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.
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:
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:
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.
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.”
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.
Anthropogenic alterations have resulted in widespread degradation of stream conditions. To aid in stream restoration and management, baseline estimates of conditions and improved explanation of factors driving their degradation are needed. We used random forests to model biological conditions using a benthic macroinvertebrate index of biotic integrity for small, non-tidal streams (upstream area ≤200 km2) in the Chesapeake Bay watershed (CBW) of the mid-Atlantic coast of North America. We utilized several global and local model interpretation tools to improve average and site-specific model inferences, respectively. The model was used to predict condition for 95,867 individual catchments for eight periods (2001, 2004, 2006, 2008, 2011, 2013, 2016, 2019). Predicted conditions were classified as Poor, FairGood, or Uncertain to align with management needs and individual reach lengths and catchment areas were summed by condition class for the CBW for each period. Global permutation and local Shapley importance values indicated percent of forest, development, and agriculture in upstream catchments had strong impacts on predictions. Development and agriculture negatively influenced stream condition for model average (partial dependence [PD] and accumulated local effect [ALE] plots) and local (individual condition expectation and Shapley value plots) levels. Friedman’s H-statistic indicated large overall interactions for these three land covers, and bivariate global plots (PD and ALE) supported interactions among agriculture and development. Total stream length and catchment area predicted in FairGood conditions decreased then increased over the 19-years (length/area: 66.6/65.4% in 2001, 66.3/65.2% in 2011, and 66.6/65.4% in 2019). Examination of individual catchment predictions between 2001 and 2019 showed those predicted to have the largest decreases in condition had large increases in development; whereas catchments predicted to exhibit the largest increases in condition showed moderate increases in forest cover. Use of global and local interpretative methods together with watershed-wide and individual catchment predictions support conservation practitioners that need to identify widespread and localized patterns, especially acknowledging that management actions typically take place at individual-reach scales.
Find more information on the ScienceDirect page.
Understanding the temporal and spatial roles of nutrient limitation on phytoplankton growth is necessary for developing successful management strategies. Chesapeake Bay has well-documented seasonal and spatial variations in nutrient limitation, but it remains unknown whether these patterns of nutrient limitation have changed in response to nutrient management efforts. We analyzed historical data from nutrient bioassay experiments (1992–2002) and data from long-term, fixed-site water-quality monitoring program (1990–2017) to develop empirical approaches for predicting nutrient limitation in the surface waters of the mainstem Bay. Results from classification and regression trees (CART) matched the seasonal and spatial patterns of bioassay-based nutrient limitation in the 1992–2002 period much better than two simpler, non-statistical approaches. An ensemble approach of three selected CART models satisfactorily reproduced the bioassay-based results (classification rate = 99%). This empirical approach can be used to characterize nutrient limitation from long-term water-quality monitoring data on much broader geographic and temporal scales than would be feasible using bioassays, providing a new tool for informing water-quality management. Results from our application of the approach to 21 tidal monitoring stations for the period of 2007–2017 showed modest changes in nutrient limitation patterns, with expanded areas of nitrogen-limitation and contracted areas of nutrient saturation (i.e., not limited by nitrogen or phosphorus). These changes imply that long-term reductions in nitrogen load have led to expanded areas with nutrient-limited phytoplankton growth in the Bay, reflecting long-term water-quality improvements in the context of nutrient enrichment. However, nutrient limitation patterns remain unchanged in the majority of the mainstem, suggesting that nutrient loads should be further reduced to achieve a less nutrient-saturated ecosystem.
Published in the Journal of Water Research, Volume 188, January 2021:
https://doi.org/10.1016/j.watres.2020.116407
The U.S. Army Corps of Engineers operates Washington Aqueduct and provides drinking water to the Washington, D.C. area. Washington Aqueduct routinely samples its source of water, the Potomac River. Each year, it reports the monthly averages for basic water parameters and several pollutants and metals. Reports since 2001 are available online. Reports from 1905 to 2000, however, had limited distribution and their legibility has faded over time.
Dr. Norbert A. Jaworski recognized the historical value of these reports. To prevent their loss, he digitized the monthly values for several parameters. The Interstate Commission on the Potomac River Basin (ICPRB) later updated his dataset through 2019 and checked the entered data for accuracy. This report focuses on changes in temperature, hardness, pH, total solids, chloride, nitrate, and sulfate over the 80 years since ICPRB was formed in 1940. Visual representations (“heatmaps”) and trend analysis show significant increasing trends in all these parameters except nitrate. The report is intended to introduce the historical Washington Aqueduct water quality data to a broader audience and highlight their potential value to Potomac studies.
The Supplemental Materials document contains additional graphical representations of the data.
See the video summary of the report:
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:
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.
Regionally scaled assessments of hydrologic alteration for small streams and its effects on freshwater taxa are often inhibited by a low number of stream gages. To overcome this limitation, we paired modeled estimates of hydrologic alteration to a benthic macroinvertebrate index of biotic integrity data for 4522 stream reaches across the Chesapeake Bay watershed. Using separate random-forest models, we predicted flow status (inflated, diminished, or indeterminant) for 12 published hydrologic metrics (HMs) that characterize the main components of flow regimes. We used these models to predict each HM status for each stream reach in the watershed, and linked predictions to macroinvertebrate condition samples collected from streams with drainage areas less than 200 km2. Flow alteration was calculated as the number of HMs with inflated or diminished status and ranged from 0 (no HM inflated or diminished) to 12 (all 12 HMs inflated or diminished). When focused solely on the stream condition and flow-alteration relationship, degraded macroinvertebrate condition was, depending on the number of HMs used, 3.8–4.7 times more likely in a flow-altered site; this likelihood was over twofold higher in the urban-focused dataset (8.7–10.8), and was never significant in the agriculture-focused dataset. Logistic regression analysis using the entire dataset showed for every unit increase in flow-alteration intensity, the odds of a degraded condition increased 3.7%. Our results provide an indication of whether altered streamflow is a possible driver of degraded biological conditions, information that could help managers prioritize management actions and lead to more effective restoration efforts.
The report has been published in Environmental Management.
The Virginia Department of Health issued a Harmful Algae Bloom (HAB) Advisory for a 53-mile stretch of the North Fork of the Shenandoah River on August 10, 2021 (Figure 1, left). Samples from multi-species algal mats on the river bottom contained harmful levels of toxins produced by cyanobacteria. Three weeks later, Tropical Storm Ida passed over the North Fork, dumping torrential rain on the watershed. Sharply rising streamflows were expected to scour the benthic algal mats, potentially lysing their cells and releasing toxins as they washed downstream. The ICPRB’s Emergency River Spill Model (ERSM) indicated the scoured material’s leading edge would reach the Potomac River mainstem by September 2nd – 4th and Great Falls near Washington, D. C. by September 3rd – 6th.
Virginia Department of Environmental Quality staff confirmed the algal mats were scoured off the river bottom. Water samples collected by ICPRB at the Shenandoah River mouth indicate the storm’s high flows diluted the algal cells and their associated toxins to below-detection levels before they reached the Potomac River. If flows had been less intense, we hypothesize the scoured material and toxins could potentially have reached the Potomac River mainstem. More advanced flow modeling and additional sampling during algal blooms could better characterize the potential transport of scoured or senescing algal blooms in the Shenandoah River under different river conditions.
Rt. 340 bridge over Shenandoah River near Harpers Ferry, WV
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