied in pesticide transfer on these agricultural catchments. The majority of compounds are detected during storm runoff events. And, the average concentrations of some pesticides are exceeded at the authorization limit of the European Union for pesticide concentrations in drinking water (0.1 µg.L-1 for individual pesticides and 0.5 µg.L-1 for total pesticides). To better understand the mechanisms of pesticide transport hysteresis, patterns on the concentration-discharge relationship (result of different concentration of pesticides in rising and falling limb of storm) were studied. However, clockwise or anticlockwise hysteresis patterns could be observed for some molecules of pesticide and their controlling factors such as dissolved organic carbon (DOC), particulate organic carbon (POC) and total suspended matters (TSM) according to their transfer dynamic in the catchment. We proceeded with hydrograph separation of the main stormflow components (surface runoff, subsurface flow and groundwater) so that the main pesticide routing could be traced for its soil-river transfers. We also came to the conclusion that there is a positive relationship between riverine TSM, DOC and pesticide, concentrations and the discharges of surface or subsurface runoffs according to pesticide properties. Pesticide flux calculation shows between 60 to 90% of the molecule transport takes place during storm periods. Specific flux calculation also demonstrated the higher flux value in Save catchment than in Aurade with higher pesticide concentration for a given specific discharge. The latter result may be due to the more consumption of pesticide in Save catchment. The analyses of pesticides both in filtered and unfiltered water enabled us to estimate the distribution of pesticides into particulate and dissolved phases. Moreover, the pesticide flux values allow calculating average partition coefficients kd between dissolved and particulate fractions which present good relationship with Kow values (octanol-water) extracted from literature. The percentage of each pesticide transported as particulate forms is also well correlated to Kow.

On-going population growth and urbanization increasingly force people to occupy environments where natural processes intensely affect the landscape, by way of potentially hazardous natural events. Tectonic plate boundaries, active volcanic regions and rapidly uplifting mountain ranges are prominent examples of geomorphically hazardous areas which today accommodate some of the world’s largest cities. These areas are often affected by more than one hazard such as volcanic eruptions, earthquakes, landslides, tsunamis, floods, storms and wildfires, which frequently interact with each other increasing the total impact on communities. Despite progress in natural hazards research over the last two decades, the increasing losses from natural disasters highlight the limitations of existing methodologies to effectively mitigate the adverse effects of natural hazards. A major limitation is the lack of effective hazard and risk assessments incorporating hazard interactions and cascade effects. Most commonly, the assessment of risks related to different hazards is carried out through independent analyses, adopting different procedures and time-space resolutions. Such approaches make the comparison of risks from different hazard sources extremely difficult, and the implicit assumption of independence of the risk sources leads to neglect of possible interactions among hazard processes. As a result the full hazard potential is likely to be underestimated and lead to inadequate mitigation measures or land-use planning. Therefore there is a pressing need to improve hazard and risk assessments and mitigation strategies especially in highly dynamic environments affected by multiple hazards. A prominent example of such an environment is the western Southern Alps of New Zealand. The region is located along an actively deforming plate boundary and is subject to high rates of uplift, erosion and orographically-enhanced precipitation that drive a range of interrelated geomorphic processes and consequent hazards. Furthermore, the region is an increasingly popular tourist destination with growing visitor numbers and the prospect for future development, significantly increasing societal vulnerability and the likelihood of serious impacts from potential hazards. Therefore the mountainous landscape of the western Southern Alps is an ideal area for studying the interaction between a range of interrelated geomorphic hazards and human activity. In an effort to address these issues this research has developed an approach for the analysis of geomorphic hazards in highly dynamic environments with particular focus on tectonically-active mountains using the western Southern Alps as a study area. The approach aims to provide a framework comprising the stages required to perform multi-hazard and risk analyses and inform land-use planning. This aim was approached through four main objectives integrating quantitative geomorphology, hazard assessments and GIS. The first objective was to identify the dominant geomorphic processes, their spatial distribution and interrelationships and explore their implications in hazard assessment and modelling. This was achieved through regional geomorphic analysis focusing on catchment morphometry and the structure of the drainage networks. This analysis revealed the strong influence and interactions between frequent landslides / debris-flows, glaciers, orographic precipitation and spatially-variable uplift rates on the landscape evolution of the western Southern Alps, which supports the need for hazard assessment approaches incorporating the interrelationships between different processes and accounting for potential event cascades. The second and third objectives were to assess the regional susceptibility to rainfall-generated shallow landslides and river floods respectively, as these phenomena are most often responsible for extensive damage to property and infrastructure, injury, and loss of lives in mountainous environments. To achieve these objectives a series of GIS-based models was developed, applied and evaluated in the western Southern Alps. Evaluation results based on historical records indicated that the susceptibility assessment of shallow landslides and river floods using the proposed GIS-based models is feasible. The output from the landslide model delineates the regional spatial variation of shallow landslide susceptibility and potential runout zones while the results from the flood modelling illustrate the hydrologic response of major ungauged catchments in the study area and identify flood-prone areas. Both outputs provide critical insights for land-use planning. Finally, a multi-hazard analysis approach was developed by combining the findings from the previous objectives based on the concepts of interaction and emergent properties (cascade effects) inherent in complex systems. The integrated analysis of shallow landslides, river floods and expected ground shaking from a M8 plate-boundary fault (Alpine fault) earthquake revealed the areas with the highest and lowest total susceptibilities. Areas characterized by the highest total susceptibility require to be prioritized in terms of hazard mitigation, and areas with very low total susceptibility may be suitable locations for future development. This doctoral research project contributes to the field of hazard research, and particularly to geomorphic hazard analyses in highly dynamic environments such as tectonically active mountains, aiming to inform land-use planning in the context of sustainable hazard mitigation.

This thesis is focused on the methods of separation of baseflow and comparing of these metods. It is analyzing concentrations of total phosphorus in the total runoff and influence of baseflow to concentrations of phosphorus in total runoff. The studied area is subcatchment P52 in the catchment Kopaninský flow. Subcatchments P52 is small (64,93 hectares), drained agro-forestry catchment in Českomoravská vrchovina (Czech-Moravian highlands), with a large proportion of forest area (64% forest and 31% of arable land). Studied the period is hydrological period 2009 - 2011. To obtain the necessary results are used daily flow, daily concentrations, daily precipitation of rain gauge station Velký Rybník and monthly precipitation from rain gauge stations of the ČHMŮ (Czech Hydrometeorological Institute) in Humpolec. For the separation of the baseflow and comparison of methods were selected five methods: - method of digital filter according to Chapman (1999), - method UKIH designed by Institute of hydrology (1980), - method RDF proposed by LINE AND Hollick (1979), - method FUKIH proposed by AKOSY AT. AL. (2009) and - method of Kille (1970). All methods are simple to perform and not challenging to input data. When comparing methods, the main problem is that, the results obtained by different methods are very different. Another point of this work is to evaluate the concentrations of total phosphorus in the tatal runoff. Here is analyzed series of daily concentrations of total phosphorus and monthly and annual average concentrations. Low and high concentrations are compared with the values ??of precipitation and clinks are searched between these values. The main problem is that, the concentration of phosphorus are not dependent only on precipitation. The last point is solution of influnence of baseflow to the amount of total phosphorus in the runoff. Here is used the procedure which described BYSTŘICKÝ in its work (2012). There are determined values concentrations typical of baseflow, for direct runoff and total runoff. Groups of values ??are mutually tested and compared. The results show that, the baseflow is negligible contributor of phosphorus to the total runoff, but to achieve more accurate results would be needed to analyse a longer time period (eg 10 years) and compare the results with several different river basins.

Submitted by Maike Costa (maiksebas@gmail.com) on 2016-01-05T12:43:51Z No. of bitstreams: 1 arquivototal.pdf: 7469211 bytes, checksum: 99e23a5e3e827ec0fdf765d03f0f8601 (MD5) / Made available in DSpace on 2016-01-05T12:43:51Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 7469211 bytes, checksum: 99e23a5e3e827ec0fdf765d03f0f8601 (MD5) Previous issue date: 2015-03-27 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The assessment of rainfall-runoff transformation mechanisms with high temporal resolution data has proven crucial to the improving of hydrological studies, by providing detailed knowledge and information about the properties and the characteristics of their main variables. This study aimed at assessing the influence of rainfall event definition criteria in determining the characteristics of hyetographs, as well as in investigating the hydrological relations of rainfall events and antecedent soil moisture with those of the runoff hydrograph, by means of statistical techniques, in experimental basins in Northeast Brazil. To this end, a portion of the data was acquired, in sub-hourly scale, from the databases maintained by the partners of the research since 2003 and the other one was monitored and taken along the hydrological year of 2013-2014 through frequent measurements, performing essays and data processing. Then, descriptive statistics, hypothesis testing, exploratory data analysis, multivariate statistical techniques and multiple linear regression were carried out either for visual inspection or for statistical data investigation, in order to establish variation patterns and evaluate the association degree among variables. The first study revealed that the variation in minimum inter-event time criteria has reduced by almost 50% the number of events, and underestimated the average intensity of events by 4 times on average. The second study showed that the tropical coastal basin has approximately 4 times more events than those of semiarid, of which 6% of all events that remain unshaped, contribute to 38% of the total precipitation, and could be reduced by up to 97%, becoming mainly on unimodal events with peak to the left. The third study showed that soil moisture has a similar variation pattern up to 3 days in advance and exerts a significant influence, along with the precipitation and duration of rainfall events on both the runoff coefficient, the peak and the discharge of hydrographs; on the other hand, the principal component responsible for the peak and intensities of hyetographs was significant only on the runoff coefficient, which was, in turn, the best feature set for the multiple linear regression analysis, as it the coefficient of determination was 0.66. Therefore, this study highlights the importance of continuous and systematic hydro-climatological data monitoring for the experimental studies that may provide input to decision-making in water resources management measures. / O entendimento dos mecanismos de transformação chuva-vazão com dados em alta resolução temporal mostra-se fundamental no aperfeiçoamento da maior parte dos estudos hidrológicos, ao provê conhecimento e informação detalhada a respeito das propriedades e características de suas principais variáveis. Este trabalho teve como objetivo avaliar a influência dos critérios de definição de evento chuvoso na determinação das características dos hietogramas, bem como investigar as relações hidrológicas dos eventos chuvosos e da umidade antecedente do solo com aquelas dos hidrogramas de escoamento superficial, por meio de técnicas estatísticas, em bacias experimentais do Nordeste Brasileiro. Para tanto, uma parcela dos dados foi adquirida, em escala sub-horária, dos bancos de dados mantidos pelos parceiros da Rede de Hidrologia do Semiárido (REHISA) desde 2003 e a outra foi monitorada e obtida ao longo do hidrológico 2013-2014, por meio de frequentes medições, realização de ensaios e tratamento de dados. Em seguida, técnicas de estatística descritiva, testes de aderência e de hipóteses, métodos exploratórios de dados, análises estatísticas multivariadas e técnicas de regressão linear múltipla foram utilizadas, quer na inspeção visual, quer na investigação estatística dos dados, a fim de estabelecer padrões de variação e avaliar o grau de associação entre variáveis. O primeiro estudo realizado revelou que a variação do critério de mínimo intervalo de tempo entre eventos fez reduzir em até quase 50% o número de eventos, além de subestimar a intensidade média dos eventos 4 vezes, em média. O segundo estudo mostrou que a bacia hidrográfica tropical costeira apresenta aproximadamente 4 vezes mais eventos do que as do semiárido, dos quais 6% da totalidade dos eventos que permanecem não caracterizados, contribuem para 38% do total precipitado, e puderam ser reduzidos em até 97%, transformando-se, sobretudo, em eventos do tipo unimodal com pico à esquerda. O terceiro estudo mostrou que a umidade do solo apresenta um padrão de variação similar até 3 dias de antecedência e exerce uma influência significante, juntamente com a lâmina precipitada e a duração dos eventos chuvosos, sobre o coeficiente de escoamento, o pico e a vazão do hidrograma; por outro lado, a componente responsável pelo pico e intensidades dos hietogramas foi significante apenas sobre o coeficiente de escoamento, este que, por sua vez, foi a característica melhor ajustada pela análise de regressão múltipla, dado o coeficiente de determinação de 0,66. Portanto, este estudo evidencia a importância do monitoramento contínuo e sistemático de dados hidroclimatológicos para a realização de estudos experimentais que venham a dar subsídios à tomada de decisões em medidas de gerenciamento de recursos hídricos.

This research project concerns changes in hydrology resulting from urbanization of the upper sub-basin of the White Rock Creek Watershed in Collin and Dallas Counties, Texas. The objectives of this study are: to calculate the percent watershed urbanized for the period of 1961 through 1968 and the period of 2000 through 2005; to derive a 1960s average unit hydrograph and a 2000s average unit hydrograph; and, to use the two averaged hydrographs to develop a range of hypothetical storm scenarios to evaluate how the storm response of the watershed has changed between these two periods. Results of this study show that stormflow occurs under lower intensity precipitation in the post-urbanized period and that stormflow peaks and volumes are substantially larger compared to the pre-urbanized period. It is concluded that changes in watershed surface conditions resulting from urbanization have lowered the precipitation-intensity threshold that must be surpassed before storm run-off is generated.