U.S. Department of the InteriorU.S. Geological Survey

Bed-material Sampling

May 2013 TESNAR Class

Mackenzie KeithHydrologistOregon Water Science CenterPortland, Oregon

The b-axis

From Bunte and Abt, 2001

Why measure bed material?

Sediment transport calculations and indications

Fish/habitat /bio studies Balance between supply and transport Sediment attrition Lithology

What’s in a D50? Plotting and reading data Bed material can range over several orders of

magnitude Log transformations and the phi scale Reading and reporting D50 (or D16, D84, or

whatever) Looking at multiple sets of data

Surface vs. Subsurface

Surface layer Subsurface layer Armoring ratio

Techniques for coarse material sampling: The grains

Operator bias Which side is the b-axis? Results from yesterday How many clasts do I count? What if I can’t pick the clast up? Surface Subsurface

Techniques for coarse material surface sampling: The counts Facies mapping Wolman pebble counts Sampling frames Ocular assessments Photogrammetric techniques Zig-Zag Bank to bank Other aquatic habitat measures

Techniques for coarse material surface sampling: Longitudinal Choosing the right location Choosing the right spacing Choosing the right grain Tiny clasts? Giant clasts?

A method for subsurface sampling: Bulk sampling Clearing the surface layer Digging, sieving, and weighing How much to dig up? Filling in the hole

Let’s go do a pebble count!

Siletz gravel bar Fill out forms Measure and record gravel Discuss subsurface sampling