Main Channel Area Research Articles

Characterization of Extra Low-Permeability Conglomerate Reservoir and Analysis of Three-Phase Seepage Law

The micro distribution of residual oil in low-permeability sandstone reservoirs is closely related to pore structure, and the differences in pore structure often determine the reservoir’s productivity and development effectiveness from a macro perspective. On the basis of in-depth research, this paper analyzes the distribution law of the remaining microscopic oil, establishes the digital core multi-stage pore network modeling of the strongly sorted heterogeneous conglomerate reservoir in the Lower Wuerhe Formation of Block 8 of the Karamay Oilfield, the three-phase seepage simulation method considering the release of dissolved gas, and the three-phase permeability curve test. The research results are as follows: (1) Conventional physical property analysis shows that the permeability of core samples exhibits an inverse rhythmic distribution with layer depth. (2) CT core analysis and mercury injection experiments indicate that the area with porosity ranging from 9% to 21% accounts for 79% and is the main seepage channel area. Larger pores play an important role in seepage. (3) Through comparative experiments on cores with different permeability, it was found that the degassing phenomenon of low-permeability rock samples is more severe. In the actual process of reservoir development, it is necessary to reasonably handle the impact of water injection on development effectiveness, select appropriate water injection methods and cycles, and avoid premature water breakthrough in ultra low-permeability reservoirs.

Riparian Land Use and Hydrological Connectivity Influence Nutrient Retention in Tropical Rivers Receiving Wastewater Treatment Plant Discharge

Riparian areas are recognized for their buffering capacity regarding phosphorus and nitrogen from agricultural and urban runoff. However, their role in attenuating nutrient loads of rivers receiving point source nutrient inputs (e.g., from wastewater treatment plants, WWTPs) is still little understood. Here, we investigated whether ammonium (NH4-N), nitrate (NO3-N), and soluble reactive phosphorus (SRP) retention were influenced by the riparian land use in three Brazilian rivers receiving WWTP effluents. We hypothesized that nutrient attenuation would be potentially influenced by the hydrological connectivity between the main channel and riparian areas with native vegetation. We estimated retention from longitudinal patterns of dilution-corrected nutrient concentrations below the WWTPs. We assessed nutrient retention during periods with high (i.e., the wet) and low connectivity (i.e., the dry season). Relationships between non-conservative (nutrients) and conservative (chloride) solutes in both seasons were used to identify potential changes in the river chemistry due to the hydrological connectivity with the riparian areas. We also evaluated the relationship between net uptake velocities (Vf-net) and the accumulated percent native vegetation cover in the 100-m buffer using linear regressions, comparing the response for each nutrient between seasons with Analysis of Covariance. Slopes of regressions between nutrients and chloride significantly differed between seasons for NO3-N and SRP but not for NH4-N. The relationships between Vf-net and accumulated native vegetation in the riparian buffer presented steeper slopes for SRP in the wet than in the dry season. No significant relationships between NO3-N Vf-net and native vegetation cover were observed in either season. In contrast, increases in Vf-net with increasing vegetation cover were observed for NH4-N in the dry season. In periods with expected higher connectivity, NO3-N and SRP concentrations tended to be lower relative to chloride concentrations, with a potential effect of native vegetation in the riparian area on SRP retention. Our results suggest that seasonal connectivity between nutrient-rich river water and riparian areas is likely to induce changes in the predominant nutrient transformation processes, thereby favoring either nutrient retention or export in such rivers.

Spatial and temporal dynamics of phytoplankton assemblages in the upper Mississippi River

AbstractPhytoplankton provide large quantities of organic carbon and biomolecules that support large river ecosystems. However, when certain groups become overabundant (e.g., cyanobacteria), they can pose a risk to human health and river biota. The purpose of this study was to examine the spatial and temporal dynamics of phytoplankton community composition within the upper Mississippi River. More specifically, we analyzed samples from main channel, impounded, and backwater areas of Navigation Pools 8 and 13 to examine lateral variability within each of these pools. We analyzed samples from the main channel of Pool 26 to examine longitudinal variation among Pools 8, 13, and 26. Phytoplankton and water quality samples were collected during the summer months of 2006–2009. The main channels of Pool 8 and Pool 13 were generally dominated by diatoms, although cyanobacteria were (at times) more abundant. The backwaters were generally dominated by cyanobacteria and typified by flagellated species (e.g., cryptomonads and euglenoids). The main channel of Pool 26 was always dominated by diatoms. Discharge influenced phytoplankton community composition. In Pool 26, taxonomic richness tended to increase with increasing discharge. There were no linear correlations between cyanobacteria total or proportional biovolume and nutrient concentrations, indicating that nutrient limitation was not common. Differences in phytoplankton communities were generally associated with physical factors such as discharge, turbidity, and residence time.

Simulating cross-sectional geometry of the main channel in response to changes in water and sediment in Lower Yellow River

To understand the non-equilibrium morphological adjustment of a river in response to environmental changes, it is essential to (i) accurately identify how past conditions of water and sediment have impacted current morphological adjustment of the river, and (ii) establish a corresponding simulation for non-equilibrium conditions. Based on discharge and suspended sediment concentration (SSC) as well as 82 cross-sectional data items for the Huayuan-kou-Lijin reach of the Lower Yellow River in the period 1965–2015, the process of adjustment of the geometry of the main channel (area, width, depth, and geomorphic coefficient), and its responses to changes in discharge and SSC for different reaches are statistically analyzed. Following this, a delayed response model (DRM) of the geometry of the main channel subjected to variations in discharge and SSC is established using a multi-step analytical model, with the discharge and SSC as the main controlling factors. The results show that the area, width, and depth of the main channel decreased initially, then increased, decreased again, and finally increased again. These features of the geometry of the channel were positively correlated with the 4-year moving average discharge and negatively with the 4-year moving average SSC. The geomorphic coefficient for the Huayuankou-Sunkou reach exhibited a trend of decrease, whereas that of the Sunkou-Lijin reach decreased initially, then increased, decreased again, and finally increased again. Except for the Huayuankou-Gaocun reach in 1965–1999, the coefficient was negatively correlated with the 4-year moving average discharge and positively with SSC. The simulated values of the morphological parameters of the main channel for all sub-reaches obtained using the DRM agreed well with the measured values. This indicates that the DRM can be used to simulate the process of response of the cross-sectional geometry of the main channel to variations in the water and sediment. The results of the model show that the adjustment of the geometry of the main channel was affected by the discharge and the SSC at present (30%) as well as for the previous 7 years (70%). The proposed model offers insights into the mechanism whereby past water and sediment influence the current morphological adjustment of the river, and provides an effective method for predicting the magnitude and trend of the geometry of the main channel under different flow conditions.

Assessment of marine debris in the stake net fisheries of Vembanad Lake, Kerala, India

The stake net fishery of Panambukad in the main channel area of Vemband Lake, Kerala was studied during the first fortnight of August 2014. The observations indicated that the average catch including the marine debris ranged from 1.04 to 2.04 kg net-1 day-1 with an average of 1.34 kg net-1 day-1. The percentage of marine debris in the stake nets ranged from 42.68 to 73.4%. Plastic items formed 97% by weight and 99% by number of the total marine litter. The observed litter stuff was categorized as per UNEP system of classification of marine litter where, they are first identified based on their material composition (litter codeeg. PL) and then by their form (RL classes). Items found in the collection included plastic covers (PL07, RL15), metal cap (ME02, RL01), plastic bottle (PL02, RL02), fishing net (PL20, RL05), plastic cup and food containers (PL06, RL09), thermocol (FP 04, RL13), rubber sheet (RB05, RL28), plastic sacks (PL24, RL23), diaper (OT02, RL18) etc. Among them, plastic covers were most dominant and their average number and weight net-1 day-1 was 28 nos and 985 g respectively. The study also showed positive signs of decline in plastic bottles as a major litter item due to its targeted collection by recycling industry within a span of three years. In a survey conducted among the stake net fishers, there was consensus on the view that plastic litter in Vembanad Lake has increased during the last 10 years and this has affected the resources and the fishery. The stakeholders also expressed their willingness to pay for restoration of the fishery resources of the lake. The study recommends the need to establish proper solid waste management systems in coastal villages, to reduce the use of plastics, and provide facilities for disposal of litter which gets collected in stake nets and to increase the awareness among the public about the impacts of marine debris on ecosystem and resources.

Analysis of stratification patterns in river-influenced mesotidal and macrotidal estuaries using 3D hydrodynamic modelling and K-means clustering

A methodology to determine the spatial and temporal evolution of stratification in estuaries driven by astronomical tides and river discharges was developed and is presented here. Using a 3D hydrodynamic model, the variation of estuarine currents, water levels and densities was investigated under different realistic forcing conditions. These conditions were classified from a long-term period (>30 years) of river flows and tidal water levels by a K-means clustering approach suggested by Bárcena et al. (2015). The methodology allows computing the location of mixed, partially mixed/stratified and stratified areas in tidal river estuaries along a continuum by means of Richardson's Layer number and the frequency of every model scenario. In order to illustrate the power of the method, it was applied to a case study, the Suances Estuary. In the application case, the Suances Estuary was vertically mixed at its innermost part due to riverine influence. At the outer part, it was also vertically mixed due to the turbulence caused by tidal action. At the intermediate section, it was partially mixed in the main channel or stratified in intertidal areas due to the combined action of forcing, depth gradients between the main channel and intertidal areas, and salinity variations in the water column.

Diversity of culturable Gram-negative bacteria isolated from irrigation water of two rice crop regions in Southern Brazil.

In this study, we assessed the diversity of Gram-negative bacteria found in water used for irrigation of rice crops in two growing areas of southern Brazil. Samples were collected from the main irrigation channel and field drain area. Twenty-two bacterial species were found in Cachoeirinha and 28 in Camaquã. In both areas, the most frequent bacterial families were Enterobacteriaceae and Aeromonadaceae. Differences in microbial diversity were observed in both study areas. Thirty-five Gram-negative species were identified; however, only 15 were common in both locations. In addition, there were found pathogenic and drug-resistant species, such as Acinetobacter sp., Brucella spp., and Chryseobacterium meningosepticum. This study demonstrates the existence of a number of pathogenic species in aquatic ecosystems analyzed in three consecutive crop years, especially water used for rice production.

Sedimentary microfacies and palaeogeomorphology as well as their controls on gas accumulation within the deep-buried Cretaceous in Kuqa Depression, Tarim Basin, China

The gas and oil exploration in Kuqa Depression has entered the deep-buried and ultra-deep areas below 5000 m. This paper represents the systematic research accomplished which included microfacies observation and sandstone modeling in the outcrop, the lithofacies interpretation with imaging logging data, and the recovery of nappe tectonics as well as the folding analysis based on the single sedimentary factors in order to define the characteristics of lithofacies and microfacies, the background of paleography and their effects on gas accumulation. This study illustrated that the climate was mainly hot and dry during the sedimentary period of Bashijiqike within the deep-buried Cretaceous, and the deposited water was characterized by low to medium salinity. The deep-buried areas were controlled by three provenances, namely, the Kapushaliang River, the Kelasuhe River, and the Kuqa River. The Dabei-Bozi area was mainly the proximal deposit, the silty-fine sandstone with subrounded and well-sorting features developed in the main channel areas of underwater distributary channel which was constructed in the braided (or fan) delta front. The Keshen area, on the other hand was the distal deposit, the medium-fine sandstone with subangular-subrounded and medium-well sorting features developed in the main channel areas of underwater distributary channel which was constructed also in the braided (or fan) delta front. In the latter stage of the Yanshanian Period, the silty-fine sandstone of the underwater distributary channel had developed with the background of residual palaeohigh and drought climate in Dabei-Bozi area-meanwhile the medium-fine sandstone of the underwater distributary channel had developed with the background of residual palaeohigh slopes and humid climate in Keshen area. In addition, the gas accumulation within the deep zone was evidently controlled by the lithofacies paleography. The gas in the medium-fine sandstone lithofacies of paleoslope was significantly richer than the silty-fine sandstone lithofacies of the paleohigh; the silty lithofacies in the paleohigh was relatively poor. It was supposed that systematic studies would accelerate the oil and gas exploration and development in the deep zones, not to mention provide guidance for the trillion cubic prospects of gas reserves in the deep zones.

Fluvial seed dispersal of riparian trees: transport and depositional processes

AbstractFluvial seed dispersal considers both the transport and deposition of seeds where channel geomorphic structures, hydrology and seed dispersal traits contribute to transport times and depositional locations. This study examines the influence of stream flow patterns on fluvial seed dispersal of buoyant white alder (Alnus rhombifolia) seeds by applying a one‐dimensional transport model. Conceptually, the model separates the stream into two components: (i) the main channel where the seeds are transported downstream; and (ii) the transient storage zone where seeds are temporarily detained or deposited on the river bank. Transport processes are characterized by an advection–dispersion equation which is coupled to a transient storage model using an exponential decay term. The model parameters: longitudinal dispersion (DL), exchange coefficient (α), main channel area (A) and storage zone (As) are estimated based on field experiments conducted in a confined, bedrock‐gravel bed river with pool‐riffle morphology located in coastal northern California. The riparian zone is inhabited by Alnus rhombifolia that disperse buoyant seeds in mid‐spring coinciding with the end of the wet, Mediterranean season. Artificial seeds, with similar traits of buoyancy and density to alder seeds, were used to quantify transport times and depositional locations. Preferential deposition resulted in stream reaches with larger As, high As/A ratios, and faster exchange coefficients corresponding to divergent stream flow (back‐eddies, re‐circulating flow, flow expansions) caused by geomorphic structures such as the ends of bar/riffle features and bends in the stream. The results demonstrate the importance of transient storage for seed transport and depositional processes. Morphological features that increase a channel's complexity create complex flow structures that detain seeds and provide a greater opportunity for deposition to occur. The model provides a simplification of river hydraulics to represent dispersal dynamics and lends itself to further understanding of hydrochory processes and associated population structure. Copyright © 2015 John Wiley & Sons, Ltd.

Real-time flood forecasting of Huai River with flood diversion and retarding areas

A combination of the rainfall-runoff module of the Xin'anjiang model, the Muskingum routing method, the water stage simulating hydrologic method, the diffusion wave nonlinear water stage method, and the real-time error correction method is applied to the real-time flood forecasting and regulation of the Huai River with flood diversion and retarding areas. The Xin'anjiang model is used to forecast the flood discharge hydrograph of the upstream and tributary. The flood routing of the main channel and flood diversion areas is based on the Muskingum method. The water stage of the downstream boundary condition is calculated with the water stage simulating hydrologic method and the water stages of each cross section are calculated from downstream to upstream with the diffusion wave nonlinear water stage method. The input flood discharge hydrograph from the main channel to the flood diversion area is estimated with the fixed split ratio of the main channel discharge. The flood flow inside the flood retarding area is calculated as a reservoir with the water balance method. The faded-memory forgetting factor least square of error series is used as the real-time error correction method for forecasting discharge and water stage. As an example, the combined models were applied to flood forecasting and regulation of the upper reaches of the Huai River above Lutaizi during the 2007 flood season. The forecast achieves a high accuracy and the results show that the combined models provide a scientific way of flood forecasting and regulation for a complex watershed with flood diversion and retarding areas.

Spatial and temporal variations of chlorophyll-a concentration from 2009 to 2012 in Poyang Lake, China

Water eutrophication in Poyang Lake, the largest freshwater lake in China, has been considered to be an obstacle to aquatic environment protection and regional sustainable development. Chlorophyll-a concentration is one of the most important indices of water eutrophication. This paper builds seasonal chlorophyll-a concentration retrieval models using a semi-analytical model. Quarterly distributions of chlorophyll-a concentration from 2009 to 2012 are explored using multi-spectra data from a moderate-resolution imaging spectroradiometer (MODIS). The correlation coefficient of the retrieval models primarily ranged from 0.6 to 0.9. The results show that the chlorophyll-a concentration in Poyang Lake has significant seasonality characteristics that present low values in the winter and spring, and present relatively high values in the summer and autumn; this report also presents an obvious, increasing trend of inter-annual variability from 2009 to 2012. The spatial distribution of the chlorophyll-a concentration has regional differences that give relatively high values adjacent to the shore in the north area of Poyang Lake, in the flow in river entries, and in the main channel area in the central and south areas of Poyang Lake. The natural hydrology features have a close relationship with the variation in the chlorophyll-a concentration. Intensive human activities are the main driving forces for the increasing chlorophyll-a concentration.

Identifiability of transient storage model parameters along a mountain stream

[1] Transient storage models are widely used in combination with tracer experiments to characterize stream reaches via calibrated parameter estimates. These parameters quantify the main transport and storage processes. However, it is implicitly assumed that calibrated parameters are uniquely identifiable and hence provide a unique characterization of the stream. We investigate parameter identifiability along with the stream conditions that control identifiability for 10 breakthrough curves (BTC) for 100 m pulse injections along Stringer Creek, Montana, USA. Identifiability is assessed through global, variance-based sensitivity analysis of the one-dimensional transport with inflow and storage model (OTIS). Results indicate that the main channel area parameter A and the dispersion coefficient D were the most sensitive parameters and, therefore, likely to be identifiable across all timescales and reaches. Identifiability of transient storage zone size As fell into two categories along Stringer Creek. As was identifiable for lower elevation regions, corresponding to a constrained valley, higher stream slopes, and in-channel roughness, but not for upper stream regions, corresponding to a wider valley floor, flatter stream slopes, and low roughness. The storage zone exchange parameter α was nonidentifiable across all study reaches. Our results suggest that only some of the processes represented in the model will be relevant and, therefore, identifiable for pulse injection data. As such, calibrated parameter estimates should be accompanied by an assessment of parameter sensitivity or uncertainty. We also show that parameter identifiability varies with stream setting along Stringer Creek, suggesting that physical characteristics directly influence the identification of dominant stream processes.

Geochemical and isotopic evolution of groundwater in the Wadi Watir watershed, Sinai Peninsula, Egypt

The Wadi Watir delta in the Wadi Watir watershed is a tourist area in the arid southeastern part of the Sinai Peninsula, Egypt, where development and growth of the community on the delta are constrained by the amount of groundwater that can be withdrawn sustainably. To effectively manage groundwater resources in the Wadi Watir delta, the origin of groundwater recharge, groundwater age, and changes in groundwater chemistry in the watershed needs to be understood. Mineral identification, rock chemistry, water chemistry, and the isotopes of hydrogen, oxygen, and carbon in groundwater were used to identify the sources, mixing, and ages of groundwater in the watershed and the chemical evolution of groundwater as it flows from the upland areas in the watershed to the developed areas at the Wadi Watir delta. Groundwater in the Wadi Watir watershed is primarily from recent recharge while groundwater salinity is controlled by mixing of chemically different waters and dissolution of minerals and salts in the aquifers. The El Shiekh Attia and Wadi El Ain areas in the upper Wadi Watir watershed have different recharge sources, either from recharge from other areas or from different storm events. The downgradient Main Channel area receives groundwater flow primarily from the El Shiekh Attia area. Groundwater in the Main Channel area is the primary source of groundwater supplying the aquifers of the Wadi Watir delta.

Evaluation of habitat quality for selected wildlife species associated with island back channels

The islands and associated back channels on the Ohio River, USA, are believed to provide critical habitat features for several wildlife species. However, few studies have quantitatively evaluated habitat quality in these areas. Our main objective was to evaluate the habitat quality of back and main channel areas for several species using habitat suitability index (HSI) models. To test the effectiveness of these models, we attempted to relate HSI scores and the variables measured for each model with measures of relative abundance for the model species. The mean belted kingfisher (Ceryle alcyon) HSI was greater on the main than back channel. However, the model failed to predict kingfisher abundance. The mean reproduction component of the great blue heron (Ardea herodias) HSI, total common muskrat (Ondatra zibethicus) HSI, winter cover component of the snapping turtle (Chelydra serpentina) HSI, and brood-rearing component of the wood duck (Aix sponsa) HSI were all greater on the back than main channel, and were positively related with the relative abundance of each species. We found that island back channels provide characteristics not found elsewhere on the Ohio River and warrant conservation as important riparian wildlife habitat. The effectiveness of using HSI models to predict species abundance on the river was mixed. Modifications to several of the models are needed to improve their use on the Ohio River and, likely, other large rivers.

Spatial and temporal patterns in erosion and deposition in the York River, Chesapeake Bay, VA

Seasonal patterns of seabed erosion and deposition in a dynamic estuarine environment, the York River (USA), are examined through acoustic studies and seabed sampling to identify the dominant environmental controls on sediment mobility. Areas near Clay Bank in the York River were surveyed monthly using a dual-frequency sonar for a 12 month period. In addition, six stations within these areas were sampled during the surveys. Strong spatial and temporal variations of a soft mud layer were identified, providing new insight to recurring seasonal and spatial patterns in deposition and erosion in the middle reaches of the York River estuary. Sub-bottom data indicated maximum thickness (5–22 cm ± 4 cm) of the soft mud layer during spring and winter from April 2008 through March 2009. Minimum thicknesses (1–12 cm ± 4 cm) of the soft mud layer were observed during summer and fall. Maximum thickness coincided with the occurrence of the secondary turbidity maximum near Clay Bank in the York River. Spatial variations in the soft-mud layer thickness were also identified between and within the York River secondary channel, the inactive oyster reef area, the south west flank of the main channel, and the main channel. The upriver secondary channel, the south west channel flank, and the main channel areas were physically dominated. The downriver secondary channel area was biologically dominated and the inactive oyster reef area reflected both physical and biological processes. Water content trends showed no correlation with seabed stability in this area. Observed changes in soft mud thicknesses are interpreted to result from both biological and physical factors, which vary markedly between winter/spring and summer/fall seasons, and among the different environments of the estuary's channel.

Habitat for Age‐0 Shovelnose Sturgeon and Pallid Sturgeon in a Large River: Interactions among Abiotic Factors, Food, and Energy Intake

AbstractThe main stems of large rivers throughout the world have been highly modified with little consideration for effects on fishes that rely on these areas to complete their life histories. Particularly important is the ability of riverine habitats to provide foraging opportunities for young fish. We explored how temperature, flow, and food availability influenced diet content, prey selection (Strauss's linear selectivity index), and energy condition of age‐0 shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus in major habitat areas (e.g., islands, channel borders, wing dikes, and side channels) of the middle Mississippi River during spring (March–May) and summer (June–August) 2008. Standardized diet mass (dry mass standardized for fish body mass) of the age‐0 sturgeon peaked at about 19°C and at a flow velocity of 0.5 m/s. Although potential prey taxa were diverse, the diets for age‐0 sturgeon of all sizes were dominated by mayflies (Ephemeroptera) and midge larvae (Chironomidae) across all habitats. As age‐0 sturgeon grew, the relative energy return per habitat appeared to diverge; island tips upstream of the main channel and channel border areas behind wing dikes provided higher gains in standardized diet mass than other habitats. No differences in energy condition (kJ/g) occurred among habitats, although large (51–200 mm total length [TL]) age‐0 sturgeon had higher energy densities than their small (≤50 mm TL) counterparts. Enhancement of areas with flow and substrates that facilitate the production and availability of midges and mayflies (e.g., instream island complexes) is critical for the recruitment of age‐0 Scaphirhynchus sturgeon in large rivers.Received August 2, 2011; accepted October 6, 2011

Impact of the magnitude and frequency of debris‐flow events on the evolution of an alpine alluvial fan during the last two centuries: responses to natural and anthropogenic controls

AbstractThe dynamics and the surface evolution of a post‐LGM debris‐flow‐dominated alluvial fan (Tartano alluvial fan), which lies on the floor of an alpine valley (Valtellina, Northern Italy), have been investigated by means of an integrated study comprising geomorphological field work, a sedimentological study, photointerpretation, quantitative geomorphology, analysis of ancient to modern cartography and consultation of historical documents and records. The fan catchment meteoclimatic, geological and geomorphological characteristics result in fast rates of geomorphic reorganization of the fan surface (2 km2). The dynamics of the fan are determined by the alternation of low‐return period catastrophic alluvial events dominated by non‐cohesive debris flows triggered by extreme rainstorms which caused aggradation and steepening of the fan and avulsion of its main channel, with periods of low to moderate streamflow discharge punctuated by low‐ to intermediate‐magnitude flood events, causing slower but steady topographic reworking. The most ancient parts of the fan surface date back at least to the first half of the 19th century, but most of the fan surface has been restructured after 1911, mainly during the debris‐flow‐dominated events of 1911 and 1987. Phases of rapid fan toe incision and fan degradation have been recognized; since the 1930s or 1940s, the Tartano fan has been subjected to a state of deep entrenchment and narrowing of the main trunk channel and distributary area. Post‐Little Ice Age climate change and present‐day surface uplift rates have been considered as possible explanations for the observed geomorphic evolution, but tectonic or climatic controls cannot account for the order of magnitude of the erosional pace. Anthropogenic controls plausibly override the natural ones: in particular, the building of a dam in the late 1920s, about 2 km upstream of the fan, seems to have triggered fan dissection, having altered the sediment discharge through sediment retention. Copyright © 2011 John Wiley & Sons, Ltd.

Experimental Study on the Flow Characteristics of ￢-Type Groyne

A hydraulic model test for ￢-type groynes (with “￢” shape) was conducted to analyze the flow characteristics around these groynes. The results of the model tests are expected to be used as fundamental information in designing the ￢-type groyne constructed in the field. Main hydraulic factors such as velocity and thalweg line changes in the main channel and separation area were analyzed in this study. The thalweg line is a stream line where the maximum velocity occurs, whereas the separation area is the boundary between the main flow and the recirculation zone. Model tests with 5 different arm lengths of the ￢-type groynes were conducted by changing the velocity. The LSPIV (Large-Scale Particle Image Velocimetry) technique was used to measure and analyze flow variation around the ￢-type groynes. The velocity in the main channel measured to be increased by 1.5 times. The velocity variation on groyne arm length is little. The width of the thalweg lines (TCL) was changed to 55 - 57% of the channel width. The Froude number did not affect the thalweg line (TCL) and separation line (Sh) changes, however.

Juvenile Chinook salmon (Oncorhynchus tshawytscha) growth in off-channel and main-channel habitats on the Sacramento River, CA using otolith increment widths

Few studies have quantified juvenile salmon growth among different habitats or evaluated the mechanisms controlling salmon growth and survival. We used otolith microstructure to compare daily relative growth rates among main-channel riverine areas, off-channel ponds, and non-natal seasonal tributaries of the Sacramento River, CA. We compared prey availability, prey preference, and stomach fullness between these sites. We observed larger average otolith growth increments, higher prey densities, and warmer water temperatures in both off-channel ponds and non-natal seasonal tributaries compared to the main-channel areas in both 2001 and 2002. Our findings suggest that warmer temperatures and abundant prey in off-channel habitats during Central Valley Chinook salmon rearing periods may lead to higher growth rates, which in turn may improve juvenile survival. Our results suggest that off-channel habitats may be critical habitats to include in conservation and management plans for juvenile salmon.

Small-scale distribution of Solea solea and Solea senegalensis juveniles in the Tagus estuary (Portugal)

The distribution of Solea solea and Solea senegalensis in the Tagus estuary was studied following a small-scale approach. Preliminary sampling revealed that sole concentrated in two areas within their nursery grounds, the main subtidal channel and a large intertidal mudflat. Beam trawls were conducted intensively in the two areas in July 2006. Depth, salinity and water temperature were measured. Substrate samples were collected for sediment type determination and macrobenthos identification and quantification. Generalized linear models were applied in order to explain the occurrence and variability of soles' densities, using depth, salinity, water temperature and abundance of polychaetes, oligochaetes, amphipods, isopods and bivalves as explanatory variables. While S. solea was more abundant in the main subtidal channel, a deeper, warmer and lower salinity area, S. senegalensis abundance was highest at the intertidal mudflat area. Presence of both species in the two areas was associated with abundance of polychaetes (generally with another variable associated), and for S. senegalensis in the subtidal channel it was associated with amphipods and depth. Abundance of S. solea in the main subtidal channel was associated mainly with polychaetes abundance, while that of S. senegalensis was associated with amphipods density. In the intertidal mudflat, bivalves and polychaetes presented significant relationships with both species densities. Some of the factors that had been reported to be important for the distribution of these species in previous studies also do so at a finer scale; however, this small-scale approach provided an in-depth knowledge on habitat selection and spatial segregation of these species within this nursery area.