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<p>Climate change, increasing demand and overuse have resulted in water stress, a condition where available water resources are not enough to meet needs, in many parts of the US. At the same time, increasing seasonal precipitation, and more intensive management practices mean subsurface drainage is expanding in the Midwest, which has resulted in significant nutrient loading to water bodies and changes to the hydrologic balance of river basins. To ensure the sustainability of water resources, it is crucial to understand how much water available, and how agricultural water use is impacted by changing weather, stress and legal conditions. Water use systems must be properly managed to ensure prosperous agricultural production, and secure water resources. The overall goal of this research is to evaluate the sustainability of groundwater resources in the US through better quantification of surface and groundwater use and the interactions with agricultural water management practices.</p> <p>Watershed-scale measures of surface water and groundwater stress were calculated to explore the spatial and temporal variability of water stress in the US. Much of the Western US, which has been in a water stress situation for 35 years (1985-2015), is shifting to increasing surface water use, but both groundwater stress and surface water stress are continuing to rise. An increase in groundwater stress has also been observed in isolated watersheds in the eastern United States. The pattern of rising surface water stress corresponds more closely to changes in water use, whereas the pattern of rising groundwater stress corresponds to changes in water supply. It has been observed that those watersheds that experienced water stress in 1985 have responded by increasing their water withdrawals from other sources, but they have not decreased their agricultural water withdrawals.  </p> <p>The decision to invest in groundwater irrigation depends on physical water availability and cost, as well as the right to use the water, as determined by groundwater doctrines. Overall, groundwater withdrawals for irrigation have increased in humid and temperate regions, and irrigation per unit area has also increased across the US. At the same time, the fraction of irrigation coming from groundwater is growing, suggesting a potential shift in the preferred water source. This is especially true in states following absolute ownership, correlative rights, and reasonable use doctrine. Correlative Rights doctrine prevalent in the western Corn Belt and Absolute Ownership doctrine (Indiana) appears to encourage increasing groundwater withdrawals during times of stress. These states increase their irrigation rate and the fraction of groundwater withdrawals for irrigation when less surface water is available.</p> <p>Subsurface drainage is common practice across vast areas of the US’ Corn Belt. Subsurface drainage can provide a better growing environment for crops, removing the excess water from the root zone and improving the trafficability of the soil. However, by lowering the water table, drainage has the potential to reduce groundwater recharge. Controlled drainage allows the user to control the water table by adjusting the height of the outlet to limit the subsurface flow during the non-growing season. To better understand the mechanism of how agricultural drainage practices influence aquifer recharge, the VIC model was utilized to represent subsurface drainage and groundwater storage in the Upper Wabash River basin. When using controlled drainage, the rate of recharge increased compared to the rate of free drainage. The mean annual difference between free drainage and controlled drainage was 16 mm/year for the 30 years study period (1983 to 2012). Controlled drainage also contributes greater stream baseflow, increasing low flows relative to free drainage. Despite excess seasonal water that requires the use of subsurface drainage, it is important to note that there have been local conflicts caused by well failures, in Indiana and neighboring states during times of drought, so the local impact of agricultural practices on groundwater is important. This dissertation increases understanding of the impact of agricultural drainage practices on water resource availability. </p>

Heavy metal contamination in the environment is a global issue that is likely to increase in the future. This report investigates a construction area in which increased concentrations of the heavy metals cadmium, cobalt, copper, nickel and zinc and a decreased pH-value has been observed in the surface water recipient. The focus is on assessing contamination characteristics and identifying suitable remediation methods to avoid a river protected by environmental quality standards further downstream from getting contaminated. The bedrock in the area is sulphide containing and releases acidic leachate when oxidising, which is assumed to have occurred due to plane blasting and filling of residual rock. The contamination characteristics were assessed with the statistical methods modified double mass analysis and principal components analysis. A water balance was established to obtain the flowrates, discharge volumes and to determine the masses of the released metals in the surface water. Identification of suitable remediation methods was performed through a literature study of available remediation methods and using the findings of the assessments as basis. The results showed that there was a significant increase in metal concentrations and decrease in pH-value roughly around the same time as blasting and filling of residual rocks in the area was begun and that there were elevated levels of sulphide and sulphur, but they could not be specifically linked to any media. The yearly masses of metals released from the area into the surface water were between 77-98 % higher than allowed by the established guidelines. By separating the water assumed to carry the majority of the contaminants from the remaining natural water in the watershed, the volume that needs to be treated can be halved. As the contamination is so extensive, a mixture of remediation methods was proposed, including installing green roofs to decrease the runoff from the area, confining the crushed rock with bentonite and installing a filter for fast, efficient reduction. For long-term remediation, it is suggested to optimise the existing sedimentation basins and wetlands. The conclusions were that it will be very expensive to remediate the contamination, due to the extent and magnitude, and that handling sulphide containing bedrock for construction purposes should be legally regulated in order to avoid negative environmental and economic impacts. / Förorening av tungmetaller i naturen är ett globalt problem som troligtvis kommer öka i framtiden. Den här rapporten undersöker en byggarbetsplats där ökade koncentrationer av metallerna kadmium, kobolt, koppar, nickel och zink samt ett minskat pH-värde har observerats i ytvattenrecipienten. Fokus ligger på att analysera föroreningskaraktärer och identifiera lämpliga åtgärdsmetoder för att undvika att en å nedströms som är skyddad av miljökvalitetsnormer ska förorenas. Berggrunden i området är sulfidförande och släpper ut surt lakvatten när den oxiderar, vilket är antaget har hänt till följd av plansprängning och utfyllnad av överblivet bergmaterial. Föroreningskaraktärerna analyserades med de statistiska metoderna modified double mass analysis och principalkomponentsanalys. En vattenbalans etablerades för att ta fram flöden, volymer och för att bestämma massorna av de frigjorda metallerna i ytvattnet. Identifiering av lämpliga åtgärdsmetoder gjordes med en litteraturstudie av tillgängliga metoder som grund. Resultaten visade att det är en signifikant ökning av metallkoncentrationer och minskning i pH-värde runt samma tid som sprängning och utfyllning av bergmaterial påbörjades samt att det är förhöjda halter av sulfid och svavel, men de kunde inte bli associerade med ett specifikt media. De årliga massorna av frigjorda metaller som släpps ut från området i ytvattnet är mellan 77-98 % högre än tillåtet av de etablerade riktlinjerna. Genom att separera vattnet som kan antas innehålla majoriteten av föroreningarna från det naturliga vattenflödet i avrinningsområdet kan volymen som behöver renas halveras. Eftersom föroreningen är så omfattande föreslås en kombination av åtgärdsmetoder; installation av gröna tak för att minska avrinningen från området, inneslutning av utfyllnadsmaterialet med bentonit och installation av ett filter för snabb, effektiv reduktion. För mer långsiktig rening föreslås det att optimera de existerande sedimentationsdammarna och våtmarken. Slutsatsen är att det kommer bli väldigt dyrt att åtgärda föroreningen på grund av dess omfattning, och hantering av sulfidförande berg för exploateringssyfte borde vara lagstadgat för att undvika miljömässiga och ekonomiska kostnader.

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<p>Streamflow prediction in ungauged basins (PUB) is a process generating streamflow time series at ungauged reaches in a river network. PUB is essential for facilitating various engineering tasks such as managing stormwater, water resources, and water-related environmental impacts. Machine Learning (ML) has emerged as a powerful tool for PUB using its generalization process to capture the streamflow generation processes from hydrological datasets (observations). ML’s generalization process is impacted by two major components: data splitting process of observations and the architecture design. To unveil the potential limitations of ML’s generalization process, this dissertation explores its robustness and associated uncertainty. More precisely, this dissertation has three objectives: (1) analyzing the potential uncertainty caused by the data splitting process for ML modeling, (2) investigating the improvement of ML models’ performance by incorporating hydrological processes within their architectures, and (3) identifying the potential biases in ML’s generalization process regarding the trend and periodicity of streamflow simulations.</p><p>The first objective of this dissertation is to assess the sensitivity and uncertainty caused by the regular data splitting process for ML modeling. The regular data splitting process in ML was initially designed for homogeneous and stationary datasets, but it may not be suitable for hydrological datasets in the context of PUB studies. Hydrological datasets usually consist of data collected from diverse watersheds with distinct streamflow generation regimes influenced by varying meteorological forcing and watershed characteristics. To address the potential inconsistency in the data splitting process, multiple data splitting scenarios are generated using the Monte Carlo method. The scenario with random data splitting results accounts for frequent covariate shift and tends to add uncertainty and biases to ML’s generalization process. The findings in this objective suggest the importance of avoiding the covariate shift during the data splitting process when developing ML models for PUB to enhance the robustness and reliability of ML’s performance.</p><p>The second objective of this dissertation is to investigate the improvement of ML models’ performance brought by Physics-Guided Architecture (PGA), which incorporates ML with the rainfall abstraction process. PGA is a theory-guided machine learning framework integrating conceptual tutors (CTs) with ML models. In this study, CTs correspond to rainfall abstractions estimated by Green-Ampt (GA) and SCS-CN models. Integrating the GA model’s CTs, which involves information on dynamic soil properties, into PGA models leads to better performance than a regular ML model. On the contrary, PGA models integrating the SCS-CN model's CTs yield no significant improvement of ML model’s performance. The results of this objective demonstrate that the ML’s generalization process can be improved by incorporating CTs involving dynamic soil properties.</p><p>The third objective of this dissertation is to explore the limitations of ML’s generalization process in capturing trend and periodicity for streamflow simulations. Trend and periodicity are essential components of streamflow time series, representing the long-term correlations and periodic patterns, respectively. When the ML models generate streamflow simulations, they tend to have relatively strong long-term periodic components, such as yearly and multiyear periodic patterns. In addition, compared to the observed streamflow data, the ML models display relatively weak short-term periodic components, such as daily and weekly periodic patterns. As a result, the ML’s generalization process may struggle to capture the short-term periodic patterns in the streamflow simulations. The biases in ML’s generalization process emphasize the demands for external knowledge to improve the representation of the short-term periodic components in simulating streamflow.</p>

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No description available.

Untreated human sewage pollution in surface water is of concern because it contributes to the degradation of aquatic ecosystems and it could be a potential hazard to human health. Also, any pollution of surface water, which ultimately supplies drinking water, may affect the drinking water quality. Improper operation and maintenance of separate storm sewer systems are prominent contributors of untreated sewage to source waters, resulting from illicit connections, leakage of sewers, or cross-connections. This thesis studied anthropogenic markers to track untreated sewage in an urban watershed with separate storm sewer system, under dry weather conditions. The main feature of these chemical markers is their degradation behavior at municipal wastewater treatment plants: some markers are completely removed (labile markers), whereas others show only partial or no removal at all (conservative markers). A set of ubiquitous chemical markers with practical analytical detection limits was selected to exploit the labile vs conservative distinction, and determine if untreated human sewage was discharged from stormwater outfalls. The presence of labile markers alone was not enough to confirm the occurrence of untreated sewage in stormwater outfalls. The concentration ratios between labile and conservative markers from several chemical groups (pharmaceuticals and personal care products, over-the-counter medications, artificial sweeteners, and human metabolites) created a chemical fingerprint of untreated sewage, and it was statistically demonstrated to track untreated human sewage in local stormwater outfalls. / Civil Engineering

Preferential flow paths are areas of substantially higher permeability than surrounding media. Macropores and soil pipes are a type of preferential flow path where conduit-like voids in the subsurface are typically greater than three millimeters in diameter. They are known to occur in agricultural and forest soils, often as a result of biological and physical processes. Macropores also exist in stream banks and have the potential to enhance the exchange of water and solutes between the channel and riparian groundwater, yet the geographic distribution of bank macropores is unknown. Here we determined the abundance, distribution, and geometry of naturally occurring surface-connected macropores in the banks of 20 streams across five physiographic provinces in the Eastern United States. We identified a total of 1,748 macropores, which were present in all 20 streams, with 3.8 cm average width, 3.3 cm average height, 11.5 cm average depth, and 27.9 cm average height above water surface elevation. Macropore abundance, distribution and geometry were statistically different between physiographic provinces, stream orders, and soil textures, with the latter being the most important. Macropores tended to be larger and more abundant in soils with a high cohesiveness and a low hydraulic conductivity compared to soils with a low cohesiveness and high hydraulic conductivity. As a result, streams with greater longitudinal heterogeneity of soil texture also had greater heterogeneity of macropore density. However, macropore size and height above baseflow water surface elevation also increased with stream order and therefore stream size. This work represents the first attempt to characterize macropores across a variety of riverine systems and presents evidence that macropores may play an important role in hyporheic exchange within stream banks. These results may have water quality implications, where macropores may enhance hyporheic exchange yet reduce the filtering capacity of riparian buffer zones. / MS

Periodic releases from an upstream dam cause rapid stage fluctuations in the Colorado River near Austin, Texas. These daily pulses modulate fluid exchange and residence times in the hyporheic region, where biogeochemical reactions are pronounced. We installed two transects of wells perpendicular to the river to examine in detail the reactions occurring in this zone of surface-water and groundwater exchange. One well transect recorded physical water level fluctuations and allowed us to map hydraulic head gradients and fluid movement. The second transect allowed for water sample collection at three discrete depths. Samples were collected from 12 wells every 2 hours for a 24-hour period and were analyzed for nutrients, carbon, major ions, and stable isotopes. The results provide a detailed picture of biogeochemical processes in the bank environment during low flow/drought conditions in a regulated river. Findings indicate that a pulse that causes a change in river stage of approximately 16-centimeters does not cause significant mixing in the bank. Under these conditions, the two systems act independently and exhibit only slight mixing at the interface. / text