Precipitation Filtration Research Articles

Analysis of the Hydrogeological and Hydrochemical Characteristics of an Immature Karst Aquifer System

This study intends, using classic and new techniques (e.g., Time Series Analysis, TSA), and hydrogeological data for the period February 2008 - May 2011, to improve the existing knowledge on the hydrogeology of the immature karst Philippi aquifer system (PHAS), Northeast Greece, in order to introduce the sustainable integrated water management of this system. The PHAS catchment consists of Mesozoic fissured and slightly karstified marbles, and covers an area of 121.7 km2. It discharges through the perennial, fault-controlled, overflow Voirani spring, which serves the needs of 85,000 inhabitants. Source of recharge is direct diffuse infiltration of precipitation. The Voirani spring mean discharge rate is 1.48 m3/s and ranges from 1 to 2.1 m3/s. Its variability index ranges from 1.73 to 2.07 m3/s. Auto- and cross-correlation and spectral analyses were used in combination with PHAS hydrogeological characteristics to study the interrelationship of daily spring discharge and rainfall, and provided useful information about the PHAS memory effect. PHAS baseflow prevailed greatly and had a behavior similar to a porous aquifer. The catchment area recharges and stores deep circulating water, while its karstification is poorly developed with high storages. The Voirani spring water is of Ca-HCO3 chemical type, of high quality, and oversaturated with respect to calcite. Examination of hydrograph and chemograph data revealed that PHAS is dominated by diffuse flow of stable hydrochemical composition. The application of TSA combined with classic hydrogeological techniques can be used in order to achieve a sustainable integrated water management of this system.

The Geoheritage of the Water Intake of Triglio Ancient Aqueduct (Apulia Region, Southern Italy): a Lesson of Advanced Technology Insensitive to Climate Changes from an Ancient Geosite

Near Taranto (Southern Italy), the water intake of a huge ancient aqueduct, develops along the deep Triglio canyon and its branches. The water intake apparatus is a hypogeum stretch for water interception formed by tunnels converging in a single pipe, with a total length of about 4 km. The tunnels, mainly dug into limestones and calcarenites, drain the surrounding vadose zone fed by delayed infiltration of precipitation, small overlying superficial aquifers at the top of canyon flanks, or alluvial deposits covering the canyon bottom. The early hydrogeologists who designed the intake work had an extraordinary knowledge on how to drain vadose flow from unsaturated masses and how to combine the drainage from different zones, thus assuring a perennial water flow. Moreover, they were able to select the most permeable levels, only today clearly identified with advanced hydrogeological knowledge. The tunnels and the pits are in fact located between 130 and 170 m AMSL: This elevation range represents one of the specific elevation ranges recently ascertained in the carbonate platform of Murgia (Southern Italy) as marks of prolonged sea level stands. The geoarcheological study highlights the role of early hydrogeologists, forerunners of an environmental culture that led to the construction of an engineering masterstroke. It has been working for not less than a millennium, despite climate fluctuations. The sophisticated intake work of Triglio reminds the qanat or foggare, heritage of Persian, Arab, and North African culture. It is currently ascribed to the Roman period; however, it may date back to more recent times, probably to a period between the Arab (around 900 AD), and the following Norman or Swabian civilization. The dimension of the work and its outstanding technical value, which allowed its use up to date, deserve disclosure, enhancement, and conservation of this geosite as geological heritage.

Groundwater recharge mechanism in an integrated tableland of the Loess Plateau, northern China: insights from environmental tracers

Assessing groundwater recharge characteristics (recharge rate, history, mechanisms (piston and preferential flow)) and groundwater age in arid and semi-arid environments remains a difficult but important research frontier. Such assessments are particularly important when the unsaturated zone (UZ) is thick and the recharge rate is limited. This study combined evaluations of the thick UZ with those of the saturated zone and used multiple tracers, such as Cl, NO3, Br, 2H, 18O, 13C, 3H and 14C, to study groundwater recharge characteristics in an integrated loess tableland in the Loess Plateau, China, where precipitation infiltration is the only recharge source for shallow groundwater. The results indicate that diffuse recharge beneath crops, as the main land use of the study area, is 55–71 mm yr−1 based on the chloride mass balance of soil profiles. The length of time required for annual precipitation to reach the water table is 160–400 yrs. The groundwater is all pre-modern water and paleowater, with corrected 14C age ranging from 136 to 23,412 yrs. Most of the water that eventually becomes recharge originally infiltrated in July–September. The Cl and NO3 contents in the upper UZ are considerably higher than those in the deep UZ and shallow groundwater because of recent human activities. The shallow groundwater has not been in hydraulic equilibrium with present near-surface boundary conditions. The homogeneous material of the UZ and relatively old groundwater age imply that piston flow is the dominant recharge mechanism for the shallow groundwater in the tableland.

Estimation of groundwater recharge in sedimentary rock aquifer systems in the Oti basin of Gushiegu District, Northern Ghana

Sustainable development and the management of groundwater resources for optimal socio-economic development constitutes one of the most effective strategies for mitigating the effects of climate change in rural areas where poverty is a critical cause of environmental damage. This research assessed groundwater recharge and its spatial and temporal variations in Gushiegu District in the Northern Region of Ghana, where groundwater is the main source of water supply for most uses. Isotopic data of precipitation and groundwater were used to infer the origin of groundwater and the possible relationship between groundwater and surface water in the partially metamorphosed sedimentary aquifer system in the study area. Though the data do not significantly establish strong relation between groundwater and surface water, the study suggests that groundwater in the area is of meteoric origin. However, the data also indicate significant enrichment of the heavy isotopes (18O and 2H) in groundwater relative to rainwater in the area. The Chloride Mass Balance (CMB) and Water Table Fluctuations (WTF) techniques were used to quantitatively estimate the groundwater recharge in the area. The results suggest groundwater recharge in a range of 13.9 mm/y - 218 mm/y, with an average of 89 mm/yr, representing about 1.4%–21.8% (average 8.9%) of the annual precipitation in the area. There is no clearly defined trend in the temporal variations of groundwater recharge in the area, but the spatial variations are discussed in relation to the underlying lithologies. The results suggest that the fraction of precipitation that reaches the saturated zone as groundwater recharge is largely controlled by the vertical hydraulic conductivities of the material of the unsaturated zone. The vertical hydraulic conductivity coupled with humidity variations in the area modulates the vertical infiltration and percolation of precipitation.

Stable isotopes of soil water: Implications for soil water and shallow groundwater recharge in hill and gully regions of the Loess Plateau, China

There is relatively abundant groundwater in some hill and gully regions of the Loess Plateau aquifer. The region has an arid to semiarid climate with low precipitation and high potential evaporation, and thus, groundwater recharge processes remain unclear. This study aimed to investigate recharge mechanisms and soil water movement in the Loess Plateau aquifer and to assess the recharge to shallow loess aquifers using soil profiles. In general, we found that the δ18O and δ2H values of soil water varied both with season and with soil profile depth. The seasonal stable isotopic values in the soil profiles also differed between wet and dry years. In particular, soil water and groundwater isotopic values responded to precipitation. This response suggests that seasonal precipitation is the main source of recharge to soil water and groundwater and that soil water is involved in groundwater recharge. The precipitation infiltration, soil water replenishment, and groundwater recharge are complicated processes. Two main modes of infiltration allow water to move downward through the unsaturated zone and recharge groundwater can be concluded. The primary mode is preferential infiltration through microtopographic features. This channel-like infiltration can rapidly move precipitation downward to deep soil layers, greatly reducing evaporation even under the arid to semiarid conditions of the study area. The secondary mode is a combination of matrix flow, which includes inside preferential infiltration though finger-like flow in the upper layer and piston-like flow in the deeper layer. The upper finger-like flow can cause rapid infiltration to below the root zone during less intense rain or snowmelt. The annual precipitation through preferential flow is the dominant recharge mode for the shallow groundwater in the loess aquifers. These two modes of recharge maintain perennial groundwater in the arid to semiarid hill and gully regions of the Loess Plateau.

Origin of hexavalent chromium in groundwater: The example of Sarigkiol Basin, Northern Greece

Hexavalent chromium constitutes a serious deterioration factor for the groundwater quality of several regions around the world. High concentrations of this contaminant have been also reported in the groundwater of the Sarigkiol hydrological basin (near Kozani city, NW Greece). Specific interest was paid to this particular study area due to the co-existence here of two important factors both expected to contribute to Cr(VI) presence and groundwater pollution; namely the area's exposed ophiolitic rocks and its substantial fly ash deposits originating from the local lignite burning power plant. Accordingly, detailed geochemical, mineralogical, hydro-chemical, geophysical and hydrogeological studies were performed on the rocks, soils, sediments and water resources of this basin. Cr(VI) concentrations varied in the different aquifers, with the highest concentration (up to 120μgL−1) recorded in the groundwater of the unconfined porous aquifer situated near the temporary fly ash disposal site. Recharge of the porous aquifer is related mainly to precipitation infiltration and occasional surface run-off. Nevertheless, a hydraulic connection between the porous and neighboring karst aquifers could not be delineated. Therefore, the presence of Cr(VI) in the groundwater of this area is thought to originate from both the ophiolitic rock weathering products in the soils, and the local leaching of Cr(VI) from the diffused fly ash located in the area surrounding the lignite power plant. This conclusion was corroborated by factor analysis, and the strongly positively fractionated Cr isotopes (δ53Cr up to 0.83‰) recorded in groundwater, an ash leachate, and the bulk fly ash. An anthropogenic source of Cr(VI) that possibly influences groundwater quality is especially apparent in the eastern part of the Sarigkiol basin.

Isotopic Implications for Vapor–Liquid Infiltration Pattern in the Desert Area of Ordos Plateau, China

Precipitation infiltration is the unique recharge source of groundwater in most arid areas. In this paper, we focus on the desert area of the Ordos Plateau by assessing the capability of water stable isotope analysis (δD–δ18O) to refine the understanding of groundwater recharge mechanism. In situ profile monitoring of temperature, moisture content, and isotopic sampling in unsaturated and saturated zones was conducted at the Bulanghe station located in the middle of the Ordos Plateau to identify the detailed infiltration process. It was found that the capillary zone has the most depleted heavy O and H isotopes in the profile. The analysis of δD–δ18O relationships of local precipitation explains the isotopic variability and indicates the following processes: (1) Liquid water evaporated at hotter layer near the surface; 2) Part of vapor moves downward and condensates at the deeper layer where it becomes cooler. The isotopic fractionation that occurs in this process makes the condensation zone the most depleted heavy O and H isotopes zone. Temperature and moisture content in the profile also supported the capillary zone as vapor moves downward. The isotopic evidence indicates that, except for direct infiltration, the newly found secondary infiltration pattern, vapor–liquid flow, makes it possible that the low intensity precipitation event contributes to groundwater recharge. The results from this study may provide useful insights into the identification of infiltration mechanism in arid areas in the world.

Pre-event water contributions and streamwater residence times in different land use settings of the transboundary mesoscale Lužická Nisa catchment

AbstractThe objective of the study was to evaluate the spatial distribution of peakflow pre-event water contributions and streamwater residence times with emphasis on land use patterns in 38 subcatchments within the 687 km2large mesoscale transboundary catchment Lužická Nisa. Mean residence times between 8 and 27 months and portions of pre-event water between 10 and 97% on a storm event peakflow were determined, using18O data in precipitation and streamwater from a weekly monitoring of nearly two years. Only a small tracer variation buffering effect of the lowland tributaries on the main stem was observed, indicating the dominant impact on the mountainous headwaters on the runoff generation. Longest mean streamwater residence times of 27 months were identified in the nearly natural headwaters of the Jizera Mountains, revealing no ambiguous correlation between the catchment area and altitude and the mean residence time of streamwater. Land use control on the pre-event water portions were determined for three land use categories with percentage of urban areas from 0 to 10%, 10 to 20% and more than 20%. The fraction of pre-event water in the first category decreases from 97% to 65% with the increasing percentage of forest from 76% to 100%, revealing that forests may provide only a limited infiltration of precipitation due to leaf interception and soil water use for transpiration. Fractions of pre-event water of 39–87% in the second (agricultural catchments) and of 10–35% in the third (urbanized catchments) category increase with percentage of non-urban areas.

Thermal and gas dynamic investigations at Lastarria volcano, Northern Chile. The influence of precipitation and atmospheric pressure on the fumarole temperature and the gas velocity

Fumaroles are hydrothermal manifestations commonly associated with active volcanoes. The dynamics of fumaroles are affected by interactions with internal and external factors, however, hazardous access and corrosive gases have so far limited successful case studies. In this study we report and discuss the results of continuous thermal monitoring carried out on three high temperature (>250°C) fumaroles at the Lastarria volcano Chile, together with simultaneously measured meteorological parameters from December 2013 to March 2016. In addition, the dynamic pressure and the CO2 concentration were recorded in a fourth vent. The investigated sites are located in the largest and most dominant fumarole field which developed in a fracture system on the north-west flank of the volcanic edifice.We detect external factors controlling the fumarole temperature and the dynamic gas pressure, for a better understanding of changes in these parameters and, consequently, to improve the evaluation of volcanic and hydrothermal activity.Selected fumaroles showed a continuous decrease in temperature, or remained unbiased from this trend showing that the influence of external effects on outlet temperature is strongly site dependent. But generally, significant decreases in all vent temperatures can be observed in response to intensive precipitation. Diurnal variations occur only in the coolest fourth fumarole, where gas temperature, gas pressure and CO2 concentration are inversely correlated with atmospheric pressure. Small barometric pressure reductions account for an increase in mass flow subsequently resulting in a higher temperature and CO2 concentration.The temperatures and thermodynamic properties of the fumarolic gas and infiltrated precipitation water were used to calculate the amount of discharging gas from the investigated field with about 67×106m3 per day which is equivalent to 3545tons.

Recharging infiltration of precipitation water through the light soil, in the absence of surface runoff

Abstract The article presents the value of recharging infiltration of precipitation through the light soil and its distribution over time, based on five-year of lysimetric research. The effect of organic and mineral fertilization on the infiltration was studied. In lysimeters does not occur the phenomenon of surface runoff, and thus, by analogy, the results of the research can be applied to agriculturally used lowland areas with sandy soils. The results showed that the infiltration is very changeable in time. On its value, in addition to precipitation, the greatest influence has evapotranspiration. The largest infiltration occurs in March after the spring thaws (IE = 70-81% monthly precipitation) and the smallest in August (IE = 1.2-15.0% precipitation, depending on the type of fertilizer used and the level of fertilization). The soil fertilization, especially by using organic fertilizer (compost), is a factor, which has significantly influence on reduction of the recharging infiltration. The soil fertilization with compost reduced the infiltration of 7.4-9.0%, and with mineral fertilization of 5.4-7.0% of annual precipitation totals, compared with the infiltration through the soil not fertilized. The average annual index of infiltration was 21.8-25.3% of annual precipitation totals in variant of soil fertilized and 30.7% in case of the soil not fertilized.

Development of a Simulation Model for Estimation of Potential Recharge in a Semi-arid Foothill Region

The SMPR (Soil Moisture and Potential Recharge) model is developed to simulate soil moisture content and potential recharge under semi-arid conditions. In SMPR model, infiltration and soil moisture redistribution follow two successive stages. In stage (I), precipitation infiltrates and is distributed into the soil profile utilizing the soil moisture accounting fashion and in stage (II), moisture is redistributed using simplified Richards’ equation (neglecting matric-potential gradient). Liquid and vapor evaporation from bare soil are estimated based on Dual-Crop methodology [Ke and optimized Kcb (0.17)]. Two commonly applied unsaturated hydraulic conductivity functions [K(θ)] of B-C (Brooks and Corey) and V-G (van-Genuchten); and an Empirical Exponential (E-E) equation are locally calibrated and used for potential recharge estimation (as main simulation objective). Model performance (calibration/validation) is based on reasonable estimation of potential recharge and acceptable simulation of soil moisture, considering local lysimeter data. According to results, B-C, V-G an E-E equations produced acceptable simulation of soil moisture content (NRMSE < 30%), however, potential recharge was underestimated/overestimated, using K(θ) by B-C/V-G. The best estimation of potential recharge (based on absolute annual recharge error, ∆Q < 10%) was achieved by the SMPR model with K(θ) of E-E. Results of the relative simple SMPR model [K(θ) by E-E equation] compared favorably with HYDRUS-1D sophisticated model [using locally calibrated V-G equation of K(θ)].The proposed SMPR model requiring minimal data, can be used in regions with limited data.

Determination of groundwater recharge mechanism in the deep loessial unsaturated zone by environmental tracers

Studying the groundwater recharge mechanism in regions with thick unsaturated zone can greatly improve our understanding of hydrological processes since these regions have complex groundwater processes. This study attempted to discuss the groundwater recharge in a region covered by loess over 130m deep in China's Loess Plateau. The water stable isotope, tritium and chloride in precipitation, groundwater and soil water were determined and used as inputs of mass balance methods. The tracer technique is found to be applicable and effective this region with thick unsaturated zone. The groundwater originates from rapid precipitation infiltration through some fast flow paths. The total recharge is likely to be 107±55mmyr−1 accounting for 19±10% of average annual precipitation, while the recharge from preferential flow accounts for 87±4% of the total recharge. The identified recharge mechanism has important implication to groundwater management and recharge modeling for regions covered by thick loess.

Evaluation of diffuse and preferential flow pathways of infiltrated precipitation and irrigation using oxygen and hydrogen isotopes

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

Interrelations between the atmospheric electric field, air pressure, and hydrogeological processes

The rise of the level of aquifers enhances soil radon transport that causes the decay of the atmospheric electric field. The decrease in aquifer levels provides the opposite effect. The aquifer level rise may be caused by precipitation infiltration, hydrofracturing, and air pressure drop. The reasons for the aquifer level decline are the pumping of artesian water and air pressure rise.

Legume Grasslands Promote Precipitation Infiltration better than Gramineous Grasslands in arid Regions

AbstractPrecipitation infiltration is the most important process for soil water supply of vegetation in the arid regions. Higher infiltration rate is advantageous for vegetation growth and maintenance in the arid areas. Four grassland types (Medicago sativa, Agropyron cristatum, Caragana korshinskii and Stipa capillata) were selected in this study. Results showed that the infiltration capacity in the legume grasslands was about 30% higher than in the gramineous grasslands and the difference was significant (p &lt; 0·05). Furthermore, the infiltration rate in legume shrub‐grassland was 16% less than the legume grasslands, but the difference was not significant (p &gt; 0·05). The below‐ground biomass, total porosity, capillary porosity, soil organic matters and soil aggregate were the main factors to determine the soil infiltration rates. The capillary porosity and soil aggregate of the top soil presented significant negative effects on soil infiltration rate (p &lt; 0·05). The below‐ground biomass in 10–30 cm soil layer was the most important factor, which significantly and positively correlates with the soil infiltration rate (p &lt; 0·01). It is possible to conclude that the legume grasslands presented the higher soil infiltration rate and promoted precipitation infiltration in the studied area. And the legume grasslands might be a more suitable option for vegetation restoration from the perspective of soil infiltration and water supply in the arid regions. Copyright © 2016 John Wiley &amp; Sons, Ltd.

GAS PERMEABILITY OF GEOSYNTHETIC CLAY LINERS

Geosynthetic clay liners (GCL) are manufactured hydraulic barriers consisting of mineral and geosynthetic components. They belong to a group of geosynthetic products whose primary purpose is to seal and they have been used in many geotechnical and hydrotechnical applications, landfi lls and liquid waste lagoons for quite a while. They are used in landfill final cover systems to prevent the infi ltration of precipitation into the landfi ll body and the penetration of gases and liquids from the landfill into the atmosphere and environment. Laboratory and fi eld research and observations on regulated landfi lls have proven the eff ectiveness of GCL as a barrier for the infi ltration of precipitation into the landfi ll body as well as the drainage of fl uid beneath the landfill. Due to the presence of high concentrations of gases in the landfill body, there is a growing interest in determining the efficiency of GCL as a gas barrier. It was not until the last twenty years that the importance of this topic was recognized. In this article, current GCL gas permeability studies, the testing methods and test results of gas permeability in laboratory conditions are described.

Rapid recharge of fresh water to the halite‐hosted brine aquifer of Salar de Atacama, Chile

AbstractWe document, analyse, and interpret direct and rapid infiltration of precipitation to the southern margin of the Salar de Atacama halite‐hosted brine aquifer during two intense precipitation events in 2012–2013. We present physical, geochemical, and stable and radioactive isotope data to detail this influx of water. The two events differ distinctly in the mechanisms of recharge. The 2012 event did not produce direct precipitation onto the salar surface, while the 2013 event did. Both events are recorded by abrupt changes in head in observation wells along the halite aquifer margin. Spatially distributed water levels rose by over 30 cm during the larger 2013 event consistent with remotely sensed observations of surface water extent. The lithium concentration and stable isotopic composition of water indicate dilution of brine and dissolution of salt with fresh water. Tritium measurements of precipitation, surface water, and groundwater all indicate modern influx of water to the halite aquifer along the southern margin. We extend these observations by examining the response of the halite aquifer as a whole to precipitation events during the period of 2000–2010. This study suggests that local recharge to the aquifer during sporadic precipitation onto the halite nucleus is an important component of the modern water budget in this hyper‐arid environment. The rapid dissolution and salinization along the southern margin of the salar halite nucleus are aided by such precipitation events contributing a modern fresh water component to the water budget of the economically valuable lithium‐rich brine. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Prediction of rainfall‐induced shallow landslides in the Loess Plateau, Yan'an, China, using the TRIGRS model

AbstractIn this work, a transient rainfall infiltration and grid‐based regional slope‐stability model (TRIGRS) was implemented in a case study of Yan'an City, Northwest China. In this area, widespread shallow landslides were triggered by the 12 July 2013 exceptional rainstorm event. A high‐resolution DEM, soil parameters from in‐situ and laboratory measurements, water table depths, the maximum depth of precipitation infiltration and rain‐gauge‐corrected precipitation of the event, were used as inputs in the TRIGRS model. Shallow landslides triggered on the same day were used to evaluate the modeling results. The summarized results are as follows: (i) The characteristics and distribution of thirty‐five shallow landslides triggered by the 12 July 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth, area and volume less than 3 m, 200 m2 and 1000 m3, respectively, (ii) Four intermediate factor of safety (FS) maps were generated using the TRIGRS model to represent the scenarios 6, 12, 18 and 24 hours after the storm event. The area with FS &lt; 1 increased with the rainfall duration. The percentage of the area with FS &lt; 1 was 0.2%, 3.3%, 3.8% and 5.1% for the four stages, respectively. Twenty‐four hours after the rainstorm, TRIGRS predicted that 1255 grid cells failed, which is consistent with the field data. (iii) TRIGRS generated more satisfactory results at a given precipitation threshold than SINMAP, which is ideal for landslide hazard zoning for land‐use planning at the regional scale. Comparison results showed that TRIGRS is more useful for landslide prediction for a certain precipitation threshold, also in the regional scale. (iv) Analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Assessment and mapping of slope stability based on slope units: A case study in Yan’an, China

Precipitation frequently triggers shallow landslides in the Loess Plateau of Shaanxi, China, resulting in loss of life, damage to gas and oil routes, and destruction of transport infrastructure and farmland. To assess the possibility of shallow landslides at different precipitation levels, a method to draw slope units and steepest slope profiles based on ARCtools and a new method for calculating slope stability are proposed. The methods were implemented in a case study conducted in Yan’an, north-west China. High resolution DEM (Digital Elevation Model) images, soil parameters from in-situ laboratory measurements and maximum depths of precipitation infiltration were used as input parameters in the method. Next, DEM and reverse DEM were employed to map 2146 slope units in the study area, based on which the steepest profiles of the slope units were constructed. Combining analysis of the water content of loess, strength of the sliding surface, its response to precipitation and the infinite slope stability equation, a new equation to calculate infinite slope stability is proposed to assess shallow landslide stability. The slope unit stability was calculated using the equation at 10-, 20-, 50- and 100-year return periods of antecedent effective precipitation. The number of slope units experiencing failure increased in response to increasing effective antecedent rainfall. These results were validated based on the occurrence of landslides in recent decades. Finally, the applicability and limitations of the model are discussed.

Application of Wavelet Coherence Method to Investigate Karst Spring Discharge Response to Climate Teleconnection Patterns

AbstractThe impact of climate teleconnections on the regional hydrometeorology has been well studied, but very little effort has been made to relate climate teleconnections with groundwater flow variation. In this study, we used a wavelet coherence method to analyze monthly climate indices, precipitation, and spring discharge data, and investigated the relation between major teleconnection patterns (the Arctic Oscillation, North Atlantic Oscillation, Pacific Decadal Oscillation, El Niño‐Southern Oscillation, and Indian Ocean Dipole) and karst hydrological process in Niangziguan Springs Basin, China. The results indicate precipitation and spring discharges correlate well with climate indices at intra‐ and inter‐annual time scales. Further, the climate indices are mainly correlated with precipitation at shorter periodicities, but correlated with spring discharge at longer scales. The difference reflects the modulation of karst aquifers on precipitation‐spring discharge during the processes of precipitation infiltration into the ground, and subsequent transformation into spring discharge. When teleconnection signals are transmitted into spring discharge via precipitation infiltration and groundwater propagation, some high‐frequency climatic signals are likely to be filtered, attenuated, and delayed, thus only low‐frequency climatic signals are preserved in spring discharge.