EpisodicRange

Time (decades)

SedimentAccumulatedon Bed

Degree of HabitatSedimentation(log scale)

orIndex of

Disruptionin

Corridor

CorridorChannel

ChronicRange

Figure 1. Schematic representation of episodic variations in bed sedimentation and/or disturbance in riparian alluvial-scrub corridors of centra or southernl California streams.

Lagunitas Creek

Corralitos Creek

Arroyo Seco, Carmel River,Salinas River

Sisquoc River

Ventura River

San Diego MSCP

San Lorenzo River

Figure 2. Locations of corridors discussed in text.

Ann

ual b

ed-lo

ad s

edim

ent

tran

spor

t (m

illio

n to

ns)

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990

5

4

3

2

1

0

12.6 million tons

5.6 million tons

Sisquoc River near SisquocDrainage Area = 281 sq. mi.

Figure 3. Simulated long-term record of bedload sediment transport in an unregulated episodic stream-- the Sisquoc River, near Santa Maria, California. More than half of the bedload (coarse) sediment transported by the river during the 60 years was probably associated with two events -- the Wellman fire (1966), which burned approximately 35 percent of the watershed, and high-recurrence storms of January and February 1969. Source: Knudsen et al. (1992).

Springs

Mouth orLagoon Ocean

Beach bar

* *

*

*

major tributary

Headwaters

? ?

Frequency of Significant Disturbance

*

= Confluence of*

Longitudinal Profile

Large Landslides

*

Bedrockgorge

Figure 4. Schematic longitudinal variability in the frequency of episodic disturbance in a represen-tative central California corridor. Reaches immediately downstream from channel confluences and other point sources of sediment are more susceptible to frequent disturbances; reaches with gorges or perennial springs tend to be more resilient to the same disturbances. Frequency diminishes from upstream to downstream, but relative severity or extent of disturbance does not.

0 200 400 600 800

Average June + July flows, 1962 to 1986800

700

600

500

400

300

200

100

0

observed pre-fire best fit1962

1977 Fire

1982

San Lorenzo (unburned) flows (cumulative mean cfs in June + July)

Gage 11160500 operated 1937 to present

Arr

oyo

Sec

o (b

urne

d) fl

ows

(cum

ulat

ive

mea

n cf

s in

Jun

e +

July

)G

age

111

5187

0, o

pera

ted

196

2 - 1

986

Figure 5. Increased summer streamflows following the Marble-Cone fire (1977) helped sustain aquatic and near-channel habitat in Arroyo Seco and adjoining streams, which were initially heavily sedimented by post-fire runoff. From 1978 through 1982 or 1983, summer flows in Arroyo Seco were nearly twice values expected based on long-term correlation with the San Lorenzo River (unburned watershed), offsetting some of sediment water-quality and temperature effects on aquatic biota. The double-mass curve shows that the pre-fire relation for June and July flows between Arroyo Seco and the San Lorenzo River resumed after 1982 or 1983.

CREEK

CR

I DE R

C R.

R.

BRO

WN

S

WATSONVILLE

HW Y

1

Qa

Tp

Tp

TeoTe

San Andreas Rift Zone

LONG-TERM STREAM GAGE

MONTEREY

BAY

Figure 6. Location and geologic influences, Corralitos and Browns Creeks.

Upper Corralitos / Browns CreeksWatershed Boundary

Unconsolidated sediments

Semi - consolidated Purisimasandstones and siltstones

Consolidated marine shales,sandstones and shales

Consolidated marine siltstonesand sandstones

Bed - Monitoring Sites

0 3 miles

N

CORR

LIT O

S

A

Tp

Qa

Teo

Te

Pro

bab

ility

of

Occ

urr

ence

in a

Giv

en Y

ear

?

Wild

fires

Te: Hard siltstones and sandstones

chaparral

Teo: Tightly-folded shales,sandstones and mudstones

mixed conifer

Tp: Semi-consolidatedsandstones and siltstones

hardwood, conifer

Predominant Substrate and Vegetation

10%

PRIMARY SECONDARY PRIMARY SECONDARY PRIMARY SECONDARY

Col

luvi

al s

lum

ps

Rea

ctiv

ated

lan

dslid

es

Larg

e r

ocks

lides

Wild

fires

Wild

fires

Bed

ding

pla

ne f

ailu

res

Rea

ctiv

ated

lan

dslid

es

Mud

flow

s

Ove

r-st

eepe

ned

slo

pes

Sw

ale-

fill

mud

flow

s

Land

-use

cha

nge

Geology:

Dominant Vegetation:

Figure 7. Estimated probability of significant sedimentation of steelhead habitat caused by episodic events, in three geologic/vegetative regimes, Corralitos Creek watershed. Probabilities based on estimated or observed frequencies and projected durations of bed sedimentation. Primary disturbances warrant site assessments by knowledgeable specialists and may merit temporary management measures. Secondary influences are more localized or less severe than primary. Source: Hecht and Woyshner (1991).