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BASIC FLUVIAL SEDIMENT CONCEPTS. Introduction to Sediment Sampling USGS Technical training in Support of Native American Relations (TESNAR) 2011 Klamath, Warm Springs, Yurok, and Karuk Tribes Chiloquin, OR September 19-23, 2011. WHAT IS SEDIMENT?.

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Basic fluvial sediment concepts

BASIC FLUVIAL SEDIMENT CONCEPTS

Introduction to Sediment Sampling

USGS Technical training in Support of Native American Relations (TESNAR) 2011

Klamath, Warm Springs, Yurok, and Karuk Tribes

Chiloquin, OR September 19-23, 2011


What is sediment
WHAT IS SEDIMENT?

  • Sediment consists of particles derived from rocks or biological materials.

  • When transported by, suspended in, or deposited by flowing water, referred to as fluvial sediment.


Fluvial sediment origins the geologic cycle
FLUVIAL-SEDIMENT ORIGINS:The Geologic Cycle

  • Weathering

    • Mechanical (freeze/thaw, abrasion, other)

    • Chemical (carbonic acid, biotic interactions, other)

  • Erosion

    • raindrop impact

    • sheet, gully, bank/channel erosion

    • mass wasting, glaciation, volcanic eruption, eolian

  • Transport (a number of mechanisms)

  • Deposition

    • streambeds, floodplains

  • Digenesis

    • compaction, cementation, mineral replacement


Sediment origins
SEDIMENT ORIGINS

Some Alterations by Human Activities:

  • Agriculture seasonally changes ground cover, exposes soil.

  • Tree harvests indirectly increase erosion rates (PNW).

  • Construction (all types).

  • Riparian vegetation removal.

  • Channel straightening (throughout Klamath Basin).

  • Dams (up to 4 PacifiCorp dams in Klamath Basin).

  • Dredging (Columbia River).

  • Jetties (Outer Banks, NC).

  • Stream Corridor Restoration (Wood River near Fort Klamath)


Physical characteristics of sediment
PHYSICAL CHARACTERISTICS OF SEDIMENT

  • Size

    • lengths of long, intermediate, short axes.

    • “fall diameter” calculated as that equivalent to a quartz sphere that falls at same rate in still water

    • Wentworth size classes (USGS TWRI Book 5 Chapter C1).

    • we often classify as 3 natural populations: pebbles & larger, sand/silt, clay.

    • coarsest material normally related to high slope (ex., mountains); finest correlated to low slopes (ex., coastal plains).


2 mm

Sands

0.062 mm

Silts

0.002 mm

Clays


Physical characteristics of sediment1
PHYSICAL CHARACTERISTICS OF SEDIMENT

  • Shape.

    • prismatic or angular ("new").

    • elliptical or spheroidal (after abrasion).

    • flat or bladed (nature of particle -- e.g., mica, halite).

  • Mineral.

    • quartz, felspars, gold, etc.


Physical characteristics of sediment2
PHYSICAL CHARACTERISTICS OF SEDIMENT

  • Density (mass per unit volume).

    • dry wood <1

    • water 1.0 (pure, 4° C)

    • coal 0.9-1.4

    • quartz & feldspar ~2.65 (prevalent minerals in nature)

    • iron 7.9

    • silver 10.5

    • lead 11.4

    • mercury 13.5

    • gold 19.3

    • ??? 22.6


Stokes law george gabriel stokes derived 1851
STOKES LAWGeorge Gabriel Stokes, derived 1851

  • For our purposes: If particles fall in a viscous fluid by their own weight due to gravity, a terminal velocity – also known as the settling velocity – is reached when this frictional force combined with the buoyant force exactly balance the gravitational force.

    where:

  • Vs = particle settling velocity (m/s) (vertically downward if ρp > ρf, upwards if ρp < ρf ),

  • g = gravitation acceleration (m/s2),

  • ρp = mass density of the particles (kg/m3),

  • ρf = mass density of the fluid (kg/m3),

  • μ = fluid's dynamic viscosity (kg/(s·m)), and

  • R = radius of the spherical object (in m).


Stokes law one way to use this equation
STOKES LAWOne way to use this equation

  • Transformed to:

    T= (constant) * (η) * (x)

    d2

    Where:

    T = fall time, in seconds

    η = absolute viscosity, in poises (g/cm . sec)

    d = fall diameter of particle , in millimeters

    constant = 0.1113, for spherical particle assumed to have density of 2.65 g.cm3 and to settle in distilled water under gravitational force of 980 cm/s2

    Used in lab pipette withdrawals of sediment mixtures

    Fine sand in quart container falls 70 mm in 34 seconds, fine silt in 32 minutes, coarse clay in 2.1 hours, medium clay 8.5 hours


Physical characteristics of sediment density
PHYSICAL CHARACTERISTICS OF SEDIMENT -- Density

August 2006, photos from

the yacht 'Maiken'

in the South Pacific


Fluvial sediment terminology
FLUVIAL SEDIMENT TERMINOLOGY

  • SEDIMENT CONCENTRATION: (actually suspended-sediment concentration)

    ratio of mass of dry sediment in a water-sediment mixture to the mass of the entire mixture. Expressed as parts-per-million, which can be converted to mass-per-volume units, such as milligrams per liter.



Fluvial sediment terminology2
FLUVIAL SEDIMENT TERMINOLOGY

  • SEDIMENT DISCHARGE: The mass, volume, or weight of sediment passing a stream cross-section in a unit time. It can be divided into categories:

  • Defined operationally, and as mode of transport:

    Suspended- sediment load (discharge), and Bedload (discharge).

  • Defined by origin: Washload, and Bed-material load.


Fluvial sediment terminology3
FLUVIAL SEDIMENT TERMINOLOGY

  • SUSPENDED-SEDIMENT LOAD: That part of the sediment load which is in suspension.

  • WASH LOAD: Finer material (<<<0.062 mm) that tends to flow into and out of a reach without bed interactions

  • BEDLOAD: Material moving on or near the stream bed by rolling, sliding, and skipping. In strict sense, material finer that about 0.2 mm in diameter is rarely a part of bedload (but can be part of near-bed suspended load).


Fluvial sediment terminology4
FLUVIAL SEDIMENT TERMINOLOGY

  • BED MATERIAL: Sediment composing the streambed.

  • BED-MATERIAL LOAD: That material in transport that is characteristic of the bed material; excludes wash load.

  • TOTAL LOAD: Equal to suspended-sediment discharge plus bedload discharge (with caveat); includes wash load. In general, the bulk of sediments transported in the world's streams occurs in the suspended phase; however, this is not a true for all streams (Wood River?).


Fluvial sediment terminology5
FLUVIAL SEDIMENT TERMINOLOGY

REPRESENTATIVE SAMPLE:

  • A characteristic of a sample that is proportional to its occurrence in the local environment at the time of collection.

  • A representative suspended-sediment sample will have a sediment concentration & size distribution “equal” (similar) to that averaged over the stream cross-section when the sample was collected.


Some factors in sediment transport
SOME FACTORS IN SEDIMENT TRANSPORT

  • Drainage area, mean slope, sinuosity, braided

  • Supply or transport limitations

  • Geology, climate, land use

  • Stage & discharge range, stream power

  • Sediment sources & flow history

  • Bank and bed characteristics

    • moveable or cohesive bed (ripples, dunes, plane bed, antidunes)

    • stable versus sloughing banks

    • riparian and floodplain vegetation

    • flow resistance


Relations among suspended sediment concentration and
RELATIONS AMONG SUSPENDED-SEDIMENT CONCENTRATIONAND:

  • Discharge: Although suspended-sediment concentration generally increases with water discharge, the relation is not simple.

    • Sediment concentration peak might match, precede, or follow water-discharge peak.

    • Physical basis for bedload peak rate lagging hydrograph.

    • System might be supply-limited, or in disequilibrium.

    • Seasonal effects.

    • Ice cover.

    • other.


Examples of Stage & Turbidity NOT Uniform

North Santiam Basin1. Landslide December 17, 20012. Mt Jefferson event of Oct 1, 2000


Examples of Stage & Turbidity NOT Uniform

North Santiam Basin1. Landslide December 17, 20012. Mt Jefferson event of Oct 1, 2000

Mt Jefferson glacial debrisflow

Landslide-debrisflow




Relations among suspended sediment concentration and1
RELATIONS AMONG SUSPENDED-SEDIMENT CONCENTRATIONAND:

  • Depth: Turbulence maintains sediments in suspension. Fine sediments tend to be uniformly distributed in the water column; the concentration of coarser sediments may increase with depth (Stoke's Law).


Box Coefficient (BC) = Cmean/Cpoint

Cmean = ~930 mg/l

BC=~1.1

BC=~1.1

BC=1.03

BC=~1

Culbertson et al., 1964


Box Coefficient (BC) = Cmean/Cpoint

Cmean = ~1,360 mg/l

BC=~5

BC=~4

Mean Values

BC=~1.7

BC=~1.5

Culbertson et al., 1964


Sampled unsampled zones with an isokinetic sampler
Sampled & Unsampled Zoneswith an Isokinetic Sampler


Relations among suspended sediment concentration and2
RELATIONS AMONG SUSPENDED-SEDIMENT CONCENTRATIONAND:

  • Width: Sediments may be non-uniformly distributed in the cross-section; this may be due to incomplete mixing (inadequate time to mix, weak turbulence, density gradient, weak secondary motion, etc.); or to difference in source and flow characteristics in the cross-section.


Methods of quantifying fluvial sediment discharge
METHODS OF QUANTIFYING FLUVIAL SEDIMENT DISCHARGE

  • Direct, sampling:

    • Suspended sediment: Collect representative suspended-sediment sample, measure discharge, calculate instantaneous suspended-sediment discharge.

    • Bedload: Collect sufficient bedload samples using a sampler such as the FISP-approved BL-84 sampler over the stream cross-section, calculate instantaneous bedload discharge.

    • Clear as mud!


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