The following five Outdoor StreamLab (OSL) projects are currently planned for spring, summer, and fall of 2008. Project details are subject to change. We encourage potential collaborators to contact us about research and educational opportunities at any of the StreamLab facilities.
Project 1 | Project 2 | Project 3 | Project 4 | Project 5
Project 1: Using current knowledge of river channel processes to predict the equilibrium topography of a sand-bed channel within a floodplain
Researchers: Anne Lightbody, Jeff Marr, Chris Paola, Gary Parker, Cailin Orr, Jacques Finlay, Peter Wilcock, NCED visitor program participants
Stream restoration projects often seek to improve physical properties and rehabilitate ecological processes of a channel; however, project designs are often based on limited scientific knowledge. In this project, focused on small sand-bed rivers, we seek to expand our fundamental knowledge of physical and ecological stream systems and develop applied knowledge and insights that will benefit stream restoration practice. With the assistance of students in the Stream Restoration Certificate Program, we will design a sinuous sand-bed channel with a specified bank-full discharge, incorporating the best current knowledge of equilibrium channel properties. In the long term, a river within an erodible floodplain will sculpt its banks to create dynamic equilibrium (that is, although any position along the channel may change, the channel's mean properties will remain constant), but we will attempt to predict the eventual product by creating a channel that is expected to be as close to equilibrium as possible and then observe whether any changes occur as the stream evolves. Various methods of channel design will be compared, including stream restoration manuals and comparison to existing sand-bed streams.
Project 2: Determination of the dominant control of cross-stream super-elevation within meander bends
Researchers: Kyle Straub, Chris Paola, Anne Lightbody
The cross-stream water elevation profile within meander bends is typically sloped, so that the water elevation at the outer bank is elevated above that of the inner bank. This slope creates a helical secondary circulation cell, which moves flow across the river bed toward the inner bank and builds point bars at the inside of meander bends. It is typically assumed that cross-stream elevation is created by a centrifugal force that is balanced by a restoring pressure force. The cross-stream slope predicted by this model has been shown to match field observations.
However, this model relies on the assumption that the longitudinal velocity follows the thalweg of the channel, yet observations have confirmed that this assumption is not appropriate for all stream systems. In those systems, the longitudinal velocity overshoots the thalweg and instead hugs the outer bank of the meander bend, resulting in flow piling up near the outer bank due to momentum. Prior work has shown that within gravity currents, predicting outer bank super-elevation using the centrifugal force alone massively underpredicts observations within density current systems, presumably because the relative friction force within those systems is much reduced over terrestrial streams.
It is hypothesized that the centrifugal force balanced by a pressure restoring force controls water surface super-elevation and the development of secondary circulation within river bends when bed friction is the dominant term within the momentum equation, but longitudinal momentum balanced by a pressure restoring force dominates when bed friction is low. To test this hypothesis, under different discharge conditions, horizontal velocity measurements will be obtained at various locations over depth along a transect parallel to the bend radius (approximately perpendicular to the channel thalweg).
Project 3: Determination of appropriate metrics for sediment-related total maximum daily loads
Researchers: Anne Lightbody, Patrick Belmont, Jeff Marr, Cailin Orr, Chris Paola, Kimberly Hill, John Gaffney
The most common cause of impaired rivers and streams in the United States is sediment pollution. High levels of suspended sediment reduce aquatic health both through direct physical mechanisms (interfering with the operation of fish gills and macroinvertebrate feeding, abrading benthic organisms, reducing hyporheic exchange, and smothering fish eggs) and indirectly by reducing light transmission and increasing turbidity. Many states, however, including Minnesota , determine lake and stream water quality based on turbidity alone. In systems with spatial and temporal variability, and thus weak correlation between turbidity and total suspended sediment, turbidity measurements may not provide adequate estimates of suspended sediment concentrations, indicating that alternative measurement techniques are needed: It is possible that stream habitat quality is being endangered by sediment pollution effects that are not captured by an analysis of water clarity alone.
In this project, we ask the question of what is the most important aspect of sediment pollution, with the goal of informing future total maximum daily load (TMDL) decisions. We will test the null hypothesis that turbidity is the most important factor by experimentally manipulating turbidity levels within an outdoor stream ecosystem and observing impacts of turbidity on physical metrics (embeddedness, permeability) and macroinvertebrates. We will introduce water with different compositions of suspended load (e.g., different proportions of fine sand, silt, and mud and different levels of organic matter and nutrients) but the same turbidity level, and compare the response of a small urban stream ecosystem. Trials will be performed under high-flow conditions, which often accompany high turbidity levels and typically exert substantial stress on aquatic ecosystems. If turbidity is the most important variable, then all load compositions should elicit a similar change in physical parameters and the biological index between upstream and downstream segments. If different load compositions elicit different responses, then we will investigate whether other physical parameters correlate well with the observed level of biological response. Results will indicate whether turbidity (i.e., NTU level) most closely correlates with benthic habitat quality, or whether another metric or combination of metrics (e.g., suspended sediment concentration, transparency, net sedimentation, or embeddedness) provides a better understanding of the effect on benthic habitat. These results are needed by federal and state agencies to modify their TMDL program and to better protect the water quality of America 's rivers and streams.
Project 4: Residence times and ecological implications of multi-scale three-dimensional geomorphology-driven surface water-ground water connections at the Outdoor Stream Lab
Researchers: Vaughan Voller, Jacques Finlay, Cailin Orr, Jeff Marr, Anne Lightbody, NCED visitors
Rivers and aquifers are three-dimensionally connected at multiple scales, and fluid flux between surface water and ground water mediates important naturally occurring biogeochemical and ecological processes. Exchange of fluids, solutes, and energy across the coupled systems are typically driven by geomorphic variability of the land surface. However, past studies have focused on two-dimensional exchange in flumes or horizontal flowpaths along river banks. Considering the importance of reactions occurring along such flowpaths, a three-dimensional (3D) understanding of hydrologic connections is the critical next step towards a quantitative holistic understanding of the fluvial landscape.
Researchers will design, install, and monitor a 3D network of near-stream and in-stream piezometers. A high-resolution network, nested within a coarser grid, will be placed along a prominent point bar. Piezometers will be used to characterize hyporheic water flow and to determine the change and variability in nutrient concentrations over the first season of flow within the OSL. In addition, surface water and benthic community samples will be obtained upstream and downstream in the channel. The end products of this study will be a high-resolution water-table and groundwater flowpath map for the OSL and an understanding of the development of nutrient processing potential and heterogeneity within the benthic and subsurface communities. These components will advance the long-term goal of understanding and predicting the feedbacks between surface geomorphology, subsurface residence times, microbial community dynamics, and nutrient processing.
Project 5: Prediction of water residence time and sedimentation within patches of aquatic vegetation
Researchers: Anne Lightbody, Chris Paola, NCED visitor program participants
The presence of aquatic vegetation in river channels results in an increase in flow resistance and a reduction in conveyance capacity. So, for many years vegetation has been removed from channels to accelerate the passage of peak flows. However, aquatic macrophytes can have a positive influence on water quality by removing nutrients and producing oxygen in stagnant regions, and some researchers now advocate replanting and ecologically-based management of channel vegetation. In fact, by enhancing water quality, creating ecologically productive riparian zones, improving in-stream habitat, and stabilizing banks, aquatic vegetation plays a crucial role in four out of the top five most commonly stated goals for river restoration in the United States. Determining how riparian vegetation influences the structure and function of the fluvial ecosystem, with the goal of manipulating this relationship for ecological benefit, requires an understanding of flow, transport, and sedimentation within and adjacent to patches of vegetation. The goals of this project are to validate models that predict the residence time and turbulence levels of a patch of aquatic vegetation under field conditions and to extend these models to predict sedimentation potential as a function of canopy morphology.
It is hypothesized that the size and stem density of aquatic vegetation patches determines turbulence levels within the vegetation and the lateral and vertical exchange of dissolved solutes and sediment between the vegetation and the free stream. Patch-scale measurements of velocity, turbulence, tracer retention, and sedimentation will be compared to simultaneous reach-scale tracer studies. The change in surveyed bed height, between the beginning and end of the experiment, will indicate the total amount of fine sediment that has been extracted from the flow by the vegetation.
Please contact us about research and educational opportunities at any of the StreamLab facilities. Click here to view the Outdoor StreamLab brochure. |
