Clogging Layer Research Articles

Two-dimensional Analytical Derivation of Incipient Desaturation Criterion in Stream-aquifer Flow Exchange

A criterion for incipient desaturation for a stream and an aquifer initially in saturated hydraulic connection is derived analytically. The riverbed acts as a clogging layer. Such a criterion cannot be derived using a one-dimensional analysis. At least a two-dimensional analysis is required. It applies for a variety of shape of cross-sections. The formulae are algebraic and show explicitly the various factors that affect the initiation of desaturation such as river width, thickness of the aquifer, thickness of the clogging layer, conductivities of the clogging layer and of the aquifer, (drainage) entry pressure of the aquifer, ponded depth over the riverbed and aquifer head at some distance from the river bank. It is shown also that neglecting the change in thickness of the capillary fringe due to flow, as opposed to its hydrostatic value, has little impact on the accuracy of the criteria for incipient desaturation.

Clogging process by suspended solids during groundwater artificial recharge: Evidence from lab simulations and numerical modelling

AbstractPermeability reduction of infiltration media due to suspended solid (SS) clogging is the bane of groundwater artificial recharge. To overcome the clogging problem and advance the understanding of the process‐based spatial‐temporal evolution of SS clogging, a 1D laboratory column simulation was carried out, followed by numerical modelling of the experimental data in this study. It was found that clogging caused a reduction in the hydraulic conductivity (K) in the upper layer at the beginning and extended deeper to approximately 50 cm, and no reduction in K was detected below 52 cm throughout the experimental period of 129 hr. The most clogged layer spanned from the surface to a depth of 11 cm, and the middle 11–52 cm was characterized by a slight decrease in K. The clogging rates of the different layers decreased with the depth, which was based on data analysis, with the largest value of 0.038 hr−1 in the upper 1 cm. The overall K began to decrease from the surface layer and was increasingly affected by clogging with time. A mathematical model was established to simulate the SS clogging process evolution based on considerations of the attachments and detachments of particles. Then the model was applied to perform several scenario analyses after calibration and validation using the data obtained in the experiment. The simulation results indicated that the SS concentration was much more sensitive than the groundwater depth below the land surface, and 10 days of constant recharge is recommended as the disposal cycle of the clogged layer under the given conditions.

Modelling of 2-D seepage from aquifer towards stream via clogged bed: The toth-trefftz legacy conjugated

Baseflow-type interaction between a river and adjacent/subjacent aquifer across a thin clogging layer of fine sediments controls the dynamics of surface-pore water resources, quality of both waters, seepage induced erosion of the river bed and other hydrological phenomena. Transient 2D phreatic flow from an unconfined aquifer into a river with a thin low-permeable cake (hydraulic skin) is approximated by a sequence of steady states, each of which assumes the water table to be horizontal. The scalar and vector fields of piezometric head, stream function and Darcian velocity are found from analytical solution of the Dirichlet and Robin (linear combination of the velocity potential and its normal derivative) boundary value problems for the piezometric head (harmonic function). The time-shrinking Tothian “unit basins” are a half-strip, half-plane or rectangle. Stream banks are assumed to be horizontal or vertical segments. Cross-flow from the aquifer into the stream is controlled by the aquifer-skin conductivity ratio and the stages of the river and adjacent aquifer. The head and cross-flux on the interface (Robin's boundary) is shown to vary along this line and therefore even for vertical river banks the Dupuit–Forchheimer approximation is not strictly valid. Numerical simulations in HYDRUS2D are reasonably close to the analytical results. Early-stage drawdown of a rectangular cake due to a sudden drop of the water level on the river side and formation of a seepage face is analysed with potential applications to stability of earth dams.

Clogging of Infiltration Basin and Its Impact on Suspended Particles Transport in Unconfined Sand Aquifer: Insights from a Laboratory Study

A laboratory study was undertaken to investigate the physical clogging of a sand medium by injecting suspended particles (SP), with diameters ranging from 0.03 to 63.41 μm, into an infiltration basin, which was installed in a sand tank under the condition of constant head. The hydraulic conductivity (K) of the saturated porous medium was found to have decreased by 27% because of re-arrangement over the seven days of self-filtration. A clogging layer was observed on the infiltration basin bottom, probably due to straining over the stormwater infiltration stage. Particle-size analyses also indicate that retention of bigger SP led to faster straining of smaller SP, despite the small fraction of bigger SP. The clogging layer weakened the hydraulic connection between the water level in the basin and the water table of the unconfined aquifer until nearly no water could infiltrate into the aquifer. The deposition of finer SP that entered into the aquifer are governed by the hydrodynamic forces. These finer SP caused non-uniform permeability reduction of the porous medium, with an estimated 35% of permeability reduction occurring beneath the infiltration basin. However, the reduction appears to be reversible, as the fine SP deposited on the pore surfaces of the porous medium can be released or detached by the continuous horizontal hydraulic gradient. Extended tailing of the outlet breakthrough curve (BTC) also strongly supported the detachment of SP. This study focused on the effects of particles’ polydispersity and hydrodynamic forces on the hydraulic characteristics of the porous medium.

Reactive Transport of Nutrients and Bioclogging During Dynamic Disconnection Process of Stream and Groundwater

AbstractBiofilm‐induced dynamic evolution of streambed permeability commonly concurs with the transition from connection to disconnection between surface water and groundwater in arid regions. However, in most previous studies, static streambeds were assumed to examine the evolution of disconnection, or despite dynamic streambeds being considered, the feedbacks between nutrients transport and microbial growth were ignored. In this study, we developed an innovative coupled variably saturated flow, microbial growth, biogeochemical reactions, and bioclogging model. We applied this model to investigate the feedbacks between nutrients transport and microbial growth and their controls on infiltration evolution. Our results showed that a new clogging layer can naturally develop due to these feedbacks and does not require prior clogging. The development of the new clogging layer promotes the occurrence of disconnection. These results illustrate that as bioclogging is a dominant process, previous static disconnection conditions cannot be used as criteria to predict whether disconnection can occur in a stream‐aquifer system. Furthermore, different from the previous assumption of constant specific microbial growth rates, biomass growth, and streambed permeability evolution are self‐limiting. Accordingly, due to initial low growth rate, infiltration increases when the water table declines, and it then decreases and reaches a minimum while a stable biofilm is developed. These trends coincide with the infiltration variations reported in previous field investigations. After reaching the minimum, infiltration increases again with decline of the water table until achieving a constant at the moment of disconnection. This stage was missing in previous studies because constant specific growth rates were assumed.

Energy Calculation of Contact Surface Adhesion at Interaction in Different Media

Investigating the kinetics of clogged layer formation on the cutting surface of a diamond grinding wheel (DGW) is necessary to avoid the loss of its working capacity. The paper considers the dependence of the adhesion energy of various materials on the dressing current of the grinding wheel and effective grinding capacity. We provide the calculations of the adhesion energy and the surface energy within the proposed assumptions in the implementation of various grinding methods, as well as the comparative analysis of the obtained results. Grinding by a combined electric diamond method (CEDG) with simultaneous dressing of the grinding wheel eliminates adhesive phenomena. The particles of the solid bodies near-surface layers are established to be characterized by long-range interaction. This is especially true for the surface active centers: microfractures, asperities, defects of the crystal lattice resulting in the dislocations and roaming atoms movement to the surface. These phenomena are typical for the adhesion of solid bodies.

Application of exchangeable carbon-bonded alumina foam filters in an industrial tundish for the continuous casting of steel

Various melt refining techniques were developed in the past and led to ongoing improvement of casting quality. One of these processes is the so-called metal melt filtration, which became state of the art especially in aluminum foundry operations by using ceramic foam filters. Attempts to adapt the technique for the continuous casting of steel showed numerous difficulties due to the severe thermomechanical conditions and the high quantity of processed melt. Premature blockage or failure of ceramic foam filters implemented in the tundish promoted the application of flow control devices and multi-hole filters as alternatives. In the present study, a new approach for ceramic foam filters in the continuous casting of steel was tested. Thereby, the main disadvantage of limited filter service lifetime was circumvented by the application of an exchangeable filter system without disturbing the underlying continuous casting process. Cylindrical carbon-bonded alumina foam filters were prepared and mounted on alumina-carbon shafts using different adhesives and slag protection measures. The filters were immersed by a crane into the steel melt in an industrial tundish with 80 t capacity. During each test, one batch with approximately 380 t of steel was cast at over 1550 °C before removing the filter. The application of high-alumina mortar as adhesive and a compact filter geometry without macro channels proved to be essential for the successful operation. Samples of the corresponding filter were analyzed by digital light microscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction. The complementary investigations revealed the formation of pronounced clogging layers based on aluminum-rich calcium aluminates, which can be clearly distinguished from the synthetic slag material containing silicon and other trace elements. At the bottom of the filter pronounced clusters of coral-like and plate-like inclusions were observed, which approached the filter surface by buoyancy.

Comparison of the Prediction Methods for Production Rate of Collector Well in Riverbank Filtration

In this study, the Milojevic formula, the Hantush formula, and the numerical method, which are the three different methods used to predict the production rate of collector wells in riverbank filtration, were compared. Given a collector well placed in a hypothetical geologic formation, the production rate of the collector predicted by each method was as follows: 5,972 m3/day by the Milojevic formula, 5,286 m3/day by the Hantush formula, and 6,600 m3 /day by the numerical method. From these results, the Hantush formula appears to make the safest prediction. However, the Milojevic formula and the Hantush formula cannot take into account the clogging of riverbed which is inevitable in riverbank filtration. Therefore, for now the best method to apply in a collector well design in riverbank filtration is the numerical method with clogging layer included. Key words: Riverbank Filtration, Production Rate, Hantush, Milojevic, Numerical Method

Reduction of clog matter in constructed wetlands by metabolism of Eisenia foetida: Process and modeling

Introducing of earthworms to constructed wetlands (CWs) has been considered as a new approach to solve the clogging problems in the long-established systems. Despite its potential advantage, the correlational researches are still in the stage of preliminary observation and speculation. This paper presents a comprehensive and in-depth research about the positive effects of earthworms (Eisenia foetida) on clog matter (CM) reduction through different pathways, including in vivo metabolism and uptake, conversion, transport, and promotion of microorganism quantities. The results showed that the metabolism and uptake by Eisenia foetida could effectively reduce the CM content at an average removal rate of 0.155 mg g−1 d−1, which was obviously higher than the rate of CM decomposition by microorganisms alone. Through the metabolism of earthworms, the amounts of proteins and polysaccharides in CM were decreased, while the amounts of humin and nucleic acids were increased. Simultaneously, the viscosity of CM was reduced by 0.0082 mPa s g−1 d−1, and the quantity of microorganisms was increased by 0.0109 mg g−1 d−1, which finally made the treated CM can be easily washed away and decomposed. Furthermore, earthworms could reduce the CM content in the clogging layer by transporting the metabolic products out. A regression model was further performed for describing the interaction between earthworm and CM. The simulated value of porosity fitted well with the measured one, suggesting that the earthworms can increase the substrate porosity at a rate of 0.33 mL g−1 d−1. This study quantitively depicted the mechanisms of earthworms on the decrement of CM content in CWs, which is of great benefit for the engineering management of constructed wetlands in the future. We also proposed that the density of introduced earthworms should exceed a certain threshold for effectively increasing the substrate porosity and solving the clogging problems.

Estimating the Spatial Extent of Unsaturated Zones in Heterogeneous River‐Aquifer Systems

AbstractThe presence of unsaturated zones at the river‐aquifer interface has large implications on numerous hydraulic and chemical processes. However, the hydrological and geological controls that influence the development of unsaturated zones have so far only been analyzed with simplified conceptualizations of flow processes, or homogeneous conceptualizations of the hydraulic conductivity in either the aquifer or the riverbed. We systematically investigated the influence of heterogeneous structures in both the riverbed and the aquifer on the development of unsaturated zones. A stochastic 1‐D criterion that takes both riverbed and aquifer heterogeneity into account was developed using a Monte Carlo sampling technique. The approach allows the reliable estimation of the upper bound of the spatial extent of unsaturated areas underneath a riverbed. Through systematic numerical modeling experiments, we furthermore show that horizontal capillary forces can reduce the spatial extent of unsaturated zones under clogged areas. This analysis shows how the spatial structure of clogging layers and aquifers influence the propensity for unsaturated zones to develop: In riverbeds where clogged areas are made up of many small, spatially disconnected patches with a diameter in the order of 1 m, unsaturated areas are less likely to develop compared to riverbeds where large clogged areas exist adjacent to unclogged areas. A combination of the stochastic 1‐D criterion with an analysis of the spatial structure of the clogging layers and the potential for resaturation can help develop an appropriate conceptual model and inform the choice of a suitable numerical simulator for river‐aquifer systems.

Thermal‐infrared remote sensing of surface water–groundwater exchanges in a restored anastomosing channel (Upper Rhine River, France)

AbstractEcohydrological processes are a key element to consider in functional river restorations. In the framework of a LIFE+ European restoration program, we have investigated the potential for airborne thermal‐infrared remote sensing to map surface water–groundwater exchanges and to identify their driving factors. We focused our attention on anastomosing channels on an artificial island of the Upper Rhine River (Rohrschollen), where a new channel was excavated from the floodplain to reconnect an older channel in its upstream part. These hydraulic engineering works led to an increased inflow from the Rhine Canal. Here, we propose an original data treatment chain to (a) georeference the thermal‐infrared images in geographic information system based on visible images, (b) detect and correct data errors, and (c) identify and locate thermal anomalies attributed to groundwater inputs and hyporheic upwellings. Our results, which have been compared to morpho‐sedimentary data, show that groundwater upwelling in the new channel is controlled by riffle–pool sequences and bars. This channel is characterized by large bedload transport and morphodynamic activity, forming riffles and bars. In the old channel, where riffle–pool sequences no longer exist, due to impacts of engineering works and insufficient morphodynamic effects of the restoration, thermal anomalies appeared to be less pronounced. Groundwater inputs seem to be controlled by former gravel bars outcropping on the banks, as well as by local thinning of the low‐permeability clogging layer on the channel bed.

Development of a Denitrifying Biofilter with Short Start-up Period

In the present work, a novel down-flow biofilter with four identical layers was developed for the de-nitrification of 100 mg L-1 nitrate contaminated wastewater, flowing horizontally from one layer to another in a continuous fashion. This biofilter can be applied for long-term continuous wastewater treatment without any need to whole system shutdown and backwashing. The clogged layer or the deactivated section can be easily spotted and repaired while the system is under continuous operation. To attain a short startup period, the effect of two main constructional parameters, namely, filter media and inoculants source, were then investigated.. Two studied filter media were sand and woodchips. The pure culture of Saccharomyces cerevisiae and the mixed cultures of activated sludge and wastewater were three common inoculants under investigation. The biofilter packed with woodchips seeded with the wastewater resulted in the least startup period of about 3 days with a steady nitrate removal efficiency of 90 %.

Riverbed Clogging and Sustainability of Riverbank Filtration

Clogging refers to a reduction of riverbed hydraulic conductivity. Due to difficulties in determining the thickness of the clogging layer, the leakage coefficient (L) is introduced and used to quantify the recoverable portion of bank filtrate. L was determined at several riverbank filtration (RBF) sites in field tests and using an analytical solution. Results were compared with data from similar experiments in the early 1970s and 1991–1993. In the 1980s, severe river water pollution in conjunction with high water abstraction led to partly unsaturated conditions beneath the riverbed. A leakage coefficient L of 5 × 10−7 s−1 was determined. After water quality improvement, L increased to 1–1.5 × 10−6 s−1. An alternative, cost and time efficient method is presented to estimate accurate leakage coefficients. The analytical solution is based on groundwater level monitoring data from observation wells next to the river, which can later feed into numerical models. The analytical approach was able to reflect long-term changes as well as seasonal variations. Recommendations for its application are given based on experience.

River Seepage Conductance in Large-Scale Regional Studies.

Flow exchange between surface and groundwater is of great importance be it for beneficial allocation and use of water resources or for the proper exercise of water rights. In large-scale regional studies, most numerical models use coarse grid sizes, which make it difficult to provide an accurate depiction of the phenomenon. In particular, a somewhat arbitrary leakance coefficient in a third type (i.e., Cauchy, General Head) boundary condition is used to calculate the seepage discharge as a function of the difference of head in the river and in the aquifer, whose value is often found by calibration. A different approach is presented to analytically estimate that leakance coefficient. It is shown that a simple equivalence can be deduced from the analytical solution for the empirical coefficient, so that it provides the accuracy of the analytical solution while the model maintains a very coarse grid, treating the water-table aquifer as a single calculation layer. Relating the empirical leakance coefficient to the exact conductance, derived from physical principles, provides a physical basis for the leakance coefficient. Factors such as normalized wetted perimeter, degree of penetration of the river, presence of a clogging layer, and anisotropy can be included with little computational demand. In addition the river coefficient in models such as MODFLOW, for example, can be easily modified when grid size is changed without need for recalibration.

Approximation of surface–groundwater interaction mediated by vertical streambank in sloping terrains

New analytical solutions are derived to estimate the interaction of surface and groundwater in a stream–aquifer system. The analytical model consists of an unconfined sloping aquifer of semi-infinite extant, interacting with a stream of varying water level in the presence of a thin vertical sedimentary layer of lesser hydraulic conductivity. Flow of subsurface seepage is characterized by a nonlinear Boussinesq equation subjected to mixed boundary conditions, including a nonlinear Cauchy boundary condition to approximate the flow through the sedimentary layer. Closed form analytical expressions for water head, discharge rate and volumetric exchange are derived by solving the linearized Boussinesq equation using Laplace transform technique. Asymptotic cases such as zero slope, absence of vertical clogging layer and abrupt change in stream-stage can be derived from the main results by taming one or more parameters. Analytical solutions of the linearized Boussinesq equation are compared with numerical solution of corresponding nonlinear equation to assess the validity of the linearization. Advantages of using a nonlinear Robin boundary condition, and combined effects of aquifer parameters on the bank storage characteristic of the aquifer are illustrated with a numerical example.

Unsteady Groundwater Flow over Sloping Beds: Analytical Quantification of Stream–Aquifer Interaction in Presence of Thin Vertical Clogging Layer

AbstractIn this paper, new analytical solutions are presented to quantify interaction of water between a sloping aquifer and stream of varying heads in presence of a thin vertical sedimentary layer. The initial hydrogeological setting consist of an unconfined sloping aquifer of semi-infinite extent, a fully penetrating stream of varying water level, and a vertical layer of streambank deposits that acts as an interface between stream and aquifer. Unsteady groundwater flow is characterized by a nonlinear Boussinesq equation subject to Robin boundary condition (also referred to as third kind and Cauchy boundary condition). Unlike existing results, which focus only on step changes in stream stage, the current study accounts for gradual rise and decline in stream level. A closed-form analytical solution for water head distribution, discharge rate, and net volumetric exchange of water between stream and aquifer are developed from the solution of a linearized advection-diffusion equation. Performance of the anal...

Impact of aquifer desaturation on steady-state river seepage

Flow exchange between surface and ground water is of great importance be it for beneficial allocation and use of the water resources or for the proper exercise of water rights. That exchange can take place under a saturated or unsaturated flow regime. Which regimes occur depend on conditions in the vicinity of the interactive area. Withdrawals partially sustained by seepage may not bring about desaturation but greater amounts eventually will. The problem considered in this paper deals only with the steady-state case. It is meant as a first step toward a simple, yet accurate and physically based treatment of the transient situation. The primary purpose of the article is to provide simple criteria for determination of the initiation of desaturation in an aquifer originally in saturated hydraulic connection with a river or a recharge area. The extent of the unsaturated zone in the aquifer will increase with increasing withdrawals while at the same time the seepage rate from the river increases. However the seepage increase will stop once infiltration takes place strictly by gravity in the aquifer and is no longer opposed by the capillary rise from the water table below the riverbed. Following desaturation simple criteria are derived and simple analytical formulae provided to estimate the river seepage based on the position of the water table mound below the clogging layer and at some distance away from the river bank. They fully account for the unsaturated flow phenomena, including the existence of a drainage entry pressure. Two secondary objectives were to verify that (1) the assumption of uniform vertical flow through a clogging layer and that (2) the approximation of the water table mound below the seepage area as a flat surface were both reasonably legitimate. This approach will be especially advantageous for the implementation of the methodology in large-scale applications of integrated hydrologic models used for management.

Composite forward osmosis hollow fiber membranes: Integration of RO- and NF-like selective layers for enhanced organic fouling resistance

Novel composite forward osmosis (FO) hollow fiber membranes with two selective skin layers were developed in the present work. The polyethersulfone (PES) hollow fiber substrate was firstly fabricated by a phase inversion method. The RO-like polyamide skin layer was then prepared on the inner surface of the hollow fiber substrate via interfacial polymerization (IP), while the NF-like outer skin layer was prepared via polyelectrolyte layer-by-layer (LBL) assembly. Three double-skinned membranes with negative (DS#1.5), positive (DS#2.0) and minimal (DS#2.5) outer surface charges under neutral pH environment were evaluated for their capabilities against organic fouling in the FO process.The newly developed double-skinned membranes possess water permeability greater than 2l/m2hbar and NaCl rejection higher than 95% under 2bar pressure, and have superior water flux and less salt leakage than the commercial HTI FO membranes as well as all the reported double-skinned FO membranes with RO-like selective layers. Most importantly, the double-skinned DS#2.5 hollow fiber membrane exhibits exciting organic fouling resistance because of its highly hydrophilic NF-like secondary layer with minimal surface charge and tightened surface structure to mitigate possible substrate pore clogging and fouling layer formation. A stable water flux of around 25l/m2h was attained for DS#2.5 membrane using <0.5M NaCl as the draw solution and a water containing 200ppm dextran (DEX) or Aldrich humic acid (AHA), or lysozyme (LYS) and 10mM NaCl as the model feed in the active layer against the draw solution (AL-DS) configuration, suggesting its great potential for practical FO applications.

A novel method to evaluate the effect of a stream restoration on the spatial pattern of hydraulic connection of stream and groundwater

Summary Stream restoration aims at an enhancement of ecological habitats, an increase of water retention within a landscape and sometimes even at an improvement of biogeochemical functions of lotic ecosystems. For the latter, good exchange between groundwater and stream water is often considered to be of major importance. In this study hydraulic connectivity between river and aquifer was investigated for a four years period, covering the restoration of an old oxbow after the second year. The oxbow became reconnected to the stream and the clogging layer in the oxbow was excavated. We expected increasing hydraulic connectivity between oxbow and aquifer after restoration of the stream, and decreasing hydraulic connectivity for the former shortcut due to increased clogging. To test that hypothesis, the spatial and temporal characteristics of the coupled groundwater-stream water system before and after the restoration were analysed by principal component analyses of time series of groundwater heads and stream water levels. The first component depicted between 53% and 70% of the total variance in the dataset for the different years. It captured the propagation of the pressure signal induced by stream water level fluctuations throughout the adjacent aquifer. Thus it could be used as a measure of hydraulic connectivity between stream and aquifer. During the first year, the impact of stream water level fluctuations decreased with distance from the regulated river (shortcut), whereas the hydraulic connection of the oxbow to the adjacent aquifer was very low. After restoration of the stream we observed a slight but not significant increase of hydraulic connectivity in the oxbow in the second year after restoration, but no change for the former shortcut. There is some evidence that the pattern of hydraulic connectivity at the study site is by far more determined by the natural heterogeneity of hydraulic conductivities of the floodplain sediments and the initial construction of the shortcut rather than by the clogging layer in the oxbow.

Riverbed clogging experiments at potential river bank filtration sites along the Ping River, Chiang Mai, Thailand

Riverbank filtration (RBF) is a process during which river water is subjected to subsurface flow prior to abstraction wells, often characterized by improved water quality. The induced infiltration of river water through the riverbed also creates a clogging layer. This decreases riverbed permeability and abstraction rates, particularly if the river water has high turbidity, as in Thailand. As Chiang Mai Province is one of the most favorable sites for future RBF construction in Thailand, two sites, Mae Rim and San Pa Tong, were selected to simulate clogging by using a channel experiment. The mobile experimental apparatus was set up at the bank of the river in order to use fresh river water. Riverbed sediment was used as channel bed and filling material for the columns. The aim was to simulate riverbed clogging using river water with high turbidity and determine the effect of clogging, which can be quantified using vertical hydraulic conductivity (Kv). An increase in channel flow velocity caused partial removal of a clogging layer in only the top 0.03 m of the sediment column. The combination of low channel flow and high turbidity leads to much more clogging than high channel flow and low turbidity. A complete manual removal of the external clogging layer led to an increase in Kv, but the initial Kv values were not recovered. The external clogging had a lower effect on Kv than internal clogging. For planning new RBF sites along high-turbidity rivers, reduction in Kv to estimate RBF well yield cannot be calculated based only on initial Kv but requires field experiments.