Geomorphic Channel Research Articles

A multi‐scale statistical approach to assess the effects of connectivity of road and stream networks on geomorphic channel condition

ABSTRACTRoads in rural, upland landscapes are important sources of runoff and sediment to waterways. The downstream effects of these sources should be related to the connectivity of roads to receiving waters. Recent studies have explored this idea, but only simple metrics have been used to characterize connectivity and few studies have quantified the downstream effects of road–stream connectivity on sediment or solute budgets and channel morphology. In this study, we evaluated traditional and newly developed connectivity metrics that utilized features of landscape position and delivery pathway to characterize road–stream connectivity in upland settings. Using data on stream geomorphic conditions developed by the Vermont Agency of Natural Resources (Montpelier, VT), we related road connectivity metrics to channel condition on a set of 101 forested, upland streams with minimal development other than predominantly gravel road networks. Logistic regression indicated that measures of road density, proximity and orientation successfully distinguished among categories of stream geomorphic condition at multiple geographic scales. Discriminant function analysis using a set of inherent channel characteristics combined with road connectivity metrics derived at the reach corridor scale successfully distinguished channel condition for over 70% of the channels evaluated. This research contributes to efforts to evaluate the cumulative downstream effects of roads on stream channels and aquatic resources and provides a new means of watershed assessment to derive metrics that can be used to predict channel condition. Copyright © 2014 John Wiley & Sons, Ltd.

An Evaluation of Data Collected by Middle School and College-Level Students in Stream Channel Geomorphic Assessment

This project tested the accuracy and repeatability of geomorphic stream channel assessments conducted by two different middle school classes from the Walt Morey Middle School in Troutdale, OR and college students from Portland State University in Portland, OR. Each group surveyed the same three cross-sections in Fairview Creek, a tributary to the Lower Columbia River, in order to assess stream channel geometry, discharge, composition of the bed material, and water quality. The three student groups were all able to accurately document the stream channel geometry, including stream width and mean depth, indicating that these data can be successfully collected by volunteers of various ages. However, stream velocity obtained using the float method was consistently overestimated leading to a biased calculation of discharge, and the low precision of the measurements did not allow for a correction of the bias. The median particle size of the bed material determined by a pebble count was also overestimated by each group, but the low precision also negated the possibility of correcting the estimate. The stored fine sediment in the bed was underestimated by each group and again with low precision. The temperature, pH, and conductivity measured with a calibrated multimeter were accurate and precise for all groups.

Geomorphic elements on modern distributive fluvial systems

Analysis of over 400 fluvial megafans (>30km in length) in aggradational continental sedimentary basins reveals that geomorphic channel and floodplain changes on these distributive fluvial systems (DFS) generally behave in predictable ways with increasing distance from the apex. These changes can include: a decrease in discharge, a decrease in bed material transport and calibre of sediment, a decrease in stream power, an overall decrease in channel width, an overall decrease in channel depth, an increase in avulsive behaviour, and sinuosity becomes more variable.Three generic geomorphic element models are proposed – reflecting observed changes in channel behaviour – based on measurable changes in channel width and planform characteristics with increasing distance downstream. The three models are derived from (1) a single braided channel that bifurcates downstream into low sinuosity channels; (2) a dominant, sinuous, single-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity; and (3) a dominant multi-thread channel that anabranches and bifurcates with distance downstream, creating smaller channels with varying sinuosity.The changes in fluvial behaviour and landforms on DFS are in response to variable discharge and sediment supply ratios from the upstream catchment. In contrast to examples described in hydrogeomorphological literature for tributary fluvial systems where channel dimensions tend to increase downstream, observations from DFS suggest that – where the formative DFS channel does not retain the same dimensions – intrinsic geomorphic thresholds lead to the breakdown of the main trunk channel into smaller anabranching and distributary channels with distance downstream; in some instances the majority of channelised flow at the DFS termination may even be disintegrated. The observed range of termination types and floodplain soils for each DFS type are interchangeable dependent on local conditions. The modern geomorphic elements and floodplain soils are dependent on climate in the upstream catchment and in the downstream receiving sedimentary basin.

LANDSCAPE‐LEVEL MODEL TO PREDICT SPAWNING HABITAT FOR LOWER COLUMBIA RIVER FALL CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA)

ABSTRACTWe developed an intrinsic potential (IP) model to estimate the potential of streams to provide habitat for spawning fall Chinook salmon (Oncorhynchus tshawytscha) in the Lower Columbia River evolutionarily significant unit. This evolutionarily significant unit is a threatened species, and both fish abundance and distribution are reduced from historical levels. The IP model focuses on geomorphic conditions that lead to the development of a habitat that fish use and includes three geomorphic channel parameters: confinement, width and gradient. We found that the amount of potential habitat for each population does not correlate with current, depressed, total population abundance. However, reaches currently used by spawners have high IP, and IP model results correlate well with results from the complex Ecosystem Diagnosis and Treatment model. A disproportionately large amount of habitat with the best potential is currently inaccessible to fish because of anthropogenic barriers. Sensitivity analyses indicate that uncertainty in the relationship between channel width and habitat suitability has the largest influence on model results and that model form influences model results more for some populations than for others. Published in 2011 by John Wiley & Sons, Ltd.

Differences in macroinvertebrate community structure in streams and rivers with different hydrologic regimes in the semi-arid Colorado Plateau

Aquatic macroinvertebrates are sensitive to changes in their chemical and physical environment, and as such, serve as excellent indicators of overall ecosystem health. Moreover, temporal and spatial differences in macroinvertebrate community structure can be used to investigate broad issues in aquatic science, such as the hypothesis that changes in climate are likely to have disproportionately large effects on small, intermittent stream ecosystems. We quantifi ed macroinvertebrate community structure and abiotic conditions at ten stream sites with different dominant hydrologic regimes in the Colorado Plateau, ranging from small, intermittent desert streams to large perennial mountain rivers. Considerable differences were observed in community structure between sites with differing hydrologic regimes. Quantitative results of non-metric multidimensional scaling (NMDS) ordination and Spearman rank correlations between physical habitat and macroinvertebrate resemblance matrices indicate that discharge, geomorphic channel unit type (% pools vs. % riffl es), percent of substrate composed of sand, and velocity were the subset of measured habitat variables that best explained the differences in macroinvertebrate community structure among sites. Of the 134 taxa identifi ed, nine taxa explained 95 % of the variability in community structure between sites. These results add to a growing base of knowledge regarding the functioning of lotic ecosystems in the Colorado Plateau, and provide timely information on anticipated changes in the structure and function of aquatic ecosystems in response to predicted future environmental conditions.

Vegetation survey in nature-friendly small streams for each protection method

Riparian vegetation distribution patterns and diversity relative to various fluvial geomorphic channel patterns, stream bank stabilization methods, and stream flow processes are described and interpreted for selected nature-friendly small stream bank protection of Goesan, central Korea. Idong Stream Pilot Project, which began in May 2003 and finished in December 2003, was selected to develop effective methods which was nature-friendly stream bank protection. The project aim to maintain or increase stream bank stabilization ecosystem goods and services while protecting downstream and stream bank ecosystem. A number of protecting methods which were a Flight of fieldstone, Vegetation block, Green river block, Stone net, Green environment block, Eco friendly cobble, Vegetation mat and Geo-green cell and Firefly block were applied on the bank of Idong stream. The stream sites have been monitored about vegetation conditions each method in 2007. We selected six points to separately investigate in left and right bank. The main purpose of this study was to find out suitable methods and to improve stream restoration techniques for ecosystem. On the stream bank, H environment block method (9.7) was the highest average of vegetation coverage and Firefly block method (3.87) was the lowest average in applied methods.

An Evaluation of the Influence of Seasonal Base Flow and Geomorphic Stream Characteristics on Coastal Plain Stream Fish Assemblages

AbstractWater regulation and use have been identified as important limiting factors influencing stream‐dwelling fishes. To develop effective water management strategies, fisheries biologists need tools for assessing the effect of reduced streamflows on fish communities. We studied fish assemblages in the lower Flint River basin, Georgia, during two drought years with very low streamflow (2001–2002) and two postdrought years (2003–2004) with average to above‐average streamflow. Fishes were sampled and stream discharge was measured during the spring, summer, and winter of each year. Analysis of fish assemblage metrics indicated that fish species richness and total fish density were strongly and positively related to seasonal 10‐d low discharge. However, the effect of discharge varied with stream size and geomorphic channel characteristics, which suggested that a single low‐flow standard was unlikely to have the same effect across all streams in the basin. The effect of seasonal base flows also was greater in the spring and summer than in winter. Hierarchical occupancy models indicated that the fish species most sensitive to low base flows were those that were large bodied as adults, were intolerant to anthropogenic alterations, and occupied deep and fast current velocity habitats. When conducting environmental flow assessments at regional scales, managers should consider the effects of local stream reach characteristics on the response of fishes to streamflow alteration.

Development and Evaluation of a Stream Channel Classification for Estimating Fish Responses to Changing Streamflow

AbstractCurrent approaches to assessing the potential effects of river regulation and water use on stream fish communities are based on physical habitat simulation and are not feasible for estimating these effects over large spatial scales. We developed a channel classification for streams in the lower Flint River basin, Georgia, based on gross channel morphology and geology and evaluated its usefulness at 23 study sites representing the four channel types in the basin. Our channel classification separated stream channel types based on dominant geology (upland residuum versus Ocala limestone) and channel form (confined versus unconfined). Fish were sampled and habitat measured at the study sites in spring, summer, and winter from 2001 to 2004, a period that included some of the lowest and highest seasonal flows ever recorded. The channel types differed with respect to diurnal variability in temperature and dissolved oxygen concentration as well as habitat characteristics (substrate, large wood). Statistical habitat modeling indicated that channel unit (e.g., pool, riffle) availability could be predicted accurately for each channel type using streamflow, with errors rates that averaged 0.7% across channel unit types. Comparisons between the accuracy of species presence and fish abundance models fit using habitat characteristics to those fit using geomorphic channel characteristics indicated similar model accuracy with slightly less bias (6% on average) for the geomorphic channel characteristics models. Our results indicate that the channel types were useful for predicting changes in habitats and stream fish presence and abundance in response to changing streamflow. Channel classification is potentially a useful and cost‐effective approach to quantifying changes in the physical environment in response to varying streamflow. Additionally, channel classification could be combined with dynamic fish population models to evaluate the effects of river regulation and water use across large spatial scales.

Interpreting Stream Physical Characteristics in Index of Biotic Integrity Classifications: General Similarities and Specific Differences

AbstractFish assemblage‐based indices of biotic integrity (IBIs) are commonly used by many states. These IBIs contain a core of common metrics and a few metrics that are specific to the local environmental setting and fish assemblage. This implies a consistency of responses as degradation increases, but the responses are modified by the local environmental setting. These implications lead to two hypotheses: (1) stream physical characteristics, such as substrate composition, geomorphologic composition, and hydraulic characteristics, will differ among integrity classes regardless of geographic location or environmental setting and (2) the differences in stream physical characteristics among integrity classes change due to the environmental setting. To test these hypotheses, fish assemblages and stream physical characteristics were examined across a priori defined degradation gradients in four diverse environmental settings by comparing species traits (preferences for substrate, preferences for geomorphic channel units, and locomotion morphology) and stream physical characteristics (substrate composition, geomorphic channel unit abundance, and stream hydraulic characteristics) among three IBI classes (high, moderate, and low). Across all environmental settings combined, Euclidean distances of species traits normalized to local reference conditions indicated differences in substrate preferences among each of the three integrity classes: substrate particle size preferences differed among all three integrity classes, geomorphic channel unit preference differed between the high‐integrity sites and the other sites, and locomotion morphology differed between low‐integrity sites and the other sites. These results indicate that degradation occurs in each of the three physical stream characteristics regardless of environmental setting. Within the individual environmental settings, there were some specific differences in the changes in substrate preferences, geomorphic unit preference, and locomotion morphology among integrity classes. Within individual environmental settings, differences in stream physical characteristics among integrity classes generally reflected the same differences as indicated by differences in fish assemblage composition.

Effect of geomorphic channel restoration on streamflow and groundwater in a snowmelt‐dominated watershed

Reengineering of stream channels is a common approach used to restore hydrologic function in degraded landscapes, but there has been little published research analyzing its effectiveness. A key challenge for impact assessment is disentangling the effects of restoration from climate variability. Trout Creek, near Lake Tahoe, California, was reengineered to reestablish hydrologic connectivity between the stream and its former floodplain. Gauges located above and below the site, along with groundwater well measurements, were used to analyze prerestoration and postrestoration hydrology. Results show that restoration has a seasonal impact with statistically significant increases in streamflow during the summer recession period and decreased groundwater table depths across a wide range of streamflow conditions. Paired gauges and statistical models that are robust to serial autocorrelation demonstrate a feasible approach for assessing hydrologic restoration in regions where climate patterns lead to substantial within‐year and between‐years variation in streamflow.

Selection of Spawning Sites by Coho Salmon in a Northern California Stream

AbstractWe assessed the relative importance of various factors contributing to spawning site use by a population of threatened coho salmon Oncorhynchus kisutch in Freshwater Creek, California, and created a predictive model of spawning habitat selection based on logistic regression analysis. We excluded sampling sites that previous studies had established as unsuitable on the basis of depth and substrate criteria and asked why fish chose particular locations and not others in seemingly suitable habitat. We evaluated surface water velocity, depth, substrate size composition, gravel inflow rates, vertical hydraulic gradient, geomorphic channel units, hyporheic water physicochemistry, cover, and proximity to other redds not in sampling sites during the 2004–2005 spawning season. In univariate comparisons with unused sites, coho salmon selected sites with a smaller median particle diameter, a larger percentage of gravel–pebble substrate, and higher gravel inflow rates. Based on multivariate logistic regression, the probability of a site's being used for spawning was best modeled as a positive function of the gravel–pebble fraction of the substrate, location at a pool or run tail, and the presence of existing redds in close proximity to the site. This model explained 38% of the variation in the data and was a better predictor of spawning habitat use than a more traditional model based on depth, velocity, and substrate. Our results highlight the potential importance of social behavior in contributing to habitat selection by spawning salmonids.

Riparian Vegetation Patterns in Relation to Fluvial Landforms and Channel Evolution Along Selected Rivers of Tuscany (Central Italy)

Riparian vegetation distribution patterns and diversity relative to various fluvial geomorphic channel patterns, landforms, and processes are described and interpreted for selected rivers of Tuscany, Central Italy; with emphasis on channel evolution following human impacts. Field surveys were conducted along thirteen gauged reaches for species presence, fluvial landforms, and the type and amount of channel/riparian zone change. Inundation frequency of different geomorphic surfaces was determined, and vegetation data were analyzed using BDA (binary discriminate analysis) and DCA (detrended correspondence analysis) and related to hydrogeomorphology. Multivariate analyses revealed distinct quantitative vegetation patterns relative to six major fluvial geomorphic surfaces. DCA of the vegetation data also showed distinct associations of plants to processes of adjustment that are related to stage of channel evolution, and clearly separated plants along disturbance/landform/soil moisture gradients. Species richness increases from the channel bed to the terrace and on heterogeneous riparian areas, whereas species richness decreases from moderate to intense incision and from low to intense narrowing.

Stream Channel Offset and Late Holocene Slip Rate of the San Andreas Fault at the Van Matre Ranch Site, Carrizo Plain, California

Sets of well-preserved channels offset across the San Andreas fault (SAF) at the Van Matre Ranch (VMR) site in the northwestern Elkhorn Hills area of the Carrizo Plain offer the opportunity to measure slip rate and examine geomorphic development of the channels. The fault zone and offset channels were exposed by excavation in one fault-perpendicular and five fault-parallel trenches. The geomor- phology and stratigraphy in the channels reveal a record of filling by fluvial sedi- mentation, lateral colluviation, and pedogenesis. The buried thalweg of the currently active channel is offset 24.8 1 m, while the geomorphic channel is offset approx- imately 27.6 1 m. Seventeen samples were collected from channel margin deposits for 14 C dating. An OxCal model of the radiocarbon dates with stratigraphic control suggests that the oldest date for channel incision was A.D. 1160. Minimum and maximum slip rates ranging from 29.3 to 35.6 mm/yr are derived from different assumptions about the timing of channel incision and offset. The resulting slip rates at VMR agree well with the late-Holocene slip rate of 33.9 2.9 mm/yr at Wallace Creek, approximately 18 km to the northwest, and imply that within measurement uncertainty the 30-37 mm/yr velocity gradient across the SAF from decadal time- scale geodetic measurements is accommodated across the several-meter-wide SAF zone at VMR over the last millennium.

Post-flooding distribution and characteristics of large woody debris piles along the semi-arid Sabie River, South Africa

The formation of large woody debris (LWD) piles has a profound impact on channel patterns and riparian succession in temperate rivers. The opportunity to study LWD along the Sabie River, a river in the semi-arid region of Kruger National Park, South Africa, arose in February 2000 after a significant flood (c. 100-year return interval) removed a large proportion of the fully mature riparian forest and other plant communities. Much of the uprooted vegetation was deposited as LWD piles (woody vegetation accumulations deposited on the ground > 0.1m 3) throughout the riparian and upland zones. In this article we describe the spatial distribution patterns of LWD as related to geomorphic channel type and flood frequency zone, and assess pile composition characteristics six months after the flood. Within the areas surveyed there were 68 LWD piles per hectare, the median size of LWD piles was 4.6 m3 but pile sizes (by volume) varied widely. Pool/rapid geomorphic channel types had the highest density of LWD piles (79 ha-1) and the largest piles (by volume) were in the bedrock anastomosing channels (mean = 124 m3). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m 3 and 55 m3) than piles in the active zone (c. 2 m3). The patterns of distribution and volume of LWD will affect the subsequent development of vegetation communities as debris piles form a mosaic of patches of surviving organisms and propagules that can strongly influence the initial trajectory of succession. The amount, distribution, and subsequent decomposition of LWD are different from that reported for temperate rivers, suggesting that the role of LWD may be different on non-floodplain rivers such as the Sabie in semi-arid South Africa.

Case Study: Sediment Transport in Proposed Geomorphic Channel for Napa River

A model study evaluates sediment transport in a geomorphic channel proposed for restoration and flood damage reduction of an 11-km tidally influenced reach of the Napa River located in California. The model study employs the unsteady quasi-2D hydrodynamic and sediment transport model MIKE 11, the simplified marsh plain accretion model MARSH 98, and the Rouse equation to predict annual average morphological changes of the geomorphic channel. The adopted modeling approach allows for the simulation of salient sediment transport processes in a river estuary, including lateral and vertical sorting of sediments, and local flushing of fine cohesive and noncohesive sediments during flooding. Accretion rates, particularly within the marsh plain terrace of the multistage channel, are found to be within acceptable limits for project maintenance and ecosystem restoration purposes. This enhanced 1D modeling approach may offer a viable and cost-effective alternative compared to fully 2D and 3D models, with relatively less model set-up and run-time requirements.

The Influence of Geomorphic Factors and Geographic Region on Large Woody Debris Loading and Fish Habitat in Alaska Coastal Streams

Large woody debris (LWD) and channel data from three Alaska coastal regions with varying geomorphic channel types were analyzed to document regional variability in LWD abundance, define geomorphic characteristics affecting LWD abundance, and identify relationships between LWD abundance and the formation of pools and gravel bars in streams. Large woody debris abundance was significantly lower at the northern edge of the coastal coniferous forest than in Southeast Alaska and was significantly greater in alluvial gravel-bedded channels than in contained boulder–bedrock channels. More pools and gravel bars were formed by LWD in alluvial channels than in contained channels. Pool spacing (the number of channel widths between pools) decreased with increasing LWD abundance (pieces/km) and was significantly influenced by the interaction between LWD abundance and channel width. As channel width increased, pool spacing was more strongly influenced by changes in LWD abundance, but the relative change in pool spacing diminished with increasing LWD load. The percentage of stream area in pools was insensitive to changes in LWD abundance and was best predicted by channel type. The percentage of habitat units with gravel as the dominant substrate was positively related to LWD abundance and negatively related to stream gradient.

Fault Tree Analysis of Bridge Failure due to Scour and Channel Instability

Fault tree analysis is a systematic method of analyzing events that lead to an undesirable event. Fault trees can be used to assess the probability of failure of a system (or top event), to compare design alternatives, to identify critical events that will significantly contribute to the occurrence of the top event, and to determine the sensitivity of the probability of failure of the top event to various contributions of basic events. In this paper, fault tree analysis is used to determine the probability of failure of a bridge caused by scour and other geomorphic channel instabilities. This analysis permits an examination of a very complex system of interactions and processes that are not well understood. Minimal knowledge regarding the actual processes of scour and channel instability is required for a fault tree analysis. Three examples of analyses for actual bridges are provided showing different combinations of scour (local and contraction) and geomorphic instabilities (channel widening and degradation) at both the abutments and piers. Riprap placed at the abutments for protection is also included in the analyses.

The Role of Riparian Corridors in Maintaining Regional Biodiversity.

Riparian corridors possess an unusually diverse array of species and environmental processes. This "ecological" diversity is related to variable flood regimes, geomorphic channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. This dynamic environment results in a variety of life history strategies, and a diversity of biogeochemical cycles and rates, as organisms adapt to disturbance regimes over broad spatio-temporal scales. These facts suggest that effective riparian management could ameliorate many ecological issues related to land use and environmental quality. We contend that riparian corridors should play an essential role in water and landscape planning, in the restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.