Arroyo

              'ARROYO
Floodwaters in southern Arizona, sometimes of high velocity and with a high concentration of runoff, scour stream
channels that then could shift and change. Severe property damage may result. Photo: Fred Wehrman
flood Hazards, a Concern ¡n Desert Areas of Arizona
Semiarid,
with a scarcity of water
resources, Arizona might seem
an unlikely state to be threatened by
flooding. Flooding in Arizona, how-ever,
does indeed pose serious
threats to life and property in the
state. In fact, because of erosion and
scouring in unstable stream chan-nels,
certain flood hazards exist in
the arid Southwest that are not
generally present in humid regions of
the United States.
As an Arizona water issue, flood-ing
has attracted some recent atten-tion.
Many officials and citizens of the
state remember the destructive floods
of 1983 in southern Arizona. Some
may also recall the four other sig-nificant
floods that occurred in the
area between 1965 and 1983, an un-usual
cluster of events in recent
Arizona flood history. These floods
helped alert the state to the occur-rence
of floods and a susceptibility to
their effects. Flooding is also of inter-est
because of climate change, a topic
of recent discussion and some con-troversy.
WATER RESOURCES RESEARCH CENTER UNIVERSITY OF ARIZONA
Vol. 4 No. 2 June 1990
Climate, Geology and Flood-ing
in Arizona
Climate
and geology, two basic
factors that determine flooding,
vary greatly in Arizona, especially
north to south. As a result, the occur-rence
and effects of floods vary great-ly
within the state. The plateaus of
northern Arizona concentrate
drainage into incised channels or
canyons. Communities are usually
built on upland surfaces and there-fore
are generally unaffected by
floods as water drains down
entrenched river systems. Other
northern communities are built on
very permeable surfaces that quickly
drain water underground. For ex-ample,
the surface of Flagstaff is most-ly
volcanic rock.
Flooding is more of a problem in
southern Arizona where water runs
off normally dry desert lands. This
region is dominated by basin and
range topography, with most com-munities
located along stream chan-nels
in the center of basins or on pied-monts
at the base of mountains.
Along with being areas subject to
various kinds of flood hazards, the
lowlands of the basin and range
province of the state are where more
than 90 percent of Arizona's popula-tion
resides.
Southern Arizona experiences
precipitation mainly during two
seasons: summer and winter. The
precipitation is the result of three dis-tinct
climatic patterns. Summer
thunderstorms usually begin in late
June or early July and initiate the
fllOflSOOfl season. The thunderstorms
may occur in a limited area, possibly
affecting only part of a watershed.
They are generally of short duration,
and the resulting runoff may quickly
fill and overtop streams and washes
causing local flooding.
Flash floods can result from sum-mer
thunderstorms. Described as too
much rain falling in too small an area
in too short a time, flash floods are a
critical natural hazard in Arizona.
Since 1970, 68 Arizona residents have
lost their lives in flash floods, often
when attempting to drive through
swollen streams at dip crossings.
Another form of precipitation
that affects Arizona comes from West
Coast tropical storms. They usually
move into the area during September
and October. With intense precipita-tion
and covering an entire region,
tropical storms cause the most
destructive flood events in southern
Arizona. Climatic conditions interact-ing
with such a storm were respon-sible
for the rainfall of September 27
to October 3, 1983, and subsequently
referred to as the 1983 floods. Conse-quences
included eight deaths and
975 reported injuries and an es-timated
$226.5 million damages.
Occurring usually between
November and March, winter rainfall
tends to be of lesser intensity than
storms in other seasons. Winter
storms, however, tend to be of longer
duration, frequently lasting several
days, and cover more geographical
area. Runoff from winter storms can
combine with snowmelt to cause sig-nificant
erosion.
Are Floods Becoming More
Frequent, More Intense?
Observations
seem to indicate
that more frequent and intense
flooding has been occurring recently
in southern Arizona. For example, the
flow of the Santa Cruz River, which
has been gauged since 1913, set a
record in 1914 that was not exceeded
until 1965 when flows established a
new record. The 1965 flow record was
in turn exceeded twice, in 1977 and
1983. Two other flows exceeded the
1914 record during the 1960s.
That the occurrence and intensity
of floods are increasing in Arizona
would seem evident. Not as clearly
defined are the causes of this develop-ment,
whether human-made or
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natural, and, if a combination, to what
extent is each a factor. The matter is
complex. For example, regional
climatic changes may be the cause of
increased flooding in southern
Arizona. If these changes are, in fact,
occurring, are they a phase of a
natural climatic cycle that operates in
the Southwest, or are they the result
of an extraordinary event, possibly re-lated
to the greenhouse effect, a
suspected human-caused
phenomenon?
The question is central to the
work of University of Arizona geo-scientist,
Victor R. Baker, and the
UA Arizona Laboratory for Paleohy-drological
and Hydroclimatological
Analysis (ALPHA). Concentrating on
the Salt and Verde Rivers during the
last 2,000 years, ALPHA researchers
found that floods equal to, or exceed-ing
the magnitude of recent flood
events in southern Arizona have oc-curred
before in the region. Interest-ingly,
though, the past floods have not
been as large as some theories have
predicted and only modestly larger
than what has been occurring recently.
Research also suggests that flood
events are possibly occurring more
frequently now than in previous
periods. How unique then is the
recent flooding that has been taking
place in southern Arizona? Baker is
reluctant to draw general conclusions
until additional, in-progress research
yields information about conditions in
other Arizona and Southwest rivers.
Urbanization is also an important
factor to consider when assessing the
intensity of floods in Arizona.
Through urbanization, the natural
land surface is often leveled and
covered with impervious surfaces -
buildings, roads, sidewalks, parking
lots, etc. Increased drainage results.
In an urbanized area, runoff is es-timated
to be four times that of a com-parable
undeveloped desert area. The
drainage from the increased runoff
that concentrates in rivers and washes
accelerates the quantity and velocity
of the flow on downstream reaches.
Channels enlarge becoming deeper
and wider, and damage from erosion
becomes a greater threat.
The above discussion identifies
factors that may contribute to the in-creased
occurrence and intensity of
floods in Arizona. Also important to
examine are the effects of various
geologic and climatic variables that in-fluence
the type of floods experienced
in the area. Because of such variables,
flooding in Arizona differs from flood-ing
in more humid regions of the
United States. Sometimes overlooked,
this is a theme with relevance to many
areas of flood concern in Arizona.
Generally, erosion and inundation
create the hazards associated with
flooding, in whatever region flooding
occurs. With its usually dry riverbeds
and arroyos and minimal vegetation,
however, Arizona is especially prone
to the effects of erosion. Floodwaters,
usually of high velocity and with a
high concentration of runoff, scour
stream channels that then shift and
change. Lateral bank erosion may
move a river channel as far as 800
feet. Land collapses, with resulting
serious property damages and loss of
land. Much of the estimated $226.5
million in damages caused by the Oc-tober
1983 floods in southeastern
Arizona resulted from bank erosion,
as farmlands were lost and in urban
areas buildings toppled with collaps-ing
stream channels.
A different situation prevails in
humid areas. River channels are likely
to already be carrying flow that
gradually increases as flood condi-tions
develop. With riverbeds
anchored by vegetation, channels are
more stable, and less erosion occurs.
As a result, overbanking is likely, as
water inundates land areas in
proximity to the river, creating the
classic scene of buildings and proper-ty
riding the crest of a flood.
Flood Control: Structural
and Nonstructu rai
Flood
control refers to various
strategies meant to reduce and,
if possible, eliminate the hazards of
floods. Before discussing the topic,
however, a note of caution is ap-propriate.
Mimbres pottery design offrog.
UA geoscientist Vic Baker, who
studies the nature, causes and effects
of floods, questions whether the term
"flood control" is truly appropriate.
He explains that flood control is
based on anticipated flood events.
These events will eventually be ex-ceeded
by larger floods that are dif-ficult
to anticipate and impossible to
control with a reasonable expenditure
of funds. As a result, Baker stresses
that flood control in reality is a degree
of flood protection and that people
should not be led to believe that
floods are controllable.
Different philosophies guide
flood control strategies. Once thought
to be a nuisance, stormwater was con-sidered
best managed and controlled
if made to flow from an area ex-peditiously.
To widen, straighten, and
channelize were the prefered strate-gies
to rid an area of floodwaters.
Such methods are considered struc-tural
since they basically consist of
physical modifications to adjust and
change the flow of floodwaters. Struc-turai
methods include such measures
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as levees, floodwalls, channel improve-ments,
and storage reservoirs.
The reliance on structural
measures, which formed the guiding
strategy of flood control for many
years, has been widely criticized.
Critics have questioned the effective-ness
of structural methods to mitigate
the adverse impacts of flood losses on
the individual and community. For ex-ample,
by directing and facilitating
the flow of runoff, structural
measures tend to increase the volume
and velocity of a flood. As a result,
more runoff flows with greater force,
resulting in increased erosion of
downstream banks and, therefore,
greater flood damage.
Also, with an increased concern
about the environment, a wariness has
developed about the physical changes
or modifications that result from
structural methods. Jeff Zauderer, a
researcher with the UA Office of
Arid Lands Studies, has studied the
beneficial effects of flooding and cau-tions
that such benefits can be lost
through structural flood-control
measures. For example, floodplain
riparian vegetation acts to disperse
flood velocity and, as a result, water
retention and infiltration is increased.
These benefits are lost if vegetation is
removed and channels are straight-ened
and lined.
Zauderer also explains that floods
of differing magnitudes structure the
riparian habitat canopy. Such structur-ing
occurs when floods with various
velocities scour surfaces at different
levels. The exposed surfaces provide
new growth opportunities at differen-tial
growth rates. The varied canopy
that results supports a greater diver-sity
of fauna in the area.
Also, along with such ecological
concerns, an aesthetic consideration
contributes to a skeptism about struc-tural
methods. It is likely that most
people would consider a natural
riverbed as considerably more attrac-tive
than a concrete-lined channel.
As a result of the above con-
cerns - many of which are now the
focus of political debate - flood-con-trol
strategies have been developed to
rely on nonstructural methods. Such
methods avoid a physical modifica-tion
of the environment and work to
maintain the natural conditions of
river channels. Nonstructural
measures generally encourage society
to adapt to natural flood conditions
when occupying or modifying a
floodplain. Various nonstructural
measures are described below.
Zoning and other land-use require-ments.
Zoning for floodplains is used
to set special standards for land uses
in flood hazard areas. Zoning regula-tions
include specifications about the
use of structures and land, the height
and bulk of structures, and the size of
lots and density of use. Other land-use
requirements might include such
stipulations as locating fences to
avoid a backup of debris during flood-ing
and specific placement of septic
tanks and sanitary sewer systems.
Acquisition programs. Acquisition
programs can set aside flood-prone
lands in two ways. Land is purchased
outright or control is purchased
through easements or development
rights to preclude future uses incom-patible
with floodplain management
programs. Acquisition is the most
widely used nonstructural alternative
Flood forecasting. Authorized by
Congress to issue flood forecast and
warnings, the National Weather Ser-vice
collects data in Arizona to send
to the Colorado Basin River Forecast
Center in Salt Lake City. The center
generates a forecast that is then
adapted by the National Weather Ser-vice
for local use. The Arizona
Department of Water Resources col-laborates
with the weather service in
this effort.
A technological flood-warning sys-tem
called ALERT also provides
flood forecasting. Rain gauges and
streamfiow gauges are positioned in
flash-flood-prone watersheds. When
it rains or streams rise, data are auto-matically
radioed to local officials.
Pima and Maricopa Counties have ex-tensive
ALERT systems, and other
Arizona counties have plans to imple-ment
it.
To base a flood forecast on
ALERT information, however, the
complex relationship between rainfall
and streamilow must be understood.
Although mathematical rainfall-runoff
models are available to calcu-late
this relationship, there is concern
that most models are not suited for
the arid conditions of southern
Arizona.
Soroosh Sorooshian, professor
and head of the UA Hydrology and
Water Resourcts Department, and
Jene Hendrickson, graduate student
of hydrology, are addressing this con-cern.
They are studying a model,
KINEROS, which was developed by
the Agricultural Research Service for
arid conditions, to determine how ac-curately
flash floods can be fore-casted
and how forecast accuracy can
be improved.
A concern is that thunderstorms
that cause flash floods are so local-ized
or spotty that even relatively
dense rain-gauge networks can miss
the high intensity center of the storm.
Sorooshian and Hendrickson will use
KJNEROS with information from the
Walnut Gulch Experimental Water-shed
near Tombstone to determine
the extent of forecast error attri-butable
to point sampling of spatially
variable rainfall.
Information and education. To
properly manage flooding, it is critical
that policymakers, the public, and
other concerned groups and in-dividuals
have access to various kinds
of flood hazard information. Federal,
state, and local agencies and private
consultants are sources of informa-tion
on topics that range from the
hydraulics of various size floods on
areas subject to inundation to advice
on how to get flood insurance.
Other strategies that are con-sidered
nonstructural include disas-
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ter preparedness and assistance, warn-ing
systems, evacuation, flood in-surance,
and floodproofing.
The above discussion is not meant
to imply that a dividing line necessari-ly
separates those who favor nonstruc-tural
measures from those who are for
structural methods. Rather than a
structural versus nonstructural
dichotomy, some believe a more basic
controversy exists between those who
would modify stream channels, usual-ly
with such structural methods as con-creting
and soil cementing to stabilize
banks, and those who advocate leav-ing
river channels natural. The latter
group might support structural
measures if, through their use, they
enable the natural conditions of river
channels to be retained. For example,
retention and detention basins, which
rely on both structural and nonstruc-tural
strategies, control runoff and
enable river channels to flow natural-ly.
A detention basin collects and
stores stormwater runoff for release
at a controlled rate. A retention basin
retains collected stormwater, usually
for evaporation or infiltration into the
subsurface. By temporarily storing
water, detention measures extend the
period of runoff, with the result of
reducing the volume and flood peak.
As a result, runoff can flow with less
hazard to the natural streambed, if
sufficient retention facilities are in
use. At the same time, infiltration is
increased by the storage of runoff,
whether through retention or deten-tion.
Retention/detention facilities are
being incorporated into various new
developments, with such facilities
often required by city and county or-dinances.
Rillito Creek Project
Although
retention/detention
basins have been primarily
used to control floods, other uses for
them have also been proposed. A mal-
tiple-use concept has been con-sidered,
with artificial recharge and
recreation to be added to flood con-trol
as goals of retention/detention
basins. To combine flood control with
artificial recharge, however, requires
technical and institutional coordina-tion,
a commitment that is often a
challenge to the ways of traditional
water management.
The Rillito Creek Project is a
plan to test the multiple-use concept.
A cooperative endeavor, the project
is an effort to determine the econ-omic,
institutional, and technical
feasibility of recharging floodwaters.
The project involves coordination
among the Arizona Department of
Water Resources' Tucson Active
Management Area, Tucson Water,
and Pima County Flood Control Dis-trict.
Designed as a research and
demonstration project, the operation
will be Arizona's first large-scale
recharge facility of stormwater runoff.
The rationale behind the project
is direct and simple. Rainfall from
storms becomes runoff that flows in
streams and washes. If the runoff is
diverted off-channel into sedimenta-tion
and recharge basins, water that
would otherwise flow downstream
could be infiltrated into the ground.
Two beneficial results would be
achieved: floodwaters would be con-trolled,
and depleted groundwater
resources would be replenished. The
potential to recharge controlled
source waters, such as effluent and
CAP water, is also to be evaluated.
Additionally, various recreational
and environmental benefits are ex-pected
to accrue. Recreational areas
are to be created at the recharge site,
and natural floodplain habitat main-tained.
California has been recharging
stormwater for over 30 years. The
California projects, however, re-charge
drainages from flows regu-lated
by upstream dams or detention
structures. The Rillito project is uni-que
since it is concerned with runoff
unregulated by upstream detention
structures and would recharge flow
from a creek subject to flash flooding.
Not all water managers, however,
are committed to the concept of artifi-cial
recharge of stormwater runoff.
Some argue that it is the rare flood
eventthe 25-, 50-, or 100-year
flood - that actually leaves a basin.
They claim that such events do not jus-tify
the expenditures for a regional
recharge facility, and the other more
frequent types of runoff recharge
naturally. Among such critics are
some who feel that the only suitable
location to justify an artificial
recharge facility for storm water
runoff would be at well locations
where drawdown is to be augmented.
Regional groundwater recharge
projects are argued to be issues of
more political than technical sig-nificance
since the concept has grass-roots
appeal.
Mimbres potreiy design of swimming
turtle.
Floodplain Management
Floodplain
management is a com-ponent
of flood control and is
concerned with land areas subject to
flooding. Relying mainly on nonstruc-tural
measures, floodplain manage-ment
generally has two goals: the
protection and maintenance of
natural floodplain values and the
reduction of existing and future flood
loss potential. The concept of
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floodplain management can be
variously interpreted.
Some natural resource managers
stress that floods, although now in-fluenced
by human activites, are
natural and often beneficial occurren-ces,
neither bad nor dangerous. It is
when floods threaten human life and
property that they are perceived to be
an intimidating menance to be con-fronted
with administrative and tech-nical
ingenuity. This view implies a
shift in a popular perception of
floodplain management. Floodplain
management might now be seen as
less of a defensive strategy against an
impending hazard and more as a
response to human carelessness and
lack of foresight in building and resid-ing
on floodplains.
The federal government has a fun-damental
interest in how the nation's
floodplains are used and managed.
Concerned with the urbanization of
floodplains, the federal government
sought to formulate an effective
floodplain management policy. Dis-couraged
by early efforts to engineer
flood-protection projects, Congress
passed the National Flood Insurance
Act of 1968. The act established a na-tional
flood-insurance fund to provide
an alternative to expensive disaster
relief from the federal government.
Further, the act determined that a
flood insurance program would be
contingent upon a unified national
floodplain management program. A
floodplain was defined as an area sub-ject
to a one-percent chance of flood
inundation in any given year or, as it
came to be known, a 100-year flood.
Congress passed the 1973 Flood
Disaster Protection Act to stem the
continued urbanization of floodplains.
Local communities were now re-quired
to participate in a flood in-surance
program. Further, such com-munities
needed to adopt adequate
floodplain management ordinances to
be eligible for such federal support as
federal flood insurance, federal loans
for floodplain property, and federal
disaster relief in the aftermath of a
flood. Local communities were also
required to develop hydraulic studies
of major watercourses to delineate
flood zones. The ordinances, which
are submitted for approval to the
Federal Emergency Management
Agency, restrict development within
these zones depending upon flood
risks.
Thus encouraged, local com-munities
worked to develop
floodplain management plans. Their
efforts were guided by the definition
of a floodplain that was established by
the 1973 act. To ensure national
uniformity, the act retained the defmi-tion
of a regulatory floodplain as an
area inundated by a 100-year flood.
Federal legislation basically estab-lished
a regulatory framework but left
local communities the freedom to
develop ordinances that best fit their
specific conditions and needs.
Various factors - social, political,
technical and geological - determine
what floodplain ordinances a com-munity
adopts. For example, com-munities
may adopt different ordinan-ces
depending upon the extent to
which they stress development and/or
environmental values. Maximum
development might benefit from mas-sive
channelization, bank protection
and dams A community that focuses
more on environmental values might
emphasize preservation, as well as a
reliance on restrictive policies toward
floodplain development.
Already a complex task, the
development of floodplain ordinances
further challenges policymakers when
premises basic to federal floodplain
management regulations are ques-tioned.
A common concern is whether
certain premises are relevant to situa-tions
in the semiarid Southwest. For
example, some researchers claim that
the 100-year floodplain, a designation
of central importance in federal
regulations, is not as readily
delineated in the Southwest as in
more humid areas. This is because the
analyses to determine the level of a
100-year flood generally assume a de-gree
of stability in channel boundaries
that is not characteristic of the South-west.
In this region it is possible for
erosion to alter river channels Sig-nificantly.
Also, concern is expressed that
federal floodplain management
regulations do not sufficiently acknow-ledge
the hazards that result from fre-quent
channel-bank erosion. In al-luvial,
ephemeral-stream systems
throughout the Southwest extensive
erosion can occur without the action
of unusual floodwaters and in areas
not designated as 100-year flood-plains.
Federal regulations do not en-sure
that residents of such areas are
adequately cautioned or protected.
Along with the federal govern-ment
and local communities, the state
also has a role in floodplain manage-ment.
The Arizona Department of
Water Resources (ADWR) is the
state coordinator for the National
Flood Insurance Program (NFIP). As
a result, ADWR is involved in such ac-tivities
as assisting communities to
adopt ordinances and to qualify for
NFIP; establishing state floodplain
management standards; implementing
flood hazard mitigation measures;
and notifying the Federal Emergency
Management Agency of community
failures in floodplain management.
Arizona Cities and County
Flood Control Districts
Both
county flood control dis-tricts
and local communities are
involved in flood control and the
development of floodplain ordinan-ces.
Established by state statute in
1978, county flood control districts
are to reduce the risk of flood loss,
minimize the impact of floods on
human safety, health, and welfare and
restore and preserve the natural and
beneficial values served by
floodplains. Established as political
taxing subdivisions of the state, dis-
6
tricts have the power to tax to support
flood-control projects. Their areas of
jurisdiction may include incorporated
and unincorporated areas.
Legislation allows an incor-porated
city or town within a county
to assume responsibility for its
floodplain management. For example,
Tucson maintains its own floodplain
management program in Pima County
as do Phoenix, Scottsdale, and Tempe
in Maricopa County, and Flagstaff in
Coconino County. The districts how-ever
support flood-control projects
throughout their areas of jurisdiction,
including incorporated areas which
have retained flood plain manage-ment
responsibilities.
The arrangement has the poten-tial
for conflict. Incorporated areas
with dense populations, such as
Scottsdale, Phoenix, and Tucson, have
expressed concern that, although they
make a significant tax contribution to
the districts, they do not necessarily
receive a proportional return of flood-control
services and projects. For ex-ample,
some Tucson city officials
believe the areas that benefit most
from the tax are mainly along major
rivers, often outside city limits, with
local stormwater drainage projects
within the city neglected by the dis-trict.
Districts respond by saying that
they take a more regional view than
does a city. If viewed in this broader
context, the purchase of flood-prone
land upstream of a city does in fact
benefit the city. If such land is
preserved in a natural state, chan-nelization
and encroachment will be
reduced; thus reducing peak dischar-ges
and flow events in the city.
In an attempt to avoid or mitigate
conifict between city and county, the
Maricopa Flood Control District es-tablished
a Citizen's Flood Control
Advisory Board, with the Phoenix city
engineer as a member. By law such a
board can be established only in coun-ties
with a population of one million
or more.
The Tucson Stormwater
Management Study
TheTucson Stormwater Manage-ment
Study is being developed
partly in response to current arrange-ments
that separate stormwater
management along political boun-daries,
with responsibilities divided
between the city of Tucson and Pima
County Flood Control District. The
study is to develop a comprehensive
stormwater management plan. The
plan is to have a regional, watershed
focus. Along with seeking technical
solutions to problems, the drainage
plan intends to work out institutional
arrangements to facilitate comprehen-sive
stormwater management, possib-ly
even consolidating city and county
efforts in this area.
Encompassing the flow of runoff
within an area, a watershed is a
hydrologically appropriate unit to
determine the management of
stormwater. Under present arrange-ments,
however, stormwater runoff
within a watershed may flow through
separate jurisdictions, managed by dif-ferent
criteria. As a result, land use
policies upstream may not be coor-dinated
with the principles for manag-ing
stormwater runoff downstream. A
comprehensive program covering an
entire watershed would provide a
much more favorable basis to plan
present and future runoff manage-ment
needs.
Phase one of the Tucson study is
complete. This phase included a
division of the urbanized area into six
mai or watersheds. Characteristics of
each watershed were described,
problems defined, and methods to
solve problems identified. Also part
of phase one was an institutional and
financial assessment between the two
governing bodies: the city of Tucson
and Pima County Flood Control Dis-trict.
Phase two, which is expected to
last about 18 months, includes
developing a pilot drainage-basin
master plan for one of the basins iden-tified
in phase one, as well as develop-ing
specific strategies for implement-ing
an equitable fmancing plan and in-tergovernmental
arrangements.
A regional approach to storm-water
management is currently
favored by many water managers.
Pima and Maricopa County Flood
Control Districts and the city of Scot-tdale
have been involved with regional
projects. Tucson's study, however,
purports to be a more comprehensive
effort, involving both institutional and
technical considerations.
Conclusion
Flooding
is a recurrent event in
the natural history of Arizona.
Scientists involved with paleoflood
hydrology, which is the study of past
or ancient flows, have determined
that extraordinary large floods have
occurred in Arizona during the past
few millenia. Distant in time, such
events are generally studied as natural
occurrences.
Floods continue today, with in-creases
in occurrence and intensity
Amyo is published quart by
Arizona Department of Environ-mental
Quality
2005 North Central
Phoenix, AZ 85004
(602) 257-2306
Arizona Department of Water
Resources
15 South 15th Avenue
Phoenix, AZ 85007
(602) 255-1554
Arizona State Land Department
1616 West Adams
Phoenix AZ 85007
(602) 542-3500
7
during the last 25 years in southern
Arizona. Although still studied as
natural events, floods are now also the
concern of policymakers and others
who must deal with the destruction
and social dislocation caused by flood-ing.
A major change has obviously oc-curred
between the paleoflood events
and modern floods. Humans have in-creased
and established centers of
population in areas affected by floods.
At issue, therefore, is developing
public policy that will enable humans
to cope with flooding. The options
available to policymakers can be sum-marized
in two questions. To what ex-tent
can and should floods be control-led?
And, to what extent can humans
be guided and prevented from actions
that expose them to the hazards of
flooding? Not mutually exclusive ques-tions,
some ground for interpretation
exists, although policymakers have
been giving more attention lately to
the latter question.
That an effective flood strategy
evolves is an issue of special impor-tance,
if, as some evidence seems to
indicate, climatic changes are occur-ring.
Floods might be an even more
prominent concern in the future.
Office of Arid Land Studies
Cnllege of Agriculture
University of Arizona
845 North Park
Tucson, AZ 85719
(602) 621-1955
Water Resources Research Center
College of Engineering and Mines
University of Arizona
Tucson, AZ 85fl1
(602)621-7607
Address comments to:
Joe Gelt, Editor/Writer
Water Resources Research Center
Geology Building, Room 314
University of Arizona
Tucson, AZ 85721
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