| 1. |
- Blösch, Günter, et al.
(författare)
-
Twenty-three unsolved problems in hydrology (UPH) - a community perspective
- 2019
-
Ingår i: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 64:10, s. 1141-1158
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come.
|
|
| 2. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Dissolution Of A Spatially Variable Non-Aqueous Phase Liquid Source: Experimental Study And Model Devolpment
- 2009
-
Ingår i: PROCEEDINGS, TOUGH Symposium 2009.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mass transfer from subsurface occurrences of non-aqueous phase liquids (NAPLs) to the surrounding groundwater is a key process, both for persistent contamination problems originating from organic liquid sources, and for dissolution trapping in geological CO2 sequestration. While the dissolution typically is governed by processes that occur on very small scales (i.e., the pore scale), there is a need to model the mass transfer coupled to transport of dissolved chemical components over field scales that are several orders of magnitude larger. Upscaled models, linking the small-scale characteristics to the total mass transfer from sources of dissolved chemicals, are therefore needed. Well-controlled laboratory experiments conducted in test cells allow for the generation of accurate data to validate such upscaling methods before applying them to much more complex field systems. Following this approach, a set of experiments were conducted in a two-dimensional sand tank, wherethe dissolution of a spatially variable, 5 cm by 5 cm DNAPL tetrachloroethene (PCE) source was carefully monitored in space and time. With a resolution of 0.2´0.2 cm, NAPL saturations were measured using x-ray attenuation techniques at approximately 1,000 individual pixels in the source zone. By continuously measuring the NAPL saturations, the temporal evolution of DNAPL mass loss by dissolution to groundwater could be measured at each pixel. The rate of dissolution varied spatially and temporally within the source, and was found to be correlated to NAPL morphology, groundwater flow velocity, and position within the source. The dissolution process was modeled using iTOUGH2/T2VOC under assumption of local equilibrium (LE) between the DNAPL and dissolved PCE. A preliminary model of rate-limited (RL) dissolution, based on a Gilland-Sherwood type relation implemented in MODFLOW/RT3D, was also tested. It was found that the LE model could not capture the observed dissolution patterns, although it predicted the total rate of mass transfer well for the given source conditions. The RL model showed potential to better capture the dissolution pattern after further model development. Ongoing work is aimed at addressing these issues by correlating the detailed measurements of NAPL entrapment morphology and local dissolution rates, with the final goal of developing an upscaled model of the total mass transfer from the source zone.
|
|
| 3. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 2. Application to stochastically heterogeneous formations
- 2007
-
Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 483-495
-
Tidskriftsartikel (refereegranskat)abstract
- We performed a series of well-controlled laboratory experimentsinvestigating the infiltration and subsequent immobilizationof nonaqueous-phase liquid (NAPL) in saturated heterogeneousmedia. A system of two distinct aquifer zones separated by adipping interface was considered. Heterogeneity was representedby a spatially correlated random field with known geostatisticalparameters in one zone in combination with a homogenous packingof the other zone. The effects of heterogeneity on NAPL flowand entrapment in each of the two zones were investigated. Thetime-varying NAPL saturations were continuously monitored inspace and the final static entrapment–saturation distributionwas accurately measured. The immobilized-NAPL distribution contributesto plume generation from source zones. The results show thatcapillary barriers produced by the small-scale heterogeneitystrongly influenced the migration paths and the final distributionof NAPL both in space and across different saturation ranges.The NAPL was immobilized both by snap-off to discontinuous blobsand ganglia and by capillary barriers at textural interfaces.Heterogeneity generally increased entrapment, because spatialvariations in capillary properties caused NAPL to be entrappedat higher saturations. Heterogeneity in the finer formationprovided points of entry into this formation where the NAPLsubsequently could spread as the pressure built up. The NAPLwas immobilized at high saturations because high displacementpressures in the fine materials inhibited flow at low saturations.The accessibility for water flow through NAPL occurrences andthereby also the dissolution of NAPL is limited by (i) highentrapped NAPL saturations that decrease the aqueous-phase relativepermeability and (ii) the location of NAPL inside a formationwith low average permeability.
|
|
| 4. |
- Fagerlund, Fritjof, 1974-, et al.
(författare)
-
Nonaqueous-phase liquid infiltration and immobilization in heterogeneous media : 1. Experimental methods and two-layered reference case
- 2007
-
Ingår i: Vadose Zone Journal. - : Wiley. - 1539-1663. ; 6:3, s. 471-482
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate data to understand the migration and entrapment ofnonaqueous-phase liquids (NAPLs) in heterogeneous formationsare presently lacking. A series of well-controlled laboratoryexperiments were conducted to investigate the infiltration andsubsequent immobilization of dense NAPLs in saturated heterogeneousmedia. The focus of this first study was the development ofa special experimental methodology for measuring the dynamicevolution of a NAPL plume in space and time. To demonstratethe method, a reference case of a two-layered formation consistingof two homogeneous sands separated by a dipping interface ispresented. The dipping formation in the reference case allowsthe study of NAPL behavior at texture interfaces under the influenceof both capillary and gravitational forces. The NAPL-saturationmeasurement methodology, based on a multiple-energy x-ray attenuationtechnique, correctly captured the known injected NAPL volumeas well as the general spreading and entrapment behavior inspace and time. Time-continuous measurements of NAPL saturationsallow the study of the history dependence of entrapped saturations.The Land model predicted the observed trend in the entrapmentbehavior well. The entrapment architecture was parameterizedusing spatial moments and moments of mass distribution at differentsaturations. The general features of the NAPL architecture weresuccessfully characterized by a simultaneous interpretationof these moments, while the domination of discontinuous or continuousNAPL was captured by the ganglia/pool ratio.
|
|
| 5. |
|
|
| 6. |
- Islam, Shafiqul, et al.
(författare)
-
Looking for Theory-Practice Synthesis for Actionable Outcomes : A Continuing Special Collection for Translational Water Research
- 2023
-
Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 59:12
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Translational research (TR) represents a promising systematic process for going from scientific discoveries to practical applications. Through conversations with academics, practitioners, decision-makers and users, there has emerged a broad level of water science community support for including TR in Water Resources Research (WRR) publications. Based on this, we now open a continuing special collection of TR papers in WRR. The aim is to facilitate a community within hydrology and water science that seeks to provide actionable knowledge for societal benefit across disciplines, scales and contexts, with a focus on water as a key societal resource or a risk (e.g., of floods, droughts, or as pollutant carrier). This Editorial discusses what the multi-faceted nature of TR may include in the context of WRR, why it is important to encourage TR papers in WRR, and how the opening of a continuing special collection of translational water research papers initiates a process to include such articles in the journal.
|
|
| 7. |
- Phenrat, Tanapon, et al.
(författare)
-
Empirical correlations to estimate agglomerate size and deposition during injection of a polyelectrolyte-modified Fe0 nanoparticle at high particle concentration in saturated sand
- 2010
-
Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 118:3-4, s. 152-164
-
Tidskriftsartikel (refereegranskat)abstract
- Controlled emplacement of polyelectrolyte-modified nanoscale zerovalent iron (NZVI) particles at high particle concentration (1-10 g/L) is needed for effective in situ subsurface remediation using NZVI. Deep bed filtration theory cannot be used to estimate the transport and deposition of concentrated polyelectrolyte-modified NZVI dispersions (> 0.03 g/L) because particles agglomerate during transport which violates a fundamental assumption of the theory. Here we develop two empirical correlations for estimating the deposition and transport of concentrated polyelectrolyte-modified NZVI dispersions in saturated porous media when NZVI agglomeration in porous media is assumed to reach steady state quickly. The first correlation determines the apparent stable agglomerate size formed during NZVI transport in porous media for a fixed hydrogeochemical condition. The second correlation estimates the attachment efficiency (sticking coefficient) of the stable agglomerates. Both correlations are described using dimensionless numbers derived from parameters affecting deposition and agglomeration in porous media. The exponents for the dimensionless numbers are determined from statistical analysis of breakthrough data for polyelectrolyte-modified NZVI dispersions collected in laboratory scale column experiments for a range of ionic strength (1, 10, and 50 mM Na + and 0.25, 1, and 1.25 mM Ca2+), approach velocity (0.8 to 55 × 10-4 m/s), average collector sizes (d50 = 99 μm, 300 μm, and 880 μm), and polyelectrolyte surface modifier properties. Attachment efficiency depended on approach velocity and was inversely related to collector size, which is contrary to that predicted from classic filtration models. High ionic strength, the presence of divalent cations, lower extended adsorbed polyelectrolyte layer thickness, decreased approach velocity, and a larger collector size promoted NZVI agglomeration and deposition and thus limited its mobility in porous media. These effects are captured quantitatively in the two correlations developed. The application and limitations of using the correlations for preliminary design of in situ NZVI emplacement strategies is discussed.
|
|
| 8. |
- Phenrat, Tanapon, et al.
(författare)
-
Particle size distribution, concentration, and magnetic attraction affect transport of polymer-modified Fe0 nanoparticles in sand columns
- 2009
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:13, s. 5079-5085
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of particle concentration, size distribution (polydispersity) and magnetic attractive forces (Fe(0) content) on agglomeration and transport of poly(styrene sulfonate) (PSS) modified NZVI was studied in water-saturated sand (d(p) = 300 microm) columns. Particle concentrations ranged from 0.03 to 6 g/L in 5 mM NaCl/5 mM NaHCO3 at a pore water velocity of 3.2 x 10(-4) m/s. Three NZVI dispersions with different intrinsic particle size distributions obtained from sequential sedimentation are compared. The influence of magnetic attraction (Fe(0) content) on NZVI agglomeration and deposition in porous media is assessed by comparing the deposition behavior of PSS-modified NZVI (magnetic) having different Fe(0) contents with PSS-modified hematite (nonmagnetic) with the same surface modifier. At low particle concentration (30 mg/L) all particles were mobile in sand columns regardless of size or magnetic attractive forces. At high concentration (1 to 6 g/L), deposition of the relatively monodisperse dispersion containing PSS-modified NZVI (hydrodynamic radius (R(H)) = 24 nm) with the lowest Fe(0) content (4 wt%) is low (attachment efficiency (alpha) = 2.5 x 10(-3)), insensitive to particle concentration, and similar to PSS-modified hematite. At 1 to 6 g/L, the attachment efficiency of polydisperse dispersions containing both primary particles and sintered aggregates (R(H) from 15 to 260 nm) of PSS-modified NZVI with a range of Fe(0) content (10-60%) is greater (alpha = 1.2 x 10(-2) to 7.2 x 10(-2) and is sensitive to particle size distribution. The greater attachment for larger, more polydisperse Fe(0) nanoparticles with higher Fe(0) content is a result of their agglomeration during transport in porous media because the magnetic attractive force between particles increases with the sixth power of particle/agglomerate radius. A filtration model that considers agglomeration in porous media and subsequent deposition explains the observed transport of polydisperse PSS-modified NZVI at high concentration.
|
|
| 9. |
- Trevisan, Luca, et al.
(författare)
-
Investigation of mechanisms of supercritical CO2 trapping in deep saline reservoirs using surrogate fluids at ambient laboratory conditions
- 2014
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 29, s. 35-49
-
Tidskriftsartikel (refereegranskat)abstract
- Geological storage of carbon dioxide relies on the effectiveness of immobilizing CO2 in the pore space of deep geological formations through a number of trapping mechanisms that include capillary, dissolution, and mineral trapping. Improved fundamental understanding of these processes is expected to contribute toward better conceptual models, improved numerical models, more accurate assessment of storage capacities, and optimized placement strategies. However, studying these processes at a fundamental level is not feasible in field settings because fully characterizing the geologic variability at all relevant scales and making observations on the spatial and temporal distribution of the migration and trapping of supercritical CO2 (scCO(2)) is not practical. The specific goal of this study is to develop and implement an experimental method in intermediate scale test tanks under ambient laboratory conditions to make observations and generate data to improve the understanding of capillary trapping affected by fluid and formation properties. Since it is challenging to visualize multiphase flow processes occurring at high pressure conditions at the meter scale, a testing method was developed based on the use of surrogate test fluids to replace the scCO(2) and formation saline water. To set a foundation for extrapolating experimental results to the field, we chose a set of dimensionless groups that define the relative contributions of buoyancy, viscous, and capillary forces to the displacement behavior of immiscible fluids. The experiments were designed with the goal of understanding and accurately quantifying the immobilization of the scCO(2) analog in a homogeneous formation confined by a slightly dipping structural barrier. A set of three displacement experiments through unconsolidated sands with variable permeability was conducted in a quasi-two-dimensional flow cell to gain insight into the influence of buoyancy forces on the propagation of the displacing phase. This work takes advantage of laboratory experiments at the intermediate scale to investigate gravitational and hysteresis effects on entrapment of scCO(2) currents in brine-saturated reservoirs. Understanding these phenomena at a fundamental level represents a critical step to improve injection strategies and to enhance capillary trapping mechanisms.
|
|
