Squamish River Research Articles

Influence of a large debris flow fan on the late Holocene evolution of Squamish River, southwest British Columbia, Canada

Cheekye Fan is a large paraglacial debris flow fan in southwest British Columbia. It owes its origin to the collapse of Mount Garibaldi, a volcano that erupted in contact with glacier ice near the ...

Ambient noise from turbidity currents

Sediment mass transport from the Squamish River delta into the adjacent fjord (Howe Sound, British Columbia) is dominated by discrete turbidity current events which have incised semi-permanent channels on the delta front and out onto the prodelta. Acoustic data were collected in the spring of 2013, including both active and passive systems. Data from the active sonars are used to determine flow speed, flow thickness and suspended sediment concentration. The noise generated by these discrete turbidity currents is broadband (10 to 200 kHz) and, based on the sediment grain size and flow speeds, is shown to be due to sediment-generated noise, most likely at the base of the flows.

Cyclic steps on a glacifluvial delta, Howe Sound, British Columbia

Howe Sound is a deep, steep-walled fjord on Canada's west coast. The primary sediment source is the glacially fed Squamish River. In the inner fjord, turbidity currents flow from the sandy Squamish River Delta at the fjord head reaching as far as the Porteau Creek Sill 15 km to the south. Recent observations from the Squamish Delta have shown that turbidity currents of various volumes are generated daily throughout almost a month of the summer meltwater period and flow through very active submarine channels characterized by active upstream-migrating cyclic step bedforms (Hughes Clarke et al. 2012 a ). Cyclic step bedforms are observed in other turbidity-current environments including the Fraser Delta (Hill 2012; Lintern et al. 2016) and Monterey Canyon (Fildani et al. 2006). The upper foreset slope of the Squamish Delta, is characterized by five incised submarine channels (Fig. 1a). The three northernmost of these channels are active while the two southernmost channels appear to have been abandoned after the artificial diversion of the Mamquam River in 1971. The younger channels and the …

Key Future Directions For Research On Turbidity Currents and Their Deposits

Turbidity currents, and other types of submarine sediment densityflow, redistribute more sediment acrossthe surface of the Earth than any other sediment flow process, yet their sediment concentration has never been measured directly in the deep ocean. The depositsof these flows are of societal importance asimperfect records of past earthquakes and tsunamogenic landslides and as the reservoir rocks for many deep-water petroleum accumulations. Key future research directions on these flows and their deposits were identified at an informal workshop in September 2013. This contribution summarizes conclusions from that workshop, and engages the wider community in this debate. International efforts are needed for an initiative to monitor and understand a series of test sites where flows occur frequently, which needs coordination to optimize sharing of equipment and interpretation of data. Direct monitoring observations should be combined with cores and seismic data to link flow and deposit character, whilst experimental and numerical models play a key role in understandingfield observations. Such an initiative may be timely and feasible, due to recent technological advances in monitoring sensors, moorings, and autonomous data recovery. This is illustrated here by recently collected data from the Squamish River delta, Monterey Canyon, Congo Canyon, and offshore SE Taiwan. A series of other key topics are then highlighted. Theoretical considerations suggest that supercritical flows may often occur on gradients of greater than , 0.6u. Trains of up-slope-migrating bedforms have recently been mapped in a wide range of marine and freshwater settings. They may result from repeated hydraulic jumps in supercritical flows, and dense (greater than approximately 10% volume) near-bed layers may need to be invoked to explain transport of heavy (25 to 1,000 kg) blocks. Future work needs to understand how sediment is transported in these bedforms, the internal structure and preservation potential of their deposits, and their use in facies prediction. Turbulence damping may be widespread and commonplace in submarine sediment density flows, particularly as flows decelerate, because it can occur at low ( , 0.1%) volume concentrations. This could have important implications for flow evolution and deposit geometries. Better quantitative constraints are needed on what controls flow capacity and competence, together with improved constraints on bed erosion and sediment resuspension. Recent advances in understanding dilute or mainly saline flows in submarine channels should be extended to explore how flow behavior changes as sediment concentrations increase. The petroleum industry requires predictive models of longer-term channel system behavior and resulting deposit architecture, and for these purposes it is important to distinguish between geomorphic and stratigraphic surfaces

Tsunami-generated sediment wave channels at Lake Tahoe, California-Nevada, USA

A gigantic ∼12 km 3 landslide detached from the west wall of Lake Tahoe (California-Nevada, USA), and slid 15 km east across the lake. The splash, or tsunami, from this landslide eroded Tioga-age moraines dated as 21 ka. Lake-bottom short piston cores recovered sediment as old as 12 ka that did not reach landslide deposits, thereby constraining the landslide age as 21–12 ka. Movement of the landslide splashed copious water onto the countryside and lowered the lake level ∼10 m. The sheets of water that washed back into the lake dumped their sediment load at the lowered shoreline, producing deltas that merged into delta terraces. During rapid growth, these unstable delta terraces collapsed, disaggregated, and fed turbidity currents that generated 15 subaqueous sediment wave channel systems that ring the lake and descend to the lake floor at 500 m depth. Sheets of water commonly more than 2 km wide at the shoreline fed these systems. Channels of the systems contain sediment waves (giant ripple marks) with maximum wavelengths of 400 m. The lower depositional aprons of the system are surfaced by sediment waves with maximum wavelengths of 300 m. A remarkably similar, though smaller, contemporary sediment wave channel system operates at the mouth of the Squamish River in British Columbia. The system is generated by turbidity currents that are fed by repeated growth and collapse of the active river delta. The Tahoe splash-induced backwash was briefly equivalent to more than 15 Squamish Rivers in full flood and would have decimated life in low-lying areas of the Tahoe region.

Debris-flow simulations on Cheekye River, British Columbia

Cheekye River fan is the best-studied fan complex in Canada. The desire to develop portions of the fan with urban housing triggered a series of studies to estimate debris-flow risk to future residents. A recent study (Jakob and Friele 2010) provided debris-flow frequency-volume and frequency-discharge data, spanning 20-year to 10,000-year return periods that form the basis for modeling of debris flows on Cheekye River. The numerical computer model FLO-2D was chosen as a modelling tool to predict likely flow paths and to estimate debris-flow intensities for a spectrum of debris-flow return periods. The model is calibrated with the so-called Garbage Dump debris flow that occurred some 900 years ago. Field evidence suggests that the Garbage Dump debris flow has a viscous flow phase that deposited a steep-sided debris plug high in organics in centre fan, which then deflected a low-viscosity afterflow that travelled to Squamish River with slowly diminishing flow depths. The realization of a two-phase flow led to a modelling approach in which the debris-flow hydrograph was split into a high viscosity and low viscosity phase that were modelled in chronologic sequence as two separate and independent modelling runs. A perfect simulation of the Garbage Dump debris flow with modelling is not possible because the exact topography at the time of the event is, to some degree, speculative. However, runout distance, debris deposition and deposit thickness are well known and serve as a good basis for calibration. Predictive analyses using the calibrated model parameters suggest that, under existing conditions, debris flows exceeding a 50-year return period are likely to avulse onto the southern fan sector, thereby damaging existing development and infrastructure. Debris flows of several thousand years return period would inundate large portions of the fan, sever Highway 99, CN Rail, and the Squamish Valley road and would impact existing housing development on the fan. These observations suggest a need for debris-flow mitigation for existing and future development alike.

Rate of floodplain reworking in response to increasing storm‐induced floods, Squamish River, south‐western British Columbia, Canada

AbstractRelations among hydroclimatic and channel planform changes on Squamish River are presented for the period 1956–2007. Squamish River basin occupies 3600 km2 of mountainous terrain in south‐western British Columbia, about 50 km north of Vancouver. The magnitude, volume and duration of extreme floods (Q ≥ 1500 m3/s) exhibit respective temporal increases of 50, 450 and 300%. The increase in extreme floods is attributed to the intensification of late‐season (August–December) Pacific storms that have produced increases in precipitation amounts, intensity and duration of respectively 340, 200 and 200% over the same period. Changes in floodplain‐surface area calculated from the geographic information system (GIS) differencing of sequential large‐scale aerial photographs indicate that the rate of geomorphic change in Squamish River has accelerated during the 1980s to the mid‐1990s. Among four study reaches of varying planform, erosional, depositional and cumulative changes in floodplain surface‐area have rapidly increased. Channel‐change activity after 1980 has increased by a factor of two to six compared with the period prior to 1980. Erosion is currently outpacing deposition in the majority of study reaches. Although channel geometry generally exhibits no uniform pattern of response to the increase in extreme floods, the meandering reaches have straightened over the duration of the study period. The increase in the magnitude and duration of the annual flood appears to be the principal cause of this recent acceleration of channel change. Copyright © 2010 John Wiley & Sons, Ltd.

Heritability and phenotypic and genetic correlations of coastal Douglas-fir (Pseudotsuga menziesii) wood quality traits

Genetic control and relationships among coastal Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii) growth and wood quality traits were assessed by estimating heritability and phenotypic and genetic correlations using 600 trees representing 15 full-sib families sampled from four progeny test sites. Heritability estimates ranged from 0.23 to 0.30 for growth traits, 0.19 for fibre coarseness, from 0.21 to 0.54 for wood density, from 0.16 to 0.97 for cell wall carbohydrates, and 0.79 and 0.91 for lignin content at two sites, Squamish River and Gold River, respectively. Glucose content, indicative of cell wall cellulose composition, and lignin were shown to be under strong genetic control, whereas fibre coarseness was shown to be under weak genetic control. Phenotypic correlations revealed that larger trees generally have longer fibres with higher fibre coarseness, lower density, lower carbohydrate content, a greater proportion of cell wall lignin, and higher microfibril angle. Genetic correlations and correlated response to selection suggest that breeding for height growth would result in a reduction in wood quality, whereas breeding for improved earlywood density in Douglas-fir would result in negligible reductions in volume and appears to be an ideal target for selecting for improved wood quality (density) while maintaining growth in the sample population.

The Fluvial Reworking of Late Pleistocene Drift, Squamish River Drainage Basin, Southwestern British Colombia

Reworked glacial sediment(s) (RGS) represents the component of paraglacial sedimentation derived from the fluvial reworking of late Pleistocene glacial deposits in the postglacial landscape. In Squamish River drainage basin, southwestern British Columbia, the primary source of the RGS transferred to Squamish Valley is fluvial incision into valley-fill deposits in the five major tributary valleys of the watershed. The total volume of RGS transferred to Squamish Valley is 415 x 106m3. The volume of RGS from the individual tributary valleys range from 6 to 130 x 106m3 with valley morphology and late Quaternary history being the important controls upon the specific amount. Geomorphic evidence indicates that the bulk of the RGS was contributed to Squamish Valley thousands of years ago. The transfer of RGS continues at a very low residual rate in the contemporary landscape. RGS appear to represent a minor portion of the Squamish valley-fill and a small component of the postglacial sediments stored in Squamish Valley.

Microsatellite DNA analysis of coastal populations of bull trout (Salvelinusconfluentus) in British Columbia: zoogeographic implications and its application to recreational fishery management

Microsatellite DNA variation was assayed among 383 bull trout (Salvelinus confluentus) from 20 Pacific coastal localities from the Skeena River (central British Columbia) to the Olympic Peninsula (western Washington State). An average of 1.7 alleles was resolved per population and heterozygosity averaged 0.35. Twenty-six fish were identified as bull trout × Dolly Varden (Salvelinus malma) hybrids. Population subdivision was substantial (θ = 0.33), but subdivision was higher (θ = 0.46) when interior populations (N = 37) were included, indicating a major genetic distinction between "coastal" and "interior" bull trout. Bull trout populations north of the Squamish River were genetically more similar to interior bull trout than to other more southern coastal populations, suggesting that they had been founded by headwater transfers from interior populations. Individual assignment of bull trout averaged 53.4% correct assignment among populations (range: 12%–95%). Mixture analysis indicated that most fish from the lower Fraser River recreational fishery originated from major nearby tributaries (e.g., Pitt, upper Lillooet, and Chilliwack rivers). Our results substantiate the existence of two major evolutionary lineages of bull trout and highlight the importance of tributary habitats for the persistence of local populations, as well as for those that forage in downstream areas on the lower Fraser River.

Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia

We investigated the effect of acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (Howe Sound, BC, Canada) on primary productivity and chlorophyll a levels in the receiving waters of Howe Sound before, during, and after freshet from the Squamish River. Elevated concentrations of copper (integrated average through the water column >0.050 mg l −1) in nearshore waters indicated that under some conditions a small gyre near the mouth of Britannia Creek may have retained the AMD from Britannia Creek and from a 30-m deep water outfall close to shore. Regression and correlation analyses indicated that copper negatively affected primary productivity during April (pre-freshet) and November (post-freshet). Negative effects of copper on primary productivity were not supported statistically for July (freshet), possibly because of additional effects such as turbidity from the Squamish River. Depth-integrated average and surface chlorophyll a were correlated to copper concentrations in April. During this short study we demonstrated that copper concentrations from the AMD discharge can negatively affect both primary productivity and the standing stock of primary producers in Howe Sound.

Younger Dryas readvance in Squamish river valley, southern Coast mountains, British Columbia

Stratigraphy and landforms in the Brohm Creek basin and lowermost Mamquam River valley provide evidence for a readvance of a valley glacier in the southern Coast Mountains of British Columbia during the Younger Dryas interval. At Brohm Creek, till containing wood 10,500 and 10,700 14C yr old (ca 12,500–12,900 cal yr old), overlies an ice-contact terrace that is correlative with similar terraces at the mouth of Mamquam River, 11 km to the south and 900 m lower in elevation. A line linking the two sites has a slope of 5°, which is similar to slopes of termini of present-day valley glaciers in the southern Coast Mountains. We used these observations to reconstruct the Younger Dryas glacier in Squamish valley at the head of Howe Sound. The glacier deflected landslide debris, derived from steep slopes at the head of Cheekye River basin on the west flank of Mt. Garibaldi, southward to an ice-marginal lake at the mouth of Mamquam River. Foreset-bedded sediments in the core of a large fan at the mouth of Cheekye River indicate the glacier terminus had retreated up Squamish valley beyond Cheekye and Mamquam rivers by 10,200 14C yr BP (11,900 cal yr old). Radiocarbon ages on the oldest postglacial sediments in a kettle on the landslide debris show that stagnant ice in the study area had melted before 10,000 14C yr BP (11,500 cal yr BP). The readvance of the Squamish valley glacier during the Younger Dryas Chronozone was probably driven by a regional climate reversal.

Ground penetrating radar facies of the paraglacial Cheekye Fan, southwestern British Columbia, Canada

Abstract Ground penetrating radar (GPR) surveys have been carried out in order to characterise reflection patterns and to assess the method's potential for imaging alluvial fan sediments in southwestern British Columbia, Canada. The results from Cheekye Fan show that GPR achieved over 40 m penetration with the 50 MHz antenna and provided data that allowed identification of 10 radar facies. Glacial till produces a reflection free configuration and bedrock radar facies is characterised by a hummocky pattern often with stacked macro-scale diffractions. Four subaerially deposited alluvial-fan facies were identified. Radar facies of the nearby meandering Squamish River are characterised by a complex, sigmoid oblique pattern that is clearly different from any configuration observed on Cheekye Fan. Based on the analysis of over 27 km radar data, the large-scale internal architecture of Cheekye Fan was reconstructed. Fan sediments are underlain by till and hummocky bedrock in the northern and eastern portion of the fan. Sedimentation was initiated by subaqueously deposited delta foresets following deglaciation of Upper Howe Sound. Subaerially deposited sediments can be divided into: (a) massive, matrix-rich diamicton that appears predominant at the core of the fan and at lower stratigraphic horizons, suggesting bouldery rock-slide or debris flow origin; and (b) horizontally-bedded sheetflood gravel dominating the upper 20–25 m of the stratigraphic column.

Dynamics of the 1984 rock avalanche and associated distal debris flow on Mount Cayley, British Columbia, Canada; implications for landslide hazard assessment on dissected volcanoes

In 1984 a mass of Quaternary pyroclastic rock (est. vol. 0.74×10 6m 3) slid from the western flank of Mount Cayley volcano in southwest British Columbia. The disintegrating rock mass entrained a further 0.20×10 6 m 3 and formed a rock avalanche that travelled a horizontal distance of 3.46 km from its source over a vertical elevation difference of 1.18 km, equivalent to a fahrböschung of 19°. From the superelevation of the debris trimline in the mid-path, it is estimated that velocities reached at least 42 m/s; in the upper part of its path velocities may have approached 70 m/s. The rock avalanche was partially transformed into a distal debris flow that travelled a further 2.6 km down Turbid Creek in a narrow channelised path to the Squamish River, temporarily blocking it. The motion of the rock avalanche, including the production of a distal debris flow, was successfully simulated using a dynamic analytical model. Both the results of this analysis and field evidence indicate that the rock avalanche did not come to a halt in the upper part of its path as suggested by Cruden and Lu (1992), but travelled to its distal limit in one uninterrupted movement. This finding has important implications for landslide hazard assessment at Mount Cayley and similar sites. The landslide is typical of those which occur on the steep slopes of dissected volcanoes and is one of seven high-velocity rock avalanches that have occurred in the Garibaldi Volcanic Belt of southwest British Columbia since 1855.

The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks

Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound. Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (C org/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The <25-μm fraction has TOC concentrations up to 2.0 wt.%, and a C org/N ratio that ranges from 14 to 16. The 53–106-μm fraction has higher TOC concentrations and C org/N ratios relative to the 25–53-μm fraction. The C org/N ratio ranges from 9 to 18 in the 53–106-μm fraction and 5.5–10.5 in the 25–53-μm fraction. Surface area values for bulk sediments are low (0.5–3.0 m 2/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration. The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks formed in other geological settings.

Annual bed‐elevation regime in the alluvial channel of Squamish River, Southwestern British Columbia, Canada

The aim of this study is to examine the annual regime of channel scour and fill by monitoring bed-elevation changes in a reach of Squamish River in southwestern British Columbia, Canada. Sonar surveys of 13 river cross-sections in a sandy gravel-bed single-channel study reach were repeated biweekly over a full hydrologic year (1995/6). The survey results show that bedload movement occurs as waves or pulses forming bedwaves that appear to maintain an overall coherence with movement downstream. These bedwaves propagate downstream by a mode here termed pulse scour and pulse fill, a process distinguished from the conventional mode of scour and fill commonly associated with flood events (here termed local scour and local fill). Bedwave celerity was estimated to be about 15·5 m d−1 corresponding to a bedwave residence time in the study reach of almost one hydrologic year. The total amount of local bed-elevation change ranged between 0·22 m and 2·41 m during the period of study. Analysis of the bed-elevation and flow data reveals that, because of the bedwave phenomenon, there is no simple relation between the mean bed-elevation and discharge nor any strong linear correlation among cross-sectional behaviour. The bed-elevation data also suggest that complex changes to the bed within a cross-section are masked when the bed is viewed in one dimension, although no definitive trends in bed behaviour were found in the two-dimensional analysis. Although a weak seasonal effect is evident in this study, the bed-elevation regime is dominated by sediment supply-driven fluctuations in bedload transport occurring at timescales shorter than the seasonal fluctuation in discharge. The study also indicates that bed-elevation monitoring on Squamish River, and others like it, for purposes of detecting and measuring aggradation/degradation must take into account very considerable and normal channel-bed variability operating at timescales from hours to months. Copyright © 2000 John Wiley & Sons, Ltd.

Annual bed-elevation regime in the alluvial channel of Squamish River, Southwestern British Columbia, Canada

The aim of this study is to examine the annual regime of channel scour and fill by monitoring bed-elevation changes in a reach of Squamish River in southwestern British Columbia, Canada. Sonar surveys of 13 river cross-sections in a sandy gravel-bed single-channel study reach were repeated biweekly over a full hydrologic year (1995/6). The survey results show that bedload movement occurs as waves or pulses forming bedwaves that appear to maintain an overall coherence with movement downstream. These bedwaves propagate downstream by a mode here termed pulse scour and pulse fill, a process distinguished from the conventional mode of scour and fill commonly associated with flood events (here termed local scour and local fill). Bedwave celerity was estimated to be about 15·5 m d−1 corresponding to a bedwave residence time in the study reach of almost one hydrologic year. The total amount of local bed-elevation change ranged between 0·22 m and 2·41 m during the period of study. Analysis of the bed-elevation and flow data reveals that, because of the bedwave phenomenon, there is no simple relation between the mean bed-elevation and discharge nor any strong linear correlation among cross-sectional behaviour. The bed-elevation data also suggest that complex changes to the bed within a cross-section are masked when the bed is viewed in one dimension, although no definitive trends in bed behaviour were found in the two-dimensional analysis. Although a weak seasonal effect is evident in this study, the bed-elevation regime is dominated by sediment supply-driven fluctuations in bedload transport occurring at timescales shorter than the seasonal fluctuation in discharge. The study also indicates that bed-elevation monitoring on Squamish River, and others like it, for purposes of detecting and measuring aggradation/degradation must take into account very considerable and normal channel-bed variability operating at timescales from hours to months. Copyright © 2000 John Wiley & Sons, Ltd.

Inter‐ and supratidal sedimentology of a fjord‐head estuary, south‐western British Columbia

ABSTRACTDetailed examination of inter‐ and supratidal delta and floodplain sediments exposed in eroding bank sections at 52 locations along the Squamish River estuary provides the basis for recognizing seven distinct facies within the 5500 m‐long estuary. Estuary sedimentation is initially driven by the development of sand bar complexes along the seaward edge of the intertidal delta. Sedimentation continues within interdistributary bay environments as intertidal sandflats and then tidal marshes develop, Aggradation of the delta within interdistributary bay environments results in a gradual transition from delta to alluvial plain. Of the seven facies identified, only the intertidal sands and tidal marsh deposits provide evidence of their tidal origin.Examination of deposits throughout the riverine estuary reveals a number of gradual yet distinct changes of sediment size, structure, and sequence architecture. These trends record the changing nature of tidal and riverine control on sedimentation along the tidal gradient. Generally, with increasing distance up‐estuary, sediment grain‐size increases, the thickness of fine‐grained overbank deposits decreases, and bedding changes from fine parallel bedding to higher energy bedforms. In addition, fining‐upward successions become capped by coarser sands, facies contacts change from gradational to abrupt and occasionally erosional, and facies successions become increasingly complex and less predictable. Squamish River estuary has been divided into four zones based on sedimentological and stratigraphical evidence, each zone reflecting changes in the relative influence of tidal and riverine control on sedimentation. Each zone contains distinctly different facies sequences, although zone boundaries generally are gradational.

The origin of a tephra-like bed near Mount Cayley volcano, southwestern British Columbia, Canada

A distinct white bed 1–2 cm thick is present within backwater deposits at the upstream end of the Turbid Creek debris fan, southwestern British Columbia, Canada. This white bed and the enclosing backwater deposits accumulated within an impoundment of Squamish River caused by a large ca. 4800 BP debris avalanche originating from Mount Cayley, a Pliocene–Pleistocene volcano. The white bed is composed of silt and clay detritus and resembles tephra. About 5% of the grains exhibit optical characteristics consistent with volcanic glass. The remainder, however, are mineral and lithic particles (mainly cristobalite and Na-feldspar, with minor quartz, and trace amphibolite, mica group, and chlorite). The white bed is interpreted to be dust derived from the debris avalanche and washed into the impoundment, based upon (i) the high proportion of mineral and lithic grains within the bed, (ii) the contemporaneity of the bed and the debris avalanche, (iii) the lack of Holocene volcanic activity at Mount Cayley, and (iv) the significant age difference between the bed and known tephras in southwestern British Columbia.

Simulating the three-dimensional distribution of sediment units in braided-stream deposits

Full hydrogeological characterization of a sediment body must include a detailed description of its three-dimensional internal geometry. Where either direct methods or remote sensing are inadequate, computer simulations can be used to approximate the internal structure. A computer code, BCS-3D, was developed that simulates the three-dimensional internal geometry of sediment units for braided-stream deposits. Code development was based on the assumption that (1) a certain part of the surface (geomorphological) system is captured and preserved in the sedimentological record, and (2) characteristics of sediment units are a function of the localized flow energy as expressed by the Froude number. BCS-3D uses a random-walk approach to describe the formation of braided-channel networks. The concept of hydraulic geometry is incorporated to translate a two-dimensional topological network to a three-dimensional topographic surface. A series of these surfaces is stacked vertically with some offset, to produce a three-dimensional description of the internal architecture. Individual elements in the architecture are associated with specific sediment units based on a description of flow energy in the form of the Froude number. No comprehensive data set is available to validate this approach fully. However, the model was compared with and adequately matched a composite set of measurements from two studies in systems with similar physical characteristics, the Ohau River in New Zealand and the Squamish River in British Columbia, Canada.