scholarly journals Interaction between Perched Epikarst Aquifer and Unsaturated Soil Cover in the Initiation of Shallow Landslides in Pyroclastic Soils

Water ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 948 ◽  
Author(s):  
Roberto Greco ◽  
Pasquale Marino ◽  
Giovanni Francesco Santonastaso ◽  
Emilia Damiano
Keyword(s):  
Water Flow ◽  
Soil Cover ◽  
Response Times ◽  
Spring Discharge ◽  
Fractured Bedrock ◽  
Groundwater Circulation ◽  
Physically Based ◽  
Perched Aquifer ◽  
Fractured Limestone ◽  
Different Response

A physically based mathematical model of the slope of Cervinara (southern Italy), which is characterized by a shallow pyroclastic soil cover laying upon a limestone fractured bedrock, has been developed. Previous and current ongoing monitoring suggested that leakage through the soil–bedrock interface occurred, with leaking water temporarily stored in a perched aquifer located in the upper part of the fractured limestone (epikarst). This aquifer supplied several springs, and recharge to the deeper groundwater circulation occurred. Hence, in the proposed model, the unsaturated water flow taking place within the soil cover is coupled with the saturated water flow in the perched aquifer. The application of the model to the simulation of the slope hydrologic behavior over a period of 11 years, between 2006–2017, provides realistic results in terms of soil storage, epikarst storage, spring discharge, and groundwater recharge. The different response times of soil and epikarst aquifer to precipitation input allow distinguishing the hydrological predisposing causes of potential landsliding (i.e., a few months of persistent rainfall that is capable of filling the epikarst aquifer) from the triggers, which are represented by single intense rainfall events. The application of the model offers a key of interpretation of the hydrological processes leading to the landslide that occurred on 16 December 1999.

Identifying distributions of response times in karst aquifers

2021 ◽  
Author(s):  
Fulvio Boano ◽  
Alberto Viglione ◽  
Bartolomeo Vigna
Keyword(s):  
Response Time ◽  
Response Times ◽  
Karst Aquifer ◽  
Response Time Distribution ◽  
Spring Discharge ◽  
Aquifer Recharge ◽  
Flow Paths ◽  
Ill Posed ◽  
Response Time Distributions ◽  
Different Response

<p>In karst catchments, aquifer recharge occurs through a composite mosaic of subsurface flow paths. Precipitation infiltrates in the subsurface and flows along a complex network of fractures – that are characterized by different sizes and degrees of saturation –  before eventually reaching the catchment outlet. The discharge of a karst spring is the result of the contributions of these flow paths, that may differ widely in terms of lengths, velocities, and travel times. Monitoring the spring discharge can thus provide information about flow within the aquifer. In particular, the spring discharge signal can be interpreted as the lagged response of the aquifer to precipitation inputs over the catchment, with the aquifer being characterized by a distribution of response times that relates input (precipitation) to output (discharge). Identifying these response times is not a trivial task as the input-output problem is often mathematically ill-posed, which leads to amplification of the errors and may prevent finding a physically meaningful solution.</p><p>In this work we propose a method to evaluate the distribution of response times of a karst aquifer. The method, that was originally developed to deal with ill-posed problems in geostatistical applications, relies on a probabilistic description of precipitation inputs and discharge outputs, and it provides an estimate of the response time distribution and of its uncertainty. The method is here tested through the application to two datasets collected in two cave systems in Northern Italy (the Bossea system and the Vene/Fuse system) with different hydrogeological properties. The results demonstrate that the method successfully identifies different response time distributions that reflect the differences in aquifer characteristics of the two systems. Furthermore, differences among response time distributions relative to different precipitation events in each system provide valuable insights on seasonal variations in aquifer recharge and fracture saturation. The method can hence be applied as a tool for the indirect investigation of karst systems.</p>

scholarly journals Estimation of recharge in mountain hard-rock aquifers based on discrete spring discharge monitoring during base-flow recession

2021 ◽  
Author(s):  
Stefano Segadelli ◽  
Maria Filippini ◽  
Anna Monti ◽  
Fulvio Celico ◽  
Alessandro Gargini
Keyword(s):  
Hard Rock ◽  
Monitoring Program ◽  
Base Flow ◽  
Low Flow ◽  
Reliable Estimate ◽  
Spring Discharge ◽  
Aquifer Recharge ◽  
Clear Cut ◽  
Groundwater Circulation ◽  
Hard Rock Aquifers

AbstractEstimation of aquifer recharge is key to effective groundwater management and protection. In mountain hard-rock aquifers, the average annual discharge of a spring generally reflects the vertical aquifer recharge over the spring catchment. However, the determination of average annual spring discharge requires expensive and challenging field monitoring. A power-law correlation was previously reported in the literature that would allow quantification of the average annual spring discharge starting from only a few discharge measurements in the low-flow season, in a dry summer climate. The correlation is based upon the Maillet model and was previously derived by a 10-year monitoring program of discharge from springs and streams in hard-rock aquifers composed of siliciclastic and calcareous turbidites that did not have well defined hydrogeologic boundaries. In this research, the same correlation was applied to two ophiolitic (peridotitic) hard-rock aquifers in the Northern Apennines (Northern Italy) with well-defined hydrogeologic boundaries and base-outflow springs. The correlation provided a reliable estimate of the average annual spring discharge thus confirming its effectiveness regardless of bedrock lithology. In the two aquifers studied, the measurable annual outputs (i.e. sum of average annual spring discharges) could be assumed equal to the annual inputs (i.e. vertical recharge) based on the clear-cut aquifer boundaries and a quick groundwater circulation inferable from spring water parameters. Thus, in such setting, the aforementioned correlation also provided an estimate of the annual aquifer recharge allowing the assessment of coefficients of infiltration (i.e. ratio between aquifer recharge and total precipitation) ranging between 10 and 20%.

Water balance based on field monitoring for the assessment of landslide predisposing conditions in a slope covered with pyroclastic deposits over fractured limestone bedrock

2021 ◽  
Author(s):  
Roberto Greco ◽  
Luca Comegna ◽  
Emilia Damiano ◽  
Pasquale Marino ◽  
Lucio Olivares
Keyword(s):  
Shear Strength ◽  
Water Balance ◽  
Soil Cover ◽  
Field Monitoring ◽  
Time Domain Reflectometry ◽  
Hydrological Processes ◽  
Soil Suction ◽  
High Porosity ◽  
Limestone Bedrock ◽  
Fractured Limestone

<p>Many mountainous areas of Campania, southern Italy, are characterized by steep slopes covered with shallow deposits of loose pyroclastic materials, usually in unsaturated conditions, mainly constituted by layers of volcanic ash and pumice lapilli. The total cover thickness is quite variable, between 1.5 m and 2.5 m in the steepest part of the slopes while it reaches several meters at the foot, and it lays upon fractured limestone bedrock. Such pyroclastic materials usually exhibit extremely high porosity (even up to 75%) and saturated hydraulic conductivity (in the order of 10<sup>-4</sup> m/s). The equilibrium of the soil cover is ensured, up to inclination angles of 50°, by the contribution of soil suction to shear strength. Wetting of the soil cover during rainfall infiltration can cause a reduction of suction and, therefore, of the effective shear strength. This action sometimes leads to the triggering of shallow landslides, which often develop in the form of fast and destructive flows.</p><p>To capture the main effects of precipitations on the equilibrium of these slopes, hydrological monitoring activities have been carried out at the slope of Cervinara, located around 40 km northeast of Naples, where a destructive flowslide occurred in December 1999. An automatic hydro-meteorological station was installed at the elevation of 585m a.s.l., immediately near the scarp of the major landslide occurred in 1999. The meteorological equipment includes a rain gauge, a thermo-hygrometer, a thermocouple for soil temperature, an anemometer, a pyranometer, and a barometric sensor. The hydrological equipment consists of six tensiometers (located at depths between -0.2 m and -3.0 m below the ground surface) and six metallic time domain reflectometry probes (buried at depths between -0.3 m and -2.0 m) for the measurements of soil suction and water content, respectively. Furthermore, the water level in two streams located at the foot of the slope has been first manually monitored every month, and then, since March 2019, one of the two stream sections was instrumented with a probe, measuring water pressure, temperature, and electrical conductivity with hourly resolution.</p><p>The measurements allowed quantifying the major hydrological processes draining the soil cover after rainwater infiltration (i.e. evapotranspiration, overland and sub-surface runoff, leakage through the soil-bedrock interface), eventually assessing the water balance of the slope for three hydrological years (2017-2018, 2018-2019, 2019-2020).  The field monitoring data allowed the identification of the complex hydrological processes involving the unsaturated pyroclastic soil and the shallow groundwater system developing in the limestone bedrock, which control the conditions that potentially predispose the slope to landslide triggering. Specifically, late autumn has been identified as the potentially most critical period, when drainage through the soil-bedrock interface is not yet effective, owing to the still dry conditions at the base of the soil cover, but the slope already receives large amounts of precipitation.</p>

The Daisy agroecological system model: A physically based model for preferential water flow and solute transport in drained agricultural fields

2021 ◽  
Author(s):  
Efstathios Diamantopoulos ◽  
Maja Holbak ◽  
Per Abrahamsen
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Preferential Flow ◽  
Column Experiment ◽  
Soil Matrix ◽  
Physically Based Model ◽  
Physically Based ◽  
Rapid Transport ◽  
Preferential Water

<p>Preferential water flow and solute transport in agricultural systems affects not only the quality of groundwater but also the quality of surface waters like streams and lakes. This is due to the rapid transport of agrochemicals, immediately after application, through subsurface drainpipes and surface water. Experimental evidence attributes this to the occurrence of continuously connected pathways, connecting the soil surface directly with the drainpipes. We developed a physically-based model describing preferential flow and transport in biopores and implemented it in the agroecological model Daisy. The model simulates the often observed rapid transport of chemicals from   the upper soil layers to the drainpipes or to deeper layers of the soil matrix. Based on field investigations, biopores with specific characteristics can be parameterized as classes with different vertical and horizontal distributions. The model was tested against experimental data from a column experiment with an artificial biopore and showed good results in simulating preferential flow dynamics. We illustrate the performance of the new approach, by conducting five simulations assuming a two-dimensional simulation domain with different biopore parametrizations, from none to several different classes. The simulation results agreed with experimental observations reported in the literature, indicating rapid transport from the soil to the drainpipes. Furthermore, the different biopore parametrizations resulted in distinctly different leaching patterns, raising the expectation that biopore properties could be estimated or constrained based on observed leaching data and direct measurements.</p>

scholarly journals UV-B Radiation Affects Photosynthesis-Related Processes of Two Italian Olea europaea (L.) Varieties Differently

Plants ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 1712
Author(s):  
Chiara Piccini ◽  
Giampiero Cai ◽  
Maria Celeste Dias ◽  
Marco Romi ◽  
Roberta Longo ◽  
...  
Keyword(s):  
Reactive Oxygen Species ◽  
Defense Mechanisms ◽  
Photosynthetic Efficiency ◽  
Response Times ◽  
Olive Tree ◽  
Antioxidant Response ◽  
Oxygen Species ◽  
Adaptation Mechanism ◽  
Long Period ◽  
Different Response

Given the economical importance of the olive tree it is essential to study its responses to stress agents such as excessive UV-B radiation, to understand the defense mechanisms and to identify the varieties that are able to cope with it. In the light of the analysis carried out in this study, we argue that UV-B radiation represents a dangerous source of stress for the olive tree, especially in the current increasingly changing environmental conditions. Both the varieties considered (Giarraffa and Olivastra Seggianese), although resistant to the strong treatment to which they were exposed, showed, albeit in different ways and at different times, evident effects. The two varieties have different response times and the Giarraffa variety seems better suited to prolonged UV-B stress, possible due to a more efficient and quick activation of the antioxidant response (e.g., flavonoids use to counteract reactive oxygen species) and because of its capacity to maintain the photosynthetic efficiency as well as a relatively higher content of mannitol. Moreover, pigments reduction after a long period of UV-B exposure can also be an adaptation mechanism triggered by Giarraffa to reduce energy absorption under UV-B stress. Olivastra Seggianese seems less suited to overcome UV-B stress for a long period (e.g., higher reduction of Fv/Fm) and has a higher requirement for sugars (e.g., glucose) possible to counteract stress and to restore energy.

scholarly journals Development of physically based liquid water schemes for Greenland firn-densification models

2019 ◽  
Vol 13 (7) ◽  
pp. 1819-1842 ◽  
Author(s):  
Vincent Verjans ◽  
Amber A. Leeson ◽  
C. Max Stevens ◽  
Michael MacFerrin ◽  
Brice Noël ◽  
...  
Keyword(s):  
Water Flow ◽  
Liquid Water ◽  
Preferential Flow ◽  
Greenland Ice Sheet ◽  
Single Domain ◽  
Richards Equation ◽  
Retention Capacity ◽  
Water Percolation ◽  
Physically Based ◽  
Dual Domain

Abstract. As surface melt is increasing on the Greenland Ice Sheet (GrIS), quantifying the retention capacity of the firn layer is critical to linking meltwater production to meltwater runoff. Firn-densification models have so far relied on empirical approaches to account for the percolation–refreezing process, and more physically based representations of liquid water flow might bring improvements to model performance. Here we implement three types of water percolation schemes into the Community Firn Model: the bucket approach, the Richards equation in a single domain and the Richards equation in a dual domain, which accounts for partitioning between matrix and fast preferential flow. We investigate their impact on firn densification at four locations on the GrIS and compare model results with observations. We find that for all of the flow schemes, significant discrepancies remain with respect to observed firn density, particularly the density variability in depth, and that inter-model differences are large (porosity of the upper 15 m firn varies by up to 47 %). The simple bucket scheme is as efficient in replicating observed density profiles as the single-domain Richards equation, and the most physically detailed dual-domain scheme does not necessarily reach best agreement with observed data. However, we find that the implementation of preferential flow simulates ice-layer formation more reliably and allows for deeper percolation. We also find that the firn model is more sensitive to the choice of densification scheme than to the choice of water percolation scheme. The disagreements with observations and the spread in model results demonstrate that progress towards an accurate description of water flow in firn is necessary. The numerous uncertainties about firn structure (e.g. grain size and shape, presence of ice layers) and about its hydraulic properties, as well as the one-dimensionality of firn models, render the implementation of physically based percolation schemes difficult. Additionally, the performance of firn models is still affected by the various effects affecting the densification process such as microstructural effects, wet snow metamorphism and temperature sensitivity when meltwater is present.

“Same” “Different” Response Times with Multi-Attribute Stimulus Differences

1967 ◽  
Vol 24 (2) ◽  
pp. 543-554 ◽  
Author(s):  
Raymond S. Nickerson
Keyword(s):  
Response Times ◽  
Visual Stimuli ◽  
Error Rates ◽  
Different Response

S's task was to decide as quickly as possible whether two simple visual stimuli were the same or different. Stimuli varied with respect to 3 attributes: size, color, and shape. Pairs of stimuli were presented either simultaneously or in sequence. “Different” RTs varied inversely with the number of attributes with respect to which the 2 stimuli of a pair differed, d. “Same” RTs were shorter than would be expected from an extrapolation of the results with d ≥ 1 (different stimuli) to include the case of d = 0 (same stimuli). Error rates were related to d in much the same way as was RT.

scholarly journals Evidence Accumulation Modelling Reveals that Gaussian Noise Accounts for Inhibition of Return

2020 ◽  
Author(s):  
Tal Seidel Malkinson ◽  
Alexia Bourgeois ◽  
Nicolas Wattiez ◽  
Pierre Pouget ◽  
Paolo Bartolomeo
Keyword(s):  
Gaussian Noise ◽  
Inhibition Of Return ◽  
Response Times ◽  
Information Criterion ◽  
Model Parameters ◽  
Noise Parameter ◽  
Evidence Accumulation ◽  
Cortical Regions ◽  
Different Response ◽  
The Right

AbstractInhibition of return (IOR) refers to the slowing of response times (RTs) for stimuli repeated at previously inspected locations, as compared with novel ones. However, the exact processing stage(s) at which IOR occurs, and its nature across different response modalities, remain debated. We tested predictions on these issues originating from the FORTIOR model (fronto-parietal organization of response times in IOR; Seidel Malkinson & Bartolomeo, 2018), and from evidence accumulation models. We reanalysed RT data from a target-target IOR paradigm (Bourgeois et al.,2013a, 2013b) by using a LATER-like evidence accumulation model (Carpenter & Williams, 1995), to test the predictions of FORTIOR, and specifically whether IOR could occur at sensory/attentional stages of processing, or at stages of decision and action selection. We considered the following conditions: manual or saccadic response modality, before or after TMS perturbation over four cortical regions. Results showed that the Gaussian noise parameter best explained both manual and saccadic IOR, suggesting that in both response modalities IOR may result from slower accumulation of evidence for repeated locations. Additionally, across stimulated regions, TMS affected only manual RTs, lowering them equally in the conditions with repeated targets (Return) and non-repeated targets (Non-return). Accordingly, the modelling results show that TMS stimulation did not significantly alter the pattern between model parameters, with the Gaussian noise parameter remaining the parameter best explaining the Return - Non-return RT difference. Moreover, TMS over the right intra-parietal sulcus (IPS) perturbed IOR by shortening the Return RT. When directly testing this effect by modelling the TMS impact in the Return condition, the Bayesian information criterion of the Gaussian noise parameter was the smallest, but this effect did not reach significance. These results support the hypothesis that target-target IOR is a predominantly sensory/attentional phenomenon, and may be modulated by activity in fronto-parietal networks.

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