Stream Channel Morphology Research Articles

Effects of Stream Channel Morphology on Golden Trout Spawning Habitat and Recruitment

Effects of Stream Channel Morphology on Golden Trout Spawning Habitat and Recruitment

EFFECTS OF STREAM CHANNEL MORPHOLOGY ON GOLDEN TROUT SPAWNING HABITAT AND RECRUITMENT

Populations of stream-dwelling salmonids (e.g., salmon and trout) are generally believed to be regulated by strong density-dependent mortality acting on the age-0 life stage, which produces a dome-shaped stock-recruitment curve. Although this paradigm is based largely on data from anadromous species, it has been widely applied to stream-resident salmonids despite the fact that the processes limiting or regulating stream-resident populations remain poorly understood. The purpose of the present study was to determine whether stream channel morphology affects the availability of spawning habitat for California golden trout, and whether spawning habitat availability influences the production of age-0 trout and recruitment into the adult population. Wide stream reaches contained significantly more spawning habitat and a higher density of nests and age-0 trout than did narrow reaches. In contrast to the idea that salmonid populations are regulated by density-dependent mortality of age-0 fish, we found that the mortality of age-0 trout was largely density independent. In addition, over most of the range of observed fish densities, the density of a particular cohort was positively correlated between years for age-0, age-1, and age-2 trout. Therefore, our golden trout study population was limited by spawning habitat, with spawning habitat availability influencing the production of age-0 trout as well as recruitment into the adult population. Grazing by cattle has widened the study streams, and our current findings help to explain why stream sections subject to grazing had more spawning habitat and higher golden trout densities than ungrazed sections. Individual growth rates of golden trout are apparently negatively density dependent, and these grazing-related increases in trout density have likely resulted in decreased growth rates. Our study demonstrates that it is only by gaining an understanding of how processes operate that we will be able to predict the effects of habitat alteration on populations.

Effects of instream enhancement structures on brown trout, Salmo trutta L., habitat availability in a channelized boreal river: a PHABSIM approach

Stream channel morphology and hydraulic conditions were measured before and after channel modification and boulder structure placements in a channelized boreal river to determine whether more favourable rearing habitat for brown trout, Salmo trutta L., was created. The assessment was performed using physical habitat simulation (PHABSIM) procedures based on summer and winter habitat preferences of brown trout for depth, velocity and substrate. The results showed that the availability of potential physical trout habitat can be increased in the study river at simulated low and moderate flow conditions by reconstruction of the river bed and placing instream boulder structures. The resulting diversity of depth and velocity conditions created a spatially more complex microhabitat structure. Improved habitat conditions were able to sustain a larger trout population. Hydraulic habitat models, like the PHABSIM framework, seem to be a suitable procedure to evaluate the benefits of physical habitat enhancement.

The effectiveness and restoration potential of riparian ecotones for the management of nonpoint source pollution, particularly nitrate

The interface found where rivers meet terrestrial systems is an ecotone that has a profound influence on the movement of water and waterborne contaminants. Maintaining or restoring ecotone functions and characteristics such as natural near stream vegetation and channel morphology are important means to safeguard water quality in agricultural landscapes. A riparian buffer zone of 20 to 30 m width can remove up to 100% of incoming nitrate. Denitrification is the major pathway of removal and rates depend on nitrate loadings, carbon availability, and hydrology. Denitrification occurs throughout the year as long as subsurface hydrology is intact, whereas plant uptake of nitrogen is limited to seasonal removal. Nitrate removal is favored in forested areas with subsurface flow and is less in grassed areas with surface flow. The balance between surface and subsurface flows and the redox conditions that result are critical to nitrate removal in riparian ecotones. Surface retention of nutrients and sediment is a function of slope length and gradient, vegetation density, and flow rates. Plant communities play a major role in nitrogen cycling by acting as a source of carbon for denitrifying bacteria, direct uptake of nutrients, and creating oxidized rhizospheres where nitrification can occur. Restoration of riparian zones requires knowledge of the area's hydrology and ecology, as well as clear goals for the project. Restoration of riparian zones for water quality improvement may provide higher economic benefits than allocating the same land to crops. While it is possible to restore the functions of natural floodplain systems, existing restoration techniques are in their infancy and success cannot be guaranteed, especially given the extent of hydrological modification that has occurred in most developed countries.

Stream Channel Morphology and Woody Debris in Logged and Unlogged Basins of Western Washington

Channel morphology and habitat characteristics of stream segments draining unharvested old-growth forests were compared with those from streams within intensively and moderately logged basins. Sites covered a broad geographic range in western Washington State and were stratified by basin area and channel gradient. Although the number of pieces of large woody debris (LWD) within stream channels was unaffected by timber harvest, there was a clear reduction in LWD size in harvested basins. Timber harvest also resulted in a shift in location of LWD towards the channel margins, outside the low-flow wetted width of the channel. Intensive harvest simplified channel habitat by increasing riffle area and reducing pool area and depth, although the commonly used index of pool-to-riffle ratio appears inadequate to document these changes. Given the natural variation from stream to stream, we conclude that simple counts of instream LWD and channel units (habitat types) are not useful as management objectives. Instead, these attributes should be used collectively as indicators of the complexity and stability of in-stream habitat with respect to the specific channel and valley geomorphology.

The RCE: a Riparian, Channel, and Environmental Inventory for small streams in the agricultural landscape

SUMMARY1. The Riparian, Channel and Environmental (RCE) Inventory has been developed to assess the physical and biological condition of small streams in the lowland, agricultural landscape. It consists of sixteen characteristics which define the structure of the riparian zone, stream channel morphology, and the biological condition in both habitats.2. The inventory is based on the view that in landscapes where non‐point source pollution and agriculture dominate, the environmental condition of small streams can be assessed by an appraisal of the physical condition of the riparian zone and stream channel. It is assumed that disturbance of this physical structure is a major cause for reduction of stream biological structure and function. This assumption is supported by a case study using fifteen Italian stream locations in which the RCE was found to be positively correlated to the benthic macroinvertebrate community as measured by the Extended Biotic Index (r = 0.80, P < 0.001) and the Shannon Diversity Index (r = 0.73; P < 0.001).3. The inventory is designed for quick use to cover a large number of streams in a short period of time. When used it generates a numerical score which can be used to compare the physical and biological condition between different streams within a region. The numerical score is divided into five, colour‐coded classes to facilitate use in streammonitoring programmes and to allow comparison with biological indices.

Analysis and Interpretation of Stream Channel Cross-Sectional Data

Stream channel cross-sectional transects can be used to evaluate effects of management on stream channel morphology and therefore on fish habitat quality. We describe four indices that summarize raw data from stream channel cross sections to detect change in channel morphology over time, The net percent change in area under the transect quantifies net degradation or aggradation. The absolute percent change in area quantifies cumulative streambed or streambank material movement. The width/depth ratio is a relative index of channel shape. The Gini coefficient describes the channel cross-sectional profile, This coefficient indicates whether the channel is becoming wider and flatter or narrower and deeper, independent of change in area under the transect. These indices provide a repeatable measurement of stream channel morphology, with estimable confidence limits. They are being used to evaluate changes in channel morphology of a stream in southwestern Montana. The selection of indices depends on the information needed to evaluate management actions.

The influence of sediment supply on the channel morphology of upland streams: Howgill Fells, Northwest England

AbstractPrevious work on stream channels in upland areas of Britain has demonstrated a close control over channel morphology and stability by the rate of coarse sediment supply from the hillslopes of the catchment. Streams fed by large amounts of coarse sediment develop unstable, wide, often braided channels, whereas those with limited coarse sediment supply develop stable, much narrower, often meandering channels. The sediment supply from hillslopes is controlled by thresholds of hillslope stability, storm event frequency, and the coupling between the hillslopes and the channel. Climatically‐induced changes in any of these three factors may have implications for channel morphology and stability. This paper examines these implications in British upland fluvial systems, with particular reference to the Howgill Fells, Cumbria, in the contexts of the adjustment of stream channels to sediment supply from erosional gully systems, and their response to and recovery from major flood events.

Differential effects of largemouth and smallmouth bass on habitat use by stoneroller minnows in stream pools

Previous investigations of within‐reach distribution patterns of the stoneroller minnow, Campostoma anomalum Rafinesque, suggest that this species behavioural response to piscivorous bass differs among streams with different bass species. This study compares the responses of Camposloma to two common piscivorous fishes, largemouth bass, Micropterus salmoides Lacepede, and smallmouth bass, M. dolomieui Lacepede. Field experiments in Brier Creek, Oklahoma, U.S.A. showed that Campostoma responded to the presence of adult largemouth bass by shifting to shallow water habitats (commonly < 20 cm), but responded weakly or not at all to adult smallmouth bass. The magnitude of the response of Campostoma was positively related to activity level of the predators. Differences in behaviour between these two predator species may contribute to the differences in spatial distribution patterns of Micropterus and Campostoma observed in earlier investigations, but differences in stream channel morphology and temperature regimes among streams may also be important.

An analysis of the relation between stream channel sinuosity and stream channel gradient

Existing literature lends credence to the idea that channel sinuosity and channel gradient are independent morphologic elements responding to characteristics of the water and sediment regime of a stream. At the same time, sinuosity and gradient are viewed as closely related variables, since sinuosity is often defined as a ratio of valley gradient to channel gradient over a stream reach. These conceptions of the sinuosity variable are essentially contradictory if viewed from the standpoint of process, since in the latter case, water and sediment characteristics have no direct bearing on the determination of sinuosity, but only the potential of indirect influence operating through the channel gradient. This paper presents an empirical analysis aimed at evaluating the validity of these two conceptions of the sinuosity variable. The results of the analysis strongly support the gradient ratio concept and suggest that the traditional sinuosity variable is not reasonably viewed as an independent element of stream channel morphology, since it is essentially determined by the same process as that which determines the channel gradient. Thus, channel sinuosity is insignificantly influenced by the direct effects of water and sediment discharge. Certain indirect effects of these factors do exist, however, given the role of channel gradient in the determination of sinuosity. A summary of these results is given in the form of a two-equation recursive model.

Changes in stream channel morphology at tributary junctions, Lower Hunter Valley, New South Wales

Many empirically derived models of downstream changes in channel form are based on the concept of hydraulic geometry, whereby changes in channel morphological variables are related by a continuous power function to increasing discharge or its surrogate. However, changes in discharge throughout a drainage basin are normally concentrated at the junctions of stream channels. At junctions, the relationship between discharge and channel morphology is discontinuous. Some Lower Hunter Valley stream channels were surveyed upstream and downstream of tributary junctions. While significant regional downstream relationships were established, consistent trends at tributary junctions were not apparent from the data. It is possible that considerable scatter evident in ratios of change on either side of each junction was due to local within‐site variability. In addition, the relative timing of discharge inputs and the nature of introduced sediment loads could be important in determining the magnitude and direction of channel change at tributary junctions. Interrelated changes in cross‐sectional, profile and planform variables may be expected below junctions. The resultant channel morphology, in terms of these variables, might not be wholly determinate.

Progress in Understanding Fluvial Processes

Our understanding of fluvial processes has been improved by recent research on controls in non-alluvial channels and on detailed field studies of fluvial mechanics. Non-alluvial controls on stream-channel morphology include such features as woody debris, bedrock outcrops, and immobile sediments. These features of stream channels, along with discharge and sediment characteristics, are independent variables in stream systems. Non-alluvial features influence channel morphology by fixing the position of pools and affecting slope, resistance, and sediment transport. In the past decade, geomorphologists, engineers, and sedimentologists have been conducting detailed field studies of fluvial processes, particularly sediment transport and deposition. These studies demonstrate the complexity of fluvial processes and provide new ideas on the mechanics of gravel-pavement formation, point-bar formation, the maintenance of riffle-pool sequences, and other processes. This exciting research trend should prove to be even ...

The Influence of Wetland Vegetation on Tidal Stream Channel Migration and Morphology

Average relative stream channel migration rates of .21 meters per year (.72 feet per year) for saline tidal wetland stream channels, and .32 meters per year (1.04 feet per year) for freshwater tidal wetland channels were calculated for a 32 year period (1940 to 1972) using photogrammetric techniques. Saline wetland stream channels averaged higher indices of sinuosity, i.e., the ratio of total channel length to linear downstream distance (1.95), when compared with sinuosities of freshwater tidal channels (1.46). The difference is attributed to differences in vegetation types and consequent soil holding capacity between saline and freshwater tidal wetland environments. Saline channels become entrenched because the banks are supported by dense root systems, while freshwater tidal channels flow through a more homogenous substrate and behave much like channels which cross mud-flats in the intertidal zone. Higher average meander amplitudes (one-half the peak to trough distance of a given meander wave) for saline channels (171 meters) versus lower amplitudes for freshwater channels (114 meters) suggest that meander loops for saline channels are determined primarily by the erosional characteristics of stream banks and by other local factors rather than by hydrodynamic factors such as flow velocity or discharge. It has been stated that meander migration features do not occur in homogenous soil materials (Leopold, et al. 1964); the tendency of saline channels to form these features is attributed to differential erosion caused by variations in root system density. Conversely, the morphology of freshwater tidal channels is influenced by hydrodynamic factors including discharge, and is due to the existence of more homogenous materials, i.e., muddy soils devoid of extensive root systems. An analysis of ebb and flood discharge data arrived at for each tidal channel using existing tidal current velocity and upland discharge records supports the fact that relatively greater erosive forces occur in salt marsh than in fresh tidal marsh areas. A poor statistical correlation between rates of stream channel migration and hydraulic stream flow data such as velocity and discharge must be accepted with caution due to the method of approximating tidal discharge values. The correlation suggests that under normal tidal conditions both saline and freshwater tidal channels migrate little, if any, and thus represent an apparently balanced relatively low energy system. For this reason it is believed that most stream channel migration in both saline and freshwater wetlands occurs as a result of increased forces due to storms.

Lithologic controls of drainage density: A study of six small rural catchments in New England, N.S.W.

The term drainage density has been operationally defined by a number of parameters characterising both static and dynamic networks (eroded channel density, perennial flow occupance, flow net, wetted channel length). The present study examines the variation of flowing stream length on six catchments of contrasting granite and sedimentary lithologies. The basic influence of lithology is analysed at three scales: between catchments, within one network, and along specific channel sections. Flow length graphs demonstrate that the drainage density of flow is greater on sedimentary rocks and is associated with higher eroded channel densities. All basins displayed a wide range of flow net fluctuations which were highly related to rainfall increments. Phases of flow network evolution were traced for each basin during one large storm. On granite basins two other components of the wetted channel network were quantified and exhibited equally dynamic characteristics when compared to flow. These were linear changes of continuous stagnant water sections and saturated segments. Field observations of episodic flows on two contrasting lithologies indicate the variable influence of rock type in surface and subsurface runoff processes and the importance of relating channelled flows to stream channel morphology.

Lithologic controls of drainage density: A study of six small rural catchments in New England, N.S.W.

The term drainage density has been operationally defined by a number of parameters characterising both static and dynamic networks (eroded channel density, perennial flow occupance, flow net, wetted channel length). The present study examines the variation of flowing stream length on six catchments of contrasting granite and sedimentary lithologies. The basic influence of lithology is analysed at three scales: between catchments, within one network, and along specific channel sections. Flow length graphs demonstrate that the drainage density of flow is greater on sedimentary rocks and is associated with higher eroded channel densities. All basins displayed a wide range of flow net fluctuations which were highly related to rainfall increments. Phases of flow network evolution were traced for each basin during one large storm. On granite basins two other components of the wetted channel network were quantified and exhibited equally dynamic characteristics when compared to flow. These were linear changes of continuous stagnant water sections and saturated segments. Field observations of episodic flows on two contrasting lithologies indicate the variable influence of rock type in surface and subsurface runoff processes and the importance of relating channelled flows to stream channel morphology.