Assessing Variability and Uncertainty in Green Infrastructure Planning Using a High-Resolution Surface-Subsurface Hydrological Model and Site-Monitored Flow Data

Green infrastructure (GI) is increasingly being used in urban areas to supplement the function of conventional drainage infrastructure. GI relies on the “natural” hydrological processes of infiltration and evapotranspiration to treat surface runoff close to where it is generated, alleviating loading on the conventional infrastructure systems. This research addresses growing interest in identification and quantification of uncertainties with distributed, infiltration-based stormwater control measures, retrofitted on private and public properties and in right-of-ways in existing urban areas. We identify four major sources of variability and uncertainty in cumulative performance of systems that rely on extensive implementation of distributed GI: non-additive effects of individual best management practices (BMPs) at the catchment scale; the spatial configuration of fine-scale land use and land cover changes; performance changes due to climate change; and noise levels present in urban flow monitoring programs. Using a three-dimensional coupled surface-subsurface hydrological model of a residential sewershed in Washington DC, we find that prolonged, large-magnitude rain events affect various spatial configurations of GI networks differently. Runoff peaks and volumes can both be influenced by the spatial permutations of infiltration opportunities in addition to the absolute magnitude of treated area. However, the magnitude of the last source of uncertainty—noise levels in urban flow monitoring programs—may be larger than sources of variability associated with spatial changes in fine-scale land use and land cover. Changes associated with climate change– more frequent and larger rainfall events– will likely intensify performance differences between spatial configurations of GI but also increase noise levels in urban flow monitoring programs

Assessment of Urban Flood Vulnerability Using theSocial-Ecological-Technological Systems Framework in Six US cities

As urban populations continue to grow through the 21 st century, more people are projected to be at risk of exposure to climate change-induced extreme events. To investigate the complexity of urban floods, this study applied an interlinked social-ecological-technological systems (SETS) vulnerability framework by developing an urban flood vulnerability index for six US cities. Indicators were selected to reflect and illustrate exposure, sensitivity, and adaptive capacity to flooding for each of the three domains of SETS. We quantified 18 indicators and normalized them by the cities’ 500-yr floodplain area at the census block group level. Clusters of flood vulnerable areas were identified differently by each SETS domain, and some areas were vulnerable to floods in more than one domain. Results are provided to support decision-making for reducing risks to flooding, by considering social, ecological, and technological vulnerability as well as hotspots where multiple sources of vulnerability coexist. The spatially explicit urban SETS flood vulnerability framework can be transferred to other regions facing challenging urban floods and other types of environmental hazards. Mapping SETS flood vulnerability helps to reveal intersections of complex SETS interactions and inform policy-making for building more resilient cities in the face of extreme events and climate change impacts

Challenges and Opportunities in the Hydrologic Sciences

This is the Table of Contents and Introduction of a Report published as Hornberger, G. M., E. Bernhardt, W. E. Dietrich, D. Entekhabi, G. E. Fogg, E. Foufoula-Georgiou, W. J. Gutowski, W. B. Lyons, K. W. Potter, S. W. Tyler, H. J. Vaux, C. J. Vorosmarty, C. Welty, C. A. Woodhouse, C. Zheng, Challenges and Opportunities in the Hydrologic Sciences. 2012: Water Science and Technology Board, Division on Earth and Life Studies, National Academy of Sciences, Washington, DC. 173 pp. Posted with permission.</p

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures; https://iopscience.iop.org/article/10.1088/1538-3873/acb29

Regional Climate Variability and Patterns of Urban Development – Impacts on the Urban Water Cycle and Nutrient Export

An overview of the Baltimore NSF Water Sustainability and Climate project initiated in January 2011 will be presented. The goal of the project is to evaluate the interactions between urban development patterns and the hydrologic cycle and its associated nutrient cycles, within the context of regional and local climate variability. Our specific objective is to create a modeling system capable of simulating the feedback relationships that control urban water sustainability. Core elements include spatial modeling of urban development patterns and individual land use and location processes at parcel and neighborhood scales and for different policy scenarios; three-dimensional modeling of coupled surface water-groundwater and land surface-atmospheric systems at multiple scales (including consideration of the engineered water system), where development patterns are incorporated as input; and field work and modeling aimed at quantifying flow paths and fluxes of water and nitrogen in this system. The project team is evaluating linkages among (1) how human locational choices, waterbased ecosystem services, and regulatory policies affect the supply of land and patterns of development over time; (2) how the changing composition and variability of urbanizing surfaces affect local and regional climate; and (3) how patterns of development (including the engineered water system) and climate variability affect fluxes, flow paths and storage of water and nitrogen in urban areas. The Baltimore Ecosystem Study LTER (http://beslter.org) is being used as a platform to carry out the work. This capability enables us to take advantage of a 14-year database of hydrologic and chemical characterization data; high-resolution land-cover, land use, and socio-demographic information; and a high-density hydrologic observing system

Evaluation of Longitudinal Dispersivity from Tracer Test Data

Scanning notes: Missing innner title page. Page 32 contains text that runs off edge of page. Disclaimer scanned.Prepared with the support of U.S. Environmental Protection Agency and National Science Foundation.Introduction: Mathematical modeling of solute transport has become a standard tool for evaluating the movement and spreading of chemical contaminants in the subsurface aquatic environment. Most frequently, numerical techniques such as finite element or finite difference methods are used to solve the governing partial differential equations of flow and solute transport over a large aquifer region, in order to predict the concentration of a chemical contaminant at some future time and at points distant in space from a source. One problem that continues to plague users of these techniques is estimation of mixing or dilution parameters, or more specifically the dispersivity (if the dispersion coefficient is assumed to be the product of dispersivity and mean pore velocity), in the governing equations. Summaries of field observations (e.g., Lallemand-Barres and Peaudecerf, 1978; Anderson, 1979; and Gelhar, et al., 1985) and theoretical studies (e.g., Gelhar and Axness, 1983) both have indicated that dispersivity is a function of the heterogeneity of the geologic formation and that there is a dependence of the value of dispersivity on the solute displacement distance in the aquifer. Typically, then, there is a need to determine a value for dispersivity for the aquifer material and scale of problem at hand. Tracer tests are often attempted as a means of estimating the required dispersivity. Figure 1-1 from Gelhar, et al. (1985), summarizes the information available on longitudinal dispersivity values determined from tracer tests conducted at various length scales and on many type of aquifer materials around the world. Figure 1-2 illustrates the ranking of the relative reliability for these same data, based on judgements about the type of experiment and method of data interpretation. This graphical summary reinforces the fact that modelers indeed face difficulties in determining the proper value of dispersivity for a given problem. It is with this motivation in mind that we explore improved methods for analysis of tracer tests to yield accurate information on dispersivity values. This will contribute to more realistic modeling of the solute transport process in evaluation of groundwater contamination cases. The two overall goals of this study are: 1) to develop and demonstrate improved methods of analyzing existing tracer test data; and 2) to use this information and experience to better define the reliability of existing data and to provide an improved basis for selecting, designing, and analyzing tracer tests

Use of a three-dimensional reactive solute transport model for evaluation of bioreactor placement in stream restoration

A three-dimensional groundwater flow and multispecies reactive transport model was used to strategically design placement of bioreactors in the subsurface to achieve maximum removal of nitrate along restored stream reaches. Two hypothetical stream restoration scenarios were evaluated over stream reaches of 40 and 94 m: a step-pool scenario and a channel re-meandering scenario. For the step-pool scenario, bioreactors were placed at locations where mass fluxes of groundwater and nitrate were highest. Bioreactors installed over 50% of the total channel length of a step-pool scenario (located to intercept maximum groundwater and nitrate mass flux) removed nitrate-N entering the channel at a rate of 36.5 kg N yr-1 (100 g N d-1), achieving about 65% of the removal of a whole-length bioreactor. Bioreactor placement for the re-meandering scenario was designed using a criterion of either highest nitrate mass flux or highest groundwater flux, but not both, because they did not occur together. Bioreactors installed at maximum nitrate flux locations (53% of the total channel length) on the western bank removed nitrate-N entering the channel at 62.0 kg N yr-1 (170 g N d-1), achieving 85% of nitrate-N removal of whole-length bioreactors for the re-meandering scenario. Bioreactors installed at maximum groundwater flux locations on the western bank along approximately 40% of the re-meandering channel achieved about 65% of nitrate removal of whole-length bioreactors. Placing bioreactors at maximum nitrate flux locations improved denitrification efficiency. Due to low groundwater velocities, bioreactor nitrate-N removal was found to be nitrate limited for all scenarios