Question of the day:
How is a Tucson flood like a redneck divorce?

Rainfall in southern Arizona
A Case of Famine and Feast
Precipitation Seasons in Southern Arizona
Pacific tropical storms
Monsoon Pacific storms
April May June July Aug Sept Oct Nov Dec Jan Feb March

Digital
Elevation
Map
General airflow from
Pacific
You are here.
Colorado
Plateau
Basin and Range

Annual Precipitation
Sky Islands of SE Arizona

Anatomy of River Valley
• Main channel is normal course of river.
• Floodplain is area covered during flood.
• Over geologic time, river meanders over floodplain.

Typical flood hazard is water covering the floodplain.

Major Drainages of Tucson Basin

Flow Gauge Records, Santa Cruz River
1914
Record Flows on Santa Cruz River
1983
1965 1977 m
1983 flow = 53,000 cfs
(Equivalent to 16 backyard swimming pools per second!)
25% above previous 100-year flood estimates.
More frequent record flows post 1960

1983 Santa Cruz River @ Congress

Santa Cruz River @ Congress

Rillito at First Avenue, Oct. 1983
Bank erosion along the outside of a meander bend

Active river channel moves by bank erosion.
This is principle flood hazard in Tucson.
Rillito Creek at First Avenue, Tucson, 1983
October, 1983 flood:
8 deaths, ~1000 injuries; $250 million damage.

Increased frequency of record
Santa Cruz flows since 1960.
A. Climatic effect?
Global warming?
Enhanced El Nino?
B. Urbanization?
Urbanized desert increases runoff by four times compared to undeveloped desert.

Effects of Urbanization on Stream Flow
Before After
Lag time Lag time
Streamflow
Time
Streamflow
Time
Urbanization decreases lag time and increases maximum flow.

10000
Flood Forecasting
?
?
1000
100
100-year flood projections depend on models of climate and hydrology.
10
1 10
Recurrence Interval (yr)
100

Flood Control Measures
A. Structural
Dams
Channelization
Diversion channels
Pima County
B. Nonstructural
Zoning and land-use restrictions
Land acquisition programs
Flood forecasting
Public education

Soil cementing, Rillito @ Campbell
Confine the flow.
Move the water out of Tucson ASAP.

Q:
How is a Tucson flood like a redneck divorce?
A:
Sooner or later, someone’s going to loose a trailer.

Teton Dam on Snake River

Beginning of water piping and erosion of earthfill.

Complete failure

Permeable volcanic rock in footings of Teton Dam