The Basin of Mexico, where the Mexico City Metropolitan Zone (MCMZ) and its 20 million inhabitants are located, has had a two-sided approach towards water management, as it has struggled to drain the lakes that once covered this region while at the same time it started to transport in water from adjacent basins in the 1950s for water supply. In addition, the large amount of water extracted from the Basin's aquifer has caused drawdown of the groundwater table and consequently, land subsidence which reaches 40 cm/yr in some areas.The inhabitants of the Basin of Mexico, which comprises five different political entities and in which different agencies are in charge of water supply rely on the Basin's aquifer system as its main water supply source. After analyzing the existing water management policies in the Basin, this work suggests that in order to improve water management a regional groundwater flow model is needed. In order to develop this regional model, different tasks need to be fulfilled: a regional database is needed and regional estimates of aquifer recharge are also required. In order to develop a regional hydrogeological database in this area, the use of both a Relational Database Management System (RDBMS) and a Geographic Information System (GIS) is proposed in order to improve regional data management in the study area. Data stored in this new database, the Basin of Mexico Hydrogeological Database (BMHDB) comprises data on climatological, borehole and runoff variables, readily providing information for the development of hydrogeological models.This work presents a daily soil water balance which uses different vegetation and soil types as well as the effect of topography on climatological variables and evapotranspiration used to estimate recharge to the regional aquifer. Through the application of this model, it has been shown that the mountains that enclose the Basin of Mexico are the main recharge areas of the Basin's regional aquifer system. The spati / La gestion de l'eau dans le bassin de Mexico (où se trouve la zone métropolitaine de la ville de Mexico avec ses 20 millions d'habitants), a eu deux approches opposées: d'abord on a lutté pour vider les lacs qui couvraient cette région auparavant puis dans les années 50 on commencé a importer de l'eau d'autres bassins.De plus, les grandes quantités d'eau extraites de la couche aquifère du bassin ont causé l'abaissement du niveau de la table d'eaux souterraines et par conséquent, l'aisément du terrain jusqu'à 40 cm/année dans quelques secteurs.Les habitants du Bassin de Mexico, qui comprend 5 entités politiques et où plusieurs organismes sont chargés de la gestion de l'eau, obtiennent leur eau essentiellement de l'aquifère. Après analyse des politiques actuelles de gestion de l'eau du bassin, ce travail suggère qu'a fin d'améliorer cette gestion, un modèle régional d'écoulement d'eaux souterraines est nécessaire. A fin de développer ce modèle régional il faut: une base de données hydrogéologiques et des évaluations de la recharge de la couche aquifère. En ce qui concerne la base de données hydrogéologiques régionale, on propose l'utilisation d'une base de données relationnelle et d'un système d'information géographique, ceci a fin d'améliorer la gestion des données. Les données stockées dans cette nouvelle base de données: "Base de Données Hydrogéologiques du Bassin de Mexico" sont des variables climatologiques, de forage et d'écoulement, fournissant aisément des informations pour le développement des modèles hydrogéologiques.Ce travail présente un bilan quotidien de l'eau (qui considère différents types de végétation et de sol ainsi que l'effet de la topographie sur des variables climatologiques et sur l'evapotranspiration) lequel est employé pour estimer la recharge à la couche aquifère régionale. Par l'application de ce modèle, on a montré que les montagnes qui renferment le bassin du Mexique sont les

Water resource planners need to develop contingency plans to deal with the potential impacts of climate variability and changes in the frequency and magnitude of riverflows. Recently, General Circulation Models (GCMs) have been recognized to be able to represent reasonably well the main features of the global atmospheric circulation for the current climate and could produce details of future climate conditions. This study is concerned with the development of statistical models that could describe accurately the linkage between large-scale GCM simulations and observations of the streamflow process at Eaton, Quebec, Canada. Such a linkage could be used to predict the resulting change of the selected streamflow characteristics from the projected change of climate conditions given by GCMs. These models are based on the application of linear regression methods to link historical streamflow data with climatic predictors at the daily scale as well as on the use of stochastic autoregressive modeling. Results of this numerical application have indicated that the combined regression-autoregressive model with log-normal random noise could provide accurate description of observed statistical daily flow properties at the study site. This model was then used to assess future streamflow conditions from CGCM1 (Coupled Global Climate Model from the Canadian Centre for Climate Modelling and Analysis, version 1) and HadCM3 (Hadley Centre Coupled Model, version 3) outputs for different climate change scenarios. / L'étude des impacts potentiels des changements du climat et de sa variabilité sur les ressources en eau demande de modéliser l'évolution future des débits de rivières. Les Modèles de Circulation Générale (GCMs) sont de récents outils qui fournissent une l'information fiable sur l'évolution future des variables atmosphériques. La présente étude a pour but de développer des modèles statistiques permettant de relier ces variables climatiques aux variables de débit. De tels outils permettraient d'obtenir de l'information sur l'évolution future des débits à partir des simulations GCM. Ces modèles sont fondés sur l'utilisation conjointe à l'échelle journalière de techniques de régression linéaires et de techniques stochastiques autorégressives. En particulier, le modèle combiné régression-autorégression avec une génération aléatoire lognormale de résidus donne des résultats satisfaisants. Ce modèle a été utilisé pour évaluer l'évolution future des conditions de débit en utilisant des scénarios de changement climatique CGCM1 (Modèle couplé climatique global du Centre Canadien de la modélisation et de l'analyse climatique, version 1) et HadCM3 (Modèle couplé du centre Hadley, version 3).

Shallow recirculating flows dominated by bed-friction effect are numerically simulated in this thesis using two-dimensional models. A two-length-scale k-epsilon turbulence model which is based on Reynolds averaged procedure, and a two-dimensional Large Eddy Simulation (2DLES) model based on subgrid stress are employed. The performance of these models is evaluated by comparing the numerical results with the available laboratory experimental data for a range of conditions from deep to shallow water depth. / In the two-length-scale k-epsilon model simulations, the small-scale turbulence is treated as a background component locally in equilibrium, while the large-scale turbulence is modeled by a second-order closure model. Two versions of wall-function models, a high-Reynolds number and a low-Reynolds number wall model, are considered in the implementation of the k-epsilon model. The reattachment length, the recirculation flow rate, and the tracer concentration distribution of shallow recirculating flows are correctly predicted by the k-epsilon model for all of the conducted tests. However, the secondary eddy observed in the experiments in the corner of the main recirculating region is reproduced only when the low-Reynolds-number wall model is implemented. The length of the secondary eddy is ≃25% of the length of the recirculating eddy. / In the 2DLES model, the Smagorinsky model for the subgrid stress is modified taking into account the bed-friction effect. A series of numerical simulations are conducted to determine the Smagorinsky coefficient, Cs, for shallow recirculating flows. The results show that the value of the Smagorinsky coefficient is not constant but it is related to a dimensionless parameter (the bed-friction number, S) and to the size of the numerical mesh. For a mesh size 180 x 60, the Cs ranges from 0.1 to 0.25 for shallow to deep recirculating flows respectively. This range of Cs becomes 0.13 to 0.30 for a mesh size 360 x 120. The secondary (corner) eddy as well as the mean flow characteristics are predicted by the 2DLES model when fine mesh sizes of 180 x 60 and 360 x 120 are used in the simulations. Using the optimum Cs values, the numerical results obtained for all parameters (such as the mean flow, the Reynolds stresses, the mean tracer concentration, and the tracer concentration fluctuations) are in agreement with the laboratory observations. The Strouhal number for the oscillations of the shallow recirculating flows is also obtained from the 2DLES. / Unlike the k-epsilon model which needs a pair of differential equations for k and epsilon, the 2DLES relates stress and strain at the subgrid scale using an algebraic relation. Provided that a correct Cs is selected, the 2DLES model is more stable, easier to implement and hence would be a more suitable simulation scheme for engineering applications.

One of the goals of the Mackenzie GEWEX Study (MAGS) is to model the critical components of the water and energy cycles that affect the climate of the Mackenzie Basin. The land surface - hydrological model WATCLASS is used to simulate the energy and water transports at and below the surface. Atmospheric input to WATCLASS is provided by the output from the atmospheric model GEM. There may be significant uncertainties in the GEM incoming solar radiation due largely to difficulties in simulating clouds and their radiative properties. The question that we address is how these uncertainties affect the simulation of the energy and water budgets of this northern river watershed. / To assess this sensitivity, two series of two WATCLASS model runs are compared. Both runs are driven by atmospheric data from GEM for the 1998--99 water-year, but in the second run shortwave radiation fluxes retrieved from satellite measurements replace the GEM fluxes. Land cover differs in the two series of runs and so provides an assessment of the sensitivity to vegetation variability. Results show that the atmospheric model overestimates the incoming solar radiation field by 36%. This results in an increase in the basin annual average surface temperature of about 1°C and an overestimation in net longwave radiation, and sensible and latent heat fluxes. Snowmelt starts earlier with a decreased first snowmelt peak in runoff and discharge hydrographs. The overall consequence is an annual discharge underestimation.

Spatiotemporal processes occur in many areas of earth sciences and engineering. However, most of the available theoretical tools and techniques of space-time daft processing have been designed to operate exclusively in time or in space, and the importance of spatiotemporal variability was not fully appreciated until recently. To address this problem, a systematic framework of spatiotemporal random field (S/TRF) models for geoscience/engineering applications is presented and developed in this thesis. / The space-tune continuity characterization is one of the most important aspects in S/TRF modelling, where the space-time continuity is displayed with experimental spatiotemporal variograms, summarized in terms of space-time continuity hypotheses, and modelled using spatiotemporal variogram functions. Permissible spatiotemporal covariance/variogram models are addressed through permissibility criteria appropriate to spatiotemporal processes. / The estimation of spatiotemporal processes is developed in terms of spatiotemporal kriging techniques. Particular emphasis is given to the singularity analysis of spatiotemporal kriging systems. The impacts of covariance, functions, trend forms, and data configurations on the singularity of spatiotemporal kriging systems are discussed. In addition, the tensorial invariance of universal spatiotemporal kriging systems is investigated in terms of the space-time trend. / The conditional simulation of spatiotemporal processes is proposed with the development of the sequential group Gaussian simulation techniques (SGGS), which is actually a series of sequential simulation algorithms associated with different group sizes. The simulation error is analyzed with different covariance models and simulation grids. The simulated annealing technique honoring experimental variograms, is also proposed, providing a way of conditional simulation without the covariance model fitting which is prerequisite for most simulation algorithms. / The proposed techniques were first applied for modelling of the pressure system in a carbonate reservoir, and then applied for modelling of springwater contents in the Dyle watershed. The results of these case studies as well as the theory suggest that these techniques are realistic and feasible.

Despite being ubiquitous in the Mackenzie River Basin (MRB) of Canada, the role of snow in its energy and water budgets are still open to much speculation. This thesis presents a multi-scale analysis of the contribution of blowing snow to the hydrometeorology of the MRB. A climatology of adverse wintertime weather events is first presented and demonstrates that blowing snow events are rare within the forested sections of the MRB but become more frequent in the northern parts of the basin covered by Arctic tundra. It is these areas which experience the largest impacts of blowing snow transport and sublimation due to large-scale processes. To further assess the mesoscale and microscale effects of blowing snow to the northern regions of the MRB, the development of a bulk blowing snow model is then described. The single- and double-moment versions of the PIEKTUK blowing snow model are shown to produce equivalent results as a previous spectral version of the numerical model while operating about 100 times faster. The application of the double-moment PIEKTUK model (PIEKTUK-D) to a Canadian Arctic tundra site near the northern tip of the MRB reveals that blowing snow sublimation depletes ≈3 mm snow water equivalent (swe) from the snowpack over a period of 210 days during the winter of 1996/1997 at Trail Valley Creek, Northwest Territories. Various assumptions on the state of the background thermodynamic profiles and their evolution during blowing snow, however, can yield significantly higher (>300%) rates of sublimation over the same period. PIEKTUK-D is then coupled to the Mesoscale Compressible Community (MC2) model for an interactive simulation of a ground blizzard at Trail Valley Creek. This coupled mesoscale simulation reveals that moistening and cooling of near-surface air associated with blowing snow sublimation is observed but mitigated in part by advective and entrainment processes. Combined, blowing snow sublimation and mass divergence are then shown to rem

Climate variability and change are expected to have important impacts on the hydrologic cycle at different temporal and spatial scales In order to build long-lasting drainage systems, civil engineers and urban planners should take into account these potential impacts in their hydrological simulations. However, even if Global Climate Models (GCM) are able to describe the large-scale features of the climate reasonably well, their coarse spatial and temporal resolutions prevent their outputs from being used directly in impact assessment models at regional or local scales. This study proposes a statistical downscaling approach, based on the scale invariance concept, to incorporate GCM outputs in the derivation of Intensity-Duration-Frequency (IDF) curves and the estimation of urban design storms for current and future climates under different climate change scenarios. The estimated design storms were then used in the estimations of runoff peaks and volumes for urban watersheds of different shapes and different levels of surface imperviousness using the popular Storm Water Management Model (SWMM). Finally, a regional analysis was performed to estimate the scaling parameters of extreme rainfall processes for locations with limited or without data. In summary, results of an illustrative application of the proposed statistical downscaling approach using rainfall data available in Quebec (Canada) have indicated that it is feasible to estimate the IDF relations and the resulting design storms and runoff characteristics for current and future climates in consideration of GCM-based climate change scenarios. Furthermore, based on the proposed regional analysis of the scaling properties of extreme rainfalls in Singapore, it has been demonstrated that it is feasible to estimate the IDF curves for partially-gaged or ungaged sites. / La variabilité et les changements climatiques devraient avoir des impacts considérables sur le cycle hydrologique aux différentes échelles spatio-temporelles. Afin de construire des systèmes de drainage durables, les ingénieurs se doivent de prendre en considération ses modifications probables dans leur simulation. Toutefois, si les Modèles de Circulation Globale (MCG) sont capables de reproduire raisonnablement bien les caractéristiques à grande échelle du climat, leurs résolutions sont trop grossières pour permettre une utilisation immédiate de leurs informations dans les modélisations urbaines.Cette étude propose une approche de mise à l’échelle statistique, basée sur les propriétés d’invariance d’échelle, afin d’incorporer les résultats des MCG dans la conception des courbes Intensité-Durée-Fréquence (IDF) futures. Ces courbes sont ensuite utilisées pour l’estimation de l’évolution des quantités de ruissèlement. Enfin, une analyse régionale permet une évaluation des paramètres de réduction d’échelle pour des stations partiellement jaugées, voir non jaugées. C’est ainsi que des courbes IDF peuvent être construites avec un nombre limité de données.

Changes in climate due to anthropogenic influences are expected to affect both hydrological and agricultural systems in southern Africa. Studies on the potential impacts of climate change on agrohydrological systems had been performed previously in the School of Bioresources Engineering and Environmental Hydrology (School of BEEH). However, refinement of these modelling tools and restructuring of the databases used was needed to enable more realistic and dynamic simulations of the impacts of changes in climate. Furthermore, it was realised that modifications and linkages of various routines would result in a faster processing time to perform climate impact assessments at the catchment scale. Baseline ("present") climatic information for this study was obtained from the School of BEEH's database. Scenarios of future climate were obtained from six General Circulation Models (GCMs). Output from the five GCMs which provided monthly climate output was used in the climate impact assessments carried out. Potential changes in variability of rainfall resulting from climate change was assessed using the daily climate output from the sixth GCM. As the spatial resolution of the climatic output from these GCMs was too coarse for use in climate impact studies the GCM output was interpolated to a finer spatial resolution. To assess the potential impact of climate change on water resources in southern Africa the ACRU hydrological modelling system was selected. The ACRU model was, however, initially modified and updated to enable more dynamic simulation of climate change. In previous hydrological studies of climate change in southern Africa Quaternary Catchments were modelled as individual, isolated catchments. To determine the potential impact of changes in climate on accumulated flows in large catchments the configuration of the Quaternary Catchments needed to be determined and this configuration used in ACRU. The changes in hydrological responses were calculated both as absolute differences between future and present values and the ratio offuture hydrological response to the present response. The large degree of uncertainty between the GCMs was reflected in the wide range of results obtained for the water resources component of this study. In addition to the climate impact studies, sensitivity and threshold studies were performed using ACRU to assess the vulnerability of regions to changes in climate. Potential change in the yields and distributions of parameters important to agriculture, such as heat units, crops, pastures and commercial tree species were assessed using simple crop models at a quarter ofdegree latitude / longitude scale. Most species were simulated to show decreases in yields and climatically suitable areas. There are many sources of uncertainties when performing climate impact assessments and the origins of these uncertainties were investigated. Lastly, potential adaptation strategies for southern Africa considering the results obtained are presented. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2001.

South African water management areas could find themselves without enough water for its users due to new methods of performing water allocation as stipulated in the National Water Act of 1998. A water accounting system would address the need for accurate metering, monitoring and auditing of South Africa’s water resources to ensure that users are complying with their allocations. Such a system should be able to provide information such as comparisons between the simulated and observed flow of water at a point, comparisons between the amount of water allocated to a user and the actual water used by that user, and the source and destination of water at a point. This document contains a literature review, an explanation of the methods used to develop a prototype water accounting system and a discussion of the results from testing the system. A literature review was undertaken which covered topics in water resources planning, water resources operations, local legislation for water allocation and new technologies which could be applied to aid the management of water resources in South Africa. The results from the literature review indicated real time water accounting systems can give effect to water allocation rules. The water accounting system is comprised of two simulation models and a database. The models used for the study were the ACRU2000 model and the MIKE BASIN model. These models require data as well as a means to automate the transfer of data between the models and thus a database was developed. The database was developed in Microsoft Access and, in addition to the construction of a number of tables required to house the data, a database dashboard was made to control the functions of the database. An assessment of the ACRU2000 and MIKE BASIN models was performed in order to determine if they are suitable for use as water accounting tools. ACRU2000 was used for its process based, daily rainfall-runoff modelling capabilities. Due to the process based modelling capabilities of ACRU2000, forecasts of rainfall can be used as input to the simulations. Hot starting is the storing of internal model state variables at a particular time and the use of these variables in a different simulation to start the model up again. It was expected that, due to long simulation run times for ACRU2000, it would be beneficial to enable ACRU2000 to be hot started and an attempt to hot start ACRU2000 is presented. This would have allowed for significantly decreased simulation run times as the model can be warmed up for two years and thereafter hot started to run only for one day at a time. An assessment of the MIKE BASIN network allocation model to be used as a water accounting system was performed by attempting to meet the project objectives through building a fictional water supply network. The network is composed of a small catchment containing six runoff generating regions, a reservoir and ten water users. Three network allocation scenarios were constructed in order to fully test the rule sets and allocation capabilities currently available in the MIKE BASIN model. The study has shown that the tools and models used are capable of forming a rudimentary water accounting system. This is encouraging as it shows that there is the potential to improve the water resources management in South Africa using tools that already exist. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

<p> Wildfires dramatically affect hydrologic processes including runoff and erosion, which in turn can impact society. Disturbance by fire creates ecosystem heterogeneity, prompting many species to adapt to fire cycles. Human impacts have altered fire frequency and affected natural systems to the point that additional landscape-scale disturbances may cause a disruption in ecosystem form and function. The altered ecosystems and increased development in forests may exacerbate post-fire impacts, affecting more of the population in fire-prone regions. </p><p> The following three studies will improve our understanding and management of post-fire impacts on stream channel processes. A catchment in eastern Arizona where runoff data were collected between 1962 and 1983 was subsequently burned by a wildfire in 2011. The direct comparison of pre and post-fire runoff showed that the fire made runoff more rapid, increased peak discharge rates, and compressed the time scale of storm hydrographs. These results can help improve post-fire runoff modeling and management efforts. </p><p> The second topic addressed the scaling of sediment delivery across hillslope and small catchment scales. Erosion data used in this study were from the Arizona site and five other sites across the western US. Results from five of the six sites showed that sediment delivery significantly decreased with increasing spatial extent, while the lack of trend at the sixth site illustrates the variability in erosion responses across ecosystems. The relationships developed in this study will help improve estimates of sediment delivery rates at the small-catchment scale using more easily acquired data from small plots. </p><p> The third study addressed whether straw bale check dams reduce post-fire sediment yields or affect ephemeral stream channel morphology. A series of laboratory flume experiments based on measured post-fire field conditions showed that check dams can store sediment from initial runoff events, but that a large number of check dams would be needed to reduce post-fire sediment yields. The stored sediment reduced the local channel gradient, but the check dams did not otherwise affect the channel morphology. These data and field observations were used to develop a check dam classification system that can be applied in ephemeral streams in burned or unburned areas.</p>