Many physically-based models of surface and groundwater hydrology are constructed without the possibility of multiple stable states. For such a conceptualisation, at the cessation of a transient hydrological disturbance of any magnitude, the model will return to the original stable state and therefore will have an infinite resilience. Ecosystem resilience science propose a very different dynamic where, if the system has a positive feedback, disturbances may shift the system over a threshold where, upon cessation of the disturbance, the system will move to a different steady state. This dissertation brings together concepts from hydrology and ecosystem resilience science to highlight this often implicit assumption within hydrology. It tests the assumption that dry land water-limited catchments always have only one steady state (henceforth referred to as 'attractor'). Following a discussion of this implicit assumption within hydrology, approaches for rigorous testing that could result in its falsification are considered and that of numerical modelling is adopted. The aims of the research were to test this assumption by proposing a biophysically plausible hydrological model; utilise it to investigate the catchment attributes likely to result in multiple attractors; and to assess the model's validity by way of implementation and calibration. (For complete abstract open document.)

At no point in history have we demanded so much from our agricultural land whilst simultaneously leaving so little room for management error. Of the many possible environmental impacts from agriculture, soil and water salinisation has some of the most long-lived and deleterious effects. Despite its importance, however, land managers are often unable to make informed decisions of how to manage the risk of salinisation due to a lack of data. Furthermore, there remains no universally agreed method for salinity risk mapping. This thesis addresses these issues by investigating new methods for producing high-resolution predictions of soil salinity, soil physical properties and groundwater depth using a variety of traditional and emerging ancillary data sources. The results show that the methodologies produce accurate predictions yielding natural resource information at a scale and resolution not previously possible. Further to this, a new methodology using fuzzy logic is developed that exploits this information to produce high-resolution salinity risk maps designed to aid both agricultural and natural resource management decisions. The methodology developed represents a new and effective way of presenting salinity risk and has numerous advantages over conventional risk models. The incorporation of fuzzy logic provides a meaningful continuum of salinity risk and allows for the incorporation of uncertainty. The method also allows salinity risk to be calculated relative to any vegetation community and shows where the risk is coming from (root-zone or groundwater) allowing more appropriate management decisions to be made. The development of this methodology takes us a step closer to closing what some have called our greatest gap in agricultural knowledge. That is, our ability to manage the salinity risk at the subcatchment scale.

At no point in history have we demanded so much from our agricultural land whilst simultaneously leaving so little room for management error. Of the many possible environmental impacts from agriculture, soil and water salinisation has some of the most long-lived and deleterious effects. Despite its importance, however, land managers are often unable to make informed decisions of how to manage the risk of salinisation due to a lack of data. Furthermore, there remains no universally agreed method for salinity risk mapping. This thesis addresses these issues by investigating new methods for producing high-resolution predictions of soil salinity, soil physical properties and groundwater depth using a variety of traditional and emerging ancillary data sources. The results show that the methodologies produce accurate predictions yielding natural resource information at a scale and resolution not previously possible. Further to this, a new methodology using fuzzy logic is developed that exploits this information to produce high-resolution salinity risk maps designed to aid both agricultural and natural resource management decisions. The methodology developed represents a new and effective way of presenting salinity risk and has numerous advantages over conventional risk models. The incorporation of fuzzy logic provides a meaningful continuum of salinity risk and allows for the incorporation of uncertainty. The method also allows salinity risk to be calculated relative to any vegetation community and shows where the risk is coming from (root-zone or groundwater) allowing more appropriate management decisions to be made. The development of this methodology takes us a step closer to closing what some have called our greatest gap in agricultural knowledge. That is, our ability to manage the salinity risk at the subcatchment scale.

Thesis (M.Sc.)--University of Adelaide, Dept. of Applied Mathematics, 2001. / "November 2001." Bibliography: leaves 128-130.

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (M.Phil.)--University of Hong Kong, 1982. / Also available in print.

Thesis (M.S.)--San Diego State University, 1989. / Includes bibliographical references (leaves 90-103).

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Douglas C. Miller, Dept. of Marine and Earth Studies. Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

FROTA JÚNIOR, José Itamar. Variabilidade espacial e temporal da qualidade das águas no trecho perenizado na Bacia Hidrográfica do Curu, Ceará. 2006. 100 f. Dissertação (Mestrado em engenharia agrícola)- Universidade Federal do Ceará, Fortaleza-CE, 2006. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-06-23T19:05:24Z No. of bitstreams: 1 2006_dis_jifrotajunior.pdf: 3574076 bytes, checksum: f65986c07ac03ff0c0c2f0826073c2fa (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-07-21T20:15:47Z (GMT) No. of bitstreams: 1 2006_dis_jifrotajunior.pdf: 3574076 bytes, checksum: f65986c07ac03ff0c0c2f0826073c2fa (MD5) / Made available in DSpace on 2016-07-21T20:15:47Z (GMT). No. of bitstreams: 1 2006_dis_jifrotajunior.pdf: 3574076 bytes, checksum: f65986c07ac03ff0c0c2f0826073c2fa (MD5) Previous issue date: 2006 / This research aims analyze the spatial and temporal variability in quality of the water used to perennialized area the hydraulic basin of river Curu, Ceara state, Brazil, evaluating the effects of the anthropic action and the influence of the different types of soils in the region. The following parameters were appraised: cations (Ca2+, Mg2+, Na+, K+), anions (HCO3 -, Cl-) and also: SAR, electric conductivity, pH and dissolved solids. During a period of one year, samples of water were collected in nine points distributed along the perennialized part of the basin of Curu and were analysed in the Soils and Water Laboratory at Federal University of Ceara State. Spatial and temporal variability were considered in the analysis of the medium values of the parameters. Spatial variability was appraised using the Analysis of Variance to 5% and the comparison of the averages with the Test of Tukey to 1%. Regarding the temporal variability, the medium values of the periods dry and rainy were compared and analyzed, in order to classificate waters using the Diagram of Piper. The results evidenced increment of salts along the basin. In the point 1 (Serrota-Pentecoste) the medium value found for sodium was of 1,92 mmolc L-1, while in the point 9 (Pedras Farm-Paraipaba) it was of 3,47 mmolc L-1. It was clear the anthropic influence in the quality of the water studied along the whole basin. The most significant differences in the parameters were observed among the points P1, P2 and P3 in the middle part of the basin of Curu, and P8 and P9 in the low part of the basin, where from the point 6, the river receives waters of drainage of irrigated perimeters and effluents of sewers. In respect of seasonality, an increment in the medium values was observed in the rainy period, justified for the increase of superficial drainage and wash of the salts, originated from the irrigated perimeters located in the basin. With the results of the analysis, the studied waters were classified as chlorinated. / O presente trabalho foi desenvolvido com o objetivo de analisar a variabilidade espacial e temporal da qualidade das águas na região perenizada da bacia hidrográfica do Curu, avaliando os efeitos da ação antrópica e influência dos tipos de solos da região. Foram avaliados os seguintes parâmetros: cátions (Ca2+, Mg2+, Na+, K+), ânions (HCO3 - e Cl-) e demais parâmetros: RAS, Condutividade Elétrica, pH e Sólidos Dissolvidos. Foram coletadas amostras de água em nove pontos distribuídos ao longo do trecho perenizado da bacia do Curu, durante o período de um ano. As analises foram realizadas no Laboratório de Solos e Água da Universidade Federal do Ceará. Os valores médios dos parâmetros foram avaliados em relação a variabilidade espacial e temporal. Realizou-se a Análise de Variância a 5% e de comparação das médias pelo Teste de Tukey a 1% para os dados referentes à variabilidade espacial. Com relação à variabilidade temporal foram analisados os valores médios dos períodos seco e chuvoso para comparação posterior dos resultados e classificação de suas águas através do Diagrama de Piper. Os resultados evidenciaram incremento de sais ao longo da bacia. No ponto 1 (Serrota-Pentecoste) o valor médio encontrado para o sódio foi de 1,92 mmolc L-1, enquanto no ponto 9 (Fazenda Pedras-Paraipaba) foi de 3,47 mmolc L-1 . Ficou nítida a influência antrópica na qualidade das águas estudadas ao longo de toda a bacia, as diferenças mais significativas entre os parâmetros foram observadas entre os pontos P1, P2 e P3 parte media da bacia do Curu e P8 e P9 (parte baixa da bacia do Curu), onde a partir do ponto 6, o rio recebe águas de drenagem dos perímetros irrigados e efluentes dos esgotos. Quanto a sazonalidade, observou-se que de maneira geral houve incremento nos valores médios encontrados no período chuvoso, fato justificado pelo aumento da drenagem superficial e lavagem dos sais oriundos dos perímetros irrigados inseridos na bacia. Com relação à classificação das águas estudadas, as mesmas foram classificadas como cloretadas.