rey th u dynamics in the critical zone combined influence of reactive bedrock accessory minerals authigenic phases and hydrological sorting mule hole watershed south india

formation and preservation of pedogenic carbonates in south india links with paleo monsoon and pedological conditions clues from sr isotopes u th series and rees the influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the western ghats karnataka plateau south west india has been studied along the climosequence the current mean annual rainfall mar varies within a 80 km transect from 6000 mm at the edge of the plateau to 500 mm inland pedogenic carbonates occur in the mar range of 500 1200 mm in the semi arid zone mar 500 900 mm carbonates occur i as rhick hardpan calcretes on pediment slopes and ii as nodular horizons in polygenic black soils i e vertisols in the sub humid zone mar 900 1500 mm pedogenic carbonates are disseminated in the black soil matrices either as loose irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size they also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate cemented lumps of centimetric to decimetric size chemical and isotopic sr 87 sr 86 compositions of the carbonate fraction were determined after leaching with 0 25 n hcl the corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed the trend defined by the sr 87 sr 86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition considering the residual fraction of each sample as the most likely lithogenic source of ca in carbonates it is estimated that from 24 to 82 55 on average of ca is derived from local bedrock weathering leading to a consumption of an equivalent proportion of atmospheric co2 these values indicate that climatic conditions were humid enough to allow silicate weathering mar at the time of carbonate formation likely ranged from 400 to 700 mm which is 2 to 3 fold less than the current mar at these locations the sr u and mg contents and the u 234 u 238 activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation the relatively high concentrations of sr u and mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite possibly due to a better confinement of the pore waters which is supported by their high u 234 u 238 signatures and or to higher content of dissolved carbonates in the pore waters the occurrence of ce mn and fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation the carbonate ages determined by the u th method range from 1 33 0 84 kyr to 7 5 2 7 kyr and to a cluster of five ages around 20 kyr i e the last glacial maximum period the young occurrences are only located in the black soils which therefore constitute sensitive environments for trapping and retaining atmospheric co2 even on short time scales the maximum age of carbonates depends on their location in the climatic gradient from about 20 kyr for centimetric nodules at mule hole mar 1100 mm yr to 200 kyr for the calcrete at gundlupet mar 700 mm yr durand et al 2007 the intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils c 2010 elsevier ltd all rights reserved

annual replenishable ground water potential of india an estimate based on injected tritium studies abstract natural recharge is a vital parameter to be known for ground water budgeting management and modelling percolation of a portion of the rainfall through the vadose zone is the principal source of natural recharge to the aquifer systems in india the tritium injection method based on piston flow model is particularly suitable for quantifying the downward flux of moisture in the vadose zone and for measuring natural recharge in indian climatic condition where about 80 of the annual rainfall is received as pulses and occurs during the four monsoon months from june to september natural recharge measurements using the tritium injection method have been carried out in india during the last 25 years in several basins and watersheds located in varying climatic and hydrogeological situations the mean natural recharge values for 35 study areas well distributed over 17 major river basins are presented the recharge rates range from 24 to 198 mm yr 1 or 4 1 to 19 7 of the local average seasonal rainfall the natural recharge data are grouped into four main hydrogeological provinces namely granitic basaltic sedimentary and alluvial and the regression equations between rainfall and natural recharge are derived for each province these equations enable one to determine the approximate value of natural recharge in any watershed basin from the rainfall data for any year the regression equations are used to compute the total annual replenishment of ground water reserves of the country for an average rainfall year the calculated annual input is about 476 10 9 m 3 yr 1 this can be considered as a minimal quantity as it represents the natural recharge due to precipitation alone and does not account for seepage from ponds lakes stream bed canals and return flow from surface water irrigation

using a structural approach to identify relationships between soil and erosion in a semi humid forested area south india biogeochemical and hydrological cycles are currently studied on a small experimental forested watershed 4 5 km 2 in the semi humid south india this paper presents one of the first data referring to the distribution and dynamics of a widespread red soil ferralsols and chromic luvisols and black soil vertisols and vertic intergrades cover and its possible relationship with the recent development of the erosion process the soil map was established from the observation of isolated soil profiles and toposequences and surveys of soil electromagnetic conductivity em31 geonics ltd lithology and vegetation the distribution of the different parts of the soil cover in relation to each other was used to establish the dynamics and chronological order of formation results indicate that both topography and lithology gneiss and amphibolite have influenced the distribution of the soils at the downslope the following parts of the soil covers were distinguished i red soil system ii black soil system iii bleached horizon at the top of the black soil and iv bleached sandy saprolite at the base of the black soil the red soil is currently transforming into black soil and the transformation front is moving upslope in the bottom part of the slope the chronology appears to be the following black soil bleached horizon at the top of the black soil streambed bleached horizon below the black soil it appears that the development of the drainage network is a recent process which was guided by the presence of thin black soil with a vertic horizon less than 2 in deep three distinctive types of erosional landforms have been identified 1 rotational slips type 1 2 a seepage erosion type 2 at the top of the black soil profile 3 a combination of earthflow and sliding in the non cohesive saprolite of the gneiss occurs at midslope type 3 types 1 and 2 erosion are mainly occurring downslope and are always located at the intersection between the streambed and the red soil black soil contact neutron probe monitoring along an area vulnerable to erosion types 1 and 2 indicates that rotational slips are caused by a temporary watertable at the base of the black soil and within the sandy bleached saprolite which behaves as a plane of weakness the watertable is induced by the ephemeral watercourse erosion type 2 is caused by seepage of a perched watertable which occurs after swelling and closing of the cracks of the vertic clay horizon and within a light textured and bleached horizon at the top of black soil type 3 erosion is not related to the red soil black soil system but is caused by the seasonal seepage of saturated throughflow in the sandy saprolite of the gneiss occurring at midslope c 2006 elsevier b v all rights reserved

the characterization of steady state in earth surface systems findings from the gradient modelling of an indian climosequence abstract gradient modelling of a steep ecocline in south india has highlighted a suite of landscape units which appear to be entirely ordained by a simple water balance index this univariate climofunction is reflected in vegetation landform weathering and soil patterns although the vegetation successions are the most spectacular consistent pedogeomorphological trends were identified at several embedded scales of reality at the microscopic scale the existence of illite rich saprolite situated between the kaolinite dominated and smectite dominated core areas of the climosequence so far a missing mineralogical link only predicted by geochemical theory was effectively verified by field evidence at the megascopic scale the variation in topographic texture from polyconvex to polyconcave land systems via a convexo concave transition zone also suggests a strong relationship between hydroclimatic budgets and landforms such an exceptional environmental cabinet is well suited to reexamining other benchmark climosequences of the tropics and to readdressing the debated theories of climatic geomorphology by a discussion on the applicability of climax and steady state to tropical landforms

water balance modelling in a tropical watershed under deciduous forest mule hole india regolith matric storage buffers the groundwater recharge process accurate estimations of water balance are needed in semi arid and sub humid tropical regions where water resources are scarce compared to water demand evapotranspiration plays a major role in this context and the difficulty to quantify it precisely leads to major uncertainties in the groundwater recharge assessment especially in forested catchments in this paper we propose to assess the importance of deep unsaturated regolith and water uptake by deep tree roots on the groundwater recharge process by using a lumped conceptual model comfort the model is calibrated using a 5 year hydrological monitoring of an experimental watershed under dry deciduous forest in south india mule hole watershed the model was able to simulate the stream discharge as well as the contrasted behaviour of groundwater table along the hillslope water balance simulated for a 32 year climatic time series displayed a large year to year variability with alternance of dry and wet phases with a time period of approximately 14 years on an average input by the rainfall was 1090 mm year 1 and the evapotranspiration was about 900 mm year 1 out of which 100 mm year 1 was uptake from the deep saprolite horizons the stream flow was 100 mm year 1 while the groundwater underflow was 80 mm year 1 the simulation results suggest that i deciduous trees can uptake a significant amount of water from the deep regolith ii this uptake combined with the spatial variability of regolith depth can account for the variable lag time between drainage events and groundwater rise observed for the different piezometers and iii water table response to recharge is buffered due to the long vertical travel time through the deep vadose zone which constitutes a major water reservoir this study stresses the importance of long term observations for the understanding of hydrological processes in tropical forested ecosystems c 2009 elsevier b v all rights reserved

parameter estimation in an anisotropic leaky aquifer system abstract parameter estimation is made for an anisotropic leaky aquifer system in which the direction of principal axes is unknown there is a declining water table in the aquitard the seven governing parameters are the direction of principal axes the degree of anisotropy the equivalent transmissivity and storage coefficient of the aquifer and the leakage coefficient specific storage and specific yield of the unconfined aquitard a modified parameter perturbation technique which is computationally efficient is used for the determination of sensitivity coefficients the parameter estimation procedure is applied to three test problems including one field problem situations where the total number of wells is only three are handled with two pump tests by locating the pump in a different well in each test

elemental weathering fluxes and saprolite production rate in a central african lateritic terrain nsimi south cameroon abstract the comparison between contemporary and long term weathering has been carried out in the small experimental watershed sew of nsimi south cameroon in order to quantify the export fluxes of major and trace elements and the residence time of the lateritic weathering cover we focus on the hillside system composed of a thick lateritic weathering cover topped by a soil layer this study is built on the recent improvements of the hillside hydrological functioning and on the analyses of major and trace elements the mass balance calculation at the weathering horizon scale performed with the parent rock as reference indicates i strong depletion profiles for alkalis na k rb and alkaline earths mg ca sr ba ii moderate depletion profiles for si p cd cu zn ni and co iii depletion enrichment profiles for al ga ge sn pb lree hree y u fe v cr mn it is noteworthy that i mn and ce are not significantly redistributed according to oxidative processes as it is the case for fe v and cr and ii ge is fractionated compared to silica with enrichment in fe rich horizons the calculations performed for the topsoil with iron crust as parent material reference reveal that the degradation of the iron crust is accompanied by the loss of most of the constituting elements among which are those specifically accumulated as the redox sensitive elements fe v cr and iron oxide related elements like th the overall current elemental fluxes from the hillside system at the springs and the seepage zones are extremely low due to the inert lateritic mineralogy ninety four percent of the whole na flux generated from the hillside corrected from atmospheric deposits 77 mol ha yr represents the current weathering rates of plagioclase oligoclase in the system the other remaining 6 may be attributed to the dissolution of hornblende the silica hillside flux is 300 mol ha yr and can be mostly attributed to the plagioclase and kaolinite dissolution al and ga are exported from the lateritic regolith and maybe due to the dissolution of kaolinite crystals compared to the other immobile elements zr hf nb and th ti is significantly exported among redox sensitive elements fe v cr mn ce only ce and mn are exported out of the hillside system the other elements fe v cr are likely able to be mobilized but over a short distance only rb sr ba ni cu zn are affected by export processes lree and y are exported but in very low amounts in the range from mol ha yr to mmol ha yr while hree and u are exported in negligible quantities a first attempt is carried out to compare the mature ridge top profile from nsimi sew with the immature ridge top weathering profile from the mule hole sew south india developed on similar granodioritic basement in order to get deeper insight into i the contemporary saprolite production rates and ii the combined effect of precipitation in terms of mean annual rainfall mar and evapotranspiration on the aggressiveness of the draining solutions considering i the contemporary na flux as representative of the dissolution of plagioclase crystals and conservative during saprolitization processes and ii steady state of the inter annual recharge r over a 10 years period the current saprolite production rates r are of 22 mm kyr for mule hole sew and 2 mm kyr for nsimi sew respectively even with a very low r mar ratio 0 04 compared to nsimi the chemical weathering at mule hole is active and related to the groundwater exports at mule hole plagioclase crystals are still present in the saprolite and the soil cover leading to a diffuse weathering front the high nsimi r mar ratio 0 2 allows the solution to be still aggressive with respect to the plagioclase and other weatherable minerals at the bedrock interface resulting in their complete breakdown in a few centimetres sharp weathering front leading to a mature saprolite for the nsimi sew if we consider i the low contemporary saprolite production rate 2 mm kyr ii the miocene age average 15 myr of the south cameron plateau landscape and ii the limited movement of africa continent since eocene the long term saprolite production rate should have remained in its lower range from 2 to 10 m myr this suggests that for thick weathering profiles the migration of the weathering front into the bedrock occurs at a relatively uniform rate regardless of present day climatic conditions climate variation leading to the alternation of setup of savanna or humid forest will have an effect on physical erosion rather than chemical erosion for such deep weathering profiles

soils and climatic geomorphology on the karnataka plateau peninsular india abstract as a result of extensive field reconnaissance in southern india a geographical traverse across the planation surface of the karnataka uplands which lie in the rainshadow of the western ghats was selected to assess the consequences of a steep rainfall gradient on soil and landform patterns the study of the traverse described in detail reveals a characteristic progression of soil type and wash divide form from the high rainfall to the semi arid end of the continuum and invites a critical reappraisal of classical notions in climatic geomorphology and the soil sciences the assumption that alternations of wet and dry climates are necessary to achieve planation is given special consideration and the often held belief that kaolinite minerals are diagnostic of humid palaeoclimates when found in a semi arid climate is challenged the findings for the indian traverse are set against the better known data for west africa where the rainfall range between the gulf of guinea and the sahel is comparable with that observed in the south western deccan differences outweighing similarities attention is drawn to the possibility that tectonic regime which also controls the degree of landscape stripping is a major key to understanding the climatic geography of soils the tread of planation surfaces and the shape of hillslopes from one region of the tropics to another

multi element geochemical modelling of crust mantle interactions during late archaean crustal growth the closepet granite south india the closepet granite in the dharwar craton of south india is a large late archaean magmatic body its composition can be explained as a result of interactions between mantle derived melts and pre existing continental crust ttg gneisses using geochemical modelling based upon major and trace element compositions the following petrogenetic model is proposed for the formation of the batholith i an enriched mantle garnet and amphibole bearing lherzolite melts to produce a basaltic liquid ii the basaltic liquid undergoes limited fractional crystallization of biotite and amphibole f 0 9 iii the differentiated liquid rises into the old continental crust and induces water saturated anatexis of the ttg gneisses k feldspar qtz plagioclase melt iv both mantle derived and anatectic liquid mix and give rise to magma compositions ranging from quartz monzonite to granite the origin of the mantle enrichment is discussed in the context of the regional geological setting the most likely possibility seems to be metasomatism by slab melts the metasomatism of a mantle wedge by slab melts this suggests a two stage evolution for the dharwar craton during the late archaean i a subduction related event with the formation of ttgs sanukitoids and with associated mantle metasomatism and ii re melting of the metasomatized mantle this evolutionary history implies that at least some of the k rich late archaean granites are juvenile rather than products of intracrustal reworking as frequently assumed

regolith mass balance inferred from combined mineralogical geochemical and geophysical studies mule hole gneissic watershed south india the aim of this study is to propose a method to assess the long term chemical weathering mass balance for a regolith developed on a heterogeneous silicate substratum at the small experimental watershed scale by adopting a combined approach of geophysics geochemistry and mineralogy we initiated in 2003 a study of the steep climatic gradient and associated geomorphologic features of the edge of the rifted continental passive margin of the karnataka plateau peninsular india in the transition sub humid zone of this climatic gradient we have studied the pristine forested small watershed of mule hole 4 3 km2 mainly developed on gneissic substratum mineralogical geochemical and geophysical investigations were carried out i in characteristic red soil profiles and ii in boreholes up to 60 m deep in order to take into account the effect of the weathering mantle roots in addition 12 electrical resistivity tomography profiles ert with an investigation depth of 30 m were generated at the watershed scale to spatially characterize the information gathered in boreholes and soil profiles the location of the ert profiles is based on a previous electromagnetic survey with an investigation depth of about 6 m the soil cover thickness was inferred from the electromagnetic survey combined with a geological pedological survey taking into account the parent rock heterogeneity the degree of weathering of each of the regolith samples has been defined using both the mineralogical composition and the geochemical indices loss on ignition weathering index of parker chemical index of alteration comparing these indices with electrical resistivity logs it has been found that a value of 400 ohm m delineates clearly the parent rocks and the weathered materials then the 12 inverted ert profiles were constrained with this value after verifying the uncertainty due to the inversion procedure synthetic models based on the field data were used for this purpose the estimated average regolith thickness at the watershed scale is 17 2 m including 15 2 m of saprolite and 2 m of soil cover finally using these estimations of the thicknesses the long term mass balance is calculated for the average gneiss derived saprolite and red soil in the saprolite the open system mass transport function indicates that all the major elements except ca are depleted the chlorite and biotite crystals the chief sources for mg 95 fe 84 mn 86 and k 57 biotite only are the first to undergo weathering and the oligoclase crystals are relatively intact within the saprolite with a loss of only 18 the ca accumulation can be attributed to the precipitation of caco3 from the percolating solution due to the current and or the paleoclimatic conditions overall the most important losses occur for si mg and na with 286 106 mol ha 62 of the total mass loss 67 106 mol ha 15 of the total mass loss and 39 106 mol ha 9 of the total mass loss respectively al fe and k account for 7 4 and 3 of the total mass loss respectively in the red soil profiles the open system mass transport functions point out that all major elements except mn are depleted most of the oligoclase crystals have broken down with a loss of 90 the most important losses occur for si na and mg with 55 106 mol ha 47 of the total mass loss 22 106 mol ha 19 of the total mass loss and 16 106 mol ha 14 of the total mass loss respectively ca al k and fe account for 8 6 4 and 2 of the total mass loss respectively overall these findings confirm the immaturity of the saprolite at the watershed scale the soil profiles are more evolved than saprolite but still contain primary minerals that can further undergo weathering and hence consume atmospheric co2

effects of juniper removal and rainfall variation on tree transpiration in a semi arid karst evidence of complex water storage dynamics brush removal is widely practiced as a tool for increasing groundwater recharge but its efficacy depends greatly on the way in which the removed species interact with the hydrological system relative to the vegetation replacing it we examined the effects of ashe juniper removal in the recharge zone of the edwards aquifer texas usa a karst aquifer the study was conducted in an ashe juniper juniperus ashei live oak quercus fusiformis woodland on a hill slope composed of rocky shallow soils over fractured limestone bedrock ashe juniper is a native species that has been encroaching grasslands and savannas over the past century in september 2008 a plot was cleared of 90 of its juniper trees tree transpiration predawn water potentials and vegetation cover across the cleared plot and an adjacent reference site were measured from may 2009 to december 2011 stand level tree transpiration from may 2009 to march 2010 was diminished by a severe summer drought in 2009 from which trees were slow to recover subsequently tree transpiration was 5 10 higher in the woodland compared to the clearing for all of 2011 also a drought year tree transpiration in the woodland exceeded precipitation inputs indicating a high capacity for water storage at the study site however site differences for oak trees were generally larger than for juniper trees while juniper removal accounted for a 431 mm year 1 difference in tree transpiration between sites vegetation cover in the clearing increased from 42 to 90 over two years suggesting that understory growth was increasingly compensating for the loss of juniper transpiration we conclude that the removal of a relatively shallow rooted tree when replaced with herbaceous vegetation and low shrubs has little effect on deep recharge by contrast successive years of precipitation extremes may be more effective increasing recharge by lowering the water transport capacity of trees in the aftermath of severe drought copyright 2016 john wiley sons ltd

dynamic damage model of crevasse opening and application to glacier calving 1 theory and applications of continuum damage mechanics for ice are discussed and on this basis an ice damage model valid at low stresses is proposed the model describes the damage itself the rheology of the damaged ice and the damage evolution a local damaging and healing law is considered and its parameterization is motivated the model parameters are inferred from published data of laboratory experiments the model is subsequently implemented in a finite element code and applied to the prediction of a calving process and to the destabilization of an ice chunk from a hanging glacier numerical results show good agreement with field measurements

characterization of seasonal local recharge using electrical resistivity tomography and magnetic resonance sounding a groundwater recharge process of heterogeneous hard rock aquifer in the moole hole experimental watershed south india is being studied to understand the groundwater flow behaviour significant seasonal variations in groundwater level are observed in boreholes located at the outlet area indicating that the recharge process is probably taking place below intermittent streams in order to localize groundwater recharge zones and to optimize implementation of boreholes a geophysical survey was carried out during and after the 2004 monsoon across the outlet zone magnetic resonance soundings mrs have been performed to characterize the aquifer and measure groundwater level depletion the results of mrs are consistent with the observation in boreholes but it suffers from degraded lateral resolution a better resolution of the regolith bedrock interface is achieved using electrical resistivity tomography ert ert results are confirmed by resistivity logging in the boreholes ert surveys have been carried out twice before and during the monsoon across the stream area the major feature of recharge is revealed below the stream with a decrease by 80 of the calculated resistivity the time lapse ert also shows unexpected variations at a depth of 20 m below the slopes that could have been interpreted as a consequence of a deep seasonal water flow however in this area time lapse ert does not match with borehole data numerical modelling shows that in the presence of a shallow water infiltration an inversion artefact may take place thus limiting the reliability of time lapse ert a combination of ert with mrs provides valuable information on structure and aquifer properties respectively giving a clue for a conceptual model of the recharge process infiltration takes place in the conductive fractured fissured part of the bedrock underlying the stream and clayey material present on both sides slows down its lateral dissipation

a generalized 3 d geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering summary the weathered layers of crystalline rocks form aquifers that are of prime interest for water supply in hard rock areas these weathering profiles generally develop under both stable geodynamic conditions weathering rate erosion rate and a hydrolysing climate they are composed of thick stratiform layers that follow the paleo landscape paleotopography and thus present a gently dipping sequence at a regional scale the structure and the hydrodynamic properties of the weathering profile of a granitic area 53 km 2 maheshwaram catchment state of andhra pradesh india were characterized in detail and mapped from observations on outcrops 80 vertical electric soundings and lithologs from 45 borewells in which flowmeter measurements and injection tests were also performed to characterize the hydraulic conductivities of the conductive fissure zones the structure of the weathering profile results from a multiphase process an ancient weathering profile was partly eroded down to its fissured layer it was later re weathered more or less parallel to the current topographic surface this peculiar structure is linked to the geodynamic history of the indian peninsula that underwent alternate weathering and erosion dominated phases the profile is thus composed from top to bottom up to a total depth of 35 m of sandy regolith saprolite 1 3 m 10 15 m of laminated saprolite containing unusual preserved fissures and a 15 20 m thick fissured layer by comparing various case studies in similar terrain a generalized 3 d geological and hydrogeological conceptual model of granite type aquifers granites gneisses etc is proposed in granite type rocks single weathering or multiphase weathering and erosion processes induce similar geological structures a few main geological differences arise from the comparison of single phase and multiphase weathering profiles i in the later the respective thicknesses of the various layers can be deeply modified ii the ancient fissured layer can be re weathered and the resulting new laminated layer may contain quite well preserved and conductive ancient fissures and iii the upper part of the fissured layer is more densely fissured as a result of the same weathering processes the fissures from the fissured layer of single phase or multi phase profiles exhibit very similar hydraulic conductivities and show both a higher density of conductive fissures at the top of the layer the preserved ancient fissures within the laminated layer of a multiphase profile are partly obliterated by the recent weathering their hydraulic conductivity is thus significantly reduced nevertheless they do significantly contribute to borewell yield these weathering induced fissures provide most of the aquifer permeability the use of such a conceptual model for the precise geological mapping of the weathering structure appears to be a prerequisite for groundwater development and management in hard rock areas as it answers to several key issues

rey th u solute dynamics in the critical zone combined influence of chemical weathering atmospheric deposit leaching and vegetation cycling mule hole watershed south india the source and proportion of rey th and u exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the sub humid tropical forested czo of mule hole southern india the study relies on a pluri annual hydro geochemical monitoring combined with a hydrological model the significant difference between the soil input si and output so solute fluxes mmol km2 yr of lree si so 13250 1500 hree 1930 235 th 64 12 and u 63 25 indicates a strong uptake by roots carried by canopy and forest floor processes the contribution of atmospheric dust leaching can reach about 60 of lree and 80 of hree at the watershed scale the u solute flux exported by groundwater 180 mmol km2 yr mainly originates from the breakdown of primary u bearing accessory minerals and dominates by a factor of 25 the stream flux the precipitation of authigenic u bearing phases and adsorption onto fe oxides and oxyhydroxides plays a significant role for limiting the u mobility in the groundwater the plagioclase chemical weathering is efficiently traced by the positive eu anomaly the very low rey to nil th contents are explained by the precipitation of authigenic phases in the stream flow dominated by the overland flow 87 of the yearly stream flow the solute exports in mmol km2 yr of rey 1080 for lree and 160 for hree and of th 14 dominate those by groundwater their mobility is enhanced by chelation with organic ligands produced by forest floor and canopy processes

combined estimation of specific yield and natural recharge in a semi arid groundwater basin with irrigated agriculture a water budget approach is developed to jointly estimate specific yield and natural recharge in an unconfined aquifer with significant seasonal water table fluctuations water table fluctuations are due to distinct seasonality in groundwater recharge the separation of the hydrologic year into two or more extended seasons of recharge wet season and no recharge dry season with accompanying changes in water table allows for a split use of the water table fluctuation wtf method first to estimate specific yield from the water table drop during the dry season no recharge and second to estimate recharge from the water table rise during the wet season after considering all other water budget components explicitly the latter includes explicit computation of groundwater storage with the wtf method the application of the wtf method requires a large number of water level measurements throughout the unconfined aquifer before and after each season the advantage of the method is that specific yield and recharge are estimated at the scale of interest to basin hydrologic studies and that the method requires no extensive in situ instrumentation network here the method is demonstrated through a case study in a fractured hard rock aquifer subject to intensive groundwater pumping for irrigation purposes

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

regolith thickness inferred from geophysical and geochemical studies in a tropical watershed developed on gneissic basement moole hole western ghâts south india

water percolation through the deep vadose zone and groundwater recharge preliminary results based on a new vadose zone monitoring system 1 a study on water infiltration and groundwater recharge was conducted in the coastal plain israel the study implemented a novel development flexible time domain reflectometry sensors ftdr which enabled the continuous monitoring of water content at selected points through the entire vadose zone data on water content variation with time and depth was collected throughout the rainy season of 2004 2005 at two sites one site was located in a sand dune area with a 21 m thick vadose zone the other was located in an undeveloped urban area with an 8 4 m thick vadose zone the lithology of both sites consisted of unconsolidated sand with silt and clay interbeds the resultant data allowed tracing of the infiltration progress through the entire vadose zone each large rain event initiated an infiltration wave that propagated into the vadose zone and pushed the wetting front farther down the wetting front appeared to progress in a step like pattern controlled by the frequency of large rain events and followed by a slower drainage process clay interbeds did not seem to prevent or significantly delay progress of the wetting front down to the groundwater the apparent wetting front signal reached the groundwater table at 21 m below land surface bls only 3 months after the first significant rain event groundwater recharge was calculated from the variations in vadose zone water storage an increase in vadose zone water storage was attributed to an infiltration event while a reduction in water storage was attributedto a draining process

characterization of groundwater chemistry under the influence of lithologic and anthropogenic factors along a climatic gradient in upper cauvery basin south india hydrogeological and climatic effect on chemical behavior of groundwater along a climatic gradient is studied along a river basin semi arid 500 800 mm of mean annual rainfall sub humid 800 1 200 mm year and humid 1 200 1 500 mm year are the climatic zones chosen along the granito gneissic plains of kabini basin in south india for the present analysis data on groundwater chemistry is initially checked for its quality using nicb ratio 40 of pollution and eliminated for the characterization piper s diagram with mean concentrations indicates the evolution of canahco3 semi arid from cahco3 humid zone along the climatic gradient carbonates dominate other anions and strong acids exceeded weak acids in the region mule hole sew an experimental watershed in sub humid zone is characterized initially using hydrogeochemistry and is observed to be a replica of entire sub humid zone with 25 wells extension of the studies for the entire basin 120 wells showed a chemical gradient along the climatic gradient with sub humid zone bridging semi arid and humid zones ca na molar ratio varies by more than 100 times from semi arid to humid zones semi arid zone is more silicaceous than sub humid while humid zone is more carbonaceous ca cl 14 along the climatic gradient groundwater is undersaturated humid saturated sub humid and slightly supersaturated semi arid with calcite and dolomite concentration depth profiles are in support of the geological stratification i e 18 m of saprolite and 25 m of fracture rock with parent gneiss beneath all the wells are classified into four groups based on groundwater fluctuations and further into deep and shallow based on the depth to groundwater higher the fluctuations larger is its impact on groundwater chemistry actual seasonal patterns are identified using recharge discharge concept based on rainfall intensity instead of traditional monsoon non monsoon concept non pumped wells have low na cl and ca cl ratios in recharge period than in discharge period dilution few other wells which are subjected to pumping still exhibit dilution chemistry though water level fluctuations are high due to annual recharge other wells which do not receive sufficient rainfall and are constantly pumped showed high concentrations in recharge period rather than in discharge period anti dilution in summary recharge discharge concept demarcates the pumped wells from natural deep wells thus characterizing the basin

comparison of surface and groundwater balance approaches in the evaluation of managed aquifer recharge structures case of a percolation tank in a crystalline aquifer in india summary to face the problem of groundwater depletion the indian government relies on large projects of managed aquifer recharge mar numerous recharge structures such as percolation tanks exist but the impact of these structures on groundwater resources remains poorly understood although the evaporation infiltration ratio of percolation tanks was determined in several studies in semi arid contexts using surface water balance methods few studies evaluated the impact on the aquifer recharge however knowledge on recharge dynamics over time and space is essential for 1 the quantitative evaluation of stored water volumes 2 the identification of beneficiaries farmers and 3 the estimation of percolation tanks recharge zone to the extent that is required to define proper management regulations at basin scale these three points are of prime importance in the case of semi arid regions where a limited number of rain events determine the water stored over the entire year assessment of the stored groundwater is even more difficult in crystalline aquifers due to the heterogeneous structure of flow paths to date no methodological guidelines exist for local assessment of percolation tanks in crystalline aquifers in this paper we develop a method for calculating a local groundwater budget and we compare it with a computed surface balance the method is applied to a case study in semi arid crystalline context from the groundwater balance we draw conclusions on 1 the limited amount of stored water in the aquifer 2 the delayed recharge of the aquifer highlighting temporary storage slow groundwater movement in the unsaturated zone and 3 the limited number of beneficiaries in years of medium monsoon rainfall these results complement the understanding of the hydrodynamic functioning of percolation tanks and their impact on the local groundwater balance

use of hydraulic tests at different scales to characterize fracture network properties in the weathered fractured layer of a hard rock aquifer the hydrodynamic properties of the weathered fractured layer of a hard rock pilot watershed in a granitic terrain are characterized using hydraulic tests at different scales the interpretation of numerous slug tests leads to characterize the statistical distribution of local permeabilities in the wells the application of flowmeter profiles during injection tests determines the vertical distribution of conductive fracture zones and their permeabilities it appears that the extension of the most conductive part of the weathered fractured layer is limited down to 35 meters depth the partition of drainage porosity between blocks 90 and fractures 10 is determined thanks to the interpretation of pumping tests using a double porosity model the application of anisotropic and single fracture analytical solutions on pumping test data allows to determine respectively the degree of anisotropy of permeability and the radius 4 to 16 meters of the horizontal conductive fractures crossed by the wells two different scales of fractures networks are identified the primary fracture network pfn which affects the matrix on a decimeter scale by contributing to an increase in the permeability and storage capacity of the blocks and the secondary fracture network sfn which affects the blocks at the borehole scale sfn is composed of two sets of fractures the main set of horizontal fractures is responsible for the sub horizontal permeability of the weathered fractured layer a second set of less permeable sub vertical fractures insures the connectivity of the aquifer at the borehole scale the good connectivity of fractures networks is shown by fractional dimension flow solutions the absence of scale effect in the study area suggests that the hydraulic conductivity at the borehole scale is laterally homogeneous finally the analysis and synthesis of the hydrodynamic properties allow to propose a comprehensive hydrodynamic model of the fractured weathered layer many geological and hydrogeological indicators suggest that a continuous and laterally homogeneous weathering process is responsible for the origin of the fractures and permeability encountered in the aquifer these results confirm the major role played by weathering in the origin of fractures and on resulting hydrodynamic parameters in the shallow part of hard rock aquifers