CE 513CE 513

Erosion in the Erosion in the Fall Creek WatershedFall Creek Watershed

Rick Faber

Erosion in the Fall Creek Watershed Erosion in the Fall Creek Watershed following the Clark Fire:following the Clark Fire:

Implications for the Hehe TimbersaleImplications for the Hehe Timbersale

Clark Fire destroyed 5000 acres of Clark Fire destroyed 5000 acres of undisturbed forest land in late 2003undisturbed forest land in late 2003

Fall Creek is home to genetically diverse Fall Creek is home to genetically diverse population of anadromous fishpopulation of anadromous fish

Current proposals are for a 2500 acre Current proposals are for a 2500 acre timber sale in the neighboring Hehe Creek timber sale in the neighboring Hehe Creek basin.basin.

The universal soil loss equation is:The universal soil loss equation is:A = R • K • L • S • C • PA = R • K • L • S • C • P

A is soil loss (tons/acre/year)A is soil loss (tons/acre/year)

R is the rainfall/runoff erosivity factorR is the rainfall/runoff erosivity factor

K is the soil erodibility factor (tons/acre/year)K is the soil erodibility factor (tons/acre/year)

L is the slope length factorL is the slope length factor

S is the slope steepness factorS is the slope steepness factor

C is the cover management factorC is the cover management factor

P is the support practice factorP is the support practice factor

Isoerodent Map of OregonIsoerodent Map of Oregon

R = 50

K-factor from STATSGO soil K-factor from STATSGO soil coverage from the USDA.coverage from the USDA.

L & S: Length & SteepnessL & S: Length & Steepness

Now combined and expressed as a single Now combined and expressed as a single factor. (Moore and Burch 1986)factor. (Moore and Burch 1986)

Spatial AnalystArcHydro

C-Factor C-Factor Land Cover Type C-Factor

Agriculture 0.09

Developed 0.24

Disturbed 0.24

Forest 0.004

Grasslands 0.06

Open Water 0.00

Riparian 0.004

Unvegetated 0.24

Woodland 0.004

LARSE DATA

C-Factor C-Factor RastersRasters

Calculate the ErosionCalculate the Erosion

Soil ErosionSoil Erosion

Soil Erosion for the Fall Creek Watershed

0.0

1.0

2.0

3.0

4.0

5.0

6.0

pre-fire post-fire post-fire,sale

Scenario

(to

ns

/ac

re/y

ea

r)

The loss of one inch of soil due to erosion is equivalent to 150 tons of soil per acre.

Mean Soil Loss for Fall Creek Mean Soil Loss for Fall Creek WatershedWatershed

LimitationsLimitations

Sedimentation vs Sedimentation vs erosionerosion

Truncate the Flow Truncate the Flow accumulation grid accumulation grid for LS factorfor LS factor

Land cover & timeLand cover & time Systematic error?Systematic error?