Watershed Response to Fire Christine May Earth & Planetary Science.

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Watershed Response to Watershed Response to Fire Fire Christine May Christine May Earth & Planetary Science Earth & Planetary Science
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Transcript of Watershed Response to Fire Christine May Earth & Planetary Science.

Page 1: Watershed Response to Fire Christine May Earth & Planetary Science.

Watershed Response to FireWatershed Response to FireWatershed Response to FireWatershed Response to Fire

Christine MayChristine May

Earth & Planetary ScienceEarth & Planetary Science

Page 2: Watershed Response to Fire Christine May Earth & Planetary Science.

Severe firesSevere fires can result in accelerated can result in accelerated erosion by:erosion by:

1.) removing the forest canopy and litter layer, exposing mineral soil to the direct impact of rainfall

2.) heating and combusting soil organic matter3.) burning logs that trap soil on steep slopes or store

sediment in stream channels 4.) reducing the root strength of the soil

Page 3: Watershed Response to Fire Christine May Earth & Planetary Science.

Rain SplashRain Splash

• Fine sediment or ash dislodged by rain splash can clog soil pores causing surface sealing.

Page 4: Watershed Response to Fire Christine May Earth & Planetary Science.

Severe firesSevere fires can result in accelerated can result in accelerated erosion by:erosion by:

1.) removing the forest canopy and litter layer, exposing mineral soil to the direct impact of rainfall

2.) heating and combusting soil organic matter3.) burning logs that trap soil on steep slopes or store

sediment in stream channels 4.) reducing the root strength of the soil

Page 5: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 6: Watershed Response to Fire Christine May Earth & Planetary Science.

Rainfall

Infiltration

Subsurface flow

Overlandflow

Overland flow occurs when rainfall rate exceeds infiltration rate.Subsurface flows brings the majority of water to the channel in humid regions.Return flow enters the channel in a saturated layer.
Page 7: Watershed Response to Fire Christine May Earth & Planetary Science.

Infiltration RatesInfiltration Rates

• Infiltration = the movement of water across the soil surface

• Influenced by• Soil texture

• Ambient moisture

Page 8: Watershed Response to Fire Christine May Earth & Planetary Science.

Time

Infi

ltra

tion

Rat

e (m

m/m

in)

clay

Page 9: Watershed Response to Fire Christine May Earth & Planetary Science.

Time

Infi

ltra

tion

Rat

e (m

m/m

in)

clay

sand

Page 10: Watershed Response to Fire Christine May Earth & Planetary Science.

Overland FlowOverland Flow

Surface erosion requires overland flow, which occurs when

1.) the rainfall rate exceeds the infiltration rate of the soil surface, or

2.) the soil is saturated

Page 11: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 12: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 13: Watershed Response to Fire Christine May Earth & Planetary Science.

0.1

1.0

10.0

100.0

0 20 40 60 80 100

% postfire herbaceous vegetation cover

av

era

ge

slo

pe

ero

sio

n (

mm

) NE YNP

Gibbon Canyon

>40 15-40 <15Runoff power index, slope (m/m) x relief:

POSTFIRE REVEGETATION and RILL EROSION IN DEBRIS-FLOW BASINS

Page 14: Watershed Response to Fire Christine May Earth & Planetary Science.

Hydrophobic SoilsHydrophobic Soils

Page 15: Watershed Response to Fire Christine May Earth & Planetary Science.

Hydrophobic SoilsHydrophobic Soils• A water-repellent layer of soil that prevents infiltration

below that layer.

• Derived from plant material burned during a hot fire. The hydrophobic compounds (hydrocarbons) penetrate the soil surface as a gas and solidify after cooling, forming a waxy coating.

• Sandy soils with large pore spaces and areas with thick litter accumulations that experience very hot fires are especially susceptible.

Page 16: Watershed Response to Fire Christine May Earth & Planetary Science.

Hydrophobic Soils (con’t)Hydrophobic Soils (con’t)

• The thickness and continuity of hydrophobic layers varies, as does their persistence.

• Recovery: plant roots, soil microorganisms, and soil fauna help break up the hydrophobic layer.

• Negative feedback: reduced infiltration will decrease the amount of water available for plant growth and biological activity in the soil.

Page 17: Watershed Response to Fire Christine May Earth & Planetary Science.

Field TestsField Tests

• Sprinkler experiments

• Infiltrometer

• Analysis: compare infiltration rates with rainfall rates from local raingages

Page 18: Watershed Response to Fire Christine May Earth & Planetary Science.

Rehabilitation MeasuresRehabilitation Measures

• On-site: revegetation– grass seeding – pitfalls?– straw mulch

• Off-site: sediment retention devices

– straw bale check dams– directional log felling– sediment retention ponds

Page 19: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 20: Watershed Response to Fire Christine May Earth & Planetary Science.

Photos by F.J. Swanson

Page 21: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 22: Watershed Response to Fire Christine May Earth & Planetary Science.

[debris flow video]

Page 23: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 24: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 25: Watershed Response to Fire Christine May Earth & Planetary Science.

Debris FlowsDebris Flows

Two initiation mechanisms:

1.) runoff-initiated - driven by low soil infiltration rates

and the bulking of sediment detached by overland flow and surface erosion

2.) landslide-initiated- driven by soil saturation (requires

high infiltration rates and low rooting strength)

Page 26: Watershed Response to Fire Christine May Earth & Planetary Science.

Rill and channel erosion (1988 fire, 1989 storm, Yellowstone)

Loss of root strength, saturation-failureof colluvium (1989 fire, 1997 storm, Idaho)

Initiation of events through runoff and sediment bulking, early post-fire

Page 27: Watershed Response to Fire Christine May Earth & Planetary Science.

Copyright © Tom Black 2002

Page 28: Watershed Response to Fire Christine May Earth & Planetary Science.

1989 debris flow-dominated event, NE Yellowstone1989 debris flow-dominated event, NE Yellowstone

Page 29: Watershed Response to Fire Christine May Earth & Planetary Science.

Initiation of events through loss of root strength, saturation and

failure of colluvium (1989 fire, 1997 storm, central Idaho)

Page 30: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 31: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 32: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 33: Watershed Response to Fire Christine May Earth & Planetary Science.

Years after forest removal / fire

Rel

ativ

e ro

ot r

einf

orce

men

t

From Ziemer 1981

Decay of dead roots

Page 34: Watershed Response to Fire Christine May Earth & Planetary Science.

Years after forest removal / fire

Rel

ativ

e ro

ot r

einf

orce

men

t

From Ziemer 1981

Decay of dead roots

Live roots

Page 35: Watershed Response to Fire Christine May Earth & Planetary Science.

Years after forest removal / fire

Rel

ativ

e ro

ot r

einf

orce

men

t

From Ziemer 1981

Decay of dead roots

Live roots

5 – 15 yrs

Page 36: Watershed Response to Fire Christine May Earth & Planetary Science.

Probability of OccurrenceProbability of Occurrence

• Depends upon post-fire storm characteristics and the spatial pattern of high severity fire patches.

Page 37: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 38: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 39: Watershed Response to Fire Christine May Earth & Planetary Science.

Temporal PatternsTemporal Patterns

Page 40: Watershed Response to Fire Christine May Earth & Planetary Science.

Time since fire

Lik

elih

ood

of la

rge-

scal

e er

osio

n

Runoff-DominatedSurface Erosion

Two-Phase Erosional Response

Page 41: Watershed Response to Fire Christine May Earth & Planetary Science.

Time since fire

Lik

elih

ood

of la

rge-

scal

e er

osio

n

Runoff-DominatedSurface Erosion

Saturation-InducedSlope Failures

Two-Phase Erosional Response

Page 42: Watershed Response to Fire Christine May Earth & Planetary Science.

Time since fire

Lik

elih

ood

of la

rge-

scal

e er

osio

n

Runoff-DominatedSurface Erosion

Saturation-InducedSlope Failures

Two-Phase Erosional Response

0 – 5 yrs

5 – 15 yrs

Page 43: Watershed Response to Fire Christine May Earth & Planetary Science.

Post-Fire Rehabilitation Efforts for Post-Fire Rehabilitation Efforts for Debris FlowsDebris Flows

Suggestions from the class…

Page 44: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 45: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 46: Watershed Response to Fire Christine May Earth & Planetary Science.

0 to 30 yrs 30 to 60 yrs 60 to 90 yrs > 90 yrs

Time Since the Previous Debris Flow

Page 47: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 48: Watershed Response to Fire Christine May Earth & Planetary Science.

Salvage LoggingSalvage Logging

• Dead wood can be an important element in sediment storage on steep hillslopes and in stream channels.

• Soil disturbance by logging operations and road construction can further accelerate erosion.

Page 49: Watershed Response to Fire Christine May Earth & Planetary Science.

Short-term PatternsShort-term Patterns

Page 50: Watershed Response to Fire Christine May Earth & Planetary Science.

LongLong-term Patterns-term Patterns

Page 51: Watershed Response to Fire Christine May Earth & Planetary Science.

Event ReconstructionsEvent Reconstructions

• Studies that attempt to decipher long-term correlations among climate, fire, and erosion and their effects on landscape evolution using a variety of dating methods and evidence for past erosional events.

Page 52: Watershed Response to Fire Christine May Earth & Planetary Science.

Copyright © Ron Dorn 2002

Page 53: Watershed Response to Fire Christine May Earth & Planetary Science.

1989 debris flow

older fan sediments

1988 charred litter layer (burned soil surface)

‘Fire-related debris flows’

Page 54: Watershed Response to Fire Christine May Earth & Planetary Science.

Yellowstone lodgepole: large, severe stand-

replacing fires, RI 200-400 yr

Page 55: Watershed Response to Fire Christine May Earth & Planetary Science.

Onset of the Little IceAge (1200 AD)

Meyer et al. 1992Meyer et al. 1992

Page 56: Watershed Response to Fire Christine May Earth & Planetary Science.

Warmer millennial-scale periods

Page 57: Watershed Response to Fire Christine May Earth & Planetary Science.

Cooler millennial-scale periods

• (terraces?)

Page 58: Watershed Response to Fire Christine May Earth & Planetary Science.

300112

169

43000

1

10

100

1000

10000

100000

Apatite fissiontracks

(Sweetkind andBlackwell, 1989)

Cosmogenicnuclides

(Kirchner et al.,2001)

7400-6600 cal yrBP rates

Sedimenttrapping and

gauging (Claytonand Megahan,

1986)

1997 debris-flowevents

sedi

men

t yie

ld in

T/k

m2/y

r

10,000,000

Time scale in years

10,000 1,000 100 1 0.01

Idaho batholith estimated mean sediment yields over different timescales

(log scale)

Page 59: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 60: Watershed Response to Fire Christine May Earth & Planetary Science.

Suspended sediment and bedload transportWatershed 3, HJA

0

4000

8000

12000

1956 1962 1968 1974 1980 1986 1992

t/km

2 /yr

Suspended sediment

Bedload

Roads Patch cut

Floods and debris flows

Page 61: Watershed Response to Fire Christine May Earth & Planetary Science.

Questions?Questions?

Page 62: Watershed Response to Fire Christine May Earth & Planetary Science.

Questions for the class:Questions for the class:

Is there evidence that fires preferentially travel through or burn hotter in steep, narrow valleys compared to planar hillslopes?

Page 63: Watershed Response to Fire Christine May Earth & Planetary Science.

Questions for the class:Questions for the class:

How can information about erosion-prone areas be incorporated into:

1.) planning fuels treatment projects?

2.) wildfire management?

Page 64: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 65: Watershed Response to Fire Christine May Earth & Planetary Science.

0

20

40

60

0 30 60 90 120 150

Time Since Fire (yrs)

Re

lati

ve

Fre

qu

en

cy

of

De

bri

s

Flo

w O

cc

ure

nc

e

Page 66: Watershed Response to Fire Christine May Earth & Planetary Science.

Central Idaho ponderosa: presettlement regime of light surface fires, RI 5-30 yr

Page 67: Watershed Response to Fire Christine May Earth & Planetary Science.

Northern Hemisphere tree-ring temperature reconstruction (from Esper et al., 2002)

Mann-Bradley-Hughes (1999) Esper et al. (2002)

multiproxy tree-rings

“Medieval Warm Period” “Little Ice Age”

Severe fire, large debris flows both areas

Frequent light fires Idaho; few fires Yellowstone

Year AD

Page 68: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 69: Watershed Response to Fire Christine May Earth & Planetary Science.

Adapted from Swanson (1981);additional point G. Meyer (pers. comm).

Page 70: Watershed Response to Fire Christine May Earth & Planetary Science.
Page 71: Watershed Response to Fire Christine May Earth & Planetary Science.

Sediment yields in fire-induced debris-flow events, western U.S.

basin area (km2)

0.1 1 10

sedi

men

t yie

ld (

Mg)

1000

10000

100000

1000000saturation-failure eventsrunoff-generated eventsrunoff-generated events, YNPsaturation-failure event(?), YNP

Page 72: Watershed Response to Fire Christine May Earth & Planetary Science.

ConclusionsConclusions

• Herbaceous revegetation reduces probability of post-fire runoff-generated events (maximum probability of occurrence 1-3+ yr after fire?)

• Later postfire saturation-induced failures –root strength control (maximum probability 4-10 yr after fire?)

• Geomorphic response to fire is transient but produces transient to persistent stream habitat alteration

• Climate is a strong control on fire regimes and associated geomorphic response, both in space and time, therefore…

• Fire-induced sedimentation is strongly episodic and variable at ~1000 yr timescales