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New York City, NY, United States

Mukundan R.,City University of New York | Van Dreason R.,Bureau of Water Supply
Journal of Environmental Quality

Chlorine, a commonly used disinfectant in most water supply systems, can combine with organic carbon to form disinfectant byproducts, including carcinogenic trihalomethanes. We used water quality data from 24 monitoring sites within the New York City water supply distribution system, measured between January 2009 and April 2012, to develop an empirical model for predicting total trihalomethane (TTHM) levels. Terms in the model included the following water quality parameters: total organic carbon, pH, water age (reaction time), and water temperature. Reasonable estimates of TTHM levels were achieved with overall R2 of about 0.75, and predicted values on average were within 6 μg L-1 of measured values. A sensitivity analysis indicated that total organic carbon and water age are the most important factors for TTHM formation, followed by water temperature; pH was the least important factor within the boundary conditions of observed water quality. Although never out of compliance in 2011, the TTHM levels in the water supply increased after tropical storms Irene and Lee, with 45% of the samples exceeding the 80 μg L-1 maximum contaminant level in October and November. This increase was explained by changes in water quality parameters, particularly by the increase in total organic carbon concentration during this period. This study demonstrates the use of an empirical model to understand TTHM formative factors and their relative importance in a drinking water supply. This has implications for simulating management scenarios and real-time estimation of TTHMs in water supply systems under changing environmental conditions. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. Source

Ryder E.,Dundalk Institute of Technology | Jennings E.,Dundalk Institute of Technology | De Eyto E.,Marine Institute of Ireland | Dillane M.,Marine Institute of Ireland | And 5 more authors.
Limnology and Oceanography: Methods

Field-based instruments measuring chromophoric dissolved organic matter (CDOM) fluorescence are often used as a proxy for dissolved organic carbon concentrations in lakes and streams. CDOM fluorescence yield is, however, affected by water temperature at the time of measurement, a factor which varies on both diel and seasonal timescales. A temperature correction must therefore be applied to these data. We present data on temporal and site-specific variability in temperature quenching of CDOM fluorescence for water from a humic lake and one of its main inflows in the west of Ireland. In addition, we present a temperature compensation equation and show that this equation is an improvement on methods previously proposed. © 2012, by the American Society of Limnology and Oceanography, Inc. Source

Frei A.,York College - The City University of New York | Frei A.,CUNY Institute for Sustainable Cities | Kunkel K.E.,North Carolina State University | Matonse A.,Bureau of Water Supply
Journal of Hydrometeorology

Recent analyses of extreme hydrological events across the United States, including those summarized in the recent U.S. Third National Climate Assessment (May 2014), show that extremely large (extreme) precipitation and streamflow events are increasing over much of the country, with particularly steep trends over the northeastern United States. The authors demonstrate that the increase in extreme hydrological events over the northeastern United States is primarily a warm season phenomenon and is caused more by an increase in frequency thanmagnitude. The frequency of extreme warmseason events peaked during the 2000s; a secondary peak occurred during the 1970s; and the calmest decade was the 1960s. Cold season trends during the last 30- 50 yr areweaker. Since extreme precipitation events in this region tend to be larger during the warmseason than during the cold season, trend analyses based on annual precipitation values are influencedmore bywarmseason than by cold season trends. In contrast, the magnitude of extreme streamflow events at stations used for climatological analyses tends to be larger during the cold season: therefore, extreme event analyses based on annual streamflow values are overwhelmingly influenced by cold season, and therefore weaker, trends. These results help to explain an apparent discrepancy in the literature, whereby increasing trends in extreme precipitation events appear to be significant and ubiquitous across the region,while trends in streamflowappear less dramatic and less spatially coherent. © 2015 American Meteorological Society. Source

Pradhanang S.M.,City College of New York | Frei A.,City College of New York | Zion M.,Bureau of Water Supply | Schneiderman E.M.,Bureau of Water Supply | And 2 more authors.
Hydrological Processes

Rain-on-snow (ROS) runoff events are important hydro-meteorological phenomenon due to their association with flooding. The severity of ROS runoff events depends on the magnitude of the precipitation, air temperature elevation, snow water equivalent (SWE), and areal extent of the antecedent snowpack. Examining the consequences of these factors acting together creates challenges for both flood prediction and flood risk assessments. This study provides information on the spatial patterns, and seasonality of ROS events in New York. We examine the spatial and temporal variability of ROS events for water years 2004 to 2012 from SNOw Data Assimilation System products for New York. Liquid and solid precipitation, snow depth, snowmelt, SWE, maximum and minimum temperature, hydrograph characteristics, and annual peak flow are examined. There is significant positive correlation of ROS days and ROS triggered events with elevation and negative correlation of these events with increasing air temperature. Our study shows that ROS events are dominant in high elevation areas of Adirondack and Catskill regions, and their distribution varies with month. Cumulative runoffs from ROS events are generally greater than the rain-only runoff events. The majorities of annual peak flows in the study watersheds are the results of ROS events and lasted from a few days to many weeks. © 2013 John Wiley & Sons, Ltd. Source

Mukundan R.,University of Louisiana at Lafayette | Pierson D.C.,Bureau of Water Supply | Schneiderman E.M.,Bureau of Water Supply | Zion M.S.,Bureau of Water Supply
Environmental Monitoring and Assessment

The use of watershed models as cost-effective tools to quantify the impact of conservation practices on water quality is often constrained by lack of data for model parameterization. This study uses short-term (3 years) detailed monitoring data to guide spatially distributed model parameterization and modeling analysis for suspended sediment in the Upper Esopus Creek Watershed (UECW) that is part of the New York City water supply. The calibrated Soil and Water Assessment Tool (SWAT) model simulated suspended sediment loading from tributary sub-basins and at the watershed outlet that were comparable to field measurements. Model simulations estimated that stream channels contributed the majority (85 %) of stream sediment in the study watershed followed by upland erosion (11 %) and point sources (4 %), consistent with previous estimates and field observations. Long-term (12 years) simulation of the calibrated model was used to apportion the average annual sediment yields from tributary sub-basins which ranged between 12 and 161 t km−2 year−1. Model simulations were also used to understand the inter-annual variability and seasonality in suspended sediment loading in the study watershed. We demonstrate the wider applicability of short-term detailed monitoring for model parameterization and calibration, and long-term simulation of water quality using the SWAT model. © 2015, Springer International Publishing Switzerland. Source

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