The slope-area method is a commonly used and widely accepted technique for estimating peak flood flows in rivers where direct discharge measurements could not be obtained during the flood. The method makes multiple assumptions to simplify calculations which include assuming uniform flow conditions between surveyed cross sections, and that losses of energy in the reach occur only due to bank friction. Even though flows in nature do not always exhibit these simplified conditions, this method has been proven to provide adequate results when compared to direct measurements and thus, has become the go-to approach. To conduct a slope-area computation, the hydrologist needs to make multiple assumptions in the field based on experience, judgment, and published resources as guides. One of these assumptions is determining where to locate cross sections for the slope-area computation such that they sufficiently represent the cross-sectional area and slope of the channel. Traditional methods suggest to place the cross sections at breaks in the water surface slope. This research focuses on the variability of results of computed discharge values when cross sections are located at many different locations in the reach. What has been found is that many combinations of cross sections in the reach, including sections not located at the breaks in water surface slope, produce similar results when compared to the traditional methods. In fact, 121 of these combinations of cross sections produce peak discharge calculations within plus or minus five percent of the traditional methodology. What also was found was that variability in channel geometry goes unnoticed when using the traditional locating method, and losses due to expansion and contraction of flow area at locations which would not have been traditionally surveyed are occurring at multiple cross sections in the reach. The results suggest that reaches be evaluated for changes in geometry and not overlooked, so that the changes in shape, and subsequent losses in energy, be considered in the computation.

Os estudos sobre rios em leitos fluviais rochosos têm servido de base para o entendimento da evolução das paisagens que se inserem. A análise mais detalhada das litologias que compõem estes leitos fluviais, se tornam desta forma, imprescindíveis para o entendimento da evolução das morfologias resultantes da interação, entre os processos fluviais e a resistência erosiva imposta pela rocha. A presente pesquisa visou obter a resposta geomorfológica de canais com leito predominantemente rochoso, sobre duas unidades litológicas da Formação Serra Geral nível superior. A primeira de origem vulcânica básica, é composta pelos Basaltos Hipoialinos e a segunda de composição ácida, é formada pelos Riodacitos. Partiu-se da análise da estruturação física de cada litologia pertencente a estas unidades e das fragilidades inerentes a cada uma, em relação aos processos fluviais mais atuantes sobre os leitos fluviais de três cursos principais e de seus principais afluentes. Utilizou-se do modelo de regressão denominado, relação declive-área (S = ks A-) para as análises das variações de declividade e de concavidade dos perfis dos rios a fim de compreender quais os principais controles que determinam a modificação dos ajustamentos morfológicos. Foi observado que as duas unidades litológicas apresentam alta erodibilidade frente a potência de escoamento. Primeiro porque o intemperismo generalizado prepara ambas as rochas para os principais processos fluviais identificados: abrasão/macro abrasão e arrancamento. Estes processos atuam mais intensamente sobre o fraturamento rochoso, que mesmo distinto entre as duas litologias (Hipoialinos = ~50 m/m2; Riodacitos = ~9 m/m2) permitem a erosão efetiva dos leitos fluviais. Segundo que, a interferência tectônica altera a dispersão dos dados da relação declive-área integral dos canais fluviais (R2), mascarando as tendências de ajustamento das declividades dos perfis longitudinais. Os valores de ajustamento da potência do escoamento, sobre a resistência erosiva das rochas, só pôde ser vislumbrados, a partir da análise dos índices de concavidade () e de declividade (ks), de acordo com os segmentos discretizados dos perfis longitudinais em domínios homogêneos, de cada litologia pertencente ao leito fluvial. A separação dos limiares superiores que representam os trechos de maior declividade, em relação aos limiares inferiores, que representam os trechos de menor declividade relativa, também foi necessária para a compreensão das tendências de ajuste morfológico pela potência do escoamento. / Studies about rivers in rocky riverbeds have served as a basis for understanding the evolution of the landscapes that are inserted. The more detailed analysis of the lithologies that composes these riverbeds are thus essential for the understanding of the evolution of the resulting morphologies from the interaction between the river processes and the erosive resistance imposed by the rocks of the riverbeds. The present research aimed at obtaining the geomorphological response of channels with rock layer, on two lithological units of the Serra Geral Formation, upper level. The first one of basic volcanic origin, is composed of basalts and the second of acid composition, is formed by rhyodacites. The starting point was the analysis of the physical structure of each lithology belonging to these units and of the inherent weaknesses in each one, in relation to the fluvial processes most active on the river layers of three main courses and their main tributaries. The regression model called the slope-area ratio (S = ks A-) was used for the analyzes of the slope and concavity variations of the river profiles in order to understand the main controls that determine the modification of the morphological adjustments. It was observed that the two lithological units present high erodibility against the flow power. First, because the general weathering prepares both rocks for the main fluvial processes identified: abrasion / macro abrasion and pulling out. These fluvial processes act more intensely on the rocky fracture, which, even distinguished between the two lithologies (basalts = 50 m / m2; rhyodacites = 9 m / m2), allows for the effective erosion of the riverbeds. Second, tectonic interference alters the data dispersion of the slope-area integral relation of the fluvial channels (R2), masking the adjustment tendencies of the slope longitudinal profiles. The values of the adjustment of the river profiles could only be glimpsed, according to the indices of concavity () and slope (ks), according to the discretized segments of the longitudinal profiles, in homogeneous domains, of each lithology belonging to the riverbed. The separation of the upper thresholds that represent the sections of greater slope, in relation to the lower thresholds, which represent the sections of smaller relative slope, was also necessary to understand the morphological adjustment tendencies of the profile slopes.

This dissertation reports on the methods and results of a three-phased investigation to estimate the annual volume of ephemeral-channel-focused groundwater recharge attributable to urbanization (urban-enhanced groundwater recharge) in the Sierra Vista subwatershed of southeastern Arizona, USA. Results were used to assess a prior estimate. The first research phase focused on establishment of a study area, installation of a distributed network of runoff gages, gaging for stage, and transforming 2008 stage data into time series of volumetric discharge, using the continuous slope-area method. Stage data were collected for water years 2008 - 2011. The second research phase used 2008 distributed runoff data with NWS DOPPLER RADAR data to optimize a rainfall-runoff computational model, with the aim of identifying optimal site-specific distributed hydraulic conductivity values and model-predicted infiltration. The third research phase used the period-of-record runoff stage data to identify study-area ephemeral flow characteristics and to estimate channel-bed infiltration of flow events. Design-storm modeling was used to identify study-area predevelopment ephemeral flow characteristics, given the same storm event. The difference between infiltration volumes calculated for the two cases was attributed to urbanization. Estimated evapotranspiration was abstracted and the final result was equated with study-area-scale urban-enhanced groundwater recharge. These results were scaled up to the Sierra Vista subwatershed: the urban-enhanced contribution to groundwater recharge is estimated to range between 3270 and 3635 cubic decameters (between 2650 and 2945 acre-feet) per year for the period of study. Evapotranspirational losses were developed from estimates made elsewhere in the subwatershed. This, and other sources of uncertainty in the estimates, are discussed and quantified if possible.

Os estudos sobre rios em leitos fluviais rochosos têm servido de base para o entendimento da evolução das paisagens que se inserem. A análise mais detalhada das litologias que compõem estes leitos fluviais, se tornam desta forma, imprescindíveis para o entendimento da evolução das morfologias resultantes da interação, entre os processos fluviais e a resistência erosiva imposta pela rocha. A presente pesquisa visou obter a resposta geomorfológica de canais com leito predominantemente rochoso, sobre duas unidades litológicas da Formação Serra Geral nível superior. A primeira de origem vulcânica básica, é composta pelos Basaltos Hipoialinos e a segunda de composição ácida, é formada pelos Riodacitos. Partiu-se da análise da estruturação física de cada litologia pertencente a estas unidades e das fragilidades inerentes a cada uma, em relação aos processos fluviais mais atuantes sobre os leitos fluviais de três cursos principais e de seus principais afluentes. Utilizou-se do modelo de regressão denominado, relação declive-área (S = ks A-) para as análises das variações de declividade e de concavidade dos perfis dos rios a fim de compreender quais os principais controles que determinam a modificação dos ajustamentos morfológicos. Foi observado que as duas unidades litológicas apresentam alta erodibilidade frente a potência de escoamento. Primeiro porque o intemperismo generalizado prepara ambas as rochas para os principais processos fluviais identificados: abrasão/macro abrasão e arrancamento. Estes processos atuam mais intensamente sobre o fraturamento rochoso, que mesmo distinto entre as duas litologias (Hipoialinos = ~50 m/m2; Riodacitos = ~9 m/m2) permitem a erosão efetiva dos leitos fluviais. Segundo que, a interferência tectônica altera a dispersão dos dados da relação declive-área integral dos canais fluviais (R2), mascarando as tendências de ajustamento das declividades dos perfis longitudinais. Os valores de ajustamento da potência do escoamento, sobre a resistência erosiva das rochas, só pôde ser vislumbrados, a partir da análise dos índices de concavidade () e de declividade (ks), de acordo com os segmentos discretizados dos perfis longitudinais em domínios homogêneos, de cada litologia pertencente ao leito fluvial. A separação dos limiares superiores que representam os trechos de maior declividade, em relação aos limiares inferiores, que representam os trechos de menor declividade relativa, também foi necessária para a compreensão das tendências de ajuste morfológico pela potência do escoamento. / Studies about rivers in rocky riverbeds have served as a basis for understanding the evolution of the landscapes that are inserted. The more detailed analysis of the lithologies that composes these riverbeds are thus essential for the understanding of the evolution of the resulting morphologies from the interaction between the river processes and the erosive resistance imposed by the rocks of the riverbeds. The present research aimed at obtaining the geomorphological response of channels with rock layer, on two lithological units of the Serra Geral Formation, upper level. The first one of basic volcanic origin, is composed of basalts and the second of acid composition, is formed by rhyodacites. The starting point was the analysis of the physical structure of each lithology belonging to these units and of the inherent weaknesses in each one, in relation to the fluvial processes most active on the river layers of three main courses and their main tributaries. The regression model called the slope-area ratio (S = ks A-) was used for the analyzes of the slope and concavity variations of the river profiles in order to understand the main controls that determine the modification of the morphological adjustments. It was observed that the two lithological units present high erodibility against the flow power. First, because the general weathering prepares both rocks for the main fluvial processes identified: abrasion / macro abrasion and pulling out. These fluvial processes act more intensely on the rocky fracture, which, even distinguished between the two lithologies (basalts = 50 m / m2; rhyodacites = 9 m / m2), allows for the effective erosion of the riverbeds. Second, tectonic interference alters the data dispersion of the slope-area integral relation of the fluvial channels (R2), masking the adjustment tendencies of the slope longitudinal profiles. The values of the adjustment of the river profiles could only be glimpsed, according to the indices of concavity () and slope (ks), according to the discretized segments of the longitudinal profiles, in homogeneous domains, of each lithology belonging to the riverbed. The separation of the upper thresholds that represent the sections of greater slope, in relation to the lower thresholds, which represent the sections of smaller relative slope, was also necessary to understand the morphological adjustment tendencies of the profile slopes.