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USGS1987

Results of a workshop concerning ecological zonation in bottomland hardwoods

Under Section 404 of the Clean Water Act, the U.S. Environmental Protection Agency (EPA) has regulatory responsibilities concerning the discharge of dredged or fill material into the Nation's waters. In addition to its advisory role in the U.S. Army Corps of Engineers' permit program, EPA has a number of specific authorities, including formulation of the Section 404(b)(1) Guidelines, use of Section 404(c) to prohibit disposal at particular sites, and enforcement actions for unauthorized discharges. A number of recent court cases focus on the geographic scope of Section 404 jurisdiction in potential bottomland hardwood (BLH) wetlands and the nature of landclearing activities in these areas that require a permit under Section 404. Accordingly, EPA needs to establish the scientific basis for implementing its responsibilities under Section 404 in bottomland hardwoods. EPA is approaching this task through a series of workshops designed to provide current scientific information on bottomland hardwoods and to organize that information in a manner pertinent to key questions, including the following. What are the characteristics of bottomland hardwoods (in terms of hydrology, soils, vegetation, fish, wildlife, agricultural potential, and the like) and how can the functions (e.g., flood storage, water quality maintenance, detrital export) that they perform best be quantified? How do perturbations like landclearing, levee construction, and drainage impact the functions that bottomland hardwoods perform and how can these effects best be quantified? And finally, how significant are the impacts and how is their significance likely to change under various management scenarios? The first workshop in this series was held December 3-7, 1984, in St. Francisville, Louisiana. The workshop was attended by over 40 scientists and regulators (see ACKNOWLEDGMENTS section) and facilitated by the editors of this report under an Interagency Agreement between EPA and the U.S. Fish and Wildlife Service. The general objective of the workshop was to examine ways in which the structure and function of BLH ecosystems can be characterized and, in particular, to investigate the utility of a conceptual framework developed at a workshop held in Lake Lanier, Georgia, in 1980. In this framework, the transition from aquatic habitats to upland habitats through a BLH ecosystem is divided into six zones based on concomitant variation in the soil moisture regime and associated vegetation (Table 1). The zonation concept is of particular interest to EPA from at least two perspectives. The first is simply as a framework for organizing information. If the zones are discernible in the field, have recognizable characteristics, and perform identifiable functions, they might form a useful basis for tasks such as assessing the impacts of a particular site-specific activity. The second is the potential utility of the zonation concept in identifying the wetland portions of BLH communities. If the zones can be recognized in the field, and if one or more of them can be shown consistently to have wetland characteristics (i.e., perform functions, such as detrital export, often attributed to wetlands), while others do not, then the zones might have utility in identifying areas that fall under the jurisdiction of Section 404. The workshop itself was divided into two parts. The first was a series of papers in which authors described current research and data-synthesis activities in the context of the zonation concept. The second was a series of six workgroups in which participants discussed the zonation concept from the perspective of hydrology, soils, vegetation, fish, wildlife, and ecosystem processes. This report is a compilation of the written material from those workgroups, much of which was produced at the workshop. The formal papers presented in the first part of the workshop have been distributed to participants under separate cover, but are referenced in this report by citations such as: (Jones, workshop presentation).

Report↗

USGS2023

Benchmarking high-resolution hydrologic model performance of long-term retrospective streamflow simulations in the contiguous United States

Because use of high-resolution hydrologic models is becoming more widespread and estimates are made over large domains, there is a pressing need for systematic evaluation of their performance. Most evaluation efforts to date have focused on smaller basins that have been relatively undisturbed by human activity, but there is also a need to benchmark model performance more comprehensively, including basins impacted by human activities. This study benchmarks the long-term performance of two process-oriented, high-resolution, continental-scale hydrologic models that have been developed to assess water availability and risks in the United States (US): the National Water Model v2.1 application of WRF-Hydro (NWMv2.1) and the National Hydrologic Model v1.0 application of the Precipitation–Runoff Modeling System (NHMv1.0). The evaluation is performed on 5390 streamflow gages from 1983 to 2016 ( ∼ 33 years) at a daily time step, including both natural and human-impacted catchments, representing one of the most comprehensive evaluations over the contiguous US. Using the Kling–Gupta efficiency as the main evaluation metric, the models are compared against a climatological benchmark that accounts for seasonality. Overall, the model applications show similar performance, with better performance in minimally disturbed basins than in those impacted by human activities. Relative regional differences are also similar: the best performance is found in the Northeast, followed by the Southeast, and generally worse performance is found in the Central and West areas. For both models, about 80 % of the sites exceed the seasonal climatological benchmark. Basins that do not exceed the climatological benchmark are further scrutinized to provide model diagnostics for each application. Using the underperforming subset, both models tend to overestimate streamflow volumes in the West, which could be attributed to not accounting for human activities, such as active management. Both models underestimate flow variability, especially the highest flows; this was more pronounced for NHMv1.0. Low flows tended to be overestimated by NWMv2.1, whereas there were both over and underestimations for NHMv1.0, but they were less severe. Although this study focused on model diagnostics for underperforming sites based on the seasonal climatological benchmark, metrics for all sites for both model applications are openly available online.

Hydrology and Earth System Sciences↗

USGS1990

Channel-changing processes on the Santa Cruz River, Pima County, Arizona, 1936-86

Lateral channel change on the mainly ephemeral Santa Cruz River, Pima County, Arizona, causes damage and has spawned costly efforts to control bank erosion. Aerial photographs, historical data, and field observations are used to document the history of channel change since 1936. Variability in the nature and degree of channel change over time and space is shown. Three major channel change processes are: (1) migration by bank erosion during meander migration or initiation; (2) avulsion by overbank flooding and flood plain incision; (3) widening by erosion of low, cohesionless banks during floods and arroyo widening by undercutting and mass wasting of deeply incised vertical walls. The first process generally is a product of low to moderate flows or waning high flows; the others result mainly from higher flows, though sensitive arroyo walls may erode during relatively low flows. Channel morphology, bank resistance, and hydrology are factors determining the dominant channel-changing process on a particular reach of the river. Present river morphology reflects high flows since the 1960's.

Conference Paper↗

USGS2004

Quality assurance report - Loch Vale watershed, 1999-2002

The National Park Service initiated the Loch Vale Watershed (LVWS) project in 1980 with funding from the Aquatic Effects Research Program of the National Acid Precipitation Assessment Program. Long-term ecological research and monitoring address watershed-scale ecosystem processes, particularly as they respond to atmospheric deposition and climate variability. Monitoring of meteorological, hydrologic, precipitation chemistry, and surface water quality parameters enable us to use long-term trends to distinguish natural from human-caused disturbances. Research into snow distribution, hydrologic flowpaths, vegetation responses to N deposition, isotopic transformations of N by forest and soil processes, trace metals, and aquatic ecological responses to disturbance enable us to understand processes that influence high elevation ecosystems.

Colorado↗

USGS2022

Assessing runoff and erosion on woodland-encroached sagebrush steppe using the Rangeland Hydrology and Erosion Model

The transition of sagebrush-dominated ( Artemisia spp.) shrublands to pinyon ( Pinus spp.) and juniper ( Juniperus spp.) woodlands markedly alters resource-conserving vegetation structure typical of these landscapes. Land managers and scientists in the western United States need knowledge and predictive tools for assessment and effective targeting of tree-removal treatments to conserve or restore sagebrush vegetation and associated hydrologic function. This study developed modeling approaches to quantify the hydrologic vulnerability and erosion potential of sagebrush rangelands in the later stages of woodland encroachment and in response to commonly applied tree-removal treatments. Using experimental data from multiple sites in the Great Basin Region, USA, and process-based knowledge from decade-long vegetation and rainfall simulation studies at those sites, we (1) assessed the capability of the Rangeland Hydrology and Erosion Model (RHEM) to accurately predict patch-scale (12 m 2 ) measured runoff and erosion from tree canopy and intercanopy hydrologic functional units in untreated and burned woodlands 9 years postfire, and (2) developed and evaluated multiple RHEM approaches/frameworks to model aggregated effects of tree canopy and intercanopy areas on patch- and hillslope-scale (50 m length) runoff and erosion processes in untreated and treated (burned, cut, and masticated) woodlands. The RHEM accurately predicted measured runoff and sediment yield from patch-scale rainfall simulations as partitioned on untreated and treated tree canopy and intercanopy areas and effectively parameterized the dominant controls on runoff and erosion process in woodlands. With few exceptions, evaluated hillslope-scale RHEM frameworks similarly predicted reduced hydrologic vulnerability and erosion potential for conditions 9 years following tree removal by burning, cutting, and mastication treatments. Regressions of RHEM-predicted hillslope runoff, sediment, and hydraulic/erosion parameters with bare ground and ground cover attributes indicate all RHEM frameworks effectively represented the dominant controls on hydrologic and erosion processes for rangelands and woodlands. The results provide RHEM frameworks and recommendations for assessing hydrologic vulnerability and erosion potential on woodland-encroached sites and predicting the effectiveness of tree removal to reestablish a water and soil resource-conserving vegetation structure on sagebrush rangelands. We anticipate our RHEM or similar modeling approaches may be applicable to analogous water-limited landscapes elsewhere subject to woody plant encroachment.

Nevada, Utah↗

USGS2022

HydroBench: Jupyter supported reproducible hydrological model benchmarking and diagnostic tool

Evaluating whether hydrological models are right for the right reasons demands reproducible model benchmarking and diagnostics that evaluate not just statistical predictive model performance but also internal processes. Such model benchmarking and diagnostic efforts will benefit from standardized methods and ready-to-use toolkits. Using the Jupyter platform, this work presents HydroBench, a model-agnostic benchmarking tool consisting of three sets of metrics: 1) common statistical predictive measures, 2) hydrological signature-based process metrics, including a new time-linked flow duration curve and 3) information-theoretic diagnostics that measure the flow of information among model variables. As a test case, HydroBench was applied to compare two model products (calibrated and uncalibrated) of the National Hydrologic Model - Precipitation Runoff Modeling System (NHM-PRMS) at the Cedar River watershed, WA, United States. Although the uncalibrated model has the highest predictive performance, particularly for high flows, the signature-based diagnostics showed that the model overestimates low flows and poorly represents the recession processes. Elucidating why low flows may have been overestimated, the information-theoretic diagnostics indicated a higher flow of information from precipitation to snowmelt to streamflow in the uncalibrated model compared to the calibrated model, where information flowed more directly from precipitation to streamflow. This test case demonstrated the capability of HydroBench in process diagnostics and model predictive and functional performance evaluations, along with their tradeoffs. Having such a model benchmarking tool not only provides modelers with a comprehensive model evaluation system but also provides an open-source tool that can further be developed by the hydrological community.

Frontiers in Earth Sciences↗

USGS2012

Directional connectivity in hydrology and ecology

Quantifying hydrologic and ecological connectivity has contributed to understanding transport and dispersal processes and assessing ecosystem degradation or restoration potential. However, there has been little synthesis across disciplines. The growing field of ecohydrology and recent recognition that loss of hydrologic connectivity is leading to a global decline in biodiversity underscore the need for a unified connectivity concept. One outstanding need is a way to quantify directional connectivity that is consistent, robust to variations in sampling, and transferable across scales or environmental settings. Understanding connectivity in a particular direction (e.g., streamwise, along or across gradient, between sources and sinks, along cardinal directions) provides critical information for predicting contaminant transport, planning conservation corridor design, and understanding how landscapes or hydroscapes respond to directional forces like wind or water flow. Here we synthesize progress on quantifying connectivity and develop a new strategy for evaluating directional connectivity that benefits from use of graph theory in ecology and percolation theory in hydrology. The directional connectivity index (DCI) is a graph-theory based, multiscale metric that is generalizable to a range of different structural and functional connectivity applications. It exhibits minimal sensitivity to image rotation or resolution within a given range and responds intuitively to progressive, unidirectional change. Further, it is linearly related to the integral connectivity scale length—a metric common in hydrology that correlates well with actual fluxes—but is less computationally challenging and more readily comparable across different landscapes. Connectivity-orientation curves (i.e., directional connectivity computed over a range of headings) provide a quantitative, information-dense representation of environmental structure that can be used for comparison or detection of subtle differences in the physical-biological feedbacks driving pattern formation. Case-study application of the DCI to the Everglades in south Florida revealed that loss of directional hydrologic connectivity occurs more rapidly and is a more sensitive indicator of declining ecosystem function than other metrics (e.g., habitat area) used previously. Here and elsewhere, directional connectivity can provide insight into landscape drivers and processes, act as an early-warning indicator of environmental degradation, and serve as a planning tool or performance measure for conservation and restoration efforts.

Ecological Applications↗

USGS2012

Crowdsourcing to Acquire Hydrologic Data and Engage Citizen Scientists: CrowdHydrology

Spatially and temporally distributed measurements of processes, such as baseflow at the watershed scale, come at substantial equipment and personnel cost. Research presented here focuses on building a crowdsourced database of inexpensive distributed stream stage measurements. Signs on staff gauges encourage citizen scientists to voluntarily send hydrologic measurements (e.g., stream stage) via text message to a server that stores and displays the data on the web. Based on the crowdsourced stream stage, we evaluate the accuracy of citizen scientist measurements and measurement approach. The results show that crowdsourced data collection is a supplemental method for collecting hydrologic data and a promising method of public engagement.

Ground Water↗

USGS2005

Effective discharge analysis of ecological processes in streams

Discharge is a master variable that controls many processes in stream ecosystems. However, there is uncertainty of which discharges are most important for driving particular ecological processes and thus how flow regime may influence entire stream ecosystems. Here the analytical method of effective discharge from fluvial geomorphology is used to analyze the interaction between frequency and magnitude of discharge events that drive organic matter transport, algal growth, nutrient retention, macroinvertebrate disturbance, and habitat availability. We quantify the ecological effective discharge using a synthesis of previously published studies and modeling from a range of study sites. An analytical expression is then developed for a particular case of ecological effective discharge and is used to explore how effective discharge varies within variable hydrologic regimes. Our results suggest that a range of discharges is important for different ecological processes in an individual stream. Discharges are not equally important; instead, effective discharge values exist that correspond to near modal flows and moderate floods for the variable sets examined. We suggest four types of ecological response to discharge variability: discharge as a transport mechanism, regulator of habitat, process modulator, and disturbance. Effective discharge analysis will perform well when there is a unique, essentially instantaneous relationship between discharge and an ecological process and poorly when effects of discharge are delayed or confounded by legacy effects. Despite some limitations the conceptual and analytical utility of the effective discharge analysis allows exploring general questions about how hydrologic variability influences various ecological processes in streams.

Water Resources Research↗

USGS2011

Predicting lake trophic state by relating Secchi-disk transparency measurements to Landsat-satellite imagery for Michigan inland lakes, 2003-05 and 2007-08

Inland lakes are an important economic and environmental resource for Michigan. The U.S. Geological Survey and the Michigan Department of Natural Resources and Environment have been cooperatively monitoring the quality of selected lakes in Michigan through the Lake Water Quality Assessment program. Sampling for this program began in 2001; by 2010, 730 of Michigan’s 11,000 inland lakes are expected to have been sampled once. Volunteers coordinated by the Michigan Department of Natural Resources and Environment began sampling lakes in 1974 and continue to sample (in 2010) approximately 250 inland lakes each year through the Michigan Cooperative Lakes Monitoring Program. Despite these sampling efforts, it still is impossible to physically collect measurements for all Michigan inland lakes; however, Landsat-satellite imagery has been used successfully in Minnesota, Wisconsin, Michigan, and elsewhere to predict the trophic state of unsampled inland lakes greater than 20 acres by producing regression equations relating in-place Secchi-disk measurements to Landsat bands. This study tested three alternatives to methods previously used in Michigan to improve results for predicted statewide Trophic State Index (TSI) computed from Secchi-disk transparency (TSI (SDT)). The alternative methods were used on 14 Landsat-satellite scenes with statewide TSI (SDT) for two time periods (2003– 05 and 2007–08). Specifically, the methods were (1) satellitedata processing techniques to remove areas affected by clouds, cloud shadows, haze, shoreline, and dense vegetation for inland lakes greater than 20 acres in Michigan; (2) comparison of the previous method for producing a single open-water predicted TSI (SDT) value (which was based on an area of interest (AOI) and lake-average approach) to an alternative Gethist method for identifying open-water areas in inland lakes (which follows the initial satellite-data processing and targets the darkest pixels, representing the deepest water, before regression equations are created); and (3) checking to see whether the predicted TSI (SDT) values compared well between two regression equations, one previously used in Michigan and an alternative equation from the hydrologic literature. The combination of improved satellite-data processing techniques and the Gethist method to identify open-water areas in inland lakes during 2003–05 and 2007–08 provided a stronger relation and statistical significance between predicted TSI (SDT) and measured TSI than did the AOI lake-average method; differences in results for the two methods were significant at the 99-percent confidence level. With regard to the comparison of the regression equations, there were no statistically significant differences at the 95-percent confidence level between results from the two equations. The previously used equation, in combination with the Gethist method, yielded coefficient of determination (R 2 ) values of 0.71 and 0.77 for the periods 2003–05 and 2007–08, respectively. The alternative equation, in combination with the Gethist method, yielded R 2 values of 0.74 and 0.75 for 2003–05 and 2007–08, respectively. Predicted TSI (SDT) and measured TSI (SDT) values for lakes used in the regression equations compared well, with R 2 values of 0.95 and 0.96 for predicted TSI (SDT) for 2003–05 and 2007–08, respectively. The R 2 values for statewide predicted TSI (SDT) for all inland lakes with available open-water areas for 2003–05 and 2007–08 were 0.91 and 0.93, respectively. Although the two equations predicted similar trophic-state classes, the alternative equation is planned to be used for future prediction of TSI (SDT) values for Michigan inland lakes, to promote consistency in comparing predicted values between States and for potential use in trend analysis.

Michigan↗

USGS2014

Analysis of projected water availability with current basin management plan, Pajaro Valley, California

The projection and analysis of the Pajaro Valley Hydrologic Model (PVHM) 34 years into the future using MODFLOW with the Farm Process (MF-FMP) facilitates assessment of potential future water availability. The projection is facilitated by the integrated hydrologic model, MF-FMP that fully couples the simulation of the use and movement of water from precipitation, streamflow, runoff, groundwater flow, and consumption by natural and agricultural vegetation throughout the hydrologic system at all times. MF-FMP allows for more complete analysis of conjunctive-use water-resource systems than previously possible with MODFLOW by combining relevant aspects of the landscape with the groundwater and surface-water components. This analysis is accomplished using distributed cell-by-cell supply-constrained and demand-driven components across the landscape within “water-balance subregions” (WBS) comprised of one or more model cells that can represent a single farm, a group of farms, watersheds, or other hydrologic or geopolitical entities. Analysis of conjunctive use would be difficult without embedding the fully coupled supply-and-demand into a fully coupled simulation, and are difficult to estimate a priori. The analysis of projected supply and demand for the Pajaro Valley indicate that the current water supply facilities constructed to provide alternative local sources of supplemental water to replace coastal groundwater pumpage, but may not completely eliminate additional overdraft. The simulation of the coastal distribution system (CDS) replicates: 20 miles of conveyance pipeline, managed aquifer recharge and recovery (MARR) system that captures local runoff, and recycled-water treatment facility (RWF) from urban wastewater, along with the use of other blend water supplies, provide partial relief and substitution for coastal pumpage (aka in-lieu recharge). The effects of these Basin Management Plan (BMP) projects were analyzed subject to historical climate variations and assumptions of 2009 urban water demand and land use. Water supplied directly from precipitation, and indirectly from reuse, captured local runoff, and groundwater is necessary but inadequate to satisfy agricultural demand without coastal and regional storage depletion that facilitates seawater intrusion. These facilities reduce potential seawater intrusion by about 45% with groundwater levels in the four regions served by the CDS projected to recover to levels a few feet above sea level. The projected recoveries are not high enough to prevent additional seawater intrusion during dry-year periods or in the deeper aquifers where pumpage is greater. While these facilities could reduce coastal pumpage by about 55% of the historical 2000–2009 pumpage for these regions, and some of the water is delivered in excess of demand, other coastal regions continue to create demands on coastal pumpage that will need to be replaced to reduce seawater intrusion. In addition, inland urban and agricultural demands continue to sustain water levels below sea level causing regional landward gradients that also drive seawater intrusion. Seawater intrusion is reduced by about 45% but it supplies about 55% of the recovery of groundwater levels in the coastal regions served by the CDS. If economically feasible, water from summer agricultural runoff and tile-drain returnflows could be another potential local source of water that, if captured and reused, could offset the imbalance between supply and demand as well as reducing discharge of agricultural runoff into the National Marine Sanctuary of Monterey Bay. A BMP update (2012) identifies projects and programs that will fund a conservation program and will provide additional, alternative water sources to reduce or replace coastal and inland pumpage, and to replenish the aquifers with managed aquifer recharge in an inland portion of the Pajaro Valley.

California↗

USGS2024

Physics to fish—Understanding the factors that create and sustain native fish habitat in the San Francisco Estuary

Executive Summary The Bureau of Reclamation (Reclamation) operates the Central Valley Project (CVP), one of the nation’s largest water projects. Reclamation has an ongoing need to improve the scientific basis for adaptive management of the CVP and, by extension, joint operations with California’s State Water Project. The U.S. Geological Survey (USGS) works cooperatively with the Bureau of Reclamation to provide scientific support for the management of Reclamation’s CVP project. Major habitat restoration efforts and a new water-diversion point are planned to benefit delta smelt ( Hypomesus transpacificus ) and other species of concern while ensuring the reliability of water supply. In addition, various flow actions and management activities have been identified as possible methods to increase populations of delta smelt and salmonid ( Oncorhynchus spp.) runs of concern. The overarching goal of this cooperative project was to provide Reclamation with the scientific information needed to evaluate the efficacy of ongoing and future adaptive management actions and to improve the scientific basis for more flexible CVP operations that would achieve water-supply reliability and fish protection. The research and monitoring described in this report comprises the period 2015–19 and focuses on management issues related to native fish species of concern, especially delta smelt. Conserving the delta smelt population while providing a reliable water supply is a primary management and policy issue in California. Our approach for this cooperative project is based on the “physics to fish” concept, the idea that high-quality habitat is generated and sustained by the interaction between physical processes and the landscape. These interactions create a template for chemical and biological processes that can change across a variety of spatial and temporal scales. Following this concept, this project (hereafter referred to as “the physics to fish project”) included monitoring and studies of water flows, sediments, water quality, and invertebrate and fish dynamics across a range of spatial and temporal scales and in regions relevant to resource managers tasked with managing water supplies and ecosystem health in the San Francisco Estuary. The intent of this approach was to document the habitat conditions, important processes, and interactions among them that create high-quality habitat for native fishes so that the likely effects of future management actions (for example, habitat restoration) can be objectively assessed at the local (site-specific), regional (within subregions of the estuary), and landscape (across the entire estuary and beyond) scales. Hydrodynamically, the upper estuary (landward of Carquinez Strait) is characterized by a fixed volume of tidally exchanged water (for example, tidal prism) that interacts with the existing channel network and bathymetry to create regions with differing hydrodynamics. Our results indicate that careful study of construction or reoperation of existing infrastructure to perform management actions can help (1) improve the accuracy of hydrodynamic models; (2) further understanding of ecological effects; and (3) enhance abilities to predict ecological outcomes. At the local scale, we developed a new concept called the Lagrangian to Eulerian (LE) ratio that can be used as a tool for understanding the importance of various hydrodynamic processes in specific channels or channel networks and for forecasting transport dynamics. Channels with LE ratios<1 in a channel network or in a dead-end slough are hydrodynamically able to develop an exchange zone between two parcels of water that may have different chemical and physical properties. In a dead-end channel, there is a landward region with long residence time (no-exchange zone) and a seaward region with short residence time (high-exchange zone) that are well mixed with seaward waters. At the transition (exchange zone) between the high and no-exchange regions, a gradient will form in water-quality constituents that differ in concentration between the landward and seaward waters. Turbidity affects fish habitat and has declined through time in the San Francisco Estuary. Average turbidity across the Sacramento–San Joaquin Delta (hereafter referred to as “the Delta”) is dependent on annual hydrology. In dry years, the region around Cache Slough (known regionally as the “Cache Slough Complex”) in the northern Delta is generally more turbid than Suisun Bay and the lower Sacramento River. When the Yolo By-Pass (known regionally as “Yolo Bypass”), a large flood bypass that runs parallel to the Sacramento River in the northern Delta, is not flooding and river flows are lower, sediment is usually transported into the Cache Slough Complex because flood tides dominate ebb tides, resulting in transport of suspended sediment from seaward areas of the upper estuary into the Cache Slough Complex. These hydrodynamic conditions also favor the formation of turbidity maximums (TMs) in the Cache Slough Complex. The TMs are areas of higher suspended-sediment concentration, providing higher-turbidity habitat favored by some fishes, including delta smelt, and they can also concentrate other constituents, including phytoplankton and organic carbon that can be important in food webs. Pelagic primary production by phytoplankton is the basis for Delta food webs supporting pelagic fishes such as delta smelt; however, phytoplankton abundance in the Delta has declined during recent decades. We examined how nutrients, hydrodynamics, and other factors affect phytoplankton blooms. Based on our results, we developed three new concepts of phytoplankton bloom formation in the Delta, each associated with a distinct set of hydrologic conditions. First, productivity cascades highlighted how local processes can contribute to phytoplankton blooms observed at the regional scale. Second, we observed phytoplankton blooms in the upper San Francisco Estuary that were associated with transport out of Yolo By-Pass (transport blooms). Third, we also documented a series of phytoplankton blooms that were in the confluence area at the landward edge of Suisun Bay. The conditions leading to creation of confluence phytoplankton blooms are not yet understood, but the confluence region connects the Cache Slough Complex with Suisun Marsh. Therefore, blooms in this area have the potential to spread to large areas of the Delta. At the landscape scale, the distribution of the invasive clams ( Potamocorbula amurensis and Corbicula fluminea , hereafter referred to as “ Corbicula ”) is driven by salinity. At smaller spatial scales, the distribution of either species is sensitive to multiple factors affecting survival and reproduction, complicating efforts to predict distribution and abundance without considering local-scale conditions across the area of interest. In the Cache Slough Complex, the area landward of the exchange zone in regions with LE ratio<1 were characterized by low abundances of Corbicula probably because recruits from seaward areas are not transported past the exchange zone and because there are no landward tributaries with adult Corbicula to provide an upstream source of recruits. Corbicula biomass was highest near or downstream from the exchange zone consistent with Corbicula grazing on phytoplankton produced in the exchange zone or transported from the no-exchange zone. The severity of Corbicula grazing could be reduced by manipulating the hydrodynamic characteristics of waterways; however, the beneficial and harmful effects on the organisms meant to benefit from increased phytoplankton production, including zooplankton and fish species of concern, should be thoroughly examined before manipulating hydrodynamic characteristics. The distribution of fishes at the landscape scale is generally driven by the position of the salinity field in the estuary. The physics to fish project compared distributions of fishes at Ryer Island, a tidal wetland in Suisun Bay and a region of variable salinity, with fish distributions at the Cache Slough Complex, a freshwater region. At Ryer Island, there was an absence of freshwater invasive species and an abundance of native species, such as Sacramento splittail ( Pogonichthys macrolepidotus ), tule perch ( Hysterocarpus traskii ), and Sacramento pikeminnow ( Ptychocheilus grandis ). The native species were almost exclusively captured in wetland and nearshore shallow-water habitat regardless of water-quality conditions. In the Cache Slough Complex, our regional scale objective was to elucidate how hydrodynamic-physical habitat interactions drive fish-community structure. Our studies showed that dendritic channel systems were better able to support native species, while intertidal habitats supported those species best able to exploit the transient character of the habitat. Habitats upstream from the exchange zone were especially important in supporting high numbers of native fishes relative to within or downstream from the exchange zone. Many of the native species were associated with tidal marsh in the no-exchange zone. More pelagic-oriented, mobile species, such as Striped Bass ( Morone saxatilis ), threadfin shad ( Dorosoma petenense ), and Sacramento pikeminnow, were more affected by water-quality conditions, such as turbidity. The physics to fish concept developed in this project provides a framework for designing individual projects and for considering the cumulative effects of multiple projects in a region, using the LE ratio as a guiding metric. The physics to fish concept may also provide a suitable framework for coordinating management actions. Tidal wetlands can function in several ways in the hydrodynamic framework. Relatively small tidal wetlands with short channel networks and with LE ratios>1 are not able to maintain a landward no-exchange zone or an exchange zone. This likely means that any contributions to pelagic food webs would be limited to resources derived from wetland vegetation, which can include dissolved and particulate organic matter (detritus) and populations of consumers that can increase in abundance based on those resources. The fate of the contributed production from these channels depends on the characteristics of the receiving waters seaward of the tidal wetland. If these channels join a large system such as Suisun Bay, then any contribution is likely to be rapidly dispersed in the larger volume; however, the channel junction might provide a focal point for consumers, such as fishes, to congregate and feed on material leaving the wetland on ebb tides before it is dispersed in the larger volume. Fishes might also access these resources by entering the wetland. The physics to fish project has established a foundation and several new concepts for understanding how habitat restoration can benefit native fish populations at the local and regional levels. Many of the ideas regarding habitat restoration and channel modifications outlined in this report could help guide management actions that could improve conditions for native fishes at little or no water cost beyond water already dedicated to other management actions. A complete list of products originating from this work is provided in appendix 1.

California↗

USGS2013

Insights and issues with simulating terrestrial DOC loading of Arctic river networks

Terrestrial carbon dynamics inﬂuence the contribution of dissolved organic carbon (DOC) to river networks in addition to hydrology. In this study, we use a biogeochemical process model to simulate the lateral transfer of DOC from land to the Arctic Ocean via riverine transport. We estimate that, over the 20th century, the pan-Arctic watershed has contributed, on average, 32 Tg C/yr of DOC to river networks emptying into the Arctic Ocean with most of the DOC coming from the extensive area of boreal deciduous needle-leaved forests and forested wetlands in Eurasian watersheds. We also estimate that the rate of terrestrial DOC loading has been increasing by 0.037 Tg C/yr2 over the 20th century primarily as a result of climate-induced increases in water yield. These increases have been offset by decreases in terrestrial DOC loading caused by wildﬁres. Other environmental factors (CO2 fertilization, ozone pollution, atmospheric nitrogen deposition, timber harvest, agriculture) are estimated to have relatively small effects on terrestrial DOC loading to Arctic rivers. The effects of the various environmental factors on terrestrial carbon dynamics have both offset and enhanced concurrent effects on hydrology to inﬂuence terrestrial DOC loading and may be changing the relative importance of terrestrial carbon dynamics on this carbon ﬂux. Improvements in simulating terrestrial DOC loading to pan-Arctic rivers in the future will require better information on the production and consumption of DOC within the soil proﬁle, the transfer of DOC from land to headwater streams, the spatial distribution of precipitation and its temporal trends, carbon dynamics of larch-dominated ecosystems in eastern Siberia, and the role of industrial organic efﬂuents on carbon budgets of rivers in western Russia.

Ecological Applications↗

USGS1970

Comparative hydrogeology: An example of its use

As a start toward needed classifications of hydrogeologic settings, a type of setting is described. The setting includes areas where soluble materials are exposed to considerable recharge from precipitation and where both the topographic relief and permeability are inappreciable. Typical areas of this setting are (1) the Black Belt of the Coastal Plain of Alabama and Mississippi, underlain by chalk of the Selma Group, and (2) a 25-sq-mi area near Harrisburg, Cabarrus County, North Carolina, underlain by gabbro in the Piedmont province. Hydrologic conditions that may be inferred and that are easily discernible from this type of setting include: excessive evapotranspiration, low water-table gradient, water table near land surface, thin soils, ground-water movement being almost inappreciable, and the zone of movement being almost limited to a thin zone that includes the contact between the soil and rock, inappreciable ground-water discharge to streams leading, in turn, to a low base flow in streams, low drainage density, and subsurface water relatively high in dissolved mineral matter. Evaluation of the hydrogeologic setting described leads inductively into the undeveloped field of comparative hydrology, which represents a quick useful means of discerning the significance of processes and principles in particular environments. The setting reveals the significance of solution by subsurface water in developing some plains. Comparative hydrology, using the described setting and typical karst settings as examples, allows an advanced analysis of some pertinent factors.

Alabama, Mississippi, North Carolina↗

USGS2019

Advances in quantifying streamflow variability across continental scales: 1. Identifying natural and anthropogenic controlling factors in the USA using a spatially explicit modeling method

Despite considerable progress in hydrological modeling, challenges remain in the interpretation and accurate transfer of hydrological information across watersheds and scales. In the conterminous United States (CONUS), these limitations are related to spatial inconsistencies and constraints in hydrological model structures, including a lack of spatially explicit process components (streams, reservoirs, and watershed development) and restricted estimation of model parameters across watersheds. Collectively, such limitations can impede identification of the causes of streamflow variations across the diversity of watershed sizes and land uses in the CONUS and contribute to model imprecision and spatial inconsistencies in prediction uncertainties. We addressed these concerns with a new approach, the first hybrid (statistical-mechanistic) SPARROW (SPAtially Referenced Regression On Watershed attributes) model of long-term mean annual streamflow, applied across diverse environmental settings of the CONUS. The hybrid model coupled previous catchment-scale (1 km) water balance predictions of “natural” unit area runoff, which are inclusive of major water cycling processes, with additional explanatory variables (e.g., soils, vegetation, land use, topography, water losses in streams, and reservoirs) that account for the effects of natural and cultural water supply and demand processes that operate over large spatial scales and explain streamflow variability across CONUS river basins. Accounting for these statistically unique effects, including a nonlinear surface area-dependent scaling of water loss in river networks, significantly improved the accuracy of mean streamflow predictions in CONUS basins. Our hybrid modeling approach provides new methods for transferring hydrological information to ungauged locations in river networks, especially those in larger and more culturally diverse CONUS watersheds.

conterminous United States↗

USGS2009

Using a coupled groundwater/surfacewater model to predict climate-change impacts to lakes in the Trout Lake watershed, Northern Wisconsin

A major focus of the U.S. Geological Survey’s Trout Lake Water, Energy, and Biogeochemical Budgets (WEBB) project is the development of a watershed model to allow predictions of hydrologic response to future conditions including land-use and climate change. The coupled groundwater/surface-water model GSFLOW was chosen for this purpose because it could easily incorporate an existing groundwater flow model and it provides for simulation of surface-water processes. The Trout Lake watershed in northern Wisconsin is underlain by a highly conductive outwash sand aquifer. In this area, streamflow is dominated by groundwater contributions; however, surface runoff occurs during intense rainfall periods and spring snowmelt. Surface runoff also occurs locally near stream/lake areas where the unsaturated zone is thin. A diverse data set, collected from 1992 to 2007 for the Trout Lake WEBB project and the co-located and NSF-funded North Temperate Lakes LTER project, includes snowpack, solar radiation, potential evapotranspiration, lake levels, groundwater levels, and streamflow. The timeseries processing software TSPROC (Doherty 2003) was used to distill the large time series data set to a smaller set of observations and summary statistics that captured the salient hydrologic information. The timeseries processing reduced hundreds of thousands of observations to less than 5,000. Model calibration included specific predictions for several lakes in the study area using the PEST parameter estimation suite of software (Doherty 2007). The calibrated model was used to simulate the hydrologic response in the study lakes to a variety of climate change scenarios culled from the IPCC Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon et al. 2007). Results from the simulations indicate climate change could result in substantial changes to the lake levels and components of the hydrologic budget of a seepage lake in the flow system. For a drainage lake lower in the flow system, the impacts of climate change are diminished.

Conference Paper↗

USGS2020

Hydrogeology and shallow groundwater quality in the tidal Anacostia River watershed, Washington, D.C.

Groundwater hydrology and geochemistry within the tidal Anacostia River watershed of Washington, D.C. are related to natural and human influences. The U.S. Geological Survey, in cooperation with the District Department of Energy & Environment, began investigating the hydrogeology and groundwater quality of the watershed in 2002. Lithologic coring, groundwater-level and tidal monitoring, and water-quality sampling have been conducted to improve understanding of the groundwater-flow system, geochemistry, water quality, and the likely interaction between groundwater and the tidal Anacostia River. The flow and interaction of shallow groundwater with the tidal Anacostia River and other area streams are affected by diversions, pumping, land reclamation, and other human activities in this highly urbanized watershed. The tidal Anacostia River watershed is underlain by a wedge of unconsolidated sediments that is part of the Atlantic Coastal Plain Physiographic Province. These sediments form a system of confined and unconfined aquifers. The coarse sediments of the Potomac Group sand-dominated lithofacies form the Patuxent aquifer. The Patuxent aquifer crops out and subcrops in the northwestern part of the study area, but is confined to the southeast by the overlying Potomac Group clay-dominated lithofacies. Overlying the Potomac Group is a series of interbedded sands and clays that form an unconfined surficial aquifer system. Regional correlation in the unconfined surficial aquifer system is complicated by local heterogeneity in aquifer sediments. Local perched and semi-confined conditions occur in some areas. Recharge of the confined Patuxent aquifer occurs primarily in the outcrop and subcrop area, although some recharge may also occur through overlying confining units. Recharge to the unconfined surficial aquifer system occurs through infiltration of precipitation and possible artificial recharge from structures such as underground water or sewer pipes. In the Patuxent aquifer, hydraulic gradients indicate downward movement in the outcrop area, whereas hydraulic heads beneath the Anacostia River are higher than land surface, indicating an upward hydraulic gradient. In the unconfined surficial aquifer system, groundwater generally flows from upland recharge areas towards discharge areas near the Anacostia River and its tributaries. Groundwater from the confined part of the Patuxent aquifer also may discharge to the Anacostia River in locations where the overlying clay-dominated lithofacies of the Potomac Group is absent as a result of past geologic and (or) alluvial processes. Geochemistry and groundwater quality are affected by hydrologic conditions as well as anthropogenic influences. Local variability in groundwater quality reflects local variability in hydrogeologic conditions and sources of chemicals. Groundwater ranges from anoxic and iron- or calcium-bicarbonate type, to oxic with elevated nitrate. The occurrence and distribution of pesticides, volatile organic compounds, and other selected chemical compounds in groundwater reflect the multitude of sources common to urban areas, as well as variable hydrogeologic and geochemical conditions that affect their fate and transport in the environment. Overall, concentrations of only a few of the over 200 chemical constituents included in laboratory analyses exceeded regulatory standards or guidance values. These include tetrachloroethene and arsenic, which were each detected one time in different wells. There were also several detections of iron and manganese that exceeded regulatory standards or guidance values that are associated with reducing conditions in aquifer sediments.

Washington, D.C.↗

USGS2020

One-Water Hydrologic Flow Model: A MODFLOW based conjunctive-use simulation software

The U.S. Geological Survey’s (USGS) Modular Ground-Water Flow Model (MODFLOW-2005) is a computer program that simulates groundwater flow by using finite differences. The MODFLOW-2005 framework uses a modular design that allows for the easy development and incorporation of new features called processes and packages that work with or modify inputs to the groundwater-flow equation. A process solves a flow equation or set of equations. For example, the central part of MODFLOW is the groundwater-flow process that solves the groundwater-flow equation; the surface-water routing process is an additional process that solves the surface-water flow equation. Packages are code related to the groundwater-flow process. For example, the subsidence package modifies the groundwater-flow process by including aquifer compaction effects on flow. With the development of new packages and processes, the MODFLOW-2005 base framework diverged into multiple independent versions designed for specific simulation needs. This divergence limited each independent MODFLOW release to its specific purpose, so that there was no longer a single, comprehensive, general-purpose hydraulic-simulation framework. The MODFLOW One-Water Hydrologic Flow Model (MF-OWHM, also informally known as OneWater) is an integrated hydrologic flow model that combines multiple MODFLOW-2005 variants in one cohesive simulation software; changes were made to enable multiple capabilities in one code. This fusion of the MODFLOW-2005 versions resulted in a simulation software that can be used to address and analyze a wide class of conjunctive-use, water-management, water-food-security, and climate-crop-water scenarios. As a second core version of MODFLOW-2005, MF-OWHM maintains backward compatibility with existing MODFLOW-2005 versions, with features that include the following: Process-based simulation. Saturated groundwater flow (three-dimensional). Surface-water flow (one- and two-dimensional). Stream and river flow. Lake and reservoir storage. Landscape simulation and irrigated agriculture. Land-use and crop simulation. Root uptake of groundwater. Actual evapotranspiration. Estimated irrigation demand. Reservoir operations. Aquifer compaction and subsidence by vertical model-grid deformation. Seawater intrusion by a sharp-interface assumption. Karst-aquifer and fractured-bedrock flow. Turbulent and laminar-pipe network flow. Unsaturated groundwater flow (one-dimensional). Internal linkages among the processes that couple hydraulic head, flow, and deformation. Redesigned code for faster simulation, increased user-input options, easier model updates, and more robust error reporting than in previous models. MF-OWHM is a MODFLOW-2005 based integrated hydrologic model that can simulate and analyze varying environmental conditions to allow for the evaluation of management options from many components of human and natural water movement through a physically based, supply and demand framework. The term “integrated,” in the context of this report, refers to the tight coupling of groundwater flow, surface-water flow, landscape processes, aquifer compaction and subsidence, reservoir operations, and conduit (karst) flow. Another benefit of this integrated hydrologic model is that models developed to run by MODFLOW-2005, MODFLOW-NWT, MODFLOW-CFP, or MODFLOW-FMP can also be simulated with MF-OWHM. At the time of this report’s publication, MF-OWHM version 2 (MF-OWHM2) does not include a direct internal simulation of snowmelt, advanced mountainous watershed rainfall-runoff simulation, detailed shallow soil-moisture accounting, or atmospheric moisture content. Atmospheric moisture may be accounted for indirectly by, optionally, specifying a pan-evaporation rate, reference evapotranspiration, and precipitation. These features are not included to ensure that simulation runtime remains short enough to enable the use of automated methods of calibrating model parameters to field observations, which typically require many simulation model runs. The MF-OWHM approach is to include as much detail as possible to simulate hydrological processes, providing the simulation runtimes remain reasonable enough to allow for robust parameter estimation and model calibration. To represent both natural and human-influenced flow, MF-OWHM integrates physically based flow processes derived from MODFLOW-2005 in a supply and demand framework. From this integration, the physically based movement of groundwater, surface water, imported water, and precipitation serve as supply to meet consumptive demands associated with irrigated and non-irrigated agriculture, natural vegetation, and urban water uses. Water consumption is determined by balancing the available water supply with water demand, leading to the concept of a demand-driven, supply-constrained simulation. The MF-OWHM Supply-and-Demand Framework is especially useful for the analysis of agricultural water use, where there are often few data available to describe changes in land-use through time, such as crop type and distribution, and the associated changes in groundwater pumpage. This framework attempts to satisfy each land-use water demand with available water supplies—that is, groundwater uptake, precipitation, and irrigation. An option provided in MF-OWHM2 is to automatically increase groundwater pumping for irrigation, which often is unknown, by the calculated residual between demand and the other available sources of supply. From large- to small-scale applications, the physically based supply and demand framework provides key capabilities for simulating and analyzing historical, current, and future conjunctive-use of surface water and groundwater. To achieve the physically based supply and demand framework, the MODFLOW-2005 standard of no inter-package and -process communication was relaxed for MF-OWHM2. Traditional MODFLOW simulation models required that all packages and processes interact through the groundwater-flow equation or by removing the water flow from the simulation domain. For example, the MODFLOW-2005 representation of a groundwater well extracts water from the groundwater-flow equation (by subtraction) and removes it from the simulation domain. This feature is available in the MF-OWHM framework, but options have been added to allow the specification of a use or destination of pumped groundwater within the model domain, for example, it can be used for irrigation, managed aquifer recharge, or return-flow to streams.

Techniques and Methods↗