L’objectif de la thèse vise à déterminer les facteurs et processus qui contrôlent l’origine et la qualité des eaux souterraines alluviales et ainsi à mieux comprendre le fonctionnement et la vulnérabilité des aquifères alluviaux qui occupent une place prééminente dans le paysage hydrogéologique mondial tant pour leur rôle économique - production d'eau potable, développement agricole - que pour leur rôle écologique. Des mesures hydrodynamiques, hydrochimiques (ions majeurs, traces, molécules phytosanitaires et pharmaceutiques) combinées à des déterminations isotopiques (oxygène-18, deuterium, carbone-13) ont ainsi été effectuées sur 19 points incluant puits, piézomètres et eaux de surface, de février 2011 à novembre 2012, afin d’évaluer l’origine et la qualité de l’eau souterraine dans l’aquifère alluvial de la rivière Allier, un des principaux tributaires de la Loire. La zone d’étude, située près de la ville de Clermont-Ferrand (France), joue par ailleurs un rôle socio-économique majeur, la nappe alluviale de l’Allier constituant la principale ressource en eau potable pour une population d’environ 100 000 habitants. D’un point de vue hydrodynamique, l'eau souterraine circule généralement du sud au nord, avec une alimentation naturelle à partir des coteaux adjacents, dans la partie non-pompée de l'aquifère. Dans la zone de pompage, cette circulation naturelle est modifiée par le pompage qui fait pénétrer l’eau de la rivière Allier dans l’aquifère. La recharge de l’aquifère dépend alors de quatre pôles de mélange : pluie, rivière Allier, coteaux adjacents et partie sud, non-pompée, de l’aquifère. Les résultats chimiques et isotopiques obtenus permettent de cartographier la contribution de chaque pôle de mélange. [...] Ces résultats mettent en évidence la vulnérabilité de l’aquifère face aux pollutions. Les parties méridionale et orientale du site sont affectées par des arrivées d’eaux de qualité médiocre démontrant l’importance de la définition d’un périmètre de protection adaptée. Près de l’Allier, une attention particulière doit être portée non seulement aux pollutions ponctuelles qui peuvent se produire sur le cours de la rivière, mais également aux pollutions chroniques liées notamment aux rejets des stations d’épuration pourvoyeurs de polluants tels les molécules pharmaceutiques. Toutes les informations acquises devront être incluses dans les stratégies de gestion d'eau souterraine afin protéger la durabilité de cette ressource de valeur. Les résultats s’appuient sur les investigations menées sur la nappe alluviale de l’Allier, néanmoins la méthodologie utilisée et sa transposition à des systèmes analogues est l’une des perspectives majeures de cette étude. / Hydrodynamic, hydrochemical (major ions, traces, pharmaceuticals and pesticides), and isotopic investigations (oxygen-18 and deuterium) were carried out on 19 points, including boreholes, piezometer, surface water, and springs from February 2011 to November 2012, to assess groundwater quality in the unconfined shallow alluvial aquifer of the Allier River (one of the main tributary of the Loire River). The study area, located near the city of Clermont-Ferrand (France), plays an important socio-economic role as the alluvial aquifer is the major source of drinking water for about 100 000 inhabitants. The objective of the project aims at understanding the functioning and the vulnerability of alluvial aquifers that occupy a pre-eminent position in the hydrogeologic landscape both for their economic role - production of drinking water and agricultural development - and for their ecological role. Moreover, this study also targets at determining the factors and processes controlling shallow groundwater quality and origin. The water circulates from the south, with a natural alimentation from the hills in the non-pumped part of the alluvial aquifer. In the pumping zone, this general behaviour is altered by the pumping that makes the water from the Allier River enter the system in a large proportion. Four end-members have been identified for the recharge of the alluvial groundwater: rainfall, Allier River, surrounding hills’ aquifer and the southern non-pumped part of the alluvial system. Results indicate that, despite the global Ca-HCO3 water type of the groundwater, spatial variations of physico-chemical parameters do exist in the study area. Ionic concentrations increase from the Allier River towards east due either to the increase in the residence time or a mixing with groundwater coming from the aquifer’s borders. Stable isotopes of the water molecule show the same results: boreholes close to the river bank are recharged by the Allier River (depleted values), while boreholes far from the river exhibit isotopic contents close to the values of hills’ spring or to the southern part of the alluvial aquifer, both recharged by local precipitation. One borehole (B65) does not follow this scheme of functioning and presents values attesting of a probable sealing of the Allier River banks. Based on these results, the contribution of each end-member has been calculated and the functioning of the alluvial system determined. According to this general scheme of functioning, origins of pollution (agricultural, urban) have been determined and clues to the protection of such hydrosystems defined.

Thesis (PhD)--University of Montana, 2009. / Title from author supplied metadata. Contents viewed on May 14, 2010. Includes bibliographical references.

The Mississippi Alluvial Plain, a robust agricultural region in the South-Central United States, provides commodities across the United States and around the world. Water for irrigation, which is necessary due to irregular rainfall patterns during the growing season, is withdrawn largely from the Mississippi River Valley Alluvial aquifer, one of the most intensely used aquifers in the United States. The groundwater-dependent region has observed recent declines in groundwater and streamflow levels, raising concerns about the availability and use of fresh-water resources. Declining water levels have prompted investigation into the current understanding of groundwater and surface-water interaction. Previous research does not adequately quantify the unobservable exchange of water between surface-water bodies and the underlying aquifer. This research was designed to advance the current understanding of the interaction between groundwater and surface water through the quantification of spatial and temporal trends in streamflow and groundwater level changes and the use of high-resolution spatial estimates of streambed hydraulic conductivity. Changes in streamflow and groundwater levels were quantified with the use of hydrograph-separation techniques and trend analyses. High-resolution estimates of streambed hydraulic conductivity were found through the correlation of waterborne continuous resistivity profiling data to hydraulic conductivity and streambed hydraulic conductivity estimates were incorporated into the existing Mississippi Embayment Regional Aquifer Study (MERAS) groundwaterlow model. Site-specific empirical relationships between resistivity and hydraulic conductivity were developed with near-stream borehole geophysical logs to improve model estimates of streambed hydraulic conductivity. Results of the quantification of changes in streamflow and groundwater levels suggested agricultural groundwater withdrawals for irrigation to be the primary source of groundwater-level declines. Results from the incorporation of high-resolution estimates of streambed hydraulic conductivity showed that the existing groundwaterlow model is sensitive to changes in streambed hydraulic conductivity, which may impact model accuracy. The incorporation of streambed hydraulic conductivity estimates derived from site-specific empirical relationships impacted MERAS model water-budget estimates. Information gained from this research will be used to improve the existing groundwaterlow model, which acts as a decision-support tool for water-resource managers at state and local levels to make informed water-use decisions for the conservation of fresh-water resources for sustainable agricultural irrigation practices.

This study investigates the downstream controls of alluvial sediment composition and river channel adjustment in the Llano River watershed, Central Texas, USA. The Llano River watershed is characterized by a highly variable, flood-prone flow regime and a complex lithology of Cretaceous carbonate rock, Paleozoic sedimentary rock, and Precambrian igneous and metamorphic rock. Sedimentary variables for this study include particle size, sorting, carbonate content, and magnetic susceptibility. Channel adjustment includes the planform dimension and cross-sectional dimensions of bankfull- and macro-channels. Nineteen sites along the Llano River and selected tributaries were visited to measure cross-sectional channel geometry and sample bed, bank, and overbank sediment. Laboratory analyses of sediment and hydraulic analyses of cross sections were accompanied by analyses of partial-duration flood frequency, flow resistance, hydrography, digital elevation models, and statistical correlation. Findings include: (1) channel-bed material reduces in size with downstream distance, despite increasing valley confinement and bedrock exposure; (2) the downstream decrease in particle size is more evident for channel-bar deposits than for low-flow-channel (thalweg) deposits; (3) an abrupt gravel-to-sand transition occurs about 20 kilometers downstream of the Paleozoic-Precambrian contact; (4) an abrupt coarse- to fine-gravel transition occurs between 75 and 90 kilometers downstream the North Llano and South Llano Rivers; (5) channel-bank material increases downstream, contrasting with decreases in bed material; (6) carbonate content and magnetic susceptibility of alluvial sediment are inversely related, with carbonate content peaking near Junction; (7) four general categories to classify reaches of the North Llano, South Llano, and Llano Rivers are based on hydrology, planform morphology, lithology, and valley confinement; (8) mean depth increasingly compensates for bankfull discharge in a downstream direction; (9) mean depth compensates more than width for macrochannels; and (10) the return periods for bankfull and macro-channels are about 1 to 2 years and greater than 10 years, respectively. The results of this study will contribute to fluvial geomorphic theory of downstream trends in sediment composition and channel adjustment; as well as inform applied efforts related to aquatic biology, flood hazards, infrastructure design, and riparian and water-resource management in the region. / text

Debris-flows pose serious hazards to communities in mountainous regions of the world and are often responsible for loss of life and damages to infrastructure. Characterised by high flow velocity, large impact forces and long runout, debris-flows have potential discharges several times greater than clear water flood discharges and possess much greater erosive and destructive potential. In combination with poor temporal predictability, they present a significant hazard to settlements, transport routes and other infrastructure located at the drainage points (fan-heads) of watersheds. Thus, it is important that areas vulnerable to debris-flows are identified in order to aid decisions on appropriate land-uses for alluvial fans. This research has developed and tested a new GIS-based procedure for identifying areas prone to debris-flow hazards in the Coromandel/Kaimai region, North Island, New Zealand. The procedure was developed using ESRI Arc View software, utilising the NZ 25 x 25 m DEM as the primary input. When run, it enabled watersheds and their associated morphometric parameters to be derived for selected streams in the study area. Two specific parameters, Melton ratio (R) and watershed length were then correlated against field evidence for debris-flows, debris-floods and fluvial processes at stream watershed locations in the study area. Overall, strong relationships were observed to exist between the evidence observed for these phenomena and the parameters, thus confirming the utility of the GIS procedure for the preliminary identification of hydrogeomorphic hazards such as debris-flow in the Coromandel/Kaimai region study area. In consideration of the results, the procedure could prove a useful tool for regional councils and CDEM groups in regional debris-flow hazard assessment for the identification of existing developments at risk of debris-flow disaster. Furthermore, the procedure could be used to provide justification for subsequent, more intensive local investigations to fully quantify the risk to people and property at stream fan and watershed locations in such areas.

Thesis (M.S.)--University of Nevada, Reno, 2006. / "May 2006." Includes bibliographical references (leaves 40-42). Online version available on the World Wide Web.

Cette thèse est une des premières études géotechniques complète. Son périmètre est la cluse de Grenoble ; le remplissage alluvial, la nappe phréatique et les versants sont étudiés.

Groundwater flow in alluvial valleys consists of two components, baseflow and underflow. The baseflow component of the Darcy flux flows normal to the river and contributes to the surface flow. The underflow component moves downstream in the same direction as the river but at a much slower rate. Underflow is important in Texas because the conjunctive use of groundwater and surface water is regulated by controlling the diversion of underflow by wells. Land owners in Texas are legally entitled to unrestricted use of the underground water beneath their property. Stream underflow, however, has been expressly excluded from the definition of underground water. The distinction is important because it allows the State to legally restrict the non-domestic pumpage of groundwater (in an "underflow zone") near streams. Regulators are interested in controlling pumpage near rivers in order to prevent streamflow depletion. Historically, the underflow exemption has not been well recognized by the courts. In large measure, this may be due to the fact that our understanding of underflow in alluvial valleys is incomplete. If the underflow rule is to be successfully implemented, a complete understanding of the nature and occurrence of underflow is imperative. This study was initiated to: 1) determine the hydrogeologic factors that control underflow (and baseflow) in alluvial valley aquifers in Texas and the United States; and 2) to examine the suitability of the underflow criterion as a management tool for the prevention of streamflow depletion by wells. To accomplish this, a data base of 23 alluvial river basins was compiled and a 3-dimensional digital model of a hypothetical alluvial valley aquifer was constructed. Examples from the data base indicate that alluvial aquifers can be classified into three types based on the predominant regional groundwater flow direction: baseflow-dominated, underflow-dominated, and mixed flow. Flow patterns can be transient, however, and respond rapidly to changing river stage if the aquifer and the riverbed are highly permeable. Therefore, the distinction must be made between local, transient underflow and baseflow occurring near the river and regional, steady state underflow and baseflow away from the river. Underflow dominated aquifers are found in classic bedload depositional settings which are characterized by high channel gradient, high width to depth ratio, low channel sinuosity, and low river penetration. Linear regressions performed on the parameter values in the data base verify the validity of the data. The degree of correlation provides the basis for a method of estimating the predominant regional groundwater flow direction in an alluvial aquifer based on geomorphologic and morphometric data. The results from the digital model agree with the findings from the data base. Digital simulations indicate that the amount of underflow is directly related to the channel gradient, the amount of recharge, the aquifer hydraulic conductivity, and the streambed hydraulic conductivity. The riverbed hydraulic conductivity is the most critical hydraulic factor controlling the amount of underflow. The output from the model is 100 percent underflow at low values of riverbed permeability. Both the model results and published field data do not support the existence of a significant local "underflow zone" adjacent to rivers in large alluvial systems. Close to the river, the baseflow component may predominate even in regionally underflow-dominated systems due to the influence of high transverse valley gradients. There are many problems associated with the use of underflow as a management tool. The definition is vague and ambiguous. Underflow can be transient and spatially variable. Texas alluvial systems are baseflow dominated and there is probably no significant "underflow zone" near rivers. Lastly, the presence of underflow has been difficult to prove in court. It is the finding of this study that the underflow criterion is insufficient to prevent streamflow depletion by wells. The underflow rule in the Texas Water Code should be reconsidered, or perhaps abandoned, in favor of criteria that are more justifiable. / text

Stratigraphic records in Middle Park in north-central Colorado provide evidence for the late Quaternary geomorphic and environmental history of a non-glaciated Southern Rocky Mountain basin. Episodes of geomorphic instability apparent in the stratigraphic record coincide with changes in paleoenvironmental records from above 2750 m in north-central Colorado, suggesting that the western Middle Park landscape was sensitive to environmental changes affecting the region over the last ~14,000 years. Tributaries were incised prior to 14.0 ka, but deposits older than 12.0 ka are rare. Upland erosion and incision followed by rapid aggradation in alluvial settings between 12.0 and 11.0 ka coincide with evidence for regional temperatures at or above present, and is interpreted to signal the onset of Holocene summer-wet precipitation. A widespread soil-stratigraphic marker represents a long period of landscape stability between <11.0 and 6.0 ka in upland and alluvial settings. Pedologic evidence from upland settings indicates the expansion of grass and forest cover to lower elevations that today are characterized by sagebrush steppe, probably during a period of increased summer precipitation relative to present. During the late Holocene, episodes of aggradation in alluvial valleys at 6.0-1.0 ka and 0.6-0.2 ka and soil formation in uplands at 5.0-3.5 ka and 2.5-1.0 ka overlap with evidence for cooling at higher elevations. Incision of valley floors documented at 1.0-0.6 ka and during the last few centuries and episodes of erosion in uplands at 3.5-2.5 ka, after 1.0 ka, and within the last few centuries, are roughly synchronous with evidence for warming. Upland and alluvial stratigraphic records are interpreted to indicate that during cool intervals summer precipitation was diminished, resulting in relative hillslope stability and gradual valley bottom aggradation, while pulses in summer precipitation accompanying warmer episodes caused basin-wide geomorphic instability. The recent increasing frequency of geomorphic instability appears to correspond with an increase in sagebrush steppe at the expense of forest and grass cover, interpreted to represent progressive drying during the late Holocene. It stands to reason that future warming, if accompanied by similar patterns in precipitation, will result in continued erosion on a landscape already at a threshold of geomorphic instability.

Designing monitoring networks that can discriminate among competing conceptual models is a key challenge for hydrologists. This issue is examined by considering the impact of network design on the utility of measurements for constraining hydrologic prediction uncertainty. Specifically, a three-staged approach was developed and is presented as a set of modeling case studies. The first case study presents a sensitivity analysis that examines conditions under which the proposed measurement method is likely to detect observations associated with the hydrologic process and properties of interest. This application is focused on the use of geomorphic information to estimate infiltration on arid alluvial fans.The second stage is an assessment of the likely utility of the measurement method to determine whether proposed measurements are likely to be useful for identifying hydraulic properties or hydrologic processes. This objective screening approach could reduce the number of unsuccessful uses of geophysical and other indirect measurement methods. A hypothetical site assessment examines whether the measurement method, temporal gravity change, is likely to detect signals associated with drawdown in an unconfined aquifer that occurs in response to pumping. Also, the utility of these measurements for identifying hydraulic conductivity and specific yield was considered.The third stage, an analysis of optimal network design, compares the projected measurement costs with the expected benefits of constraining hydrologic prediction uncertainty. The final case study presents a network design approach for a feasibility assessment of a proposed artificial recharge site. Predefined sets of proposed measurements of temporal gravity change were considered for various measurement times. An ensemble approach was used to assess the likely impact of measurement error on prediction error and uncertainty for different combinations of measurement sets. The ensemble of prediction errors was translated to probability-weighted performance costs for each measurement set using a cost function. Total cost was calculated as the sum of the performance and measurement costs. The optimal measurement set, defined as the set with the lowest total cost, depends on the prediction of interest, the per measurement cost, the maximum risk-based cost associated with the hydrologic prediction, and the treatment of uncertainty in defining performance costs.