debris fan constrictions and flood hydraulics in river canyons some implications from two dimensional flow modelling rapids in river canyons are frequently found at sites where debris fans constrict flow along the channel whereas some fans may have persisted in the same location with unchanging geometry for centuries to millennia others have changed in response to flow conditions imposed by successive floods such a change in boundary conditions may alter local flow hydraulics this paper utilizes two dimensional flow modelling to compare flood hydraulics along two alternative versions of an idealized reach of a river canyon one with uniform width gradient and cross section and a second perturbed by a prominent debris fan along the valley wall the flow pattern along the reach with the fan is far more complex than the pattern along the uniform reach maximum velocity along the debris fan reach is up to 50 per cent higher than along the uniform reach maximum bed shear stress is up to three or four times higher and an area of supercritical flow is predicted extending from the nose of the fan into the zone of flow expansion immediately downstream comparison of model output along longitudinal profiles of the two reaches indicates that the backwater effect of the fan extends several valley widths upstream predicted flows based on the same stage are as much as 190 to 230 per cent greater along the uniform reach than along the debris fan reach reconstruction of palaeoflood discharge based on remnant flood marks in the vicinity of the fan would be sensitive to assumptions about boundary conditions that existed in the past this effect relaxes over a longitudinal distance of several hundred metres furthermore there are significant cross stream gradients that change slope and direction several times in the vicinity of the fan calling into question the utility of one dimensional step backwater hydraulic models for predicting high water marks in areas of complex valley morphology

the fate of sediment wood and organic carbon eroded during an extreme flood colorado front range usa identifying and quantifying the dominant processes of erosion and tracking the fate of sediment wood and carbon eroded during floods is important for understanding channel response to floods downstream sediment and carbon loading and the influence of extreme events on landscapes and the terrestrial carbon cycle we quantify sediment wood and organic carbon oc from source to local sink following an extreme flood in the tectonically quiescent semi arid colorado usa front range erosion of 500 000 m3 or as much as 115 yr of weathering products occurred through landsliding and channel erosion during september 2013 flooding more than half of the eroded sediment was deposited at the inlet and delta of a water supply reservoir resulting in the equivalent of 100 yr of reservoir sedimentation and 2 loss in water storage capacity the flood discharged 28 mg c km2 producing an event oc flux equivalent to humid tectonically active areas post flood remobilization resulted in a further 100 yr of reservoir sedimentation plus export of an additional 1 3 mg c km2 of wood demonstrating the ongoing impact of the flood on reservoir capacity and carbon cycling pronounced channel widening during the flood created accommodation space for 40 of flood sediment and storage of wood and eroded carbon we conclude that confined channels normally dismissed as transport reaches can store and export substantial amounts of flood constituents

isotope geochemistry of fluid inclusions in permian halite with implications for the isotopic history of ocean water and the origin of saline formation waters abstract d and 18o values have been determined for fluid inclusions in 45 samples of permian halite the inclusions are enriched in 18o relative to the meteoric water line but are depleted in d relative to ocean water inclusions with the more positive values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a d 18o diagram inclusions with more negative values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines the isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that permian sea water was isotopically similar to modern sea water connate evaporite brines can have negative values because of the probable hooked isotope trajectory of evaporating sea water and or synsedimentary mixing of evaporite brines with meteoric waters subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested

geomorphological understanding of floods abstract the summer 1993 flooding of the upper mississippi river valley reminds us that floods are the most globally pervasive environmentally diverse and continually destructive of all natural hazards the fact that flood damages continue to rise raises commonsense questions about conventional flood science like much modern environmental science conventional flood science has followed the model of theoretical physics it advanced from early emphasis on streamflow measurement to the use of simple formulae and finally to the abstract theoretical sophistication of modern modeling studies two approaches are now used to predict flood phenomena 1 beginning with the conventional database of measured properties of small common floods a conceptual generalization is made to the idealized properties of the large rare floods from which society is assumed to be at risk and 2 explanation of detailed specific flood phenomena is achieved through theoretical generalization models based on first principles which are assumed to apply to the entire class of phenomena unfortunately both approaches devote almost all their attention to methodology increasingly mathematical without questioning basic underlying assumptions increasingly it is the assumptions often unstated that serve to embody the understanding of floods as real world particular phenomena rather than as conceptual generalities such trends lead to an unease that it is not floods that are being researched by much of conventional flood science rather such flood science is increasingly becoming the mathematical manipulation of idealized parameters that are assumed to have flood like properties these idealizations of flood attributes are generalized and the resulting predicted consequences are imposed upon society through engineering designs flood hazard zonations and the like geomorphological understanding of floods derives a from along geological tradition of studying indices of real processes operating in the past in contrast to the conceptual theoretical treatment of floods as classes or generalizations geomorphologists study particular floods revealed as a natural experience that is recorded in the sediments landforms and erosional scars of past floods the strength of this approach is in its affinity to the commonsense perceptional basis that underpins human action geomorphological flood studies including recent advances in paleoflood hydrology are needed as a complement to conventional hydrological approaches the resulting complementarity will allow the predictions of the conventional approach to be grounded in the concrete particulars of experience without such grounding flood science risks continuing as an empty quest for universal ideals while humanity paralyzed by inaction continues to suffer from the reality of particular floods

a 1300 year reconstruction of paleofloods using oxbow lake sediments in temperate southwestern quebec canada the study of paleofloods provides important information on past flood frequency and intensity for regions where there is a paucity of records it therefore extends our knowledge of flood occurrence

comment on reinterpretation of 36cl data physical processes hydraulic interconnections and age estimates in groundwater systems by e mazor abstract mazor 1992 has reinterpreted several previous 36 cl studies the studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36 cl measurements major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry the studies then used simple geochemical models to account for cl behavior in the subsurface the result of these 36 cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies mazor 1992 has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified discontinuities in the flow regime the conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36 cl interpretations but also from the findings of virtually all previous hydrogeological and geochemical investigations although mazor s reinterpretations are provocative he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow until this is satisfactorily accomplished i will continue to prefer the original 36 cl interpretations

origin and mixing history of brines palo duro basin texas u s a formation waters in the palo duro basin texas u s a fall into four major groups based on integrated chemical and isotopic characteristics 1 interbed brines within the major permian evaporite aquitard these are the most chemically concentrated and18o rich fluids in the basin and are interpreted as evaporatively concentrated sea water which has been hydrologically isolated since the permian 2 brines below the salt on the eastern side of the basin have clbr divalent cation and isotopic systematics indicating a mixture of evaporatively concentrated sea water and meteoric water of d 20 3 brines below the salt on the western side of the basin have chemical and isotopic systematics suggesting a mixture of two pulses of meteoric water one with d 20 and the other with d 55 and 4 waters above the salt have the isotopic composition of meteoric waters diagenetic alteration of the cation chemistry has occurred for brines within and below the salt aquifers below the salt on the eastern side are interpreted as having been charged with dense permian evaporite brines which subsequently mixed in various amounts with a basin wide pulse of triassic meteoric water on the western side the descending triassic meteoric waters became saline by dissolution of halite and are currently mixing with a tertiary pulse of meteoric water initiated by the laramide uplift to the west the hydrochemistry suggests flow on the western side of the basin and static conditions on the eastern side an unrecognized approximately n s permeability restriction or discontinuity in the potentiometric flow surface is inferred for major aquifers in the central area of the basin

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

accuracy of post bomb 137cs and 14c in dating fluvial deposits abstract the accuracy and precision of 137cs and 14c for dating post 1950 alluvial deposits were evaluated for deposits from known floods on two rivers in arizona the presence of 137cs reliably indicates that deposition occurred after intensive above ground nuclear testing was initiated around 1950 there was a positive correlation between the measured level of 137cs activity and the clay content of the sediments although 137cs was detected even in sandy flood sediments with low clay content 137cs is a valuable dating tool in arid environments where organic materials for 14c or tree ring dating are scarce and observational records are limited the 14c activity measured in different types of fine organic detritus yielded dates within 1 to 8 yr of a 1980 flood deposit and the accuracy was species dependent however undifferentiated mixtures of fine organic materials from several post bomb deposits of various ages repeatedly yielded dates between 1958 and 1962 and detrital charcoal yielded a date range of 1676 1939 in semiarid environments the residence time of most types of organic debris precludes accurate annual resolution of post bomb 14c dates

paleohydrology of southwestern texas current statistical methods may be unable to accurately predict recurrence intervals of rare large magnitude floods especially in semiarid regions having positively skewed annual flood distributions great hydrologic variability and widely spaced gaging stations current approaches rely on historical data but catastrophic floods may have recurrence intervals far greater than the length of historical records in the lower pecos and devils rivers of southwestern texas paleoflood discharge and frequency estimates are extended over 10 000 years by the study of slack water flood sediments slack water deposits are typically fine grained sand and silt that accumulate during floods in areas where current velocity is reduced i e in back flooded tributary mouths channel expansions downstream from bedrock spurs and or slump blocks and in shallow caves along bedrock walls radiocarbon dating of organic detritus in slack water deposits establishes the flood chronology while paleoflood discharges can be estimated by slope area techniques paleoflood information extracted from slack water sediments can greatly extend flood records these floods may be weighted like historical data in log pearson type 3 calculations of flood frequency our morphostratigraphic approach combines recorded data with geomorphic evidence to derive estimates of flood frequency this technique offers an inexpensive and rapid way to assess catastrophic flood risk

potential salinity driven free convection in a shale rich sedimentary basin example from the gulf of mexico basin in south texas we investigate the plausibility of salinity driven free thermohaline convection in sedimentary rocks of the south texas part of the gulf of mexico basin using salinity data rayleigh number calculations and numerical models previous studies speculated that free convection could account for high fluxes evidently required for diagenesis in the basin but low permeability shales are calculated to be a barrier to free convection in the study area salinity inversions occur either above or within the transition zone from hydropressures to overpressures the positioning of brines over less saline fluids provides a significant buoyancy force rayleigh number calculations and numerical simulations suggest that homogeneous shaly systems are unstable near the high end of the expected ranges of shale permeability 10 15 10 16 m2 numerical simulations show that the influx of brine into the permeable layers and permeability heterogeneity in the shales are both conducive to free convection simulations indicate that salinity driven free convection can occur at lower permeabilities 10 16 10 18 m2 that may approximate the permeabilities of shales in the zone of extreme overpressures over geologic time simple rayleigh numbers are inadequate to predict the occurrence of free convection in heterogeneous systems salinity driven free convection at depths in some large sedimentary basins such as the gulf of mexico may be more common than expected

a 2000 year natural record of magnitudes and frequencies for the largest upper colorado river floods near moab utah using well established procedures for paleoflood hydrology and employing optically stimulated luminescence osl geochronology we analyzed a very well preserved natural record of 44 upper colorado river extreme floods with discharges ranging from 1800 to 9200 m3s 1 these are the largest floods occurring during the last 2140 220 years and this natural record indicates that large floods are much more frequent than can be estimated by extrapolation from the stream gaging record that extends back to 1914 most of these large floods occurred during the last 500 years and the two largest floods in the record both exceeded the probable maximum flood pmf estimated at 8500 m3s 1 300 000 cfs for nearby moab utah another four floods with discharges greater than 7000 m3s 1 occurred during the last two millennia flood frequency analyses using the fldfrq3 model yields the following values depending on the manning n roughness coefficients 100 yr flood 4670 4990 m3s 1 500 yr flood 6675 7270 m3s 1 1000 yr flood 7680 8440 m3s 1 the presumed pmf discharge 8500 m3s 1 gets assigned a recurrence interval of about 1000 years and the largest historical 1884 flood 3540 m3s 1 a recurrence interval of 100 years flood frequency analysis for the moab valley based on the gaged record 1914 2012 yield 2730 m3s 1 for the 100 yr flood and 3185 m3s 1 for the 500 yr flood this underestimation of the frequency of large floods from the gage data results from effects on that record by modern regulation of upstream river flow and associated water extraction for agriculture

groundwater and microbial processes of alabama coastal plain aquifers 1 we integrate groundwater geochemistry microbiology and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of alabama our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface sequential peaks of ca2 mg2 k and na along flow paths indicate that separation of ions may be driven by cation exchange microbial mediated reactions are important for the formation of several discrete hydrochemical zones containing fe2 mn2 sr2 and so42 rich groundwaters elevated fe2 mn2 and sr2 concentrations may be derived from bacterial iron and manganese reduction high sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction denitrification the presence of denitrifying and sulfur oxidizing bacteria in water further supports these reactions major ion compositions and d and 18o values are used to determine the source of salinity and the nature of mixing of different groundwaters three water types were identified these include carbonate groundwater brines associated with evaporites and groundwater of meteoric origin groundwater age differences and flow velocities were calculated using the 36cl cl ratios calculated groundwater flow velocities within the eutaw and tuscaloosa aquifers are about 0 20 m yr and 0 15 m yr respectively we modeled basin scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the gulf coast the modeling result shows that the buried jurassic louann salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density driven advection and hydrodynamic dispersion the modeling results are consistent with cl br ratios and o h isotope signatures which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation the predicted groundwater flow pattern reveals the mixing of meteoric water carbonate groundwater from the ordovician knox group and saline brines associated with the louann salt the hydrologic model is consistent with the hydrochemical facies distribution in the alabama coastal plain

geochemistry and isotope chemistry of michigan basin brines devonian formations detailed chemical and isotope analysis of 87 formation waters collected from six devonian aged units in the michigan basin are presented and discussed in terms of the origin of the dissolved components and the water total dissolved solids in these waters range from 200 000 to 400 000mg 1 upper devonian formations produce dominantly nacacl brine while deeper formations produce canacl water ratios of cl br and na br along with divalent cation content mcl2 indicate that these brines are derived from evapo concentrated seawater other ion concentrations appear to be extensively modified from seawater values by water rock reactions the most important reactions are dolomitization which explains the ca content of the brines and reactions involving aluminosilicate minerals stable isotope 18o and d compositions indicate that water molecules in the deeper formations are derived from primary concentrated seawater isotope enrichment by exchange with carbonates and perhaps gypsum cannot be discounted isotope values indicate water in the upper devonian formations is a mixture of seawater brine diluted with meteoric derived water dilution has predominantly occurred in basin margins two scenarios are presented for the origin of the brines in the devonian formations 1 they originated when the devonian sediments and evaporites were first deposited or 2 they are residual brine liberated from the deeper devonian and possibly silurian salt deposits

aspect dependent soil saturation and insight into debris flow initiation during extreme rainfall in the colorado front range hydrologic processes during extreme rainfall events are poorly characterized because of the rarity of measurements improved understanding of hydrologic controls on natural hazards is needed because of the potential for substantial risk during extreme precipitation events we present field measurements of the degree of soil saturation and estimates of available soil water storage during the september 2013 colorado extreme rainfall event at burned wildfire in 2010 and unburned hillslopes with north and south facing slope aspects soil saturation was more strongly correlated with slope aspect than with recent fire history south facing hillslopes became fully saturated while north facing hillslopes did not our results suggest multiple explanations for why aspect dependent hydrologic controls favor saturation development on south facing slopes causing reductions in effective stress and triggering of slope failures during extreme rainfall aspect dependent hydrologic behavior may result from 1 a larger gravel and stone fraction and hence lower soil water storage capacity on south facing slopes and 2 lower weathered bedrock permeability on south facing slopes because of lower tree density and associated deep roots penetrating bedrock as well as less intense weathering inhibiting soil drainage

relationships among oils and water compositions in niger delta in some fields of the tertiary niger delta of nigeria heavy asphaltic oil is found in shallow reservoirs and light waxy oil is found in deeper reservoirs in the same field both oils appear to have had the same source the change with depth from heavy to light oil is usually abrupt and occurs at a reservoir temperature between 150 and 180 f 66 and 82 c in other areas similar degradation of oil has been ascribed to bacteria brought into the oil reservoir by invading meteoric water in nigeria meteoric water is low in dissolved solids and high in bicarbonate whereas connate water is saltier and contains more chloride samples of both types of oil and associated water from six fields were analyzed and compared with previously acquired analyses f om these fields no clear relationship between meteoric water and degraded oil was found degraded oil may occur with either meteoric or connate water and undegraded oil is sometimes found with meteoric water this suggests extensive secondary migration of oil from one structure to another as well as deep penetration of meteoric water

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

radiocarbon and stable isotopes in water and dissolved constituents milk river aquifer alberta canada abstract origin and age of groundwater in the milk river aquifer alberta canada was the focal point of the present study to answer related questions wells in this aquifer were sampled and 2 h and 18 o in water 13 c and 2 h in methane 34 s and 18 o in so 4 13 c and 14 c in dissolved inorganic carbon dic and dissolved organic carbon doc and tritium contents determined stable isotope analyses on ground water permitted the recognition of at least three different zones within the aquifer starting at the recharge zone modern type groundwaters are encountered for the first few kilometers these are followed by groundwater with slightly higher 18 o and 2 h contents i e waters which do not show a glacial signature and were probably recharged under warmer climatic conditions groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift they show the gradual admixture of far more saline formation waters from the alberta basin sulphate s and sulphate o isotope values indicate a till source for the so 4 however so 4 in wells close to the area where so 4 virtually disappears show isotopic values which suggest that so 4 reduction is occurring although other studies could not find bacterial populations of so 4 reducers methane is present in most wells and based on c and h isotope data has a biogenic origin methane production occurs close to some wells and or it diffuses from the confining shales into the aquifer radiocarbon is measurable only in the first 20 km from the recharge zone however transformation of measured concentrations to water ages is very difficult because of the complexity of the geochemical system comparison with 14 c data on doc was therefore very interesting and this new technique may complement the dic radiocarbon dating two wells near the recharge zone yielded dic doc high molecular weight hmw and doc low molecular weight lmw results the dic dates were much older than doc dates but the differenve in years between the wells for all three types of c were within 1000 a of each other the doc dates led to the conclusion that the initial dic radiocarbon content was as low as 30 modern when the water entered the aquifer the age of the water 20 km from the recharge zone was assessed at 20 000 a resulting in a velocity of 1 m a this result is much higher than estimates by other techniques

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

palaeoflood hydrology of the salt river arizona geomorphic evidence along bedrock confined reaches of the salt river in east central arizona provides a record of the river s largest flood events fine grained flood slackwater deposits accumulated at channel margin irregularities several metres above the low flow channel discharges associated with flow events responsible for the deposits were estimated by computer flow modelling these estimates document flood magnitudes in excess of gauged historic streamflows relative and radiocarbon dating suggest that a flood record in excess of 600 y is preserved in the slackwater sequences a prominent flood scar cut into grussy hillslope soils allows the extension of the prehistoric flood record to several thousand years a maximum discharge estimate of 4600 m3s 1 affixed to the flood scar represents the largest flood event in the record and is given a minimum recurrence interval of 1000 2000 y the 1952 flood is the largest historic flow event experienced along the study reach and is estimated at 2900 m3s 1 two palaeoflood events preserved in the slackwater stratigraphy exceed the 1952 event and are given recurrence intervals of 300 and 600 y the latter flood event had an estimated discharge of 3200 m3s 1 it is apparent that discharge estimates affixed to these infrequent large magnitude flood events approach a maximum with decreased probabilities large recurrence intervals this suggests that a physical limit on discharge may exist within the salt river drainage basin and is perhaps directly related to drainage basin size

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

geochemistry and hydrodynamics of deep basin brines palo duro basin texas u s a abstract permeable strata of the deep basin brine aquifer system underlie bedded permian evaporites in the palo duro basin texas panhandle formation water samples collected from four u s department f of energy test wells and two independent oil and gas company wells in the basin were analyzed for chemical and isotopic compositions to characterize the geochemical environment and to determine the origin and compositional evolution of the water formation waters are na cl brines that contain 140 to 290 g l total dissolved solids tds chemical and isotopic compositions suggest grouping the brine samples into one of two types samples from western palo duro basin have high cl br ratios sr isotopic ratios that are significantly more radiogenic than permian seawater or precipitates from permian seawater and oxygen isotopic compositions that are depleted with respect to values predicted for equilibrium with calcite under in situ conditions samples from central and eastern palo duro basin have low cl br ratios sr isotopic ratios only slightly radiogenic relative to permian marine sr and oxygen isotopic compositions that suggest equilibration with calcite the concentrations of major and minor ions appear to be controlled by equilibrium with calcite dolomite anhydrite celestite low albite microcline and na smectite high na activities drive ion exchange reactions which coupled with maintenance of chemical equilibrium elevate the concentrations of divalent cations and lower the concentrations of dissolved so 4 and carbonate the origin and evolution of deep basin brines are interpreted from chemical and isotopic compositions integrated with results of previous geological and hydrogeological investigations brines from western palo duro basin acquired salinity by dissolving halite along a lateral flow path from the recharge zone radiogenic sr was derived from detrital silicate minerals and oxygen isotopic equilibrium with aquifer minerals has not been attained brines from central and eastern palo duro basin originated as either recharge that achieved chemical and isotopic equilibrium with the host rock during long residence times or as permian seawater concentrated by evaporation regional chemical and isotopic variations augment the results of hydrogeological modeling brines in the western part of the basin flow from the west and southwest where siliciclastic sedimentary rocks predominate brines in the central and eastern parts of the basin flow from the south and southwest where carbonate strata predominate

geochemistry of tectonically expelled fluids from the northern coast ranges rumsey hills california usa tectonic compression has created abnormally high pressure on deep basinal fluids causing their expulsion from areally exposed upper cretaceous rock along the eastern margin of the california coast ranges the fluids emerge as near neutral perennial sodium chloride springs at high elevations with flow rates as high as 10 l per min higher spring discharges are more common around the exposure of a west vergent fault propagation fold axis spring waters range from 1000 to 27 000 mg l tds the least saline water 18o 7 5 closely represents local meteoric water that mixes with saline fluid 18o 5 3 and forms a slope of 3 5 on a d vs 18o plot a na 125 to 8000 mg l vs cl 150 to 17 000 mg l plot shows a linear dilution trend that extends close to but below the values for modern seawater calcium 75 3000 mg l is considerably enriched relative to seawater and forms a nonlinear trend with chloride in detail the na deficit defined by the difference between the measured na content and the na concentration on a hypothetical seawater dilution line is approximately balanced by the ca excess similarly defined by the seawater dilution line this relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths simultaneous b and 18o enrichment of the fluids accompanied by deuterium depletion further suggest that the seawater modification is influenced by clay diagenesis bicarbonate and sio2 concentrations show an inverse correlation with cl with most waters being saturated or slightly oversaturated with calcite and quartz at the discharge temperatures some freshwater springs with near meteoric stable isotope values may represent mixing of young groundwater from perched aquifers but in many cases the freshwater springs emerge along the same structures and have the same perennial nature as the saline fluids and expulsion of an older fresh groundwater component that is under abnormal fluid pressures cannot be ruled out basinal fluids elsewhere commonly show dilution trends with local meteoric water and in the case of the rumsey hills some of the dilute saline waters may indicate deep penetration of meteoric water 1 km in the pleistocene before the latest tectonic uplift geothermometry of the spring waters maximum 90 c suggest an origin from as deep as 4 0 km this depth is consistent with the depth of the core of a fault propagation anticline below the surface of the rumsey hills developed by active internal deformation of an east tapering wedge beneath the southwestern sacramento valley active tectonic compression causes near lithostatic fluid pressures in the shallow subsurface below the rumsey hills and volume strain within the core of the anticline that results in upward expulsion of the saline fluids from the indicated depths

radiocarbon dating of flood events katherine gorge northern territory australia radiocarbon analyses of organic materials provide accurate dating of flood events in the katherine gorge northern territory australia selected flood events in the period 1955 1980 can be very precisely dated essentially to the calendar year through the use of curves showing the time variation of anomalously high 14 c activity in the troposphere that was generated by nuclear testing conventional radiocarbon analysis of alluvial charcoal and organic litter is used to establish dates for the largest katherine river floods of the past several centuries the improved geochronologic techniques demonstrated here will help improve paleoflood hydrologic interpretations

holocene climatic events recorded in palaeoflood slackwater deposits along the middle yiluohe river valley middle yellow river basin china abstract palaeohydrological investigations were carried out in the middle reaches of the yiluohe river a major tributary in the lower middle yellow river basin typical palaeoflood slackwater deposits swds were identified in the holocene pedostratigraphy on the cliffy river banks analytical results including magnetic susceptibility and grain size distribution data indicated that these swds were deposited from the suspended sediment load in flood water these swds are different from eolian loess soils and aeolian sands in the riverbank profile they recorded several episodes of extraordinary palaeoflood events in the longmenxia reaches of the yihe river valley these flood events were dated at 3100 3000 a 1800 1700 a 770 610 a and 420 340 a using the optically stimulated luminescence method in combination with the pedostratigraphic correlations in the longhutan reaches of the luohe river valley the palaeoflood events were dated at 1975 1466 a i e from the han to wei dynasties ad 25 534 during which the capital city on the river banks was flooded many times as recorded in the literature these extraordinary flood events are well correlated chronologically with the known holocene climatic events that occurred in the northern hemisphere thus the monsoonal climate was highly variable with both floods and droughts occurring frequently during these episodes these results are important for understanding the response of river systems in eastern asia to global changes

the influence of vegetation on debris flow initiation during extreme rainfall in the northern colorado front range we explored regional influences on debris flow initiation throughout the colorado front range colorado usa by exploiting a unique data set of more than 1100 debris flows that initiated during a 5 day rainstorm in 2013 using geospatial data we examined the influence of rain hillslope angle hillslope aspect and vegetation density on debris flow initiation in particular we used a greenness index to differentiate areas of high tree density from grass and bare soil the data demonstrated an overwhelming propensity for debris flow initiation on south facing hillslopes however when the debris flow density was analyzed with respect to total rainfall and greenness we found that most debris flows occurred in areas of high rainfall and low tree density regardless of hillslope aspect these results indicate that present day tree density exerts a stronger influence on debris flow initiation locations than aspect driven variations in soil and bedrock properties that developed over longer time scales

minerological and o isotope studies of diagenesis and porewater evolution in continental sandstones cretaceous belly river group alberta canada abstract the mineralogy and o isotope geochemistry of diagenetic phases from continental sandstones of the upper cretaceous belly river group west central and south western alberta have been determined diagenesis of the continental sandstones is dominated by crystallization of clay minerals including fe rich chlorite 18 o 3 3 to 9 3 i s c s and illite 18 o 9 5 to 10 7 kaolinite 18 o 5 9 to 12 7 s i and smectite 18 o 11 0 to 14 0 other diagenetic phases include quartz overgrowths 18 o 12 0 to 21 0 and calcite 18 o 8 5 to 12 9 13 c x02212 14 3 to 2 0 chlorite generally crystallized first in the paragenetic sequence followed by quartz i s calcite and kaolinite and then s i and smectite interpretation of these data suggests that early diagenesis occurred in the presence of low 18 o meteoric water whose 18 o value rose moderately during subsequent burial highest burial temperatures 110 c were probably achieved in the south western portion of the study area and are reflected by the appearance of r1 ordered i s in this locality post laramide influx of meteoric water subsequently resulted in a substantially lower porewater 18 o value values of 18 o for diagenetic minerals from the continental sandstones and immediately underlying deltaic and shoreline basal sandstones are systematically lower by 1 to 6 than equivalent phases from the lower cretaceous marine sandstones of the viking formation relative differences in the oxygen isotopic compositions of connate waters freshwater vs sea water have been preserved surviving 18 o enrichment during burial and 18 o depletion during post laramide influx of meteoric water while substantial meteoric dilution of the porewater has occurred flushing of evolved connate waters has not been complete

a preliminary assessment of the regional dispersivity of selected basalt flows at the hanford site washington u s a abstract dispersivity is one of the hydraulic parameters that controls the distribution in groundwater of chemical constituents migrating from a source region therefore knowledge of the range of dispersivity values along likely flow paths from proposed high level nuclear waste repositories is important for assessing how well a site will perform in limiting releases of radionuclides to the environment a primary reason why dispersivity has not been analyzed with regional scale data is the general lack of suitable environmental tracers that have been in the hydrologic environment for long periods of time such tracers could normally result from some natural event perhaps disruptive that may have transpired in the geologic past such an event may have occurred at the u s department of energy hanford site in the state of washington resulting in a chemical enclave of regional proportions a preliminary interpretation is that the enclave occurs immediately down gradient from a hydraulic barrier possibly a fault which may have placed deeper formations in hydraulic connection with the upper basalts with this hypothesized source for constituents making up the enclave the observed concentrations are employed in a preliminary attempt to assess the regional dispersivity this is the single conceptual model being tested in this paper the mathematical method employed assumes that the concentration data conform to what would be expected of a perfectly symmetrical enclave and part of the problem deals with identifying that symmetry the results obtained are quite reasonable when compared to the range in dispersivities determined in laboratory tracer and model scale studies

holocene paleofloods related to climatic events in the upper reaches of the hanjiang river valley middle yangtze river basin china abstract holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world paleoflood hydrological investigations were carried out in the upper reaches of the hanjiang river china four bedsets of paleoflood slackwater deposits were found interbedded in the holocene loess soil sequence within the cliff riverbanks they were studied by field observations and laboratory analysis including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these provide a complete catalog of holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change four episodes of holocene overbank flooding have been recorded over the basin these hydroclimatic events were dated to 8500 8400 4200 4000 3200 2800 and 1800 1700 ybp by using the osl method in combination with pedostratigraphic correlations with the previously studied holocene pedostratigraphy in the hanjiang river basin the peak discharges of these flood episodes vary in a range from 26 610 to 47 900 m 3 s 1 as estimated by using the slope area method of streamflow measurement these flood events are therefore considered a regional expression of known climatic events and demonstrate holocene climatic instability the study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world

role of salinity derived variable density flow in the displacement of brine from a shallow regionally extensive aquifer portions of many regional scale aquifers in midcontinent sedimentary basins exhibit large salinity gradients that significantly impact the velocity field and solute distribution through time a two dimensional numerical transport model was constructed to examine the role of salinity derived variable density flow on changes in the velocity field and solute distributions in a near surface regionally extensive aquifer as brine is displaced by infiltrating meteoric water the silurian devonian carbonate aquifer in the western portion of the appalachian basin was used as a framework to insure that realistic flow velocities and salinities were used in the assessment the variable density effects on brine displacement are observed by examining the differences in the velocity fields and solute distributions produced by uniform density and variable density simulations the effects include the change from an intraformational displacement pattern to a cross formational displacement pattern with the development of flow reversals and partitioning of regional flow cells into smaller flow cells variable density effects also are manifest in the solute distributions by slowing the displacement of brine and influencing the magnitude of the salinity gradient a sensitivity analysis used to examine the influence of flow and transport parameters on the transient development and migration of salinity gradients shows that increasing cross formational leakage into the regional aquifer causes flow velocities to decrease which magnifies the influence of the variable density behavior by slowing the displacement of brine the sensitivity analysis also shows that increasing the value of dispersivity causes an increase in the variable density effects however the effects of variable density flow are relatively insensitive to changes in values of horizontal and vertical anisotropy assigned to the aquifer or to the presence of an overlying transmissive layer

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

paleoflood evidence for a natural upper bound to flood magnitudes in the colorado river basin the existence of an upper limit to the magnitude of floods in a region is a long standing and controversial hypothesis in flood hydrology regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation wolman and costa 1984 however the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit in the colorado river basin there are 32 120 station years of gage data but the average period at a gaging station is only 20 years with most stations having less than 70 years of observation paleoflood magnitudes derived from sediments of large prehistoric floods from 25 sites on rivers in arizona and utah provide additional data to extend the records of the largest floods the paleoflood data identify the maximum flood discharges that have occurred on individual rivers over the last several hundred to several thousand years even with this increase in the observational period the largest paleoflood discharges do not exceed the upper bound of maximum peak discharges delineated by the envelope curve derived from the available gaged and historical records this result accords with the hypothesis of an upper physical limit for flood magnitudes and suggests that for the colorado river basin the upper limit can be approximated by existing systematic and historical data for large floods similar relationships also hold when paleofloods and gaged records are presented for the subregion of southern arizona

brines in the carboniferous sydney coalfield atlantic canada abstract formation waters within upper carboniferous sandstones in the sub sea prince and phalen coal mines nova scotia originated as residual evaporative fluids probably during the precipitation of windsor group lower carboniferous salts which underlie the coal measures salinity varies from 7800 to 176 000 mg l and the waters are na ca cl brines enriched in ca sr and br and depleted in na k mg and so4 relative to the seawater evaporation curve br cl and na cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30 the brines lie close to the meteoric line on h o isotopic plots but with a compositional range of 18o from 4 18 to 6 99 and of d from 42 4 to 23 5 distant from modern meteoric or ocean water mine water composition contrasts with that of nearby salt spring brines which are inferred to have originated through dissolution of windsor group evaporites by modern meteoric waters however a contribution to the mine waters from halite dissolution and from br in organic matter cannot be ruled out present concentrations of several elements in the brines can be explained by water rock interaction the original windsor brines probably moved up into the overlying coal measure sandstones along faults prior to the late triassic the high salinity and irregular salinity distribution in the phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile in contrast prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters basinal brines from which these modern formation fluids were derived may have been important agents in base metal and ba mineralisation from the mid carboniferous onwards as saline fluid inclusions are common in zn pb sulphide deposits in the region

exploring weathering and regolith transport controls on critical zone development with models and natural experiments the architecture of the critical zone including mobile regolith thickness and depth to the weathering front is first order controlled by advance of a weathering front at depth and transport of sediment at the surface differences in conditions imposed by slope aspect in the gordon gulch catchment of the boulder creek critical zone observatory present a natural experiment to explore these interactions the weathering front is deeper and saprolite more decayed on north facing than on south facing slopes simple numerical models of weathering front advance mobile regolith production and regolith transport are used to test how weathering and erosion rates interact in the evolution of weathered profiles as the processes which attempt are being made to mimic are directly tied to climate variables such as mean annual temperature the role of quaternary climate variation in governing the evolution of critical zone architecture can be explored with greater confidence

geochemistry of hco 3 na thermal water from the gudian slope insights into fluid origin formation mechanism and circulation in the yitong basin northeast china abstract the goal of this paper is to systematically analyze the geochemical and isotopic characteristics 18o d t 13chco3 and doc of a hco3 na thermal water to determine its origin formation mechanism and circulation pattern in the gudian slope yitong basin northeast china schoeller diagrams and isotope data indicate that this thermal water is not connected to groundwater or river water and that its recharge source is immature water with low 18o and d values that originates from the changbaishan area this result was also confirmed by its doc 13c value approximately 24 which indicates that the c originates from c3 plants the analysis of na k mg diagrams indicates that the thermal waters except for one sample sjxk are fully equilibrated this observation combined with the results of the analysis for 18o d t and cation geothermometry data for the thermal water indicates that no water underwent mixing with cold water before arriving at the surface instead high temperature immature water flowed up from a deep reservoir and mixed with old formation water approximately 35 4 in the eocene reservoir these data indicate the occurrence of an interesting phenomenon in which the thermal water samples of the gd area exhibit a regression line with a negative slope and similar 18o values potentially due to the fractionation of co2 gas and a buffer of high hco3 concentrations rather than their short circulation times the high so4 cl b cl f cl and hco3 cl ratios and 13chco3 values ranging from 0 84 to 1 24 of these samples imply that magmatic volatiles have been dissolved in the thermal water however we cannot ignore the contributions of 13c from the leaching of limestone with a13c value of approximately 3 4 which is further supported by the br cl and hco3 cl ratios thus we analyzed the geological background and data collected from well chang 27 and deduced that a limestone stratum exists below the study area magmatic volatiles flow up through the lithospheric faults along the northwestern and southeastern edges of the basin encounter changbaishan area recharge water in the limestone reservoir form hot water with high concentrations of hco3 and then recharged into the eocene sandstone reservoir long term mineral hydrolysis and transformation reactions in the reservoir cause the concentrations of na to increase and lead to the formation of hco3 na water

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

assessment of dam failure flood and a natural high magnitude flood in a hyperarid region using paleoflood hydrology nahal ashalim catchment dead sea israel 1 a dam failure flood in 1993 with a peak discharge of 600 700 m3 s 1 volume of 0 5 106 m3 and a natural rainfall runoff flood with a peak discharge of 420 m3s 1 volume of 2 0 106 m3 in 2004 in the nahal ashalim catchment 75 km2 in the hyperarid dead sea region were comparatively analyzed the two floods which caused serious damage to the dead sea works industries were analyzed for magnitude and frequency using regional analysis extrapolation from the short systematic record rainfall runoff modeling and paleoflood hydrology the 7600 year paleoflood record was reconstructed at the ashalim cave at the upper nahal ashalim peak discharges in this high gradient mountainous wadi are highly sensitive to the roughness coefficient and the flow regime the dam failure peak discharge is lower than the envelope curves of measured floods of the dead sea region and of paleofloods of the negev and the dead sea deserts the probability of the dam failure flood and the natural flood were estimated by various methods at 1 to 0 2 and 0 5 respectively adding the peak discharge of the october 2004 flood increased the probability from 0 2 to 0 5 0 2 the long paleoflood record encompasses different hydrological regimes related to climatic fluctuations which are not relevant to the present hydrological regime therefore the chosen period for frequency analysis was a d 1673 1996

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

frequency of boulders transport during large floods in hyperarid areas using paleoflood analysis an example from the negev desert israel abstract direct measurements of boulder entrainment in desert wadis are not available the 2004 flood peak discharge 470 m3 s 1 recurrence interval 120 years in the hyperarid ungauged nahal hatzera ephemeral stream 45 km2 transported and deposited 0 85 2 1 m concrete boulders and slabs detached from infrastructure upstream and natural boulders edm and drone air photographic surveys documented the geometry of the study reach and the location of boulders analyses of flood slackwater deposits established a paleoflood record of 23 floods with peak discharges of 200 760 m3 s 1 during the last 600 years 1 d hec ras hydraulic analysis provided water surface profiles discharges and hydraulics along the study reach and velocity shear stress and stream power for each boulder max program and pearson 3 distribution were used for flood frequency analysis most of the concrete boulders were deposited in the sub critical backwater of channel constrictions where velocities were 1 5 2 1 m s 1 the largest boulders were deposited in super critical flow where velocity was 8 9 2 m s 1 the alluvial channel enabled to transport these concrete boulders reflecting the unstable active sandy layer of the channel bed over which the boulders moved the maximum flood shear stress and stream power characterize medium large floods with return period of 20 120 years and not for the largest floods as expected boulders about 2 1 m and weighing about 15 t can be transported at least once in 120 years the shear stress and stream power indicate that the moderate large floods are the most geomorphically effective floods rather than the largest floods in nahal hatzera basin nevertheless the geomorphic effectiveness of the 2004 flood a typical desert flash flood with high peak and short duration was small based on the minor changes along the channel and banks indicating that their resistance thresholds were not exceeded and energy expenditure was mainly on boulders entrainment and transport

an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada the milk river artesian aquifer underlies 15 000 km2 of southern alberta canada it consists of thin 30 75 m thick sandstone and is confined above by the pakowki shale typically 120 m thick and below by the colorado shale the aquifer subcrops in southern alberta and northern montana groundwater movement is to the north west and east from the outcrop area dominant recharge area cl and i concentrations increase in the direction of flow from less than 0 05 and 0 001 mmol l respectively near the recharge area to more than 140 and 0 15 mmol l at the northern edge of the aquifer similarly waters become more enriched in oxygen 18 and deuterium from less than 21 0 and 167 near the recharge area to values approaching 8 0 and 70 0 in the north isotope values in the recharge area plot on the global meteoric water line and indicate that the recharge waters are isotopically unaltered meteoric waters downgradient from the recharge area the data deviate from the meteoric water line slope of 6 3 instead of 8 0 three mechanisms have been advanced to explain the origin of the chemical and isotopic patterns the introduction of connate formation water through the colorado shale and subsequent mixing with infiltrating meteoric water a finite source of meteoric recharge mixing with more saline water in the aquifer and chemical and isotopic enrichment due to ion filtration hydraulic conductivity and hydraulic head data cl concentrations of drill cuttings and isotopic values from groundwater from the colorado shale provide arguments for reevaluating these ideas an alternative mechanism based on diffusion between saline isotopically enriched water in the colorado shale and fresher isotopically depleted water in the aquifer is tested using an analytical mass transport model although uncertainty exists in the model parameters results showed that the patterns in cl i 18o and 2h in the aquifer can be explained by aquitard diffusion further aquitard diffusion must be considered when using chlorine 36 dating methods in aquifer aquitard systems such as the milk river aquifer

caesium 137 dating applied to slackwater flood deposits of the llobregat river ne spain abstract during a palaeoflood study of the llobregat river ne spain analysis of 137cs was carried out on slackwater flood deposits to obtain an improved flood chronology for the most recent flood sediments at the monistrol study reach 137cs was measured in flood deposits preserved in valley side rock alcoves with a range of 137cs concentrations of 2 80 10 06 mbq g measured the 137cs was associated with sediment mobilised from the upstream catchment by erosion and transported to the alcoves during floods the onset of measured caesium activity in the sedimentary profiles permitted the deposits to be divided between those from floods that occurred before the mid 1950s and those from events after this period combining the information derived from the slackwater flood stratigraphy the minimum discharge estimates associated with the flood deposits 137cs analysis and the instrumental peak discharge series it was possible to identify the particular flood events responsible for the majority of the slackwater flood units at vilomara however 137cs activity was measured in palaeoflood deposits dated to the late bronze age and located at an elevation not reached by the floodwaters of the largest modern events the data from this site indicated that the 137cs was not associated with sediments transported by floods but was rainfall derived the rainwater reaching the deposits through fissures in the rock to ensure the successful application of caesium dating to slackwater flood deposits preserved within rock alcoves or caves some general guidelines are proposed the technique is best applied 1 when there is a sedimentary profile of greater than 1 m depth 2 when the profile is sampled away from zones affected by direct percolation or springwater entering the alcove and 3 where there are various levels of contrasting textures within the profile

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

uranium series radionuclides in fluids and solids milk river aquifer alberta canada abstract samples from 21 wells completed in the milk river aquifer were sampled and analysed for u isotopes in general u concentrations decrease with distance from the recharge area groundwater samples can be delineated into a small oxic group u content 101t 5 mmol 1 and a more predominant anoxic group u content of 10 7 mmol 1 all groundwater samples were undersaturated with respect to the common u minerals such as uraninite coffinite and rutherfordine the dominant u complexes were uranyl carbonates the234u 238u activity ratios increased from 2 to 11 with distance downflow of the outcrop the highest activity ratio of 11 8 was measured at a well defined redox front whereupon a steady decrease downdip to 4 was observed this decrease was interpreted to be due to the decay of234u excess with age of the groundwater and due to u loss by sorption precipitation processes from solution to solid surfaces two u isotope dating models were used to estimate the age of the groundwater in the milk river aquifer model 1 is a simple model of downdip decay of234u excess in solution under steady state conditions model 2 is a phenomenological model for the evolution of u isotope groundwater composition downdip based on a transport dispersion equation incorporating radioactive decay and assuming that sorption processes are of first order kinetics both models were applied to the u isotope data collected along the same flow path in the aquifer they yielded flowrates of 0 1 0 2 m a and 0 2 0 6 m a respectively the latter range is in good agreement with flowrates of 0 3 m a obtained from hydraulic considerations the lower value derived from model 1 is interpreted in terms of u migration velocity rather than as groundwater flowrate model 2 was also applied to an additional flowpath the calculated flowrate range of 0 1 0 4 m a is in excellent agreement with the hydraulic model flowrate of 0 2 m a the main conclusion of this work is that u isotopes can be used for dating very old groundwaters provided the local hydrogeology and u geochemistry are understood well

exhumation by debris flows in the 2013 colorado front range storm the relative importance of extreme events in the long term exhumation of landscapes is difficult to determine the degree to which modern records capture long term mean process rates is therefore commonly unknown in september 2013 a massive precipitation event in the front range of colorado usa triggered over 1100 landslides and debris flows in a historically sedate landscape here we employ topographic differencing utilizing repeat aerial lidar to quantify net sediment transport volumes in 120 of these mass movements within an area of 102 km 2 west of boulder colorado comparing our results against published long term erosion rates we find that these mass movements evacuated the equivalent of hundreds to thousands of years of hillslope weathering products we conclude that 1 rare debris flows perform the majority of sediment transport and channel erosion within steep channels along the eastern edge of the front range potentially explaining discrepancies between modern sediment yields and long term erosion rates in such settings and 2 the high spatial density of debris flows along the corridors bounding steep canyons suggests that the landscape switches to debris flow dominance as knickpoints pass headward along the canyons

a long term flood discharge record derived from slackwater flood deposits of the llobregat river ne spain abstract slackwater palaeoflood deposits were identified along two bedrock gorge study reaches of the llobregat river at pont de vilomara and monistrol de montserrat the compiled palaeoflood record consists of two principal flood series a a relatively complete record of low to high magnitude flood events from the last ca 100 years and b evidence of the largest palaeoflood events that have occurred over the last ca 2700 years the longer term extreme palaeoflood record indicates that the discharge of the 1971 flood the largest on record was exceeded on at least eight occasions with two periods of high magnitude flooding identified a the late bronze age 2500 2700 years ago and b the little ice age ad 1500 1700 at pont de vilomara palaeodischarge estimates of 3700 4300 m 3 s compare to a discharge of 2300 m 3 s for the 1971 event downstream at monistrol an estimate of 4680 m 3 s for flood deposits dated as ad 1516 1642 and believed to be those of the ad 1617 flood compared to 2500 m 3 s for the 1971 flood

paleohydrology of variable density ground water flow systems in mature sedimentary basins example of the palo duro basin texas usa abstract the paleohydrology of mature sedimentary basins undergoing uplift and tilting deposition and erosion is studied by numerically modeling the flow of variable density ground water in regional flow systems consisting of both shallow freshwater aquifers and deep saline aquifers complex ground water flow patterns can exist when buoyancy forces dominate the hydraulic head gradients arising from topographic relief the relative magnitude of the two driving forces hydraulic gradient and buoyancy changes during the hydrodynamic development of a sedimentary basin that is undergoing topographic changes the relationship between the two driving forces and their effect on flow and transport is studied through coupled flow and solute transport simulations using an idealized model scenario modeling shows that increases in recharge rates can rapidly change hydrodynamic conditions from buoyancy dominated flow governed by variable density to gravity driven flow governed by topography because the dissolved mass responds much slower to changes in hydrologic boundary condition than does fluid pressure transient conditions occur whereby the solute distribution may not correspond to the simulated ground water flow pattern hydrodynamic scenarios were examined in the palo duro basin texas where observed fluid densities range between 1000 and 1150 kg m 3 the palo duro basin was affected by cenozoic uplift deposition and erosion causing modifications in topography and major changes in regional hydrodynamics during the last 15 myear although fluid pressures have largely equilibrated with topographic changes in the recent geologic past the distribution of dissolved mass evolves over a much longer time and the observed solute distribution in the basin as suggested by the geochemistry of the deep basin brines may represent some past state of the hydrodynamic system paleohydrologic simulations describe buoyancy dominated flow phenomena in the recent geologic past when the topographic relief across the basin was much lower than it is today prior to maximum basin uplift simulated flow patterns in the deep aquifers are characterized by convection cells in the western part of the basin where fluid densities increase with depth convection cells show clockwise fluid motion restricting recharge of shallow ground water to the upper part of the deep aquifers in the eastern part of the basin where fluid densities decrease with depth convection cells are characterized by counterclockwise fluid motion and reflect thermohaline convection with enhanced recharge due to continued basin uplift and subsequent erosional events buoyancy dominated flow phenomena diminish and the gravity driven flow component arising from topographic relief becomes dominant this study demonstrates that although present ground water flow circulation in the basin is not affected by the observed fluid densities the flow pattern history during cenozoic basin development is much more complex than that which would be expected from a gravity driven flow conceptualization assuming uniform fluid densities more important the model scenarios describe the interrelationship between geologic processes regional hydrodynamics and transport phenomena and its importance in explaining hydrologic and geochemical phenomena in sedimentary basins

bedrock erosion by root fracture and tree throw a coupled biogeomorphic model to explore the humped soil production function and the persistence of hillslope soils 1 in 1877 g k gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker subsequent analyses of this humped functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil to explore this issue we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw the coupled biogeomorphic model combines data on conifer population dynamics rootwad volumes tree throw frequency and soil creep from the pacific northwest usa although not hardwired into the model a humped relationship emerges between bedrock erosion and soil thickness the magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized hillslope soils do not exhibit runaway thinning or thickening the pit and mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope thus although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches local areas of thick soils remain these soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production model results also suggest that where tree throw is a dominant weathering process the initial mantling of bedrock is not only a vertical process but also a lateral process soil mounds created by tree throw flatten over time spreading soil over bedrock surfaces

the palaeoflood record of a hyperarid catchment nahal zin negev desert israel the palaeohydrology of nahal zin a 1400 km2 catchment in the hyperarid negev desert is inferred from slackwater deposits and palaeostage indicators in a canyon near its lower end the palaeoflood record augmented by the instrumental and historical records of the last decade includes 28 floods ranging from 200 to 1500 m3s 1 over the last 2000 years this helps to reanalyse the frequency of floods in this drainage system the clusters of floods around 1000 years bp and again during the last 60 years are characterized by high flow magnitudes periods with many floods correspond well to periods with high dead sea levels and are probably relatively wet periods while periods with few floods correspond well to low dead sea levels indicating a drier climate fluctuations in the frequency of floods are typical of periods of transition from one climate regime to another copyright 2000 john wiley sons ltd

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

flash flood hydrology in karstic terrain flumineddu canyon central east sardinia abstract in the last five winters 2004 2008 several exceptional meteorological events producing flash floods have been registered in central east sardinia the first of these december 2004 was the most severe and caused important geomorphic changes in the riu flumineddu watershed where the influence of human activity is limited the hydrological characterisation of this flood is extremely difficult because of the lack of streamflow gauges and the relative paucity of meteorological stations in the region peak discharge of the fluviokarstic riu flumineddu canyon has been estimated based on a distributed hydrological model topkapi and on empirical methods based on geomorphic and sedimentological observations the comparison between the results derived from these independent methods allows us to obtain the best possible estimate of peak discharge differences between modelled and measured peak flows can be attributed to water losses and or gains along the river channel from interactions with the underground karst drainage network the december 2004 flood with an estimated recurrence interval of at least 65 years generated overbank flow and destroyed several bridges in upstream reaches caused important changes in channel morphology and sediment distribution and was able to move boulders up to 1 m in diameter in downstream reaches

response of extreme floods in the southwestern united states to climatic variations in the late holocene a regional synthesis of paleoflood chronologies on rivers in arizona and southern utah reveals that the largest floods over the last 5000 years cluster into distinct time periods that are related to regional and global climatic fluctuations the flood chronologies were constructed using fine grained slackwater deposits that accumulate in protected areas along the margins of bedrock canyons and selectively preserve evidence of the largest events high magnitude floods were frequent on rivers throughout the region from 5000 to 360014c yrs bp dendrocalibrated age 3800 2200 bc and increased again after 2200 bp 400 bc with particularly prominent peaks in magnitude and frequency around 1100 900 bp ad 900 1100 and after 500 yrs bp ad 1400 in contrast the periods 3600 2200 bp 2200 400 bc and 800 600 yrs bp 1200 1400 ad are marked by sharp decreases in the occurrence of large floods on these rivers in the modern record storms that generate large floods 10 year in the region fall into three categories 1 winter north pacific frontal storms 2 late summer and fall storms that draw in moisture from recurved pacific tropical cyclones and 3 summer storms mainly convective thunderstorms winter storms and tropical cyclones are associated with the most severe floods on the rivers in this study and are the most probable causes of the paleofloods over the last 5000 years floods from both winter storms and tropical cyclones occur when deep mid latitude troughs steer storm systems into the region composite anomaly maps of daily 700 mbar heights indicate that these floods are associated with a low pressure anomaly off the california coast and a high pressure anomaly over the aleutians or gulf of alaska a strong connection exists between the negative phase of the southern oscillation index often associated with el nin o conditions and the large floods associated with winter storms and tropical cyclones the paleoflood records confirm the existence of centennial scale variations in the conditions conducive to the occurrence of extreme floods and flood generating storms in this region the episodes with an increased frequency of high magnitude floods coincide with periods of cool wet climate in the western u s whereas warm intervals such as the medieval warm period are times of dramatic decreases in the number of large floods a positive relationship between the paleofloods and long term variations in the frequency of el nin o events is evident over the last 1000 years this relationship continues over at least the last 3000 years with warm coastal sea surface temperatures indicative of el nin o like conditions

the variability of root cohesion as an influence on shallow landslide susceptibility in the oregon coast range decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes forests however have variations in vegetation species and age which can dominate the local stability of landslide initiation sites to assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in february and november of 1996 in the oregon coast range and hand dug soil pits on stable ground at 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength species depth orientation relative health and the density of roots 1 mm in diameter within a measured soil area we found that median lateral root cohesion ranges from 6 8 23 2 kpa in industrial forests with significant understory and deciduous vegetation to 25 6 94 3 kpa in natural forests dominated by coniferous vegetation lateral root cohesion in clearcuts is uniformly 10 kpa some 100 year old industrial forests have s

paleofloods and a dam failure flood on the virgin river utah and arizona abstract flood deposits on the virgin river in southern utah and northern arizona preserve a record of the magnitude and frequency of the largest natural floods that have occurred on the river since ad 900 in the virgin river gorge several of the natural paleoflood discharges were comparable with or even greater than the flood from a catastrophic dam failure in 1989 that produced an estimated peak discharge of 1730 m3 s 1 in this reach of the virgin river to estimate the paleoflood discharges the heights of slackwater flood deposits in the lower bedrock gorge of the virgin river were compared with water surface elevations calculated with the hec 2 step backwater hydraulic model the timing of the paleofloods was determined by the ages of layers rich in human artifacts that are interbedded with the flood deposits the estimates of both the 1989 flood and the paleofloods were carried out in the virgin river gorge about 60 km downstream of the dam break site no natural floods of this magnitude have occurred within the relatively short period of the gaged record this study illustrates how incorporating rare extreme events from the long term paleoflood record improves the database for flood frequency analysis the 1989 flood serves as an analog to the effects of rare natural floods with similar magnitudes along the lower virgin river

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

spatial variability of small basin paleoflood magnitudes for a southeastern arizona mountain range paleohydrological procedures were used to analyze spatial variations in flood magnitude in drainage basins of the santa catalina mountains maximum elevation 2791 m southeastern arizona paleoflood reconstructions in eight watersheds ranging from 10 to 110 km2 were obtained for the largest floods in stable canyon reaches yielding discharges ranging from 50 to 270 m3 s 1 although there is a high correlation between drainage area and flood magnitude it is also clear that basins located in the southern half of the santa catalina mountains have larger unit discharges peak discharge divided by drainage area and that these values decrease toward the northern part of the range this spatial pattern is probably the result of local hydroclimatological conditions whereby the largest floods are associated with the northward influx of moist tropical and subtropical air for this atmospheric circulation the northern part of the range experiences a rain shadow effect that decreases the unit discharges generated in those basins the unusually high unit discharge for one of the south facing basins is explained by its basin morphometry inverse problem solutions using a rainfall runoff model demonstrate that both this basin and another with a comparable drainage area but a much lower estimated peak paleoflood discharge can have their peak flood outputs produced by the same storm intensity the results demonstrate the potential of paleoflood data collection for understanding spatial variability in small basin flood hydrology

paleoflood hydrology on the lower green river upper colorado river basin usa an example of a naturalist approach to flood risk analysis abstract through a comprehensive paleoflood hydrological investigation we document natural evidence for at least 27 high magnitude paleofloods at six sites on the lower green river utah hydraulic analysis using the sedimentation and river hydraulic 2d model srh 2d shows that the responsible peak paleoflood discharges ranged between 500 and 7500 m3 s at least 14 of these paleoflood discharge peaks exceed a level twice that of the maximum systematic record of gauged flows 1929 m3 s geochronological analyses employing optically stimulated luminescence osl and radiocarbon dating techniques demonstrate that these 14 largest paleoflood peaks occurred during the past 700 years integration of the paleoflood data into flood frequency analyses ffa reveals considerably higher values for the upper tails of the flood distribution than does a ffa based solely on the systematic gauged record indicating that extreme floods are larger and more frequent than implied by the relatively short gauged record through examination of three approaches to extreme flood estimation conventional ffa probable maximum flood estimation pmf and paleoflood hydrology pfh we show the significance of the natural evidence for advancing scientific understanding of extreme floods that naturally occur in the colorado river system we argue that this kind of scientific understanding is absolutely essential for achieving a credible evaluation of extreme flood risk in a watershed of immense importance to economic prosperity of the southwestern u s

a high magnitude storm and flood in a hyperarid catchment nahal zin negev desert israel in october 1991 a high magnitude rainstorm flood estimated return period 40 years occurred in nahal zin a 1400 km2 catchment in the hyperarid negev desert the meso scale structure of the storm was a curved squall line that developed from a thunderstorm in accordance with the topography of the catchment divide by which it was strongly affected tropical moisture reached the area via the subtropical jet stream in conjunction with a lower level northward intrusion of the red sea trough rst n into the mediterranean sea rainfall as measured at the few and sparse gauging stations was much too small to account for the resulting large flood peak flow and other hydraulic characteristics of the flood were indirectly reconstructed the techniques of palaeoflood hydrology used were based on sedimentological evidence of fine grained flood sediments deposited in back flooded tributaries as well as on other stage indicators the hec 2 procedure was employed to determine water surface profiles the spatial and temporal characteristics of the event were studied through a combination of rainstorm analysis remote sensing hydrological and sedimentological data they jointly explain the magnitude and timing of tributary contributions producing the integrated flood in the main channel the flood as reconstructed reveals a three peak hydrograph two peaks were generated by the same storm but had different floodwave arrival times in the main channel the third resulted from a local rainstorm which occurred on the following day and covered only one tributary the curved structure of the storm and its dynamics in relation to catchment orientation resulted in storm move ment in tandem with the floodwave the synchronous contribution from all main tributaries preserved evidence of the floodwave both in stage and volume by replacing the transmission losses in the sections with thick alluvium other high magnitude floods on record for the large negev desert catchments are caused by a cold upper air incursion associated with the rst n most of them occur in the autumn and are caused by storms with high intensity rainfall this is in stark contrast with the flooding behaviour of the semi arid zone further north which is linked primarily to the core of the mediterranean winter the complexities involved in the generation of a large desert flood as revealed by this study illustrate the fallacy of applying routine hydrological modelling to such events and underline the need to study the processes involved in adequate detail 1998 john wiley sons ltd

integrating soils and geomorphology in mountains an example from the front range of colorado soil distribution in high mountains reflects the impact of several soil forming factors soil geomorphologists use key pedological properties to estimate ages of quaternary deposits of various depositional environments estimate long term stability and instability of landscapes and make inferences on past climatic change once the influence of the soil forming factors is known soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected the front range of colorado rises from the plains of the colorado piedmont at about 1700 m past a widespread dissected tertiary erosion surface between 2300 and 2800 m up to an alpine continental divide at 3600 to over 4000 m pleistocene valley glaciers reached the western edge of the erosion surface parent rocks are broadly uniform granitic and gneissic climate varies from 46 cm mean annual precipitation map and 11 jc mean annual temperature mat in the plains to 102 cm and 4 jc respectively near the range crest vegetation follows climate with grassland in the plains forest in the mountains and tundra above 3450 m soils reflect the bioclimatic transect from plains to divide a bw or bt bk or k grassland to a e bw or bt c forest to a bw c tundra corresponding soil ph values decrease from 8 to less than 5 with increasing elevation the pedogenic clay minerals dominant in each major vegetation zone are smectite grassland vermiculite forest and 1 0 1 8 nm mixed layer clays tundra within the lower forested zone the topographic factor aspect results in more leached colder soils with relatively thin o horizons well expressed e horizons and bt horizons alfisols on n facing slopes whereas soils with thicker a horizons less developed or no e horizons and bw or bt horizons mollisols are more common on s facing slopes the topographic factor in the tundra results in soil patterns as a consequence of wind redistributed snow and the amount of time it lingers on the landscape an important parent material factor is airborne dust which results in fine grained surface horizons and if infiltrated contributes to clay accumulation in some bt horizons the time factor is evaluated by soil chronosequence studies of quaternary deposits in tundra upper forest and plains grassland few soils in the study area are 10 000 years old in the tundra 100 000 years old in the forest and 2 million years old in the grassland stages of granite weathering vary with distance from the continental divide and the best developed is grus near the sedimentary granitic rock contact just west of the mountain front grus takes a minimum of 100 000 years to form

salinization of groundwater in the north german basin results from conjoint investigation of major trace element and multi isotope distribution conjoint consideration of distribution of major rare earth elements ree and y combined to rey and of h o c s sr isotopes reveals that four types of groundwater are distinguishable by their chemical composition presented by spider patterns rey patterns indicate thermo saline deep water and two types of shallow saline groundwaters presence of connate waters is not detectable sr isotope ratios distinguish three sources of sr fast and slow weathering of biotite and k feldspar in pleistocene sediments respectively and dissolution of limestones 13c dic indicate dissolution of limestone under closed and open system conditions numerous samples show 13c dic 13 which is probably caused by incongruent dissolution of calcite and dolomite the brines from below 1 000 m represent mixtures of pre pleistocene seawater or its evaporation brines and infiltrated post pleistocene precipitation the shallow waters represent mixtures of pleistocene and recent precipitation salinized by dissolution of evaporites or by mixing with ascending brines the distribution of water types is independent on geologic units and lithologies even the tertiary rupelian aquiclude does not prevent salinization of the upper aquifer

post fire hillslope debris flows evidence of a distinct erosion process abstract after wildfire a hitherto unexplained erosion process that some authors have called miniature debris flows on hillslopes and that leave behind levee lined rills has been observed in some regions of the world despite the unusual proposition of debris flow on planar hillslopes the process has not received much attention the objectives of this study were to 1 accumulate observational evidence of hillslope debris flows hdf as we have defined the process to 2 understand their initiation process by conducting runoff experiments on hillslopes to 3 propose a conceptual model of hdf and to 4 contrast and classify hdf relative to other erosion and transport processes in the post wildfire hillslope domain hdf have been observed at relatively steep slope gradients 0 4 0 8 on a variety of geologies and after fire of at least moderate severity and consist of a lobe of gravel to cobble sized material 0 2 1 m wide that is pushed by runoff damming up behind it during initiation runoff moved individual particles that accumulated a small distance downslope until the accumulation of grains failed and formed the granular lobe of the hdf hdf are a threshold process and runoff rates of 0 5 l s 1 2 l s 1 were required for their initiation during the experiments the conceptual model highlights hdf as a geomorphic process distinct from channel debris flows because they occur on planar unconfined hillslopes rather than confined channels hdf can erode very coarse non cohesive surface soil which distinguishes them from rill erosion that have suspended and bedload transport on a matrix of slope and grain size hdf are enveloped between purely gravity driven dry ravel and mostly runoff driven bedload transport in rills

flood related channel change in an arid region river a review of 112 years of change in the channel of the salt river central arizona u s a shows that this arid region river has a main flow channel that has migrated laterally up to 1 6 km 1 mi in response to floor events maps showing locational probabilities indicate that along the channel zones of relative locational stability alternate with zones of relative instability at a 3 2 km 2 mi interval construction of upstream reservoirs has reduced sediment input into the main river but has not controlled floods the channel width has not changed except for moderate fluctuations around mean values the main flow channel has incised approximately 6 m 20 ft over most of the 48 km 30 mi study reach during six recent floods gradient has remained unchanged during floods bed material was mobilized to a depth below the original bed level that was greater than the height of the water surface above the original bed calculations based on tractive force indicate a threshold discharge of instability that is equal to the flow with a five year return interval the river exhibits remarkable stability with respect to gradient and sinuosity irrespective of water and sediment discharges but horizontal channel location exhibited selective instability over the record period of more than a century the channel appears not to have been in equilibrium considering geometry discharge and sediment

paleohydrology of pool and riffle pattern development boulder creek utah the low flow channel morphology of boulder creek is characterized by a well developed pool and riffle pattern the riffles consist of accumulations of basaltic boulders deposited from upstream source areas during extremely large flows paleoflood water surface profiles defined by high water indicators such as slack water sediments and silt lines indicate that discharges of up to 400 50 m 3 s have affected the lower reaches of this bedrock stream system stratigraphic relationships and archaeologic and radiometric age constraints indicate that at least four large magnitude low frequency flow events have occurred within the past 500 to 1 000 radiocarbon years b p step backwater hydraulic reconstructions of these large flows suggest that the positions of the boulder comprised riffles are controlled by spatial variations in large flow stream power boulder deposition occurs where channel stream power drops below critical power thresholds necessary for boulder transport high discharge stream power minima occur in reaches immediately upstream of canyon bends and constrictions and downstream of canyon expansions the low flow riffles occur at these sites comparison of calculated stream power values and measured boulder sizes with established coarse particle transport relationships indicates that a 400 m 3 s flow is approximately the minimum discharge competent to affect this pool and riffle pattern

elucidating the role of vegetation in the initiation of rainfall induced shallow landslides insights from an extreme rainfall event in the colorado front range more than 1100 debris flows were mobilized from shallow landslides during a rainstorm from september 9 13 2013 in the colorado front range with the vast majority initiating on sparsely vegetated south facing terrain to investigate the physical processes responsible for the observed aspect control we made measurements of soil properties on a densely forested north facing hillslope and a grassland dominated south facing hillslope in the colorado front range and performed numerical modeling of transient changes in soil pore water pressure throughout the rainstorm using the numerical model we quantitatively assessed interactions among vegetation rainfall interception subsurface hydrology and slope stability results suggest that apparent cohesion supplied by roots was responsible for the observed connection between debris flow initiation and slope aspect results suggest that future climate driven modifications to forest structure could substantially influence landslide hazards throughout the front range and similar water limited environments where vegetation communities may be more susceptible to small variations in climate