Data Analysis

Samples from suspended and bed collection were processed for analysis to define the quantity and particle sizes of the sediment collected.

Suspended Sediment

All suspended-sediment samples were composited and analyzed at the USGS Cascade Volcano Observatory (CVO) Sediment Laboratory. Sediment concentration and particle-size distribution were determined from the analysis. The CVO laboratory analyzed 29 suspended-sediment samples, 25 of which were analyzed for concentration, total weight, and half‑phi scale particle-size distributions (PSD). The remaining four samples were analyzed for concentration only. Suspended-sediment discharge was estimated for sand (diameter greater than or equal to 0.063 mm) and silt/clay (diameter less than 0.063 mm) using the concentration and PSD along with the equation from Guy (1978):

      (1)

Bedload Sediment

Bedload-sediment samples were analyzed at the USGS Idaho Water Science Center laboratory in Boise. Each bagged sample was weighed individually, and then composited for the entire cross-section. Sieve analysis was completed on composited samples to determine the PSD of the cross section. The bedload sediment was sieved down to the 0.5 mm sieve, corresponding to the mesh size of the bag used to capture the sediment. Eighteen sieves were used to create the PSD. Sizes of the sieves used for analysis and the classification of the sieved particles are shown in table 2.

Bedload-sediment transport rates were estimated using the midsection method (eq. 2; Edwards and Glysson, 1999) and account for a varying width for the first and last sample.

      (2)

Total Sediment Loading

Total sediment loading is the sum of all sediment moving downstream at a cross section during a given period. Then, in a deep channel like the white sturgeon critical habitat of the Kootenai River, the total sediment is the sum of total suspended-sediment discharge and total bedload-sediment discharge. Suspended sediment was sampled from the top of the water surface to within 102.0 mm of the channel bed. Bedload sediment was sampled 76.0 to 102.0 mm from the bottom of the channel bed. Two zones were not sampled: (1) the 25.0 mm separation between the Helley-Smith sampled zone and the limits of the suspended-sediment sampler and (2) the fine sediment that passed through the 0.025 and 0.050 mm mesh bedload sediment sample bags.