Small Drainage Areas Research Articles

Apportionment of oxygen demand contributions from aircraft and pavement deicer freezing point depressants in airport runoff, Milwaukee, Wisconsin, 2005-2022.

Aircraft anti-icers and pavement deicers improve the safety of airport operations during winter precipitation events. Runoff containing these products can contribute elevated biochemical oxygen demand (BOD) to receiving streams. We monitored runoff from Milwaukee Mitchell International Airport at one upstream site, three outfall sites, and one downstream site from 2005 to 2022 for BOD, chemical oxygen demand (COD), and freezing point depressants used in deicing and anti-icing fluids to determine the primary sources of BOD and COD in the receiving stream. The greatest concentrations of BOD, COD, and freezing point depressants occurred at the primary outfall, which drains the main terminal area, and the secondary outfall, which drains cargo operations. The greatest loadings occurred at the primary outfall; loadings were an order of magnitude less at the secondary outfall due to a small drainage area with relatively low flow volumes. At the three outfalls, median concentrations of five-day BOD (BOD5) and COD were 100-1,300 mg L-1 and 200-2,100 mg L-1 respectively. Apportionment computations indicated that propylene glycol from aircraft deicers and anti-icers was responsible for at least half of the BOD5 and COD concentrations and loadings. Acetate from pavement deicers contributed another 7%-15% at each site. These findings suggest that management actions in the primary outfall drainage area that target propylene glycol-containing deicers have the greatest potential to decrease BOD5 in airport runoff. This work demonstrates the usefulness of BOD and COD apportionment for identifying the deicing products and locations within an airport to prioritize for reduction or recovery and treatment.

Fast spatial simulation of extreme high-resolution radar precipitation data using integrated nested Laplace approximations

Abstract Aiming to deliver improved precipitation simulations for hydrological impact assessment studies, we develop a methodology for modelling and simulating high-dimensional spatial precipitation extremes, focusing on both their marginal distributions and tail dependence structures. Tail dependence is crucial for assessing the consequences of extreme precipitation events, yet most stochastic weather generators do not attempt to capture this property. The spatial distribution of precipitation occurrences is modelled with four competing models, while the spatial distribution of nonzero extreme precipitation intensities are modelled with a latent Gaussian version of the spatial conditional extremes model. Nonzero precipitation marginal distributions are modelled using latent Gaussian models with gamma and generalized Pareto likelihoods. Fast inference is achieved using integrated nested Laplace approximations. We model and simulate spatial precipitation extremes in Central Norway, using 13 years of hourly radar data with a spatial resolution of 1×1km2, over an area of size 6,461km2, to describe the behaviour of extreme precipitation over a small drainage area. Inference on this high-dimensional data set is achieved within hours, and the simulations capture the main trends of the observed precipitation well.

Secondary production and biomass in mussel assemblages relate to species richness and stream size but not life history

AbstractIncreases in species richness with habitat area (species–area relationship, or SAR) and increases in ecosystem function with species richness (biodiversity–ecosystem functioning, or BEF) are widely studied ecological patterns. Incorporating functional trait analysis into assemblage datasets may help clarify interpretations of SAR and BEF relationships in natural ecological systems. For example, life history theory can be used to make predictions about what species are most important in generating ecosystem function given a certain set of environmental conditions. We used quantitative assemblage data for freshwater mussels at nine sites in western Alabama, USA, to test for SAR and BEF relationships. At each site, we calculated species richness, mussel assemblage density, and two fundamental metrics of ecosystem function: biomass and secondary production. We also tested whether the proportional biomass and production contributions from species belonging to each of three life history strategies—opportunistic strategists adapted to unstable or frequently disturbed habitats, periodic strategists adapted to habitats subject to predictable large‐scale disturbances, and equilibrium strategists adapted to stable habitats—varied longitudinally with stream drainage area, a proxy for habitat area. Species richness increased with stream size (SAR), and both biomass and production increased with species richness (BEF) and mussel density. There were few longitudinal changes in the proportional contributions of the different life history strategy classifications that we used, but the invasive clam Corbicula fluminea contributed proportionally more biomass and production at sites that had smaller drainage areas. This study provides further evidence for a clear longitudinal SAR in stream‐dwelling taxa. It also suggests BEF relationships for biomass and secondary production in natural assemblages but underscores the importance of assemblage density in BEF studies that use observational field data. Variation in proportional biomass and production contributions by different life history strategies was likely limited by the size of the stream size gradient in our study, as contributions were uniformly high for species with life history traits better adapted to stable and productive habitats such as mid‐sized rivers with low or predictable hydrologic disturbance frequencies. This highlights the need to understand how organisms' functional traits govern their relationships to the environment at different scales.

Impacts of future climate and land use/land cover change on urban runoff using fine-scale hydrologic modeling

Future changes in land use/land cover (LULC) and climate (CC) affect watershed hydrology. Despite past research on estimating such changes, studies on the impacts of both these nonstationary stressors on urban watersheds have been limited. Urban watersheds have several important details such as hydraulic infrastructure that call for fine-scale models to predict the impacts of LULC and CC on watershed hydrology. In this paper, a fine-scale hydrologic model—Personal Computer Storm Water Management Model (PCSWMM)—was applied to predict the individual and joint impacts of LULC changes and CC on surface runoff attributes (peak and volume) in 3800 urban subwatersheds in Midwest Florida. The subwatersheds a range of characteristics in terms of drainage area, surface imperviousness, ground slope and LULC distribution. The PCSWMM also represented several hydraulic structures (e.g., ponds and pipes) across the subwatersheds. We analyzed changes in the runoff attributes to determine which stressor is most responsible for the changes and what subwatersheds are mostly sensitive to such changes. Six 24-h design rainfall events (5- to 200-year recurrence intervals) were studied under historical (2010) and future (year 2070) climate and LULC. We evaluated the response of the subwatersheds in terms of runoff peak and volume to the design rainfall events using the PCSWMM. The results indicated that, overall, CC has a greater impact on the runoff attributes than LULC change. We also found that LULC and climate induced changes in runoff are generally more pronounced in greater recurrence intervals and subwatersheds with smaller drainage areas and milder slopes. However, no relationship was found between the changes in runoff and original subwatershed imperviousness; this can be due to the small increase in urban land cover projected for the study area. This research helps urban planners and floodplain managers identify the required strategies to protect urban watersheds against future LULC change and CC.

Hydrological Verification of Two Rainfall Short-Term Forecasting Methods with Floods Anticipation Perspective

Abstract Flood forecasting remains a significant challenge, particularly when dealing with basins characterized by small drainage areas (i.e., 103 km2 or lower with response time in the range 0.5–10 h) especially because of the rainfall prediction uncertainties. This study aims to investigate the performances of streamflow predictions using two short-term rainfall forecast methods. These methods utilize a combination of a nowcasting extrapolation algorithm and numerical weather predictions by employing a three-dimensional variational assimilation system, and nudging assimilation techniques, meteorological radar, and lightning data that are frequently updated, allowing new forecasts with high temporal frequency (i.e., 1–3 h). A distributed hydrological model is used to convert rainfall forecasts into streamflow prediction. The potential of assimilating radar and lightning data, or radar data alone, is also discussed. A hindcast experiment on two rainy periods in the northwest region of Italy was designed. The selected skill scores were analyzed to assess their degradation with increasing lead time, and the results were further aggregated based on basin dimensions to investigate the catchment integration effect. The findings indicate that both rainfall forecast methods yield good performance, with neither definitively outperforming the other. Furthermore, the results demonstrate that, on average, assimilating both radar and lightning data enhances the performance.

Pulse power plasma stimulation: A technique for waterless fracturing, enhancing the near wellbore permeability, and increasing the EUR of unconventional reservoirs

The inherent characteristic of unconventional and ultra-low permeability reservoirs is a small drainage area that negatively affects the production rate and ultimate recovery (UR). Drilling horizontal wells, coupled with a stimulation process such as hydraulic fracturing, are applied to wells in these reservoirs to enhance well productivity. Although hydraulic fracturing has been the most famous stimulation technique in these reservoirs and has contributed to the increased US oil and gas production during the last several years, other stimulation techniques may be competitive with (or complementary to) hydraulic fracturing. This is because the main contribution to production in these reservoirs would be from complex fracture networks (often micro-cracks) combined with enhanced formation permeability rather than the classical two-wing fractures. Hence, a near-wellbore stimulation technique for improving the permeability of these reservoirs by activating the existing natural fractures and creating secondary microfractures would be highly desired. This paper investigates the pulse plasma stimulation technique to investigate such an approach of waterless stimulation/fracturing that creates multiple fractures and is also a permeability enhancement method. In this method, plasma is generated by discharging a high voltage and high current electrical energy in a very short time into two electrodes submerged in a wellbore filled with aqueous fluid. This study is divided into two sections. The first part presents experimental and numerical examples of stimulation/fracturing induced by pulse plasma in different rocks. Several parameters, including the effect of discharge with and without wire, input energy, confining stress, and rock type, on the induced fractures are studied. The second part uses the insights and results from the first part to numerically investigate pulse plasma's effects on production. Measurement of the formation permeability around the generated fractures indicated that the shock wave generated multiple fractures and increased the rock permeability by more than one or two orders of magnitude. The second part of the numerical section discusses the increased estimated rate and ultimate recovery (EUR) of horizontal wellbores due to fracturing and modified permeability resulting from pulse plasma. We present a sensitivity analysis on the magnitude and extent of the improved permeability region and its impact on EUR.

From fisher tales to scientific evidence: revealing the significance of estuarine and mangrove habitats as nursery grounds for juveniles of the largest Atlantic Ocean snapper

The knowledge held by local and indigenous communities has been recognized as an invaluable yet underused resource for understanding how the environment, local conditions, and fish populations change over time. Empirical information on population sizes, ecology, and threats to fish species and their habitats can be complemented with local knowledge to better guide management and conservation efforts, particularly for understudied species. Here, we investigated the habitat preferences, population status, fishing, sightings patterns, threats, and habitat characteristics of juveniles of the cubera snapper, the largest snapper in the Atlantic Ocean. We used a combination of empirical evidence from underwater surveys by using small-action cameras and an ethnological perspective based on fishers’ perceptions who are cubera-snapper fishing specialists to have a comprehensive understanding of the species and habitat use during its early life stages. A range of estuarine habitats was examined over a year to assess the association between cubera snapper juveniles and different estuarine characteristics and conservation scenarios. Both sources of data indicated that cubera snapper juveniles heavily rely on mangrove habitats, exhibiting a clear temporal pattern of residence within these habitats. However, the probability of occurrence varied based on the level of coastal development in each estuarine system. Estuaries with small drainage areas, directly connected to the ocean, and presenting larger mangrove areas accounted for the highest abundances of juveniles. Factors such as mangrove removal, overfishing, and water pollution significantly reduced the occurrence and reliance of cubera snapper juveniles in the studied estuaries. The study represents the first attempt to shed light on the ecological aspects of cubera snapper juveniles, addressing a gap in their life cycle. It underscores the importance of integrating complementary sources of evidence to understand the relationships between the crucial life stage of cubera snappers, their habitats, and the threats they face. The ecological and ethnographic knowledge gained from this research should be incorporated into biomonitoring and conservation policy to effectively preserve this vulnerable top predator.

Evaluation of statistical models: Perspective of water quality load estimation

The accurate representation of the load of water quality constituents, transported by rivers and streams, is crucial to understand the impact on the quality of the lakes, the behavior of the rivers and streams. Statistical models have been developed to predict the water-quality constituent loads from the available data of sampled concentration (low-frequency/grab chemistry data) and continuous discharge (high frequency) at a particular sampled location and to further analyze trends and changes in water quality. However, the performance of statistical models to estimate water quality constituent loads depends on many aspects including the type of water quality constituent, sampling strategy and frequency, and the land use and areas of the watershed. This study evaluates the performance of a wide range of statistical models for the estimation of total suspended solids (TSS) and total phosphorus (TP) loads under various sampling scenarios and monitoring stations in Southern Ontario, Canada. Trends in TSS and TP concentrations and loads were further analyzed in major tributaries. The Weighted Regression on Time, Discharge, and Season Kalman Filter (WRTDS_K) model was found to be the most suitable model (p > 0.05 and Percentage Difference (%) (PDIFF) between ±20) for predicting TSS loads at most sampling stations and under most sampling scenarios, while, the Weighted Regression on Time, Discharge, and Season (WRTDS) model was found to be the most suitable model (p > 0.05 and flux bias statistics (FBS) between ±0.1) for predicting TP loads. The applied statistical models (LOADEST simple and curvilinear models, WRTDS, WRTDS_k, Beale’s estimator, composite and interpolation models) have shown a limited potential to estimate load accurately at monitoring stations covering small drainage areas.

A global review of beaver dam impacts: Stream conservation implications across biomes.

Beaver are recolonizing previously occupied regions, expanding into new territories, and increasingly being introduced and protected for stream conservation and restoration across numerous biomes. However, beaver dam effects on the physical, chemical, and biological characteristics of streams may vary within and among biomes. A comprehensive review of these impacts is lacking. The goals of this review were to: 1) summarize the distribution of studies by biome on beaver dam effects related to channel morphology, hydrology, water quality, and aquatic biota, as well as on beaver habitat selection, 2) summarize the extent to which beaver dam impacts have been consistent within and among biomes, and 3) share testable hypotheses regarding beaver impacts within understudied biomes. We quantify the directionality of beaver dam impacts from 267 peer-reviewed studies. Results show that the majority of studies have been completed within temperate forest environments and that many biomes are understudied. Across biomes, beaver preferred sites for dam development characterized by relatively low gradients and unconfined reaches with small drainage areas. Overall, parameters related to stream morphology and hydrology showed relatively consistent responses to beaver dams within and among biomes, yet water quality and biotic responses were variable among biomes. Responses also varied by parameter within water quality and biotic impact categories. The findings of this study can be useful for stream conservation and restoration efforts that introduce or protect beaver. Additional studies are needed within arid and cold biomes historically occupied by beaver and in novel biomes where beaver populations are currently expanding.

Intra-gully mapping of the largest documented gully network in South Africa using UAV photogrammetry: Implications for restoration strategies

Gully erosion can reach alarming dimensions, and in several cases contributes significantly to soil loss and sediment yield in catchments. The studied example is one of the largest known gully networks in the world (its surface area is approximately 0.5 million m2 and volume 5 million m3), more than twice as large compared to the largest gullies described in peer-reviewed literature. To improve gully management strategies, it is not only critical to understand the factors that lead to erosion, but also to identify the extent of in-channel erosional and depositional features. Few studies consider in-channel patterns of erosion and deposition within gully systems. This study utilises a fixed-wing Unmanned Aerial Vehicle (UAV) and Structure-from-Motion (SfM) photogrammetry to create a high resolution orthomosaic and Digital Surface Model (DSM) to determine the position and spatial extent of erosional and depositional features within a large gully network in South Africa. Formation of such a large gully in relation to a relatively small drainage area is unusual but can be explained by the presence of dispersive soils and regional landscape incision. Longitudinal and cross-sectional profiles indicate that the gully network consists of three channel types (i.e. V-shaped, U-shaped and trapezoidal), each with a unique combination of erosional and depositional features. This study demonstrates the value of identifying and mapping of intra-gully features to better understand sediment transfer within the gully network to implement appropriate restoration strategies, which in this instance should focus on depositional zones to enhance channel decoupling.

Eustatic knickpoint dynamics in an uplifting sequence of coral reef terraces, Sumba Island, Indonesia

An emerged coral reef terrace sequence flanks the northern coast of Sumba Island in Indonesia. The sequence was created by the joint effects of uplift and Quaternary sea level oscillations. Since its emergence, it undergoes chemical erosion, which is facilitated by its carbonate lithology. The morphology is dissected by multiple catchments drained by deep canyons, whose stream profiles display several knickpoints. We applied a multi-methods approach using high-resolution topographic data (Pleiades imagery), geomorphological analysis and denudation rates derived from 36Cl cosmogenic nuclide concentrations to characterize the dynamics of these coastal drainages. We specifically investigate (1) the channel response to eustatic forcing, by analyzing knickpoint dynamics along a longitudinal river profile, and (2) the control of internal and external forcing over the catchment-scale erosion. Firstly, knickpoints form at the distal edge of the emergent reef at each regressive stage following a sea level highstand. The knickpoint propagates and rotates upward by regressive erosion. Knickpoint propagation rate decreases sharply over time until it becomes negligible before the next sea-level rise, which implies a marked decline in knickpoint retreat rate before its resorption. We attribute the inability of the river at Cape Laundi to fully propagate eustatic oscillations to its low stream discharge and low sediment supply, related to its small drainage area, to the karstic nature of the coral reef terraces composing the sequence, and to the high frequency of eustatic forcing. Secondly, average denudation rates calculated from 36Cl cosmogenic nuclide concentrations of sands collected at the outlet of five catchments draining the sequence amount to 69 ± 8 mm·ka−1. We emphasize the role of canyon areas in driving the denudation of the major catchments. However, no first-order correlation has been observed between catchment metrics, uplift rates and denudation rates. Finally, our correlations between catchment finite eroded volumes and uplift rates highlight the tendency of catchments to widen with low uplift rate and to lengthen while incising the sequence deeply with higher uplift rates.

Hydrogeochemical characterization and suitability of water for irrigation in new and old reservoirs in northern Espirito Santo, Brazil

During the water crisis of 2015–2016, the construction of small earth-filled dams grew to supply irrigated crops of the north of Espirito Santo-ES, Brazil. This paper reports the hydrogeochemical study of eight reservoirs conducted between 10/2016 to 11/2017 to assess the water suitability for agricultural purposes and its risk to irrigation systems. The reservoirs of Sao Mateus (SM) are located in large drainage basins with many impoundments upstream. Nova Venecia's reservoirs (NV) have small and circular drainage areas with few, or any, upstream dams. The results are consistent with freshwater classification and Na-Cl composition to all reservoirs. Nevertheless, canonical discriminant analysis and Spearman's coefficients revealed distinct composition and patterns of correlations between municipalities. The mean permeability index of 53 and the low risk of sodicity and salinization (C1S1) demonstrate that these waters' use is harmless to the soil and crops. However, the phosphate contents make the new reservoirs susceptible to algae blooms. The same reservoirs also presented total solids and Fe levels above the tolerable limit for safety irrigation use, imposing a severe risk of clogging. The low replenishment of SM's reservoirs reflects the dispute over water resulting from the high number of impoundments in these drainage areas. The drought that preceded the study diminished the drainage basins' vegetation cover, favoring soil particles' runoff, elevating the TS and Fe levels, especially in the recently built reservoirs. Farmers must control soil erosion to avoid water quality compromise, to reduce the risk of failure and the irrigation system's maintenance cost.

Do forests provide watershed services for farmers in the humid tropics? Evidence from the Brazilian Amazon

Forests are a key component of hydrological cycles, and thus deforestation is likely to affect the availability and quality of water for downstream agricultural production. However, in humid tropical regions where water is relatively abundant and the terrain is relatively flat, it is unclear whether these changes in ecosystem services matter to local farmers. We test whether the extent of forest in upstream drainage areas affects downstream farm production in an agricultural colonization zone in the Brazilian Amazon. We first estimate panel models of the output of milk, which is the primary farm product in our study region. We then test for effects on pasture stocking and cow productivity as possible pathways for the effect of upstream forests on milk output. Estimation results suggest that upstream forest increases the productivity of properties with small drainage areas. The effects are strongest when water is either scarce (dry season of drought years) or excessive (rainy season of flood years). The contribution of Amazonian forests to the resilience of the local farm economy is likely to become more important as rainfall becomes more variable due to regional and global climate change.

Flood mapping employing local, regional and global scale modeling methods for the Uruguay river

The delimitation of flooded areas is important information for natural disaster management, environmental impact prediction and for territorial planning. Flooding occurs when water levels overflow the limits of a river’s channel and seep into the floodplains. When they affect people, they are considered a natural disaster. The delimitation of a flooded area, in the occurrence of an extreme event, can be performed by using field techniques, such as mapping, surveying through the afflicted area or by taking aerial photographs. However, field survey is not a trivial task and not always does it allow for the attainment of the necessary data for a given project. For that purpose, there are various techniques that can be used to assess flood-spots. Some techniques are simpler, being based only on a Digital Elevation Model (DEM), and such is the case of the HAND model (Height Above Nearest Drainage), which has garnered plenty of fame recently in the process of applying delimitations to possibly flooded areas. Other techniques are more complex, like the use of hydrodynamic modeling. There are large-scale hydrologic-hydrodynamic models that simulate runoff generation and water transportation processes in the river basin from rainfall, basin, and meteorological data. This is the case of the large-scale distributed hydrological model called MGB (Modelo de Grandes Bacias), which has been developed and employed in these types of cases. However, there are no studies in the literature that compare the results produced by these multiple approaches using differing degrees of complexity and spatial scales. It was precisely to fill this gap in scientific literature that this work was developed. Featured here, for the first time, is the validation of the MGB model’s performance in two versions, one of regional scale and another of continental scale (MGB AS), in delimiting the flooded areas, compared to a satellite image of the inundation; and with two versions of the HAND model, one generated by a local study and the other by a global reference. The case study used in this validation was a major flood that occurred in the Uruguay River, near the town of Itaqui (Rio Grande do Sul), which borders Brazil and Argentina, in October 1997. The results show that the MGB model, both in the regional and the continental scales, could delimit the flooded area, with a few overestimations in the northern portion of the image. The HAND method at the local scale also allowed a mapping of the flooded area, with overestimates for more springhead-like areas in small tributaries. The HAND method at the global scale, on the other hand, proved to be inadequate for the purpose of delimiting flooded areas in this region. The leading cause is believed to be the small drainage area threshold linked to the utilized global HAND product. From the calculation of performance metrics, like hit rate, false alarm ratio and criticality index, Regional MGB was the one that most adequately expressed the extent of the flood observed in the Landsat 5 image when compared to the others, followed by MGB AS.

Hydropower Potential of Run of River Schemes in the Himalayas under Climate Change: A Case Study in the Dudh Koshi Basin of Nepal

In spite of the very large hydropower potential given from the melting snow and ice of Himalayas, Nepal’s population has little hydropower production. The high use of fossil fuels and biomasses results in measurable air pollution, even in the mountain areas. Hydropower planning and implementation, in the face of the changing climate, is therefore paramount important. We focus here on Nepal, and particularly on the Dudh Koshi river basin, with a population of ca. 170,000 people, within an area with large potential for hydropower production. Our main objectives are to (i) preliminarily design a local hydropower grid based on a distributed run of river ROR scheme, and (ii) verify the resilience of the grid against modified hydrology under perspective climate change, until the end of the century. To do so, we set up and tune the Poli-Hydro semi-distributed glacio-hydrological model, mimicking the complex hydrology of the area. We then modify a state of the art algorithm to develop and exploit a heuristic, resource-demand based model, called Poli-ROR. We use Poli-ROR to assess the (optimal) distribution of a number of ROR hydropower stations along the river network, and the structure of the local mini-grids. We then use downscaled outputs from three general circulation models GCMs (RCPs 2.6, 4.5, 8.5) from the Intergovernmental Panel on Climate Change IPCC AR5, to assess the performance of the system under future modified hydrological conditions. We find that our proposed method is efficient in shaping ROR systems, with the target of the largest possible coverage (93%), and of the least price (0.068 € kWh−1 on average). We demonstrate also that under the projected hydrological regimes until 2100, worse conditions than now may occur, especially for plants with small drainage areas. Days with energy shortage may reach up to nf = 38 per year on average (against nf = 24 now), while the maximum daily energy deficit may reach as high as edef% = 40% (against edef% = 20% now). We demonstrate that our originally proposed method for ROR grid design may represent a major contribution towards the proper development of distributed hydropower production in the area. Our results may contribute to improve energy supply, and living conditions within the Dudh Koshi river. It is likely that our approach may be applied in Nepal generally. Impending climate change may require adaptation in time, including the use of other sources which are as clean as possible, to limit pollution. Our Poli-ROR method for grid optimization may be of use for water managers, and scientists with an interest in the design of optimal hydropower schemes in topographically complex catchments.

Seepage Erosion in the Luquillo Mountains, Puerto Rico, Relict Landscapes

AbstractSeminal research into geomorphic shaping of landscapes by emerging groundwater suggest that the relationships governing channel form and incision rate are distinct from other fluvial systems (Howard, 1995; Dunne, 1980, 1990). While some recent work has connected these models to natural settings (Abrams et al., 2009; Petroff et al., 2011), other studies have shown that seepage erosion may be erroneously invoked in landscapes shaped by flooding and overland flow (Lamb et al., 2006, 2007). We investigate the impact of seepage erosion on the geomorphology of a tropical mountain watershed, the Rio Blanco in the Luquillo Mountains of northern Puerto Rico. We focus on a population of amphitheater‐shaped channels that incise into deeply weathered saprolite profiles in the upland reaches of the watershed, where the river is disconnected from regional base‐level lowering (Brocard et al., 2015, 2016). We measured high rates of baseflow from springs feeding these catchments, despite their small drainage areas. We constructed an empirical model relating baseflow discharge to catchment area within the watershed. We quantified long‐term (103‐104 yrs) catchment erosion from 10Be in sediment and measured the short‐term volumetric flux of bedload transport at baseflow. Rates of transport and erosion in this group of channels scale linearly with the feeding drainage area and baseflow discharge. This finding supports a stream incision model proposed for groundwater‐driven channels (Howard, 1995). We propose that deepening saprolite and coincident entrenchment of the subsurface water‐routing system initiated seepage erosion and are actively expanding the headwaters in the Rio Blanco.

Analysis of Athabasca Oil Sands Investigates SAGD Performance Variability

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 195348, “Steam-Assisted Gravity Drainage Performance Variability—Analysis of Actual Production Data for 28 Athabasca Oil Sands Well Pairs,” by Quang T. Doan, Vincano; S.M. Farouq Ali, SPE, University of Houston; and Thomas B. Tan, SPE, Petrostudies Consultants, prepared for the 2019 SPE Western Regional Meeting, San Jose, California, 23–26 April. The paper has not been peer reviewed. Steam-assisted gravity drainage (SAGD) performance in bitumen-recovery projects in Alberta is affected by geological deposits, reservoir quality, and operational experience. The authors reviewed and analyzed actual field production and injection data for 28 Athabasca oil-sands-deposit SAGD well pairs (WPs). Based on analysis of field-production data, a numerical model was built and calibrated against production data from two of the poorer-performing WPs among the 28 studied. Agreement between simulated and actual cumulative oil and steam/oil ratio (SOR) was within 10% after 6 years of operations on a first-iteration basis. Problem and Investigation Methodology A survey of the literature reveals that some aspects of the SAGD process, particularly with regard to the behavior of gas, still largely are not understood. While successful history-matching simulations of SAGD WPs exist for several different projects, these rely on dead-oil pressure/volume/temperature treatment and exclude any findings and discussion on gas production. Such history-matched models likely would need to be modified significantly to be useful for modeling the wind-down stage of SAGD operations. Recent numerical studies modeling the generation of aquathermolysis gases focused on the injection of noncondensable gas into a mature SAGD steam chamber. In preparation for a series of numerical studies on aspects of SAGD performance, a reservoir model simple enough to be relatively adaptable for different geological settings was built. Such a model had to be calibrated rigorously with actual production data to provide a high degree of confidence in its results and predictive capability in appropriate contexts. The investigation in the complete paper is aimed at addressing several fundamental aspects of SAGD operations, including the effects of reservoir heterogeneities and the behavior of gas. The first part of the complete paper is focused on reviewing and analyzing actual field production data spanning more than 1,700 days from 28 SAGD WPs from four different pads (A, B, C, and D) of the Jackfish 1 project; this synopsis will not include that extensive data. Jackfish 1 Project. Jackfish 1 consists of 42 WPs divided into six pads (including the 28 WPs in Pads A, B, C, and D analyzed for the authors’ study) and is part of the geological oil-sands trend of the Athabasca oil-sands deposit. Jackfish 1 has a nameplate capacity of 35,000 BOPD, with a designed SOR of 2.7. Consistently exceeding 90% of its nameplate capacity since first steam, it is commonly considered to be a successful SAGD project. The results of data analysis for the WPs studied indicated the following: Considerable variance exists in the recovery performance of SAGD WPs on the same pad. Considering the small drainage area of the 7-WP pad (800×800 m), such variances bear important implications for the planning and execution of SAGD projects (particularly greenfield development but also with regard to brownfield expansion). The authors stress that forecasting project productivity should not be based on a single-WP, deterministic simulation model without any consideration for distributions in reservoir geology and parameters affecting SAGD performance. This assessment is equally applicable in the estimation of reserves.

Sediment modeling of a large-scale basin supported by remote sensing and in-situ observations

Sediment models are important for estimating soil erosion, sediment transport, and deposition at different scales and for disparate scenarios; however, the availability of in-situ measurements may not be sufficient for the appropriate evaluation of model performance. For this reason, this study investigated how surrogate data (water quality [WQ] and remote sensing) could be used as a proxy for suspended sediment concentration (SSC) in order to evaluate the performance of a large-scale erosion and sediment transport model. To achieve this, the daily SSC was simulated, using the Large Scale Sediment Model (MGB-SED), a semi-distributed and conceptual model in which the Modified Universal Soil Loss Equation (MUSLE) is used to estimate sediment yield and an advection-diffusion equation is used to route suspended loads along rivers. Four experiments were performed that compared simulated SSC against: (1) in-situ SSC; (2) turbidity; (3) total suspended solids (TSS); and (4) surface spectral reflectance (SSR). Correlation analysis showed that r-values above 0.5 were found in 62%, 91%, 89% and 83% of the SSC, turbidity, TSS and SSR stations, respectively. Spatially, the model was evaluated in smaller drainage areas, using WQ data. Temporally, the number of SSR observations was greater than the number of in-situ measurements, allowing a better analysis of the temporal dynamics of the simulated SSC. Also, the SSR data improved the spatial coverage and could be employed for even large-scale, ungauged basins. These results bring a new perspective to the application of sediment models in poorly or ungauged basins, since surrogate data can improve the spatial and temporal suspended sediment coverage when compared to traditional SSC measurements, which is a common issue in large-scale sediment modeling.

The use of support vectors from support vector machines for hydrometeorologic monitoring network analyses

Hydrometeorologic monitoring networks are ubiquitous in contemporary earth-system science. Network stakeholders often inquire about the importance of sites and their locations when discussing funding and monitoring design. Support vector machines (SVMs) can be useful by their assigning each monitoring site as either a support or nonsupport vector. A potentiometric surface was created from synthetic data and 800 random observation locations (sites) as an analog to a groundwater-level network. Using generalized additive models for potentiometric surface prediction, simulations show that a subsample of support vectors from the 800 sites will out perform random samples of sample size equaling the support vector count. Support vector percentages from simulation quantify the recurrence that SVMs assign each site as a support vector, and these percentages in turn measure site importance. An example application of support vector percentages identifies important monitoring sites needed to regionalize the 0.1 annual exceedance probability peak streamflow. The results indicate that 152 of 283 streamgages with support vector percentages equalling 100 percent have not operated since about 2000 and generally have much smaller drainage areas than the greater streamgage network in Texas. The drainage area disparity is an indication of historical imbalance in peak streamflow data acquisition from various stream sizes in Texas.

Cholecystohepatic duct detected during laparoscopic cholecystectomy: a case report

BackgroundThe cholecystohepatic duct is a rare form of an aberrant hepatic duct that connects to the gallbladder. Although cholecystohepatic duct is reported to be a very rare anomaly, injury of cholecystohepatic duct during cholecystectomy may result in serious complications. Herein, we present a case of cholecystohepatic duct in the ventral branch of the right posterior inferior segmental bile duct detected during laparoscopic cholecystectomy.Case presentationA 77-year-old woman with cholecystolithiasis had been referred to our hospital for surgery. Drip infusion cholecystocholangiography-computed tomography revealed a bile duct branch without communication between the intra- and extrabiliary systems, although the existence of this aberrant hepatic duct was not suspected preoperatively. A 4-port laparoscopic cholecystectomy was performed. After critical view of safety was confirmed, the cystic artery and duct were divided after double clipping. During antegrade mobilization of the gallbladder from the gallbladder bed, a thin, white cord-like material connecting the gallbladder neck and bed was detected. After clipping and dividing it, a cholecystohepatic duct injury was recognized through rechecking the results of the preoperative examinations. Biliary reconstruction was considered unnecessary because of the lesion’s small drainage area. The postoperative course was uneventful, and an enhanced computed tomography performed 6 months after the surgery revealed a dilation in the ventral branch of the right posterior inferior segmental bile duct. The patient’s liver function remained normal, and she had no symptoms of cholangitis 42 months after the surgery.ConclusionsAlthough cholecystohepatic duct is a rare anomaly compared to other aberrant hepatic ducts, surgeons performing cholecystectomy should always keep its existence in mind to avoid serious postoperative complications. Ideally, preoperative detection of cholecystohepatic duct is preferable, but even if it is detected during surgery, the appropriate management according to the drainage area is also important.