River deltas are dynamic ecosystems of environmental, ecological, and societal importance. In coastal Louisiana, land loss and increased nutrient loading are altering the eco-geomorphic equilibrium, raising concern for the environmental concerns associated with climate and anthropogenic change. Over the last 100 years, nearly 5000 km2 of wetlands have been submerged due to a variety of environmental and anthropogenic forces. Wetland drowning and costal retreat is predicted to continue, threatening both human and environmental interests. As a result, mitigation efforts in the form of planned river diversions designed to build new land by natural delivering sediment to the once-leveed floodplains have been proposed. Denitrification in coastal wetlands has the potential to limit the risks of hypoxia and related eco-geomorphic issues by reducing the nitrogen export to receiving waters. The goal of this research project is to understand and quantify to propagation of environmental fluxes through a delta distributary system. Water fluxes in the delta distributary network are not solely propagated within the distributary channels and interdistributary areas, taking the form of inundated island interiors surrounded by subaerial levees, are hydrologically important. At Wax Lake Delta (WLD) in coastal Louisiana, roughly 50% of the flow is exchanged to the island swamps, suggesting that significant portions of nutrients are transported to the island interiors. The hydraulic residence times (HRTs) of the islands are estimated to be 15 – 29 hours and 11 – 18 hours on Mike and Pintail Islands, respectively; both being well below HRT estimates for significant denitrification. Spatial variability in network structure, specifically channel width and frequencies of confluences and bifurcations, influences the transport dynamics within the delta. However, flow partitioning in major distributary channels at WLD is relatively constant with time, supporting the hypothesis that network structure controls flux dynamics. / text

This three part study attempted to enhance our understanding of vegetation change and its potential effects on ecohydrology in drylands. The first study developed a method to measure the velocity of shallow overland flow. Under rainfall simulation, dye tracers were applied to runoff and photographed to calculate mean surface velocity. Results showed this approach was a significant improvement explaining 13% more of the variation in mean velocity compared to traditional methods. Results from the first study were used to compare hydraulic parameters on shrub- and grass-dominated plots in the second study. Previous research has suggested microtopography in shrublands acts to concentrate flow, leading to increased runoff velocity compared to grasslands. However, present findings showed that flow velocities were similar on many grass and shrub plots; only plots with ground cover > 90% exhibited significantly lower flow velocities, and some shrub-dominated plots had lower flow velocities than grass-dominated plots implying that horizontal water flux is reduced under certain states of woody plant encroachment. In terms of ground cover characteristics, velocity increased rapidly with increases in the fraction of bare soil, up to a value of ~20% bare soil. Above ~20% bare soil, basal gap became a dominant factor suggesting a possible threshold where spatial metrics related to the distance between plants become important indicator of shallow flow velocity. The third study tested an approach to quantify woody plant canopy metrics over large areas. Radar has been used to map biomass in forests but few studies have examined open canopy ecosystems. Field measurements of shrublands were compared to satellite images to identify the relationship between radar signal and height and cover of woody vegetation. Results indicated that radar signal increased positively with shrub height or shrub volume explaining 74% and 90% of the variation, respectively. The effect of surface roughness and sub-canopy species on radar signal appears reduced when images are collected at large incidence angles.

Land surface processes play an important role when modeling weather and climate, and understanding and representing such processes in South America is a particular challenge because of the large variations in regional climate and surface features such as vegetation and soil. Numerical models have been used to explore the climate and weather of continental South America, but without appropriate initiation of land surface conditions model simulations can rapidly diverge from reality. This initiation problem is exacerbated by the fact that conventional surface observations over South America are scarce and biased towards the urban centers and coastal areas. This dissertation explores issues related to the apt representation of land surface processes and their impacts in numerical simulations with a regional atmospheric model (specifically the Eta model) over South America. The impacts of vegetation heterogeneity in regional weather forecast were first investigated. A South American Land Data Assimilation System (SALDAS) was then created analogous to that currently used in North America to estimate soil moisture fields for initializing regional atmospheric models. The land surface model (LSM) used in this SALDAS is the Simplified Simple Biosphere (SSiB). Precipitation fields are critical when calculating soil moisture and, because conventional surface observations are scarce in South America, some of the most important remote sensed precipitation products were evaluated as potential precipitation forcing for the SALDAS. Spin up states for SSiB where then compared with climatological estimates of land surface fields and significant differences found. Finally, an assessment was made of the value of SALDAS-derived soil moisture fields on Eta model forecasts. The primary result was that model performance is enhanced over the entire continent in up to 72h forecasts using SALDAS surface fields

A numerical modelling analysis of climate change’s precipitation effects on the long-term, averaged surface and subsurface hydrology of the Grand River Watershed (GRW) was undertaken in order to assess possible areas of concern for decision makers in the water management sector. The physically-based, fully-integrated and variably-saturated 3-D surface-subsurface numerical simulator, HydroGeoSphere, was used to drive five mid-21st century climate change scenarios, developed from multiple general circulation models. Calibration involved altering measured and literature-derived hydraulic conductivity and precipitation distribution estimates, resulting in very good matching between observed and simulated long-term average surface flow at all gauge stations. Subsurface head results, too, matched observed heads quite well, though groundwater linkage to neighbouring watersheds was not included. When groundwater linkage to neighbouring watersheds was allowed, via regional Dirichlet boundary conditions used in a parent study, groundwater throughput was deemed to be unrealistic. All but one of the climate change scenarios caused an increase in both river discharge and water table elevation, with the greatest climate perturbations causing the greatest increases. For Scenario 1 (5% less precipitation than the 1960-to-1999 average), percentage discharge changes averaged -15% over all gauge stations. For the other scenarios (more precipitation than average), the inter-scenario discharge response ranged from approximately +12% to +59%. In general the range of inter-subcatchment response was greater than was the range for intra-subcatchment response; the greatest percentage response was consistently in the Speed River subcatchment, while the least was consistently in the Nith and Conestogo subcatchments. The exception was the application of less-than-average precipitation to the Grand River, whose gauge stations reported percentage changes in discharge that varied more substantially from one another. Subsurface hydrology reacted to the climate change scenarios in much the same manner as did the surface hydrology, with all climate change scenarios associated with a precipitation increase unsurprisingly resulting in higher total hydraulic heads throughout the entire domain. Specifically, the minimum and maximum mean head increases among the climate change scenarios were 0.41 m and 1.25 m respectively, while the only decrease was an average of 0.55 m. Similarly, the depth from the ground surface to the water table decreased in most scenarios, the maximum water table rise being 1.08 m and the minimum 0.36 m. When precipitation was allowed to decrease by 5% relative to the long-term average, the average water table elevation decreased by 0.48 m. However the water table’s pattern of high and low points remained very much the same among all climate change scenarios, suggesting that basin-wide groundwater flow patterns may not be among the hydrological measures most sensitive to climate change. Groundwater recharge, like almost all other components of the water budget, changed in linear proportion to the climate forcing and in agreement with GRW recharge estimates developed by others. Evapotranspiration, which met potential evapotranspiration in all scenarios due to the constant application of precipitation, was the only element of the water budget that did not increase, even though the water table was elevated closer to the rooting zone by most of the climate scenarios. On a smaller scale, changes in flow patterns may well be expected, given that zones of infiltration were observed to intensify with most of the climate forcing.

A numerical modelling analysis of climate change’s precipitation effects on the long-term, averaged surface and subsurface hydrology of the Grand River Watershed (GRW) was undertaken in order to assess possible areas of concern for decision makers in the water management sector. The physically-based, fully-integrated and variably-saturated 3-D surface-subsurface numerical simulator, HydroGeoSphere, was used to drive five mid-21st century climate change scenarios, developed from multiple general circulation models. Calibration involved altering measured and literature-derived hydraulic conductivity and precipitation distribution estimates, resulting in very good matching between observed and simulated long-term average surface flow at all gauge stations. Subsurface head results, too, matched observed heads quite well, though groundwater linkage to neighbouring watersheds was not included. When groundwater linkage to neighbouring watersheds was allowed, via regional Dirichlet boundary conditions used in a parent study, groundwater throughput was deemed to be unrealistic. All but one of the climate change scenarios caused an increase in both river discharge and water table elevation, with the greatest climate perturbations causing the greatest increases. For Scenario 1 (5% less precipitation than the 1960-to-1999 average), percentage discharge changes averaged -15% over all gauge stations. For the other scenarios (more precipitation than average), the inter-scenario discharge response ranged from approximately +12% to +59%. In general the range of inter-subcatchment response was greater than was the range for intra-subcatchment response; the greatest percentage response was consistently in the Speed River subcatchment, while the least was consistently in the Nith and Conestogo subcatchments. The exception was the application of less-than-average precipitation to the Grand River, whose gauge stations reported percentage changes in discharge that varied more substantially from one another. Subsurface hydrology reacted to the climate change scenarios in much the same manner as did the surface hydrology, with all climate change scenarios associated with a precipitation increase unsurprisingly resulting in higher total hydraulic heads throughout the entire domain. Specifically, the minimum and maximum mean head increases among the climate change scenarios were 0.41 m and 1.25 m respectively, while the only decrease was an average of 0.55 m. Similarly, the depth from the ground surface to the water table decreased in most scenarios, the maximum water table rise being 1.08 m and the minimum 0.36 m. When precipitation was allowed to decrease by 5% relative to the long-term average, the average water table elevation decreased by 0.48 m. However the water table’s pattern of high and low points remained very much the same among all climate change scenarios, suggesting that basin-wide groundwater flow patterns may not be among the hydrological measures most sensitive to climate change. Groundwater recharge, like almost all other components of the water budget, changed in linear proportion to the climate forcing and in agreement with GRW recharge estimates developed by others. Evapotranspiration, which met potential evapotranspiration in all scenarios due to the constant application of precipitation, was the only element of the water budget that did not increase, even though the water table was elevated closer to the rooting zone by most of the climate scenarios. On a smaller scale, changes in flow patterns may well be expected, given that zones of infiltration were observed to intensify with most of the climate forcing.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-11-06T16:08:46Z No. of bitstreams: 1 PAULO ROMERO GUIMARÃES SERRANO DE ANDRADE - DISSERTAÇÃO PPGECA 2000..pdf: 36173335 bytes, checksum: 8c355842ff686dced645eaae16c63cfd (MD5) / Made available in DSpace on 2018-11-06T16:08:46Z (GMT). No. of bitstreams: 1 PAULO ROMERO GUIMARÃES SERRANO DE ANDRADE - DISSERTAÇÃO PPGECA 2000..pdf: 36173335 bytes, checksum: 8c355842ff686dced645eaae16c63cfd (MD5) Previous issue date: 2000-12-14 / A notória subutilização dos reservatórios do Nordeste do Brasil, mormente em sua região semi-árida, derivando, regra geral, da ausência de um manejo adequado e de instrumental técnico eficiente aplicáveis à funcionalidade dos seus perímetros de irrigação, desperta, quase sempre, o receio de esgotá-los. O uso mais racional dos recursos hídricos e a busca da maximização dos benefícios advindos de aproveitamentos hidráulicos já existentes, a fim de que as populações dessa área possam ser melhor atendidas, motivaram a elaboração deste trabalho. Neste contexto, procurou-se estudar a operação do sistema hídrico formado pelos reservatórios Jucazinho e Carpina, e três perímetros de irrigação, localizados na bacia do rio Capibaribe, em Pernambuco, com o objetivo de maximizar os benefícios financeiros líquidos advindos da agricultura irrigada e da piscicultura, atendidos o requerimento de água para o abastecimento urbano, prioritariamente, necessidades hídricas da regularização e controle de cheia. Para analisar o comportamento do sistema hídrico e tentar prover solução ótima para a sua operação, foi aplicado o modelo ORNAP (Curi e Curi, 1999) de otimização, de base mensal, apoiado em técnicas de programação não linear. A função objetivo que visa a maximização do lucro da prática agrícola irrigada e piscicultura, é sujeita a restrições diversas, representadas por equações de natureza linear e não linear, que traduzem no processo de otimização, a nível mensal, as limitações físicas dos reservatórios, perímetros e equipamentos hidráulicos, limitações hidrológicas, legais, econômicas e sociais, que são próprias de sistemas de múltiplos usos Abordagens determinísticas foram necessárias, idealizando-se o futuro do sistema hídrico como conhecido através de cenários de planejamento, caracterizados por três situações climáticas distintas (média, seca e chuvosa), que são completados, basicamente, pela definição de valores para variáveis de entrada para o modelo, relacionadas aos elementos naturais e artificiais identificados como pertinentes ao sistema, que envolvem reservatórios, demandas de abastecimento urbano, calhas de rio e perímetros de irrigação. Os resultados otimizados para as diversas variáveis de decisão, como descargas dos reservatórios e áreas irrigadas, máximas e mínimas, são gerados para cada situação climática, combinadas com diferentes aspectos operacionais adotados para os reservatórios Jucazinho e Carpina. O estudo de otimização mostrou que, respeitadas as restrições operacionais impostas, neste estudo, à funcionalidade do sistema hídrico, as áreas máximas cogitadas para os perímetros não seriam totalmente irrigadas. Os resultados alcançados mostram a viabilidade do modelo ORNAP na prática do planejamento e gerenciamento de reservatórios e perímetros, constituindo-se numa interessante ferramenta de apoio à tomada de decisão. / The not utilization in its full potential of the reservoirs in the Northeast of Brazil, especially in its semi-arid area, derives, most of the time, of the absence of an appropriate handling and the fear of empty them. The motivation for this work was the achievement of a more rational use of the water resources and the search of the maximization of the benefits generated by the hydraulic uses already existent, so that the population of that area can be better assisted. In this context, it is studied the operation of the water resource system formed by the reservoirs Jucazinho and Carpina, and three irrigation sites, located in the basin of the Capibaribe river, in Pernambuco, North-east Brazil, with the objective of maximizing the net income generated by the irrigated agriculture and fish farming, respecting the needs of water for urban uses, flow and flood control. To analyze the behavior of the water resources system in order to obtain an optimal solution for its operation, was applied an optimization model called ORNAP (Curi and Curi, 1999), of monthly base, based on a nonlinear optimization technique. The objective function that seeks the maximization of the profit of the irrigated agricultural and and extensive fishing activities, is subject to several constraints, represented by equations of linear and non linear nature that accounts, in the optimization process, at monthly level, for the physical limitations of the reservoirs, perimeters and hydraulics equipment, hydrological limitations, legal, economical and social requirements, that are inherent of water resource systems of multiple uses. A deterministic approach was necessary, where the future was idealized through planning scenarios, characterized by three different climate situations (average, dry and rainy). The optimal values assumed by the several decision variables, such as discharges of the reservoirs and irrigated areas for each crop, are generated for each climatic situation, taking in account the several operational aspects adopted for the reservoirs Jucazinho and Carpina. The optimization study showed that, respected the imposed operational constraints, in this study, the maximum areas cogitated for the perimeters would not be totally irrigated. The reached results show the viability of the model ORNAP for the planning and management of reservoirs and irrigated sites, constituting in an interesting tool for a decision support system.