Hydrogeological explanation of seepage diseases in stone grottoes: a case study of Maijishan Grottoes, China

This research studied the seepage diseases (water discharge and salt precipitation) in Maijishan Grottoes from the perspective of hydrogeology. Maijishan Grottoes is one of the extent large group of grottoes in China, where its cliff, on mount Maiji, the carrier of the grottoes, has been reinforced by concrete cover in a large area. As a case study, the physical and chemical processes of the seepage are deduced through the relationships between the flow rate of discharge water (DW) and precipitation, and through the water chemistry diversity including pH, electrical conductivity (EC), and Ionic composition between DW and rainwater (RW) and a controlled spring water (SW). Constructive results are obtained. Firstly, a perched aquifer is confirmed in the mount. All the RW will gather at the aquifer, and then discharge through 3 independent routes that connect the aquifer and grotto site. 3 kinds of water discharge response to precipitation are defined to correspond to the 3 routs: Immediate Response (I.Resp), Delay Response (D.Resp), and Stealth Response (S.Resp), these responses make up the majority of the DW. On the other hand, 2-staged chemical evolution is also been confirmed during the seepage, where stage I took place in the aquifer and stage II took place at shallow, the concrete only participate in the chemical evolution at stage II, resulted in high pH [7.77, 11.69] and EC [513, 3540] (µS/cm) in DW compared to the SW and RW.

Linking Hydrogeology and Ecology in Karst Landscapes: The Response of Epigean and Obligate Groundwater Copepods (Crustacea: Copepoda)

Groundwater invertebrate communities in karst landscapes are known to vary in response to multiple environmental factors. This study aims to explore the invertebrate assemblages’ composition of an Apennine karst system in Italy mainly described by the Rio Gamberale surface stream and the Stiffe Cave. The stream sinks into the carbonate rock and predominantly feeds the saturated karst into the cave. For a minor portion, groundwater flows from the epikarst and the perched aquifer within it. The spatial distribution of the species belonging to the selected target group of the Crustacea Copepoda between the surface stream and the groundwater habitats inside the cave highlighted a different response of surface-water species and obligate groundwater dwellers to the hydrogeological traits of the karst unit. Our results suggest that fast endorheic infiltration routes promoted the drift of epigean species from the surface to groundwater via the sinking stream while most of the obligate groundwater dwellers come from the perched aquifer in the epikarst from diffuse infiltration pathways.

Formation of box canyons by mass failure in limestone: A modelling study of the role of groundwater seepage

<p>Groundwater seepage has been shown to unambiguously lead to channel formation inunconsolidated sand to gravel sized sediments. However, its role in the evolution of bedrocklandscapes remains controversial. In this study, we use the coastline of the Maltese Islands as a case study to establish if and how groundwater seepage can form box canyons in limestones. The study area comprises up to 40 m high coralline limestone cliffs, with a mean fracturedensity of 1 in 5 m, overlying a ductile marl layer. The permeability contrast promotes the development of a perched aquifer and groundwater seepage at the cliff face. We  ran numerical simulations using a 3D distinct element model based on geological, geotechnical and hydrological baseline information from the study state, and explored three potential mechanisms: (i) fracture widening by fluid pressure and dissolution associated to groundwater flow and seepage, (ii) fracture widening by loss of support at the base due tomarl displacement resulting from increased water content, and (iii) a combination of (i) and (ii). We also took into consideration two scenarios: (a) uniform groundwater seepage, and (b)focused groundwater seepage. Our results suggest that the combination of mechanisms (iii) and the scenario with focused groundwater seepage (b) give rise to the box canyonmorphology observed at the site. Box canyons thus initiate and grow via detachment of limestone blocks and their toppling, which is more concentrated at the head where groundwater seepage occurs.</p>

Connecting hillslope and runoff generation processes in the Ethiopian Highlands: The Ene-Chilala watershed

Effective watershed planning requires an understanding of the hydrology. In the humid tropical monsoon climates and especially in volcanic highland regions such as the Ethiopian Highlands, the understanding of watershed processes is incomplete. The objective is to better understand the hydrology of the volcanic regions in the humid highlands by linking the hillslope processes with the discharge at the outlet. The Ene-Chilala watershed was selected for this study. The infiltration rate, piezometric water levels and discharge from two nested sub watersheds and at the watershed outlet were measured during a four-year period. Infiltration rates on the hillsides exceeded the rainfall intensity most of the time. The excess rain recharged a perched hillside aquifer. Water flowed through the perched aquifer as interflow to rivers and outlet. In addition, saturation excess overland flow was generated in the valley bottoms. Perched water tables heights were predicted by summing up the recharge over the travel time from the watershed divide. Travel times ranged from a few days for piezometers close to the divide to 40 days near the outlet. River discharge was simulated by adding the interflow from the upland to overland flow from the saturated valley bottom lands. Overland flow accounted only for one-fourth of the total flow. There was good agreement between predicted and observed discharge during the rain phase therefore the hillslope hydrologically processes were successfully linked with the discharge at the outlet.

Groundwater characterization and monitoring at a complex industrial waste site using electrical resistivity imaging

A contaminated industrial waste site in Washington State (USA) containing buried, metallic-waste storage tanks, pipes, and wells, was evaluated to determine the feasibility of monitoring groundwater remediation activities associated with an underlying perched aquifer system using electrical resistivity tomography. The perched aquifer, located ~65 m below ground surface and ~10 m above the regional water table, contains high concentrations of nitrate, uranium, and other contaminants of concern from past tank leaks and intentional releases of wastes to surface disposal sites. The extent of the perched water aquifer is not well known, and the effectiveness of groundwater extraction for contaminant removal is uncertain, so supplemental characterization and monitoring technologies are being evaluated. Numerical simulations of subsurface flow and contaminant transport were performed with a highly resolved model of the hydrogeologic system and waste site infrastructure, and these simulations were used as the physical basis for electrical resistivity tomography modeling. The modeling explicitly accounted for metallic infrastructure at the site. The effectiveness of using surface electrodes versus surface and horizontal subsurface electrodes, for imaging groundwater extraction from the perched water aquifer, was investigated. Although directional drilling is a mature technology, its use for electrode emplacement in the deep subsurface under a complex industrial waste site via horizontal wells has not yet been demonstrated. Results from this study indicate that using horizontal subsurface electrode arrays could significantly improve the ability of electrical resistivity tomography to image deep subsurface features and monitor remediation activities under complex industrial waste sites.

Storage and routing of water in the deep critical zone of a snow dominated volcanic catchment

This study combines major ion and isotope chemistry, age tracers, fracture density characterizations, and physical hydrology measurements to understand how the structure of the critical zone (CZ) influences its function, including water routing, storage, mean water residence times, and hydrologic response. In a high elevation rhyolitic tuff catchment in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve of northern New Mexico, a periodic precipitation pattern creates different hydrologic flow regimes during spring snowmelt, summer monsoon rain, and fall storms. Hydrometric, geochemical, and isotopic analyses of surface water and groundwater from distinct stores, most notably a perched aquifer in consolidated collapse breccia and deeper groundwater in a fractured tuff aquifer, enabled us to untangle the interactions of these groundwater stores and their contribution to streamflow across one complete water year. Despite seasonal differences in groundwater response due to water partitioning, major ion chemistry indicates that deep groundwater from the highly fractured site is more representative of groundwater contributing to streamflow across the entire water year. Additionally, comparison of streamflow and groundwater hydrographs indicates hydraulic connection between the fractured welded tuff aquifer and streamflow while the perched aquifer within the collapse breccia deposit does not show this same connection. Furthermore, analysis of age tracers and stable water isotopes indicates that groundwater is a mix of modern and older waters recharged from snowmelt and downhole neutron probe surveys suggest that water moves through the vadose zone both as vertical infiltration and subsurface lateral flow, depending on lithology. We find that in complex geologic terrain like that of the JRB-CZO, differences in CZ architecture of two hillslopes within a headwater catchment control water storage and routing through the subsurface and suggest that the perched aquifer does not contribute significantly to streams while deep fractured aquifers contribute most to streamflow.

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

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.

Is the construction of a sanitary landfill acceptable in a karstic area? The case of the sanitary landfill site in Fokida, Central Greece

This paper investigates the suitability of a specific site for the construction of a sanitary landfill. The following works were performed: detailed geological mapping at a scale of 1:5,000, a geological-hydrogeological cross-section of the sanitary landfill, drilling exploration including the construction of a deep borehole for the detection of any perched aquifer, core logging and in situ permeability tests, implementation of the DRASTIC and EPIC methods to estimate the aquifer’s vulnerability. Finally estimation of the total annual amount of solid waste that will be deposited into the sanitary landfill and determination of the pollution load.