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USGS1986

Determination of the components of stormflow using water chemistry and environmental isotopes, Mattole River basin, California

The chemical and isotopic composition of rainfall and stream water was monitored during a storm in the Mattole River basin of northwestern California. About 250 mm of rain fell during 6 days (∼80% within a 42 h period) in late January, 1972, following 24 days of little or no precipitation. River discharge near Petrolia increased from 22 m 3 s −1 to a maximum of 1300 m 3 s −1 while chloride and silica concentrations decreased only from 3.2 to 2.1 and 11.5 to 8.6 mgl −1 , respectively. Meanwhile, the isotopic composition of the river changed from δD = -42%, δ 18 O = -6.8% and 40 tritium units (T.U.) to extreme values at highest flow of δD = -35%, δ 18 O = -5.9% and 25 T.U. in response to volume-weighted rainfall averaging δD = -19.5%, δ 18 O = -3.1% and 18 T.U. Despite much rainfall of a composition quite different from that of the prestorm river water, “buffering” processes in the watershed greatly restricted changes in the chemical and isotopic content of the river during storm runoff. Because of the physical and hydrologic characteristics of the watershed, major contributions of groundwater to stormflow are very unlikely. The large increase in dissolved chemical load observed at maximum river discharge required that extensive interaction with, and presumably penetration of, soils occurred within a few hours time. Such a large increase in chemical load also required subsurface stormflow throughout a high proportion of the watershed. Chemical and isotopic stabilization of stormflow is believed to be due mainly to displacement of prestorm soil water, with some effects on river chemistry due to rapid rain-soil interactions. The isotopic and chemical composition of prestorm soil moisture cannot readily be predicted a priori because of possible variability in rainfall composition, evaporation, and exchange with atmospheric moisture, nor can it be assumed that baseflow has a predictable relation to the chemical or isotopic composition of water displaced from soils during storms. Therefore, it seems inappropriate to draw conclusions as to the relative proportions of groundwater and rainfall in runoff from a particular storm based only on the average compositions of rainfall, stormflow, and prestorm river water, as has been done in most previous isotope hydrograph studies. Given the great variation in hydrology, topography, soil characteristics, rainfall intensity and quantity, etc. from place to place, the relative amount of overland flow, subsurface flow from the unsaturated zone and of groundwater in stormflow can vary greatly in time and space.

California↗

USGS2019

Estimating quick-flow runoff at the monthly timescale for the conterminous United States

The quantitative estimation of the quick-flow runoff component of streamflow is required for many hydrologic applications. Estimation at the monthly timescale and national spatial scale would be particularly useful for national water availability modeling. This paper reviews a sample of commonly used equations for quick-flow runoff, including several currently in use in continental-scale models. The review shows the wide range of equation forms or heuristics currently in use to predict quick-flow runoff, the limited spatial scale over which these equations are often developed or calibrated, and the scarcity of well-tested equations available for quick-flow runoff at the monthly timescale. Data were gathered from a set of 1301 gaged watersheds across the United States to test a range of equations from the literature, along with several alternative equations, to assess and compare their performance in predicting quick-flow runoff at the monthly timescale. The highest-performing equation was selected for application to monthly maps of explanatory variables to produce monthly quick-flow runoff water budget contribution maps. This equation is a regression against precipitation, soil saturated hydraulic conductivity, surficial geology type, and slope data. Its application indicates that average quick-flow runoff across the conterminous United States in the winter exceeds that in the summer by up to a factor of three. The monthly maps were explored and evaluated for the timespan of 2000-2015. The comparison of equation forms and produced monthly maps will be useful for a variety of hydrologic modeling and monitoring applications.

Journal of Hydrology↗

USGS1973

Karst hydrology: A review

Karst regions of the world are characterized by limestones and other soluble rocks at or near land surface that have been modified by solutional erosion. Such surface features as sinks, long dry valleys, sparse streams, and bare rock and such subsurface features as caverns, arterial solution openings leading to large springs, and a deep water table are typical of karst terranes. These features result in an uneven distribution of permeability in karst systems and surface and subsurface hydrologic conditions that require special hydrogeologic studies. Local high permeability at shallow depth in mature karst regions leads to an ecology associated with a soilless and water-scarce surface environment. Many practical problems result from this high permeability, including: (1) scarcity and poor predictability of groundwater supplies; (2) scarcity of surface-water supplies; (3) instability of the ground; (4) leakage of surface reservoirs; and (5) an unreliable waste-disposal environment. Interest in karst hydrology has increased greatly in the past decade; this interest has resulted in the international exchange of numerous published reports on local areas and on special topical karst problems. Many of these reports have been used by the authors in preparing this paper, which synthesizes results of many workers and focuses attention on: (1) the development of karst features through hydrologic processes; and (2) hydrologic systems of karst terranes.

Journal of Hydrology↗

USGS2009

Trends in streamflow in the Yukon River Basin from 1944 to 2005 and the influence of the Pacific Decadal Oscillation

Streamflow characteristics in the Yukon River Basin of Alaska and Canada have changed from 1944 to 2005, and some of the change can be attributed to the two most recent modes of the Pacific Decadal Oscillation (PDO). Seasonal, monthly, and annual stream discharge data from 21 stations in the Yukon River Basin were analyzed for trends over the entire period of record, generally spanning 4-6 decades, and examined for differences between the two most recent modes of the PDO: cold-PDO (1944-1975) and warm-PDO (1976-2005) subsets. Between 1944 and 2005, average winter and April flow increased at 15 sites. Observed winter flow increases during the cold-PDO phase were generally limited to sites in the Upper Yukon River Basin. Positive trends in winter flow during the warm-PDO phase broadened to include stations in the Middle and Lower Yukon River drainage basins. Increases in winter streamflow most likely result from groundwater input enhanced by permafrost thawing that promotes infiltration and deeper subsurface flow paths. Increased April flow may be attributed to a combination of greater baseflow (from groundwater increases), earlier spring snowmelt and runoff, and increased winter precipitation, depending on location. Calculated deviations from long-term mean monthly discharges indicate below-average flow in the winter months during the cold PDO and above-average flow in the winter months during the warm PDO. Although not as strong a signal, results also support the reverse response during the summer months: above-average flow during the cold PDO and below-average flow during the warm PDO. Changes in the summer flows are likely an indirect consequence of the PDO, resulting from earlier spring snowmelt runoff and also perhaps increased summer infiltration and storage in a deeper active layer. Annual discharge has remained relatively unchanged in the Yukon River Basin, but a few glacier-fed rivers demonstrate positive trends, which can be attributed to enhanced glacier melting. A positive trend in annual flow during the warm PDO near the mouth of the Yukon River suggests that small increases in flow throughout the Yukon River Basin have resulted in an additive effect manifested in the downstream-most streamflow station. Many of the identified changes in streamflow patterns in the Yukon River Basin show a correlation to the PDO regime shift. This work highlights the importance of considering proximate climate forcings as well as global climate change when assessing hydrologic changes in the Arctic.

Journal of Hydrology↗

USGS2019

Calibration of the USGS National Hydrologic Model in ungauged basins using statistical at-site streamflow simulations

In the absence of measured streamflow, statistically simulated daily streamflow can be used to support the ability of physical models to represent hydrologic processes at ungauged locations. The objective of this study was to determine the feasibility of using statistical simulations in place of measured streamflow to calibrate physical models in ungauged basins. Daily streamflow was simulated at each of the 1,410 gauged watersheds using a cross-validated implementation of pooled ordinary kriging (POK). In this manner, the streamflow at each gauge was simulated as if no at-site streamflow information were available. The National Hydrologic Model application of the Precipitation-Runoff Modeling System was then calibrated through two separate procedures: (1) with measured streamflow, and (2) with statistically simulated streamflow in lieu of measured streamflow. Calibrating with statistically simulated streamflow produced performances within 23% of applications with knowledge of at-site measurements. Furthermore, statistically generated streamflow produced accurate timing information, which, when combined with alternative data sets (e.g., evapotranspiration, recharge, etc.), can be used to improve representation of hydrologic processes at ungauged locations.

Journal of Hydrologic Engineering↗

USGS1993

Interactions between ground water and wetlands, southern shore of Lake Michigan, USA

Wetlands between, and within, dune-beach complexes along the south shore of Lake Michigan are strongly affected by ground water. The hydrogeology of the glacial drift aquifer system in a 26 km 2 area was investigated to determine the effects of ground water on the hydrology and hydrochemistry of Cowles Bog and its adjacent wetlands. The investigation showed that ground water from intermediate- and regional-scale flow systems discharges to Cowles Bog from confined aquifers that underlie the wetland. These flow systems are recharged in moraines south of the dune-beach complexes. Water from the confined aquifers discharges into the surficial aquifer mainly by upward leakage through a buried till sheet that serves as the confining layer. However, the till sheet is breached below a raised peat mound in Cowles Bog, allowing direct upward discharge from the confinef aquifer into the surficial sand, marl, and peat. The shallow ground and wetland water in the area influenced by this leakage is a calcium magnesium bicarbonate type, with low tritium concentrations consistent with mixing of older ground water and more recent precipitation. Ground water and wetland water from surrounding areas are less mineralized and have higher tritium concentrations characteristic of precipitation in the late 1970s. The results of this study suggest that wetlands in complex hydrogeologic settings may be influenced by multiple ground-water flow systems that are affected by geomorphic features, stratigraphic discontinuities, and changes in sediment types. Discharge and recharge zones may both occur in the same wetland. Multidisciplinary studies incorporating hydrological, hydrochemical, geophysical, and sedimentological data are necessary to identify such complexities in wetland hydrology.

Journal of Hydrology↗

USGS1991

Hydrogeologic inferences from drillers' logs and from gravity and resistivity surveys in the Amargosa Desert, southern Nevada

The Amargosa Desert of southern Nevada, in the Basin and Range province, is hydraulically downgradient from Yucca Mountain, the potential site of a repository for high-level nuclear waste. Groundwater flow paths and flow rates beneath the Amargosa Desert are controlled in part by the total saturated thickness and the hydraulic properties of basin-fill alluvial sediments. Drillers' logs of water wells completed in alluvium were analyzed to help characterize the hydrogeologic framework underlying the Amargosa Desert. Fractions of coarse-grained sediments, calculated from each of these logs, were contoured using a universal-kriging routine to interpolate values. Results from a previous electrical sounding survey also were contoured, including the estimated depth to Paleozoic (?) basement rocks. The vertical electric sounding results were obtained from individual depth-to-resistivity profiles, from which the average resistivity of the total profile and the resistivity of the upper 75 m were calculated. The distribution and variations in average resistivity of the total depth correlated reasonably well with the distribution of variations in regional gravity. Patterns of contours of the resistivity of the upper 75 m of alluvium were similar to patterns of regional contours of the predominant cation (sodium) in ground water. Gravity lows correspond in some places to the presence of lacustrine, eolian, or marsh surface deposits, which may function as barriers to groundwater flow. Gravity lows also correspond to areas with thick basin-fill sediments, which was corroborated by depth-to-basement data determined from vertical electric soundings. Depths to Paleozoic (?) basement rocks may be as much as 1600 m based on data from the resistivity survey, which were corroborated in part by seismic-refraction survey data. Small variations exist in the percentage of the basin fill that is saturated. The unsaturated zone is always < 15% of the alluvial column. Analysis of depth-to-water and hydrochemical data, in conjunction with average resistivity data for the upper 75 m of alluvium, suggest a hydrologic barrier near the center of the Amargosa Desert.

Nevada↗

USGS2025

Systematic approach to prioritize wells for effective groundwater monitoring and management in the Arkansas Headwaters Basin, Colorado, USA

Study region The Arkansas Headwaters Basin, an intermountain basin in the Southern Rocky Mountains of North America. Study focus Our specific focus is choosing a set of wells to support a possible future regional groundwater-surface water model that would support water management. We present a three-step process using multiple criteria to score, predict, and choose prioritized wells that capture the full distribution of data including extremes. The three-step process provides accessible visualizations, fiscally efficient well prioritization, and screening useful for subsequent groundwater modeling. The novelty of the proposed methodology is the systematic approach integrating a scoring and a predictive approach to support a selection path. The systematic approach may be broadly adapted for other basins. New hydrological insights for the region Understanding regional hydrology hinges on efficient collection of hydrologic data that captures the relevant dynamics including extremes. The present study, a case study for a particular basin in the Southern Rocky Mountains, is the first use of a scripted (R software) strategy to select an economical and representative set of monitoring wells. Our findings suggest caution when using proximity as a proxy for correlation, because proximal wells in the same geologic formation and similar depths are not always correlated. In the Arkansas Headwaters Basin, subsurface geology may be less influential on groundwater elevations than broader hydrologic influences, such as regional drought.

Colorado↗

USGS2022

Connecting diverse disciplines to improve understanding of surface water-groundwater interactions

Laura K. Lautz is a premier mentor, collaborator, and researcher at the intersection of natural hydrologic systems and humans. Her research has shifted the paradigm around measuring and understanding the impacts of surface water and groundwater interactions across spatial and temporal scales. She has done this by testing and refining new methods and by collaborating with, training, supporting, and mentoring diverse scientists. Here, we review her research across five themes, summarizing the prior status of the field, what Lautz contributed, as well as new directions in the field inspired by her work. Lautz’s research expanded our understanding of the impacts of stream restoration on surface water-groundwater interactions, where she tested new field methods and showed that restoration structures increase hyporheic exchange, locally altering biogeochemical function of the streambed. She refined novel methods for measuring surface water-groundwater exchanges and worked to make these methods easily accessible through freely available software. Her research group greatly expanded the use of heat as a quantitative tracer of hydrologic processes via the well-used VFLUX and HFLUX programs. Her research evaluated the impacts of surface water-groundwater interactions in urban streams, showing the substantial fluxes of nutrients and chloride that can move through those exchanges and the potential for groundwater to help buffer contamination. To assess groundwater impacts on streamflow below tropical glaciers, she used a wide range of field methods to reveal the sensitivity of these systems to climate change. Finally, she built tools to quantify natural brine contamination of drinking water wells in areas that may later be subject to high-volume hydraulic fracturing, creating a needed ‘pre-fracking’ dataset. Through this process, she identified multiple sources of salinity that are already reaching wells in these systems. Overall, this research has been done with a focus on mentoring and training the next generation of hydrologists, including work to specifically train for careers beyond academia, and facilitating early career scientists to realize their innate potentials. With former trainees in careers across industry, government, and academia, Dr. Laura K. Lautz is now working to build cross-disciplinary research at even larger scales, across federal research units, guaranteeing that an even larger impact on hydrology is still to come.

Journal of Hydrology X↗

USGS2014

Effects of distributed and centralized stormwater best management practices and land cover on urban stream hydrology at the catchment scale

Urban stormwater runoff remains an important issue that causes local and regional-scale water quantity and quality issues. Stormwater best management practices (BMPs) have been widely used to mitigate runoff issues, traditionally in a centralized manner; however, problems associated with urban hydrology have remained. An emerging trend is implementation of BMPs in a distributed manner (multi-BMP treatment trains located on the landscape and integrated with urban design), but little catchment-scale performance of these systems have been reported to date. Here, stream hydrologic data (March, 2011–September, 2012) are evaluated in four catchments located in the Chesapeake Bay watershed: one utilizing distributed stormwater BMPs, two utilizing centralized stormwater BMPs, and a forested catchment serving as a reference. Among urban catchments with similar land cover, geology and BMP design standards (i.e. 100-year event), but contrasting placement of stormwater BMPs, distributed BMPs resulted in: significantly greater estimated baseflow, a higher minimum precipitation threshold for stream response and maximum discharge increases, better maximum discharge control for small precipitation events, and reduced runoff volume during an extreme (1000-year) precipitation event compared to centralized BMPs. For all catchments, greater forest land cover and less impervious cover appeared to be more important drivers than stormwater BMP spatial pattern, and caused lower total, stormflow, and baseflow runoff volume; lower maximum discharge during typical precipitation events; and lower runoff volume during an extreme precipitation event. Analysis of hydrologic field data in this study suggests that both the spatial distribution of stormwater BMPs and land cover are important for management of urban stormwater runoff. In particular, catchment-wide application of distributed BMPs improved stream hydrology compared to centralized BMPs, but not enough to fully replicate forested catchment stream hydrology. Integrated planning of stormwater management, protected riparian buffers and forest land cover with suburban development in the distributed-BMP catchment enabled multi-purpose use of land that provided esthetic value and green-space, community gathering points, and wildlife habitat in addition to hydrologic stormwater treatment.

Journal of Hydrology↗

USGS2000

Development and application of a comprehensive simulation model to evaluate impacts of watershed structures and irrigation water use on streamflow and groundwater: The case of Wet Walnut Creek Watershed, Kansas, USA

This paper presents the results of a comprehensive modeling study of surface and groundwater systems, including stream-aquifer interactions, for the Wet Walnut Creek Watershed in west-central Kansas. The main objective of this study was to assess the impacts of watershed structures and irrigation water use on streamflow and groundwater levels, which in turn affect availability of water for the Cheyenne Bottoms Wildlife Refuge Management area. The surface-water flow model, POTYLDR, and the groundwater flow model, MODFLOW, were combined into an integrated, watershed-scale, continuous simulation model. Major revisions and enhancements were made to the POTYLDR and MODFLOW models for simulating the detailed hydrologic budget for the Wet Walnut Creek Watershed. The computer simulation model was calibrated and verified using historical streamflow records (at Albert and Nekoma gaging stations), reported irrigation water use, observed water-level elevations in watershed structure pools, and groundwater levels in the alluvial aquifer system. To assess the impact of watershed structures and irrigation water use on streamflow and groundwater levels, a number of hypothetical management scenarios were simulated under various operational criteria for watershed structures and different annual limits on water use for irrigation. A standard 'base case' was defined to allow comparative analysis of the results of different scenarios. The simulated streamflows showed that watershed structures decrease both streamflows and groundwater levels in the watershed. The amount of water used for irrigation has a substantial effect on the total simulated streamflow and groundwater levels, indicating that irrigation is a major budget item for managing water resources in the watershed. (C) 2000 Elsevier Science B.V.This paper presents the results of a comprehensive modeling study of surface and groundwater systems, including stream-aquifer interactions, for the Wet Walnut Creek Watershed in west-central Kansas. The main objective of this study was to assess the impacts of watershed structures and irrigation water use on streamflow and groundwater levels, which in turn affect availability of water for the Cheyenne Bottoms Wildlife Refuge Management area. The surface-water flow model, POTYLDR, and the groundwater flow model, MODFLOW, were combined into an integrated, watershed-scale, continuous simulation model. Major revisions and enhancements were made to the POTYLDR and MODFLOW models for simulating the detailed hydrologic budget for the Wet Walnut Creek Watershed. The computer simulation model was calibrated and verified using historical streamflow records (at Albert and Nekoma gaging stations), reported irrigation water use, observed water-level elevations in watershed structure pools, and groundwater levels in the alluvial aquifer system. To assess the impact of watershed structures and irrigation water use on streamflow and groundwater levels, a number of hypothetical management scenarios were simulated under various operational criteria for watershed structures and different annual limits on water use for irrigation. A standard `base case' was defined to allow comparative analysis of the results of different scenarios. The simulated streamflows showed that watershed structures decrease both streamflows and groundwater levels in the watershed. The amount of water used for irrigation has a substantial effect on the total simulated streamflow and groundwater levels, indicating that irrigation is a major budget item for managing water resources in the watershed.A comprehensive simulation model that combines the surface water flow model POTYLDR and the groundwater flow model MODFLOW was used to study the impacts of watershed structures (e.g., dams) and irrigation water use (including stream-aquifer interactions) on streamflow and groundwater. The model was revised, enhanced, calibrated, and verified, then applied to evaluate the hydrologic budget for Wet Wal

Journal of Hydrology↗

USGS2006

Effects of long-term water table drawdown on evapotranspiration and vegetation in an arid region phreatophyte community

Evapotranspiration rates and the ground water component of evapotranspiration at a site in Colorado's San Luis Valley that is dominated by shrubby phreatophytes (greasewood and rabbitbrush) were compared before and after a water table drawdown. Evapotranspiration (ET) rates at the site were first measured in 1985-1987 (pre-drawdown) when the mean water table depth was 0.92 m. Regional ground water pumping has since lowered the water table by 1.58 m, to a mean of 2.50 m. We measured ET at the same site in 1999-2003 (post-drawdown), and assessed physical and biological factors affecting the response of ET to water table drawdown. Vegetation changed markedly from the pre-drawdown to the post-drawdown period as phreatophytic shrubs invaded former wetland areas, and wetland grasses and grass-like species decreased. Lowering the water table reduced estimated total annual ET from a mean of 409.0 to 278.0 mm, a decrease of 32%, and the ground water component of ET (ETg), from a mean of 226.6 to 86.5 mm, a decrease of 62%. Two water table depth/ET models that have been used in the San Luis Valley overestimated the reduction in ETg due to lowering the water table by as much as 253%. While our results corroborate the generally observed negative correlation between ET rates and water table depth, they demonstrate that specific models to estimate ET as a function of water table depth, if not verified, may be prone to large errors. Both the water table drawdown and the vegetation change are continuing 20 years after the drawdown began, and it is unclear how site ET rates and processes will differ after the water table has stabilized and vegetation has adjusted to the new site hydrologic conditions. ?? 2005 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2021

The influence of land cover and storm magnitude on hydrologic flowpath activation and runoff generation in steep tropical catchments of central Panama

Despite abundant research documenting that land use/land cover (LULC) have substantial impacts on the hydrology of humid tropical systems, field-based evidence for the physical mechanisms behind these impacts are still lacking. In particular, our understanding of the hydrologic flowpaths that generate runoff in these systems, and how they vary with respect to LULC is insufficient to inform both physically-based hydrologic modeling and land-use decision-making. In this study, we use end-member mixing analysis (EMMA) of stream chemistry, and hydrometric characterizations of hillslope soil moisture to identify hydrologic flowpaths in humid tropical steep-land catchments of varying LULC: mature tropical forest, young secondary tropical forest, cattle pasture. EMMA was applied to data from 14 storm events (six at the mature forest, five at the young secondary forest, and three at the cattle pasture) that were intensively sampled during the 2017 wet season representing a wide range of rainfall magnitudes and intensities. Additionally, volumetric-soil-moisture responses at multiple depths were characterized during and after 74 storm events occurring from 2015 to 2017. EMMA results indicated that lateral preferential flow within the top 30 cm of the soil profile was a dominant source of runoff generation at the two forested catchments, with the contribution of this flow path increasing with rainfall magnitude and intensity. This was corroborated by volumetric-soil-moisture data, that showed that a perched zone of saturation developed at 30 cm at the time of peak storm runoff during the largest events and lasted for the remaining duration of the event. EMMA indicated that runoff was a combination of infiltration-excess overland flow and lateral subsurface flow in the actively grazed pastoral catchment. There, overland flow contributed 62 % of runoff during the highest runoff rate sampled (35.3 mm/hr) and this contribution increased substantially with storm magnitude. This flowpath identification was also supported by volumetric-soil-moisture data at the pasture, with peak saturation at all depths during the largest storm events occurring up to 30 min after peak runoff. These results provide a mechanistic explanation for previously observed hydrologic differences among tropical LULCs. Additionally, the wide range of hydrologic conditions during these storm events provide a basis for understanding how future changes to this, and similar humid tropical regions will impact hydrological processes and water availability.

Journal of Hydrology↗

USGS2021

Post-wildfire hydrologic recovery in Mediterranean climates: A systematic review and case study to identify current knowledge and opportunities

Post-fire hydrologic research typically focuses on the first few years after a wildfire , leading to substantial uncertainty regarding the longevity of impacts. The time needed for hydrologic function to return to pre-fire conditions is critical information for post-fire land and water management decisions. This is particularly true in Mediterranean climates , where water is scarce and in high demand, and the severity and area burned by wildfires are increasing. In part, uncertainty about hydrologic recovery is due to lack of a consistent definition or interpretation of what constitutes “recovery.” Here, we systematically reviewed empirical studies from Mediterranean climates with at least three years of post-fire hydrologic data with the objectives of (a) assessing the recovery period, (b) identifying a definition of post-fire hydrologic recovery, (c) demonstrating a simple analytical approach to aid in assessment of recovery, and (d) outlining research needs and opportunities to better quantify post-fire recovery. We assessed the hydrologic effects reported in 38 sites that were monitored for 3–20 years. Eighteen sites were considered recovered within seven years; however, the recovery time was inconsistent across sites and was not related to location, response variable, or study design. The likelihood of recovery within the study period also decreased with increasing proportion of the watershed area burned. Importantly, we have also proposed a standardized definition and an approach to quantifying hydrologic recovery that may facilitate cross-study comparisons and a deeper understanding of recovery. Specifically, we propose hydrologic recovery has occurred when a specific post-fire hydrologic function or condition of interest returns to the 95% confidence interval of the pre-fire condition. In support of this definition, we have demonstrated applying this simple approach to assess recovery and presented future research topics to improve our understanding of long-term post-fire catchment responses. In addition to the need for more studies that quantify hydrologic responses farther into the post-fire period, understanding post-fire changes in soil structural and hydraulic properties through time will improve our mechanistic understanding of post-fire hydrologic responses and recovery.

Journal of Hydrology↗

USGS2022

Hydrologic recovery after wildfire: A framework of approaches, metrics, criteria, trajectories, and timescales

Deviations in hydrologic processes due to wildfire can alter streamflows across the hydrograph, spanning peak flows to low flows. Fire-enhanced changes in hydrologic processes, including infiltration, interception, and evapotranspiration, and the resulting streamflow responses can affect water supplies, through effects on the quantity, quality, and timing of water availability. Post-fire shifts in hydrologic processes can also alter the timing and magnitude of floods and debris flows. The duration of hydrologic deviations from a pre-fire condition or function, sometimes termed hydrologic recovery, is a critical concern for land, water, and emergency managers. We reviewed and summarized terminology and approaches for defining and assessing hydrologic recovery after wildfire, focusing on statistical and functional definitions. We critically examined advantages and drawbacks of current recovery assessment methods, outline challenges to determining recovery, and call attention to selected opportunities for advancement of post-fire hydrologic recovery assessment. Selected challenges included hydroclimatic variability, post-fire land management, and spatial and temporal variability. The most promising opportunities for advancing assessment of hydrologic recovery include: (1) combining statistical and functional recovery approaches, (2) using a greater diversity of post-fire observations complemented with hydrologic modeling, and (3) defining optimal assemblages of recovery metrics and criteria for common hydrologic concerns and regions.

Journal of Hydrology and Hydromechanics↗

USGS1969

Hydrology of carbonate rock terranes — A review: With special reference to the United States

Limestone and other carbonate rocks are characterized by many unusual features and extreme conditions, either involving the hydrologic system within them or wrought by hydrologic conditions on them or through them. Perhaps there could be little agreement as to what is typical or average for the many features of carbonate rocks, as indicated by the following conditions: bare rock and thin soils are common, but so are thick soils; very highly permeable limestones are common, but so are poorly permeable ones; and rugged karst topographic features with underlying solution caverns are common, but so are flat, nearly featureless topographic conditions. Some conditions of carbonate terranes are suitable to man's needs and interests, such as the use of some permeable aquifers for water supply and the exploitation of caves for tourist attractions. On the other hand, many problems may exist, including: permeability too low for adequate water supply or so high that the aquifer retains too little water for use during periods of fair weather, soils too thin for growing of crops and for adequate filtration of wastes near the ground surface, instability of the ground for buildings and foundations in sinkhole areas, and unusually rugged topography. Some of the many variable conditions are readily observable, but others can be determined only by careful geologic and hydrologic studies. The need for knowing the specific geologic and hydrologic conditions at various places in limestone terranes, as well as the variations in hydrologic conditions with changing conditions and time, has resulted in many published reports on local areas and on special topical problems of limestone hydrology. Many of these reports have been used to advantage by the present writers in preparing this paper. The concept that secondary permeability is developed by circulation of water through openings with the accompanying enlargement of these openings by solution is now universally accepted in limestone terranes. Emphasis is placed on the hydrogeologic framework, or structural setting, in relation to the ease or difficulty of water to move from a source of recharge, through a part of the limestone, to a discharge area. Parts of the limestone favored by circulating ground water tend to develop solution openings, commonly in the upper part of the zone of saturation; as base level is lowered (sea level or perennial stream level), the related water table lowers in the limestone leaving air-filled caverns above the present zone of saturation in sinkhole areas. Reconstruction of the geologic and hydrologic history of a limestone area aids in determining the extent of development and the positions of fossil and present permeability. References are made to the hydrology of many limestone regions, especially those of the United States.

Journal of Hydrology↗

USGS2007

Isotopic characterization of three groundwater recharge sources and inferences for selected aquifers in the upper Klamath Basin of Oregon and California, USA

Stable isotope (??D and ??18O) signatures of three principal groundwater recharge areas in the 21,000-km2 upper Klamath Basin are used to infer recharge sources for aquifers in the interior parts of the basin. Two of the principal recharge areas, the Cascade Range on the western and southern margin of the basin and uplands along the eastern margin, are defined by mean annual precipitation that exceeds approximately 60 cm. A third recharge area coincides with the extensive irrigation canal system in the south central part of the basin. The stable isotope signature for Cascade Range groundwater falls near the global meteoric water line (GMWL). The stable isotope signature for the groundwater of the eastern basin uplands also falls near the GMWL, but is depleted in heavy isotopes relative to the Cascade Range groundwater. The stable isotope signature for water from the irrigation canal system deviates from the GMWL in a manner indicative of fractionation by evaporation. Groundwater provenance was previously unknown for two aquifers of interest: that supplying deep (225-792 m), large-capacity irrigation wells along the Oregon-California border, and that of the geothermal system near Klamath Falls. Groundwater produced by the deep irrigation wells along the Oregon-California border appears to be a mixture of eastern-basin groundwater and water with an evaporative isotopic signature. The component with an evaporative isotopic signature appears in some places to consist of infiltrated irrigation water. Chloride data suggest that much of the component with the evaporative isotopic signature may be coming from an adjacent subbasin. After accounting for the 18O shift common in geothermal waters, isotope data suggest that the geothermal groundwater in the upper Klamath Basin may emanate from the eastern basin uplands. Findings demonstrate that stable isotope and chloride data can illuminate certain details of a regional groundwater flow system in a complex geologic setting where other hydrologic data are ambiguous. ?? 2007 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2012

Regional regression models of watershed suspended-sediment discharge for the eastern United States

Estimates of mean annual watershed sediment discharge, derived from long-term measurements of suspended-sediment concentration and streamflow, often are not available at locations of interest. The goal of this study was to develop multivariate regression models to enable prediction of mean annual suspended-sediment discharge from available basin characteristics useful for most ungaged river locations in the eastern United States. The models are based on long-term mean sediment discharge estimates and explanatory variables obtained from a combined dataset of 1201 US Geological Survey (USGS) stations derived from a SPAtially Referenced Regression on Watershed attributes (SPARROW) study and the Geospatial Attributes of Gages for Evaluating Streamflow (GAGES) database. The resulting regional regression models summarized for major US water resources regions 1–8, exhibited prediction R 2 values ranging from 76.9% to 92.7% and corresponding average model prediction errors ranging from 56.5% to 124.3%. Results from cross-validation experiments suggest that a majority of the models will perform similarly to calibration runs. The 36-parameter regional regression models also outperformed a 16-parameter national SPARROW model of suspended-sediment discharge and indicate that mean annual sediment loads in the eastern United States generally correlates with a combination of basin area, land use patterns, seasonal precipitation, soil composition, hydrologic modification, and to a lesser extent, topography.

Journal of Hydrologic Engineering↗