12 research outputs found
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
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Field investigation of hydraulic structures facilitating fish abundance and passage through bridges in western Iowa streams
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EFFECTS OF GRADE CONTROL STRUCTURES ON FISH PASSAGE, BIOLOGICAL ASSEMBLAGES AND HYDRAULIC ENVIRONMENTS IN WESTERN IOWA STREAMS: A MULTIDISCIPLINARY REVIEW
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.This proceeding is from World Environmental and Water Resources Congress 2009: Great Rivers (2009): 3082, doi:10.1061/9780784410363.</p
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.This article is from River Research and Applications 29 (2013): 389, doi:10.1002/rra.1600.</p
Quantifying the changes of soil surface microroughness due to rainfall impact on a smooth surface
This study examines the rainfall-induced change in soil microroughness of a
bare smooth soil surface in an agricultural field. The majority of soil
microroughness studies have focused on surface roughness on the order of
∼ 5–50 mm and have reported a decay of soil surface roughness with
rainfall. However, there is quantitative evidence from a few studies suggesting
that surfaces with microroughness less than 5 mm may undergo an increase in
roughness when subject to rainfall action. The focus herein is on initial
microroughness length scales on the order of 2 mm, a low roughness condition
observed seasonally in some landscapes under bare conditions and chosen to
systematically examine the increasing roughness phenomenon. Three rainfall
intensities of 30, 60, and 75 mm h−1 are applied to a smoothened bed
surface in a field plot via a rainfall simulator. Soil surface microroughness
is recorded via a surface-profile laser scanner. Several indices are utilized
to quantify the soil surface microroughness, namely the random roughness (RR)
index, the crossover length, the variance scale from the Markov–Gaussian
model, and the limiting difference. Findings show a consistent increase in
roughness under the action of rainfall, with an overall agreement between all
indices in terms of trend and magnitude. Although this study is limited to a
narrow range of rainfall and soil conditions, the results suggest that the
outcome of the interaction between rainfall and a soil surface can be
different for smooth and rough surfaces and thus warrant the need for a
better understanding of this interaction