Publications are listed by year

Potomac Basin Trends in Water Use

This pamphlet summarizes projected reported water withdrawals and consumptive use (CU) in the Potomac basin. This work, along with the results
presented in the Potomac Basin Reported Water Use pamphlet and Wallace et al. (2023), addresses the technical recommendation, “Report on Basin-Wide Water Uses, Projected Demands, and Consumptive Demands” in the Potomac Basin Comprehensive Water Resources Plan (Recommendation 3.3.2 A).

Stream Biological Health in the Chesapeake Bay Watershed

To learn more about this project and find interactive maps, check out the webpage for “Chessie BIBI” Index for Streams .

Executive Report

This report offers a numeric value for the 2008 Baseline referenced in the 2014 Chesapeake Agreement’s stream health goal as well as evidence of a net improving trend in stream health in the Chesapeake watershed. The report demonstrates a process for tracking progress in achieving the stream health goal to “improve health and function of ten percent of stream miles above the 2008 baseline.” The bioregion, family-level version of the Chesapeake Basin-wide Index of Biotic Integrity, or “Chessie BIBI,” is used to quantify stream health. The index is calculated from macroinvertebrate data collected by state, federal, county, and volunteer monitoring programs with kick net methods and was developed specifically for 1st – 4th order streams in the Chesapeake watershed (Smith et al. 2017). The 2008 Baseline is the 2006 – 2011 period because it encompasses all sampling schedules of the watershed’s state monitoring programs, most of which employ rotational sampling.

Gaps in the monitoring data’s spatial and temporal coverage make it difficult to directly estimate percentages of healthy streams in the pre-baseline (2000 – 2005), baseline, and subsequent “first interval” (2012 – 2017) periods. Statistical analyses indicate approximately 61.7% (~89,317 miles) of non-tidal stream miles likely supported healthy macroinvertebrate communities in the baseline period. The percentage increased to 67.8% (~98,049 miles) in the first interval. Despite this roughly 6% net improvement, some areas of the watershed show degrading trends. The net improving trend, however, suggests the collective impact of multiple environmental stressors on streams may be slowly lessening in many parts of the Chesapeake watershed. Identifying which factors are responsible for the net improvement would be speculative at this point, although long-term efforts to conserve forests, preserve and restore riparian corridors and wetlands, mitigate acid rain and mine drainage, slow stormwater runoff, and reduce nutrients and sediment loads have all likely contributed. Metrics for a variety of environmental stressors are currently being explored and will help future investigations of stream macroinvertebrate responses to those stressors. They can help explain why the current trend is happening.

The purpose of this report is to present the monitoring-based results and provide CBP with a process for tracking progress in achieving the Chesapeake watershed’s stream health goal. The process differs in some respects from those of the state agencies who use the data differently and for state regulatory purposes. We fully expect the Chessie BIBI results will also differ from state results at times, even though the underlying raw data are the same. The Chessie BIBI can be used for inter-jurisdictional, watershed-based planning and evaluation.

2022 Washington Metropolitan Area Drought Exercise

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).

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

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.

Considerations for Monitoring Microplastics in the Non-Tidal Potomac River

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.

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

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.

Considerations for Benthic Harmful Algal Bloom Detection and Monitoring in Virginia Free-flowing Freshwater Rivers (Version 1)

The Commonwealth of Virginia currently does not have an active Harmful Algal Bloom (HAB) surveillance program for benthic algae. Rather, it has a response-based program triggered by reports of suspected benthic HABs from the public and/or field observations made by state agency staff. The Virginia Department of Health (VDH) coordinates the Commonwealth’s responses to suspected benthic HAB events. Virginia Department of Environmental Quality (DEQ) normally conducts the initial response to any potential HAB, which may include visits to the HAB site for visual observations and collection of water column samples above or near the benthic algal mats. DEQ does not collect algal material from solid mats, benthic or floating, and has limited resources to commit beyond the initial response investigation of reported potential HABs. VDH is charged with the responsibility to weigh the available evidence and determine whether there is sufficient information to issue an advisory or alert notifying the public of possible risk due to the presence of harmful algae.

Advisories may be issued based on confirmed, quantitative data such as an exceedance of a toxin threshold measured in the water column. Alerts may be based, partially or fully, on qualitative information such as the widespread presence, or suspected presence, and extent of solid floating/benthic mats or scums. The subsequent benthic HAB response monitoring program must therefore consider protocols to be implemented in both circumstances, i.e., an advisory based on confirmed, quantitative measurements versus a qualitative “abundance of caution” alert informing the public of a possible health risk.

This project report describes systematic protocols that could be implemented if an advisory or alert is issued by VDH for a benthic HAB event. The report identifies the information needed to issue an advisory or alert, the recommended actions, an effective schedule of activities, and the resources needed to characterize the nature and extent of the HAB and implement the protocols. The suggested monitoring program considers the conditions and information that led to the HAB advisory or alert. The report describes how decision-makers are informed of the health risks associated with recreational swimming, fishing, and other water contact activities.

An Analysis of Pooled Monitoring Data in Maryland to Evaluate the Effects of Restoration on Stream Quality in Urbanized Watersheds. Final report

The project examined whether stormwater management practices implemented under MS4 permits can lead to measurable differences in stream conditions compared to similar watersheds with few or no stormwater practices and to highly forested reference watersheds.

Copies of Appendix A and Appendix B are available online.

Potomac Environmental Flows Workshop 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.

Potomac Basin Reported Water Use

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.”