Quantifying groundwater storage dynamics in the Chesapeake Bay watershed (USA) using a large-scale integrated hydrologic model with detailed three-dimensional subsurface representation Archives

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Quantifying groundwater storage dynamics in the Chesapeake Bay watershed (USA) using a large-scale integrated hydrologic model with detailed three-dimensional subsurface representation

June 29, 2023

Expanding on current efforts to evaluate the role of groundwater dynamics in managing and restoring Chesapeake Bay (USA), the integrated hydrologic model ParFlow-CLM was applied to a 374,976-km2 area encompassing the Chesapeake Bay watershed. The model included a representation of surface water, groundwater and land-surface energy fluxes with spatially variable atmospheric forcing at an hourly time step. The study tackled issues of data availability, access, assembly, and synthesis for estimating hydrogeologic properties in the context of the development of a large-scale model. Hydrogeologic properties from literature and other sources were assembled, processed, and synthesized to derive a conceptual hydrogeologic model consisting of 29 hydrofacies and a three-dimensional hydraulic conductivity field. Evaluation of the ParFlow-CLM model output showed that the constructed model captured seasonal and spatial variability in subsurface storage, surface storage and surface runoff, and produced water-table depths consistent with the topography, meteorological forcing, and hydrogeology. Comparison with well data from the US Geological Survey showed good agreement of model output with observed hydraulic heads for most of the data. Modeled terrestrial water storage changes compared well with GRACE satellite data with a root mean square error of 2.3 cm. Model results showed the dominant contribution of subsurface storage changes (90%) to terrestrial water storage changes in the region.

The publication is available on Springer Nature.

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2022 Washington Metropolitan Area Drought Exercise

May 24, 2023

The Washington, D.C., metropolitan area (WMA) relies on the Potomac River for over three-quarters of its water supply. The area’s three major water suppliers (“CO-OP suppliers”), Fairfax County Water Authority (Fairfax Water), Washington Suburban Sanitary Commission (WSSC Water), and Washington Aqueduct (a Division of the U.S. Army Corps of Engineers) participate in a cooperative system of water supply planning and management. This participation includes joint funding of water supply storage in reservoirs located upstream of the suppliers’ Potomac River intakes and coordinated operations during droughts.

During times of drought, the Section for Cooperative Water Supply Operations on the Potomac (CO-OP) of the Interstate Commission on the Potomac River Basin (ICPRB) plays a crucial role in coordinating water supply operations. By coordinating withdrawals from the Potomac River, Patuxent, and Occoquan reservoirs, the CO-OP staff help ensure that water resources are being utilized efficiently and effectively for the benefit of the system. When the forecasted flow in the river is not sufficient to meet expected demands, the CO-OP staff make requests for releases from upstream reservoirs. These demands include the water supply needs of the WMA and an environmental flow-by of 100 million gallons per day (MGD), or 155 cubic feet per second (cfs), on the Potomac River below the Little Falls Dam near Washington, D.C.

The ICPRB CO-OP section conducts an annual drought exercise to maintain readiness for drought conditions. These exercises serve as a platform for CO-OP staff to evaluate and discuss water management strategies with relevant stakeholders, prior to a real drought scenario. The activities aid in training CO-OP staff on regional agreements, tools, and decision-making processes. Moreover, they offer participants the chance to refine their communication processes and enhance organizational efficiency.

This report describes activities conducted during the 2022 Drought Exercise. The virtual training took place on Tuesday, Wednesday, and Thursday, November 15-17, from 7:30 A.M. to 2:00 P.M. Communications during the exercise were via telephone, email, and Microsoft Teams, and all operations were “simulated.” Stakeholders received twice-daily email reports on “actual” precipitation, river flow, water withdrawals, and “simulated” operations and reservoir storages. This year’s exercise included the following elements:

  • A regional Drought Coordination Technical Committee (DCTC) conference call to discuss potential water use restrictions associated with the Metropolitan Washington Council of Governments (MWCOG) “Warning” stage,
  • Communication with Washington Aqueduct on the Low Flow Allocation Agreement (LFAA) thresholds, and
  • Data collection and operational forecasts through CO-OP’s Data Portal and daily flow forecast tool to determine the need for “simulated” releases from Little Seneca and North Branch reservoirs (Jennings Randolph and Savage).
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Considerations for Monitoring Microplastics in the Non-Tidal Potomac River

December 9, 2022

The Interstate Commission on the Potomac River Basin’s 2022 Clean Water Act Section 106 Potomac Basin Water Quality Improvement grant included an activity to “assist water suppliers in VA, MD, and DC in developing microplastic sampling and analysis methodologies and conduct field sample collection.” This white paper, which explores the feasibility of a microplastic monitoring program in the nontidal Potomac basin, represents the output for this activity. Section 2 describes considerations for collecting and processing samples for microplastics analysis. Section 3 provides a brief explanation of analytical methods and quality control recommendations for the detection, quantification, and identification of microplastics.

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Improving probabilistic monthly water quantity and quality predictions using a simplified residual-based modeling approach

August 26, 2022

Uncertainty quantification between simulated and observed water quality simulations needs to be improved. This study generated and evaluated probabilistic hydrologic and water quality predictions in 18 locations across the U.S. using residual-based modeling. A Box-Cox transformation scheme group provided the best predictive uncertainties for all case studies. The tradeoffs in the performance metrics for a single variable predictive uncertainty in a single study watershed were more obvious than those for all hydrologic or water quality cases. Compared to a single realization of simulations, the ensemble average of hydrologic and water quality simulations better represented the predictive uncertainty, especially for large watersheds. This study recommends various opportunities via residual error scheme selection, data monitoring improvement, and hydrologic model enhancement to robust hydrologic and water quality predictive uncertainties. The results could improve the quantification of the predictive uncertainty of hydrologic and water quality simulations and guide probabilistic prediction enhancement.

More information about the paper is available on ScienceDirect.com.

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Potomac Basin Reported Water Use

August 26, 2022

In accordance with one of the technical recommendations of the Potomac Basin Comprehensive Water Resources Plan’s water use and supplies challenge area, this pamphlet has been produced to document and share high-level results. This pamphlet provides a “report on basin-wise water uses,” and ultimately acts as a first step toward estimating, “projected demands and consumptive demands.”

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Potomac Environmental Flows Workshop 2022

July 12, 2022

In 2021, Commissioners of the Interstate Commission on the Potomac River Basin (ICPRB) passed a Resolution on Enhancing Water Supply Resilience for the Washington Metropolitan Area. This resolution is the first step in updating the two foundational agreements of the Washington metropolitan area cooperative water supply system: the Low Flow Allocation Agreement (LFAA) of 1978 and the Water Supply Coordination Agreement (WSCA) of 1982. To facilitate such an update the resolution called for the following action items:

  • Develop a Task Force on the WSCA to reinitiate dialogue on revisions that would accurately reflect changing conditions. This includes the need for strengthening water security against spills, cybersecurity attack, and water scarcity and the ability to include additional suppliers;
  • Convene a Work Group to discuss the ten sets of options identified in the 2018 review of the LFAA; and
  • Convene scientific workshops on state-of-the-art approaches to environmental flows for large river systems.

To address the third action item, a virtual workshop was held over one-and-a-half days in May 2022, with the explicit purpose of answering the following questions with respect to the Potomac River, which supplies most of the Washington, D. C., metropolitan area drinking water:

  • Are there other approaches now for determining environmental flows in large, relatively unregulated rivers like the Potomac?
  • If there are, what data, analysis tools, and assessments are needed to make a scientifically defensible change?

The information presented and discussed during the workshop provides input to the LFAA workgroup in the event the group recommends revisiting the current environmental flow-by target used during low flow periods. The question of whether or not to study the flow-by was informally discussed during the workshop but the intent of the workshop was to gather the relevant information, not recommend a course of action.

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An Inventory of Potomac Basin Entities with a Role in Sustainable Water Resources Management

May 20, 2022

This pamphlet is used in concert with a spreadsheet inventory to identify entities in the Potomac basin that either directly or indirectly affect the realization of the Potomac Basin Comprehensive Water Resource Plan’s vision for the basin. It also summarizes the roles, responsibilities, and areas of authority of those entities to inform and integrate future comprehensive planning and implementation activities.

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2020 Washington Metropolitan Area Drought Exercise

March 4, 2021

This report describes activities conducted during the 2020 drought exercise. The exercise was virtual, and took place on Monday, Tuesday, and Wednesday, November 16-18, from 7:30 AM to 4:00 PM.
Communications during the exercise were via telephone, email, and Microsoft Teams Meeting, and all
operations were “simulated.” Twice daily email reports were sent out to stakeholders reporting on current flow and demand conditions and on simulated operations. The exercise included two special events:

  • An actual test release from Little Seneca Reservoir, which was conducted over an approximately
    12-hour period, beginning at 10:00 AM on Tuesday, November 17.
  • A webinar by Hazen & Sawyer on the use of the Potomac OASIS model to provide probabilistic
    information on future streamflows and reservoir storage levels. A PDF of the webinar on forecast informed reservoir operations is available.

Learn more about previous drought exercises and the ICPRB’s Section for Cooperative Water Supply Operations on the Potomac on the Drought Monitoring and Operations page.

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2020 Washington Metropolitan Area Water Supply Reliability Study: Demand and Resource Availability Forecast for the Year 2050

December 4, 2020

Every five years since 1990, ICPRB’s Section for Cooperative Water Supply Operations on the Potomac (CO-OP) has conducted a water demand and resource availability forecast for the Washington, D.C., metropolitan area. These studies assess whether or not the current water supply system will be able to meet the needs of the region 20 or more years in the future.

Learn more about these reports on the CO-OP Long-Term Planning page.

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