Lateral Migration in a Wandering Reach of the Middle Yellow River in Response to Different Boundary Conditions

The Xiaobeiganliu reach is a typical wandering reach of the Middle Yellow River that has rapid and significant channel lateral migration, which may threaten the safety of riparian land and flood control structures. To investigate the characteristics and mechanism of lateral migration in the Xiaobeiganliu reach, the temporal and spatial variations in bankfull width and thalweg migration distance were identified during the continuous deposition period, quantitatively analyzing the effect of different boundary conditions on the lateral migration index. The reach-scale bankfull width decreased by 32% from 1986 to 2001 because hyperconcentrated floods often occurred in this reach. The thalweg migration distance varied dramatically at cross-sections, with the maximum annual thalweg migration distance reaching 4290 m. The lateral migration index of the Xiaobeiganliu reach responded well to the upstream and downstream boundary conditions. The previous 3-year average water discharge and 4-year average sediment concentration at the upstream station were two key fluvial factors influencing lateral migration, with the relation being established between the lateral migration index and the two parameters. The Tongguan (TG) elevation was the key downstream boundary condition affecting thalweg migration, and a power function was proposed between the lateral migration index and the variations in annual TG elevation.

Watercourse Crossing Program: 10 Years Performance

Plains Midstream Canada (PMC) completes a watercourse crossing program as part of its overall integrity management program. The approximately 9,900 kilometers of operating and discontinued pipelines are evaluated within the watercourse crossing program. The pipelines are located throughout the Canadian Provinces of Alberta, Saskatchewan, Manitoba and Ontario. The terrain traversed ranges from relatively steep near the Rocky Mountains to extremely flat in northern Alberta and Southern Ontario. Since 2008, PMC’s systematic watercourse crossing program has evolved and now consists of approximately 5,000 individual watercourse crossings. The bankfull width of the watercourses ranges from less than 1 m for intermittent streams to more than 700 m at major rivers. The watercourse crossing program is subjected to a continuous improvement process, with a focus on key learnings from pipeline failures, free spans and exposure. This paper describes the results from the program over the last 10 years and highlights program improvements. In addition, data from a failure and three free spans on the pipelines now owned by PMC, but where the exposure, free span or failure occurred prior to PMC purchasing the pipelines were added to expand the available data for the key learnings.

Conceptual Model for Simulating the Adjustments of Bankfull Characteristics in the Lower Yellow River, China

We present a conceptual model for simulating the temporal adjustments in the banks of the Lower Yellow River (LYR). Basic conservation equations for mass, friction, and sediment transport capacity and the Exner equation were adopted to simulate the hydrodynamics underlying fluvial processes. The relationship between changing rates in bankfull width and depth, derived from quasiuniversal hydraulic geometries, was used as a closure for the hydrodynamic equations. On inputting the daily flow discharge and sediment load, the conceptual model successfully simulated the 30-year adjustments in the bankfull geometries of typical reaches of the LYR. The square of the correlating coefficient reached 0.74 for Huayuankou Station in the multiple-thread reach and exceeded 0.90 for Lijin Station in the meandering reach. This proposed model allows multiple dependent variables and the input of daily hydrological data for long-term simulations. This links the hydrodynamic and geomorphic processes in a fluvial river and has potential applicability to fluvial rivers undergoing significant adjustments.

Mechanisms and source distances for the input of large woody debris to forested streams in British Columbia, Canada

The geomorphic process domain concept predicts consistent associations between stream channel geomorphology and large woody debris (LWD) input mechanisms. We used synoptic surveys at 51 stream reaches adjacent to undisturbed mature or old-growth forests in central and southern British Columbia to test associations between stream geomorphology and the input processes, source distances, physical characteristics, and geomorphic functions of LWD within the bankfull channel. Standing dead tree fall was the dominant input mechanism, but bank erosion was important in low- and medium-gradient channels >3 m bankfull width. Wind-induced inputs (stem breakage and windthrow) were relatively more important in small or steep channels. LWD piece size and source distance varied among delivery processes. LWD originated at ground distances up to 65 m from the streams, but 90% of the LWD at a site originated within 18 m of the channel at 90% of the sites. Statistical models incorporating tree size and stream characteristics (bankfull width, channel type) explained 40%–64% of the variation among sites in the distances from which LWD entered streams. In general, LWD source distances increased with increasing tree height and decreased with increasing stream width; however, the strengths of these relationships were modified by channel type.

Predicting cutthroat trout (Oncorhynchus clarkii) abundance in high-elevation streams: revisiting a model of translocation success

Assessing viability of stream populations of cutthroat trout (Oncorhynchus clarkii) and identifying streams suitable for establishing populations are priorities in the western United States, and a model was recently developed to predict translocation success (as defined by an index of population size) of two subspecies based on mean July water temperature, pool bankfull width, and deep pools counts. To determine whether the translocation model applied to streams elsewhere with more precise abundance estimates, we examined the relation between electrofishing-based estimates of cutthroat trout abundance and these habitat variables plus occupied stream length. The preferred model was (population size)1/2 = 0.00508(stream length (m)) + 5.148 (N = 31). In contrast, a model based on data from the original translocation model included stream temperature and deep pool counts as variables. Differences in models appear to largely have a methodological rather than biological basis. Additional habitat coupled with increased habitat complexity may account for the form of the abundance – stream length relation in the electrofishing-based model. Model-derived estimates imply that many cutthroat trout populations are below thresholds associated with reduced risk of extinction. We believe that this model can reduce uncertainty about projected population sizes when selecting streams for reintroductions or evaluating unsampled streams.