Making up for losses: A critical analysis of Section 404 compensatory stream mitigation banking in Illinois

U.S. Department of the InteriorU.S. Geological SurveyOpe

Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics

© 2016. American Geophysical Union. All Rights Reserved. Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow characteristics. Three-dimensional velocities were measured during two different events—a near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops

Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure

Toward a philosophy of geomorphology

ABSTRACT Few attempts have been made to examine philosophically the scientific nature of geomorphology. The reluctance of geomorphologists to engage in philosophical analysis reflects, at least in part, a widespread skepticism of nonempirical forms of inquiry among practicing scientists. This perspective is an outgrowth of the a priori prescriptive nature of traditional philosophy of science. Contemporary philosophers of science have responded to the skepticism of practicing scientists by developing naturalized philosophies that illuminate the complexity of scientific inquiry through direct examination of scientific practice. The objective of this chapter is to illustrate the potential for philosophical analysis to strengthen the intellectual foundation of geomorphology by providing insight into the scientific nature of the discipline. Several issues are introduced that have relevance for understanding geomorphology as a science, including classification, laws and causality, theory and models, discovery, gender issues, and applied studies. The discussion calls attention to unexamined aspects of these issues in geomorphology and briefly reviews contemporary perspectives on them in the philosophy of science. The purpose of the discussion is not to provide a penetrating philosophical investigation of each issue, but to establish an informative framework for future analysis

Standardizing No Net Loss Stream Mitigation Assessment Methods: Tradeoffs between Expediency and River Science

Environmental regulators use No Net Loss policies to minimize the damaging impacts of development projects on water resources. In this context, regulators prefer standard environmental assessment protocols over ad hoc approaches. This article examines how the St. Louis District of the U.S. Army Corps of Engineers (the Corps) directed the development of statewide standard stream mitigation assessment protocols in Missouri and Illinois to comply with Section 404 of the Clean Water Act. Protocol development in each state included Corps district representatives along with river scientists and various stakeholders. A primary tension in these discussions centered on the tradeoff between the efficiency of using the protocol vs. its scientific rigor. While consensus in Missouri was achieved by leveraging statewide agreements, Illinois lacked similar agreements and included a wider range of scientific participants, which hindered consensus. Despite these differences, the two states produced remarkably similar stream assessment methods. The similarity largely reflected the authority that Corps districts had over the Section 404 process and their privileging of simple and flexible stream mitigation assessments that can be used across different Corps districts. This study provides insights into the social processes that shape no net loss assessment protocols and the practical challenges of protecting the environmental quality of streams

The influence of geomorphological variability in channel characteristics on sediment denitrification in agricultural streams

ABSTRACT Within fluvial systems, the spatial variability of geomorphological characteristics of stream channels and associated streambed properties can affect many biogeochemical processes. In agricultural streams of the midwestern USA, it is not known how geomorphological variability affects sediment denitrification rates, a potentially important loss mechanism for N. Sediment denitrification was measured at channelized and meandering headwater reaches in east-central Illinoi

Hydrodynamic and geomorphologic dispersion: scale effects in the Illinois River Basin

The objective of this work is to determine the relative effects of hydrodynamic and geomorphologic dispersion on the hydrological response of the Illinois River Basin (IRB) as scale increases. The specific hypothesis that was tested is that as basin size increases, the river network structure, as compared to channel hydrodynamic properties, plays an increasingly dominant role in determining the hydrologic response. The analysis was performed on eight of the major watersheds in the IRB in order to provide an adequate representation of basins that contain streams of order six or greater. The basins studied include the Des Plaines, Mackinaw, Vermilion, Fox, La Moine, Spoon, Kankakee, and the Sangamon, and have magnitudes ranging from order six to order eight. The geometric and hydrodynamic properties were derived from the analysis of digital elevation model data and from the hydraulic geometry equations for various subcatchments of the IRB put forth by Stall and Fok [Univ. of Ill. Water Res. Center Res. Rep. 15, 1968]. The hydrodynamic and geomorphologic dispersion coefficients were determined for each order stream of the eight basins and for constant flow frequencies, then compared. The results contradict the original hypothesis, for at small scales, geomorphologic dispersion tends to dominate, the extent of which depends upon the flow frequency, and at large scales, geomorphologic dispersion is less dominant. This occurs because of the behavior of the path lengths of a stream network, which geomorphologic dispersion depends upon. In addition, at high flow frequencies the geomorphologic dispersion dominates, and at low frequencies the hydrodynamic dispersion begins to play an increasingly important role, although the geomorphologic dispersion still dominates. This dominance suggests that the geomorphologic parameters of a watershed could be more important in characterizing the hydrologic response of a river basin than hydrodynamic parameters

Simulated instream restoration structures offer smallmouth bass (Micropterus dolomieu) swimming and energetic advantages at high flow velocities

Restoration practices aimed at fish habitat enhancement often include installation of instream structures. However, mixed outcomes have been reported regarding structure effectiveness, while mechanisms underlying success remain unclear. The interactions between fish and flow conditions generated by instream structures and their subsequent impact on fish energetics may provide some insight. This study seeks to quantify how restoration structures, simulated by cylinders in three orientations, alter the energetics and swimming stability of smallmouth bass (Micropterus dolomieu). Accelerometers measured swimming stability while a respirometer measured energy expenditure at multiple velocities. Particle image velocimetry was used to characterize flow fields behind structures. Structures generated flow conditions that benefited fish energetically. Fish had a smoother gait and expended less energy when swimming near a structure, regardless of its orientation. Benefits varied with flow conditions; reductions in energy expenditure were especially apparent at high flow velocities. Results suggest that restoration structures may be most energetically beneficial in stream systems with consistently high velocities and inform restoration by indicating flow conditions in which structures provide the greatest energetic benefits for fish.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author