Stream Sediment

Stream Sediment

• Sediment - particles transported or deposited in stream channels

• Sediment levels - good indicator of effectiveness of watershed mangement

Erosion is a natural process

Clearwater River, Idaho

The name says what the watershed management goal is.

Clearwater River, Idaho

Clean gravel beds for spawning

Erosion Process

• Detachment• Transport• Deposition

Eroded skid trail

Watershed Gross Erosion

• Components of gross erosion– Interrills– Rills– Ephemeral gullies– Channels– Landslides or slumping

Interril Erosion

Raindrops striking exposed soil detach the soil particles and splash them into the air and into shallow overland flows. Raindrops striking these shallow flows enhance the flows's turbulence and help to transport more of the detached sediment to a nearby rill or flow concentration

Rill Erosion

Gully Erosion

Channel Erosion

Landslides

Grand Ditch, Rocky Mountain National Park

Estimates of rill erosion

• Universal soil loss equation– Developed by US Dept. Agriculture– Oldest and most accepted estimator– Over-estimates for forest land– Use as a starting point only

Universal Soil Loss Equation

A = R K LS C PA = tons/acre/yearR = rainfall energy factorK = soil erodibility factorsLS = effect of topographyC = ratio of soil loss with specified cover and with

continuous tillageP = conservation practice factor

R factor

R = [∑ ∑ (E I30)] / 100 n)

E = storm kinetic energy, ft-t/acre/inch of rainfallI = maximum 30 minute storm intensity, in./hr.n = total number of yearsm = number of storms in each year

R = 150 to 200 for Indiana

n m

K factor

Describes soil detachability and transport-ability due to soil texture, structure, organic matter, density, compaction, and biological characteristics

K = A / (RLSCP)K is given in NRCS soil survey reports

K factor

100 K = 2.1M1.14(10-4)(12-a) + 3.25(b-2) + 2.5 (c-3)

M = (%silt + %very fine sand) (100 - % clay)a = % organic matterb = soil structure code used in soil classificationc = profile permeability class

LS factor

LS = (λ/22.13)a (0.065 + 0.0454 S + 0.0065 S2

λ = slope lengtha = 0.5 for slope ≥ 5%, and 0.3 for 1 to 3% slopeS = slope steepness in %

C factorC = A (with treatment) / A (with clean tillage)

Undisturbed mature forest

Thinned to 50%

density

Clearcut, no site

preparation

Clearcut, roller

chopped

Clearcut, complete site prep.

Clearcut, site prep., fallowed

0.0001- 0.001

0.002 -0.004

0.003 -0.009

0.03 NA 0.11- 0.17

0.001 – 0.0034

NA 0.0003 – 0.01

0.001 – 0.022

0.004 – 0.028

0.023 – 0.068

0.00014 0.00019 0.00165 0.00325 0.0242 0.097

C values reported in 3 studies of forested site conditions

P factor

P = A (with conservation practice) / A (up-and-down hill cultivation)

P = 1 if no conservation practices

P < with conservation practices

Recommended Values for P Factor

Land slope %

ContouringContour

stripcroppingTerrace and

stripcropping

1 to 2 0.60 0.45 0.30

3 to 5 0.50 0.38 0.25

6 to 8 0.50 0.38 0.25

9 to 12 0.60 0.45 0.30

13 to 16 0.70 0.52 0.3517 to 20 0.80 0.60 0.40

21 to 25 0.90 0.68 0.45

Example

Drum chopper for site preparation Windrow of logging slash

Burning piles of logging slash

Erosion rates for clear cuttings in SE USTreatment Recovery time Annual erosion

(t/ha)Natural NA 0.00 – 0.05

Logged and roaded 3 0.10 – 0.50

Burned 2 0.05 – 0.7

Chopped 3 0.05 – 0.25

Chopped and burned 4 0.15 – 0.40

Windrowed 4 0.20 – 0.24

Disked 4 2.50 – 10.0