ventura river: fluvial geomorphology e.a keller ucsbgeomorphology e.a keller ucsb transverse ranges...

Ventura River: Fluvial GeomorphologyE.A Keller UCSB

Transverse Ranges

The Ventura River is an often bed-rock, braided river, that flows across many active structures

Ventura River Terraces are Folded Over Anticline

Oak ViewFaults

FaultedTerraces near Oak View

Geologic History:Ventura River terraces show river has migrated west for thousands of years.Most of floodplain is to west

100,000yrs60,000yrs

40,000yrs 30,000yrsAcross river: 20,000yrs

100,000 yrs

40,000yrs

Ventura River

60,000 yrs

Why is the Ventura R. Migrating West?

• Active uplift ,mostly to the east on faults and folding of the rocks is responsible.

• The bluff top at Monte Vista is several 10s of thousands of years old.

• The Devil's Gulch Fault (discovered by Keller in the 1970s)is a south side up fault pushing the bluffs up when displacement occurs.

Bedrock pool nearMeinersOak

Major Floods Ventura River

• Since 1933 the 6 largest floods have occurred since1969.The largest was in 1978,followed by 1969.Average return period was about 37 and 74 years respectively.

• The floods in 1992 and 1995 were larger than 2005,but not by much

• The flood of 2005 was a moderate event with average return period of about 15 years

Ventura River in 1929

1938 flood damage

1978 following largest flood of record:note river is mostly to the west

After 2005 flood :note channel against Monte Vista Bluffs(photo 2005)

Loss of trees following 2005 flood (2006 photo)

February 1992 Delta Flood

Delta Floods 1992

Delta Flood1992

Second Mouth, Ventura River

Flood ControlNear Oak View

Landslides on Monte Vista Bluff 2006

Natural Channel form: braided,close to bedrock

Matilija Dam

Matilija Lake

Upstream of Dam

Downstreamof dam

The Objective:Sustainable Rivers