Upstream control of river anastomosis by sediment overloading,upper Columbia River,British Columbia,Canada

Anastomosing rivers, systems of multiple interconnected channels that enclose floodbasins, constitute a major category of rivers for which various sedimentary facies models have been developed. While the sedimentary products of anastomosing rivers are relatively well‐known, their genesis is still debated. A rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin, including important hydrocarbon reservoirs, urge the development of robust models for the genesis of anastomosis, to facilitate better interpretation of ancient depositional settings and controls. The upper Columbia River, British Columbia, Canada, is the most‐studied anastomosing river and has played a key role in the development of an anastomosing river facies model. Two hypotheses for the origin of upper Columbia River anastomosis include the following: (i) downstream control by aggrading cross‐valley alluvial fans; and (ii) upstream control by excessive bedload input from tributaries. Both upstream and downstream control may force aggradation and avulsions in the upper Columbia River. In order to test both hypotheses, long‐term (millennia‐scale) floodplain sedimentation rates and avulsion frequencies are calculated using ¹⁴C‐dated deeply buried organic floodplain material from cross‐valley borehole transects. The results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach, which is consistent with dominant upstream control by sediment overloading. The data here link recent avulsion activity to increased sediment supply during the Little Ice Age (ca 1100 to 1950 ad ). This link is supported by data showing that sediment supply to the upper Columbia study reach fluctuated in response to Holocene glacial advances and retreats in the hinterland. Upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems. The present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low‐gradient floodplains, a situation commonly found in intermontane and foreland basins.     

Avulsions, channel evolution and floodplain sedimentation rates of the anastomosing upper Columbia River, British Columbia, Canada

Ages of channels of the anastomosing upper Columbia River, south‐eastern British Columbia, Canada, were investigated in a cross‐valley transect by ¹⁴C dating of subsurface floodplain organic material from beneath levees. The avulsion history within the transect was deduced from these data, and morphological stages in channel development were recognized. Additionally, floodplain sedimentation rates were established. The new data demonstrate that the upper Columbia River is a long‐lived, dynamic anastomosing system. Results show that anastomosis at the study location has persisted since at least 2700 cal. years BP, with avulsions occurring frequently. At least nine channels have formed in the studied cross‐valley transect within the past 3000 years. Channel lifetimes from formation to abandonment appear to be highly variable, ranging from approximately 800 to 3000 years. Log jams provoking avulsions and/or silting up of old channels are proposed as reasons for this variability. Long‐term average floodplain sedimentation rates appear to be significantly lower than previously proposed by Smith (1983, Int. Assoc. Sedimentol. Spec. Publ., 6, 155–168). A long‐term (4550 years) average of 1·75 mm year^?1 (after compaction) was based on ¹⁴C dates, while a short‐term sedimentation rate of 0·8 mm was determined for a single, relatively small, seasonal flood in 1994 using sediment traps. However, short‐term sedimentation rates vary considerably over the floodplain, with levees aggrading up to four times faster than floodbasins. Channels of the upper Columbia River anastomosed reach follow a consistent pattern in their development, with each stage being characterized by different morphology and processes. Channel evolution comprises the following succession: (1) avulsion stage, in which a crevasse splay channel deepens by scour and levee sedimentation; (2) widening and deepening stage, in which bank slumping and bed scouring dominates; (3) infilling stage, in which either channel narrowing (bank accretion) or channel shallowing (bed accretion) takes place; and (4) abandonment stage, in which the residual (remnant) channel is filled exclusively by silt, clay and organic material. Vertical stacking (super‐ imposition) of active channels on recent channel‐fill sand bodies is a notable feature of the upper Columbia River, which suggests that reoccupation of residual channels is a common process.     

The Khyex River landslide of November 28, 2003, Prince Rupert British Columbia Canada

On November 28, 2003, at about 00:30 PST, 35 km east of Prince Rupert in northwestern British Columbia, an extremely rapid, retrogressive liquefaction earth flow, or a clay flow-slide, severed the natural gas pipeline. As a result, Prince Rupert residents were without natural gas heat for 10 days. The landslide has a steep main scarp that is 45 m high by 345 m wide. It consists of glaciomarine sediments mantled by rubbly colluvium lying on, and against smooth bedrock of the valley wall. It covers an area of 32 ha, and displaced about 4.7 M m³ of material. This displaced material flowed up and down river over a distance of 1.7 km, blocked the river, and caused flooding upstream for a distance of 10 km. This landslide is the most recent of four large landslides that have occurred over the last four decades in glaciomarine sediments in northwestern British Columbia.     

Bar and dune development during a freshet: Fraser River Estuary, British Columbia, Canada

Bi-weekly multi-track sonar surveys collected along a 2-km reach of the estuarine South Arm of the Fraser River, British Columbia, Canada, during seasonal high flows document the initiation, development and interaction of dune and bar morphologies. Bedforms of several scales developed in well-delineated fields. Bedforms that appear to fit accepted equilibrium depth-scaling developed in the main channel during rising discharge when there was little local aggradation. During the rising stage, a bar also formed along the tidal shelf of the channel, migrated downstream and expanded into the main channel. Dunes that formed along the bar crest, a region of rapid deposition, lagged flow conditions and were larger than expected based on depth-scaling relations. The larger dunes developed simultaneously, although bar growth lagged dune development and was initially partially obscured by the more rapidly developing dune field. It appears that rapid deposition enhances dune development along the channel tidal shelf to dimensions larger than would be expected by simple depth-scaling rules. Smaller dunes that fit equilibrium depth-scaling relations re-established themselves throughout the study area during falling discharge when there was again little or no aggradation. Bed-material transport rates estimated from the migration rates of the large dunes suggest that, at high flows, the dunes transport the majority of the material found within the bar.     

Example of a debris-flow risk analysis from Vancouver Island,British Columbia,Canada

In July 2005, a debris flow and a water flood occurred on two adjacent gullies in the White River area, on northern Vancouver Island in British Columbia, Canada. The 16,000 m³ debris flow buried approximately 7.5 ha of second-growth trees, buried approximately 500 m of a forestry road, and reached two fish-bearing streams. The water flood eroded approximately 240 m of the same forestry road and plugged four culverts before overtopping and inundating the road. To better plan for future events, risk analyses of debris flows, debris floods, and water floods were carried out for the two gullies involved, plus a third adjacent gully. The elements at risk that were analyzed included, in order of priority: users of the forestry road, the fish-bearing streams, the forestry road itself, and a timber bridge. Using a series of qualitative, but defined, relative-risk matrices, the following components of specific risk were estimated for each of the three types of events on each of the three gullies for each of the four elements at risk: probability of occurrence, probability that the event will reach or otherwise affect the site of the element at risk, the probability that the element at risk will be at the site when the event occurs, and the probability of loss or damage resulting from the element being at the site when the event occurs.     

Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550-10,250 cal yr BP (9230 ± 50 ¹⁴C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.     

黄河下游漫滩洪水冲淤规律

滩地的淤积层分布记录着以往漫滩洪水的特征,即反映漫滩洪水的量级、频率和持续时间等,同时河漫滩也是预估河流泥沙、洪水灾害防治和湿地生态系统保护等的重要组成部分。根据黄河下游水文年鉴资料,分析滩地的淤积与漫滩洪水的定量关系,为未来河流泥沙预估提供依据。经分析得到大漫滩洪水在来沙系数S/Q<0.030 kg·s/m6时,主槽冲刷而滩地淤积,反之则滩槽同淤。当S/Q<0.030 kg·s/m6时,大漫滩洪水滩地的淤积量主要与漫滩系数Q_max/Q_p、上滩水量W₀和含沙量S有关;大漫滩洪水的主槽冲刷量则除了与洪水期水量W和沙量W_s有关外,还与滩地的淤积量有关。一般漫滩洪水,当来沙系数S/Q<0.023 kg·s/m6时,主槽冲刷而滩地淤积,反之则滩槽同淤。一般漫滩洪水主槽冲刷量与来沙系数S/Q和洪水期水量W有关,而滩地淤积量仅与含沙量S有关。黄河下游漫滩洪水滩地的淤积和主槽的冲刷主要发生在孙口以上河段,而孙口以下河段主槽冲刷和滩地淤积量均较少。     

Extensive deformations of rock slopes in southern Coast Mountains, southwest British Columbia, Canada

Extensive deformations of mountain slopes occur in crystalline intrusive rocks in the southern Coast Mountains of British Columbia. Typical morphological evidence of slope movement includes extensive systems of tension cracks, grabens, and antislope scarps (collectively referred to here as linears). These landforms involve displacements along penetrative joints observed in surface exposures. Kinematic tests on rock-structural data indicate that the observed patterns of linears are generally consistent with the feasible gravitational movements along the dominant discontinuities. Most sites indicate sliding as the most likely initial mode of movement, followed by or accompanied by toppling and toppling-induced sliding movements, and do not support the view that linears are the traces of active faults.     

Navigating the tensions in collaborative watershed governance: Water governance and Indigenous communities in British Columbia,Canada

First Nations in British Columbia (BC), Canada, have historically been—and largely continue to be—excluded from colonial governments’ decision-making and management frameworks for fresh water. However, in light of recent legal and legislative changes, and also changes in water governance and policy, there is growing emphasis in scholarship and among legal, policy and advocacy communities on shifting water governance away from a centralized single authority towards an approach that is watershed-based, collaborative, and involves First Nations as central to decision-making processes. Drawing on community-based research, interviews with First Nations natural resource staff and community members, and document review, the paper analyzes the tensions in collaborative water governance, by identifying First Nations’ concerns within the current water governance system and exploring how a move towards collaborative watershed governance may serve to either address, or further entrench, these concerns. This paper concludes with recommendations for collaborative water governance frameworks which are specifically focused on British Columbia, but which have relevance to broader debates over Indigenous water governance.     

Concepts for diamond exploration in “on/off craton” areas—British Columbia, Canada

The tectonic setting of British Columbia (BC) differs from classic diamond-bearing intracratonic regions such as the Northwest Territories and South Africa. Nevertheless, several diamond occurrences have been reported in BC. It is also known that parts of the province are underlain by Proterozoic and possibly Archean basement. Because the continents of today are composites of fragments of ancient continents, it is possible that some of the regions underlain by old crystalline basement in eastern British Columbia were associated with a deep crustal keel. The keel may have predated the break-up of the early Neoproterozoic supercontinent called Rodinia and was preserved possibly until the Triassic. Some of these old continental fragments may have been displaced relative to their position of origin and dissociated from their keel, or the keel may have since been destroyed. Such fragments represent favourable exploration grounds in terms of the “Diamondiferous Mantle Root” model (DMR model) if they were intersected by kimberlites or lamproites prior to displacement or destruction of their underlying deep keel. Therefore, extrapolation of fragments of the diamond-bearing Precambrian basement from the Northwest Territories or Alberta to BC provides a sufficient reason for initiating reconnaissance indicator mineral surveys. The “Eclogite Subduction Zone” model (ES model) predicts formation of diamonds at lower pressure (i.e., depth) than required by the DMR model in convergent tectonic settings. Although not proven, this model is supported by thermal modeling of cold subduction zones and recent discoveries of diamonds in areas characterized by convergent tectonic settings. If the ES model is correct, then the parts of BC with a geological history similar to today's “cold” subduction zones, such as Honshu (Japan), or to continental collision zones, such as Kokchetav massif (Kazakhstan) and the Dabie–Sulu Terrane (east central China), may be diamondiferous. The terranes where geological evidences suggest an ultrahigh pressure (UHP) metamorphic event followed by rapid tectonic exhumation (which could have prevented complete resorption of diamonds on their journey to the surface) are worth investigating. If UHP rocks were intercepted at depth by syn- or post-subduction diamond elevators, such as kimberlites, lamproites, lamprophyres, nephelinites or other alkali volcanic rocks of deep-seated origin, the diamond potential of the area would be even higher.     

The Zymoetz River landslide, British Columbia, Canada: description and dynamic analysis of a rock slide–debris flow

The Zymoetz River landslide is a recent example of an extremely mobile type of landslide known as a rock slide–debris flow. It began as a failure of 900,000 m³ of bedrock, which mobilized an additional 500,000 m³ of surficial material in its path, transforming into a large debris flow that traveled over 4 km from its source. Seasonal snow and meltwater in the proximal part of the path were important factors. A recently developed dynamic model that accounts for material entrainment, DAN3D, was used to back-analyze this event. The two distinct phases of motion were modeled using different basal rheologies: a frictional model in the proximal path and a Voellmy model in the distal path, following the initiation of significant entrainment. Very good agreement between the observed and simulated results was achieved, suggesting that entrainment capabilities are essential for the successful simulation of this type of landslide.     

Early growth of the last Cordilleran ice sheet deduced from glacio-isostatic depression in southwest British Columbia, Canada

Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation.     

Morphology and evolution of bars in a wandering gravel-bed river; lower Fraser river, British Columbia, Canada

A hierarchical typology for the channels and bars within aggradational wandering gravel-bed rivers is developed from an examination of a 50 km reach of lower Fraser River, British Columbia, Canada. Unit bars, built by stacking of gravelly bedload sheets, are the key dynamic element of the sediment transfer system, linking sediment transport during individual freshets to the creation, development and remoulding of compound bar platforms that have either a lateral or medial style. Primary and secondary unit bars are identified, respectively, as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels. The record of bar accretion evident in ground-penetrating radar sequences is consistent with the long-term development of bar complexes derived from historical aerial photographs. For two compound bars, inter-annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer-term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys. Annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel, indicating that relatively little bed material bypasses the bars. Bar construction and change are accomplished mainly by lateral accretion as the river has limited capacity to raise bed load onto higher surfaces. Styles of accretion and erosion and, therefore, the major bar form morphologies on Fraser River are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features. For example, 65-year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers.     

Tracking recorded fires using charcoal morphology from the sedimentary sequence of Prosser Lake, British Columbia (Canada)

Quantitative analyses of variations in morphological features of charcoal were undertaken in a ²¹⁰Pb-dated sediment core from Prosser Lake (British Columbia, Canada). Seven morphological types of charcoal were defined by particle shape, major-minor axis ratio, apparent porosity and progradation to unburned material. The distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation-sedimentation to lake sediments. Charcoal morphotypes showed distinct relationships to recorded area burned by fires. Fragile charcoal fragments with highly irregular porosity (termed Type M) displayed the strongest correlation to burned area (r² = 0.51; P = 0.0001) and did not produce any false-positive signal for fires recorded within a radius of 20 km around the lake. We infer that high porosity and low density Type M fragments are aerially transported and directly deposited on the lake, and that the fragility of Type M charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record. We propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type, proximity and transportation-sedimentation processes.     

DRASTIC-Fm: a modified vulnerability mapping method for structurally controlled aquifers in the southern Gulf Islands,British Columbia,Canada

DRASTIC, the methodology for mapping the intrinsic vulnerability of aquifers, is modified to incorporate the structural characteristics of fractured bedrock aquifers. In these aquifers, groundwater flow is predominantly through fractures, with large-scale fracture zones and faults acting as primary conduits for flow at the regional scale. The methodology is applied to the southern Gulf Islands region of southwestern British Columbia, Canada. Bedrock geology maps, soil maps, structural measurements, mapped lineaments, water-well information and topographic data, assembled within a comprehensive GIS database, form the basis for assigning traditional DRASTIC indices, while adding the structural indices necessary for capturing the importance of regional structural elements in recharge and well capture zone determinations.     

Stability analysis of a horizontal coalbed methane well in the Rocky Mountain Front Ranges of southeast British Columbia, Canada

This study describes a wellbore stability analysis undertaken for a horizontal coalbed methane well in the Mist Mountain Formation, SE British Columbia, Canada. Three triaxial compression tests, with ultrasonic velocities, were conducted on 38-mm-diameter core plugs taken from a large, fresh block of Seam 7. Due to the small size of the tested samples, the laboratory-derived strength values were reduced to reflect the in-situ stress conditions considered relevant for a 156-mm-diameter horizontal well. The vertical stress gradient was calculated by integrating a bulk density log from an offset well. Horizontal maximum and minimum stresses were estimated from regional stress data, whereas formation pressure was estimated on the basis of a local hydrological study. The 2D elastoplastic STABView™ numerical modeling code was used to forecast horizontal wellbore stability. The sensitivity of the predicted yielded zone size was examined for varying linear and non-linear rock strength criteria, horizontal in-situ stresses, bottom-hole pressures, formation pressure, drilling depth, and wall-coating efficiency. Stability analysis was performed at bottom-hole pressures ranging from overbalanced to underbalanced in order to simulate the conditions expected during drilling and production. The effects of weak bedding planes and varying well trajectories were also investigated. When drilling at 650 m depth under underbalanced to slightly overbalanced conditions, a high probability of getting the drill pipe stuck was predicted. STABView™ showed that, if the 38-mm-diameter core plug strengths were used directly for forecasting purposes, the predicted yielded zone would be almost 20% overgauge when drilling at balanced conditions. When peak cohesion of coal was reduced by 50% to reflect the conditions expected along weak intervals of a horizontal wellbore, the predicted enlarged borehole was almost 85% overgauge under the same drilling conditions. The most unstable trajectory has N–S azimuth, which is perpendicular to the maximum horizontal stress in the study area. STABView™ indicates that a production liner should be inserted immediately following the drilling of the horizontal well in this structurally complex geologic setting since pressure drawdown and reservoir pressure depletion would undoubtedly lead to enlarged yielded zones and collapse of the wellbore over time.     

辫状河现代沉积研究与相模式──中国永定河剖析

永定河是一条多河型河流,自上而下,包括了辩状河→曲流河→分流网状河的河型空间转换。其间辫状河段可明显区分为两类亚型:即冲积扇区的高坡降辫状河和冲积平原区低坡降辫状河。二者在河流形态、沉积物特征等方面显示不同。而沉积作用机制和砂体沉积模式是近似的,二者均进行垂向加积作用,均发生五个级次的沉积再作用面,均发育三个级次类型的薄夹层:滞留层、落淤层、颗粒降纹层与颗粒流纹层。其中落淤层最具指相意义。在河道经常摆动迁移过程中,最终形成砂体广泛展布的“叠覆泛砂体”。这种辫状河沉积模式──“叠覆泛砂体”为油气储集提供了良好的储集空间和场所。     

Powerful unconfined turbidity current captured by cabled observatory on the Fraser River delta slope,British Columbia,Canada

Turbidity currents are one of the main sediment transport processes on Earth, yet are notoriously difficult to monitor directly. This article presents the first direct and high bandwidth observation of a turbidity current using a cabled sea floor observatory. On 5 June 2012, a platform on Ocean Networks Canada, located in 107 m of water on the Fraser River delta slope, was displaced downslope and severed from its data cable. The platform weighed ca 1000 kg in water. The event took place during high river discharge, high tides and rapid sediment accumulation on adjacent upslope areas of the sea floor. Data recorded as it tumbled downslope allow a reconstruction of the flow, which is inferred to have been an unconfined turbidity current. Lines of evidence indicate that the flow came in as a bed hugging wedge, and built up to between 1 m and 4 m in height as the head passed through. Comparison with laboratory data suggest that the flow was initially supercritical. While the adjacent slope offset to the north clearly exhibits change over an annual resurvey period, the bathymetry directly at the event location show no resolvable change over a period from seven months before the event to one month after. Sediment cores collected after the event were pervasively biototurbated and they contain no obvious deposit connected with this event. The remarkable aspects of this research follow. The flow was powerful enough to carry a 1 tonne platform and sever a heavily armoured cable. The current occurred on the unchannelized open slope. This powerful event failed to cause discernible seabed elevation change. The flow was triggered by tidal conditions. The event was detected by a purpose‐designed cabled observatory, thus providing high bandwidth data and also alerting researchers in real time to mount follow‐on investigations.