HydroVisions | Fall 2025

Hydro Visions Official Publication of the Groundwater Resources Association

VOLUME THIRTY-FOUR

NOVEMBER 2025

2025 Fall Issue

V.34

Hydro Visions

Hydro Visions

HYDROVISIONS is the official publication of the Groundwater Resources Association of California (GRA).

GRA’s mailing address is 808 R Street. Suite 209, Sacramento, CA 95811. Any questions or comments concerning this publication should be directed to the newsletter editor at hydrovisions@grac.org The Groundwater Resources Association of California is dedicated to resource management that protects and improves groundwater supply and quality through education and technical leadership.

EDITOR Rodney Fricke hydrovisions@grac.org EDITORIAL LAYOUT Smith Moore & Associates EXECUTIVE OFFICERS PRESIDENT Christy Kennedy Woodard & Curran Tel: 925-627-4122 VICE PRESIDENT Erik Cadaret Yolo County Flood Control & Water Conservation District Tel: 530-756-5905 SECRETARY Abhishek Singh INTERA Tel: 217-721-0301 TREASURER Rodney Fricke GEI Consultants Tel: 916-407-8539 DIVERSITY, EQUITY AND INCLUSION OFFICER Annalisa Kihara State Water Resources Control Board IMMEDIATE PAST PRESIDENT R.T. Van Valer ADMINISTRATIVE DIRECTOR Amanda Rae Smith Groundwater Resources Association of California asmith@grac.org

DIRECTORS Jena Acos Brownstein Hyatt Farber Schreck Tel: 805-882-1427 Christopher Baker CA DWR Tel: 562-331-4507 Matthew Becker California State University Long Beach Tel: 562-985-8983 Trelawney Bullis AC Foods, Central Valley Tel: 530-205-8387 Dave Ceppos Public Policy Mediation and Facilitaion Tel: 916-539-0350 Elie Haddad Haley & Aldrich Tel: 408-529-9048 Dr. Hiroko Hort GSI Environmental, Inc Marina Deligiannis Sacramento Area Sewer District Tel: 916-418-8242 Clayton Sorensen West Yost Associates Tel: 925.949.5817 Melissa Turner MLJ Environmental Tel: 530-756-5200 Savannah Tjaden Environmental Science Associates Tel: 208-350-3566

ISSN 2837-5696

Roohi Toosi APEX Environmental & Water Resources Tel: 949-491-3049

To contact any GRA Officer or Director by email, go to www.grac.org/board-of-directors

John Xiong Haley & Aldrich, Inc. Tel: 714-371-1800

The statements and opinions expressed in GRA’s HydroVisions and other publications are those of the authors and/or contributors, and are not necessarily those of the GRA, its Board of Directors, or its members. Further, GRA makes no claims, promises, or guarantees about the absolute accuracy, completeness, or adequacy of the contents of this publication and expressly disclaims liability for errors and omissions in the contents. No warranty of any kind, implied or expressed, or statutory, is given with respect to the contents of this publication or its references to other resources. Reference in this publication to any specific commercial products, processes, or services, or the use of any trade, firm, or corporation name is for the information and convenience of the public, and does not constitute endorsement, recommendation, or favoring by the GRA, its Board of Directors, or its members.

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Hydro ydro Visions isions

Hydro Visions

Official Publication of the Groundwater Resources Association

6 Data Analysis Tools and

Contents President’s Message

Page 4

Basin Characterization Tools

Page 6

Hydrologic Modeling

Page 14

AEM Data Collection

Page 22

BSMAR19

Page 30

GeoH2OMysteryPix

Page 32

Parting Shot

Page 34

Processes to Support Basin Characterization

14 Toward Integrated ISSN 2837-5696

Hydrologic Modeling for Climate Adaptation and River Operations

22 Seeing Beyond: Pushing

the Bounds of AEM Data Collection and Interpretation in the Salinas Valley Basin, CA

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President’s Message

Groundwater's Moment Has Arrived As I write my final letter as your GRA President, I find myself reflecting not with nostalgia, but with an overwhelming sense of excitement for GRA’s future. I recently came across an insight from Burnt Island Ventures that perfectly captures where we are, the article title says it all “Water is Now Unignorable”.

For those of us who have dedicated our careers to what happens beneath the surface, this isn’t news.

But what IS new is that the rest of the world has finally caught up with what we’ve always known — groundwater isn’t the quiet, awkward cousin of the water family anymore. It’s center stage, and the spotlight isn’t dimming.

The Through-Lines of Our Journey Looking back through these Letters from the President over my two-year term, certain themes have woven themselves consistently through every message, every call to action, every moment of challenge and celebration: •

We embraced the audacity of innovation. From AI-powered flood forecasting to creative subsidence technologies, we’ve challenged ourselves to think beyond pump curves and cones of depression. We’ve welcomed the tech industry into our historically closed ecosystem. We’ve stopped chuckling dismissively at unconventional ideas and started asking “what if?”

And most importantly, we’ve recognized that the most stubborn challenges — subsidence, contamination, depletion — won’t yield to incrementalism. They require creative courage.

•

We’ve navigated unprecedented change. Federal policy shifts, SGMA implementation, PFAS, Chrome-VI, atmospheric rivers followed by droughts — we’ve weathered it all while expanding GRA’s sphere of influence. We’ve built partnerships beyond our traditional boundaries, recognizing that cross-disciplinary collaboration isn’t just nice to have — it’s survival.

•

We’ve championed our members as the solution. Throughout every letter, I’ve asked you to bring your wildest ideas, contribute your expertise, attend that branch meeting, write that article, teach that course. Because GRA’s strength has never been in its organizational structure — it’s been in YOU, our members. The hydrogeologists, scientists, engineers, regulators, planners, academics, consultants, and dreamers who show up, do the work, and refuse to accept that “this is how it’s always been done.”

•

We’ve looked forward with strategic intent. Our 2024-2026 Strategic Plan wasn’t just paperwork — it was our compass.

Expand and engage membership. Continue to lead in groundwater. These priorities are guiding our evolution from a regional association to a thought leader that other sectors — technology, finance, policy — actively seek out.

Why This Moment Matters Twenty-four years ago, I sat at a GRA Branch dinner table in an Oakland Chinese restaurant, a young professional just finding her way in this industry. I never imagined I’d one day be writing to you as the President of GRA. But here’s what I’ve learned in this role: leadership isn’t about having all the answers. It’s about creating the space for the right questions and partnerships to emerge. And the questions facing us now are bigger and more urgent than ever: •

How do we stabilize aquifers experiencing subsidence?

•

How do we integrate surface water and groundwater management in an era of climate extremes?

•

How do we attract the next generation of talent to an industry that strongly benefits from fresh thinking?

•

How do we make innovation less scary and failure more acceptable?

To answer these questions, you need each other, you need GRA as your platform, and you need the courage to pursue solutions that don’t yet exist.

Passing the Torch Tom Ferguson from Burnt Island Ventures is spot on with his article, water is now unignorable. Investment is flowing. Technology is advancing. Policies are evolving. The barriers that once kept groundwater in the shadows are crumbling. This is our moment — not to rest on decades of credibility, but to sprint toward what’s possible.

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President’s Message

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To the next President and Board in 2026: you inherit an organization that is vibrant, financially stable, strategically focused, and positioned to lead. Continue to push hard. Say yes to uncomfortable partnerships. Don’t be afraid to fail.

Keep asking “what communities are we missing?” and my favorite “what should we say no to, so we can achieve our (beep) yes?” Trust our membership — they’re brilliant.

To our members: Stay curious. Stay bold. Amplify those ideas that feel a little too wild for the room. Keep bridging disciplines we don’t fully understand. Keep showing up for branch meetings and conferences and casts. Keep teaching the next generation. Keep holding us accountable to our vision of sustainable groundwater for all.

What I’ll Carry Forward I’m not disappearing — I’ll still be around, probably causing trouble at conferences and asking overly enthusiastic questions at panel discussions. Most of all, I’m stepping back with hope. Because water may now be unignorable, but groundwater professionals? We’ve been impossible to ignore for decades. And the best chapters of our story are still ahead.

Next year at the SGMA Summit or Western Groundwater Congress, when someone asks what solutions we have for our toughest challenges, let’s make sure the question sparks not silence, but a flood of ideas!

Thank you for letting me serve. Thank you for your passion, expertise, and unwavering commitment to the groundwater industry. Thank you for making groundwater visible, valued, and undeniably vital.

With deep appreciation and boundless optimism for what’s next,

Christy Kennedy Outgoing President, Groundwater Resources Association Still a clumsy AI enthusiast, forever a groundwater nerd.

P.S. – My final "asks" for you: •

Attend your local branch meeting and meet someone new

•

Share one unconventional idea with your team this week

•

Thank a volunteer who made your GRA experience better

•

Renew your membership and bring a colleague along for 2026

•

Stay unignorable!

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GROUNDWATER EXPERTS PROVIDING INNOVATIVE SOLUTIONS FOR MANAGING OUR CRITICAL WATER RESOURCES Related Services Water Resources Modeling Managed Aquifer Recharge Interconnected Surface Water Analysis Groundwater Dependent Ecosystems Subsidence Analysis Stormwater Management PFAS Sustainable Groundwater Management Groundwater Quality

Locations IRVINE 7595 Irvine Center Drive, Suite 250, Irvine, California 92618 SAN FRANCISCO BAY AREA 2000 Powell Street, Suite 820, Emeryville, California 94608 FOLSOM 1839 Iron Point Road, Suite 150, Folsom, California 95630

GSIEnv.com

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Hydro Vis Data Analysis Tools and Processes to Support Basin Characterization

by Katherine Dlubac1, Steven Springhorn1, Mesut Cayar2, Jack Baer2, Nicole Jacobsen2, Sercan Ceyhan2, Victoria (Tori) Ward2, Liz DaBramo2, Vivek Bedekar3, Matt Tonkin3, Leland Scantlebury3, Gengxin (Michael) Ou3

analyze a wide range of data, including geologic, geophysical, and hydrogeologic information. By combining and assessing various datasets, these tools help create a more complete picture of California’s groundwater basins.

DWR’s Groundwater Basin Characterization Program provides the latest data and information about California’s groundwater basins to help local communities better understand their aquifer systems and support local and statewide groundwater management.

The data analysis tools and process documents are made publicly available for stakeholders to support the development of maps and models. A beta release of the tools was shared with the Basin Characterization Exchange (BCX) network; join the BCX listserv to access meeting recordings and to download the beta release of the tools. The final release of the tools and associated documentation and workshops is expected in Fall/Winter 2025. Final versions of the tools will be made available through the CNRA Basin Characterization, Data Analysis Tools and Process Documents landing page.

Under the Basin Characterization Program, texture models, hydrostratigrahic models (HSM), and recharge potential maps will be developed. These tools and maps will describe the distribution of aquifer materials, aquifer structures, and recharge pathways. To support the development of maps and models, new tools (Figure 1) were created to integrate and

Figure 1 - Tools Overview

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sions A brief description of the following tools and processes is provided below: • • • •

Data2Texture Data2HSM Texture2Par Aquifer Recharge Potential Mapping

Data2Texture The Data2Texture tool is an advanced interpolation tool that estimates the spatial distribution of sediment textures. The Data2Texture tool integrates different types of subsurface data and interpolates them into a 3D texture model. These data types may include boring logs, AEM-based texture data, NMR/e-logs, or other datasets related to sediment texture.

Data2Texture primarily combines and interpolates these data through ordinary cokriging, a geostatistical spatial analysis method that calculates a potentially anisotropic weighted moving average of point data using a variogram. By

interpolating point data without enforcing hydrostratigraphic units, the tool can produce an initial 2D or 3D texture model revealing large-scale patterns and correlative relationships.

Data2HSM The Data2HSM suite of tools utilizes a variety of machine learning models to develop HSMs from AEM data, lithology logs, geophysical logs, and/or texture models. Users can choose between three analysis processes, which may be used individually or in series: Smart Interpretation (SI), Gaussian Mixture Model (GMM), and Geological Pseudolabel Deep Neural Network (GeoPDNN).

Advancements in machine learning tools allow for the automation and enhancement of hydrogeologic modeling from AEM data. SI is a semi-automatic tool that reduces manual effort by training a regression model to delineate article continues on next page

Figure 1: AEM 3D Viewer showing the AEM derived percent coarse grained material as fence diagrams.

Figure 2 - Hydrogeologic conceptual model of the subsurface, aquifer recharge potential types, and associated ARP maps

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hydrostratigraphic surfaces based on a limited set of userselected points. The GMM is an unsupervised classification tool that groups AEM data into user-defined clusters, representing stratigraphic units, while applying geostatistical transformations to maintain geologic continuity. The GeoPDNN is a semi-supervised tool that integrates pointbased datasets into realistic stratigraphic surfaces using a neural network, which can also be applied to mapping features such as the water table, base of freshwater, or top of bedrock. These tools streamline hydrostratigraphic modeling, improving efficiency, accuracy, and automation in groundwater analysis.

Texture2Par Texture2Par is a tool developed to work with the IWFM and MODFLOW groundwater models. It processes texture data to infer aquifer properties like hydraulic conductivity, specific yield, and specific storage. Texture2Par integrates AEM data and lithologic log data into 3D numerical models using power-law averaging of sediment parameters to develop bulk aquifer properties for numerical models.

Table 1 - Aquifer Recharge Potential Map Types

ARP Map Infiltration Type

Deep Preferential Pathways (Built)

Pathways from the surface to the deep portion of the aquifer

Through soil layer

Bypassing soil layer

Through soil layer

Bypassing soil layer

Recharge Goal

Flood control, shallow groundwater well supply, habitat restoration

Shallow groundwater well supply, habitat restoration

Flood control, deep groundwater well supply, mitigate subsidence

Deep groundwater well supply, mitigate subsidence

Recharge Methods

Ag-MAR, surface water spreading, managed natural lands

Reverse tile drains, dedicated groundwater recharge facilities

Minimally developed groundwater recharge facilities, Ag-MAR, surface water spreading

Dedicated groundwater recharge facilities, dry wells

Aquifer Recharge Potential Mapping The Aquifer Recharge Potential (ARP) mapping analysis produces maps that provide insight into areas with relatively higher potential for managed aquifer recharge (MAR).

Different ARP map types can be developed for various MAR methods, including surface spreading, on-farm recharge, recharge basins, dry wells (gravity-fed pits), and aquifer storage and recovery (ASR) wells.

The ARP analysis incorporates multiple subsurface properties that serve as proxies for infiltration rates and subsurface storage capacity. It produces a series of maps, each tailored to a specific recharge type and goal, that help identify areas with higher recharge potential and groundwater recharge infiltration pathways. The ARP map types are: Shallow (Natural), Shallow (Built), Deep Preferential Pathways (Natural), and Deep Preferential Pathways (Built). The infiltration type, recharge goal, and recharge method for each ARP map are described in Table 1. The aquifer recharge potential flow paths for various methods and associated aquifer recharge potential maps are shown in Figure 2.

The ARP mapping process considers multiple subsurface 8

Deep Preferential Pathways (Natural)

Shallow (Natural) Shallow (Built) Pathways from the surface to the shallow portion of the aquifer

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properties, including soil conditions, groundwater levels, and aquifer texture. These parameters are organized into the following five sub-indices that represent conditions affecting MAR: • • • • •

Soil conditions Depth to groundwater Depth to shallow fine-grained layer Shallow sediment texture Interconnected coarse bodies.

Each sub-index describes a range of considerations for MAR, from near-surface conditions (e.g., soil hydraulic conductivity) to deeper subsurface conditions (e.g., access to flow pathways and sediment coarseness). After the subindices are gathered, they are grouped and weighted according to their relative importance to recharge and applicability to the recharge method. A list of sub-indices, along with their purpose, data source, and binning criteria is included in Table 2. ARP maps developed for the Madera and North Kings Local Investigation are provided in Figure 3. article continues on next page

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Figure 3 - Aquifer Recharge Potential maps for the Madera and North Kings Local Investigation Area for Shallow (Natural), Shallow (Built), Deep Preferential Pathways (Natural), and Deep Preferential Pathways (Built) Map Types Table 2 - Summary of Sub-Indices Description, Data Source, and Binning Criteria for Each ARP Map Type

Sub-Indices

Purpose

Data Source

Soil Conditions Infiltration capacity through surface soils

Depth to Groundwater Storage capacity

SAGBI

Groundwater level data

Depth to Shallow Fine-Grained Shallow Sediment Interconnected Coarse Layer Coarseness Bodies Depth to clay Infiltration Efficient percolation layer that may potential in shallow pathways to deeper inhibit infiltration subsurface (top 50 aquifer (e.g., paleofeet) valleys or incised valley fills) 3D subsurface texture model *

High resolution 3D subsurface texture models can be developed using the Data2Texture tool. A description of how the sub-indices were calculated from the 3D subsurface texture model is provided in the ARP Process Document (Appendix A). *

Additional information on developing ARP maps can be found in the ARP Mapping Process Document.

1 California Department of Water Resources (DWR) 2 Woodard & Curran 3 S.S. Papadopulos & Associates

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To help California water agencies implement their SGMA programs, a unique public-privatenonprofit partnership joined forces to develop the Groundwater Accounting Platform.

This flexible software enables water managers, landowners, and water users to track groundwater availability and usage with user-friendly dashboards and workflows, empowering local communities to meet their water usage goals.

It has been successfully deployed in 6 subbasins across the state, with new agencies and users joining every year.

Learn more at groundwateraccounting.org 12

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Hydro Vis Toward Integrated Hydrologic Modeling for Climate Adaptation and River Operations

by Ayman Alzraiee and Richard Niswonger, GSI Environmental Inc. Introduction California’s water management faces a growing challenge of balancing rising demands across different sectors, ensuring groundwater sustainability, meeting environmental flow requirements, and allocating water fairly amid intensifying drought and climate change. Historically, these challenges were addressed using fragmented tools and models that treated groundwater, surface water, water use estimation, and reservoir operations separately. This approach occurred within a legally divided governance framework, where surface water was regulated by the State Water Resources Control Board, while groundwater remained under local control for many years. The legal and hydrologic separation is now being reconciled through the Sustainable Groundwater Management Act (SGMA), which mandates locally driven groundwater sustainability planning supported by the Department of Water Resources and enforced by the State Water Board.

SGMA requires consideration of interconnected surface water (ISW), groundwater, and groundwater-dependent ecosystems (GDEs) as part of the groundwater sustainability plan (GSP) development. As analysis of water systems grows more holistic, the need for integrated modeling tools that simulate nonlinear feedback across legal and hydrologic boundaries is becoming clear.

Integrated hydrologic models offer a path forward by simulating surface water, groundwater, water use, land use changes, and water operations within a single framework, as fragmented models fail to realistically simulate complex interactions among different legal and hydrologic processes.

Such integrated models allow decision-makers to evaluate trade-offs, test climate adaptation strategies, evaluate management scenarios, and coordinate water use more 14

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effectively. They can also be used to support near-real-time reservoir operations in systems that use the paradigm of Forecast-Informed Reservoir Operations (FIRO; Delaney et al. 2020).

This article highlights a case study that employed the integrated GSFLOW-MODSIM modeling framework to simulate interconnected surface and subsurface hydrology, agricultural water demands driven by soil zone moisture dynamics, and managed river-reservoir operations. The modeling system was applied to simulate the Santa Rosa integrated hydrologic system and explore diverse management scenarios to balance water demand and environmental minimum flow requirements.

Integrated Modeling System The integration of GSFLOW (Markstrom et al. 2008) and MODSIM (Labadie 2006) represents a significant advancement in hydrologic modeling, evolving from earlier efforts to link MODFLOW-NWT (Niswonger et al. 2011) with water allocation tools. Morway et al. (2016) coupled MODFLOW with MODSIM, where stream flow impact on groundwater flow informed river management decisions.

However, this coupling lacked key surface water processes and dynamic agricultural water use, which prevented feedback between hydrologic processes and water allocation responses and limited its usefulness for dynamic water planning (Kitlasten et al., 2021).

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sions GSFLOW is a USGS-developed modeling system that links MODFLOW and PRMS (Markstrom et al., 2015), enabling continuous, integrated simulation of surface and subsurface hydrologic processes.

MODFLOW captures subsurface flow in both saturated and unsaturated zones, along with interactions with streams and lakes. PRMS models surface hydrology including precipitation and temperature variability, snow accumulation and melt, vegetation interception, land surface storage, runoff generation, infiltration, evapotranspiration, and soil zone moisture dynamics. The coupling of MODFLOW and PRMS improves the estimation of focused and diffused recharge, and also allows for better prediction of streamflow, based on precipitation, snowmelt timing, and other physical characteristics of a watershed. The integrated model also simulates dynamic land use changes and estimates agricultural water use by dynamically modeling moisture in the root zone.

Figure 1. Schematic diagram illustrating GSFLOW-MODSIM, which couples a groundwater flow model (MODFLOW), the watershed model (PRMS), and the river operations model (MODSIM). The integrated system captures the interactions among groundwater, surface water, and managed river operations to support comprehensive water resources management.

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MODSIM is a river basin management decision support system that uses a network flow optimization algorithm to simulate water allocation. Developed at Colorado State University, it models complex river systems as a network of nodes (reservoirs, diversions, demands) and links (canals, river segments). By assigning costs (or priorities) to water deliveries, the model can efficiently allocate water according to a variety of constraints, including water rights, operational rules, and economic values, while ensuring a mass balance is maintained.

MODSIM is a tool for analyzing various water management scenarios, such as longarticle continues on next page 2025 Fall Issue

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term planning, drought contingency, and the impacts of proposed policy changes.

GSFLOW was tightly coupled with MODSIM, enabling bidirectional exchange of information. GSFLOW simulates streamflow to inform MODSIM of available water, and MODSIM responds by adjusting surface water diversions and reservoir releases that feed back into GSFLOW (Figure 1). The modular structure of GSFLOW-MODSIM allows it to run with or without PRMS, MODFLOW, or MODSIM components, depending on the complexity needed. When all modules are active, the system supports detailed simulations of climate-driven hydrology, aquifer responses, and legal allocation priorities. This evolution toward dynamic feedback among components enhances the realism of simulations, especially for forecasting under changing climate, land use, or regulatory conditions. The integrated GSFLOW-MODSIM system thus represents a major step toward operational tools that support both hydrologic accuracy and practical water governance.

Application to Santa Rosa Plain The integrated GSFLOW-MODSIM framework was piloted in the Santa Rosa Plain Hydrologic Model (SRPHM 2.0; Alzraiee et al. 2025) to evaluate its ability to simulate the integrated hydrologic system and water allocation decisions in a unified model. Building on more than a decade of data collection and earlier modeling work, the U.S. Geological Survey has developed a modernized version of the Santa Rosa Plain Hydrologic Model (Figure 2A). This represented a major advancement over the original SRPHM (Woolfenden and Nishikawa 2014), which lacked a dynamic water-rights component. By coupling MODSIM within GSFLOW, the

updated model could account for institutional controls—such as priority-based allocation and diversion curtailments—in addition to simulating natural groundwater–surface water interactions. The result is a modeling system capable of reflecting both the physical and legal complexities of water management, especially under variable hydrologic conditions such as droughts.

In the Santa Rosa application, the integrated model was used to simulate water allocations from Mark West Creek (Figure 2B) to multiple demand nodes representing various water-rights holders and use types, including agricultural irrigation, indoor residential use, outdoor landscaping, commercial activities, and instream flow requirements (Figure 2C). Each demand node was assigned a priority level (weight). To account for instream flow requirements, nonconsumptive flow-through nodes were placed on tributaries with designated minimum environmental flow thresholds.

The weights for these environmental flows were adjusted to evaluate different management scenarios, such as curtailment policies triggered during drought conditions. When streamflow was insufficient to meet all demands, MODSIM applied legal allocation rules to determine which uses would be curtailed. These adjusted diversions were then passed back into GSFLOW, creating a dynamic feedback loop between simulated hydrologic conditions and institutional water management decisions.

The integrated model also enables detailed analysis of sectorspecific water demands, accounting for indoor residential use, outdoor irrigation, and agricultural practices, while ensuring compliance with environmental flow targets. By simulating groundwater pumping, surface diversions, and return flows within the same framework, the model provides a

Figure 2. (A) The MODSIM network for the Santa Rosa Plain basin. (B) A zoomed-in view of the Mark West watershed.

(C) A logical construct showing water allocation between urban, agricultural, and environmental sectors.

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Experts from Concept to Operations Comprehensive Solutions for Water Supply Management Æ

Managed Aquifer Recharge

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holistic view of the water budget. Water managers can explore scenarios that adjust these demands—such as implementing conservation measures or changing cropping patterns—to evaluate their impact on both human water availability and ecosystem health. Figure 3 showcases results from two scenarios in which different water use categories were curtailed based on whether instream flow requirements were assigned a senior or junior priority. In the scenario where instream (environmental) flows were given senior priority, the GSFLOW-MODSIM model projected larger water shortages for both agricultural and indoor water use, with the most significant impacts occurring in the summer and fall.

A key strength of this modeling system is its ability to capture how groundwater pumping could affect water rights associated with surface water. For example, although

MODSIM’s network-based design does not include direct control over groundwater pumping, its integration with GSFLOW allows simulation of the resulting impacts of pumping on surface water allocations. This facilitates analysis of regulatory measures like curtailment policies, instream flow requirements, and water-use prioritization.

While the implementation in Mark West Creek was limited in scope—focusing on a single watershed and a subset of demand nodes—it successfully demonstrated the practical value of the GSFLOW-MODSIM framework for regional-scale water planning. The pilot simulation provides a foundation for scaling up to include more complex systems with multiple streams, water rights holders, and interconnected hydrologic components.

Figure 3. The impact of surface water diversion curtailment on two water-use types (Agricultural and Indoor domestic) in Mark West Creek, Sonoma County, California. The figure compares scenarios where instream flows have senior water priority (Left) versus junior water priority (Right) (Modified from Alzraiee et al., 2025)

Future of Integrated Modeling The future of integrated hydrologic modeling, particularly with tools like GSFLOW-MODSIM, is poised for significant advancements in water resource management. One critical development is the ongoing work by GSI Environmental Inc. to enhance the underlying GSFLOW code. GSI is actively working on developing Unstructured Grid GSFLOW, in which the PRMS is coupled with the MODFLOW-USG (the unstructured grid version of MODFLOW, Panday, 2013) to allow for the simulation of complex unstructured grids.

More importantly, these advancements will extend to solute transport capabilities. Ultimately, this will enable models to not only simulate water flow but also the movement and fate of solutes, paving the way for sophisticated water allocation strategies, based not just on quantity, but also on water quality constraints. This future capability will be crucial for ensuring 18

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water is allocated for beneficial uses while protecting public health and environmental integrity.

Another critical area for the future application of GSFLOWMODSIM is in the context of Forecast-Informed Reservoir Operations (FIRO), an innovative approach to water management that uses advanced weather forecasts to inform reservoir release decisions, aiming to balance flood control, water supply, and environmental needs (Delaney et al., 2020). Integrating GSFLOW-MODSIM into FIRO frameworks is essential because it can simulate the complex interactions between surface water and groundwater under dynamic forecast-driven conditions. This allows for real-time assessment of how reservoir releases impact downstream groundwater levels, stream-aquifer exchange, and ultimately, water availability for various demands, including critical environmental flows, while minimizing the risk of floods. The

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predictive power of GSFLOW-MODSIM will enable more adaptive and resilient water management in response to increasingly variable climate patterns.

References Alzraiee, Ayman H., Andrew Rich, Linda R. Woolfenden, Derek W. Ryter, Enrique Triana, and Richard G. Niswonger. 2025.

“Updating and Recalibrating the Integrated Santa Rosa Plain Hydrologic Model to Assess Stream Depletion and to Simulate Future Climate and Management Scenarios in Santa Rosa, Sonoma County, California.” In Scientific Investigations Report, Nos. 2024–5121. U.S. Geological Survey. https://doi.org/10.3133/sir20245121.

Delaney, Chris J., Robert K. Hartman, John Mendoza, et al.

2020. “Forecast Informed Reservoir Operations Using Ensemble Streamflow Predictions for a Multipurpose Reservoir in Northern California.” Water Resources Research 56 (9): e2019WR026604. https://doi. org/10.1029/2019WR026604.

Kitlasten, W., Morway, E. D., Niswonger, R. G., Gardner, M., White, J. T., Triana, E., & Selkowitz, D. (2021). Integrated hydrology and operations modeling to evaluate climate change impacts in an agricultural valley irrigated with snowmelt runoff. Water Resources Research, 57(6), e2020WR027924.

Labadie, John W. 2006. MODSIM: Decision Support System for Integrated River Basin Management. https:// scholarsarchive.byu.edu/iemssconference/2006/all/242/.

Markstrom, Steven L., Richard G. Niswonger, R. Steven Regan, David E. Prudic, and Paul M. Barlow. 2008. “GSFLOWCoupled Ground-Water and Surface-Water FLOW Model Based on the Integration of the Precipitation-Runoff Modeling System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005).” US Geological Survey Techniques and Methods 6: 240.

Experts in Water Resource Planning and SGMA Implementation 6 Groundwater Modeling 6 Managed Aquifer Recharge 6 Hydrogeologic Investigations 6 Subsidence Evaluation and Mitigation 6 Seawater Intrusion Analysis 6 Municipal Well Design 6 Regulatory Compliance 6 Water Accounting Frameworks

Markstrom, Steven L., R. Steve Regan, Lauren E. Hay, et al.

2015. PRMS-IV, the Precipitation-Runoff Modeling System, Version 4. US Geological Survey. https://pubs.usgs.gov/ tm/6b7/.

Morway, Eric D., Richard G. Niswonger, and Enrique Triana. 2016. “Toward Improved Simulation of River Operations through Integration with a Hydrologic Model.”

Environmental Modelling & Software 82: 255–74.

Niswonger, Richard G., Sorab Panday, and Motomu Ibaraki.

2011. “MODFLOW-NWT, a Newton Formulation for MODFLOW-2005.” US Geological Survey Techniques and Methods 6 (A37): 44.

Panday, Sorab, Langevin, C.D., Niswonger, R.G., Ibaraki, Motomu, and Hughes, J.D., 2013, MODFLOW–USG version 1: An unstructured grid version of MODFLOW for simulating groundwater flow and tightly coupled processes using a control volume finite-difference formulation: U.S. Geological Survey Techniques and Methods, book 6, chap.

A45, 66 p.

Woolfenden, Linda R., and Tracy Nishikawa. 2014. Simulation of Groundwater and Surface-Water Resources of the Santa Rosa Plain Watershed, Sonoma County, California. US Geological Survey. https://pubs.usgs.gov/publication/ sir20145052.

For more information, visit our website or contact:

Lisa Porta, P.E. | lporta@elmontgomery.com Principal Water Resources Engineer California Water Strategy Lead

ARIZONA | CALIFORNIA | NEVADA | UTAH | CHILE | ARGENTINA Sacramento | Oakland | Monterey | San Luis Obispo | Pasadena

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Celebrating 46 Years!

▪ Modeling Software Development ▪ Hydrogeological Modeling ▪ Geochemical Investigation & Modeling ▪ Contaminant Fate & Transport ▪ Water Supply Evaluations ▪ Aquifer Storage & Recovery ▪ Managed Aquifer Recharge ▪ Monitoring Well and Pump Performance Optimization ▪ Remediation Engineering for Soil, Groundwater, and Surface Water ▪ Sampling and Field Services ▪ Expert Testimony & Litigation Support

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Geosyntec combines hydrogeology, engineering, and modeling expertise to guide clients toward SGMA compliance and lasting water resilience.

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Hydro Vis Seeing Beyond: Pushing the Bounds of AEM Data Collection and Interpretation in the Salinas Valley Basin, California

Figure 1. Conceptual Diagram of the Salinas Valley Basin

by Victoria Hermosilla1, Max Halkjaer2, and Ahmad-Ali Behroozmand2

Addressing these data gaps was a top priority to begin the path toward sustainable groundwater management.

Introduction and Study Background/Set-Up

A comprehensive Salinas Valley Deep Aquifers Study (Study) was funded through multiple collaborating partners and kicked off in 2021 to address critical questions regarding the geology and hydrogeology of the Deep Aquifers. The Study first defined the Deep Aquifers as the water-bearing sediments that are below a relatively continuous aquitard or area of higher clay content encountered between approximately 500 feet and 900 feet below land surface within the Salinas Valley. In order to determine the extent of this aquitard, and subsequently the Deep Aquifers, any form of data collection needed to have the capability of at least reaching these depths and confidently identifying this defining subsurface feature.

This paper focuses on the technology used to observe the subsurface at greater depths with more clarity, and on the outcomes for the Deep Aquifers Study.

The Salinas Valley Groundwater Basin (Salinas Valley) is known for its lettuce, John Steinbeck, and a long history of groundwater challenges. There are 6 subbasins fully or partially managed by the Salinas Valley Basin GSA (SVBGSA).

The critically over-drafted 180/400-Foot Subbasin has 3 principal aquifers: the 180-Foot Aquifer, the 400-Foot Aquifer, and the Deep Aquifers, as shown on Figure 1. The 2020 GSP focused on the 2 shallowest aquifers, but lacked sufficient data to adequately characterize the Deep Aquifers. Despite known increases in extraction and declining water levels, the GSP identified the need for additional data to manage the latter as a principal aquifer. Prior to SGMA and the GSPs, there was not much data or information about the Deep Aquifers, including its extents, recharge pathways, or composition.

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sions Figure 2. Photo of the System for the Deep Aquifers AEM Survey

Selecting the Right Geophysical Tool One goal of the Study was to map the distinguishing aquitard and identify aquifers at and deeper than 800 feet (244 meters) - and ideally down to 1,500 feet (457 meters). Airborne Electromagnetic (AEM) data seemed the most promising method; however, the biggest concern was depth of data collection. The Study target depths of 800 to 1,500 feet (244 to 457 meters) were beyond the capability of Standard Transient Electromagnetic Method (TEM) systems. Other geophysical techniques that can probe deeper were initially considered due to this limitation.

One such method is seismic reflection, which can image very deep underground layers. However, it requires powerful energy sources and is labor-intensive, making it too costly and impractical for this project. Another method considered was Controlled-Source Audio-frequency Magnetotellurics (CSAMT), which has successfully been used to study deeper geological structures (1–2 km deep). The Salinas Valley, however, is relatively developed and active, raising concerns about whether CSAMT could provide high-quality data in such a noisy environment. The higher costs, lower spatial coverage, and complicated mobilization of various other geophysical techniques removed them from consideration by the investigators.

Airborne electromagnetic (AEM) became the most promising data collection method for cost and aerial coverage, but the question of depth was still concerning to investigators.

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Recently available surveys by California Department of Water Resources (DWR) were reanalyzed to assess whether TEM could reliably be used to map the Salinas Valley Deep Aquifers. The 2020 DWR AEM survey for the Salinas Valley had an average depth of investigation of 300 meters (984 feet), which barely skimmed the top of what the Deep Aquifers investigators were searching for. The Deep Aquifers generally began at approximately 800 feet (244 meters) below land surface, and productive zones were still being encountered at 2,000 feet (610 meters) below surface. In order to “see” to a greater depth, a more powerful AEM tool and adjusted data collection methods needed to be used.

The geophysical team discussed this challenge with SkyTEM Surveys and proposed using a high-power AEM system tailored for deep mineral exploration. The proposed highpower system, SkyTEM312HP, transmits more electrical current and has a better signal-to-noise receiver system.

The combination of this more powerful setup with an extended length of recorded sounding timeseries enabled the geophysical team to collect even deeper data. This approach provided unique insights into the Salinas Valley in service of both identifying the Deep Aquifers and providing a strong scientific basis for their sustainable management.

Figure 3. Figure Showing the Standard TEM Noise Floor and the Modified Deep Aquifers Noise Floor; Data from Later Times Correlate to Deeper “Views” of Subsurface Features

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To explore greater depths, the TEM data needed to include measurements from later time intervals (“time gates”), which provide information about deeper subsurface geology. In the 2020 DWR data, the AEM signal reached the “noise floor” before later time gates could be used, and the depth of investigation was limited to the top 300 meters (984 feet) of subsurface. To reach the Study goals of collecting data at greater depths, the high-power SkyTEM312HP system was modified to be twice as powerful and used receiver coils with more wire turns, which helped reduce noise and made it possible to detect deeper underground features. The data collected using the modified SkyTEM312HP system provided clean electromagnetic data for the entire sounding curve to 20 milliseconds.

Results of the Modified TEM System The Deep Aquifers AEM survey flew over 300 kilometers (186 miles) of lines, providing a large spatial coverage of the Study area. The depth of investigation was improved significantly and penetrated down 500 to 600 m (1,640 to 1,968 ft) in many parts of the survey area, as shown on Figure 4. The transect shown on Figure 4 is from the Deep Aquifers Survey, and includes intersecting transects from the DWR AEM Survey Area 1. The depth of investigation (DOI) from each survey is noted on the transect and demonstrates the significant difference in depth of data collection: 300 m versus 550 m (984 ft versus 1804 ft).

The improved depth of investigation revealed not only the distinguishing aquitard separating the Deep Aquifers from shallower aquifers, but also key geologic features that govern the flow of groundwater throughout the Basin including bedrock and extensive alluvial fans. In some places, an indication of the bottom of the Deep Aquifers was also seen in the models, exceeding the original project goal.

The investigators and geophysical team had previously discussed that the target depth of the modified SkyTEM312HP would subsequently reduce the resolution in the shallow subsurface. Since the goal of the Study was the deeper subsurface, this condition was not particularly concerning.

However, previous AEM survey data were still compared to

the new AEM survey data to understand how the resolutions might differ, and the observed differences in resolution were only related to the very near-surface layers; the bulk majority of the resistivity was in perfect agreement, also shown on Figure 4. This meant that the AEM surveys and subsequent resistivity models could be combined seamlessly when variations in the depth of investigation were taken into account, resulting in a richer dataset for future investigations and managers.

Hydrogeological Interpretation The new AEM data were brought into a LeapFrog model and synthesized with existing data to develop the conceptual model of the Deep Aquifers. These existing data included well completion reports, borehole geophysical logs, previously published cross sections, geologic maps, and water quality data. The purpose of this effort was to identify the aquitard that separates the Deep Aquifers from other overlying, identified principal aquifers. The aquitard had been previously identified in deep well completion reports and had been shown to adequately separate the hydrologic conditions between waterproducing zones. The aquitard was characterized as a zone of higher clay content in the subsurface and is encountered as the middle member of the Paso Robles Formation.

Areas of high clay-content in well completion reports were correlated with low resistivity zones in the AEM data at similar depths, shown in blue hues on Figure 5. These zones were also compared to previously published cross sections. The analyses started in areas with high data concentration and subsequently high confidence in interpretation to build strong relationships with the new AEM data. As confidence grew, the analyses extended outward to areas with fewer available data, tracing out the signatures in the AEM data through the Study area and defining the presence of the aquitard.

Importantly, the AEM data were also used to delineate areas of the subsurface where the Deep Aquifers did not extend. Many subsurface materials have similar resistivity profiles; however, they may represent very different depositional environments and aquifer/aquitard systems. Investigators took careful steps to review all data and reports and conferred with other professionals

Figure 4. Comparison of AEM Transect Depth of Investigation from DWR Survey Area 1 (two vertical bars) and Deep Aquifers Survey (continued colors)

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Thinking of water in new ways Creating sustainable water supplies for the future requires reimagining the water cycle

Environmental Consulting and Engineering At LWA, we understand that groundwater is vital for California’s water future. We’re here to help communities manage this precious resource wisely and in line with state regulations.

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Figure 5. Example of How Multiple Datasets were Synthesized in LeapFrog to Build Confidence in the AEM data and Extend Analyses to Data-scarce Locations

with local experience to ensure that the delineations were strongly data-supported and scientifically sound.

The full lateral extent of the Deep Aquifers, determined through analyzing several sources of data including the AEM survey, is shown as solid yellow on Figure 6. Some data indicate the extent may be even greater, but not enough of that data were available to conclusively delineate the presence of the Deep Aquifers, shown as the hatched yellow areas also on Figure 6. Further data collection and analysis will provide additional clarity.

Conclusions and Final Remarks The Deep Aquifers Study was a critical early step to characterize the Deep Aquifers and their current conditions, laying the foundation for groundwater management. Central to the Study was identifying the extent of the Deep Aquifers, as defined by the presence of the continuous aquitard that separated them from other overlying productive zones in the subsurface. This delineation was made possible with AEM surveys. The geotechnical team employed the SkyTEM 312HP and introduced multiple modifications to the data collection process, extending the standard 300-meter depth of investigation to between 500 and 600 meters. This enhanced capability enabled investigators to analyze the deep subsurface in unprecedented detail over a larger geographic area and, for the first time, determine the location and extent of the Deep Aquifers.

With the conclusion of the Deep Aquifers Study, the SVBSGA is incorporating the extent of the Deep Aquifers and all correlated data into their GSPs for each of the subbasins where the Deep Aquifers are encountered. Historically, groundwater level and extraction data have been concentrated in coastal areas, where deep wells were installed to avoid seawater-intruded areas in the shallower aquifers (Figure 1). As part of GSP implementation efforts, SVBGSA and partner agencies are installing additional monitoring wells to expand the data available to support groundwater management.

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Figure 6. Final Extent of the Deep Aquifers (M&A, 2024)

1 Montgomery & Associates 2 Geophysical Imaging Partners, Inc.

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Hydro Visi Call for Abstracts and Sponsors!

Herman Bouwer Award — April 31, 2026 Optional Field Trip: April 2 In Progress Herman Bouwer Award: March 31 In honor of Dr. Herman Bouwer’s contributions to the field of MAR, an award named for Dr. Bouwer will be presented during a special luncheon on March 31. The award will be given to an individual or agency that has had a significant impact on increasing the understanding or utilization of MAR. To learn more and nominate someone for the award, go to https://www.grac.org/page/hermanbower.

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Sponsor and Exhibitor Opportunities If you are interested in exhibiting your organization’s services or products, or being an event co-sponsor, please contact Katrina Duncan at kduncan@grac.org or 916-446-3626.

Please visit the GRA website at https://www.grac.org/ page/BSMAR19 for updates. For additional information contact Adam Hutchinson at ahutchinson@ocwd.com or 714-378-3214.

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ions The Nineteenth Biennial Symposium on Managed Aquifer Recharge, Building Resiliency with MAR: Convey, Store and Deliver, will take place on March 31 to April 2, 2025, at the Doubletree Hotel in Sacramento, CA. This event continues a long-standing series of symposia originating in Arizona in 1978. The Groundwater Resources Association of California and the Arizona Hydrological Society have teamed up to host BSMAR with the location alternating between California and Arizona.

regulators, managers, and operators plus exhibitor and networking opportunities followed by an optional half-day field trip on the final day of BSMAR19 (April 2).

Join us for 2 full days of presentations, workshops and poster sessions by leading MAR experts: technical specialists,

Submit an abstract today for oral and poster presentations on the topics listed below.

MAR Testing, Design and Construction

MAR and Water Resources Management

• • • • • •

Advanced methods for selection of aquifers, sites and methods Designing for storm water capture Predicting sediment loading/clogging Alternative recharge systems Innovation in harvesting and storing flood waters Overcoming the hydrogeology/engineering disconnect

MAR Operations and Maintenance • • • • • • • • •

Monitoring and modeling Tracer testing Clogging management Fate of pathogens and pollutants Geochemistry and hydrogeology Groundwater hydraulics and storage recovery Training for MAR operators Long-term maintenance requirements/budgeting Modifying operations for long-term sustainability

MAR Governance • • • • •

Integrated water resources management Recharge policies, standards and regulations Community engagement and MAR awareness MAR to complement groundwater demand management Legal issues related to storm water capture by MAR systems

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Engage with a community of groundwater experts and water resource professionals. Learn through technical presentations, panel sessions, and best practice case studies. Discover new avenues for field-based tours, workshops, and networking opportunities. Contribute to shaping the future of aquifer recharge for resilient water management

• • • • • • • • • •

Reclaimed water reuse via MAR Storm water harvesting via MAR (MS4 permitting, etc.)

Quantification of benefits and costs of MAR MAR for drinking water quality improvement MAR with desalinated water Mining and industrial applications of MAR MAR to source heat pumps and geothermal injection Mitigating geological problems using MAR - land subsidence, seawater intrusion, etc.

MAR for rural and irrigation water supplies MAR in conjunctive use of surface water and groundwater

MAR Case Studies • •

Success factors for projects that worked Lessons learned from projects that did not work

Other Issues related to MAR • • •

MAR and climate change MAR in urban areas Greenhouse gas considerations in MAR operations

Abstracts deadline: December 5, 2025.

To submit an abstract go to https://www.grac.org/general/ custom.asp?page=bsmar19-abstracts 2025 Fall Issue

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Hydro Vis GeoH2OMysteryPix

by Chris Bonds - DWR, Sacramento Branch Member at Large

GeoH2OMysteryPix is a fun addition to HydroVisions that started in Fall 2022, so going on 3 years now. The idea is simple; I provide one or more photograph(s) and two questions, along with a hint, and HydroVisions’ readers email in their guesses.

In a future issue of HydroVisions, I will share the answer(s) along with some brief background/historical information about the photos and acknowledge the first person(s) to email me the correct answer(s).

GRA looks forward to your continued participation in GeoH2OMysteryPix. SUMMER 2025 ANSWERS

What is this? Where is it Located?

Hint: A world-class sedimentary basin in southern CA within which there lies a significant water storage facility named after a unique nearby geographic feature.

Congratulations to Trevor Pontifex, PG, Hydrogeologist, Montgomery & Associates, and Michael Taraszki, PG, CHG, Sr. VP & Hydrogeologist, WSP, for jointly providing the following correct responses, respectively, to the Summer 2025 GeoH2OMysteryPix Questions: TP: “Thanks for researching another geography challenge. Is that the old U.S. Route 99 with Pyramid Rock in the background? That section of the highway was abandoned when Pyramid Lake was

constructed and was replaced by Interstate 5. I’ve driven by there many times on my way to field work in the Antelope Valley.”

MT: “As for the “what”, this is an old (1950s? 1960s?) “drilling table” or rotary drill rig. Given the proximity to the road/highway and apparent timeframe, I’ll guess that they were performing geotechnical work in preparation for building Pyramid Dam.” Background/History: The above DWR photograph dated 7-27-64 shows a geotechnical drilling rig, drill crew, and DWR engineering geologists collecting soil and rock core samples along the historic US Route 99 in preparation for the construction of Pyramid Dam, a critical component of the West Branch of the CA Aqueduct and State Water Project (Figure 1). The interesting and large topographic feature in the background of the photograph is the famous Pyramid Rock, after which the dam was named. Pyramid Dam was built by DWR from 1969-1973 and provides water storage, recreation, and fishery enhancement for the greater Los Angeles area. The dam is an earth and rock embankment type structure with a height of 400 feet, length of 1,090 feet, and a storage capacity of about 170,000 acre-feet (Figure 2). The dam is built across Piru Creek in Los Angeles County.

The area in which Pyramid Dam and Lake are located is called the Ridge Basin, a down-dropped graben, bounded on the northeast by the San Andreas Fault and the southwest by the San Gabriel Fault. The Ridge Basin is remarkable in that it contains a nearly continuous stratigraphic section of Miocene- to Pliocene-age marine to continental sedimentary rocks reaching a thickness of well over 45,000 feet (Figure 3). The stunning geology and stratigraphy of the Ridge Basin can be easily viewed while driving on I-5 between Castaic and Gorman, CA. 32

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sions Figure 1. 1969 aerial photograph showing US-99, Pyramid Rock, and future Pyramid Dam location.

Figure 2. 2022 aerial photograph of Pyramid Dam and Lake.

References: DWR 2025. Pixel - DWRs Digital Photography Webpage. https://pixel-ca-dwr.photoshelter.com/index

Figure 3.

Diagrammatic Cross Section of Ridge Basin

DWR 2022. Pyramid Dam Modernization Program Fact Sheet, May. https://water.ca.gov/-/media/DWR-Website/Web-Pages/ Programs/State-Water-Project/SWP-Facilities/Southern-Division/ DWR_PyramidDamFactSheet_5_2022_ay11.pdf SJGS 2018. Ridge Basin Field Trip Guide. San Joaquin Geological Society. November 3. http://www.psaapg.info/cloud/sjgs/2018_ Field_trip2.pdf#:~:text=Ridge%20Basin%20is%20located%20 in%20the%20central,in%20depositional%20styles%20oil%20 fields%20one%20might

FALL 2025 QUESTIONS

What is this? Where is it Located?

Hint: An amazing and world-famous railroad feature in the western U.S. Think you know What this is and Where it is Located? Email your guesses to Chris Bonds at goldbondwater@gmail.com

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Hydro Visi Parting Shot

by John Karachewski, PhD

Photograph of sea caves in granitic bedrock on South Farallon Island.

The Farallon Islands are located about 27 miles west of San Francisco and are visible from the mainland on clear days. The secluded archipelago consists of 7 islands with a total area of about 211 acres. The U.S. Fish & Wildlife Service manages the Farallon Islands National Wildlife Refuge, which is closed to the public in order to protect the wildlife. The islands are also located within the Greater Farallones National Marine Sanctuary, a NOAA-managed marine sanctuary that spans 3,295 square miles of ocean and coast. The Farallon Islands and their surrounding waters are a globally important hotspot for marine biodiversity and are especially known for whales, seals and sea lions, great white sharks, and a large and diverse seabird 34

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ions population. The rocky shores and adjacent continental shelf, slope, and submarine canyons make this area a critical feeding and resting destination for wildlife.

The Cretaceous granitic rocks in the San Francisco Bay region, such as those on the Farallon Islands, Point Reyes Peninsula, and Montara Mountain, are part of the Salinian terrane located west of the San Andreas Fault. These granitic rocks are like those of the southern Sierra Neveda and are thought to have been transported northwestward along the San Andreas Fault from southern California during the past tens of millions of years.

During the last glacial maximum, sea level was approximately 410 to 425 feet lower than today. This worldwide drop in sea level was caused by the growth of glaciers and ice sheets on the continents. During that time, the shoreline was located west of the Farallon Islands and San Francisco Bay did not exist.

The Farallon Islands are positioned amidst the California Current, a strong current of cool water originating in British Columbia and flowing southward to Baja California. In addition, the region’s strong, sustained northwest winds contribute to upwelling, a process by which deeper, colder and nutrient-rich water flows upward toward the surface. Together, the California Current and upwelling processes create a highly productive and diverse food web that attracts wildlife to the area.

The nonprofit Oceanic Society has been leading trips to the Farallon Islands since 1972. Departing from San Francisco, a round trip takes about eight hours. The whale watching trips are led by expert naturalists who describe the beauty, biodiversity, and rich history of the Farallon Islands.

Photographed on August 9, 2015, by John A. Karachewski, PhD. The guesstimated GPS coordinates are 37.7° and -123°.

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GROUNDWATER. GROUND TRUTH. GEI.

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Experts in Applied Geophysics for Groundwater Investigations Survey design Data acquisition (AEM, tTEM, ERT, MAG, GPR) Data processing and inversion Interpretation

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www.geophysicalimaging.com +1 415-430-7173 Address: Pleasant Hill, California 2025 Fall Issue

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Thank You to Our Contributors Dr. Ayman Alzraiee is a Senior Hydrologist with extensive experience in integrated hydrologic modeling, groundwater and surface water systems, and data assimilation tools. His previous work at the USGS included serving as technical lead in developing the national public supply water-use machine learning model and building robust groundwater surface water models for regions like the Russian River, Santa Rosa watershed, and Yucaipa Valley. He also played a key role in the development of pyGSFLOW and PESTPP-DA, open source tools advancing hydrologic modeling and uncertainty analysis.

Jack Baer, PG, is a Hydrogeologist at Woodard & Curran with over seven years of experience in groundwater, surface water, and geological modeling. His work leverages computer programming and interdisciplinary methods to develop novel solutions to complex problems in groundwater and flood risk management. He earned a B.S. in Geological Sciences from Tufts University and an M.S. in Earth and Marine Sciences at the University of North Carolina, Chapel Hill, and is a licensed Professional Geologist in California.

Dr. Vivek Bedekaris a water resources and environmental consultant at S.S. Papadopulos & Associate with extensive experience in groundwater modeling and software development. He has worked on a wide range of projects involving local and regional groundwater models, surface water–groundwater interaction, solute transport, and variable-density flow systems. Dr. Bedekar has developed several modeling tools and is the lead author of MT3D-USGS, an enhanced version of the widely used groundwater solute transport code. In addition to his consulting work, he actively contributes to the scientific community through peer-reviewed publications, technical reviews, and instruction at modeling and software training workshops.

Chris Bonds is a Senior Engineering Geologist (Specialist) with the California Department of Water Resources (DWR) in Sacramento. Since 2001, he has been involved in a variety of statewide projects including groundwater exploration, management, monitoring, modeling, policy, research, and water transfers. Chris has over 31 years of professional work experience in the private and public sectors in California, Hawaii, and Alaska and is a Professional Geologist and Certified Hydrogeologist. He received two Geology degrees from California State Universities.

Chris has been a member of GRAC since 2010, a Sacramento Branch Officer since 2017, and has presented at numerous GRAC events since 2004.

Dr. Mesut Cayar , PE, is a Senior Water Resources Engineer and Principal at Woodard & Curran. Mesut has 20 years of experience specializing in programming, numerical analysis, and the development of computer applications for groundwater, hydrology and water resources planning. He has extensive experience in water resources, hydrologic, and hydrogeologic investigations for integrated water management programs and sustainable groundwater management. Mesut is committed to developing innovative, sustainable, and unique solutions to complex water resource challenges, integrating advanced modeling, data-driven analysis, and interdisciplinary approaches to enhance water management, conservation, and resiliency.

Dr. Sercan Ceyhan is a Water Resources Engineer at Woodard & Curran with over 10 years of experience in integrated hydrological modeling, water budget development, and hydrologic data analysis. He has developed and supported numerous IWFM and MODFLOW models and brings expertise in programming, GIS, data analysis, and machine learning to advance innovative approaches in water resources planning and management.

Dr. Ceyhan is currently serving as a Technical Manager at Woodard & Curran.

Liz DaBramo, PE, has seven years of experience and provides services in water resource planning and management. She specializes in integrated water resources planning, managed aquifer recharge, and numerical modeling. Liz has contributed to several Groundwater Sustainability Plans and regional planning projects throughout California. With a formal background in both Environmental Engineering and Public Policy, Liz concentrates on innovative, sustainable, and robust water sustainability strategies in California.

Dr. Katherine Dlubac, PG, is a Senior Engineering Geologist in the Sustainable Groundwater Management Office at the California Department of Water Resources (DWR) where she is the Project Manager for the Statewide Airborne Electromagnetic (AEM) Surveys and the Basin Characterization Program. In this role, Katherine defines project tasks and oversees all project work, including data collection and analyses, and the development of tools, maps, and models. Katherine engages in coordination with local, state, and federal agencies and ensures timely data publication and visualization. Katherine supports the implementation of the SGMA and contributes to DWR’s California Water Plan and California’s Groundwater Bulletin 118 publications. Katherine holds degrees in Geophysics from Stanford University with a focus on using geophysical data to characterize groundwater aquifers.

Nicole Jacobsen, PG, is a Hydrogeologist at Woodard & Curran with over seven years of experience in groundwater and surface water monitoring, data analysis, and the development of innovative tools that leverage advanced datasets and machine learning

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tools. She has developed a robust skill set in interpreting hydrogeologic data and communicating insights across both research and public agency settings. Nicole earned a B.S in Geology from Texas A&M University and is a licensed Professional Geologist in California.

John Karachewski, PhD, retired recently from the California-EPA in Berkeley after serving as geologist for many years in the Geological Support Branch of the Permitting & Corrective Action Division for Hazardous Waste Management. John has conducted geology and environmental projects from Colorado to Alaska to Midway Island and throughout California. He leads numerous geology field trips for the Field Institute and also enjoys teaching at Diablo Valley College. John enjoys photographing landscapes during the magic light of sunrise and sunset. Since 2009, John has written quarterly photo essays for Hydrovisions.

Christy Swindling Kennedy, PE, PG, CHG, is a hydrogeologist, water resources engineer, and strategy lead for Woodard & Curran. She has served in numerous roles such as engineering, operations, people leadership, and was the CMO for RMC Water & Environment. She has over 20 years in the consulting engineering business focused on water management and resiliency. With her technical background in hydrogeology and water resources engineering coupled with her business development expertise, she serves as an advisor to a water industry-focused accelerator and two venture funds.

Richard Niswonger is a Principal Hydrologist with GSI. As a hydrologist and water resources scientist, Richard specializing in hydrologic modeling, water use estimation, and geospatial analysis. He is experienced in developing and applying physics-based/ machine learning models for water resource assessments, integrating remote sensing data, and parameterizing groundwater models. Richard is skilled in GIS, Python-based data analysis, and leveraging AI for hydrologic applications.

Dr. Gengxin (Michael) Ou , is a hydrologic and groundwater modeler at S.S. Papadopulos & Associates with extensive experience in model implementation and development, water resources planning and assessments, development of graphical user interfaces, and statistical and spatial analysis. He brings strong computational and advanced mathematics skills and experience programming with Python, Fortran, R, and VBA. He has developed many software applications including several MODFLOW packages to enhance model capability. Dr. Ou analyzes and customizes modeling software architecture, performs model simulations, and provides data analysis and data integration.

Leland Scantlebury is an environmental consultant at S.S. Papadopulos & Associate and PhD candidate at the University of California, Davis, specializing in groundwater– surface water modeling. He has worked on numerical model development and is the lead author of Texture2Par, a geostatistical tool for translating texture data into hydrogeologic parameters. Proficient in a variety of programming and scripting languages, he builds custom workflows for data processing, visualization, modeling, optimization, and uncertainty analysis. His current research integrates airborne electromagnetic (AEM) data into a basin scale groundwater-surface water model used for decision support at the local and state level.

Steven Springhorn, PG, is a Supervising Engineering Geologist and leads the Technical Assistance Section in the Sustainable Groundwater Management Office at the California Department of Water Resources (DWR). With nearly two decades of experience at DWR, Steven leads technical assistance and aquifer characterization efforts to support the implementation of California’s Sustainable Groundwater Management Act (SGMA) and oversees activities related to California’s Groundwater Bulletin 118, the state’s official compendium of groundwater information. His expertise spans groundwater monitoring, management, and data publication, with a strong focus on integrating technical and policy solutions for long-term water sustainability.

Throughout his career, Steven has worked across multiple DWR offices, contributing to strategic planning, oversight, and assistance programs that advance sustainable groundwater management.

Dr. Matt Tonkin is the president of S.S. Papadopulos & Associate. Dr. Tonkin manages or advises on many projects. He specializes in data synthesis and modeling to guide groundwater, surface water, soil, and contamination studies for public, private and legal clients. This includes planning sampling and monitoring programs; collaborating with other experts; developing and applying models; and presenting to stakeholders.

He received his PhD on the topic of model calibration and uncertainty analysis under Dr. John Doherty and has instructed on these and other topics.

Victoria (Tori) Ward is a Technical Manager at Woodard & Curran with 10 years of experience as an environmental data scientist. Her work as an environmental and water resources consultant has included quantitative hydrogeology, programming in Python and R, stochastic modeling, database management, and risk analysis.

She earned a B.S. in Hydrology with a minor in French from the University of New Hampshire and an M.S. in Environmental and Water Resources Systems Engineering from Cornell University.

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2025 Fall Issue

Hydro Visions