Posted Fri, 2009-10-09 08:45
The NCED seminar series informs and educates audiences about active research in the Center.
NCED seminars will be held during the fall 2009 semester on Mondays from 1-2 p.m (CT).
 
Location:
Saint Anthony Falls Laboratory, Room 305
 
Videoconferencing and Webcast:
Current members of NCED can use videoconferencing to access the seminars. Outside access will be available soon via UMConnect. In the interim, the live stream will be available at: stream1.video.state.mn.us:8080/ramgen/broadcast/met-nced.rm.
 
Interested in presenting?  Contact Arvind Singh: sing0336@umn.edu
 
Schedule:

 

Challenges and opportunities in geomorphic feature extraction in flat areas

Abstract:

We use LiDAR (Light Detection and Ranging) data available for the Le Sueur basin in Minnesota and GeoNet, a recently developed channel network extraction algorithm [Passalacqua et al., 2009], to explore the challenges and opportunities encountered in the geomorphic feature extraction in flat areas. We focus in particular on the extraction of natural and artificial features (channels and ditches) and the possibility of distinguishing them. We also propose a technique for the automatic extraction of cross-sections, the automatic detection of channel banks, and automatic measurement of bank and bluff heights continuously along the channel.

PowerPoint Presentation

 

Evolution of fluvial sediment research and monitoring for suspended-sediment, bedload, and bed material in the nation's surface waters

Abstract:

John R. Gray, U.S. Geological Survey Senior Sediment Specialist, will be presenting the current status and latest technologies related to sediment in natural surface waters and describe the impacts of human-accelerated transport of suspended sediments in the nation’s waterways. He will present a brief history of sediment monitoring and demonstrate the importance of sediment in surface-water quality restoration. Other topics will include (1) surrogate technologies for monitoring suspended sediment and bedload; (2) ranking of fluvial sediment among other contaminants; (3) progress in mitigating the amount of human induced sediment in rivers and streams; (4) Minnesota River sediment impact to the Mississippi River; and (5) the benefits of implementing a long-term sediment monitoring network. The seminar will last approximately 1 – 1.5 hours and will be followed by an informal discussion period for anyone who would like Mr. Gray to address specific questions related to research and monitoring of fluvial sediment in Minnesota.

 

In-stream wood transport, and effects of forest harvest on geomorphology and fish, in northern Minnesota streams

Abstract:

Trees provide critical functions to the ecology of streams. Trees affect hydrology, mitigate sediment inputs, and buffer water temperatures by providing shade. Watersheds with a higher proportion of mature forest tend to have less variable hydrographs, and older trees provide larger pieces of wood to streams. Instream wood itself affects nearly every process in stream ecology. Despite their ecological importance, trees and instream wood have been greatly modified by humans. The studies described in this presentation advance current knowledge as follows:
We demonstrate that headwater streams in northern forests can require ten years to recover from a large input of fine sediment, depending on the occurrence of stormflows. Our analyses suggest that, at the basin scale, warmer air temperatures in summer are more important to the abundances of some headwater fish species than instream habitat or spring precipitation. The analyses also lend support to previous findings that riparian forest harvest can cause local stream warming.
Wood transport in streams is a dynamic process. Forty-one percent of over 800 wood pieces were mobilized (at least 10m) during a study period by a single high flow event. Thirty-two percent of the mobilized pieces became entrapped again before leaving their study reach.
Mobilization of wood in streams is a complex function of both mechanical and hydraulic factors. Eleven potential predictor variables were studied, and seven were identified as significant to wood mobilization using multiple logistic regression. The seven predictors were burial, effective depth, length ratio, bracing, rootwad presence, downstream force ratio, and draft ratio.
Entrapment of wood in streams is related primarily to the length ratio and weight of the wood pieces. The mechanisms for entrapment are not always clear; wood pieces may simply be entrapped wherever they are located when high water recedes.
Together, these projects suggest that forest harvest should avoid excess sediment inputs (due to persistence) and stream warming (due to effects on fish). We also develop models that can be used for more informed management of instream wood. Stream managers and restorers can apply the results presented to reverse the impacts of historic logging and wood removal on streams.

PowerPoint Presentation
 

The Effect of sediment cohesion on delta morphology

Abstract:

The morphologies of the world’s deltas are thought to be mainly determined by river discharge, tidal range, and wave climate as summarized in the well known ternary classification of deltas . More recently sea level rise and human engineering have been implicated, but sediment discharge and type are still considered secondary factors. By holding other factors constant we show that sediment cohesion, and by implication sediment size and vegetation type, also plays a major role in determining the shapes, cumulative number of distributaries, and wetland areas of river-dominated deltas. Thirty simulations of delta growth were conducted using a morphodynamic flow and transport model (Delft3D v. 3.28) in which a river with uniform discharge of 1000 m3 s-1 carries equilibrium concentrations of sediment into a standing body of water devoid of waves, tides, and buoyancy forces. Self-formed deltas arise through the processes of mouth bar growth and avulsion, similar to real deltas. Elongate (or Bird’s-foot) deltas with rugose shorelines and topographically rough floodplains are created if the incoming sediment is highly cohesive. Fan-like deltas with smooth shorelines and flat floodplains are created by less cohesive sediment. The cumulative number of channels in a delta and the average bifurcation angle also depend strongly on the cohesiveness of the sediment. Although it is difficult to separate cause and effect in real deltas, the results appear consistent with limited empirical data.

PowerPoint Presentation

Meandering channels in laboratory flumes

Abstract:

Our ability to construct predictive numerical models for meandering rivers is hampered by the inability to create meandering channels in the laboratory where individual variables can be isolated and controlled. To create a meandering channel in the laboratory, we added alfalfa sprouts to provide bank strength and fine sediment to attach point bars to the floodplain. The 6.1 by 17 m flume has a floodplain slope of approximately 0.005 with a sandy bed and banks that scales as a gravel bed river. The alfalfa sprouts slow bank erosion allowing time for the bars to create new floodplain deposits. The sprouts also increase floodplain roughness, armor new bar deposits, and promote deposition of overbank sediment adjacent to the channel. We used a lightweight plastic with a specific gravity of 1.2 as fine sediment. The fines were crucial for blocking chutes formed between the bar and the floodplain, isolating cut-off channels from the main flow, and creating levees. During this 136-hour long experiment, the channel width stabilized as the channel migrated across the floodplain, and the curvature was recreated following cutoffs. Although the sinuosity (about 1.2) was low relative to meandering channels observed in the field, the spacing of bends was within the upper bounds of field examples. Subsequent experiments with higher bank strength had more limited chute development and were able to generate a sinuosity of about 1.5. Scaling analysis indicates that the bank migration rates in the lower sinuosity experiment were approximately 10 times faster than migration rates in the field. A particular challenge in these experiments is maintaining a healthy alfalfa crop. After 15-20 hours of flood flows, the alfalfa begins to die off and new emergent bars need to be seeded. It then takes about 7 days for the alfalfa to grow to the size used in these experiments. The 15-20 hours scale to about one year of flood flows in the field.

PowerPoint Presentation (Office 97-2003)
PowerPoint Presentation (Office 2007)
Quick Time Movie

Glossosoma (Trichoptera) Interaction with Hydraulic Variables in Three Coastal Mountain Streams

The stream-dwelling larvae of the caddisfly Glossosoma spp. are dominant grazers in lotic food webs and are capable of suppressing stream periphyton. Quantitative description of the hydraulic regime preferred by larval stone-cased caddisflies Glossosoma nigrior and Glossosoma penitum in three coastal mountain streams in northern California is the topic of this presentation. Surface particle image velocimetry may indicate a hydraulic environment favorable for Glossosoma presence in riffles. Field data from the Angelo Coast Range Reserve in California indicates that Glossosoma densities were positively correlated with depth-averaged velocity magnitude and negatively correlated with water depth and with energy dissipation derived from surface particle image velocimetry. A functional relationship developed from a power law based on hydraulic and larval abundance dimensionless variables describes 40% of the variability in the spatialdistribution of glossosomatid larvae. This expression could be useful in predicting how spatial distributions and impacts of these important grazers will change under variable hydraulic regimes.