Review of the New York City Watershed Protection Program (2020) / Chapter Skim
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12 Understanding the Watershed: Monitoring, Assessment, and Modeling
12 Understanding the Watershed: Monitoring, Assessment, and Modeling
Pages 315-360
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From page 315... ...
NYC DEP's monitoring and modeling programs are not officially a part of the Watershed Protection Program, yet the study Statement of Task (Box 1-1) appropriately asks the Committee to review these programs.
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From page 316... ...
and suggests ways NYC DEP could enhance the information content and usefulness of their monitoring results. The goal of the section is to relate how the assessments, based on the data, can better guide the Watershed Protection Program in the future and enhance understanding of the whole system for the water supply managers, regulators, and stakeholders.
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From page 317... ...
These models are needed to prioritize management actions and investments to help ensure that the best quality of water is delivered by the NYC water supply system. Overview of NYC DEP Monitoring and Assessment Program The overall NYC DEP monitoring and assessment program can be categorized as follows, which is described as a "pyramid." Compliance monitoring is described by NYC DEP as the pinnacle (highest priority)
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From page 318... ...
In addition to this extensive system of grab-sample monitoring sites, NYC DEP collects data on a near-continuous basis with sensors located in several types of environments at a set of robotic monitoring sites, known as RoboMon. These include stream-monitoring sites, reservoir profiling buoys, fixed-depth buoys and also an under-ice buoy operated during the winter season.
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From page 319... ...
and valuable in analysis systems designed to interpret water quality data. NYC DEP does not appear to engage (or contract with others for this purpose)
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From page 320... ...
The idea of using turbidity as a statistical surrogate for suspended sediment concentration or total phosphorus concentration is well known and used by NYC DEP and the U
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From page 321... ...
to in situ flow cytometry that captures images of individual organisms1 and can provide near-real-time notification of the presence of potentially harmful algae. NYC DEP could explore these newly emerging in situ monitoring technologies as warning signals for trihalomethane production, taste and odor, and the potential for harmful algal blooms.
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From page 322... ...
NYC DEP could make more effective use of their large water quality data sets to obtain more accurate estimates of daily fluxes of nutrients and sediment. Trend Analysis The Plan provides some general discussion of how the NYC DEP uses monitoring data for trend detection.
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From page 323... ...
These kinds of analyses and graphical displays of results would help track and compare water quality results across the NYC watersheds and over time. NYC DEP is already using one such analysis (WRTDS; Hirsch et al., 2010)
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324 Review of the New York City Watershed Protection Program FIGURE 12-1 Graph of trend magnitudes for flow-normalized orthophosphorus flux at monitoring sites in the Chesapeake Bay, nontidal network, for the monitoring period 2009-2018. Figure in color at https:// www.nap.edu/catalog/25851/.
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From page 325... ...
of total phosphorus for nine wa tersheds that constitute the river input monitoring network for the Chesapeake Bay. SOURCE: Hirsch et al.
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From page 326... ...
In these watersheds, the upward trend in discharge has been an important contributor to the overall increase in SRP flux, accounting for approximately one-third of the total increase at each site. These graphical approaches have some potential application to the display of trend analysis results for NYC DEP.
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From page 327... ...
Also, the ability to combine data from the NYC DEP data set with data from other watersheds increases the potential for developing new insights. It might be particularly valuable to compare water quality trends observed in the NYC watersheds with other nearby watersheds with similar landscape and land use attributes but without the investment in BMPs that has taken place in the NYC watersheds.
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From page 328... ...
Indeed, the data analysis presented used only graphical approaches, with no attempt to build a statistical model from the data. Without a formal statistical model that considers the sources of variation in stream concentration of phosphorus (such as river discharge or seasonality)
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In fact, given the importance of the question about progress, NYC DEP should be undertaking a variety of statistical approaches with their data set and publishing them in the peer-reviewed literature. Following a formal statistical analysis that suggests whether BMPs are effective, the process-based model SWAT-HS can be used to tease out which BMPs may be most effective.
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From page 330... ...
In the case of the Chesapeake Bay, a significant change in the understanding of the role of legacy phosphorus in soils, streambeds, and streambanks, along with results of long-term anal ysis of trends in river transport of phosphorus, has led to significant modifications of the Chesapeake Bay Watershed Model (Kleinman et al., 2019)
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From page 331... ...
However, it does not appear from the studies that NYC DEP has published that the monitoring data have been used in this manner. Rather, they tend to be used to simply demonstrate a match of observed and predicted concentrations at the short-term scale (hours to days)
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From page 332... ...
The general goal of this program is to develop and apply quantitative tools, supporting data, and data analyses in order to evaluate effects of land use change, watershed management, reservoir operations, ecosystem health, and climate change on water supply quantity and quality. Hence, NYC DEP has developed a multi-tiered modeling system that includes short-term and longer-term weather predictions; watershed models that simulate runoff generation and basic runoff water quality; reservoir models that simulate water balances and fate and transport of heat, suspended solids and other contaminants; and operational models that balance water availability, domestic supply needs, environmental flows, water quality, and treatability (see Figure 12-5)
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. In all of these applications, NYC DEP employed the common practice for calibration and validation of water quality models by splitting the time series of water quality data into a few years for calibration and the following few years for validation.
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From page 334... ...
NYC DEP and partners have worked extensively with SWAT, both developing new model routines to better capture relevant regional hydrologic and water quality processes (Easton et al., 2008b, Hoang et al., 2017; White et al., 2011) and for evaluating water quality management and/or climate impacts (Hoang et al., 2019; Pradhanang et al., 2013)
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From page 335... ...
This becomes a decision analytic approach when the cost of each BMP is compared to the cost of the corresponding additional monitoring. Future of Watershed Modeling Within NYC DEP The primary need for watershed modeling in support of the Watershed Protection Program is to inform decisions on actions that the subprograms (e.g., the Watershed Agricultural Program and Watershed Forestry Program)
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From page 336... ...
This provides an objective statistical approach for evaluating alternative hypotheses about the effects of land use changes, watershed management, point-source controls, or climate change in controlling the seasonal patterns of surface water quality. The estimation techniques used in SPARROW also have the advantage of providing measures of uncertainty in model parameters and predictions (Alexander and Gorman Sanisaca, 2019; Schwarz et al., 2006)
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. Because NYC DEP has nutrient monitoring data that span several decades, they could create a dynamic SPARROW model for the NYC watershed, taking advantage of the broader SPARROW framework and data sets that already exist in the northeastern U.S.
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From page 338... ...
The Committee recommends that the NYC DEP make use of the SPARROW statistical modeling framework to quantify nutrient sources and delivery to individual reaches within the watersheds. A SPARROW model that would best serve NYC DEP would need to extend beyond the geographic domain of the NYC watersheds which means that it would need to build on the foundation of the most recent regional SPARROW model.
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. TABLE 12-3 Sources and Loadings of Total Phosphorus in Selected NYC Water Supply Reservoirs SOURCE: Based on a SPARROW Model Application for the Northeastern U.S.
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There have been applications in the northeastern United States and around the world (Boyer et al., 2002, 2006; Boyer and Howarth, 2008; Galloway et al., 2004; Hong et al., 2017; Howarth et al., 1996, 2012; Swaney et al., 2018)
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RESERVOIR WATER QUALITY MODELS Reservoir water quality models are mathematical representations of aquatic systems that simulate physical, chemical and biological properties and processes in lakes and reservoirs. Water quality modeling of the source water supply has been conducted by the NYC DEP for decades to assist in complying with the regulatory requirements of the FAD.
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From page 342... ...
The Water Quality Modeling Group at the NYC DEP has recently developed GLM models of the Cannonsville and Neversink reservoirs and completed water-balance and temperature-stratification simulations for the 2007-2008 period, with the longer-term objective to simulate organic carbon dynamics and formation of disinfection byproduct precursors provided by the more comprehensive biogeochemical capabilities of GLM-AED (compared with CE-QUAL-W2)
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From page 343... ...
. Other NYC DEP Water Quality Modeling Efforts The NYC DEP water quality modeling group has proven to be quite adept at identifying the correct level of model complexity to match the scientific, operations and/or management questions at hand.
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From page 344... ...
For example, turbidity levels in Kensico Reservoir outflow are a primary decision node. It is not clear, based on available documents and presentations, how closely predictions FIGURE 12-10 One-dimensional model application to Cannonsville Reservoir evaluating nutrient control strategies.
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From page 345... ...
. Empirical regressions have been developed by NYC DEP that capture central tendencies in turbidity-flow relationships, but they fail to adequately capture the inherent variability present.
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The model, used with forecasts in Position Analysis mode to assess the timing and magnitude of peak turbidity delivered to the Delaware Aqueduct, struggled to capture observed turbidity levels (NYC DEP, 2017)
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The temperatures and concentrations of turbidity in inflows were provided by NYC DEP; a complete set of values was available for Chestnut Creek, Pepacton, Cannonsville, and Neversink inflows, although instrument malfunction on Rondout Creek over the period July 9-13 required estimation of values upon available historical observations, flow rates and reservoir monitoring data. Gelda et al.
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From page 349... ...
Discussions with NYC DEP on June 27, 2019 indicated that high-flow conditions generate only about 10 percent of particles <2 µm and about 40 percent of particles >5 µm. In light of above considerations, two size classes were simulated in this analysis (2 µm and 5 µm comprising 35 percent and 65 percent, respectively)
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2 µm and (B) 5 µm suspended solids at reservoir outlet withdrawal port #2 (depth of 242 m)
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From page 351... ...
and as such it is not a focus of this study. However, to understand the full range of actions and policies used by NYC DEP to achieve its watershed protection goals under the FAD, it is important that the reader have some familiarity with this analytical tool.
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From page 352... ...
The watershed models discussed earlier in this chapter have not yet been linked to OST; if they were, they would replace the ensemble streamflow forecasts that are currently used as input. CONCLUSIONS AND RECOMMENDATIONS The NYC DEP deserves praise for their monitoring system design and for the accumulation of such data as streamflow, snowpack, turbidity, phosphorus, and nitrogen, which will become increasingly valuable as these
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From page 353... ...
Responding to this recommendation requires that NYC DEP develop formal statistical models and establish statistical protocols for the analysis of the many types of data that they collect. Statistically based tools can be used to provide projections of the consequences of future watershed protection activities and various land use changes on watershed fluxes.
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Uncertainty estimates are not comprehensively assessed for any of the currently applied NYC DEP watershed models. Uncertainty analysis can be undertaken for statistical models such as SPARROW, since the model fitting (typically regression analysis)
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From page 355... ...
Presentation at Meeting 3 of NASEM Committee to Re view the NYC DEP Watershed Protection Program. West Harrison, NY.
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From page 356... ...
, with an application to Chesapeake Bay River Inputs1. Journal of the American Water Resources Association 46(5)
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From page 357... ...
Washington, DC: The National Academies Press. NYC DEP (New York City Department of Environmental Protection)
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Journal of the American Water Resources Association 49(6)
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From page 359... ...
2011. The challenge of documenting water quality benefits of conservation practices: a review of USDA-ARS's conservation effects assessment project watershed studies.
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