Stream Channel Response Research Articles

Predicting Hydromodification in Streams Using Nonlinear Memory-Based Algorithms in Southern California Streams

AbstractHydromodification is a serious management concern in semiarid regions and is expected to become worse with land use and climate change. Potential stream channel responses range from increas...

Predicting gravel bed river response to environmental change: the strengths and limitations of a regime‐based approach

AbstractRivers respond to environmental changes such as climate shifts, land use changes and the construction of hydro‐power dams in a variety of ways. Often there are multiple potential responses to any given change. Traditionally, potential stream channel response has been assessed using simple, qualitative frameworks based largely on professional judgement and field experience, or using some form of regime theory. Regime theory represents an attempt to use a physically based approach to predict the configuration of stable channels that can transport the imposed sediment supply with the available discharge. We review the development of regime theory, and then present a specific regime model that we have created as a stand‐alone computer program, called the UBC Regime Model (UBCRM). UBCRM differs from other regime models in that it constrains its predictions using a bank stability criterion, as well as a pattern stability criterion; it predicts both the stable channel cross‐sectional dimensions as well as the number of anabranches that the stream must have in order to establish a stable channel pattern. UBCRM also differs from other models in that it can be used in a stochastic modelling mode that translates uncertainty in the input variables into uncertainty in the predicted channel characteristics. However, since regime models are fundamentally based on the concept of grade, there are circumstances in which the model does not perform well. We explore the strengths and weaknesses of the UBCRM in this paper, and we attempt to illustrate how the UBCRM can be used to augment the existing qualitative frameworks, and to help guide professionals in their assessments. Copyright © 2016 John Wiley & Sons, Ltd.

Stream channel responses and soil loss at off-highway vehicle stream crossings in the Ouachita National Forest

This study investigates the geomorphic effects of ford-type stream crossings in an off-highway vehicle (OHV) trail complex in the Ouachita National Forest, Arkansas. At a total of 15 crossing sites, we used a disturbed vs. undisturbed study design to assess soil truncation and an upstream vs. downstream design to assess in-channel effects. The 15 sites ranged from OHV crossings active for over 20years to those on trails that have been closed to regular use for >5years. All of the sites designated for OHV use (14 sites) exhibit soil loss of ~30 to 45cm within the trail segments on either side of the crossings. In-channel responses attributable to the crossings were observed at 14 (93%) of the sites and include increased bank erosion, increased mud coatings on coarse channel clasts, increased in-channel fine-sediment accumulations, changes in the size distributions of coarse bed material, and occurrence of large channel-filling sediment plugs. However, while every site but one shows at least one channel impact, only one site exhibits all of them. Despite the relatively homogeneous geographic area sampled, only limited generalizations are evident. Sediment impacts seem to predominate over runoff impacts from the trails. Small channels (basin areas <0.4km2) show greater consistency in their response behavior than larger channels. Where OHV use is currently allowed, downstream increases in mud coatings and sediment deposition features are more common. What seems more certain is that individual effects are strongly contingent on local details of channel and valley geomorphology.

Stream Channel Enlargement Response to Urban Land Cover in Small Coastal Plain Watersheds, North Carolina

Stream channel response to urban land use has not been well documented for southeastern Coastal Plain streams. In this study, urban channel response was evaluated in small Inner Coastal Plain watersheds (<5 km2) in eastern North Carolina. Reaches were selected across a range of watershed total impervious area (0-67% TIA). Channel dimensions and sediment grain size data were collected along 20 urban (>10% TIA) and 20 rural reaches (<10% TIA), and at 10 stormwater outfall sites (180 cross-sections). Urban cross-sectional area, channel incision ratio, and channel grain size (gravel%, D50, and D84) were greater, relative to rural channels. Bankfull cross-sectional areas were approximately 1.78 times greater for urban watersheds than for rural watersheds. Channels in urban watersheds were incised and had median full-channel capacities approximately 3.4 times greater than channels draining rural watersheds. Watershed TIA explained 65-72% of channel capacity enlargement. Urban expansion in the region began in the 1960s, with major urbanization occurring over the last 25 years. Channels draining urban watersheds are still responding to this land use change by downcutting and widening. Urban channel incision has frequently cut off streams from their floodplains, reducing floodplain sediment retention and water quality functions.

The Response of Salmon Populations to Geomorphic Measurements at Three Scales

AbstractProtocols to assess stream channel response to disturbances often focus on physical aspects of the stream at the reach scale without measurements of fish populations. In this study, estimates of juvenile salmon abundance in 511 habitat units within 25 reaches of 12 streams were made over 4 years and juxtaposed with measurements of physical habitat at the habitat unit, reach, and watershed scales. Fish ranged in size from about 50 to 160 mm fork length. The amount of variation among densities differed by species and geographic scale. For most species, the habitat unit scale accounted for the most variation. Relationships between salmon density and measurements at the habitat unit scale varied. At the reach scale, we observed a negative relationship between abundance of coho salmon Oncorhynchus kisutch parr and number of pools. A positive relationship appeared between coho salmon parr and large wood. At the watershed scale, a positive relationship was observed between coho salmon parr and valley morphology. Valley morphology also entered the model for cutthroat trout O. clarkii. Differences in salmonid densities observed between northern and southern watersheds were attributed to differences in landforms, geology, and soils among islands in southeast Alaska. Simple habitat measures, such as pool counts, were not good predictors of fish abundance. However, geomorphic measures from multiple scales that are accompanied by estimates of fish abundance can provide managers with an integrated picture of watershed productivity and a better means to evaluate features that influence productivity.

Channel stability in bed load–dominated streams with nonerodible banks: Inferences from experiments in a sinuous flume

Experimental and computational evidence shows that bed state adjustments can accommodate a twofold to fourfold change in sediment supply without otherwise affecting the morphology of a sinuous gravel bed stream channel with nonerodible banks. In contrast, previously published experiments of the same kind but with erodible channel banks suggest that changes in sediment supply are taken up almost exclusively by changes in channel sinuosity and hence the reach‐average water surface gradient. It appears that stream channel response to changes in sediment supply is strongly conditioned by the nature of the stream boundary, and that determines which of several potential adjustments are possible.

Grazed Riparian Management and Stream Channel Response in Southeastern Minnesota (USA) Streams

The U.S. Department of Agriculture-Natural Resources Conservation Service has recommended domestic cattle grazing exclusion from riparian corridors for decades. This recommendation was based on a belief that domestic cattle grazing would typically destroy stream bank vegetation and in-channel habitat. Continuous grazing (CG) has caused adverse environmental damage, but along cohesive-sediment stream banks of disturbed catchments in southeastern Minnesota, short-duration grazing (SDG), a rotational grazing system, may offer a better riparian management practice than CG. Over 30 physical and biological metrics were gathered at 26 sites to evaluate differences between SDG, CG, and nongrazed sites (NG). Ordinations produced with nonmetric multidimensional scaling (NMS) indicated a gradient with a benthic macroinvertebrate index of biotic integrity (IBI) and riparian site management; low IBI scores associated with CG sites and higher IBI scores associated with NG sites. Nongrazed sites were associated with reduced soil compaction and higher bank stability, as measured by the Pfankuch stability index; whereas CG sites were associated with increased soil compaction and lower bank stability, SDG sites were intermediate. Bedrock geology influenced NMS results: sites with carbonate derived cobble were associated with more stable channels and higher IBI scores. Though current riparian grazing practices in southeastern Minnesota present pollution problems, short duration grazing could reduce sediment pollution if managed in an environmentally sustainable fashion that considers stream channel response.

Experimental study of the transport of mixed sand and gravel

We measured a wide range of transport rates for five different sand/gravel mixtures in a laboratory flume. Each mixture used the same gravel, and sand was added to produce mixtures containing 6, 15, 21, 27, and 34% sand. Control of other variables allows us to isolate the effect of bed sand content on transport. As sand content increases, gravel transport rates increase by orders of magnitude, even though the proportion of gravel in the bed decreases. The increase in gravel transport rate is most rapid over the range of bed sand content between 15 and 27%. The increase in transport rate is larger than predicted using standard scaling relations between transport rate and grain size, indicating that models of transport and sorting and predictions of stream channel response to sand inputs need to be revised to account for the influence of sand content. Bed surface grain size was measured at the end of each run. Surface grain size varied with sand content but showed little or no coarsening with flow strength and transport rate. This casts doubt on the idea that armor layers form at small flows and weaken or vanish with increasing flow and transport rate.

A Method of Analysing Stream Channel Response to Environmental Change: Gauge data for the Tully River

Gauging data are available from numerous streams throughout Australia, and these data provide a basis for historical analysis of geomorphic change in stream channels in response to both natural phenomena and human activities. We present a simple method for analysis of these data, and a brief case study of an application to channel change in the Tully River, in the humid tropics of north Queensland. The analysis suggests that this channel has narrowed and deepened, rather than aggraded: channel aggradation was expected, given the intensification of land use in the catchment, upstream of the gauging station. Limitations of the method relate to the time periods over which stream gauging occurred; the spatial patterns of stream gauging sites; the quality and consistency of data collection; and the availability of concurrent land-use histories on which to base the interpretation of the channel changes.

Patterns of stream channel response to urbanization in the humid tropics and their implications for urban land use planning: a case study from southwestern Nigeria

Analysis of the nature of static allometric changes in seven streams affected by urbanization in Ado-Ekiti, southwestern Nigeria, and their comparison with four natural streams in the region reveals that while the channel capacities of the natural streams increase at the same rate with stream discharge, their urban counterparts exist in varying degrees of disequilibrium, becoming fully adjusted to the urban hydrological situation only when urbanization is complete and stable. The degree and location of urbanization in the watersheds appear to be the main determinants of the nature of stream channel response to urbanization. An increase in urban agriculture is suggested as a panacea to reduce urban environmental hazards such as accelerated sheet and gully erosion, sedimentation, and floods in the humid tropics.

Contrast in stream-channel response to major storms in two mountainous areas of California

The generally catastrophic effects of major storms on the geometry of intermediate- and high-order channels in northwestern California contrast with localized storm-related channel changes found in the Santa Cruz Mountains. Sediment delivery in northwestern California during storms overwhelms transport capacities throughout the length of most intermediate- and high-order channels and causes long-lasting changes in geometry. In contrast, sediment delivery during storms in the Santa Cruz Mountains overwhelms transport capacities only in localized reaches. This contrast in channel behavior is at least partially caused by contrasts in the style of landsliding found in the two areas.

Stream-channel response to floods, with examples from central Texas

The principle that most geomorphic work is accomplished by relatively frequent events of moderate intensity requires modification for application to stream channels in certain climatic and physiographic settings. Small drainage basins in regions of highly variable flood magnitudes appear to have a high potential for catastrophic response. Flash-flood potential for small basins can be regionally mapped by computing the standard deviation of the logarithms of the annual flood peaks. Highly right-skewed flood-frequency distributions indicate that a high potential exists in certain arid regions of the southwestern United States and in the seasonal subtropical-to-steppe climate region of central Texas. High-magnitude flood response is also promoted by physiographic factors, such as hillslope morphology, soils, rock type, and drainage density. The relative importance of overland flow, which produces intense flood peaks, versus interflow and ground-water flow, which produce more uniform streamflow, appears to integrate both the climatic and the physiographic influences on the potential for catastrophic floods. Another factor in realizing the climatic-hydrologic potential for catastrophic stream-channel response is the resistance of the channel itself to scour. Small limestone streams in central Texas show significant channel modification only during the rare high-magnitude floods characteristic of that region. This is mainly because of the high response threshold required to scour bouldery alluvium and dense valley-bottom vegetation. Effects of especially intense floods on such streams include the following: entrainment of jointed bed rock and boulders as much as 3 m in diameter, uprooting of trees that usually bind coarse-grained point bars, macroturbulent transport of boulders even over divides into adjacent drainages, local scour of chutes on meander bends, and passive boulder deposition on other preflood valley-bottom surfaces.