Sinking Streams Research Articles

Geophysical and geochemical studies on sinking stream occurrence in Ayankulam village of South Tamilnadu, India

Geophysical and geochemical studies on sinking stream occurrence in Ayankulam village of South Tamilnadu, India

Caves, Karst Features and Speleological Heritage in Chapada Diamantina, Bahia, Brazil

Chapada Diamantina is among the best known and most visited landscapes in Brazil. Located in the state of Bahia, Northeast region of the country, it is characterized by mountains and plateaus that developed on Proterozoic sedimentary and metasedimentary rocks. Much of its territory is covered by carbonate and siliciclastic rocks, where relevant karst systems develop, marked by the occurrence of sinking streams, sinkholes, and caves with a great diversity of morphologies, speleothems, subterranean fauna, and paleontological and archaeological records. Relevant carbonate systems occur in Iraquara, such as the Lapa Doce, Torrinha, and Pratinha caves, which represent important tourist attractions. Also in these rocks, stand out the Brejões Cave, with a 106-m high entrance, and the Toca da Boa Vista, the largest cave in South America, extending across 114 km. Cultural manifestations are present in the prehistoric cave paintings at Santa Marta Shelter and recent religious pilgrimages at Mangabeiras Cave, in Ituaçu. In turn, siliciclastic karst systems are mainly in Serra do Sincorá. The Lapão and Castelo caves have expressive speleogens and speleothems, as well as the Torras Cave, in the Igatu region, ranked as the second largest in Brazil considering siliciclastic rocks.

Analysis of river drying in Slovenia

Intermittent watercourses lack water during some periods of the year, which especially applies to karst sinking streams. Droughts also occur in dry periods with no rainfall over a longer period of time. The drying up of Slovenian rivers was analysed using the data from the state hydrological monitoring of the Slovenian Environment Agency. By analysing the periodic statistics of minimum low discharges (nQnp), 18 gauging stations were extracted where the watercourses dried up during the measurement period. For these stations, sets of mean daily discharges were analysed, and dry days where the flow was equal to zero were listed. The number of dry days and the number of consecutive dry days were analysed by month and year, and the longest dry periods were determined. The results are presented graphically. At most of the gauging stations considered, the number of dry days was the highest in the years characterized by extreme hydrological droughts, namely 2003, 2012, and 1993. In some watercourses, drying up is a constant phenomenon that occurs almost every year, while others only dry up in years characterized by extreme droughts. Exceptions to this are the karst rivers, which sink and are therefore dry for part of the year. The Pivka and Branica Rivers regularly dry up. Watercourses in Pomurje and Velunja, Kožbanjšček, and Dragonja also dry up very often. Analysis results demonstrated that river drying has become more frequent in the past two decades. The driest month is August, followed by July and September.

Coupling major ions and trace elements to turbidity dynamics for allogenic contribution assessment in a binary karst system (Sierra de Ubrique, S Spain)

This investigation deals with the application of a multi-technique approach combining data from turbidity, major ions, and trace elements to characterize the implications of allogenic recharge in a binary karst system and assess the relative hydrochemical contribution to karst springs captured for drinking use. Hydrodynamic and hydrochemical responses of the outlets to storm events were continuously monitored during four selected flooding events, and water samples were collected at the main sinking stream in the recharge area and discharge points (Cornicabra and Algarrobal springs) for chemical analysis. The obtained hydrogeochemical dataset was analyzed through mean of time-series and statistical analysis and allowed to describe the fate and origin of trace elements. Despite that most of analyzed components present a natural origin, the existence of a Wastewater Treatment Plant in the recharge area was determined to be the main source of P (phosphorus) concentrations measured in the karst springs. Sediment (particulate) transport constitutes the most important factor in the mobilization of Al, Mn, Ni, and Ba in both surface and groundwater, whilst Li, Sr, and P are mainly controlled by solute migration. The hydrochemical signature of allogenic water component was constrained by identifying characteristic correlations between Ba and Ca/Sr ratio in water samples. The combination of specific hydrogeological processes as ion solution and sorption processes onto solids between solutes and particles as well as water mixing processes (allogenic vs diffuse) result more evident in Algarrobal spring, which receives a higher contribution of allogenic component due to a greater feeding catchment.

Characterizing the transitory groundwater-surface water interaction and its environmental consequence of a riverside karst pool

Exchange between groundwater (GW) and surface water (SW) is a common occurrence in karst water systems through sinking stream disappearance or groundwater emergence. However, the transitory GW-SW interaction caused by river backflowing into a spring is poorly observed and understood. In this study, we present an approach for characterizing the influence of GW-SW interaction in a karst spring by integrating high-resolution hydrology, carefully selected hydrochemistry monitoring and precise microbe measurements. The spring-fed pool water conditions can be distinguished as high, medium, and low-water level periods in a hydrological year. The high-water level accounts for <1 % in a year, while it is associated with the hydrological regimes of backflooding states. The inflow of river backflow was found to be 4.4 times that of the natural discharge of spring water during a rainfall event. The duration of river intrusion into the spring or karst conduit could be assessed by jointly interpreting hydrography and physicochemical signatures, while the lasting environmental consequences should be evaluated together with biotic factors such as Escherichia coli. The GW-SW interaction induced by river backflow has led to the retention of river water in a pool, spring, and karst conduit for 132, 94, and 56 h, respectively. Despite turbidity returning to normal levels after 56 h, E.coli continued to persist for an extended duration. Our study reveals that despite the transient nature of GW-SW induced by river backflow on the hydrograph, they present a lasting risk of contamination from heavy metals, organic matter, and microorganisms. This extended influence can persist within a karst aquifer lacking a hyporheic zone. This research contributes to the quantification of processes involved in transitory GW-SW interaction in a karst spring, and it highlights the underestimation of GW-SW interactions in karst water systems, which might negatively impact water resources management.

COCKPIT-PLUS: A proposed method for rapid groundwater vulnerability-driven land use zoning in tropical cockpit karst areas

Karst groundwater is highly vulnerable to contamination, which urges better land use zoning. This paper proposes a new approach, called COCKPIT-PLUS, to minimize groundwater contamination within cockpit karst regions. The method employed four parameters: P (the existence of ponor/swallow hole), L (lineament density), U (sinking stream to an underground river), and S (distance to spring/pumping site). These parameters are essential for identifying contaminant pathways and transport from the surface to the karst groundwater/springs. COCKPIT-PLUS has been developed and validated in the Gunungsewu karst in Java, Indonesia. This research considers a cockpit as a single hydrological unit that uniquely recharges karst groundwater. We analyzed 2,811 cockpits and 81 other closed depressions to develop a land use planning map. The research used the time to first arrival (Ta), time to peak (Tp), and Qmax/min ratio parameters of two karst springs and two underground pumping sites for validation. Cockpits with ponors/swallow holes, sinking streams, high lineament density, and short distances to springs are vulnerable to groundwater and thus must be restricted areas for any land uses. The findings show that though the COCKPIT-PLUS uses a limited karst dataset, the proposed method seems reliable enough for a rapid land-use zoning approach in cockpit karst areas.

Multivariate Statistical Analysis of Hydrochemical and Microbiological Natural Tracers as a Tool for Understanding Karst Hydrodynamics (The Unica Springs, SW Slovenia)

AbstractVarious multivariate statistical techniques (MST) can provide valuable insights into water quality variability. Despite numerous studies in which these methods have been used, their potential has not been fully exploited. This paper presents an improved approach to better understand the hydrodynamics of karst systems. The integrated application of hierarchical cluster and principal component analysis in combination with factor analysis allowed the construction of an advanced multivariate chemograph. The analytical procedure was applied in a binary karst aquifer known for its complex hydrodynamics and mixing of water with similar hydrochemical composition. In addition, the study area provides access to an integral groundwater flow system (ponor‐cave‐spring) and offers extensive prior hydrogeological knowledge. The approach allowed reduction and discrimination of the main parameters affecting water quality characteristics. Their identification enabled recognition of three predominant recharge components: (a) stored water impact with Cl and electrical conductivity, (b) sinking stream impact with turbidity and bacteria composition and (c) karst aquifer impact with Ca/Mg ratio as principal parameters. The results supported innovative characterization of the dominant processes and isolation of temporal hydrodynamic phases of individual monitoring points within the aquifer system. On this basis, a spatio‐temporal conceptual model was developed and the hydrodynamic behavior of the main springs was revealed. The applied methodology demonstrated to be useful in ascertaining functioning of a complex karst system under flood event conditions.

Sediment transport investigation in a karst aquifer hypothesizes controls on internal versus external sediment origin and saturation impact on hysteresis

Karst springs serve as major drinking water sources for the global population, yet there remains uncertainty regarding how contaminants like sediment are routed through karst. We find knowledge gaps pertaining to the processes that control the timing and magnitude of sediment delivery. To close these knowledge gaps, we: (1) collected high-frequency sediment and conductivity data from three surface streams and two cave sites in the inner bluegrass region of Kentucky, USA; (2) analyzed sediment hysteresis for 51 storm events over a two year period; (3) numerically modeled sediment transport through the aquifer; and (4) contextualized our results with a meta-analysis of ten karst springs in Europe and North America. Our results showed that 80% of storm events derived their sediment from external inputs through sinking streams while the remaining 20% were characterized by only internal resuspension of previously deposited cave sediment. We found that internal sediment transport was proportional to fluid shear stress in the cave and occurred exclusively during fully saturated aquifer conditions prior to the storm event. During partially-saturated aquifer conditions, externally sourced sediment pulses were efficiently routed to the spring irrespective of shear in the conduit network. Sediment hysteresis in surface streams was clockwise whereas the cave sites experienced counter-clockwise behavior. Clockwise and counter-clockwise hysteresis typically refer to proximal and distal sourcing for streams, but our findings suggest that this interpretation is not valid for subsurface karst settings. Hysteresis patterns for karst show dependence on the antecedent water conditions in the aquifer and internal versus external sourcing. meta-analysis results show that, despite high variability, counter-clockwise patterns of sediment hysteresis are very common for karst, which contrasts sediment hysteresis in surface streams. Results suggest that external sediment loading rather than internal resuspension is the most common control of sediment load at springs, which should inform management of karst groundwater resources.

Comparative Phylogeography of Phoxinus, Delminichthys, Phoxinellus and Telestes in Dinaric Karst: Which Factors Have Influenced Their Current Distributions?

The waters of the Dinaric Karst drain into both the Adriatic and the Black Sea basins. Precipitation is high, yet surface waters are scarce, with the exception of sinking streams. Dinaric Karst is a biodiversity hotspot, with diverse speleo- and epigean freshwater fauna. The distribution patterns of taxa in Dinaric Karst have arisen from a combination of vicariance and dispersal and their alteration over time. Within fishes, there are genera that include both species that are widespread and species with restricted ranges (e.g., Phoxinus, Telestes), and genera with only restricted distributions (e.g., Delminichthys, Phoxinellus). Some (Delminichthys, Phoxinellus and Dinaric Telestes) have a similar lifestyle, specialized for dwelling in sinking streams in karst poljes. The present study compares the distribution ranges of Phoxinus, Delminichthys, Phoxinellus and Telestes in Dinaric Karst based upon their mitochondrial genetic lineages, including dating of divergence times and reconstruction of ancestral geographic ranges. The biology of Phoxinus has played a major role in its wider distribution than the other three genera, which exhibit some limited ability to migrate underground, but which cannot disperse along main river courses due to their specific adaptation for dwelling in the sinking streams of karst poljes.

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.

Speleology of Kospi Spi Cave in Northern Iraq

The Kospi Spi Cave is situated in the well-karstified Qamchuqa limestone of the Cretaceous age. This study encompasses the facts on the medium sized cave. The entrance of the cave is located at 1,400 meters above sea level, the highest amongst the adjacent discovered caves. Its total sightseen extent is around 200 meters. The cave is a remnant gulp hole expanded by a sinking stream throughout the Late Neogene Time.

Analysis of underground river network connectivity in Barat Cave, Karst Karangbolong, Central Java, using the Artificial Tracer Test Method

The connectivity of the Barat Cave underground river system needs to be known to support the implementation of proper environmental management so that water resources can be maintained sustainably. However, the mapping of underground river paths is often hindered by conditions of narrow cave passages, a barrier blocking the flow of water (siphon), deep underground lakes, underground waterfalls, as well as paths filled with water. This research was conducted in Barat Cave, Karangbolong Karst Area. The purpose of this study is to determine the upstream-downstream connectivity system in this underground river and define the characteristics of the passageway based on quantitative analysis of the transport parameters from the tracer test results. This underground river network analysis needs to be done because previous research has never analyzed this underground river network. The research method used in this study is divided into three stages, namely the pre-field stage, the field stage, and the post-field stage. The pre-field step includes determining the location of the study, collecting secondary data, and studying the literature. The field stage consists of a hydrogeological survey to find information on the presence of caves, springs, sinking stream ponors, or luweng in the study area, instantaneous discharge measurements, and tracer tests. The post-field stage includes data processing and analysis. The results showed that the Barat underground river system originated from the Kalimas sinking stream, Mblabak Cave, Pendok Cave, and Pagilangan sinking streams, then merged into a single tunnel without a flow breaker to the Barat Cave, Pengantin Cave, and appeared in the Kalikarak springs to become a surface river, with a tunnel pattern in the form of curvilinear branchwork. The transport parameters for the underground system tracing of the Barat cave have an advection value of 86.528 m/hour, a dispersion of 0.092 m2/second, a dispersivity of 3.38 meters, and a recovery of 63%. The transport value of the tracing test parameter is influenced by the characteristics of the passageway and underground river flow conditions.

Sediment transport and riverbed evolution of sinking streams in a dammed karst river

Little knowledge has been gained about the mechanics of the sediment transport and riverbed evolution of sinking streams in a karst river, because of inadequate data of field investigation and laboratory experiments. Numerical simulation of mixed flow and sediment transport on moveable riverbed in sinking streams is seldom reported, due to difficulties in modeling irregular closed cross-sections (CS). In this study, a unified hydrodynamic and sediment transport model is developed for the free-surface and the pressurized mixed reaches of a karst river with sinking streams, where a technique of symmetric shadow subgrid is proposed to describe and account for an irregular closed CS and its riverbed evolution. Mechanics of riverbed evolution of sinking streams in a dammed karst river are studied using a real karst-river reservoir (Jiayan reservoir), which is still conducted in a data-scarce environment. Under damming effects, a delta deposition of sediment develops at the end of reservoir backwater and steps forward. It is found that the deposition delta is able to go through the sinking streams while a narrow passage is finally reserved in sinking streams and keeps conveying flow. The riverbed elevation of a closed CS, mainly determined by the lower one of CS ceiling and reservoir water level, is dynamically stable. In a dammed karst river, a fully developed (shrunk) sinking stream has periodic morphological dynamics, one cycle of which can be described as a successive process of “siltation → reduction of conveyance area → flow lag upstream of sinking streams → large hydraulic gradient → increase of velocity → large sediment transport capacity → erosion of closed CS → increase of conveyance area”. Sensitivity studies of the parameters of the hydrodynamic and the sediment transport models are performed, whose results indicate that the periodic morphological dynamics of a fully developed sinking stream in a dammed karst river is not changed. The sinking stream in a dammed karst river will not be silted completely, when the condition for forming a large gradient of piezometric head along a sinking stream is not broken by special geomorphologies or anthropogenic influences. This fact is supported by both the numerical simulations and our field investigation of sinking streams in an existing karst-river reservoir.

Can Karst Conduit Models Be Calibrated? A Dual Approach Using Dye Tracing and Temperature.

Modeling flow and transport using both temperature and dye tracing provides constraints that can improve understanding of karst networks. A laminar flow and transport model using the finite element subsurface flow model simulated the conduit connection between a sinking stream and spring in central Pennsylvania to evaluate how conduit morphology might affect dye transport. Single and overly tortuous conduit models resulted in high concentrations as dye flowed back into the conduit from the matrix after dye injections ceased. A forked conduit model diverted flow from the main conduit, reducing falling limb dye concentration. Latin hypercube sampling was performed to evaluate the sensitivity of 52 parameter combinations (conduit hydraulic conductivity, conduit cross-sectional area, matrix transmissivity, matrix porosity, and dispersivity) for four conduit geometry scenarios. Sensitivity of arrival time for 50% of the dye indicated no parameter combinations which simulate falling limb dye concentrations for tortuous geometries, confirming the importance of the forked geometry regardless of other parameters. Temperature data from high-resolution loggers were then incorporated into the forked conduit model to reproduce seasonal spring temperature using variable sink inflow. Unlike the dye trace models, the thermal models were sensitive to other model parameters, such as conduit cross-sectional area and matrix transmissivity. These results showed this dual approach (dye and temperature) to karst network modeling is useful for (1) exploring the role of conduit and matrix interaction for contaminant storage, (2) constraining karst conduit geometries, which are often poorly understood, and (3) quantifying the effect of seasonal trends on karst aquifers.

Characterizing the cavities of Anjani Cave in Jonggrangan Karst Area, Purworejo, Central Java, Indonesia

Anjani Cave is located administratively in Tlogoguwo Village, Kaligesing District, Purworejo Regency, Central Java, Indonesia. It is one of the objects of cave tourism. The cave entrance is on a cliff with a triangle-like shape, and the cave roof is 1.9 m in height. The local communities utilize the water flow of the underground river in Anjani Cave for tourist attraction, domestic purposes, and animal husbandry. The research aimed to 1) map the passages of Anjani Cave and 2) to characterize the unmappable passages in the cave. It employed a survey method that included cave mapping and tracer test on the groundwater flow to achieve the first and second objective, respectively. The results showed that the Anjani Cave passage was approximately 400 meters long with an average diameter of 4.1 meters and the total volume of the accessible cave was 6,881 m3. Furthermore, the tracer test identified that the underground river in Anjani Cave was connected to two surface river systems, namely the Cebong Sinking Stream and Jumbleng Sawah Sinking Stream.

Deducing flow path mixing by storm-induced bulk chemistry and REE variations in two karst springs: With trends like these who needs anomalies?

Karst aquifers are dynamic hydrologic systems which can be sensitive to short-term recharge events (storms) and heterogeneous recharge characteristics (point recharge at sinks, irregular soil thicknesses). In this study, two adjacent karst springs, Tippery Spring and Near Tippery Spring, were monitored to better understand flow and source mixing characteristics in response to two storms in May and June 2017. Monitoring techniques included high-resolution discharge and temperature logging and collection of spring water using automatic samplers to analyze chemical parameters such as stable water isotopes and Mg/Ca ratios along with Ca/Zr ratios and rare earth elements (REEs) which have had limited testing in karst systems. The two springs exhibited behaviors which were both unique to each spring and shared depending on which parameter is considered. Spring-specific behaviors included discharge and isotopic response, with Tippery Spring having a flashier and faster conduit flow behavior relative to Near Tippery Spring’s delayed storm response. Absolute Mg/Ca values were spring-specific, owing to the relative fraction of limestone and dolostone in their respective recharge areas, although both springs showed similar Mg/Ca ratio shifts after storms. While Ca/Zr ratios changed in timing and intensity with storm intensity, both springs exhibited a decline in Ca/Zr ratios as calcium-rich carbonate matrix water was displaced by zirconium-rich storm recharge water from sinking streams off the clastic upland ridges. Flushing of recharged storm water resulted in an increase in total REE concentrations at both springs (from <0.15 ppb to >1.0 ppb), with the timing and magnitude of concentration increases determined by the degree of surface connectivity intrinsic to each spring and the intensity of the recharge event. REEs and Ca/Zr ratios provided additional and complementary tracer techniques to better understand transient recharge and flow behaviors in karst springs.

Assessment of the origin and transport of four selected emerging micropollutants sucralose, Acesulfame-K, gemfibrozil, and iohexol in a karst spring during a multi-event spring response

The assessment of vulnerability in karst systems reveals to be extremely challenging since it varies significantly with time and highly depends on the identification of diffuse and concentrated infiltration from surface karst features. The origin, consumed loads, and transport mode of selected micropollutants (MPs) including two artificial sweeteners (ASWs) Sucralose (SUC) and Acesulfame-K (ACE-K), in addition to other less investigated pharmaceuticals such as the lipid regulator Gemfibrozil (GEM), and the contrast media Iohexol (IOX) were investigated in a karst system under dynamic conditions. A detailed analysis of selected spring responses' chemograph and hydrograph following a multi precipitation event shows that three of the tracked MPs, especially ACE-K, and to the exception of IOX, can be used as specific indicators for point source domestic wastewater in karst systems. They have revealed to be persistent, source specific, conservative, and highly correlated with in-situ parameters easily measurable at the spring (chloride and turbidity). Even if the selected MPs are found in the system during low flow periods, they are mostly transported to the spring through fast flow pathways from flushed wastewater with surface water or flood rainwater. The highest mass inflow of ACE-K, IOX and GEM originated from a sinking stream, while SUC infiltrated exclusively through fast infiltration points (dolines). Their breakthrough curves coincide with the arrival of new waters and turbidity peaks. Unlike IOX, the mass fluxes of ASWs, and GEM to a lesser extent, can be linearly correlated with chloride mass fluxes and turbidity flux. Moreover, the variance of the normalized breakthrough curves of the MPs with respect to a mean transit time, increases in that order IOX<GEM<Turbidity<SUC<ACE-K indicating a higher restitution time for ACE-K with respect to other spring signals.

Hydrogeological controls of variable microbial water quality in a complex subtropical karst system in Northern Vietnam

Karst aquifers are particularly vulnerable to bacterial contamination. Especially in developing countries, poor microbial water quality poses a threat to human health. In order to develop effective groundwater protection strategies, a profound understanding of the hydrogeological setting is crucial. The goal of this study was to elucidate the relationships between high spatio-temporal variability in microbial contamination and the hydrogeological conditions. Based on extensive field studies, including mapping, tracer tests and hydrochemical analyses, a conceptual hydrogeological model was developed for a remote and geologically complex karst area in Northern Vietnam called Dong Van. Four different physicochemical water types were identified; the most important ones correspond to the karstified Bac Son and the fractured Na Quan aquifer. Alongside comprehensive investigation of the local hydrogeology, water quality was evaluated by analysis for three types of fecal indicator bacteria (FIB): Escherichia coli, enterococci and thermotolerant coliforms. The major findings are: (1) Springs from the Bac Son formation displayed the highest microbial contamination, while (2) springs that are involved in a polje series with connections to sinking streams were distinctly more contaminated than springs with a catchment area characterized by a more diffuse infiltration. (3) FIB concentrations are dependent on the season, with higher values under wet season conditions. Furthermore, (4) the type of spring capture also affects the water quality. Nevertheless, all studied springs were faecally impacted, along with several shallow wells within the confined karst aquifer. Based on these findings, effective protection strategies can be developed to improve groundwater quality.

Occurrence of selected domestic and hospital emerging micropollutants on a rural surface water basin linked to a groundwater karst catchment

The occurrence of specific micropollutants (MPs), indicators of domestic and hospital wastewater, was investigated in a river connected to a karst spring based on two sampling campaigns under varying flow conditions. The MPs characterized by a high frequency of occurrence (acesulfame-K, ibuprofen, gemfibrozil, nonylphenol, and iohexol) were highly reflective of wastewater discharged in ephemeral streams and tributaries, as well as specific point sources such as farms and hospital effluents. A mixing model based on chloride mass fluxes allows the quantification of the percentage of untreated wastewater effluents in inflowing water from river tributaries, which varied between 0.7–99% and 5.0–10% in low flow and high flow, respectively. The frequency of occurrence of MPs is related to the volume of wastewater input, extent of river dilution, persistence of the MPs, and type of point source contamination on the river. Relationships were established between MPs such as ibuprofen and acesulfame-K (ACE-K), indicating their co-existence in highly consumed generic medicine and their suitability as wastewater co-tracers. Additionally, the number of consumers of gemfibrozil (GEM) and acesulfame-K were estimated based on mass loads in the river tributaries for management purposes. Groundwater contamination is mostly due to diffuse and point sources infiltration occurring on the spring catchment, including the sinking stream that could contribute up to 17% to the mass loads of some micropollutants (e.g., ACE-K and GEM) at the spring. Nevertheless, the increase of MPs use with growing urbanization is expected to have a much significant impact on the groundwater quality in the future.

Spatial and Temporal Flood Characterization of Pindul Karst System, Gunungkidul Regency

Pindul karst system has cave system and sinking stream recharge that cause it prone against flash flood. This research will study flood characteristics in the karst system. Water level logger was installed on karst system outlet and sinking stream of Kedungbuntung to obtain discharge data at 15 minutes interval. Rainfall data is obtained by installing automatic rain gauge on middle parts of karst system. Recording of both was done for six months (January – June). Flood characteristics was obtained by flood hydrograph and rainfall characteristics. The results indicated that Pindul karst system have faster time lag (Tlag) (1.1 and 1.7 hours) than rainfall duration (1.9 hours). Excess rainfall (Pe) is rainfall characteristic that is most influencing flood incident. Temporarily, rainfall percentage becoming surface runoff (% Pe) in outlet and Kedungbuntung were greater at end of rainy season (37% and 14%) than in early rainy season (16% and 8%). Pe percentage below 50% indicated that Pindul karst system is still good in storing groundwater. In spatial term, faster flood behavior in outlet was caused by recharge from cave system and sinking stream. Meanwhile, Kedungbuntung was recharged by aquifer with domination of diffuse fracture.