Conceptual Model Review of Napa Valley Groundwater Model

Napa County | November 15th, 2010

The purpose of this technical memorandum is to provide a general review of the Napa Valley Groundwater model (groundwater model) produced by DHI Water & Environment (

The purpose of this technical memorandum is to provide a general review of the Napa Valley Groundwater model (groundwater model) produced by DHI Water & Environment (DHI) as part of the 2005 Napa County Baseline Data Report (2005 BDR) (Jones & Stokes et al., 2005). This memorandum is not intended to be a full peer-review in which model code, input/output files, and output results would be analyzed. Opinions stated herein are based solely on a review of the 2006 Final BDR Technical Appendix (DHI, 2006a), which presents the model code, model construction, calibration, and application of modeling efforts introduced in Chapters 15, 16, and 17 of the BDR. Further information on the groundwater model was reviewed from the 2005 BDR and a 2007 technical memorandum Modeling Analysis in Support of Vineyard Development Scenarios Evaluation (DHI, 2007) in which the groundwater model was updated/expanded and applied in evaluating various vineyard development scenarios. The scope of Luhdorff & Scalmanini, Consulting Engineers’ (LSCE) work, described herein, included a review of the conceptual model developed by DHI from which the inputs to the groundwater model were based. In addition, information provided on the model code, construction, and development of the groundwater model and model calibration were also reviewed. The focus of LSCE’s work was to assess whether the information provided in the reviewed documents was complete and whether the model can be used for the stated purpose for which it was developed.

Conceptual Model to Support PCB Management and Monitoring in the San Leandro Bay Priority Margin Unit, Phase One

San Francisco Estuary Institute (SFEI) | June 1st, 2018

The goal of RMP PCB special studies over the next few years is to inform the review and possible revision of the PCB TMDL and the reissuance of the Municipal Regional P

The goal of RMP PCB special studies over the next few years is to inform the review and possible revision of the PCB TMDL and the reissuance of the Municipal Regional Permit for Stormwater, both of which are tentatively scheduled to occur in 2020. Conceptual model development for a set of four representative priority margin units will provide a foundation for establishing an effective and efficient monitoring plan to track responses to load reductions, and will also help guide planning of management actions. The Emeryville Crescent was the first PMU to be studied in 2015-2016. The San Leandro Bay PMU is second (2016-2017), Steinberger Slough in San Carlos is third (2017), and Richmond Harbor will be fourth (2018). The conceptual model reports for these four PMUs will be developed and presented using a consistent framework, and will build on each other to form an integrated assessment of these four areas. The lessons learned from these analyses will also be more generally applicable to similar contaminated sites on the margins of the Bay.

Contribution of Changes in Atmospheric Circulation Patterns to Extreme Temperature Trends

Nature Portfolio (Springer Nature) | July 24th, 2015

Surface weather conditions are closely governed by the large-scale circulation of the Earth’s atmosphere. Recent increases in the occurrence of some extreme wea

Surface weather conditions are closely governed by the large-scale circulation of the Earth’s atmosphere. Recent increases in the occurrence of some extreme weather phenomena have led to multiple mechanistic hypotheses linking changes in atmospheric circulation to increasing probability of extreme events. However, observed evidence of long-term change in atmospheric circulation remains inconclusive. Here we identify statistically significant trends in the occurrence of atmospheric circulation patterns, which partially explain observed trends in surface temperature extremes over seven mid-latitude regions of the Northern Hemisphere. Using self-organizing map cluster analysis, we detect robust circulation pattern trends in a subset of these regions during both the satellite observation era (1979–2013) and the recent period of rapid Arctic sea-ice decline (1990–2013). Particularly substantial influences include the contribution of increasing trends in anticyclonic circulations to summer and autumn hot extremes over portions of Eurasia and North America, and the contribution of increasing trends in northerly flow to winter cold extremes over central Asia. Our results indicate that although a substantial portion of the observed change in extreme temperature occurrence has resulted from regional- and global-scale thermodynamic changes, the risk of extreme temperatures over some regions has also been altered by recent changes in the frequency, persistence and maximum duration of regional circulation patterns.

Coupling a spatiotemporally distributed soil water budget with stream-depletion functions to inform stakeholder-driven management of groundwater-dependent ecosystems

Water Resources Research, American Geophysical Union | November 12th, 2013

Groundwater pumping, even if only seasonal, may significantly impact groundwater-dependent ecosystems through increased streamflow depletion, particularly in semiarid and

Groundwater pumping, even if only seasonal, may significantly impact groundwater-dependent ecosystems through increased streamflow depletion, particularly in semiarid and arid regions. The effects are exacerbated, under some conditions, by climate change. In social sciences, the management of groundwater-dependent ecosystems is generally considered a “wicked” problem due to the complexity of affected stakeholder groups, disconnected legal frameworks, and a divergence of policies and science at the cross road between groundwater and surface water, and between ecosystems and water quality. A range of often simplified scientific tools plays an important role in addressing such problems. Here we develop a spatiotemporally distributed soil water budget model that we couple with an analytical model for stream depletion from groundwater pumping to rapidly assess seasonal impacts of groundwater pumping on streamflow during critical low flow periods. We demonstrate the applicability of the tool for the Scott Valley in Northern California, where protected salmon depend on summer streamflow fed by cool groundwater. In this example, simulations suggest that increased recharge in the period immediately preceding the critical low streamflow season, and transfer of groundwater pumping away from the stream are potentially promising tools to address ecosystem concerns, albeit raising difficult infrastructure and water trading issues. In contrast, additional winter recharge at the expense of later spring recharge, whether intentional or driven by climate may reduce summer streamflows. Comparison to existing detailed numerical groundwater model results suggests that the coupled soil water mass balance—stream depletion function approach provides a viable tool for scenario development among stakeholders, to constructively inform the search for potential solutions, and to direct more detailed, complex site-specific feasibility studies. The tool also identifies important field monitoring efforts needed to improve the understanding and quantification of site-specific groundwater-stream interactions.

Cumulative effects of fire and drought in Mediterranean ecosystems

Ecological Society of America (ESA) | August 18th, 2017

The occurrence of multiple disturbances can jointly affect the recovery capacity of ecosystems, potentially leading to changes in vegetation dynamics or loss of resilien

The occurrence of multiple disturbances can jointly affect the recovery capacity of ecosystems, potentially leading to changes in vegetation dynamics or loss of resilience. The effects of interacting disturbances on ecosystems are, however, not well understood. We use a model system based on Mediterranean-type ecosystems (MTEs) to examine how the interplay between vegetation regeneration traits andcompound, stochastic disturbances modulate ecosystem dynamics. We developed a state-and-transition simulation model including two tree species with contrasting regeneration strategies (seeder vs. resprouter) and a shrub-land formation. We aim to assess potential compositional switches under contrasted scenarios of compound fire–drought regimes, and to characterize the cumulative effects of fire–drought(synergism vs. antagonism) relative to the effects of individual disturbance regimes. Our simulation results indicate that interaction between moderate fire and sporadic drought recurrence—as opposed to chronic dryness—can act as a strong mechanism generating highly heterogeneous landscapes in which different regeneration types coexist, as observed in MTEs. Resprouters dominated under individual, moderate disturbance regimes of fire or drought, whereas the interaction of the two disturbances promoted the long-term coexistence of both tree regeneration strategies. However, shrub-land expansion and persistence at the expanse of forests was favored by increases in drought recurrence and associated fire–drought interactions, highlighting the potential for important vegetation changes in MTEs under climate change. Overall, the cumulative effects of fire and drought can lead to distinct landscape configurations under moderate disturbance regimes that are otherwise only attained under high frequency of individual disturbances. At the ecosystem level, however, we suggest that disturbance-induced vegetation dynamics can modify vegetation sensitivity and resilience to further disturbances precluding the prevalence of synergistic effects of the two disturbances.

Cuyama Valley, California Hydrologic Study: An Assessment of Water Availability

U.S. Geological Survey (USGS) | May 29th, 2015

Dam effects on bedload transport on the upper Santa Ana River, California, and implications for native fish habitat

River Research and Applications (Wiley) | May 23rd, 2019

Dams disrupt the flow of water and sediment and thus have the potential to affect the downstream geomorphic characteristics of a river. Though there are some well‐known

Dams disrupt the flow of water and sediment and thus have the potential to affect the downstream geomorphic characteristics of a river. Though there are some well‐known and common geomorphic responses to dams, such as bed armouring, the response downstream from any particular dam is dependent on local conditions. Herein, we investigate the response of the upper Santa Ana River in southern California, USA, to the construction of a large dam at the transition from mountains to valley, using calculations of bedload transport capacity on the mainstem below the dam and for major tributaries. Approximate sediment budgets were constructed for downstream reaches to estimate deposition and erosion rates for sand, gravel, and cobble particle sizes. Our results indicate that the classical response of bed armouring and erosion is likely limited to a short reach immediately below the dam. Farther downstream, though transport capacity is reduced by flow regulation by the dam, the channel reaches are likely to remain depositional but with reduced deposition rates. Persistent deposition, as opposed to erosion, is the result of the replenishment of flow and sediment supply by large downstream tributaries. In addition, the calculations indicate that the composition of the bed is unlikely to change substantially in downstream reaches. A Monte Carlo approach was employed to estimate the uncertainty in the sediment budget predictions. The impacts of the dam on the geomorphic character of the river downstream could have implications for native fish that rely on coarse substrate that supports their food base.

Data Measured on Water Collected from Eastern Mojave Desert, California

U.S. Department of Energy (DOE) | August 18th, 2017

In March of 2000 field collection of water from the Eastern Mojave Desert resulted in the measurement of stable isotope, radiocarbon, tritium, and limited dissolved nobl

In March of 2000 field collection of water from the Eastern Mojave Desert resulted in the measurement of stable isotope, radiocarbon, tritium, and limited dissolved noble gases. This work was follow-on to previous studies on similar systems in southern Nevada associated with the Nevada Test Site (Davisson et al., 1999; Rose and Davisson, 2003). The data for groundwater from wells and springs was never formally published and is therefore tabulated in Table 1 in order to be recorded in public record. In addition 4 years of remote precipitation data was collected for stable isotopes and is included in Table 2. These studies, along with many parallel and subsequent ones using isotopes and elemental concentrations, are all related to the general research area of tracing sources and quantifying transport times of natural and man-made materials in the environment. This type of research has direct relevance in characterizing environmental contamination, understanding resource development and protection, designing early detection in WMD related terrorism, and application in forensics analysis.

Death Valley regional ground-water flow system, Nevada and California—Hydrogeologic framework and transient ground-water flow model

U.S. Geological Survey (USGS) | July 1st, 2010

A numerical three-dimensional (3D) transient groundwater flow model of the Death Valley region was developed by the U.S. Geological Survey for the U.S. Department of Ener

A numerical three-dimensional (3D) transient groundwater flow model of the Death Valley region was developed by the U.S. Geological Survey for the U.S. Department of Energy programs at the Nevada Test Site and at Yucca Mountain, Nevada. Decades of study of aspects of the groundwater flow system and previous less extensive groundwater flow models were incorporated and reevaluated together with new data to provide greater detail for the complex, digital model. A 3D digital hydrogeologic framework model (HFM) was developed from digital elevation models, geologic maps, borehole information, geologic and hydrogeologic cross sections, and other 3D models to represent the geometry of the hydrogeologic units (HGUs). Structural features, such as faults and fractures, that affect groundwater flow also were added. The HFM represents Precambrian and Paleozoic crystalline and sedimentary rocks, Mesozoic sedimentary rocks, Mesozoic to Cenozoic intrusive rocks, Cenozoic volcanic tuffs and lavas, and late Cenozoic sedimentary deposits of the Death Valley regional groundwater flow system (DVRFS) region in 27 HGUs. Information from a series of investigations was compiled to conceptualize and quantify hydrologic components of the groundwater flow system within the DVRFS model domain and to provide hydraulic-property and head-observation data used in the calibration of the transient-flow model. These studies reevaluated natural groundwater discharge occurring through evapotranspiration (ET) and spring flow; the history of groundwater pumping from 1913 through 1998; groundwater recharge simulated as net infiltration; model boundary inflows and outflows based on regional hydraulic gradients and water budgets of surrounding areas; hydraulic conductivity and its relation to depth; and water levels appropriate for regional simulation of prepumped and pumped conditions within the DVRFS model domain. Simulation results appropriate for the regional extent and scale of the model were provided by acquiring additional data, by reevaluating existing data using current technology and concepts, and by refining earlier interpretations to reflect the current understanding of the regional groundwater flow system. Groundwater flow in the Death Valley region is composed of several interconnected, complex groundwater flow systems. Groundwater flow occurs in three subregions in relatively shallow and localized flow paths that are superimposed on deeper, regional flow paths. Regional groundwater flow is predominantly through a thick Paleozoic carbonate rock sequence affected by complex geologic structures from regional faulting and fracturing that can enhance or impede flow. Spring flow and ET are the dominant natural groundwater discharge processes. Groundwater also is withdrawn for agricultural, commercial, and domestic uses. Groundwater flow in the DVRFS was simulated using MODFLOW-2000, the U.S. Geological Survey 3D finitedifference modular groundwater flow modeling code that incorporates a nonlinear least-squares regression technique to estimate aquifer parameters. The DVRFS model has 16 layers of defined thickness, a finite-difference grid consisting of 194 rows and 160 columns, and uniform cells 1,500 meters (m) on each side. Prepumping conditions (before 1913) were used as the initial conditions for the transient-state calibration. The model uses annual stress periods with discrete recharge and discharge components. Recharge occurs mostly from infiltration of precipitation and runoff on high mountain ranges and from a small amount of underflow from adjacent basins. Discharge occurs primarily through ET and spring discharge (both simulated as drains) and water withdrawal by pumping and, to a lesser amount, by underflow to adjacent basins simulated by constant-head boundaries. All parameter values estimated by the regression are reasonable and within the range of expected values. The simulated hydraulic heads of the final calibrated transient model generally fit observed heads reasonably well (residuals with absolute values less than 10 meters) with two exceptions: in most areas of nearly flat hydraulic gradient the fit is considered moderate (residuals with absolute values of 10 to 20 meters), and in areas of steep hydraulic gradient along the Eleana Range and western part of Yucca Flat, southern part of the Owlshead Mountains, southern part of the Bullfrog Hills, and the north-northwestern part of the model domain (residuals with absolute values greater than 20 meters). Groundwater discharge residuals are fairly random, with as many areas where simulated flows are less than observed flows as areas where simulated flows are greater. The highest unweighted groundwater discharge residuals occur at Death Valley, Sarcobatus Flat (northeastern area), Tecopa, and early observations at Manse Spring in Pahrump Valley. High weighted-discharge residuals were computed in Indian Springs Valley and parts of Death Valley. Most of these inaccuracies in head and discharge can be attributed to insufficient representation of the hydrogeology in the HFM and(or) discharge estimates, misrepresentation of water levels, and(or) model error associated with grid-cell size. The model represents the large and complex groundwater flow system of the Death Valley region at a greater degree of refinement and accuracy than has been possible previously. The representation of detail provided by the 3D digital hydrogeologic framework model and the numerical groundwater flow model enabled greater spatial accuracy in every model parameter. The lithostratigraphy and structural effects of the hydrogeologic framework; recharge estimates from simulated net infiltration; discharge estimates from ET, spring flow, and pumping; and boundary inflow and outflow estimates all were reevaluated, some additional data were collected, and accuracy was improved. Uncertainty in the results of the flow model simulations can be reduced by improving on the quality, interpretation, and representation of the water-level and discharge observations used to calibrate the model and improving on the representation of the HGU geometries, the spatial variability of HGU material properties, the flow model physical framework, and the hydrologic conditions.

Death Valley regional groundwater flow system, Nevada and California—Hydrogeologic framework and transient ground-water flow model

U.S. Geological Survey (USGS) | August 23rd, 2010