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Syracuse, NY, United States

Endreny T.,Environmental Resources Engineering | Lautz L.,Syracuse University | Siegel D.I.,Syracuse University
Water Resources Research | Year: 2011

The conceptual model of hyporheic exchange below river steps may oversimplify exchange flow paths if it depicts a uniform pattern of downstream-directed upwelling. This research used nonmobile, porous bed flume experiments and hydrodynamic simulation (CFD) to characterize hyporheic flow paths below a river step with a hydraulic jump. Bed slope was 1%, step height was 4 cm, downstream flow depth was 4 cm, substrate was 1 cm median diameter gravel, and hydraulic jump length was 25 cm in the flume and CFD experiments. With the hydraulic jump, flow paths changed to include downwelling beneath the water plunging into the pool and upstream-directed upwelling at the base of the step and beneath the length of jump. Failure to represent the influence of static and dynamic pressures associated with hydraulic jumps leads to erroneous prediction of subsurface flow paths in 75% of the streambed beneath the jump. A refined conceptual model for hyporheic flow paths below a step with a hydraulic jump includes reversed hyporheic circulation cells, in which downwelling water moves upstream and then upwells, and flow reversals, in which the larger flow net of downstream-directed upwelling encounters a nested flow path of upstream-directed upwelling. Heterogeneity in hyporheic flow paths at hydraulic jumps has the potential to explain field-observed mosaics in streambed redox patterns and expand structure-function relationships used in river management and restoration. Copyright 2011 by the American Geophysical Union. Source

Yang Y.,Environmental Resources Engineering | Endreny T.A.,Environmental Resources Engineering | Nowak D.J.,U.S. Department of Agriculture
Journal of Geophysical Research: Atmospheres | Year: 2013

Spatial variation of urban surface air temperature and humidity influences human thermal comfort, the settling rate of atmospheric pollutants, and plant physiology and growth. Given the lack of observations, we developed a Physically based Analytical Spatial Air Temperature and Humidity (PASATH) model. The PASATH model calculates spatial solar radiation and heat storage based on semiempirical functions and generates spatially distributed estimates based on inputs of topography, land cover, and the weather data measured at a reference site. The model assumes that for all grids under the same mesoscale climate, grid air temperature and humidity are modified by local variation in absorbed solar radiation and the partitioning of sensible and latent heat. The model uses a reference grid site for time series meteorological data and the air temperature and humidity of any other grid can be obtained by solving the heat flux network equations. PASATH was coupled with the USDA iTree-Hydro water balance model to obtain evapotranspiration terms and run from 20 to 29 August 2010 at a 360 m by 360 m grid scale and hourly time step across a 285 km 2 watershed including the urban area of Syracuse, NY. PASATH predictions were tested at nine urban weather stations representing variability in urban topography and land cover. The PASATH model predictive efficiency R2 ranged from 0.81 to 0.99 for air temperature and 0.77 to 0.97 for dew point temperature. PASATH is expected to have broad applications on environmental and ecological models. Key Points Present a physically-based analytical spatial air temperature model.Incoporate the impact of topography and land cover on local climate.The model has been proven efficient. ©2013. American Geophysical Union. All Rights Reserved. Source

Kroll C.N.,Environmental Resources Engineering | Croteau K.E.,Environmental Resources Engineering | Croteau K.E.,Windward | Vogel R.M.,Tufts University
Journal of Hydrology | Year: 2015

Hydrologic systems can be altered by anthropogenic and climatic influences. While there are a number of statistical frameworks for describing and evaluating the extent of hydrologic alteration, here we present a new framework for assessing whether statistically significant hydrologic alteration has occurred, or whether the shift in the hydrologic regime is consistent with the natural variability of the system. Four hypothesis tests based on shifts of flow duration curves (FDCs) are developed and tested using three different experimental designs based on different strategies for resampling of annual FDCs. The four hypothesis tests examined are the Kolmogorov-Smirnov (KS), Kuiper (K), confidence interval (CI), and ecosurplus and ecodeficit (Eco). Here 117 streamflow sites that have potentially undergone hydrologic alteration due to reservoir construction are examined. 20 years of pre-reservoir record is used to develop the critical value of the test statistic for type I errors of 5% and 10%, while 10 years of post-alteration record is used to examine the power of each test. The best experimental design, based on calculating the mean annual FDC from an exhaustive jackknife resampling regime, provided a larger number of unique values of each test statistic and properly reproduced type I errors. Of the four tests, the CI test consistently had the highest power, while the K test had the second highest power; KS and Eco always had the lowest power. The power of the CI test appeared related to the storage ratio of the reservoir, a rough measure of the hydrologic alteration of the system. © 2015. Source

Yang Y.,Environmental Resources Engineering | Endreny T.A.,Environmental Resources Engineering | Nowak D.J.,U.S. Department of Agriculture
Journal of the American Water Resources Association | Year: 2011

This article presents snow hydrology updates made to iTree-Hydro, previously called the Urban Forest Effects-Hydrology model. iTree-Hydro Version 1 was a warm climate model developed by the USDA Forest Service to provide a process-based planning tool with robust water quantity and quality predictions given data limitations common to most urban areas. Cold climate hydrology routines presented in this update to iTree-Hydro include: (1) snow interception to simulate the capture of snow by the vegetation canopy, (2) snow unloading to simulate the release of snow triggered by wind, (3) snowmelt to simulate the solid to liquid phase change using a heat budget, and (4) snow sublimation to simulate the solid to gas phase via evaporation. Cold climate hydrology routines were tested with research-grade snow accumulation and weather data for the winter of 1996-1997 at Umpqua National Forest, Oregon. The Nash-Sutcliffe efficiency for open area snow accumulation was 0.77 and the Nash-Sutcliffe efficiency for under canopy was 0.91. The USDA Forest Service offers iTree-Hydro for urban forest hydrology simulation through. © 2011 American Water Resources Association. Source

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