Determining safe yield of an existing water supply is a basic aspect of water supply planning. Where water is withdrawn from a river directly without any storage, the withdrawal is constrained by the worst drought flow in the river. There is no flexibility for operational adjustments other than implementing conservation measures. Where there is a storage reservoir, yields higher than the flow in the source stream can be maintained for a period of time by releasing the water in storage. The determination of safe yield in this situation requires elaborate computation. This thesis presents a synthesis of methods of drought flow analysis and yield estimation. The yield depends on both the magnitude of the deficit and its temporal distribution. A new Markov chain analysis for assessing frequencies of annual flows is proposed. The Markov chain results compare very well with the empirical data analysis. Another advantage of the Markov chain analysis is that both high and low flows are considered simultaneously; no separate analyses for the lower and upper tails of the distribution are necessary. The temporal distribution of drought flows is considered with the aid of the generalized bootstrap method, time series analysis, and cluster sequencing of worsening droughts called Waitt's procedure. The methods are applied to drought inflows for three different water supply reservoirs in Spotsylvania County, Virginia, and different yield estimates are obtained. / Master of Science

2 pp. / Drip irrigation is the slow, measured application of waer through devices called emitters. Now a wide variety of quality products has been developed to make drip irrigation reliable and easy.

La prévision d'étiage à long terme est l'une des questions émergentes en hydrologie en raison de la demande croissante en eau en période sèche. Des prévisions fiables de débits à longue échéance (quelques semaines à quelques mois à l'avance) peuvent améliorer la gestion des ressources en eau et de ce fait l'économie de la société et les conditions de vie aquatique. Les études limitées sur les étiages dans la littérature nous a conduit à traiter certaines des questions existantes sur l'hydrologie des étiages, principalement sur la simulation et la prévision des étiages. Notre objectif final de développer une approche d'ensemble pour la prévision à long terme des étiages se décline en plusieurs étapes préalables, telles que la caractérisation des étiages, l'évaluation de mesures existantes d'efficacité des simulations des modèles, le développement d'une version améliorée d'un modèle de simulation des étiages, et enfin l'intégration d'une approche de prévision d'ensemble. Un ensemble de bassins distribués partout en France avec une variété de conditions hydro-météorologiques a été utilisé pour l'évaluation des modèles. Cet échantillon de données a d'abord été analysé et les étiages ont été caractérisés en utilisant divers indices. Notre objectif de mieux évaluer les simulations des étiages par les modèles a conduit à proposer un critère basé sur le critère de Nash-Sutcliffe, calculé sur l'inverse des débits pour mettre davantage de poids sur les erreurs sur les très faibles débits. Les résultats montrent que ce critère est mieux adapté à l'évaluation des simulations des étiages que d'autres critères couramment utilisés..Une analyse de sensibilité structurelle a ensuite été menée pour développer une structure de modèle améliorée pour simuler les étiages. Des modèles couramment utilisés ont été choisis ici comme modèles de base pour commencer l'analyse de sensibilité. Le modèle développé, GR6J, atteint de meilleures performances à la fois sur les faibles et les hauts débits par rapport aux autres modèles existants testés. En raison de la complexité du processus pluie-débit et de l'incertitude liée aux conditions météorologiques futures, nous avons développé une approche d'ensemble pour émettre des prévisions et quantifier les incertitudes associées. Ainsi l'approche d'ensemble fournit une gamme de valeurs futures de débits sur la plage de prévision. Ici, la climatologie a été utilisée pour fournir les scénarios météorologiques en entrée du modèle pour réaliser les prévisions. Pour réduire le niveau d'incertitude lié au modèle hydrologique, des combinaisons variées de procédures de mise à jour et de corrections de sortie ont été testées. Une approche directe, similaire à ce qui peut être fait pour la prévision des crues, a été sélectionnée comme la plus efficace. Enfin, des essais ont été réalisés pour améliorer la qualité des prévisions sur les bassins influencés par les barrages, en tenant compte des variations de stockage dans les barrages amont. Testée sur les bassins de la Seine et de la Loire, l'approche a donné des résultats mitigés, indiquant le besoin d'analyses complémentaires. / Long-term stream low-flow forecasting is one of the emerging issues in hydrology due to the escalating demand of water in dry periods. Reliable long-lead (a few weeks to months in advance) streamflow forecasts can improve the management of water resources and thereby the economy of the society and the conditions for aquatic life. The limited studies on low flows in the literature guided us to address some of the existing issues in low-flow hydrology, mainly on low-flow simulation and forecasting. Our ultimate aim to develop an ensemble approach for long-term low-flow forecasting includes several prior steps such as characterisation of low flows, evaluation of some of the existing model's simulation efficiency measures, development of a better model version for low-flow simulation, and finally the integration of an ensemble forecasting approach. A set of catchments distributed over France with various hydrometeorological conditions are used for model evaluation. This data set was first analysed and low flows were characterized using various indices. Our objective to better evaluate the models' low-flow simulation models resulted in the proposition of a criterion based on the Nash-Sutcliffe criterion, but calculated on inverse flows to put more weight on the errors on extreme low flows. The results show that this criterion is better suited to evaluate low-flow simulations than other commonly used criteria. Then a structural sensitivity analysis was carried out to develop an improved model structure to simulate stream low flows. Some widely used models were selected here as base models to initiate the sensitivity analysis. The developed model, GR6J, reaches better performance in both low- as well as high-flow conditions compared to the other tested existing models. Due to the complexity of rainfall-runoff processes and the uncertainty linked to future meteorological conditions, we developed an ensemble modelling approach to issue forecasts and quantify their associated uncertainty. Thus the ensemble approach provides a range of future flow values over the forecasting window. Here observed (climatological) rainfall and temperature were used as meteorological scenarios fed the model to issue the forecasts. To reduce the level of uncertainty linked to the hydrological model, various combinations of simple updating procedures and output corrections were tested. A straightforward approach, similar to what can be done for flood forecasting, was selected as it proved the most efficient. Last, attempts were made to improve the forecast quality on catchments influenced by dams, by accounting for the storage variations in upstream dams. Tested on the Seine and Loire basins, the approach showed mixed results, indicating the need for further investigations.

Implementation of the National Water Act in South Africa requires that an ecological Reserve be determined for all significant resources. The ecological Reserve determination is the estimation of the amount of water required to maintain the system in a particular ecological condition. Because aquatic habitats are defined in terms of local hydraulic variables rather than amounts of water, hydraulic analysis provides a crucial link in relating hydrological conditions and river ecosystem integrity. Over the last decade, considerable effort has been devoted to developing hydraulics for the Reserve determination. The hydraulics needs for Reserve determination are primarily for low flow analysis, and appropriate methods still need to be developed. This thesis deals with hydraulics under low flow conditions. Its emphasis is on developing appropriate methods for describing the hydraulic characteristics of South African rivers under conditions of low discharge, and the influence of vegetation and large bed roughness. The following methods have been developed: · A new equation for prediction of overall flow resistance under large-scale roughness, and a new approach for estimation of intermediate-scale roughness resistance that distinguishes the influences of large and intermediate scale roughness components. · Prediction methods for velocity distributions with large roughness elements. Under low flows, rocks and boulders may control the local velocity and depth distributions. Distributions of velocities and depth are related to rapidly spatially varied flow caused by the boundary geometry rather than flow resistance phenomena. With increasing discharge, the multiple local controls become submerged and the flow tends towards a resistance controlled condition. Available information addressing the distinction between resistance controlled and multiple local controls conditions is limited. This thesis contributes to understanding the transformation between multiple local controls and the resistance controlled conditions. · Practical conveyance prediction methods for three situations pertaining to the occurrence of vegetation in rivers and wetlands. In-channel and riparian vegetation makes an important contribution to the creation of physical habitats for aquatic animals, but also has significant effects on flow resistances that need to be predicted.

Upon the enactment by the United States Congress of the 1992 Energy Policy Act, it became mandatory that all water closets in residential and commercial settings reduce the volume of water that they consume per flush. In 1994, after installations began of the new low-flush or low-flow water closets that used less than half the water that their predecessors used, many owners of the new plumbing fixtures began to complain that their performance was sub par. Many complained about plumbing backups and of complete bowl clearance problems. There have been studies conducted to evaluate the new water closets’ bowl evacuation properties. This study focuses on what happens to the solid waste that is flushed through the water closet after leaving the bowl, namely how far the solid media is transported down waste piping. The main focus of this study is to compare the performance of the low-flush, 1.6 gallons (6 liters) per flush water closets with the performance of the formerly standard flush 3.5 gallons (13 liters) per flush in regards to how far they transport solid waste through waste lines. It was found that the media flushed through the high volume water closets traveled significantly farther that the media flushed through the low-flush water closets. It was often more than double the average distance. It was also found that media traveled farther down pipes composed of PVC than those composed of cast iron and also traveled farther down three inch pipes than four inch pipes.

Cette thèse a pour objectif d'apporter une contribution scientifique et technique à la problématique opérationnelle visant l'évaluation de la ressource en eau disponible en période d'étiage. Cet état des lieux constitue en effet un pré-requis indispensable à toute action de gestion destinée à concilier et équilibrer les différents usages à l'échelle du bassin versant. Il est alors essentiel de tenir compte des particularités du milieu en question pour adapter les différents dispositifs de gestion au contexte hydro-climatique local. A cet égard, l'indicateur statistique retenu par la réglementation française pour caractériser l'état de la ressource en période de basses eaux correspond au débit moyen mensuel minimum annuel de fréquence quinquennale sèche (noté QMNA5). Ce dernier constitue donc notre principal objet d'étude. Dans l'idéal, la détermination d'un tel débit de référence requiert néanmoins un suivi des débits en continu sur une période suffisamment longue pour constituer une archive statistiquement exploitable et n'est par conséquent possible qu'au droit d'un nombre limité de stations hydrométriques. Ailleurs il est alors nécessaire de faire appel à des techniques d'estimation que l'on souhaite aussi fiables que possible. Cette problématique offre encore à l'heure actuelle de nombreuses perspectives de recherche auxquelles cette thèse, en s'inscrivant dans la continuité de travaux analogues réalisés ces dernières années aussi bien en France qu'à l'étranger (décennie PUB), tente d'apporter quelques éléments de réponse et de réflexion. Au cours de ces travaux nous nous sommes ainsi donnés pour objectif d'élaborer et d'optimiser, sur la base des techniques existantes, un cadre méthodologique cohérent adapté à l'estimation du QMNA5 et passant notamment par la valorisation de l'ensemble de l'information à caractère hydrologique disponible localement le long du réseau hydrographique, que ce soit sous la forme de jaugeages épisodiques ou de chroniques courtes. Cet effort d'exhaustivité et de synthèse, s'il n'est pas tout à fait novateur, reste assez peu courant et constitue probablement l'un des principaux points forts de ce travail. Parallèlement et quelle que soit l'approche d'estimation envisagée, nous nous sommes constamment attachés à fournir une indication sur la fiabilité de chaque valeur estimée au travers d'un intervalle de confiance. Bien qu'apparaissant comme un critère essentiel pour apprécier la validité des résultats obtenus, la détermination d'une incertitude encadrant les valeurs estimées s'avère le plus souvent négligée dans la littérature scientifique relative à la régionalisation de variables hydrologiques ; cette démarche apparaît ainsi comme le second point fort de ces travaux. Pour répondre à ces objectifs, les modalités optimales d'estimation du QMNA5 ont été identifiées au travers d'une procédure systématique de validation croisée et finalement appliquées pour notamment aboutir à une cartographie nationale du QMNA5 spécifique en tout point du réseau hydrographique. A l'issue de cette application, l'un des résultats présentant sans doute le plus d'intérêt passe par la comparaison des performances d'estimation selon la quantité d'information disponible au site cible. Celle-ci montre bien que la valorisation d'une information hydrologique locale, même très fragmentaire, est susceptible d'accroître de manière significative la fiabilité des estimations obtenues par rapport à une estimation en sites non jaugés. Bien entendu le gain de performance est d'autant plus intéressant que la quantité de données disponible est importante. Ainsi l'exploitation de chroniques courtes apparaît logiquement comme plus avantageuse que la valorisation de données de jaugeages. / Estimating water availability along the river network is a pre-requirement for water management purposes before defining water allocation at catchment scale. In France, rules for water allocation is partly based on QMNA5, the annual minimum monthly flow with a return period of 5 years ; QMNA5 is derived from time series with extended records of natural or naturalized discharges at gauged sites. In most cases, data is not warranted. Three contexts can be identified: (i) gauged site with short records, (ii) site with spot gauging data and (iii) no data available.This thesis aims at developing a general framework for estimating QMNA5 by using all the hydrological data available in the neighbouring of the location of interest (including short discharge records and spot gauging data). Different methods and strategies were adapted to data availability and tested on a large dataset. Their efficiency and sensitivity to the data collection strategy, the definition of neighbouring,… were assessed by cross validation and uncertainties were provided through a confidence interval. Lastly the most efficient methods for deriving QMNA5 are used to draw a national map with estimates along the main river network.In conclusion, one of most significant result can be illustrated by comparing the efficiency of the estimates according to the quantity of information available on the target location. Results show that a significant gain in accuracy in the estimated QMNA5 values, even when using only a few sporadic measurements to supplement regional information. The improvement depends on the amount of available data and the use of short record is logically more advantageous than the valuation of spot gauging data. Nevertheless, spot gauging data may offer obvious advantages in terms of monitoring at locations where embedment of a permanent gauging station is uneasy. Therefore using spot gauging data can be seen as a possible cost-effective trade-off to supply a reliable enough estimation for particular location of interest.

The reliability of future water supplies comes into question with the onset of global climate change and the variations in local weather patterns that it brings. Changes in temperature, precipitation, soil moisture, and sea level can all have an impact on drinking water storage and supply. As these impacts are realized, it is increasingly important to use forward projecting estimates of future supply through the use of general circulation models (GCMs). GCMs can be used to predict changes in local weather over the next century. Using GCM data as input to a hydrologic model of local water supplies, water supply managers can assess and be better prepared for the impact of these possible changes. Land use/demand in particular has an impact on runoff characteristics within a watershed. By incorporating changes in land use/demand into hydrologic model simulations, a more complete picture can be generated of the possible runoff characteristics, and thereby source water supply. The four land use scenarios used in this study are: 1) present day land use/demand; 2) projected land use/demand to 2040; 3) projected land use/demand to 2070; and 4) projected land use/demand to 2100. This study uses established techniques to incorporate both climate and land use/demand change into a hydrologic model of the Occoquan watershed, which encompasses an area of approximately 1,550 square kilometers in Northern Virginia, U.S.A., and is part of the drinking water supply to approximately 1.7 million residents. / Master of Science

During periods of reduced precipitation, flow in low-order, upland streams may be reduced and may stop completely. Under these "low flow" conditions, fecal bacteria directly deposited in the stream dominate in-stream bacteria loads. When developing a Total Maximum Daily Load (TMDL) to address a bacterial impairment in an upland, rural watershed, direct deposit (DD) fecal bacteria sources (livestock and wildlife defecating directly in the stream) often drive the source-load reductions required to meet water quality criteria. Due to limitations in the application of existing watershed-scale water quality models, under low-flow conditions the models can predict unrealistically high in-stream fecal bacteria concentrations. These unrealistically high simulated concentrations result in TMDL bacteria source reductions that are much more severe than what actually may be needed to meet applicable water quality criteria. This study used the Hydrological Simulation Program-FORTRAN (HSPF) to compare three low-flow DD simulation approaches and combinations (treatments) on two Virginia watersheds where bacterial impairment TMDLs had been previously developed and where low-flow conditions had been encountered. The three methods; Flow Stagnation (FS), DD Stage Cut-off (SC), and Stream Reach Surface Area (SA), have all been used previously to develop TMDLs. A modified version of the Climate Generation (CLIGEN) program was used to stochastically generate climate inputs for multiple model simulations. Violations of Virginia's interim fecal coliform criteria and the maximum simulated in-stream fecal coliform concentration were used to compare each treatment using ANOVA and Kruskal Wallis rank sum procedures. Livestock DD bacteria sources were incrementally reduced (100%, 50%, 15%, 10%, 5%) to represent TMDL load reduction allocation scenarios (allocation levels). Results from the first watershed indicate that the FS method simulated significantly lower instantaneous criterion violation rates at all allocation levels than the Control. The SC method reduced the livestock DD load compared to the Control, but produced significantly lower instantaneous criterion violation rates only at the 100% allocation level. The SA method did not produce significantly different instantaneous criterion violation rates compared to the Control. Geometric mean criterion violation rates were not significantly different from the Control at any allocation level. The distributions of maximum in-stream fecal coliform concentrations simulated by the combinations SC + FS and SC + SA + FS were both significantly different from the Control at the 100% allocation level. The second watershed did not produce low-flow conditions sufficient to engage the FS or SC methods. However, the SA method produced significantly different instantaneous violation rates than the Control at all allocation levels, which suggests that the SA method continues to affect livestock DD loads when low-flow conditions are not simulated in the watershed. No significant differences were found in the geometric mean violation rate or distribution of maximum simulated in-stream fecal coliform concentrations compared to the Control at any allocation level. This research suggests that a combination of the SC and FS methods may be the most appropriate treatment for addressing unrealistically high concentrations simulated during low-flow conditions. However, this combination must be used with caution as the FS method may increase the maximum simulated in-stream fecal coliform concentration if HSPF simulates zero volume within the reach. / Master of Science

Master of Science / Department of Architectural Engineering and Construction Science / Thomas Logan / Typical building sanitary lines are sloped at a minimum of 1/8” to utilize gravity and prevent liquid separation from solid waste. The purpose of this research is to analyze how a lesser amount of water from a 1.6 gallon per flush water closet affects drainage in a four inch diameter pipe at 1/4" slope. Low flow water closet manufacturers ensure that waste clears the bowl, but there is no significant research following the flushed water further down the pipe line. This research utilizes a 1.6 gallon per flush floor-mounted water closet connected to 30 feet of sloped four inch PVC Drain Waste Vent piping. Data presented from 25 flush trials indicates that further research needs to be conducted at a smaller pipe diameter. Four-inch piping is too large, causing the 1.6 gallons of water to quickly lose the required force over the course of 30 feet, resulting in pipe line clogs. An average of four additional water-only flushes are necessary to completely clear the test media and toilet paper from the pipe. This research references previously published research and focuses on test results presented by the Plumbing Efficiency Research Coalition. Two case studies of city wide replacements of old water closets are presented to discuss the viability of city wide mandates in relation to water conservation.

Thesis advisor: Noah Snyder / Increasing attention has been drawn to the need for reliable streamflow estimates at ungaged locations under a range of climatic and hydrologic conditions. Climate projections for the northeastern United States over the 21st century--which include significant increases in temperature and precipitation--could have broad impacts on streamflows, potentially reducing the accuracies of existing streamflow models for the region. This thesis investigates recent changes in daily flow-durations in southern New England, and examines their influence on the reliability of the low-flow models for Massachusetts presented by Ries and Friesz (2000). An analysis of discharge data collected at gaging sites through water year 2012 revealed increases in nearly all flow durations at sites across southern New England since the mid-20th century, whereas very low flows (quantiles at or above the 95-percent exceedance probability) generally showed decreases, especially since the 1990s. Twenty-year moving streamflow quantiles at each of ten selected exceedance probabilities were examined for the periods of record of 16 streamflow-gaging stations in southern New England. The beginning of water year 1992 appeared to mark an inflection point in low-flow quantiles, before which very low flows were steady or increasing, and after which these flows showed near-universal decreases. While the observed peak in 20-year low-flow quantiles around 1992 may be due to the statistical method used to calculate the quantile trends, the inflection point could also be an indicator of when increasing evapotranspiration surpassed increasing precipitation as the principal climatic driver of changes in low flows in southern New England. The general upward translation of the flow-duration curve observed over the last 60 years is very likely linked to increases in annual precipitation during this period, while the decreases in very low flows are likely due to changes in climatic variables (increasing summer temperatures and evapotranspiration rates), and amplified by anthropogenic factors (greater areas of impervious surfaces and increasing rates of surface- and ground-water withdrawal). The data suggest that increasing precipitation rates have already caused the Ries and Friesz (2000) equations for the median low flows (Q50 to Q75) to become biased towards underestimation, and decreases in very low flows threaten to render the models for these flows biased towards overestimation in the coming decades. The streamflow quantile trends (for both the entire period of record of the gaging stations and just the post-1992 period) for each of the ten flow-durations of interest were extended into the future to the point where the corresponding Ries and Friesz (2000) model would fail (when actual flow durations would be outside the 90-percent prediction intervals for the estimated flows for greater than 10% of sites). The models for the lowest streamflows are estimated to lose validity by as early as 2018. Climate change is predicted to have significant effects on streamflow characteristics in southern New England over the 21st century, and the results of this study indicate that the Ries and Freisz (2000) low-flow models should be reformulated using more recent streamflow data within the next decade, and validated every 20 years thereafter to ensure their accuracies are maintained despite the effects of regional nonstationarity. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.