Enhanced insight on the effects of boulders on bedload transport

River morphodynamics and sediment transportMechanics of sediment transpor

Fish Passage and Abundance around Grade Control Structures on Incised Streams

This paper summarizes research from separate studies of fish passage over weirs (Larson et al., 2004; Litvan, 2006; Litvan, et al., 2008a-c) and weir hydraulics (Papanicolaou and Dermisis, 2006; Papanicolaou and Dermisis, in press). Channel incision in the deep loess region of western Iowa has caused decreased biodiversity because streams have high sediment loads, altered flow regimes, lost habitat, and lost lateral connectivity with their former floodplains. In-stream grade control structures (GCS) are built to prevent further erosion, protect infrastructure, and reduce sediment loads. However, GCS can have a detrimental impact on fisheries abundance and migration, biodiversity, and longitudinal connectivity. Fish mark-recapture studies were performed on stretches of streams with and without GCS. GCS with vertical or 1:4 (rise/run) downstream slopes did not allow fish migration, but GCS with slopes ≤ 1:15 did. GCS sites were characterized by greater proportions of pool habitat, maximum depths, fish biomass, slightly higher index of biotic integrity (IBI) scores, and greater macroinvertebrate abundance and diversity than non-GCS sites. After modification of three GCS, IBI scores increased and fish species exhibiting truncated distributions before were found throughout the study area. Another study examined the hydraulic performance of GCS to facilitate unimpeded fish passage by determining the mean and turbulent flow characteristics in the vicinity of the GCS via detailed, non-intrusive field tests. Mean flow depth (Y) and velocity (V) atop the GCS were critical for evaluating GCS performance. Turbulent flow measurements illustrated that certain GCS designs cause sudden constrictions which form eddies large enough to disorient fish. GCS with slopes ≤ 1:15 best met the minimum requirements to allow catfish passage of a flow depth of ≥ 0.31 m and a mean flow velocity of ≤ 1.22 m/s

Effects of Grade Control Structures on Fish Passage, Biological Assemblages and Hydraulic Environments in Western Iowa Streams: A Multidisciplinary Review

Land use changes and channelization of streams in the deep loess region of western Iowa have led to stream channel incision, altered flow regimes, increased sediment inputs, decreased habitat diversity and reduced lateral connectivity of streams and floodplains. Grade control structures (GCSs) are built in streams to prevent further erosion, protect infrastructure and reduce sediment loads. However, GCS can have a detrimental impact on fisheries and biological communities. We review three complementary biological and hydraulic studies on the effects of GCS in these streams. GCS with steep (≥1:4 rise : run) downstream slopes severely limited fish passage, but GCS with gentle slopes (≤1:15) allowed greater passage. Fish assemblages were dominated by species tolerant of degradation, and Index of Biotic Integrity (IBI) scores were indicative of fair or poor biotic integrity. More than 50% of fish species had truncated distributions. After modification of GCS to reduce slopes and permit increased passage, IBI scores increased and several species were detected further upstream than before modification. Total macroinvertebrate density, biomass and taxonomic diversity and abundance of ecologically sensitive taxa were greater at GCS than in reaches immediately upstream, downstream or ≥1 km from GCS. A hydraulic study confirmed results from fish passage studies; minimum depths and maximum current velocities at GCS with gentle slopes (≤1:15) were more likely to meet minimum criteria for catfish passage than GCS with steeper slopes. Multidisciplinary approaches such as ours will increase understanding of GCS-associated factors influencing fish passage, biological assemblage structure and other ecological relationships in streams

Numerical and Experimental Study of Wave Over Coastal Levee Structures

Louisiana coast experiences significant erosion due to wave actions. The loss of beaches in some coastal areas in Louisiana is severe. There are wetlands and marshes located in the coastal areas. Wetland loss is a major threat to the coast areas. 3D numerical simulations of wave-levee interactions were conducted, and the results were analyzed to determine the flow characteristics and surface shear distributions. The simulation setup is exactly the same as an experiment conducted in a wave tank facility. The velocity histories on different locations near the test levee surface were compared, and the agreement is very good, therefore the simulation is validated. A test levee system was also constructed on a test Gulf beach site, approximately 4.6 miles west of Holly Beach in Cameron Parish, Louisiana. Long term observation of erosion was conducted, and survey data showing the change of the test levee were produced. From the observations, the loss of this portion of Gulf beach is significant during the 2-year research period. Real-time images were recorded to show this significant change in topography. The losses of the levee materials during the entire project period were quantified based on the survey data. The history of the loss was plotted. It indicates some major storm event contributed to significant losses and erosion of the test structure. It can be seen from the results that the real-time erosion pattern on the test site agrees reasonably with the surface shear patterns from the simulations. In the numerical simulation, commercial package ANSYS-FLUENT was used. A free-surface flow model is adopted with open channel wave boundary conditions. A grid-independence study was performed to determine to appropriate grid resolution to be used in the simulation. Parallel computing was conducted due to the expensive cost of this 3D simulation with relatively fine grid resolutions.</jats:p

Field investigation of hydraulic structures facilitating fish abundance and passage through bridges in western Iowa streams

Prepared for the Iowa Department of Transportation, Highway Divison by IIHR-Hydroscience and Engineering, The University of Iow