factors controlling riffle scale hyporheic exchange flows and their seasonal changes in a gaining stream a three dimensional groundwater flow model 1 subsurface flow within a single riffle of a low gradient gravel bed stream was modeled in three dimensions using modflow a finite difference groundwater flow model model simulations showed that exchange flows can only occur in this low gradient gaining stream because of a zone of alluvial sediment around the stream that has much higher permeability than the surrounding catchment k 10 4 m s 1 compared with k 10 6 to 10 8 m s 1 the key factors controlling exchange flow within the alluvial zone were identified as the hydraulic conductivity of the alluvium the hydraulic gradient between upstream and downstream ends of the riffle and the flux of groundwater entering the alluvium from the sides and beneath in the study riffle each of these factors changes with season causing a reversal of flow paths in the alluvium and a reduction in exchange flows from about 0 2 0 5 m 3 d per meter stream length in summer to about 0 008 0 04 m 3 d 1 per meter stream length during fall to spring the model also revealed that exchange flows are up to twice as strong but more variable at the sides of the stream than near the center and that vertical flow paths beneath the channel are more persistent under the range of conditions modeled than lateral flow paths into the banks

the influence of ambient groundwater discharge on exchange zones induced by current bedform interactions summary we use numerical modeling to investigate the interactions between laminar flow in a water column current bedform induced flow in underlying permeable sediments and discharge of deep groundwater to the water column groundwater discharge reduces the spatial extent of current induced exchange zones within the sediments and may completely prevent the development of current bedform induced flow at high groundwater discharge although exchange zone size is reduced by groundwater discharge the reduction in exchange flux is not significant suggesting reduced residence times of materials cycled through these smaller zones fluid exchange zones tend to be centered around the reattachment points of eddies that also mark the location of flow divides within the sediments while deep groundwater is discharged preferentially along troughs exchange zone depth and the water column reynolds number are functionally related through a morgan mercer flodin model the relationship between the current induced flux through the sediments and the reynolds number is described by low order monotonic polynomial functions

particle dynamics the continuum of bedrock to alluvial river segments abstract particle dynamics refers to production erosion transport and storage of particulate material including mineral sediment and organic matter particle dynamics differ significantly between the end members of bedrock and alluvial river segments and between alluvial river segments with different grain size distributions bedrock segments are supply limited and resistant to change with relatively slow linear adjustments and predominantly erosion and transport particle dynamics in alluvial segments in contrast are transport limited and dominated by storage of mineral sediment and production of organic matter alluvial segments are resilient to change with relatively rapid multidirectional adjustments and stronger internal influences because of feedbacks between particles and biota bedrock segments are the governors of erosion within a river network whereas alluvial segments are the biogeochemical reactors fundamental research questions for both types of river segments center on particle dynamics which limit network scale incision in response to base level fall bedrock segments and habitat biogeochemical reactions and biomass production alluvial segments these characterizations illuminate how the spatial arrangement of bedrock and alluvial segments within a river network influence network scale resistance and resilience to external changes in relative base level climate and human activities

reshaping of the hyporheic zone beneath river restoration structures flume and hydrodynamic experiments 1 in channel stream restoration structures readjust surface water hydraulics streambed pressure and subsurface hyporheic exchange characteristics in this study we conducted flume experiments pool riffle amplitude of 0 03 m and wavelengths of 0 5 m and computational fluid dynamic cfd simulations to quantify how restoration structures impacted hyporheic penetration depth dp and hyporheic vertical discharge rate qv restoration structures were channel spanning vanes with subsurface footers placed in the gravel bed at each riffle hyporheic vertical discharge rate was estimated by analyzing solute concentration decay data and maximum hyporheic penetration depth was measured as the interface between hyporheic water and groundwater using dye tracing experiments the cfd was verified with literature based flume hydraulic data and with dp and qz observations and the cfd was then used to document how dp and qz varied with flume discharge q ranging from 1 to 15 l s 3e 03 re 5e 04 flume experiments and cfd simulations showed that restoration structures increased qz and decreased dp creating a shallower but higher flux hyporheic zone qz had a positive linear relationship with q while dp initially grew as q increased but then shrunk when a hydraulic jump with low streambed pressured formed downstream of the structure the restoration structures created counter acting forces of increased downwelling head due to backwater effects and increased upwelling due to low streambed pressure and standing waves downstream of the structure

pool spacing in forest channels field surveys of stream channels in forested mountain drainage basins in southeast alaska and washington reveal that pool spacing depends on large woody debris lwd loading and channel type slope and width mean pool spacing in pool riffle plane bed and forced pool riffle channels systematically decreases from greater than 13 channel widths per pool to less than 1 channel width with increasing lwd loading whereas pool spacing in generally steeper step pool channels is independent of lwd loading although plane bed and pool riffle channels occur at similar low lwd loading they exhibit typical pool spacings of greater than 9 and 2 4 channel widths respectively forced pool riffle channels have high lwd loading typical pool spacing of 2 channel widths and slopes that overlap the ranges of free formed pool riffle and plane bed channel types while a forced pool riffle morphology may mask either of these low lwd loading morphologies channel slope provides an indicator of probable morphologic response to wood loss in forced pool riffle reaches at all study sites less than 40 of the lwd pieces force the formation of a pool we also find that channel width strongly influences pool spacing in forest streams with similar debris loading and that reaches flowing through previously clear cut forests have lower lwd loading and hence fewer pools than reaches in pristine forests

hyporheic flow path response to hydraulic jumps at river steps hydrostatic model simulations 1 this research examined hydrostatic groundwater model modflow predictive adequacy and sensitivity in simulating hyporheic flow paths across a river step with a hydraulic jump in a companion paper we used flume and hydrodynamic model analysis to develop a refined conceptual model depicting these flow paths with zones of downwelling and upstream directed flux below the step the previous coarse conceptual model predicted uniform downstream directed upwelling below the step the hydrostatic model accurately predicted the downwelling and upstream directed fluxes beneath the wave and jump but failed to predict the plunge pool downwelling which is driven by dynamic pressures sensitivity tests varied riverbed topography and water surface profile geometry for a river with 1 slopes 10 cm flow depths and 50 150 cm long jets and jumps the flow paths below the jet jump region were driven by hydrostatic pressures and were highly sensitive to water surface profile and riverbed topography parameters failure to simulate the hydraulic jump caused errors in hyporheic flow path predictions beneath the jump region 1 m long by 0 5 m deep if the jump was poorly parameterized several meters of riverbed flow paths could be erroneously modeled as pointing upstream the hyporheic zone may contain a spatial mosaic of aerobic and anaerobic waters regulating nutrient transformations and biologic productivity accurate parameterization of hydraulic jumps in hyporheic simulation has the potential to improve predictions and explain heterogeneous subsurface flow paths and associated nutrient patterns and ecosystem functions

determining in channel dead zone transient storage by comparing solute transport in a bedrock channel alluvial channel sequence oregon 1 current stream tracer techniques do not allow separation of in channel dead zone e g eddies and out of channel hyporheic transient storage yet this separation is important to understanding stream biogeochemical processes we characterize in channel transient storage with a rhodamine wt solute tracer experiment in a 304 m cascade pool type bedrock reach with no hyporheic zone we compare the solute breakthrough curve btc from this reach to that of an adjacent 367 m alluvial reach with significant hyporheic exchange in the bedrock reach transient storage has an exponential residence time distribution with a mean residence time of 3 0 hours and a ratio of transient storage to stream volume of 0 14 demonstrating that at moderate discharge bedrock in channel storage zones provide a small volume of transient storage with substantial residence time in the alluvial reach though pools are similar in size to those in the bedrock reach transient storage has a power law residence time distribution with a mean residence time of 100 hours estimated at nearly 1200 hours and a ratio of storage to stream volume of 105 because the in channel hydraulics of bedrock reaches are simpler than alluvial step pool reaches the bedrock results are probably a lower end member with respect to volume and residence time though they demonstrate that in channel storage may be appreciable in some reaches these results suggest that in stream dead zone transient storage may be accurately simulated by exponential rtds but that hyporheic exchange is better simulated with a power law rtd as a consequence of more complicated flow path and exchange dynamics

impact of heterogeneity bed forms and stream curvature on subchannel hyporheic exchange 1 advection through hyporheic zones hz consisting of heterogeneous channel bend streambed deposits and their equivalent homogenous medium was investigated using finite difference groundwater flow and transport simulations and forward particle tracking the top prescribed head boundary was varied in order to mimic various stream channel head distributions resulting from the presence of bed forms and channel curvature flux calculations show that heterogeneity causes significant additional hz flux compared to an equivalent homogenous medium however the major cause of hz flux is a spatially periodic sinusoidal head distribution along the boundary representing the effect of bed forms the additional influence of heterogeneity on the total channel bed exchange and the overall hz geometry are increased when boundary head sinusoidal fluctuation is more subdued we present dimensionless numbers that summarize these relationships heterogeneity s influence is further magnified by considering the effect of channel curvature on boundary heads the simulations illustrate the dynamic influence of heterogeneity on the hyporheic zone since the various head boundaries employed in our modeling efforts are a proxy for different surface water conditions and bed form states that may occur during a single flood furthermore we show that residence times total tracking times of particles originating from the streambed follow a lognormal distribution in the presence of heterogeneity residence times can decrease or they can increase compared to residence times for homogeneous conditions depending on the relative positions of the heterogeneities and the bed forms hence streambed heterogeneity and stream curvature factors often neglected in previous modeling efforts combine with bed form configuration to dynamically determine hz geometry fluxes and residence time distributions

a patch hierarchy approach to modeling surface and subsurface hydrology in complex flood plain environments geomorphology interacts with surface and ground water hydrology across multiple spatial scales nonetheless hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale using an existing hydrogeologic computer model we implemented a simple hierarchical approach to modeling surface and ground water hydrology in a complex geomorphic setting we parameterized the model to simulate ground and surface water ow patterns through a hierarchical three dimensional quantitative representation of an anabranched montane alluvial ood plain the nyack flood plain middle fork flathead river montana usa comparison of model results to eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge temporal patterns of ood water storage on the ood plain and rates of ground water movement from the main river channel into a large lateral spring channel on the ood plain and water table elevation in the alluvial aquifer these results suggest that a hierarchical approach to modeling ground and surface water hydrology can reproduce realistic patterns of surface and ground water ux on alluvial ood plains and therefore should provide an excellent quantitative laboratory for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales copyright 2004 john wiley sons ltd

origin of xenoliths in the trachyte at puu waawaa hualalai volcano hawaii rare dunite and 2 pyroxene gabbro xenoliths occur in banded trachyte at puu waawaa on hualalai volcano hawaii mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir subsequently the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their mg numbers in addition olivine lost cao and plagioclase lost mgo and fe2o3 during subsolidus reequilibration the xenoliths also reacted with the host trachyte to form secondary mica amphibole and orthopyroxene and to further modify the compositions of some olivine clinopyroxene and spinel grains the reaction products indicate that the host trachyte melt was hydrous clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting apparently in response to addition of water to the xenolith these xenoliths do not contain co2 fluid inclusions so common in xenoliths from other localities on hualalai which suggests that co2 was introduced from alkalic basalt magma between the time co2 inclusion free xenoliths erupted at 106 6 ka and the time co2 inclusion rich xenoliths erupted within the last 15 ka

in stream geomorphic structures as drivers of hyporheic exchange 1 common in stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams exchange is important for ecological stream function and restoring function is a goal of many stream restoration projects yet the connection between in stream geomorphic form hydrogeologic setting and hyporheic exchange remains inadequately characterized we used the models hec ras modflow and modpath to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange we also conducted a field study to support model results model results indicated that structure size background groundwater discharge rate and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange followed by geomorphic structure type depth to bedrock and channel slope model results indicated channel spanning structures were more effective at driving hyporheic flow than were partially spanning structures and weirs were more effective than were steps across most structure types downwelling flux rate increased linearly with structure size yet hyporheic residence time exhibited nonlinear behavior increasing quickly with size at low structure sizes and declining thereafter important trends in model results were observed at the field site and also interpreted using simple hydraulic theory thereby supporting the modeling approach and clarifying underlying processes

transfer of nonsorbing solutes to a streambed with bed forms theory a theoretical analysis of the exchange of nonsorbing solutes between a permeable streambed and the overlying water of a stream or river is presented in this paper in a companion paper elliott and brooks this issue the results of experimental studies of such exchange are presented the analysis focuses on water movements into within and out of the bed which result from the presence of bed forms ripples and dunes and highlights the mechanisms of pumping and turnover pumping is the movement of fluid through the bed induced by steady dynamic pressure variations over bed forms turnover occurs as moving bed forms trap and release interstitial fluid the detailed analysis was used to generate the distribution of the residence time of solute within the bed which can be used to calculate the net mass exchange due to pumping and turnover

seasonal variation in surface subsurface water exchange and lateral hyporheic area of two stream aquifer systems abstract we used two dimensional unconfined transient groundwater flow models to investigate the interface between stream and groundwater flow systems or hyporheic zone of two first order streams that drain catchments with distinctly different alluvial sediments and bedrock lithology particle tracking showed that lateral hyporheic area planimetric area of flow paths lateral to the stream that are recharged by and return to the stream with travel times of 10 days or less differed between the two study streams and varied with discharge within each system at the rio calaveras welded tuff lateral hyporheic area ranged from 1 7 to 4 m 2 over the annual cycle in the aspen creek system sandstone lateral hyporheic area 1 1 5 m 2 was restricted to roughly half of that observed at rio calaveras the size of the hyporheic zone lateral to the streams at both sites decreased by approximately 50 during high flows sensitivity analyses indicated that changes in the hydraulic conductivity of alluvial and streambed sediments and variation in recharge rates have greatest impact on the magnitude direction and spatial distribution of stream groundwater exchange

a modelling study of hyporheic exchange pattern and the sequence size and spacing of stream bedforms in mountain stream networks oregon usa studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale namely slope breaks in the longitudinal profile of streams that generate subsurface head distributions we recently completed a field study that suggested channel unit spacing in stream longitudinal profiles can be used to predict the spacing between zones of upwelling flux of hyporheic water into the stream and downwelling flux of stream water into the hyporheic zone in the beds of mountain streams here we use two dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of stream flow in second third and fourth order mountain stream reaches modelling allowed us to 1 represent visually the effect that the shape of the longitudinal profile has on the flow net beneath streambeds 2 isolate channel unit sequence and spacing as individual factors controlling the depth that stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones 3 evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real streams we simulated hyporheic exchange in two sets of idealized stream reaches and one set of observed stream reaches idealized profiles were constructed using regression equations relating channel form to basin area the size and length of channel units step size pool length etc increased with increasing stream order simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased from 2 7mt o 7 6 m and downwelling lengths increased from 2 9mt o 6 0 m with increase in stream order from second to fourth order step spacing in the idealized reaches increased from 5 3mt o 13 7 m as stream size increased from second to fourth order simulated downwelling lengths increased from 4 3m in second order streams to 9 7 m in fourth order streams with a pool riffle step channel unit sequence and increased from 2 5m to 6 1 m from second to fourth order streams with a pool step riffle channel unit sequence upwelling lengths also increased with stream order in these idealized channels our results suggest that channel unit spacing size and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed stream reaches than in idealized stream reaches similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches this article replaces a previously published version hydrological processes 19 17 2915 2929 2005 doi 10 1002 hyp 5790 copyright 2006 john wiley sons ltd

leaky rivers implications of the loss of longitudinal fluvial disconnectivity in headwater streams article i nfo naturally induced longitudinal disconnectivity in the form of channel spanning logjams creates backwaters along headwater streams that reduce velocity and transport capacity create at least temporary storage sites for finer sediment and organic matter and enhance biological processing and uptake of nutrients land uses that reduce wood recruitment and instream storage result in reduced stream complexity and in creased longitudinal connectivity in headwater rivers we examine three scales of naturally occurring longi tudinal disconnectivity in headwater streams of the colorado front range and the implications for channel process and form of historical alterations in disconnectivity basin scale disconnectivity at channel lengths of 10 2 10 3 m results from downstream alternations between steep narrowly confined valley segments with single thread channels and lower gradient wider valley segments with multi thread channels this variation in valley geometry likely reflects differences in average spacing between joints in bedrock outcrops which influences bedrock weathering and erosion greater volumes of wood stored in the wide valley seg ments correlate with more closely spaced channel spanning logjams and greater storage of fine sediments and organic matter reach scale disconnectivity at channel lengths of 10 1 10 2 m results from the presence of numerous closely spaced channel spanning logjams which cumulatively store substantial amounts of fine sediment and organic matter the backwater effects associated with an individual jam can result in the accumulation of up to 11 m 3 of fine sediment upstream from the jam of which as much as 21 is organic

hyporheic exchange with heterogeneous streambeds laboratory experiments and modeling 1 hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone in reality streambed sediments have a heterogeneous structure and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns to assess the basic effects of sediment structure on hyporheic exchange we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative exponential correlated random hydraulic conductivity fields dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high and low permeability regions of the streambed as no existing model could represent these effects we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form induced boundary head distribution and the heterogeneous sediment structure a numerical particle tracking approach was then used to assess the resulting hyporheic exchange the combined flow transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours the heterogeneous hydraulic conductivity field caused both greater spatial variability in the water flux through the bed surface and a greater average interfacial flux than would have occurred with a homogeneous bed the layered correlation structure of the streambed produced an effective anisotropy that favored longitudinal pore water flow and caused a relatively rapid decrease of the mean pore water velocity with depth as a result solute penetration into the bed was confined to a more shallow region than would have occurred with a homogeneous bed the combination of faster near surface transport and shallower solute penetration produced a shorter mean hyporheic residence time on the basis of the combination of experimental results and model simulations we conclude that the structural heterogeneity of streambed sediments produces more spatially limited hyporheic exchange that occurs with greater spatial variability and at a higher overall rate

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

morphological and morphostructural features of kuwait abstract morphostructural analysis and interpretation of the geomorphic features of the surface of kuwait are essentially dependant on the recognition of the structural configuration of the top of the upper eocene dammam formation and its influence on the overlying sediments of the kuwait group the top surface of the dammam formation has an undulatory form representing a series of n s to nnw sse trending domal and flexural structures this surface has regulated to a variable extent the depositional regime and thickness of the overlying kuwait group structures of the dammam formation have directly left an impression on the surface as morphostructural forms and also indirectly controlled the geomorphic forms of the overlying sediments fifteen geomorphic zones characterized by distinct physiographic patterns slope gradients and dependant features are presented on a map data based on the recognition of drainage patterns and slope characteristics were incorporated significant deflection in topographic contours was also identified and geomorphic discontinuities and anomalies were delineated further treatment of the geomorphic zonation data with input from existing geological structural and tectonic data has resulted in the construction of the first morphostructural map of kuwait

organic carbon export in the form of wood during an extreme tropical storm upper rio chagres panama widespread intense rainfall over the upper rio chagres watershed 414 km2 in central panama during december 2010 triggered numerous landslides that introduced large numbers of trees to the river network we flew by helicopter along the mainstem upper chagres and the adjacent margins of lake alhajuela into which the upper chagres flows in february and june 2011 we used low elevation video photography from these flights to tally the number of wood pieces stored along the lake margin and within the channel and the number of landslides reaching the mainstem we used these tallies with ground verified estimates of average wood piece size and landslide surface area and assumptions about wood density carbon content and aboveground biomass to develop a first order estimate of carbon export in the form of wood from the upper chagres following the 2010 storms based on the wood tally we estimate 9 6 to 16 mg c km2 export and from the landslide tally we estimate 24 mg c km2 we believe the landslide tally provides a more accurate minimum estimate of carbon export from the upper chagres during the december 2010 storms these values are an order of magnitude higher than limited data for average or background rates of wood based carbon export from other catchments but two orders of magnitude lower than wood based carbon export during extreme storms in taiwan the findings suggest that duration of flood flow above a threshold for mobilizing wood within the channel network exerts a more important control on wood export from the upper chagres than magnitude of flood peak copyright 2013 john wiley sons ltd

the floodplain large wood cycle hypothesis a mechanism for the physical and biotic structuring of temperate forested alluvial valleys in the north pacific coastal ecoregion abstract a floodplain large wood cycle is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested alluvial river valleys of the pacific coastal temperate rainforest of north america in the cycle pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams which in turn create alluvial patches and protect them from erosion these stable patches provide sites for trees to mature over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer thus providing a future source of large wood and reinforcing the cycle different tree species can function in the floodplain large wood cycle in different ecological regions in different river valleys within regions and within individual river valleys in which forest composition changes through time the cycle promotes a physically complex biodiverse and self reinforcing state conversely loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity reestablishing large trees is thus necessary to restore such rivers although interactions and mechanisms may differ between biomes and in larger or smaller rivers available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone