Downstream Springs Research Articles

Potential for Natural Attenuation of Domestic and Agricultural Pollution in Karst Groundwater Environments

In karst areas, anthropogenic contaminants reach the subsurface with detrimental effects on the groundwater ecosystem and downstream springs, which often serve as drinking water sources for the local human communities. We analyzed the water chemistry and microbial community composition in upstream and downstream locations of five hydrokarst systems (HKS) during four seasons. Conductivity and nitrates were higher in the downstream springs than in the pre-karst waters, whereas the concentration of organic matter, considered here as a pollution indicator, was lower. The microbial community composition varied largely between upstream and downstream locations, with multiple species of potentially pathogenic bacteria decreasing in the HKS. Bacteria indicative of pollution decreased as well when passing through the HKS, but potential biodegraders increased. This suggests that the HKS can filter out part of the polluting organic matter and, with it, part of the associated microorganisms. Nevertheless, the water quality, including the presence of pathogens in downstream springs, must be further monitored to control whether the water is appropriate for consumption. In parallel, the human populations located upstream must be advised of the risks resulting from their daily activities, improper stocking of their various wastes and dumping of their refuse in surface streams.

Future changes in sub‐seasonal variability of Indian winter precipitation

AbstractThe winter precipitation over north India is due to the passage of synoptic systems known as Western Disturbances (WDs), which are embedded in large‐scale subtropical westerly jet (SWJ). The winter (December, January, February [DJF]) precipitation is vital to maintaining glaciers, sustenance of rivers, replenishing downstream springs, and agriculture. Any change in winter precipitation has a profound impact on agriculture, socio‐economic status, and water security of the nation. Thus, a close understanding of future changes in winter precipitation is critical to the country. The present study evaluates the future changes in sub‐seasonal variability of winter precipitation over north India using ICHEC‐EC‐EARTH‐SMHI‐RCA4 CORDEX‐SA experiment. Wet bias in precipitation and cold bias in temperature are observed in model. Almost all days in the winter season witnessed a shift towards a warm‐wet climate in a future warming scenario. A large amount of precipitation is observed in February in model as well as observation. A 10‐day interval scale spanning during DJF is considered to evaluate these changes. Future changes in winter precipitation are analysed under RCP4.5 and 8.5 scenarios. The percentage change in winter precipitation shows a maximum increase during the first fortnight of December and the first week of February. Precipitation intensity weakens during January. Two hundred hectopascal wind, 850 hPa wind, and moisture flux influence the increase in precipitation over the region.

Snow Phenology and Hydrologic Timing in the Yukon River Basin, AK, USA

The Yukon River basin encompasses over 832,000 km2 of boreal Arctic Alaska and northwest Canada, providing a major transportation corridor and multiple natural resources to regional communities. The river seasonal hydrology is defined by a long winter frozen season and a snowmelt-driven spring flood pulse. Capabilities for accurate monitoring and forecasting of the annual spring freshet and river ice breakup (RIB) in the Yukon and other northern rivers is limited, but critical for understanding hydrologic processes related to snow, and for assessing flood-related risks to regional communities. We developed a regional snow phenology record using satellite passive microwave remote sensing to elucidate interactions between the timing of upland snowmelt and the downstream spring flood pulse and RIB in the Yukon. The seasonal snow metrics included annual Main Melt Onset Date (MMOD), Snowoff (SO) and Snowmelt Duration (SMD) derived from multifrequency (18.7 and 36.5 GHz) daily brightness temperatures and a physically-based Gradient Ratio Polarization (GRP) retrieval algorithm. The resulting snow phenology record extends over a 29-year period (1988–2016) with 6.25 km grid resolution. The MMOD retrievals showed good agreement with similar snow metrics derived from in situ weather station measurements of snowpack water equivalence (r = 0.48, bias = −3.63 days) and surface air temperatures (r = 0.69, bias = 1 day). The MMOD and SO impact on the spring freshet was investigated by comparing areal quantiles of the remotely sensed snow metrics with measured streamflow quantiles over selected sub-basins. The SO 50% quantile showed the strongest (p < 0.1) correspondence with the measured spring flood pulse at Stevens Village (r = 0.71) and Pilot (r = 0.63) river gaging stations, representing two major Yukon sub-basins. MMOD quantiles indicating 20% and 50% of a catchment under active snowmelt corresponded favorably with downstream RIB (r = 0.61) from 19 river observation stations spanning a range of Yukon sub-basins; these results also revealed a 14–27 day lag between MMOD and subsequent RIB. Together, the satellite based MMOD and SO metrics show potential value for regional monitoring and forecasting of the spring flood pulse and RIB timing in the Yukon and other boreal Arctic basins.

An integrated approach to estimate the mixing ratios in a karst system under different hydrogeological conditions

Study regionThe karst system of the Syemareh Dam site with the reservoir capacity of 3.2 bm3, located in the Zagros fold belt, southwestern of Iran, was studied under two conditions: before and after the reservoir impoundment as pre-reservoir and post-reservoir conditions, respectively. Study focusDespite a mixing of several water resources including the dam reservoir contributed to the flow rate of the downstream springs, the number of end-members was still unknown and their mixing ratio was unquantified. In this study, firstly a statistical approach (e.g. loading plot and matrix plot) was utilized to identify possible chemical reactions. Then, End Member Mixing Analysis (EMMA) was used to determine the number of end members. Lastly, the MIX code was utilized to quantify the mixing ratios. Three scenarios (i.e. assuming three, four and five end members) were compared to find a reliable mixing model based on the best match between the observed and estimated values of species concentration. In order to improve the calibration of the reliable mixing model, the species concentrations were corrected by deduction of the effect of plausible chemical reactions. New hydrological insights for the regionThe five end-members mixing model consisted of three aquifers, deep groundwater, and the reservoir was suggested as the dominant mixing process. Leakage from the reservoir as an end member was quantified by calculating the mixing ratio of the reservoir through mixing modeling for the first time.

ОСОБЕННОСТИ ПРОГНОЗА ДИНАМИКИ РОДНИКОВОГО СТОКА В БЕРЕГОВОЙ ЗОНЕ ИВАНЬКОВСКОГО ВОДОХРАНИЛИЩА

Ivankovo reservoir is the main source of drinking water supply in Moscow. Its coastal zone, where different types of springs are unloaded, is a barrier (or source) for the entry of pollutants into the reservoir. The aim of this research is to forecast increments in descending springs water flow and to evaluate trends of hydrochemical indicators (calcium, magnesium ions, hydrocarbonates and chlorine) of springs water quality over 13 years. The basis of the work are materials of regime observations on reference spring located on the Volga II floodplain terrace, for the period 2006-2018. When processing hydrochemical data in order to compare the results, two approaches were used. One is separation of data array into two groups in chronological order (2006-2012 and 2013- 2018), the other – is arrangement according to water content of the year, where the first group is the years of low and medium water content, the second is high. It is proposed to describe the relationship between amount of precipitation and increment of flow rate by an ordinary differential equation, which will allow to predict the flow rate of the downstream springs of the region using amount of precipitation in increments by the next six months. The obtained result was verified on groundwater level regime data for the well 3020, drilled on the II floodplain terrace, for the period 2001-2003. The maximum correlation coefficient between the increment of the groundwater level and the amount of precipitation is observed at a similar step. When analyzing the equation, the value of the amount of precipitation was obtained, which separates the mode of increasing or decreasing the flow rate of the spring (groundwater level). For the spring, this figure is 296, for the well – 316 mm. A statistical analysis of long-term dynamics of the spring runoff hydrochemical components showed that a median value is a more sensitive characteristic to changes in external conditions than an arithmetic average for hydrocarbonates and calcium. An upward direction shift of the median value of bicarbonates and calcium ions concentration in spring waters was revealed when using a nonparametric criterion. The long-term average gradient was 1 mg dm-3 year-1 for bicarbonates, and 0.17 mg dm-3 year-1 for calcium. The approaches used to divide the data into groups for calcium and magnesium give different estimates of trends, for hydrocarbons they were the same, for chlorides they are contradictory. Statistical analysis of the data, separated in chronological order, showed that for calcium and magnesium there was a significant upward trend, while with the approach for water availability of year no trends were found.

Geothermal drilling in an Alpine karst aquifer and its impact on downstream springs – A case study from Finkenberg, Tyrol, Austria

A borehole heat exchanger array was installed in an Alpine karst aquifer for the first time in Europe. It is composed of nine 400 m deep boreholes in the dolomitic marble of the Hochstegen Formation. New approaches were developed for this unprecedented application and potential risks were checked throughout the sinking of the initial exploratory wellbore. As Finkenberg is located in a tourist area, drilling operations had to be executed within only a few weeks. Several springs downstream from the drilling site are sources of drinking water and tap water supply. Given that the degree and distribution of the Hochstegen Formation karstification was unknown, a spring monitoring program was mandatory in order to obtain drilling permission from public authorities. A practicable and affordable spring monitoring program including several physical and chemical parameters was developed and implemented to document the potential impact of the drilling activities on the spring water. A temporary and locally limited impact of the drilling works on groundwater quality was detected by turbidity measurements. This paper reports the implementation of geothermal drilling in a karst aquifer with a focus on karstification as well as planning, implementation and the results of the spring monitoring program. Such a program can be recommended for comparable projects or questions, adapting the characteristic parameters to be collected and the measurement intervals in consultation with the relevant authorities. It might also increase the chances of gaining approval for geothermal projects in karst and could enhance public acceptance. Key words: Pneumatic down hole hammer drilling, Borehole heat exchanger, Groundwater monitoring, Turbidity, Hochstegen Formation. Geotermalno vrtanje v alpskem kraskem vodonosniku in njegov vpliv na dolvodne izvire - studija primera Finkenberg, Tirolska, Avstrija V alpskem kraskem vodonosniku je bilo prvic v Evropi vzpostavljeno polje geosond. Vkljucuje devet 400 m globokih vrtin, izvrtanih v dolomitnem marmorju Hochstegenove formacije. Razvili smo nove pristope za to aplikacijo brez primere in potrdili morebitna tveganja v casu potopitve prvotne raziskovalne vrtine. Ker je studijsko obmocje Finkenberg na turisticnem obmocju, je bilo treba opraviti vrtanje v samo nekaj tednih. Vec izvirov od mesta vrtanja so viri oskrbe s pitno vodo. Glede na to, da stopnja in porazdelitev zakraselosti Hochstegenove formacije nista bili znani, je bilo treba za pridobitev dovoljenja za vrtanje nujno opazovati izvire. Da bi dokumentirali vpliv vrtanja na izvirsko vodo, je bilo pri spremljanju izvirov treba upostevati vec fizikalnih in kemijskih parametrov. Zaznali smo obcasen in lokalno omejen vpliv vrtanja na kakovost podzemne vode. V prispevku smo predstavili izvajanje geotermalnega vrtanja v kraskem vodonosniku s poudarkom na identifikaciji zakraselosti ter nacrtovanju ter na izvedbi in spremljanju kakovosti voda na izviru. Tak program se lahko uporabi pri primerljivih projektih ali iskanju odgovorov na podobna vprasanja s prilagojenim programom opazovanih parametrov in intervalov merjenja. Prav tako bi lahko povecal možnosti za pridobitev soglasja za geotermalne projekte na krasu in povecal ozavescenost javnosti. Kljucne besede: vrtanje s pnevmatskim kladivom, geosonda, spremljanje podzemne vode, motnost, Hochstegenova formacija. A borehole heat exchanger array was installed in an Alpinekarst aquifer for the first time in Europe. It is composed of nine400 m deep boreholes in the dolomitic marble of the HochstegenFormation. New approaches were developed for thisunprecedented application and potential risks were checkedthroughout the sinking of the initial exploratory wellbore. AsFinkenberg is located in a tourist area, drilling operations hadto be executed within only a few weeks. Several springs downstreamfrom the drilling site are sources of drinking water andtap water supply. Given that the degree and distribution of theHochstegen Formation karstification was unknown, a springmonitoring program was mandatory in order to obtain drillingpermission from public authorities. A practicable and affordablespring monitoring program including several physical andchemical parameters was developed and implemented to documentthe potential impact of the drilling activities on the springwater. A temporary and locally limited impact of the drillingworks on groundwater quality was detected by turbidity measurements.This paper reports the implementation of geothermaldrilling in a karst aquifer with a focus on karstification aswell as planning, implementation and the results of the springmonitoring program. Such a program can be recommended forcomparable projects or questions, adapting the characteristic

Leakage paths at the Lar Dam site, northern Iran

The Lar Dam was constructed from 1974 to 1980 in the Lar River valley at the foot of the Damavand Volcano. The valley walls consist of Mesozoic limestone and Quaternary volcanic rocks, overlain by thick lacustrine deposits. Prior to dam construction, a few sinkholes were observed in the reservoir area, but after impoundment, several new sinkholes formed and leakage occurred through downstream springs. Despite extensive treatment works, the reservoir has currently impounded only 40% of its designed capacity, about 35 years after the commencement of operations. The Lar Reservoir is located inside the area of a large palaeo-lake, which formed as a result of blockage of the river valley by eruption of the Damavand Volcano during the Pleistocene. This lake existed for thousands of years, developing deep karst conduits in the limestone below the volcanic rocks toward downstream springs. With the construction of the Lar Reservoir, relict karst conduits were revived and leakage occurred. Two paths are proposed for reservoir leakage, considering the region's historical geology, present hydrogeological setting, tracer tests and isotopic studies, as well as the response of spring discharge and borehole water level to reservoir filling.

Understanding Karst Leakage at the Kowsar Dam, Iran, by Hydrogeological Analysis

The Kowsar Dam is constructed on the Kheyrabad River at the northern limb of the Duck Anticline, close to its NW plunge, SW Iran. The dam is built on the karstic Asmari Formation, and the reservoir is in direct contact with this formation from the dam body to the upstream impermeable Gachsaran Formation. After reservoir impounding, several new springs emerged from the Asmari Formation, adjacent to the old small springs at the southern limb of the Duck Anticline. The discharge of these downstream springs was not reduced despite grout curtain treatment works. The main water leakage route is not below or through the grout curtain, as shown by considering rock permeability in pilot and check holes, cement consumption in grouting boreholes, borehole water levels, spring locations, and discharge of the dam galleries. The Duck Anticline is hydrogeologically connected to the adjacent Dill and Pahn Anticlines, comprising the Asmari Karst Aquifer, which is divided into three karst sub-aquifers. The general flow direction of karst water in each sub-aquifer was determined using hydrogeological analysis and water balance calculations. Two alternative models are proposed for water flow at the northern limb of the Duck Anticline. The main leakage route toward the downstream springs is most probably through a relict karst conduit system, developed along bedding planes of the Asmari Formation at the NW plunge of the anticline, according to the first proposed model. In this case, the water leakage can be significantly reduced by extension of the grout curtain further into the upstream impermeable Gachsaran Formation.

Hydrogeology and the Declaration of Protection Area of Tavra Springs (Sivas - Turkey)

The basin of Tavra Springs located 7km North of Sivas Province has a drainage area of 101 km2. Sivas City provides a portion of the drinking and potable water with the average flow (Q) of 880 l/s from groundwater (underground drainage) in the valley. The springs in this valley are generally located in the northwest and south of the valley. There is no single exit point of Tavra Springs. Some springs flow in the form of surface stream (surface water). The groundwater flow was measured in the collection chamber downstream of the valley. This study was conducted in order to determine the spring field and the protection of the borders of the Tavra Springs in accordance with “The Communication about Drinking Water Supply and the Aquifer Protection of Sources” protocol published in 10th October 2012, [10]. According to the reports in this type of springs, “Absolute Protection Area” is accepted to be 50 meters. Additionally, “First Degree Protection Area” is defined as an area beginning from “Absolute Protection Border” to the distance travelled by the infiltrated water into the aquifer in 10 days. In order to calculate the border of “First Degree Protection Area” of the Tavra Spring, one borehole having 35 meter in depth was drilled 130 m away from the upstream springs. The salt solution (500kg salt/ 2000 l water) with electrical conductivity (EC) value of 222.000μS/cm was injected and the changes in the electrical conductivity were then tested and monitored in the downstream springs. Moreover, this area was estimated by using the empirical equations derived from Darcy's formula. The results of these two methods (testing-monitoring, empirical estimation) were compared. As a main result of this study, the distance between “Absolute Protection Area” and “First Degree Protection Area” was determined to be 437 meters.

A mathematical model for simulating spring discharge and estimating sinkhole porosity in a karst watershed

Documenting and understanding water balances in a karst watershed in which groundwater and surface water resources are strongly interconnected are important aspects for managing regional water resources. Assessing water balances in karst watersheds can be difficult, however, because karst watersheds are so very strongly affected by groundwater flows through solution conduits that are often connected to one or more sinkholes. In this paper we develop a mathematical model to approximate sinkhole porosity from discharge at a downstream spring. The model represents a combination of a traditional linear reservoir model with turbulent hydrodynamics in the solution conduit connecting the downstream spring with the upstream sinkhole, which allows for the simulation of spring discharges and estimation of sinkhole porosity. Noting that spring discharge is an integral of all aspects of water storage and flow, it is mainly dependent on the behavior of the karst aquifer as a whole and can be adequately simulated using the analytical model described in this paper. The model is advantageous in that it obviates the need for a sophisticated numerical model that is much more costly to calibrate and operate. The model is demonstrated using the St. Marks River Watershed in northwestern Florida.

Hydrogeological characterization of Gold Valley: an investigation of precipitation recharge in an intermountain basin in the Death Valley region, California, USA

Gold Valley is typical of intermountain basins in Death Valley National Park (DVNP), California (USA). Using water-balance calculations, a GIS-based analytical model has been developed to estimate precipitational infiltration rates from catchment-scale topographic data (elevation and slope). The calculations indicate that groundwater recharge mainly takes place at high elevations (>1,100 m) during winter (average 1.78 mm/yr). A resistivity survey suggests that groundwater accumulates in upstream compartmentalized reservoirs and that the groundwater flows through basin fill and fractured bedrock. This explains the relationship between the upstream precipitational infiltration in Gold Valley and the downstream spring flow in Willow Creek. To verify the ability of local recharge to support high-flux springs in DVNP, a GIS-based model was also applied to the Furnace Creek catchment. The results produced insufficient total volume of precipitational infiltration to support flow from the main high-flux springs in DVNP under current climatic conditions. This study introduces a GIS-based infiltration model that can be integrated into the Death Valley regional groundwater flow model to estimate precipitational infiltration recharge. In addition, the GIS-based model can efficiently estimate local precipitational infiltration in similar intermountain basins in arid regions provided that the validity of the model is verified.

Inversion for the Input History of a Dye Tracing Experiment

2 * Abstract: The advection-dispersion model (ADM) is a good tool for simulating transport of dye or solutes in a solution conduit. Because the general problem of transport can be decomposed into two problems, a boundary-value problem and an initial-value problem, the complete solution is a superposition of the solutions for these two problems. In this paper, the solution for the general problem is explained. A direct application of the solution for the boundary-value problem is dye-tracing experiments. The purpose is inclusion of the input history of a solute dye into the ADM. The measured breakthrough curve of a dye-tracing experiment is used to invert for the release history of the dye at the input point through the ADM. It is mathematically shown that the breakthrough curve can not be directly used to invert for the boundary condition at a tracer release point. Therefore, a conductance-fitting method is employed to obtain the input history. The inverted history for a simple example is then shown to be a step function with amplitude of 420 mg/L and a duration of 10 minutes. Simulations illustrate that the breakthrough curves at downstream springs provide a means for understanding the migration of dye. A discussion of the implication of the solution for an initial-value problem (e.g., simulating transport of preexisting solutes such as dissolved calcium carbonate in solution conduits) is also included.

Hydrodynamic and isotopic investigations for evaluating the mechanisms and amount of groundwater seepage through a rockslide dam

AbstractThis study addresses the influence of landslide dams on surface water drainage and groundwater flow. In the study area of Scanno Lake and Sagittario River (Central Italy), a limestone rockslide‐avalanche formed a lake, which has an outlet that is occasionally active, showing infiltration into the rockslide dam. Several springs are present at the lake's base and are partly fed by seepage through the rockslide debris. Piezometric surveys, discharge measurements, pumping tests and chemical analyses are tools used to build a conceptual model of the groundwater flow and to evaluate the flow through the rockslide debris. Seasonal water isotopic signatures validate the assumed model, showing a mixing of infiltration recharge and groundwater seepage throughout the rockslide debris. Various recharge areas have been found for springs, pointing out those directly fed by the rockslide debris aquifer. Hypotheses about seasonal groundwater mixing between the regional carbonate aquifer and the rockslide debris aquifer are supported by isotope results. Seasonal changes in groundwater table level due to recharge and surface losses from seasonal outlet have been correlated with isotopic groundwater composition from the rockslide debris aquifer and the downstream springs; this relationship highlights the role of the rockslide dam body on the hydrodynamics of the studied area. Relationships between surface waters and groundwater in the area have been completely understood on the basis of water isotopic fingerprinting, finally obtaining a complete evaluation of groundwater renewable resources and its regimen. Copyright © 2010 John Wiley & Sons, Ltd.

Spatial and temporal hydrochemical variations of the spring-fed travertine-depositing stream in the Huanglong Ravine, Sichuan, SW China

Automatic hydrochemical logging and in situ titration com­bined withlaboratory analysis were used to understand the spatial and temporal hydrochemical variations of the spring-fed, travertine-depositing stream in celebrated Huanglong Ravine, Sichuan, SW China. This is essential for protection of the Huanglong World Natural Heritage travertine land­scape. It was found that the deposition of travertine was due to very strong CO 2 degassing from the water, leading to de­crease in pCO 2 and specific conductivity (SpC), and increase in pH and SIc downstream from the Spring. However, regular downstream hydrochemical evolution was interrupted by di­lution withsnow-melt water and by renewed CO 2 from some downstream springs. The chemistry of Huanglong Spring itself was stable at a diurnal scale thoughit was altered by the great Wenchuan earthquake of May 12 2008. However, in spring-fed pools downstream, pCO 2 and SpC were lower, and pH and SIc were higher in daytime than at night, whichindicates that the deposition of travertine was faster during the daylight hours. This was due to the combined effects of higher water tempera­tures and higher aquatic algae photosynthesis. In addition, it was found that the phosphate concentration in the stream in­creased remarkably downstream in the tourist midseason, in­dicating water pollution by tourism activities. The increase of phosphate (an inhibitor of calcite precipitation) may be one of the reasons for the decrease in travertine deposition rates and accelerated propagation of discoloration by diatoms during the past decades, whichneeds to be given more comprehensive study and tackled in future for the protection of these world famous travertine deposits.

Environmental impacts of Sheba tannery (Ethiopia) effluents on the surrounding water bodies

The levels of hexavalent chromium from direct and treated Sheba tannery effluents, downstream river and spring water samples and upstream river water samples were determined spectrophotometrically by the s-diphenylcarbazide method at 540 nm. Temporal and representative samples were collected from the untreated tannery effluent (S1), sedimentation pond (S2), chromium oxidation pond (S3), downstream river (S4), downstream spring (S5) and 5 kms upstream river (S6). The mean levels of hexavalent chromium in S1, S2, S3, S4, S5 and S6 were 10.54, 9.15, 7.82, 0.58, 0.54 and 0.015 mg/L, respectively. The levels of hexavalent chromium in the downstream river and spring water samples exceed the World Health Organization (WHO) permissible limit of total chromium in drinking waters (0.05 mg/L) as opposed to the levels in the upstream waters. The increased concentrations of Cr(VI) in the water samples indicate the possible environmental pollution of the downstream water bodies by the Sheba tannery effluents. In view of the toxicity and related environmental hazards, the levels of hexavalent chromium from the Sheba tannery effluents must be reduced to a permissible limit before discharging into the down stream waters being used for domestic purposes by the nearby communities.

Tracing of the Stream Flowing Through the Cave Ferranova Buža, Central Slovenia

The article discusses the characteristics of the recently discovered ground water stream in the cave Ferranova buža and its possible karstic hydrological system. Its upstream connections have been narrowed to few possible springs by means of logical exclusion and have yet to be confirmed. For the purpose of establishing its linkage to the downstream springs around Vrhnika a water tracing experiment has been performed. Uranine was used as a tracer and sampled in intervals of eight hours at Primc’s spring, Bečkaj’s spring and Kožuh’s spring. The connection was proved in all three observation points, with Kožuh’s spring draining the largest quantity of the tracer. The tracer experiment evidenced that the dye was completely flushed downward in single transition curve almost without any retention.

Tracer-test design for losing stream-aquifer systems

Hydrological tracer testing is an effective way for assessing the significance and extent of leakage through the bed of an influent (losing and sinking) stream. In karstic terranes, leakage from losing and sinking streams typically resurge at downstream springs, but flow may be intercepted by production wells. Although sinking streams that disappear into swallow holes and caves are relatively easy to trace, developing a tracer test design for a losing stream that allows slow percolation through its bed is complicated by the lack of basic knowledge regarding leakage rate, leakage locations along its length, and temporal variability. To overcome these complications, modification to the Efficient Hydrologic Tracer-test Design (EHTD) program were undertaken. Simultaneous use of both pumping wells and springs as sampling stations constituted initial modifications to EHTD. Additional modifications were then taken to address the problem of losing streams by using the total volume of flow leaking through the bed of a losing stream as determined by taking the difference between upgradient and downgradient discharge measurements or as estimated from the effective porosity of the stream bed. Leakage rate may be set if measured or may be taken as a function of the estimated mean travel time for the losing stream. These modifications are also effective for dry stream channel in which an artificial flow is necessarily added to facilitate a tracer test.

Treatment of the seepage problems at the Kalecik Dam (Turkey)

This paper describes the seepage prevention measures at Kalecik Dam. Water leaked from the foundation of the dam after the impoundment. The dam, 77 m in height, was constructed for irrigation purposes. The foundation consists of Mesozoic ophiolite, Paleocene allochthonous units composed of different lithologies and Miocene conglomerate. Karstified and fractured Paleocene limestone outcrops on the right bank of the dam foundation. This unit extends into, and its thickness increases within, the right abutment. The leakage occurs towards the downstream springs through the right bank limestone. The main grout curtain is 200 m long and 60 m deep and was constructed on the right bank. After reservoir impounding, new springs were observed in the downstream area. Therefore, after the construction of the dam, remedial curtain grouting was required and carried out in three stages. Firstly, the main grout curtain was supplemented by additional grouting to seal the fractures and infill karstic cavities. The diversion tunnel was also repaired. The curtain depth was the same as the depth of the previous curtain. The second stage of additional treatment consisted of new deep grouting. Some investigation holes were also drilled along the same alignment as the main curtain to locate the seepage in the region. These holes were extended to an elevation of 442 m. The final stage of grouting measures was between the spillway and the dam body and underneath the spillway. As a result of the additional grouting measures, the spring discharges observed downstream of the dam embankment decreased. However, the seepage paths were extended and were moved with time so that the seepage problems are still continuing.