Master of Arts / Department of Geography / Jida Wang / Monitoring salt pans is important especially for agricultural management in arid or semi-arid regions because salt pans can negatively affect human life, wildlife, and ecology. Some of the harmful impacts of salt pans are accelerated desertification, cropland loss, economic downturn, wildlife loss, and forced migration of humans and animals due to salt storms. Spectral salt pan indices based upon remotely sensed data (using spectral properties of Landsat-8 imagery) suggested in previous studies vary by location. In other words, the spectral configuration of a salt index for a given location may not be readily applicable to another location due to spatial heterogeneity of salt components across the continental surface. Using Landsat-8 OLI imagery and climate data sets, this study aims to develop a mapping framework which can effectively extract salt pans and salt playas under various spectral conditions in different geographic locations. Based on training samples selected in eight major salt pans/playas in North America, Central Asia, Africa, and Australia, the mapping framework was designed to include the following steps: i) a conservative salt index to highlight potential salt-covered regions, ii) a calibrated support vector machine (SVM) to extract high-salinity areas in the mask regions, and iii) a posterior quality assurance/ quality control (QA/QC) with assistance of auxiliary datasets (e.g., surface slope and land covers) to eliminate commission errors and refine the extracted saltpan areas. The developed mapping framework was validated in the arid endorheic regions across the western United States, with a total area of 699 thousand square kilometers. Both qualitative and quantitative assessments of the results show reliability of the developed framework. The overall accuracy of the extracted salt pans prior to QA/QC is 97%. The final product after QA/QC achieves an overall accuracy of 99.95% and a Kappa statistic of 0.99.According to the results of salt pans areas and endorheic basins areas, it can be concluded that two aforementioned variables of this study are positively correlated to each other, and 1.10 percent of the entire case study area is covered by salt pans. The accuracy of the results suggests a potential that the mapping framework, together with the collected training sample and algorithms, may be applicable to identify salt pan and salt playa regions across the Earth’s land surface.

La dépression du Chott El Djérid constitue l'un des bassins endoréiques salins les plus importants dans le monde. Au cours du stade d'inondation, le Chott est rempli par deux lacs temporaires localisés au centre du Chott et séparés par la digue-route P16, suite à des pluies abondantes et/ou la remontée de la nappe souterraine. Les variations spatiales du cycle inondation-assèchement sont marquées par une inondation et un assèchement plus rapide dans la partie au sud de la digue-route que celle au nord. Les variations temporelles sont illustrées par la comparaison de ce cycle entre les inondations de l’hiver 2009, du printemps 2007 et de juin 2014 au cours de la période sèche. Au cours de ce cycle entre avril et août 2007, les valeurs de réflectance ont varié de 2 à 37 % au sud de la digue-route et de 2 à 31 % au nord. Elles sont donc plus élevées et leur augmentation est en moyenne plus rapide au sud de la digue-route qu’au nord. Les processus évaporitiques du Chott sont contrôlés par les processus hydriques et éoliens. Après l'assèchement du lac, les croûtes évaporitiques du Chott comprennent un assemblage de minéraux dominé par la halite sur la marge méridionale de la digue-route et par le gypse au nord de celle-ci. Les croûtes gypseuses apparaissent dynamiques dans l'espace et le temps et sont distribuées plus largement que les croûtes de halite. Les données LSR (Landsat Surface Reflectance) ont fourni des indications sur la minéralogie des évaporites, même si elles sont à moyenne résolution spectrale. L’étude a apporté également des informations sur les autres unités de paysage telles que les aïoun, la bordure sableuse, etc. / Chott El Jerid is one of the most important endorheic salt lake or playa lakes in the world. During the flooding stage, the Chott is mainly filled by two temporary lakes separated by the causeway P16, after high rainfalls and/or groundwater recharge. Spatial variations of flooding-desiccation cycle are illustrated by a faster flooding and drying on the southern edge of Chott than the northern. The temporal variation was illustrated by the comparison between the winter flood in 2009, the spring flood in 2007 and the flood of June 2014 (the only flood during the dry period). During this cycle between April and August 2007, the reflectance values varied from 2 to 37 % to the south of the causeway and from 2 to 31 % to the north. The reflectance values are higher and their increase was faster to the south of the causeway than to the north. The behaviour of precipitation, concentration and distribution of the evaporites on the Chott follows the behaviour of flooding and desiccation. After the final desiccation of the playa lake, the mineralogy of salt crusts comprised an assemblage dominated by halite to the south of the causeway and by gypsum to the north. Gypsum crusts appear highly dynamic in space and time, and they are more widely distributed than halite crusts. The LSR (Landsat Surface Reflectance) data provide information about the mineralogical nature of evaporites of the Chott, although LSR offers only a medium spectral resolution. The study also provided information on the other landscape-units such as aioun, the sandy border, etc.

Le bassin crétacé de Tsagaan Els est situé dans le désert de Gobi en Mongolie. L’objectif de cette thèse est de mieux comprendre le fonctionnement hydrogéologique et hydrochimique de ce bassin endoréique afin de faciliter l’implantation de futurs projets miniers. Dans cette optique, un modèle hydrogéologique régional 3D a tout d’abord été développé sous MODFLOW. La calibration à partir des niveaux piézométriques mesurés sur les ouvrages présents au sein des licences et quelques puits nomades, aboutit à plusieurs solutions. Elles présentent chacune des conductivités hydrauliques en accord avec les tests de pompages, et des taux de recharge entre 0.6 et 3.1 mm/an, cohérents avec le climat actuel. Ce modèle a ainsi permis d’étendre nos connaissances piézométriques au-delà des licences et d’effectuer un bilan hydrique régional. Ensuite, l’âge des eaux a été estimé numériquement via ce modèle puis par des datations 14C. Une comparaison des résultats de ces méthodes a indiqué que les solutions présentant des taux de recharges élevés étaient plus probables que celles en présentant de plus faibles à conditions que les écoulements soient restés les mêmes durant les trente derniers milliers d’années. En parallèle, une étude hydrochimique portant sur les ions majeurs, le brome et les isotopes stable de l’eau (18O et 2H) a montré que l’origine de la salinité des eaux était principalement liée à la dissolution d’évaporites superficielles. En dernier lieu, un modèle 3D local, centré sur la playa terminale du bassin a permis de mieux comprendre le fonctionnement actuel et passé du bassin en s’appuyant sur l’évolution spatiotemporelle de la salinité. / The Tsagaan Els basin is located in the Gobi desert, in Mongolia. This thesis aims to better understand the hydrogeology and hydro-chemistry of the basin in order to optimize the future mining projects. To this end, a 3D groundwater flow model of the basin has first been developed under MODFLOW. The latter was calibrated using piezometric network data and levels in a few nomadic wells. Several solutions were found with hydraulic conductivity values in agreement with pumping tests and recharge rates between 0.6-3.1 mm/yr in agreement with the current climate. The model helped us to extend our piezometric knowledge beyond AREVA’s mining licenses and to establish a regional water balance model. Groundwater age was then estimated with this model and with 14C dating. A comparison of the results of these two methods showed that calibrated solutions with higher recharge are more likely than those with lower recharge under the hypothesis that groundwater flow has not changed significantly during the last 30 kyrs. Meanwhile, a hydrochemical study using major ions, bromines and the stable isotopes of water (18O and 2H) showed that groundwater salinity mainly comes from dissolution of surficial evaporites: likely gypsum and halite and possibly thenardite. Even though evaporation is the main driving force of the groundwater flow, this process, when taking place in subsurface, seems to have no real influence on δ18O and δ2H values of the groundwater. Last a 3D local groundwater flow model centered on the terminal playa and based on the spatiotemporal evolution of the salinity, led us to a better understanding of the past and current hydrogeological functioning of the basin.

This dissertation examines the influence of urbanization on urban drainage and rainwater management. This is a study focusing on the endorheic basin located north of the plateau of the city of Maceió-AL. This basin has the function to recharge underground aquifers used for water supply. Since the twentieth century, Maceió-AL is growing rapidly through urban peripheral areas, especially on the part of the plateau. The growth of the waterproofing, with the construction of housing, unbalanced the basin hydrological cycle and impaired endorheic infiltration of rainwater. The urban growth has caused flooding because of non-efficient urban drainage system. The urbanization of the basin endorheic is not compatible with their environmental needs, this is your main problem. There is a hypothesis of two sides: one hand, the pattern of occupation in the built environment causes damage because it is horizontal with large impermeable area; on the other hand, the not built spaces are many and help the water cycle because they can be used for rainwater management, reducing the flooding. The main goal of research is to analyze the relationship between the pattern of occupation in the built environment and on not built spaces and implications for drainage and rainwater management of basin endorheic. Four steps were used to research: (i) document review and bibliography; (ii) data gathering; (iii) organization of information collected; (iv) suggestion of preliminary solutions. The results indicated that occupancy rates in the built environment are high and reach 100% in most homes, because of new buildings and retreat waterproofed. The spaces not built are underutilized, there is little vegetation and few community facilities moreover there is a tendency to occupation by new construction. It was concluded that the basin endorheic needs a kind of construction with low occupancy rates, with not built spaces and permeable, which facilitates the recharge of aquifers through rainwater management. / Fundação de Amparo a Pesquisa do Estado de Alagoas / A presente dissertação tem como proposta central analisar a influência da urbanização sobre a drenagem urbana e o manejo das águas pluviais. Trata-se de um estudo de caso centrado na bacia endorreica localizada a norte do tabuleiro da cidade de Maceió-AL, que possui a função particular de recarregar os aquíferos subterrâneos essenciais para o abastecimento de água local. A intensificação da impermeabilização com a construção de diversos conjuntos habitacionais, em meados do século XX, provocou um severo desequilíbrio ao ciclo hidrológico da bacia endorreica, chegando a prejudicar a infiltração das águas pluviais e a recarga dos aquíferos. Em paralelo ao crescimento urbano tornaram-se constantes os alagamentos provenientes de medidas pouco eficazes de drenagem urbana. O trabalho parte de duas premissas. A primeira parte do princípio que o padrão de ocupação dos espaços construídos provoca prejuízos, pois é do tipo horizontal com grande área impermeável. A segunda parte do princípio que os espaços livres de construção se distribuem em grande número e são benéficos ao ciclo hidrológico já que podem ser utilizados para o manejo das águas pluviais como forma de sanar os constantes alagamentos ocorridos no local. Desta forma, a pesquisa tem como objetivo principal analisar a relação padrões de ocupação dos espaços construídos versus espaços livres de construção e sua influência sobre os processos naturais da bacia endorreica. Para tanto, utilizou-se de quatro etapas de pesquisa, são elas: (i) revisão documental e bibliográfica; (ii) levantamento de dados; (iii) sistematização das informações coletadas; e (iv) proposição de soluções preliminares. Os resultados indicaram que o padrão de ocupação dos espaços construídos de uso residencial é o que mais se destaca, os loteamentos predominam e possuem elevadas taxas de ocupação do solo. Os espaços livres de construção encontram-se, em sua maioria, subutilizados, a vegetação é rarefeita e há poucos equipamentos comunitários, além disso, sofrem pressão do setor imobiliário para sua rápida ocupação. Concluiu-se que a bacia endorreica necessita de baixas taxas de ocupação do solo e que seus espaços livres devem ser permeáveis, de modo a viabilizar a infiltração e a recarga dos aquíferos subterrâneos.