Methods 421 Study Area

The O'Ne-eil Creek catchment is approximately 75 km2 and is located in an experimental forest in the central interior of northern British Columbia. It is a tributary to the Middle River which drains into the Stuart Lake system which is well known for its highly productive sockeye salmon runs. Fish escapements to streams in this region, including O'Ne-eil, have been monitored using counting fences for nearly 50 years. The O'Ne-eil catchment drains part of the Hogem Range of the Omenica Mountains, and has its mouth at 700 metres above sea level (masl) and its drainage divide at approximately 1980 masl.18 The channel is approximately 20 km in length with a steep upper reach which drains well-developed cirques, a steeper middle reach that passes through a rock-walled canyon, and a gentle, low gradient depositional reach in the lower 2 km.19 In the lower reaches of the stream, the channel bed is comprised of clean gravel with very low concentrations of fine sediments, well suited for salmon redds. This lower reach is underlain by fine grained glaciolacustrine sediments and the only anthropogenic disturbance to date consists of a road (constructed in 1980) which cuts through this material. This road bridges the stream and allows access approximately 1500 m upstream of the river mouth. There has been no harvesting in the catchment, so the system represents a nearly pristine environment.

4.2.2 Field Methods

Data collected over five seasons of sampling are presented here comprising various periods of 1995, 1996, 1997, 2000, and 2001. Within each year various hydrolo-gical or biological events were sampled including spring melt floods, active salmon spawning, post-spawning die-off, and low flows when no visual evidence of adult fish were evident, which in this chapter is called post-fish, were represented. Table 4.1 identifies the events, the conditions, and the variables that were collected each year. The conditions of sampling are characterized as either "ambient" or "resuspended" with ambient conditions representing the undisturbed, natural suspended sediment concentration conditions. In order to characterize the gravel stored fine sediment, a resuspension technique that was an attempt to rework the surface gravels using approximately the same energy expended by spawning salmon, was used. Several minutes after the collection of the ambient sample, a second sample of suspended sediment was taken, following the disturbance, or mixing, of the top layer (0.04 to 0.06 m) of gravels by a field assistant, positioned 3 to 5 m upstream of the collection site. This distance provided sufficient travel time for the resettling of heavier sand particles thereby allowing the collected material to comprise the aggregated fine sediment stored within the surface gravel matrix. In this chapter, that material is termed "resuspended gravel stored fines."

Stream velocities and depths at the time of sampling were determined using a Swoffer current meter and are presented in Table 4.1.

4.2.3 Suspended Sediment Measurements

Stream water with suspended sediment was collected approximately 10 cm below the surface of the water in several large mouthed 1 l Nalgene bottles for the determination of

(i) suspended particulate matter (SPM) concentration

(ii) the disaggregated or absolute particle size distribution (APSD)

(iii) the aggregated or effective particle size distribution (EPSD)

(iv) morphometric characteristics of the aggregated suspended sediment population

(v) the fractal dimensions of the filtered particle population

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