Seepage Measurements Research Articles

IDENTIFYING WEAK ZONES PRONE TO SEEPAGE AT DUDHGANGA MASONRY DAM BY NUCLEAR DENSITY LOGGING

ABSTRACT Excessive seepage from the masonry dams/reservoirs generally occurs through the body of the dam; the geological formations in the vicinity of the reservoir; or through the structure- foundation interface. The economic consequences of this seepage can be large because of the likelihood of the induced structural instability. It is, therefore, essential to identify the areas of water loss and seepage entry points in the body of dams. This information is vital for adapting the remedial measures necessary to reduce or prevent the water loss. Nuclear logging techniques, being non-destructive and cost-effective, are extensively applied for identifying seepage entry points in dam for solving problems related to repairs and restoration of hydraulic structures. The paper deals with nuclear density logging carried at Dudhganga Dam, for evaluating the in situ density required for dam safety and stability analysis and also identifying weak zones prone to excessive seepage and remedial measures suggested for reducing the seepage.

Characterizing lakebed seepage and geologic heterogeneity using resistivity imaging and temperature measurements

ABSTRACTThe contribution of groundwater‐surface water exchange to lake budgets is poorly understood and depends in part on lakebed heterogeneities. These heterogeneities are difficult to characterize using traditional point sampling methods. The goal of this project was to use electrical resistivity to identify potential zones of groundwater discharge and recharge, providing focus for point measurements. Multiple resistivity surveys were conducted at Lake Lacawac, a small, glacially‐formed lake in northeastern Pennsylvania. Two types of resistivity surveys were conducted. In a continuous resistivity profile, a multi‐electrode cable was towed parallel to shore to look for spatial variability in resistivity around the lake. Two parallel to shore surveys were conducted, an inner and outer loop, to help characterize the lateral extent of sediment types. The results of these surveys suggested lithology changes both along the shoreline and with distance from shore. Follow‐up resistivity data were collected using cables laid along the lake bottom perpendicular to the shoreline to look for finer scale zonation that affects seepage as a function of distance from shore.Follow‐up seepage measurements showed that seepage rates are very low, which is consistent with the resistivity data from which we concluded that most of Lake Lacawac is lined with glacial clay and that the lake is essentially perched above the groundwater flow system, with just minor amounts of seepage in a few locations where fingers of sandy sediments extend a short distance from the shore. Discontinuities in these patches of transmissive sediments can result in reversals in the direction of seepage at nearby locations.We conclude that towed resistivity is useful as a rapid reconnaissance tool for mapping geologic heterogeneity. The results can be used to guide the more time‐consuming but higher‐resolution, lake bottom resistivity measurements, which in turn can guide the placement of seepage meters.

Wave effects on submarine groundwater seepage measurement

Variation of sea-surface and water pressure above the sea bed induces temporal variation of submarine groundwater discharge over time scales ranging from seconds to years. Hydrodynamic theory and measurements suggest that wave-induced exchange between a permeable sediment bed and overlying water column is significant but conventional seepage-meter studies have focussed mainly on tidal dynamics and ignored waves. At Cockburn Sound in Western Australia we measured wave-induced flow reversals through a seepage meter of amplitude 60 cm d - 1 ; however, it was unclear whether the measured flows were real seepage or, partly or wholly, an artifact of wave action on the seepage meter. A numerical model of seepage patterns beneath a vented benthic chamber demonstrated an observer effect introduced by the chamber and not previously identified. Placing a chamber on the sediment bed disturbed the pressure field and changed both the pattern and magnitude of the wave-induced flow. A separate analysis of benthic-chamber movements under the action of shallow surface waves established that micron-scale movements of the chamber at the wave frequency were sufficient to produce apparent seepage amplitudes of O(1–100) cm d −1. We concluded that wave action is a key control on bed seepage and should not be neglected without justification in direct-measurement studies of marine bed discharge. A systematic error during each wave cycle can accumulate to a significant measurement error if the wave cycle error is large or if wave-induced flow is the dominant component of the seepage. In the latter case, the error could potentially be misinterpreted as a steady seepage component.

Isotope tracing of submarine groundwater discharge offshore Ubatuba, Brazil: results of the IAEA–UNESCO SGD project

Results of groundwater and seawater analyses for radioactive ( 3H, 222Rn, 223Ra, 224Ra, 226Ra, and 228Ra) and stable (D and 18O) isotopes are presented together with in situ spatial mapping and time series 222Rn measurements in seawater, direct seepage measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge (SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0 cm d −1 to 360 cm d −1; the unit represents cm 3/cm 2/day), as well as during a few hours (from 0 cm d −1 to 110 cm d −1), strongly depending on the tidal fluctuations. The average SGD flux estimated from continuous 222Rn measurements is 17 ± 10 cm d −1. Integrated coastal SGD flux estimated for the Ubatuba coast using radium isotopes is about 7 × 10 3 m 3 d −1 per km of the coast. The isotopic composition ( δD and δ 18O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore distance became negligible. Automated seepage meters and time series measurements of 222Rn activity concentration showed a negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1–2 weeks for water within 25 km offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential environmental concern and has implications on the management of freshwater resources in the region.

A seepage meter designed for use in flowing water

Summary Seepage meters provide one of the most direct means to measure exchange of water across the sediment–water interface, but they generally have been unsuitable for use in fluvial settings. Although the seepage bag can be placed inside a rigid container to minimize velocity head concerns, the seepage cylinder installed in the sediment bed projects into and disrupts the flow field, altering both the local-scale fluid exchange as well as measurement of that exchange. A low-profile seepage meter designed for use in moving water was tested in a seepage meter flux tank where both current velocity and seepage velocity could be controlled. The conical seepage cylinder protrudes only slightly above the sediment bed and is connected via tubing to a seepage bag or flowmeter positioned inside a rigid shelter that is located nearby where current velocity is much slower. Laboratory and field tests indicate that the net effect of the small protrusion of the seepage cylinder into the surface water flow field is inconsequentially small for surface water currents up to 65 cm s −1 . Current velocity affects the variability of seepage measurements; seepage standard deviation increased from ∼2 to ∼6 cm d −1 as current velocity increased from 9 to 65 cm s −1 . Substantial bias can result if the shelter is not placed to minimize hydraulic gradient between the bag and the seepage cylinder.

Natural emissions of methane from geological seepage in Europe

Recent studies have shown that geological emissions of methane are an important greenhouse-gas source. Remarkable amounts of methane, estimated in the order of 40–60 Tg yr −1, are naturally released into the atmosphere from the Earth's crust through faults and fractured rocks. The main source is natural gas, both microbial and thermogenic, produced in hydrocarbon-prone sedimentary basins and injected into the atmosphere through macro-seeps (onshore and offshore mud volcanoes and other seeps) and microseepage, an invisible but pervasive flux from the soil. This source is now evaluated for Europe on the basis of a literature survey, new field measurements and derived emission factors. The up-scaling criteria recommended by the EMEP/CORINAIR guidelines are applied to the local point and area source data. In Europe, 25 countries host oil and/or natural gas reservoirs and potentially, or actually, emit geological methane. Flux data, however, are available only from 10 countries: the onshore or offshore petroliferous sectors of Denmark, Italy, Greece, Romania, Spain, Switzerland, United Kingdom and Black Sea countries (Bulgaria, Ukraine, Georgia). Azerbaijan, whose emissions due to mud volcanism are known to be relevant, is included in the estimate. The sum of emissions, regional estimates and local measurements, related to macro-seeps leads to a conservative total value of about 2.2 Tg yr −1. Together with the potential microseepage fluxes from the petroliferous basins, estimated on the basis of the Total Petroleum System concept (around 0.8 Tg yr −1), the total European seepage is projected to 3 Tg yr −1. This preliminary figure would represent, in terms of magnitude, the second natural methane source for Europe after wetlands. The estimate will have to be refined by increasing the number of seepage measurements both on lands, where there is high potential for microseepage (e.g., Germany, Hungary, Romania, Ukraine, Belarus, Russia, Georgia) and in coastal marine areas (the North Sea, the Black Sea, offshore Greece and Italy) where emission factors and the extent of the underwater seeping area are not completely known.

Exonerating Bernoulli? On evaluating the physical and biological processes affecting marine seepage meter measurements

Seepage meters, like most benthic flux chamber techniques, come with inherent concerns about how their presence may alter the environment and flow regimen of the benthic boundary layer and underlying sediments. Flow due to wave and current movement across topographic features induces a downward and upward flow field within the sediments surrounding the feature. We found this Bernoulli-induced flow is a real, but maybe minor, component of measured advection using seepage meters. This study was conducted in a Florida coastal lagoon to test the physical forcing mechanisms that may influence seepage measurements from sediments. Calculated Bernoulli seepage was within the measured background (~1 to 2 cm day−1) expected from seepage meters when a plastic barrier beneath the device is used to inhibit natural seepage contributions. Nearby seepage measurements made with Lee-type seepage meters placed directly in the sediments ranged from 1 to 12 cm day−1. Thus, when seepage flow is very slow from sediments, Bernoulli-induced seepage may obscure the measurement. However, this study demonstrates that seepage in the Indian River Lagoon must be driven by forces other than Bernoulli-induced (pumped) flow. Suggestions for these forcing mechanisms highlight the uncertainty of the water source(s) in seepage measurements. In these Florida lagoon sediments, bioirrigation and terrestrial groundwater inputs are the most likely drivers, depending on distance from shore, benthic community composition, and continental recharge. Seepage measurements can be an excellent measure of advection in shallow-water marine sediments if Bernoulli-induced seepage is taken into account either experimentally or calculated based on local hydrographic and meteorological data.

Submarine groundwater discharge measured by seepage meters in sicilian coastal waters

Seepage measurements of submarine groundwater discharge (SGD) were carried out in March 2002 in the Donnalucata boat basin in the southeastern Sicily. SGD rates measured by manual seepage meters ranged from 5.5 to 19.3 L/min/m (with an average of 12.1 L/min/m), which was 0.6 and 5.9 times the SGD determined in Florida and Perth, respectively. The spatial distribution of SGD was found to be highly variable along ∼300 m long coast area. Semi-diurnal SGD variations which anti-correlated with tide were found using newly developed automated seepage meters that can provide continuous SGD data with high resolution. These variations may be attributed to the tidal effect, when a greater hydraulic gradient, observed at low tide, moves groundwater from land to the ocean, and an opposite effect is observed at high tide.

Characterisation of submarine groundwater discharge offshore south-eastern Sicily

A complex approach in characterisation of submarine groundwater discharge (SGD) off south-eastern Sicily comprising applications of radioactive and non-radioactive tracers, direct seepage measurements, geophysical surveys and a numerical modelling is presented. SGD fluxes in the Donnalucata boat basin were estimated by direct seepage measurements to be from 4 to 12 L s −1, which are comparable with the total SGD flux in the basin of 17 L s −1 obtained from radon measurements. The integrated SGD flux over the Donnalucata coast estimated on the basis of Ra isotopes was around 60 m 3 s −1 per km of the coast. Spatial variations of SGD were observed in the Donnalucata boat basin, the average 222Rn activity concentration in seawater varied from ∼0.1 kBq m −3 to 3.7 kBq m −3 showing an inverse relationship with salinity. The continuous monitoring carried out at the site closest to the coast has revealed an inverse relationship of 222Rn activity concentration on the tide. The 222Rn concentrations in seawater varied from 2.3 kBq m −3 during high tides to 4.8 kBq m −3 during low tides, thus confirming an influence of the tide on submarine groundwater discharge. Stable isotopes (δ 2H and δ 18O) showed that SGD samples consist up to 50% of groundwater. Geo-electrical measurements showed a spatial variability of the salt/fresh water interface and its complex transformation in the coastal zone. The presented results imply that in the studied Donnalucata site there are at least two different sources of SGD, one superficial, represented by mixed fresh water and seawater, and the second one which originates in a deeper limestone aquifer.

Evaluating the use of canal seepage and solute concentration observations for aquifer parameter estimation

We evaluate the benefit of using field observations on groundwater flux to canals and pore-water solute concentration, in addition to hydraulic head, to estimate model parameters for groundwater flow. The field site was a 100 km 2 area of the Biscayne Aquifer in Southeast Florida. A total of seven models were calibrated to different combinations of 196 observations of groundwater head, 56 measurements of seepage between the aquifer and canals, and 196 measurements of pore-water chloride concentration. The calculated initial parameter correlations indicated that the model with higher parameter freedom (six instead of five) and calibrated solely on hydraulic head or canal seepage estimated unreliable parameters due to the non-uniqueness of the solution. Calculated parameter sensitivities of the final values further suggested that the six-parameter models calibrated solely on hydraulic head did not have sufficient information to estimate the parameters independently. Each of the seven calibrated models was evaluated by comparing simulated (predicted) and measured values taken during a 10-day canal drawdown test and during a 4-month time period, neither of which were used in the calibration. The model evaluations demonstrate that (1) the models calibrated solely on head measurements predict poorly regardless of the number of parameters estimated; (2) the models calibrated solely on seepage fluxes predict accurately if the number of estimated parameters is restricted; and (3) the models calibrated on at least two types of data (e.g. hydraulic head and seepage fluxes) exhibit good predictive capabilities with both the five- and six-parameter models.

Tidally induced groundwater circulation in an unconfined coastal aquifer modeled with a Hele-Shaw cell

We use a scaled Hele-Shaw cell to mimic tidally induced nearshore groundwater motion in an unconfined aquifer. The low slope angle of sandy beaches contributes to a strongly asymmetric pattern of fluid exchange across the water-sediment interface during tidal cycles. This asymmetry leads to a time-averaged groundwater circulation centered beneath the low-tide level; horizontal and vertical components of motion are of the same order. Horizontal seaward flow extends a significant depth beneath the interface, consonant with a time-averaged water table that is elevated above mean sea level, providing the hydraulic gradient necessary to drive this deeper export of mass equal to the time-averaged inflow by infiltration. This tidally forced flow behavior likely contributes to observed fluctuations in submarine seepage rates. Moreover, the circulation largely involves a subsurface cycling of seawater that infiltrates during the rising tide. Measurements of submarine seepage near the tidal zone therefore likely involve this cycled seawater as well as freshwater flows.

Comparative evaluation of canal seepage investigation techniques

Various methods are used to estimate the canal seepage rate such as empirical formulae, analytical or analogue studies and the direct seepage measurement techniques, i.e. seepage meters, ponding tests and inflow–outflow tests. Considering significance of physical measurement techniques both ponding and inflow–outflow methods were used to evaluate the seepage losses. These methods have their merits, demerits and limitations which are well understood. However, while interpreting seepage loss evaluations, there can be independent random errors, like the fluctuations in flow conditions affecting different current meter positions, and systematic errors, like the use of different instruments or different methods to measure different terms in the balance. These errors have to be distinguished. The data from various studies in the region have been reviewed and analyzed. A statistical analysis of a number of replications of ponding and inflow–outflow test data of the seepage estimation work on various canals under the Fordwah Eastern Sadiqia (South) project, Bahawalnagar, Pakistan has been done to show the accuracy of results achieved through both the methods. It has been shown that the ponding method is more accurate than the inflow–outflow method as variability of various statistical parameters from the ponding tests is comparatively less. It is proved that inflow–outflow tests should not be used for seepage investigations where seepage rates are fairly small and there is no possibility to use sufficiently long reaches.

Errors with Small Volume Elastic Seepage Meter Bags

The use of small volume elastic collection bags (condoms) has become popular in seepage meter studies in recent years, despite minimal field or laboratory validation of their use and, specifically, the impact of their elasticity on seepage measurements. A laboratory study was initiated after field results using small elastic collection bags produced seepage data that did not correlate with hydrometric data. The laboratory data demonstrate that condoms undergo significant mechanical relaxation during seepage measurement times typically observed in field settings. Unlike conventional nonelastic collection bags, which mechanically relax over several minutes, the condoms suffered from a slow mechanical relaxation or equilibration. Over nine hours, condoms gained 43 mL of water, approximately 50% of maximum workable volume (between mechanical relaxation effect and elastic limit), under stagnant flow conditions. This long-term equilibration invalidates simple subtraction of equilibration volumes from collection volumes as a correction technique. Previously published studies using flexible small-volume elastic measurement bags (condoms) have not reported a mechanical relaxation effect. Overall, because the condom's small workable volume and inherent variability, we would not recommend any small-volume elastic measurement bags for quantitative seepage measurements.

The contribution of water and chloride to Lake Kinneret through unfocused seepage, based on in situ seepage measurements

The contribution of water and chloride to Lake Kinneret through unfocused seepage, based on in situ seepage measurements

Theory and practice of hydrostatic lysimeters for direct measurement of net seepage in a patterned mire in north Scotland

Abstract. A novel design of lysimeter for use in mires (peatlands) with shallow water tables is described. It employs an hydraulic mechanism for the automatic equilibration of soil moisture distribution between the outside and the inside of the lysimeter tank but uses no electronic components or electrical power; and it can be installed with minimal disturbance in surfaces with poor load-bearing capacity. The system was deployed on a mire in northern Scotland to investigate the distribution of shallow seepage associated with catenary arrays of different types of surface (microtopes). During the three-year period 15 November 1988 to 19 November 1991, the fraction of rainfall dispersed as seepage was 52% in a pool system; 62% in ridge-furrow microtopography; and 59-67% in unpatterned sloping mire. The data provide preliminary confirmation of the hypothesis of K. E. Ivanov that different microtopes within the same mire differ in their hydrological norms; and suggest that the range of ecohydrological differences at the study site may be similar to those obtained by Ivanov in western Siberia. Details of lysimeter design, construction, installation and operation are appended together with a discussion of the theory of the lysimeter. Keywords: acrotelm, blanket mire, ecohydrology, evapotranspiration, pool system, valleyside flowe, water balance

Dynamic temporal patterns of nearshore seepage flux in a headwater Adirondack lake

Although seepage in lakes is known to vary as a function of precipitation and watershed characteristics, temporal patterns of seepage flux over daily and weekly time scales have not been extensively studied with a concentrated effort of direct measurement of seepage in nearshore areas. In this study, seepage was intensively measured with seepage meters over two summers and during snowmelt in Lower Sylvan Pond, a small lake in the Adirondack Mountains region of New York State, USA. A consistent pattern of slight discharge (never exceeding 105 mL m −2 h −1) was observed at three stations along a segment of the shoreline near the inlet stream. A distinct temporal pattern of seepage was observed at three stations along another portion of the shoreline. Seepage discharged (>400 mL m −2 h −1) for a portion of the summer in 1998 and then shifted to recharge (<−500 mL m −2 h −1) for the remainder of the summer. A similar temporal pattern was observed again in 1999 but the transition to recharge occurred earlier and higher rates of discharge (610 mL m −2 h −1) and recharge (−608 mL m −2 h −1) were recorded. Additionally, seepage at these three stations increased after large rainfall events and a pronounced episodic increase of seepage was measured during snowmelt. Distinct seepage patterns along portions of the shoreline show that seepage can vary considerably within seasons and suggests a need to consider changes of seepage over time periods of days to weeks as well as among seasons and years. This study demonstrates that the resolution of temporal seepage data can be important to the understanding of water fluxes to aquatic ecosystems.

Detection of seepage paths in earth dams using self-potential and electrical resistivity methods

Earth and rockfill dams are designed to operate under steady state seepage. Anomalous seepage may be a threat to the integrity of the structure. In spite of advances made in the fields of geotechnical engineering, it is not possible to have 100% leak-proof structure. Any excessive and unplanned seepage may lead to the failure of the dam, especially in unconsolidated or fractured terrains. Geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time, enabling to plan technically and economically worthwhile remedial measures. In the present paper, utilisation of electrical methods for delineation of seepage zones at two of the four Saddle dams of the Som-Kamla-Amba project, Rajasthan State, India; which is founded on heterogeneous rock mass, is discussed. Electrical resistivity method was used to delineate zones favourable for seepage, whereas, self-potential (SP) method was used to delineate the seepage paths. SP measurements have shown negative anomaly of the order of 10–20 mV in amplitude, indicating low seepage, coinciding with the seepage measurements made by the project authorities.

The Effects of Bag Type and Meter Size on Seepage Meter Measurements

AbstractSeepage meters provide a useful, inexpensive method of measuring seepage flux through unconsolidated sediments in lakes, reservoirs, and stream channels. In the literature, the bag type used is usually not indicated, and its effect on seepage measurement has not been evaluated. The effects of bag type and seepage meter size have been evaluated in a laboratory setting.A sandbox 100.4 (L) × 76.2 (W) × 24 (H) cm size was half filled with coarse sand and water to a depth of 10 cm. Four seepage meters and two bag types (balloon and condom) were used in the seepage measurements.There was no significant difference between the seepage measurements obtained from the two bag types. A two‐sample t‐test (df=56, Wt‐sat=2.58, alpha=0.01, p=0.0013) failed to reject the null hypothesis of similarity between measurements from the two bag types. The seepage measurements from four seepage meters were similar with no significant difference; however, the smaller diameter seepage meters had a greater variance.

Field Evaluation of Seepage Meters in the Coastal Marine Environment

The response of seepage meters was evaluated in a nearshore marine environment where water motion effects are more pronounced than in lake settings, where these meters have been used traditionally. Temporal and spatial variations of seepage, as well as potential artifacts, were evaluated using empty and 1000-ml pre-filled bag measurements. Time-series measurements confirmed earlier observations that anomalously high fluxes occur during the early stages (≤10min) of collection. As deployment times increased (30–60min), measured flow rates stabilized at a level thought to represent the actual seepage flux. Pre-filling the plastic measurement bags effectively alleviated this anomalous, short-term influx. Reliable seepage measurements required deployment times sufficient to allow a net volume of at least 150ml into the collection bag. Control experiments, designed by placing seepage meters inside sand-filled plastic swimming pools, served as indicators of external effects on these measurements, i.e. they served as seepage meter blanks. When winds were under 15 knots, little evidence was found that water motion caused artifacts in the seepage measurements. Tidal cycle influences on seepage rates were negligible in the present study area, but long-term temporal variations (weeks to months) proved substantial. Observed long-term changes in groundwater flux into the Gulf of Mexico correlated with water table elevation at a nearby monitoring well.

Seepage measurements from Long Lake, Indiana Dunes National Lakeshore

Long Lake, located near Lake Michigan within the dune-complexes of Indiana Dunes National Lakeshore, USA, was formed some time during the Pleistocene and Holocene epochs. A surficial aquifer underlies Long Lake, which is either a source or sink for the later. The hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural, municipal, and industrial development of the region. Limited data suggest that the organisms of Long Lake have elevated levels of several contaminants. This study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality. Seepage measurements and minipiezometric tests were used to determine seepage within the lake. Seepage measurements and minipiezometric tests suggest that water seeps out of Long Lake, thus recharging the groundwater that flows southwest away from the lake. There is a great deal of variability in the seepage rate, with a mean of 11.5×10-4±11.2×10-4 m d-1. The mean seepage rate of 0.3 m yr-1 for Long Lake is greater than the 0.2 m yr-1 recharge rate estimated for the drainage basin area. The Long Lake recharge volume of 2.5 × 105 m3 yr-1 is approximately 22% of the volume of the lake and is significant when compared to the total surface recharge volume of 4.8 × 105 m3 yr-1 to the upper aquifer of the drainage area. There is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions.