Geology topics

Christopher P. Konrad

Publications and source records attributed to Christopher P. Konrad.

At least 19 recordsLinked to original sources

USGS2022

BFS—A non-linear, state-space model for baseflow separation and prediction

Streamflow in rivers can be separated into a relatively steady component, or baseflow, that represents reliably available surface water and more dynamic components of runoff that typically represent a large fraction of total streamflow. A spatially aggregated numerical time-series model was developed to separate the baseflow component of a streamflow time-series using a state-space framework in which baseflow is a non-linear function of upstream storage, an unmeasured state variable. The state-space framework allows forecasting of baseflow for periods with no rainfall or snowmelt and estimation of residence times in contrast to other hydrograph separation models. The use of a non-linear relation between baseflow and storage maintains model performance over a wide range of time scales but will only provide reliable predictions for periods when the rate of streamflow recession as a fraction of streamflow decreases over time. The baseflow separation model, BFS, is implemented as set of functions in the statistical computing language R. BFS is run using the main function, bf_sep, which reads model input (a time series of streamflow), calculates the baseflow component of streamflow, writes model output to a file, and returns an error to the user to facilitate automated calibration. The function, bf_sep, has six arguments, which a user must enter: a numerical vector with the time series of measured streamflow volume for each time step; a character string, timestep , that has a value of either “daily” or “hourly” indicating the time step; a character string, error_basis, indicating which simulated streamflow components are used for error calculations; a six-element numeric vector, flow , with parameters characterizing streamflow; a six-element vector, basin_char , with parameters characterizing the geometry of stream basin and reservoirs; and a six-element vector, gw_hyd , with hydraulic parameters. The function bf_sep calls a series of other functions to calculate surface and base reservoir storage and fluxes. Calibration of a non-linear model for baseflow recession must confront three issues. First, baseflow is a component of streamflow, so it is always less than or equal to streamflow but there is no independent standard for the baseflow component of streamflow. Second, optimization routines can converge on a set of model parameters that result in relatively steady but minimal baseflow that does not exceed streamflow, Q , but has a limited dynamic range. Third, the power function used to generate non-linear first-order baseflow recession ( dQ/dt )/Q ≠ constant) may only be sensitive to parameters over a limited range of values, which may not be found by optimization routines. To address these issues, BFS calculates error as the mean of weighted differences between measured streamflow and either simulated baseflow or the sum of simulated baseflow and surface flow as a fraction of measured streamflow. The difference for each time step is weighted by an exponential function of the length of recession for each time step ranging from 0 for periods when streamflow increases and approaching 1 for long recessional periods. The weight is set to 1 for any time step when simulated streamflow exceeds measured streamflow. Error calculation incorporates limited precision of streamflow measurements. A four-step calibration process was developed to find a set of viable parameters that maximize the baseflow component within the constraints of the conceptual model (a first-order recession rate that decreases during dry periods). BFS was calibrated at 13,208 U.S. Geological Survey streamgages with available daily streamflow records for at least 300 days from water years 1981 to 2020. The total simulated baseflow component as a fraction of streamflow (BFF) was generally less than the baseflow index (BFI) for 8,368 streamgages where BFF and BFI were available. The median difference was BFF–BFI = 0.11. Large differences were most common in the Interior West where streamflow in many rivers is regulated and is generated predominantly by snowmelt. The baseflow separation model generally allocates less streamflow to baseflow than graphical hydrograph separation in snowmelt rivers. BFS can be used to forecast streamflow during dry periods by using a time series of real-time streamflow with values of Not Available (NA), appended to the time-series to represent missing (future) streamflow values. The forecast skill of BFS was evaluated in terms of difference between simulated baseflow and measured streamflow as a fraction of measured streamflow on the days of the annual maximum recession period at 5,916 of the sites with at least 10 years of record. The median annual error was less than 50 percent at one-half of the sites and generally improved for drier years with longer recession periods.

Scientific Investigations Report↗

USGS2021

Assessment and significance of the frequency domain for trends in annual peak streamflow

Risk management of nonstationary floods depends on an understanding of trends over a range of flood frequencies representing small (frequent) to large (infrequent) floods. Quantile regression is applied to the annual peak streamflow distributions at 2683 sites in the contiguous United States to test for trends in the 10th quantile (floods with a 0.9 annual exceedance probability), the 50th quantile (median annual flood), and 90th quantile (floods with a 0.1 annual exceedance probability). Trends are most common (36% of sites) for the median annual flood (50th quantile) and often coherent with trends in both frequent small floods (10th quantile) and infrequent large floods (90th quantile). Changes in the at-site variance of annual peak streamflow, indicated by convergence (decreasing variance) or divergence (increasing variance) of the 10th and 90th quantiles over time, are primarily in response to reservoir operation or urban development rather than climate. An analysis of synthetic series generated from nonstationary distributions demonstrates that quantile regression and standard trend tests used in flood frequency analysis have limited power and high rates of false negatives (>70%) when a test has a significance of p = 0.05. Quantile regression and tests with lower significance complement standard trend testing to inform flood risk management.

Journal of Flood Risk Management↗

USGS2021

Multiple in-stream stressors degrade biological assemblages in five U.S. regions

Biological assemblages in streams are affected by a wide variety of physical and chemical stressors associated with land-use development, yet the importance of combinations of different types of stressors is not well known. From 2013 to 2017, the U.S. Geological Survey completed multi-stressor/multi-assemblage stream ecological assessments in five regions of the United States (434 streams total). Diatom, invertebrate, and fish communities were enumerated, and five types of potential stressors were quantified: habitat disturbance, excess nutrients, high flows, basic water quality, and contaminants in water and sediment. Boosted regression tree (BRT) models for each biological assemblage and region generally included variables from all five stressor types and multiple stressors types in each model was the norm. Classification and regression tree (CART) models then were used to determine thresholds for each BRT model variable above which there appeared to be adverse effects (multi-metric index (MMI) models only). In every region and assemblage there was a significant inverse relation between the MMI and the number of stressors exerting potentially adverse effects. The number of elevated instream stressors often varied substantially for a given level of land-use development and the number of elevated stressors was a better predictor of biological condition than was development. Using the adverse effects-levels that were developed based on the BRT model results, 68% of the streams had two or more stressors with potentially adverse effects and 35% had four or more. Our results indicate that relatively small increases in the number of stressors of different types can have a large effect on a stream ecosystem.

Science of the Total Environment↗

USGS2020

Accounting for temporal variability of streamflow in estimates of travel time

Retention, processing, and transport of solutes and particulates in stream corridors are influenced by the travel time of streamflow through stream channels, which varies dynamically with discharge. The effects of streamflow variability across sites and over time cannot be addressed by time-averaged models if parameters are based solely on the characteristics of mean streamflow. We develop methods to account for the effects of streamflow variability on travel time and compare our estimates to flow-weighted (“effective”) travel time at 100 streams in the southeastern United States. Velocity time series were generated for each stream from multiple-year (median 15.5 years), high-frequency (15 min interval) records of instantaneous streamflow and field measurements of velocity and inverted to produce time series of specific travel time [T/L]. The effective travel times for streams are 60–90% of the specific travel time of mean streamflow because a large fraction of the total streamflow volume is discharged during higher flows with higher velocities. We find that adjusting the specific travel time of mean streamflow at a site by a factor of 0.81 generally accounts for the effect of a skewed streamflow distribution, but at-site estimates of the coefficient of variation of streamflow are necessary to resolve differences in streamflow variability between streams or changes in variability over time. For example, the effective travel time of urban streams is less than the effective travel of forested streams in the southeastern United States as a result of increased streamflow variability in urban streams. Effective travel time accounts for both the variation in velocity with streamflow and the large fraction of streamflow discharged during high flows in most streams and provides time-averaged models with limited capability to account for effects of streamflow variability that otherwise they lack. This capability is needed for continental-scale modeling where streamflow variability is not uniform because of heterogeneous surficial geology, hydro-climatology, and vegetation and for applications where streamflow variability is not stationary as a response to climate change or hydrologic alteration.

Alabama, Georgia, North Carolina, Virginia, South ↗

USGS2020

Spectral analysis to quantify the response of groundwater levels to precipitation — Northwestern United States

Persistent atmospheric patterns that lead to wet and dry seasons and droughts over periods of months to decades and longer-term climate change over periods of decades to millennia affect groundwater resources. Changes in groundwater storage and the resulting groundwater discharge from most aquifers is relatively slow and steady compared to the variability of daily precipitation. The response of groundwater levels to precipitation can be complex because of a combination of processes that include evapotranspiration, surface runoff, and infiltration of net recharge from precipitation through the vadose zone. Typically, this response is delayed and results in a change in groundwater storage reflected in a time series of groundwater levels. Understanding the relations between variations in precipitation and changes in groundwater storage is essential to water resources planning. The objectives of this study were to (1) characterize the relation between precipitation and responses in groundwater levels at seasonal to decadal scales and (2) to develop methods that are transferable on a continental scale to any groundwater-level record. Spectral analysis was applied to daily precipitation and groundwater levels for eleven monitoring wells in the northwestern Unites States with records ranging in length from 5.9 to 23.9 years. The analysis provided a quantitative characterization for each monitoring well that met both objectives and indicated that maximum and minimum precipitation rates generally occurred in December and August, respectively. Maximum groundwater levels occurred from February to August, and minimum values occurred from January to December. The lag in the annual peak response of groundwater to peak precipitation ranged from 2.2 to 8.8 months, with a median value of 5.3 months. Groundwater responses to wet and dry seasons were evident in the relatively high amplitude frequencies of 10 and 20 cycles per decade (cpdec). A high amplitude frequency at 1 cpdec represents a drought cycle that resulted in larger groundwater level changes than typical seasonal water level fluctuations.

Oregon, Washington↗

USGS2019

Flow modification in the Nation’s streams and rivers

This report summarizes a national assessment of flowing waters conducted by the U.S. Geological Survey’s (USGS) National Water-Quality Assessment (NAWQA) Project and addresses several pressing questions about the modification of natural flows in streams and rivers. The assessment is based on the integration, modeling, and synthesis of monitoring data collected by the USGS and the U.S. Environmental Protection Agency at more than 7,000 streams and rivers across the conterminous United States from 1980 to 2014. Key findings include the following. First, flow in many of the Nation’s streams and rivers is different from what it would be under natural conditions. In particular, low flows are more frequent, are of shorter duration, and vary less from one year to the next than they would naturally. In addition, high flows have been reduced in magnitude, are of shorter duration, are less frequent, and vary less from one year to the next than they would naturally. Other characteristics of natural flows also have been modified. Second, over the last 60 years (1955–2014), climatic trends have caused a change of 50 percent or more in one or more streamflow attributes at two-thirds of climate-sensitive streamgaging sites. However, these climate-induced changes have been less influential on streamflow modification than have land and water-management practices. Third, in every region assessed, streamflow modification was associated with reduced ecological health, as indicated by two biological communities—invertebrates and fish. Biological communities were increasingly likely to be impaired (defined as having lost a statistically significant number of species) in streams with flows most different from natural conditions. Finally, several case studies are presented that illustrate viable management strategies for balancing the water needs of people and ecosystems.

Circular↗

USGS2019

An integrated framework for ecological drought across riverscapes of North America

Climate change is increasing the severity and extent of extreme droughts events, posing a critical threat to freshwater ecosystems, particularly with increasing human demands for diminishing water supplies. Despite the importance of drought as a significant driver of ecological and evolutionary dynamics, current understanding of drought consequences for freshwater biodiversity is very limited. We describe key barriers that hinder integrative drought research and monitoring across riverscapes. The primary constraint limiting understanding of ecological drought is an existing monitoring framework focused on human water consumption and flood risk in mainstem rivers. This approach is misaligned with escalating needs for research and data collection that illuminate exposure, sensitivity, and adaptive capacity (i.e., vulnerability) of biota to drought across entire riverscapes. We present a hierarchical framework for integrated ecological drought monitoring and research that addresses drought vulnerability across riverscapes, and describe how this approach can directly inform natural-resource management.

BioScience↗

USGS2019

Estimating minimum streamflow from measurements at ungauged sites in regions with streamflow‐gauging networks

Estimation of low flows in rivers continues to be a vexing problem despite advances in statistical and process‐based hydrological models. We develop a method to estimate minimum streamflow at seasonal to annual timescales from measured streamflow based on regional similarity in the deviations of daily streamflow from minimum streamflow for a period of interest. The method is applied to 1,019 gauged sites in the Western United States for June to December 2015. The gauges were clustered into six regions with distinct timing and magnitude of low flows. A gamma distribution was fit each day to the deviations in specific discharge (daily streamflow divided by drainage area) from minimum specific discharge for gauges in each region. The Kolmogorov–Smirnov test identified days when the gamma distribution was adequate to represent the distribution of deviations in a region. The performance of the gamma distribution was evaluated at gauges by comparing daily estimates of minimum streamflow with estimates from area‐based regression relations for minimum streamflow. Each region had at least 8 days during the period when streamflow measurements would provide better estimates than the regional regression equation, but the number of such days varied by region depending on aridity and homogeneity of streamflow within the region. Synoptic streamflow measurements at ungauged sites have value for estimating minimum streamflow and improving the spatial resolution of hydrological model in regions with streamflow‐gauging networks.

Hydrological Processes↗

USGS2019

Sediment storage and transport in the Nooksack River basin, northwestern Washington, 2006–15

The Nooksack River is a dynamic gravel-bedded river in northwestern Washington, draining off Mount Baker and the North Cascades into Puget Sound. Working in cooperation with the Whatcom County Flood Control Zone District, the U.S. Geological Survey studied topographic, hydrologic, and climatic data for the Nooksack River basin to document recent changes in sediment storage, long-term bed elevation trends, rates of sediment transport, and factors influencing surficial drainage in order to support ongoing river management. Differences in elevations between topographic and bathymetric surveys in 2005/06 and 2013/15 indicate the active channel aggraded about 1–2 feet locally near the cities of Ferndale and Everson but was primarily stable between them. The active channel upstream of Nugent’s Corner generally incised. Total incision upstream of Nugent’s Corner to Glacier Creek generated 2.3 ± 1.7 million cubic yards of sediment from 2005/06 to 2013 and likely represented a significant source of coarse sediment to the lower mainstem river over that time. Long-term records of local channel-bed elevation, derived from U.S. Geological Survey streamgage data, show bed-elevation changes of about 1–3 feet. The river bed at most streamgages exhibits long-term trends, with relatively consistent rates of change on the order of 1 foot per decade that persist years to decades. Lagged correlations in bed-elevation trends at all seven streamgages in the North Fork Nooksack and mainstem Nooksack suggest that decadal periods of persistent aggradation and incision originate in the North Fork and translate downstream. The channel-change signal propagates downstream 0.5–2.5 miles per year, with the rate of propagation scaling closely with channel slope. The pattern of incision and aggradation in the North Fork correlates with regional climate, where persistent incision follows extended cold and wet periods, and persistent aggradation follows extended warm and dry periods. Climate-driven variation in coarse-sediment delivery, primarily from the North Fork Nooksack, then appears to be a strong control on long-term vertical channel adjustments at sites downstream. The downstream-translating climate signal generated in the North Fork would account for recently observed aggradation at Everson and Ferndale but not the observed incision in unconfined reaches upstream of Nugent’s Corner from 2005–06 to 2013. This mismatch indicates that understanding how changes in sediment-supply influence those unconfined reaches remains a key uncertainty for predicting future channel change. Continuous turbidity monitoring integrated with suspended sediment and limited bedload sampling were used to calculate annual sediment loads at five sites in the basin. The sediment load in the lower river at Ferndale ranged from 0.78 to 1.17 million tons per year and averaged 0.97 million tons per year for WYs 2012–17. Suspended sediment made up 93 percent of the load, and bedload made up 7 percent. Most of the fine sediment load of the lower river is supplied from headwaters of the North, Middle, and South Fork Nooksack basins, with relatively little net increase in fine sediment loads in the lower mainstem basin. The three forks supply approximately equal proportions of the lower-river fine sediment load. However, the glacially sourced North and Middle Fork Nooksack basins carry a notably sandier suspended-sediment load than the South Fork Nooksack. A comparison of monthly streamflow and precipitation trends since 1981 indicate statistically significant increases in total spring precipitation and the number of spring days with measurable precipitation in much of the basin, as well as increases in mean spring river stage near Ferndale. Since no trends in mean spring discharge are observed, the trends in river stage are attributed primarily to observed changes in bed elevation. Changes in bed elevation and precipitation may then both have plausibly impacted field drainage in the lower river below Ferndale.

Washington↗

USGS2019

Downstream‐propagating channel responses to decadal‐scale climate variability in a glaciated river basin

Regional climate is an important control on the rate of coarse sediment mobilization and transport in alpine river systems. Changes in climate are then expected to cause a cascade of geomorphic responses, including adjustments in downstream channel morphology. However, the mechanics and sensitivity of channel response to short‐term climate variability remain poorly documented. In the Nooksack River, which drains a glaciated stratovolcano in Washington State, bed elevation changes were inferred from shifting stage–discharge relations at seven USGS stream gages. Decadal‐scale elevation trends at most sites can be explained as a downstream‐propagating channel response to regional climate variability, where periods of persistent warm, dry [cool, wet] conditions corresponded to periods of aggradation [incision]. The channel elevation response propagated downstream at a rate of one to four kilometers per year; propagation rate scaled closely with channel slope. Historical trends in glacier extent and flood intensity both show some potential to explain climate–sediment linkages, though assessing causation is complicated by the shared climate signal in both records. Results show the influence of the Pacific Decadal Oscillation, with relatively high coarse sediment yields prior to 1950 and since 1980, and notably lower sediment yields from 1950 to 1980. Measured sediment yields from nearby glaciated basins corroborate this history, suggesting a regional coherence to these climate–sediment linkages. These results document consistent relations between climate, sediment supply and downstream channel response at the basin‐scale, with channel responses propagating downstream over periods of decades with little apparent attenuation.

Washington↗

USGS2019

Effects of urban multi-stressors on three stream biotic assemblages

During 2014, the U.S. Geological Survey (USGS) National Water-Quality Assessment(NAWQA) project assessed stream quality in 75 streams across an urban disturbance gradient within the Piedmont ecoregion of southeastern United States. Our objectives were to identify primary instream stressors affecting algal, macroinvertebrate and fish assemblages in wadeable streams. Biotic communities were surveyed once at each site, and various instream stressors were measured during a 4-week index period preceding the ecological sampling. The measured stressors included nutrients; contaminants in water, passive samplers, and sediment; instream habitat; and flow variability. All nine boosted regression tree models – three for each of algae, invertebrates, and fish – had cross-validation R 2 (CV R 2 ) values of 0.41 or above, and an invertebrate model had the highest CV R 2 of 0.65. At least one contaminant metric was important in every model, and minimum daytime dissolved oxygen (DO), nutrients, and flow alteration were important explanatory variables in many of the models. Physical habitat metrics such as sediment substrate were only moderately important. Flow alteration metrics were useful factors in eight of the nine models. Total phosphorus, acetanilide herbicides and flow (time since last peak) were important in all three algal models, whereas insecticide metrics (especially those representing fipronil and imidacloprid) were dominant in the invertebrate models. DO values below approximately 7 mg/L corresponded to a strong decrease in sensitive taxa or an increase in tolerant taxa. DO also showed strong interactions with other variables, particularly contaminants and sediment, where the combined effect of low DO and elevated contaminants increased the impact on the biota more than each variable individually. Contaminants and flow alteration were strongly correlated to urbanization, indicating the importance of urbanization to ecological stream condition in the region.

Science of the Total Environment↗

USGS2018

Effect of river confinement on depth and spatial extent of bed disturbance affecting salmon redds

Human impacts on rivers threaten the natural function of riverine ecosystems. This paper assesses how channel confinement affects the scour depth and spatial extent of bed disturbance and discusses the implications of these results for salmon-redd disturbance in gravel-bedded rivers. Two-dimensional hydrodynamic models of relatively confined and unconfined reaches of the Cedar River in Washington State, USA, were constructed with surveyed bathymetry and available airborne lidar data then calibrated and verified with field observations of water-surface elevation and streamflow velocity. Simulations showed greater water depths and velocities in the confined reach and greater areas of low-velocity inundation in the unconfined reach at high flows. Data on previously published scour depth of bed disturbance during high flows were compared to simulated bed shear stress to construct a probabilistic logistic-regression model of bed disturbance, which was applied to spatial patterns of simulated bed shear stress to quantify the extent of likely bed disturbance to the burial depth of sockeye and Chinook salmon redds. The disturbance depth was not observed to differ between confined and unconfined reaches; however, results indicated the spatial extent of disturbance to a given depth in the confined reach was roughly twice as large as in the unconfined reach.

Washington↗

USGS2018

Assessing the influence of multiple stressors on stream diatom metrics in the upper Midwest, USA

Water resource managers face increasing challenges in identifying what physical and chemical stressors are responsible for the alteration of biological conditions in streams. The objective of this study was to assess the comparative influence of multiple stressors on benthic diatoms at 98 sites that spanned a range of stressors in an agriculturally dominated region in the upper Midwest, USA. The primary stressors of interest included: nutrients, herbicides and fungicides, sediment, and streamflow; although the influence of physical habitat was incorporated in the assessment. Boosted Regression Tree was used to examine both the sensitivity of various diatom metrics and the relative importance of the primary stressors. Percent Sensitive Taxa, percent Highly Motile Taxa, and percent High Phosphorus Taxa had the strongest response to stressors. Habitat and total phosphorous were the most common discriminators of diatom metrics, with herbicides as secondary factors. A Classification and Regression Tree (CART) model was used to examine conditional relations among stressors and indicated that fine-grain streams had a lower percentage of Sensitive Taxa than coarse-grain streams, with Sensitive Taxa decreasing further with increased water temperature (>30 °C) and triazine concentrations (>1500 ng/L). In contrast, streams dominated by coarse-grain substrate contained a higher percentage of Sensitive Taxa, with relative abundance increasing with lower water temperatures (<29 °C) and shallower water depth (<0.3 m). Quantile regression indicated that maximum water temperature appears to be a major limiting factor in Midwest streams; whereas both total phosphorus and percent fines showed a slight subsidy-stress response. While using benthic algae for assessing stream quality can be challenging, field-based studies can elucidate stressor effects and interactions when the response variables are appropriate, sufficient stressor resolution is achieved, and the number and type of sites represent a gradient of stressor conditions and at least a quasi-factorial design.

Ecological Indicators↗

USGS2018

Factors influencing fine sediment on stream beds in the Midwestern United States

Fine sediment (particles <2 mm in diameter) in stream beds has wide-ranging effects on hydraulics, geomorphology, and ecology and is a primary focus for stream quality management in many regions. We identify reach- and basin-scale factors associated with fine sediment in the beds of 83 stream reaches in the Midwestern United States using recursive partitioning of sand-bed and gravel-bed streams and a generalized linear model for the fraction of a stream bed covered by fine sediment. A water-surface gradient of 0.00075 is the best single determinant (80% correct classification) distinguishing sand-bed streams (lower gradient) from gravel-bed streams (higher gradient). In the higher gradient category, sand-bed streams generally had more variable monthly precipitation than gravel-bed streams. The fractional response model indicated that the proportion of a stream bed composed of fine sediment is related to high sediment supply and low transport capacity but also high gravel transport capacity. This result is consistent with both theory and observations that bed material can be transported indiscriminately with respect to particle size under high shear stress, which will drive the particle size distribution of bed material toward the distribution of supply. Management of fine sediment in Midwestern streams has been approached largely by focusing on sediment supply, which may be immutable in some places due to the landscape position or glacial history. Retention of coarse sediment is an alternative management approach to reduce the fraction of fine sediment in the beds of some Midwestern streams.

Journal of Environmental Quality↗

USGS2017

Characterizing aquatic habitats for long‐term monitoring of a fourth‐order, regulated river in the Pacific Northwest, USA

A pragmatic approach to the long‐term monitoring of rivers leverages available information with targeted field investigations to address key uncertainties relevant to management decisions. An over‐arching management issue for many rivers is how reservoir operation affects the amount and location of in‐channel sediment and the resulting distribution of aquatic habitats. We integrate remotely acquired and field‐survey morphologic data for the Cedar River, Washington, to constitute the current status of aquatic habitats and benchmarks for long‐term monitoring that will inform streamflow management. Four key habitats (river edge, side channels, riffles, and pools) are feasible to monitor with high‐resolution aerial imagery, a longitudinal profile of the river, and a side channel inventory, but full characterization of the functional differences within these habitats requires additional information. Habitat use information such as redd surveys will continue to be important for long‐term monitoring where it cannot be inferred reliably from physical habitat characteristics.

Washington↗

USGS2017

Flood runoff in relation to water vapor transport by atmospheric rivers over the western United States, 1949–2015

Atmospheric rivers (ARs) have a significant role in generating floods across the western United States. We analyze daily streamflow for water years 1949 to 2015 from 5,477 gages in relation to water vapor transport by ARs using a 6 h chronology resolved to 2.5° latitude and longitude. The probability that an AR will generate 50 mm/d of runoff in a river on the Pacific Coast increases from 12% when daily mean water vapor transport, DVT , is greater than 300 kg m −1 s −1 to 54% when DVT > 600 kg m −1 s −1 . Extreme runoff, represented by the 99th quantile of daily values, doubles from 80 mm/d at DVT = 300 kg m −1 s −1 to 160 mm/d at DVT = 500 kg m −1 s −1 . Forecasts and predictions of water vapor transport by atmospheric rivers can support flood risk assessment and estimates of future flood frequencies and magnitude in the western United States.

Geophysical Research Letters↗

USGS2017

Hydrologic metrics for status-and-trends monitoring in urban and urbanizing watersheds

Local governmental agencies are increasingly undertaking potentially costly “status-and-trends” monitoring to evaluate the effectiveness of stormwater control measures and land-use planning strategies, or to satisfy regulatory requirements. Little guidance is presently available for such efforts, and so we have explored the application, interpretation, and temporal limitations of well-established hydrologic metrics of runoff changes from urbanization, making use of an unusually long-duration, high-quality data set from the Pacific Northwest (USA) with direct applicability to urban and urbanizing watersheds. Three metrics previously identified for their utility in identifying hydrologic conditions with biological importance that respond to watershed urbanization—T Qmean (the fraction of time that flows exceed the mean annual discharge), the Richards-Baker Index (characterizing flashiness relative to the mean discharge), and the annual tally of wet-season day-to-day flow reversals (the total number of days that reverse the prior days’ increasing or decreasing trend)—are all successful in stratifying watersheds across a range of urbanization, as measured by total contributing area of urban development. All metrics respond with statistical significance to multi-decadal trends in urbanization, but none detect trends in watershed-scale urbanization over the course of a single decade. This suggests a minimum period over which dependable trends in hydrologic alteration (or improvement) can be detected with confidence. The metrics also prove less well suited to urbanizing watersheds in a semi-arid climate, with only flow reversals showing a response consistent with prior findings from more humid regions. We also explore the use of stage as a surrogate for discharge in calculating these metrics, recognizing potentially significant agency cost savings in data collection with minimal loss of information. This approach is feasible but cannot be implemented under current data-reporting practices, requiring measurement of water-depth values and preservation of the full precision of the original recorded data. With these caveats, however, hydrologic metrics based on stage should prove as or more useful, at least in the context of status-and-trends monitoring, as those based on subsequent calculations of discharge.

Hydrological Processes↗

USGS2017

Streambed scour of salmon spawning habitat in a regulated river influenced by management of peak discharge

In the Pacific Northwest of the United States, salmon eggs incubating within streambed gravels are susceptible to scour during floods. The threat to egg-to-fry survival by streambed scour is mitigated, in part, by the adaptation of salmon to bury their eggs below the typical depth of scour. In regulated rivers globally, we suggest that water managers consider the effect of dam operations on scour and its impacts on species dependent on benthic habitats. We instrumented salmon-spawning habitat with accelerometer scour monitors (ASMs) at 73 locations in 11 reaches of the Cedar River in western Washington State of the United States from Autumn 2013 through the Spring of 2014. The timing of scour was related to the discharge measured at a nearby gage and compared to previously published ASM data at 26 locations in two reaches of the Cedar River collected between Autumn 2010 and Spring 2011. Thirteen percent of the recovered ASMs recorded scour during a peak-discharge event in March 2014 (2-to 3-year recurrence interval) compared to 71% of the recovered ASMs during a higher peak-discharge event in January 2011 (10-year recurrence interval). Of the 23 locations where ASMs recorded scour during the 2011 and 2014 deployments, 35% had scour when the discharge was ≤87.3 m 3 /s (3,082 ft 3 /s) (2-year recurrence interval discharge) with 13% recording scour at or below the 62.3 m 3 /s (2,200 ft 3 /s) operational threshold for peak-discharge management during the incubation of salmon eggs. Scour to the depth of salmon egg pockets was limited during peak discharges with frequent (1.25-year or less) recurrence intervals, which managers can regulate through dam operations on the Cedar River. Pairing novel measurements of the timing of streambed scour with discharge data allows the development of peak-discharge management strategies that protect salmon eggs incubating within streambed gravels during floods.

Washington↗