Bankfull Width Research Articles

Estimation of error in bankfull width comparisons from temporally sequenced raw and corrected aerial photographs

This study investigates the propagation of error through image-to-image comparison of 285 river bankfull width measurements of the Afon Trannon, mid-Wales. Bankfull width is quantified from both aerial photographs analysed as rectified images in ERDAS Imagine OrthoMax and raw images in Paintshop Pro. A method for the robust estimation of bankfull width measurement error through temporal sequences of scanned aerial photographs is presented and the improvement in accuracy achieved using rectified imagery is quantified. Results from this study are placed in the context of previously published rates of bankfull width change, from a wide range of river scales, and the bankfull change rates for robust medium-term analysis using approximately 1:10,000 historical aerial photography are identified.

Ecological Characteristicsof Streams in the Barrenlands near Lac de Gras, N.W.T., Canada

We examined spatiotemporal variation in the physical, chemical, and biological characteristics of pristine streams that represent a range of conditions near Lac de Gras in the Barrenlands region of the Northwest Territories, Canada. Principal component analysis organized streams into four groups on the basis of seven physical characteristics. Despite broad differences among groups in physical characteristics, variation in chemical and biological characteristics was generally not large, with only pH and coarse particulate organic matter differing among the four groups. Nevertheless, several chemical and biological variables were correlated with physical characteristics, particularly measures of stream size (bankfull width and depth, drainage area, and stream discharge). Annual variability in climate affected stream temperature and discharge and influenced several biotic characteristics, particularly the growth of young-of-the-year arctic grayling ( Thymallus arcticus ). Barrenland streams share basic characteristics of Alaskan tundra streams, as a result of similar climatic regimes. Key differences between the two areas, however, appear related to the lake-outlet nature of the Barrenland streams, which may contribute to higher growth of young-of-the-year arctic grayling than would be expected from regional climate.

Large wood recruitment and redistribution in headwater streams in the southern Oregon Coast Range, U.S.A.

Large wood recruitment and redistribution mechanisms were investigated in a 3.9 km2 basin with an old-growth Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. forest, located in the southern Coast Range of Oregon. Stream size and topographic setting strongly influenced processes that delivered wood to the channel network. In small colluvial channels draining steep hillslopes, processes associated with slope instability dominated large wood recruitment. In the larger alluvial channel, windthrow was the dominant recruitment process from the local riparian area. Consequently, colluvial channels received wood from further upslope than the alluvial channel. Input and redistribution processes influenced piece location relative to the direction of flow and thus, affected the functional role of wood. Wood recruited directly from local hillslopes and riparian areas was typically positioned adjacent to the channel or spanned its full width, and trapped sediment and wood in transport. In contrast, wood that had been fluvially redistributed was commonly located in mid-channel positions and was associated with scouring of the streambed and banks. Debris flows were a unique mechanism for creating large accumulations of wood in small streams that lacked the capacity for abundant fluvial transport of wood, and for transporting wood that was longer than the bank-full width of the channel.

Ice storm impacts on woody debris and debris dam formation in northeastern U.S. streams

In January 1998, an ice storm damaged forests in northeastern United States and eastern Canada, causing coarse woody debris (CWD) deposition in riparian areas and associated streams. During 1999 and 2000, tree canopy damage, stream physical habitat, and wood deposition were evaluated within 51 first-, second-, and third-order streams located within five eastern Adirondack Mountain watersheds (New York, U.S.A.). In first- through third-order streams, the number and volume of stream debris dams increased in response to streamside trees with canopy damage. Tree canopy damage was not a significant predictor for individual pieces of stream CWD but was correlated with CWD >10 cm in diameter in third-order, but not first-order, streams. At debris dam locations, bankfull width was greater and stream substrates consisted of increased fines. Woody debris resulting from the 1998 ice storm was not associated with increased pool formation; instead, boulders and rocky substrate were the dominant pool-forming elements. CWD length in first-order streams generally exceeded bankfull width, but in third-order streams, CWD length was shorter than bankfull width and therefore was subject to greater transport and accumulation into debris dams. Our results indicate that ice storm disturbances can increase wood inputs to first- through third-order forested stream ecosystems.

Transport and retention of coarse woody debris in mountain streams: An in situ field experiment of log transport and a field survey of coarse woody debris distribution

Although coarse woody debris (CWD) is an important component of stream ecosystems in forested areas, the processes of CWD distribution, transport, and retention have not been clarified. In this study the distribution process of CWD pieces shorter than the bankfull width (S‐CWD) is discussed using an in situ field experiment of log transport and a field survey of CWD distribution in mountain streams. The transport experiment showed that transport distance has a close relation to flow depth and also implied that the magnitude and sequence of a series of flows were important factors for S‐CWD transport and retention in streams. The survey of CWD distribution indicated that in‐stream obstructions played an important role in the S‐CWD retention in deeper channels where S‐CWD pieces were potentially transported distances more than spacing between trapping sites of CWD. Overall, the in situ field experiment and the segment‐ to reach‐scaled analysis using h* (=depth/diameter) helped us understand the actual movement and distribution of CWD.

Stochastic Variability of Fluvial Hydraulic Geometry: Mississippi and Red Rivers

Major reasons for uncertainty in engineering predictions of river flows are the spatial variability and measurement error associated with depicting channel geometry. This paper develops a descriptive spatial stochastic model of depth-based hydraulic geometry in application to four dense data sets from the Mississippi and Red Rivers. To represent the irregularity in flow area and hydraulic radius as functions of flow depth, at-a-station cross-section geometry is defined using regressed power functions, accompanied by random residuals. More than 1600 surveyed cross sections are analyzed to describe trends in the spatial variance, and gradual (large-scale) and periodic (medium-scale) trends in the spatial mean of cross-sectional geometry parameters and channel bed slope. Also described are the probability distribution and correlation structure of each parameter’s random component. The relationships between spatial statistics of hydraulic geometry and bankfull width, channel sinuosity (meander patterns), bed elevation and riffle-pool spacing, and bank composition are explored. Conclusions and implications are discussed regarding the variable nature of fluvial hydraulic geometry and regarding the incorporation of geometric parameter uncertainty into prescriptive models of river processes.

Relative Influence of Environmental Variables on Macroinvertebrate Assemblages from an Iberian Basin

The composition of macroinvertebrate assemblages was studied at 31 sites in the Sado basin, a lowland area with intermittent rivers located in southern Portugal. Riparian features of the sites, including bankfull width, composition, cover, shade, and relative amount of tree debris, were also measured, and local and basin abiotic variables were determined. Woody vegetation in the Sado basin was species poor and was dominated by the ash Fraxinus angustifolia, the alder Alnus glutinosa, and the willows Salix alba and S. salvifolia. The study sites included a broad range of cover and riparian longitudinal integrity. Macroinvertebrate assemblages revealed low levels of richness (4-29 taxa, average 17.6) and Shannon's diversity (0.65-2.87 bits, average 1.89), and were dominated by species or groups (especially chironomids) that tolerate organic pollution and habitat disturbance. Assemblages were composed of collector-gatherers (5.4-100%, average 58.1), and to a lesser extent collector-filterers (0-81.3%, average 14.1) and shredders (0-25.5%, average 10.6). Partial canonical correspondence analysis was used to relate the macroinvertebrate assemblages to the riparian characteristics of a site and to local and basin abiotic variables. Out of 8 riparian variables, overhanging tree shade, total tree cover, and abundance of F. angustifolia and A. glutinosa were significant predictors of assemblage variation. Of the 21 abiotic variables considered, only conductivity, distance from source, and the average number of flowless summer months were significant predictors of assemblage variation. Total macroinvertebrate variation was divided into portions that were: 1) explained solely by abiotic variables (∼14%); 2) explained solely by riparian variables (∼18%); 3) explained by both riparian and abiotic variables (∼2%); and 4) unexplained (∼66%). Riparian features had greater influence than other environmental characteristics on the composition of macroinvertebrate assemblages in the Sado basin, perhaps because riparian features are closely related to food types.

Impact of Kiri dam on the lower reaches of river Gongola, Nigeria

Changes in Geomorphic characteristics in the lower reaches of the Gongola River channel following construction of Kiri dam have been investigated. The study focused on changes in the channel bankfull width and of riverbed width after the control of the river flow, variation in discharge characteristics between pre- and post- dam periods and the impact of discharge variation on post- dam river channel. Results of the analysis revealed that the main effect of the impoundment of the Gongola channel is a drastic decrease in flood peaks below the reservoir by 11.5% (from 1,420 m3/sec to 1,256 m3/sec). The low flows have on the other hand increased by 268% (from 5.7 m3/sec to 21 m3/sec). The resultant effect of decrease in the discharge was reduction in the channel bankfull and riverbed widths by 38.3% and 72.2% respectively. Also, the post- dam channel became less sinuous and braided in some of the reaches downstream. Discharges of high peaks were found during the period of maximum precipitation (June to September) whereas low discharges were recorded during the period of minimum or no precipitation (December to May). Some of the observed implications of the flow control on the geometric variables were reduction in the overall channel width, concave bank erosion and emergence of vegetation in some of the reaches.

Ecomorphological survey of large rivers - Monitoring and assessment of physical habitat conditions and its relevance to biodiversity.

An ecomorphological survey for large rivers above 10 m in width with special emphasis on navigable rivers is presented. It was elaborated on the basis of more than 500 km of survey on 8 different rivers including the major waterways in Germany. The method focuses on three quality elements of a functioning river ecosystem, i.e. hydrodynamics, morphodynamics and habitat structure. In this regard, 17 indicators are used for assessing the ecological functioning. The river system is divided into the riverbed, the riparian zones and the floodplain, each compartment being assessed with a defined group of indicators. The usual survey unit for larger rivers comprises one kilometre, some morphological indicators, however, require survey units related to bankfull width. The assessment is based on a scoring system which was defined independently of the actual survey. With a 5-step classification, the survey complies with EC standards. A preliminary analysis of the correlation between the structures of the fish and invertebrate communities and the ecological status obtained by the survey suggests that the assessment produces plausible results.

Random controls on semi‐rhythmic spacing of pools and riffles in constriction‐dominated rivers

AbstractAverage pool spacing between five and seven bankfull widths has been documented in environments throughout the world, but has limited theoretical justification in coarse‐bedded and bedrock environments. Pool formation in coarse‐bedded and bedrock channels has been attributed to bedrock and boulder constrictions. Because the spacing of these constrictions may be irregular in nature, it is difficult to reconcile pool‐formation processes with the supposedly rhythmic spacing of pools and riffles. To address these issues, a simulation model for pool and riffle formation is used to demonstrate that semi‐rhythmic spacing of pools with an approximate spacing of five to seven bankfull widths can be recreated from a random distribution of obstructions and minimum pool‐ and riffle‐length criteria. It is assumed that a pool–riffle couplet will achieve a minimum length based on dominant‐discharge conditions. Values for the minimum‐length assumption are based on field data collected in New England and California, while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation. Results from the simulations show that the location of pools can be primarily random in character, but still assume an average spacing between four and eight bankfull widths for a variety of conditions. Field verification data generally support the model but highlight a highly skewed distribution of pool‐forming elements and pool spacing. The relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant‐discharge conditions. Copyright © 2001 John Wiley & Sons, Ltd.

Consideration of Stream Morphology in Culvert and Bridge Design

In 1992, the Maryland State Highway Administration (SHA) initiated new design procedures to limit the impact of constructing culverts and bridges in streams. Elements of the new procedures included studies to define the characteristics of Maryland streams regarding bankfull widths, depths, and discharges; training of engineers in basic and advanced courses in stream morphology presented by David Rosgen; and updating the SHA culvert design manual to address consideration of stream morphology, fish passage, and other environmental features. The revised design procedure emphasizes the need to identify all appropriate objectives at the start of the design process so the best overall solution can be determined. The design concept is to construct a stream system that is stable and that neither scours nor aggrades. Elements of this approach include maintaining the consistency of dimension, pattern, and profile of the stream with particular attention given to maintaining bankfull width and width/depth ratio. Flood plain culverts are provided where appropriate to relieve the hydraulic load on the main channel culvert to limit downstream scour and erosion. Several culverts recently were constructed by using the stream morphology concepts discussed. These initial efforts have been quite successful and indicate that it is practical to consider stream morphology concepts in culvert design.

COMPARISON OF MODELS FOR ESTIMATING FLOOD QUANTILES IN NEW HAMPSHIRE AND VERMONT1

ABSTRACTWe develop and compare three regression models for estimating flood quantiles at ungaged stream reaches in New Hampshire and Vermont. These models emerge from systematic analysis and validation of relations between flood magnitude and six candidate predictors reflecting basin size, topography, and climate and channel size at 36 gaging stations with record lengths exceeding 20 years. Of the candidate predictors, bank full width is most highly correlated with flood magnitude and the best prediction equation is based on width. Thus channel geometry is closely related to the current hydrologic regime in spite of geologically recent glaciation and apparently non‐alluvial bank materials. We also develop models that use information obtainable from maps or GIS. The best of these uses drainage area and drainage‐basin elevation as predictors, but it is substantially less precise than the width‐based relation. A third relation using only drainage area as a predictor is even less precise but may be useful for some purposes. No other single predictors or combinations yielded useful predictions, although some had been included in previously‐established models for the region. Model comparison included examination of residuals generated by regression using one‐at‐a‐time suppression of data points and comparison with precision obtainable with gaging records of varying lengths.

Large woody debris in bull trout (Salvelinus confluentus) spawning streams of logged and wilderness watersheds in northwest Montana

We measured large woody debris (LWD) in 20 known bull trout (Salvelinus confluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m ranging from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggregates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attached to the stream bank were the most likely to be positioned perpendicular to stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg. Observations indicated that the majority of pools were formed as scour pools by either very large LWD pieces that were perpendicular to the stream or multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without rootwads were relatively consistent. However, among reaches with logging in the watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substantive change in stream habitats.

Impacts of Gravel Mining on Gravel Bed Streams

Abstract The impacts of gravel mining on physical habitat, fine-sediment dynamics, biofilm, invertebrates, and fish were studied in three Ozark Plateaus gravel bed streams. Intense studies were performed upstream, on site, and downstream from one large mine on each stream. Invertebrates and fish were also sampled in disturbed and reference riffles at 10 small mines. Gravel mining significantly altered the geomorphology, fine-particle dynamics, turbidity, and biotic communities. Stream channel form was altered by increased bank-full widths, lengthened pools, and decreased riffles in affected reaches. Fine particulate organic matter transported from riffles to pools was decreased. Biofilm organic content was decreased on flats and increased on remaining riffles. Density and biomass of large invertebrates and density of small invertebrates were reduced at the small, more frequently mined sites. Total densities of fish in pools and game fish in pools and riffles were reduced by the large mines. Silt-sensitive...

Artificial riffles in river rehabilitation: setting the goals and measuring the successes

1. Replacement of artificial riffles in canalized rivers is a widely-used tool in river rehabilitation but its effectiveness is only infrequently evaluated. In this paper artificial riffles, placed in a 2-km length of lowland stream in eastern England, were evaluated using geomorphological, functional habitat, and ecological techniques 3 years after installation. 2. Mean riffle spacing was approximately double that predicted from first principles, due to several large ‘gaps’ in the 2-km length where riffles had not been originally reconstructed. Two sequences, of 14 riffles, did approximate to the spacing predicted for natural riffles based upon the relationship with mean annual discharge and with bankfull width. Twenty out of 26 riffles retained their original physical character whilst six were deep, slow flowing and covered with sand or silt. 3. Shallow riffles in an approximately correct spacing retained their coarse particle dominance and caused the scouring between themselves of deeper pools than were found elsewhere in the stretch. Shallow riffles had high flow velocities which resulted in richness of functional habitats not found elsewhere in the stretch. 4. Invertebrate colonization showed a clear distinction between communities of shallow, fast-flowing riffles and deeper slow-flowing runs and silted riffles. Indicator taxa of riffles were the genera Baetis,Simulium,Hydropsyche,Eukieferiella, and Rheotanytarsus. Indicator genera of silted riffles and runs were Caenis,Planorbis,Sphaerium,Microtendipes, and Stichtochironomus. 5. Riffle reinstatement in lowland rivers of low energy will produce desirable geomorphological and ecological changes if the riffles are spaced according to geomorphological ‘first principles’, and are shallow (<30 cm depth) under low-flow conditions: thus, simple science can set adequate goals at the design stage. Appraisal using the development of functional habitats at riffle sites provides a rapid technique for post-project appraisal, thus evaluating by ecological success the original hydrological goals. © 1998 John Wiley & Sons, Ltd.

STREAM CHANNEL ADJUSTMENTS FOLLOWING ELIMINATION OF CAVFLE GRAZING1

ABSTRACT: Cattle grazing practices in the western United States have contributed to widespread riparian degradation resulting in unstable channel morphologies and the loss of fish habitat. Because of prolonged disturbance, numerous riparian areas on both public and private lands have been fenced to exclude cattle in order to promote vegetation establishment and riparian improvement. We selected four gravel‐bedded, steep alluvial streams in eastern Oregon with cattle exclosures greater than 14 years old for an analysis of geomorphic adjustments following the removal of cattle grazing. We compare channels inside exclosures and in adjacent grazed reaches to identify the salient stream channel properties that respond to the removal of riparian stresses and to document the magnitude of these changes. Results indicate that significant changes occur, with reductions in bankfull dimensions and increases in pool area being the most common and identifiable changes. At all four sites, bankfull widths are narrower by 10 to 20 percent, and the percentage of channel area occupied by pools is higher in the exclosure by 8 to 15 percent. The increase in pool area is primarily offset by a reduction in the percent glide area. Not all of the channel properties demonstrate adjustment, indicating that perhaps 14 years is an insufficient duration for these variables to adjust.

Reconstruction of changes in bankfull width: A comparison of surveyed cross-sections and aerial photography

Measurements of bankfull width determined from aerial photography are compared to measurements determined from surveyed river cross-sections for a low-gradient, sinuous, lowland alluvial river. Excellent agreement between independent datasets suggests that along such rivers downstream and/or temporal changes in bankfull width can be quickly and accurately reconstructed from aerial photography without the need for a large number of surveyed channel cross-sections. Guidelines are provided as to the minimum width of river channels that can be accurately measured with an optical micrometer from aerial photography, and the number of measurements necessary to determine accurate ‘average’ values for comparisons of bankfull width between reaches along the same river channel, and for comparisons between separate rivers.

Evolution of Miocene fluvial environments, eastern Potwar plateau, northern Pakistan

ABSTRACTThe Miocene‐Pliocene Siwalik Group records changing fluvial environments in the Himalayan foreland basin. The Nagri and Dhok Pathan Formations of this Group in the eastern Potwar Plateau, northern Pakistan, comprise relatively thick (tens of metres) sandstone bodies and mudstones that contain thinner sandstone bodies (metres thick) and palaeosols. Thick sandstone bodies extend for kilometres normal to palaeoflow, and are composed of large‐scale stratasets (storeys) stacked laterally and vertically adjacent to each other. Sandstone bodies represent single or superimposed braided‐channel belts, and large‐scale stratasets represent channel bars and fills. Channel belts had widths of km, bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3. Individual channel segments had bankfull widths, maximum depths, and slopes on the order of 102 m, 101 m and 10−4 respectively, and sinuosities around 1‐1. These rivers are comparable to many of those flowing over the megafans of the modern Indo‐Gangetic basin, and a similar depositional setting is likely. Thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe, wedge, sheet and channel‐form geometries: they represent crevasse splays, levees and floodplain channels. Mudstones are relatively bioturbated/disrupted and represent mainly floodbasin and lacustrine deposition. Mudstones and sandstones are extremely disrupted in places, showing evidence of prolonged pedogenesis. These ‘mature’ palaeosols are m thick and extend laterally for km. Lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate.The 500 m‐thick Nagri Formation has a greater proportion and thicker sandstone bodies than the overlying 700 m‐thick Dhok Pathan Formation. The thick sandstone bodies and their large‐scale stratasets thicken and coarsen through the Nagri Formation, then thin and fine at the base of the Dhok Pathan Formation. Compacted deposition rates increase with sandstone proportion (0‐53 mm/year for Nagri, 0‐24 mm/year for Dhok Pathan), and palaeosols are not as well developed where deposition rates are high. Within both formations there are 100 m‐scale variations (representing on the order of 105 years) in the proportion and thickness of thick sandstone bodies, and tens‐of‐m‐scale alternations of thick sandstone bodies and mudstone‐sandstone strata that represent on the order of 104 years. Formation‐scale stratal variations extend across the Potwar Plateau for at least 100 km, although they may be diachronous: however, 100‐m and smaller scale variations can only be traced laterally for up to tens of km.Alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel‐belt sizes (mainly), average deposition rate and avulsion frequency on a megafan comparable in size to modern examples. 100‐m‐scale variations in thick sandstone‐body proportion and thickness could result from ‘regional’ shifts in the position of major channels, possibly associated with ‘fan lobes’on a single megafan or with separate megafans. However, such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system.Formation‐scale and 100‐m‐scale stratal variations are probably associated with interelated changes in tectonic uplift, sediment supply and basin subsidence. Increased rates of hinterland uplift, sediment supply and basin subsidence, recorded by the Nagri Formation, may have resulted in diversion of a relatively large river to the area. Alternatively, changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland (possibly linked to tectonic uplift). Climate during deposition of the Siwalik Group was monsoonal. Although the deposits contain no direct evidence for climate change, independent evidence indicates global cooling throughout the Miocene, and the possibility of glacial periods (e.g. around 10‐8 Ma, corresponding to base of Nagri Formation). If the higher Himalayas were periodically glaciated, a mechanism would exist for varying sediment supply to megafans on time scales of 104‐105 years. Although eustatic sea‐level changes are related to global climatic change, they are not directly related to Siwalik stratigraphic changes, because the shoreline was many 100 km away during the Miocene.

Stream Channel Changes Associated with Mining and Grazing in the Great Basin

AbstractCharacteristics of channel morphology and streambed sediment were sampled at 5‐ and 10‐m intervals, respectively, along a 6.4‐km reach of Birch Creek in 1989 and 1992. In this case study we evaluate changes in these channel features using kernel regression analysis. The watershed is located high in the Toiyabe Mountains of central Nevada and has experienced historical grazing and more recent (1986–1989) mining for gold. Exclusion of grazing in the incised lower 1 km of the channel since 1990 did not lead to substantial geomorphic recovery by 1992. The bankfull width did decrease a bit in the grazing exclosure, but baseflow width increased. In both years, bankfull width was about 4 m greater in the exclosure compared with the upstream reaches, reflecting the long‐term grazing influences. The shift of grazing pressure into wet riparian areas upstream apparently caused decreases in thalweg depth, increases in fine sediment deposition in the channel, and loss of pool volume in these upstream areas. Some of these changes in substrate sediment could be attributed to inputs from the mine dumps; however, since either fine sediment did not increase or D50 did not decrease in the vicinity of the mines, the changes appear to be more related to recent changes in grazing patterns. Increased fine deposition also occurred in reaches with high volumes of large woody debris. Because of the episodic nature of peakflows that occur in the Great Basin, it may take many years for the full impacts of mining and grazing to be assimilated by the fluvial and riparian systems.

GEOMORPHIC AND PEDOLOGIC INFLUENCE ON SMALL‐SCALE EPHEMERAL CHANNEL DIMENSION IN RANGELANDS1

ABSTRACT: Geomorphic processes may partly determine channel geometry. Soil particle uplift during freezing and thawing cycles and bank sloughing during wetting and drying periods were observed. Soil properties and channel dimension were measured to determine the dominant processes controlling channel geometry in eight small (mean area 0.096 km2) drainages in Logan Canyon, Utah. Soil cohesion was low (plasticity index &gt; 15) for all but one of the drainages sampled. Basin scale geomorphic variables were examined to determine if they control channel dimension. Bankfull width was highly correlated to channel length and valley length with r2 values of 0.85 and 0.84, respectively. A strong canonical correlation (0.64) showed that distance from the watershed divide, bank liquid limit, and bank sand content were effective predictor variables of bankfull width and depth. The interrelations between geomorphic and pedogenic processes were the strongest determinants of ephemeral channel dimension in this study.