The Eel River watershed has a high concentration of slow-moving landslides, or earthflows, due to argillaceous mélange bedrock and high tectonic uplift. Earthflows within this area are highly dissected by ephemeral channels, or gullies. Despite the pervasiveness of gullying in this area, the role of fluvial systems in relation to earthflows and varying uplift is poorly understood. To understand the role of earthflows and tectonics in dictating channel processes, we investigate channels in areas of differential uplift and mass failure activity. Channel networks are connected and continuous in catchments without earthflows, and disconnected and prone to bank failure on earthflow surfaces. Gully profiles are influenced BY earthflow undulations, which attenuate with fluvial incision after earthflows cease activity. We find notable differences in fluvial dissection between areas of high and low landslide activity. We find that mass wasting and local bedrock have a strong influence on formation and organization of channels.

Variations in drainage density have been observed in a range of environments as the perennial stream network expands into headwater reaches. This network expansion and contraction results in large changes in drainage density and as such, has implications for the connectivity of the catchment and the associated flux of water, sediments and solutes. One environment where these changes have been observed is peatlands. The accurate characterisation of catchment connectivity in peatlands is desirable for a number of reasons, not least to understand the controls on carbon flux. In addition, the accurate characterisation of these systems will help us to predict the impacts of a changing climate. It is hitherto been difficult to quantify changes in connectivity due to the logistical difficulties of monitoring this phenomenon. The use of Electrical Resistance (ER) technology has shown potential to detect the presence and absence of water. This method is built on here and a range of sensors are developed to monitor connectivity at high temporal and spatial resolutions, specifically flow in ephemeral portions of the channel network, pipeflow and overland flow. The study takes places in the Upper North Grain research catchment, a small peatland headwater catchment in the south Pennines, UK. The data collected on ephemeral streamflows highlight the importance of water table as a control on changes in network extent in the study catchment, as the presence or absence of flow at each site is strongly controlled by local water table. This allows the minimum and maximum drainage density within the catchment to be determined, as well how frequently these states occur. Pipe stormflow generation appears to be strongly linked to the production of saturation excess overland flow. The pipe network is very sensitive to small inputs of rainfall. In contrast, pipe baseflows seem to be controlled by water table level as pipes are fed by seepage from the peat mass. Pipe behaviour could not be related to any of the morphological characteristics presented here and is though to be dependent on the subsurface morphology of the pipe network. Overland flow production was monitored at a gully head and gully side location. At the gully head the incidence of overland flow increased with distance from the gully edge due to higher local water tables encouraging the production of saturation excess overland flow. At the gully side, extreme water table drawdown has caused the peat to become hydrophobic and the incidence of overland flow is high here, due to infiltration excess. This signifies a major advancement in our knowledge of runoff pathways in peatlands as the importance of infiltration excess overland flow has not been acknowledged until now. In general, ephemeral streamflows occur before the production of either overland flow or pipeflow as incident rainfall causes saturation of the gully floors. The temporal pattern of overland flow and pipeflow is similar, although pipeflow continues after overland flow ceases and is thought to be fed by shallow subsurface flow on the recession limb. Both overland flow and pipeflow precede discharge at the catchment outlet by several minutes. The interaction of these processes is examined under both ‘wet’ and ‘dry’ antecedent conditions. The data collected here provide an accurate characterisation of the dynamics of, and controls on, peatland connectivity under current climatic conditions, providing a reference point to which future observations can be compared.

Headwater streams change in wet length in response to storm events and seasonal moisture conditions. These low-order channels with temporary flow are pervasive across arid and humid environments yet receive little attention in comparison to perennial waterways. This dissertation examines headwater stream length dynamics at multiple spatial and temporal scales across the Appalachians. I mapped wet stream length in four Appalachian physiographic provinces--the Appalachian Plateau, Blue Ridge, New England, and Valley and Ridge--to characterize seasonal expansion and contraction of the wet network at a broad, regional scale. Conversely, most existing field studies of stream length in headwaters are limited to a single study area or geographic setting. Field mappings showed that wet stream length varies widely within the Appalachians; network dynamics correlated with regional geology as well as local site lithology, geologic structure, and the depth, size, and spatial distribution of surficial sediment deposits. I used the field data to create logistic regression models of the wet network in each physiographic province at high and low runoffs. Topographic metrics derived from elevation data were able to explain the discontinuous pattern of headwater streams at different flow conditions with high classification accuracy. Finally, I used flow intermittency sensors in a single Valley and Ridge catchment to record channel wetting and drying at a high temporal resolution. The sensors indicated stream length hysteresis during storms with low antecedent moisture, with a higher wet network proportion on the rising limb than on the falling limb of events. As a result, maximum network extension can precede peak runoff by minutes to hours. Accurate maps of headwater streams and an understanding of wet network dynamics through time are invaluable for applications surrounding watershed management and environmental policy. These findings will contribute to the burgeoning research on temporary streams and are additionally relevant for studies of runoff generation, biogeochemical cycling, and mass fluxes of material from headwaters. / Ph. D. / During a rain storm, we may think of streams increasing in depth, width, and velocity. However, we may not necessarily envision streams also getting longer. Headwaters, which form the upstream extremities of river systems, consist of many temporary streams that expand and contract in length due to storms and changes in seasonal moisture conditions. Headwaters are spatially expansive, comprising a majority of total river length, and serve as a primary control on downstream water quality. Therefore, understanding stream length dynamics can inform policy and land use decisions to effectively conserve and manage headwater regions and protect water sources for human use and consumption. This dissertation examines changes in stream length across four study areas of the Appalachian Mountains. I mapped the wet, or active, stream network multiple times at different flow conditions in each study area. Stream length dynamics varied considerably across the Appalachians and demonstrated the same range of network expansion and contraction as other studies observed in diverse settings around the world. Wet stream length greatly depended on regional and local geology. I then sought to predict the location of wet streams at high and low flows using metrics such as slope and drainage area that I calculated from digital elevation information. Comparisons with the field maps I made showed that simple terrain metrics explained the location, length, and disconnected nature of wet networks in each province with high accuracy. I also observed stream length dynamics during storm events in one watershed using sensors that recorded the presence or absence of water. These observations demonstrated that stream length was often higher for a given flow at the beginning of a storm on the rising limb than on the falling limb when flow was decreasing, particularly if conditions were dry before the storm. The findings of this dissertation contribute to existing knowledge of temporary streams and are relevant for future studies investigating the hydrology, biology, and ecology of headwaters.

Orientador: Archimedes Perez Filho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-12T04:31:07Z (GMT). No. of bitstreams: 1 Rodrigues_TaniaReginaInacio_D.pdf: 3472498 bytes, checksum: 26f703aa2200639abb45fc005310cf05 (MD5) Previous issue date: 2006 / Resumo: É sabido que o arranjo da rede de drenagem é reflexo da interação de um conjunto de variáveis físicas, como clima, relevo, solos, substrato rochoso e vegetação. Assim sendo, torna-se possível tecer considerações acerca dessas variáveis, com base na análise criteriosa da rede de drenagem. O presente trabalho utilizou a rede de drenagem como geoindicador das modificações ocorridas no período de 43 anos no meio físico na Bacia Hidrográfica do baixo curso do Rio São José dos Dourados que integra a porção baixo curso Rio São José dos Dourados. As mudanças das características da paisagem na Bacia foram estabelecidas com base nos seguintes atributos: (i) modificações ocorridas na rede de drenagem (densidade de drenagem e densidade hidrográfica); (ii) o tipo de atividade antrópica registrada na área; (iii) características referentes ao meio físico: solos e declividade do terreno. A verificação das alterações neste período foi obtida por meio das análises temporais tanto das variáveis morfométricas da rede de drenagem como da caracterização de ocupação do meio físico. Os dados foram obtidos por atividades de campo, interpretação de fotomosaicos aéreos (escala 1:25.000) de 1962 e de imagem de satélite Landsat-5 TM (escala aproximada 1:50.000) de 2005. Os documentos cartográficos gerados pelo Software Envi 4.0®, AutoCAD Map2000i® e Idrisi Kilimanjaro foram mapas de hipsometria, declividade, redes de drenagem e uso e ocupação do solo. O sistema da rede de drenagem configurou-se como um adequado indicador das alterações ambientais ocorridas na área de estudo. A análise morfométrica indicou um aumento no número de canais de primeira ordem e no comprimento total dos canais em toda a Bacia. Conseqüentemente, estas mudanças condicionaram as modificações dos parâmetros de densidade de drenagem e de densidade hidrográfica. Tais alterações foram condicionadas pela construção dos reservatórios das Usinas Hidrelétricas de Ilha Solteira e Três Irmãos e as alterações no uso e ocupação da terra. / Abstract: It is very well known that drainage net design reflects the interaction of a set of physical variables as clime, landscape, soil type, soil substrate as well as vegetation. This way, it is possible to study the behavior of these variables through a detailed analysis of the drainage net. This research work employed the a drainage net as an indicative of the modifications experienced by the São José dos Dourados river baixo curso watershed physical environment which integrates the São José dos Dourados river baixo curso. Landascape characteristics changes were analyzed under the following attributes, considering a period of 43 years: (i) modifications occurred in the drainage net (drainage density and hydrographic density); (ii) type on antropic activity observed in the area; (iii) characteristics associated to the physical landscape: soil changes and land slope. The alterations observed during the period under study were studied by means of temporal analysis of the net morphological variables as well as land occupation characterization. Obtained data were associated to field activity, photomosaic interpretation (scale of 1:25.000) from 1962 as well of the Landsat-5 TM image (approximate scale of 1:50.000) from 2005. The cartographic documents generated by the Envi 4.0®, AutoCAD Map2000i® and Idrisi kilimanjaro software are represented maps of hypsometry, slope, drainage nets as well as land use and occupation. Drainage net system showed to be adequate to indicate the environmental alterations experienced by the area under study. Morphological analysis indicated an increment on the number of first order channels and on the total channel length in watershed. Consequently, these changes influenced the drainage density and hydrographic parameters. Such alterations were influenced by the constructions Ilha Solteira and Tres Irmãos Hydroelectric Power Plants as well as by the alterations of land use and occupation. / Doutorado / Agua e Solo / Doutor em Engenharia Agrícola

Temporary streams have received undeservedly little scientific attention and as a result their role in hydrological, biogeochemical and ecological processes is not yet fully understood. The ultimate goal of the research was to gain a better understanding of the temporary stream network and the processes that control it and determine how the active and connected stream length change with catchment wetness conditions to find simple methods to map seasonal and event-based changes in temporary flowing stream networks. Streams, springs and wetlands of four relatively small headwater catchments (11.7 – 25.3 km2) and one wetland in the steep and remote Zwäckentobel catchment in Alptal, canton Schwyz (Switzerland), were mapped and stream segments were classified by flow type during different weather conditions using direct observations. The mapping was performed by an elite orienteer with mapping experience. The variation in streamflow was analysed and related to the catchment wetness and topography using the TWI-values and the upslope accumulated area of the stream segments. As the catchments wetted up in response to fall rainfall events after a dry summer the flowing stream density increased up to five times and the connected stream density increased up to six times with a 150-fold increase in discharge. Also the number of flowing stream heads increased up to ten times. The best description of the pattern of stream expansion is a combination of the variable source area and the element threshold concepts, where surface topography, particularly TWI (Topographic Wetness Index) and upslope accumulated area (A), and local storage areas controls where streamflow is initiated and how flow in different stream segments connects. Streams in the Alptal show a seasonally bottom up or disjointed connection pattern. Mapping the temporary streams in steep and remote watersheds as a function of hydrological conditions is not an easy task. It is however necessary in order to fully understand where water is flowing or not. A combination of field observations with monitoring equipment can facilitate this extensive work by providing a more detailed temporal resolution.

La constante de temps du débit de base (τ) représente le temps moyen pour que l'eau souterraine arrive à la rivière depuis la zone de recharge dans un bassin donné. C’est un élément clé pour simuler le débit de base dans les modèles simples des eaux souterraines, tels qu’ORCHIDEE. τ a été estimée à l’échelle globale à partir d’une solution de l’équation de Boussinesq pour les aquifères libres en pente. τ dépend de la porosité efficace, de la transmissivité, de la pente de l'aquifère et de la densité de drainage (δ). Calculées à partir de bases de données globales, les valeurs de τ sont surestimées par rapport à celles obtenues par analyse des courbes de récession. Une analyse de sensibilité a montré que la transmissivité et δ sont les principales sources d’incertitude de τ. L’extraction d’un nouveau réseau de drainage, qui dépend de la lithologie, du climat, de la pente et des δ observées, a permis d’obtenir des δ conformes aux valeurs observées aux échelles régionales et à la variabilité spatiale. L’utilisation de ces nouvelles δ et la combinaison de deux jeux de données de conductivité hydraulique pour le sol et l’aquifère a réduit τ de deux ordres de grandeur, mais les valeurs calculées restent surestimées. L’utilisation de τ dans le modèle de surface ORCHIDEE a montré une forte sensibilité du débit simulé à l’augmentation de τ, qui dégrade les débits simulés par rapport aux observations. Cette méthodologie nécessite des valeurs plus adaptées de transmissivité et porosité efficace par rapport aux jeux de données globaux actuellement disponibles pour obtenir des valeurs de τ plus proches de celles attendues et qui permettent de reproduire les débits observés. / The base flow time constant (τ) represents the mean amount of time the groundwater takes to reach the stream from the recharge zone in a given watershed. τ is a key element to simulate base flow in simple groundwater models as ORCHIDEE. τ was estimated at global scale based on a solution of the Boussinesq equation for unconfined sloping aquifers. τ depends on the effective porosity, transmissivity, aquifer slope, and drainage density (δ). When estimated from global available datasets, τ results are overestimated when compared to recession analysis results. A sensitivity analysis showed that transmissivity and δ are the main uncertainty sources of τ. A river network extraction based on lithology, climate, slope, and observed δ allowed to obtain δ values close to reference data and spatially variable at regional scale. The use of a new δ and the combination of two hydraulic conductivity datasets of soil and aquifer reduced τ of two orders of magnitude, however the values remained overestimated. The use of τ in ORCHIDEE land surface model showed a strong sensitivity of the river discharge buffer effect to τ, which worsen simulated river discharge when compared to observations. This methodology needs more adequate porosity and transmissivity values when compared to global available datasets that will result in close results to observed river discharge.

<p> Studies to date involving the network properties of drainage systems have been theoretical in nature; and the environmental implications of these network characteristics have not been exploited to the extent that would appear warranted. This situation exists due to the lack of an accurate data source. Many studies have recognized this. inadequacy of the conventional data sources to meet the necessary requirements of efficiency (in data production and handling), accuracy, consistency and uniformity. </p> <p> The present study demonstrates that high altitude, small scale colour infrared photography is capable of providing drainage network data that fulfill all these basic requirements. Data derived from the three drainage basins, mapped from a variety of data sources, demonstrate three important points. The level of detail obtained from the small scale colour infrared photography far exceeds that available from more traditional data sources. Secondly, these network data are statistica+ly consistent with the traditional data sources. Thirdly, the basin characteristics derived from the high altitude data source show a marked association with the known surficial environments and an expected variation from one surficial environment to another. </p> / Thesis / Master of Arts (MA)