WATER RESOURCES RESEARCH GRANT PROPOSAL
Paleohydrological and Hydroclimatological Analysis of the
Magnitude and Frequency of Large Floods in the Verde River Basin, Central
Arizona
Submitted to: The Regional Water Resources Competitive
Grants Program, Western Region
Duration of project: 24 months, beginning September 30,
1996
Federal funds requested: $84,604
Non-federal funds pledged: $169,331
Principal Investigator(s): S.G. Wells, V. R. Baker, P. K. House, P.A. Pearthree
1. Quaternary Sciences Center, Desert Research Institute, P.O. Box 60220,
Reno, NV 89506
2. Department of Geosciences, University of Arizona, Tucson, AZ 85721
3. Arizona Geological Survey, 416 W. Congress St., #100,
Tucson, AZ 85701
Congressional district: Nevada 02
Statement of Problem
Spatial and temporal variations in the magnitude and
frequency of large floods in the southwestern United States are strongly
influenced by hydroclimatic variability. Large floods in most large river
basins in the region result almost exclusively from regional-scale
extratropical and/or tropical weather systems. The spatial and temporal
distribution of these storm types are strongly influenced by persistent,
anomalous patterns in hemispheric to global-scale atmospheric and oceanic circulation.
Short- and long-term variability in flood frequency in this region are thus
good indicators of variability in the larger-scale climatic phenomena over
similar time scales. Flood runoff processes from flood-producing storms in
individual basins in semi-arid and arid portions of the western U.S. can also
vary significantly over space and time. This is often the case for large river
basins that integrate areas of strikingly diverse physiography ranging from
extensive, high elevation forested areas to rugged, low elevation desert areas.
The resulting complex characteristics of individual flood events coupled with
the variability in their occurrence induced by larger-scale hydroclimatic
controls present unique challenges to water resource management and flood
control practices in the region. The relatively short lengths of stream gage
records in the Southwest preclude attempts to evaluate effects of these
hydrologic and climatic phenomena on flood magnitude and frequency over time
scales greater than about 100 years. A comprehensive study of the paleoflood
hydrology and flood hydroclimatology of an individual, regionally significant
river basin would constitute a valuable contribution towards greater
understanding of the implications of hydrologic and hydroclimatic variability
for water resources management and flood control in the western U.S.
We propose to study the influence of hydroclimatic
variability on flood magnitude and frequency in the Verde River basin of
central Arizona (total area approx. 15,000 km2) over a period of
time extending beyond the historical record by 100s to 1000s of years using
techniques of paleoflood hydrology and flood hydroclimatology. The Verde River
is chosen as an excellent representative for large basins throughout the
southwestern U.S. because its flood regime is sensitive to hydroclimatic
variability, it has an extensive gage network with fairly long records, it has
several excellent sites for paleoflood studies, and it was affected by extreme
floods in 1993 for which a wealth of hydrological and meteorological data
exist. The largest floods on the Verde River have occurred as a result of
anomalous winter atmospheric circulation patterns but dissipating tropical
storms have resulted in large floods on many of its tributaries. Flood runoff
in the basin during individual events can be highly variable in space and time
such that similar hydroclimatic circumstances can result in floods of
significantly different magnitudes. We will examine links between hydroclimatic
phenomena and the gaged and historical record of large floods on the mainstem
of the Verde River and its gaged tributaries. We will characterize the
hydrologic response of the entire basin to a variety of flood producing
hydroclimatic scenarios and will greatly augment the length of the flood record
by conducting paleoflood investigations at several key sites near gages. The
paleoflood studies will provide real, accurate data on extreme floods,
extending the record of flooding at individual sites by 100s to 1000s of years.
Results from the paleoflood studies will be used to infer trends in climatic
variability over the associated time scales through comparisons with strong
climate-flood linkages apparent in the modern and historical records. The study
will take advantage of recent, important advances in paleoflood research,
including refinements in flood frequency analysis with paleoflood data and
quantification of paleoflood discharge-modeling uncertainties, to establish
significantly improved flood frequency relations at each gaging station on the
Verde River.
Anticipated Results and Benefits of Research
The proposed research will provide real data on extreme
floods that are critical of evaluating the magnitude and frequency of flooding
in the Verde River basin central Arizona over at least the last 1000 years. A
combined analysis of the modern and historical flood data with the paleoflood
data will allow us to characterize the hydrological response of the Verde River
basin to individual extreme events and to the variability of large-scale
flood-producing hydroclimatic phenomena. This will improve the understanding of
flood hydrology and flood magnitude-frequency characteristics in the
southwestern U.S. The research methods that will be employed can serve as
models for similar studies in other regions. A principal goal of the project is
to augment data from previous paleoflood studies in the basin by describing
newly identified sites with longer and better preserved records and estimating
corresponding flood magnitudes. Important contributions from the project will
include substantial improvements in flood frequency estimates for each gaging
station on the river and estimates of the largest magnitude floods at each site
during the last 1000 years or more. Detailed analyses of the flood
hydroclimatology of the basin and its principal constituent sub-basins will be
performed to evaluate the hydroclimatic context of the largest floods and how
it may vary in relation to basin scale. The flood-climate relations characteristic
of the modern and historical records will serve as analogs for the paleoflood
record. The hydroclimatic analysis will help further the understanding of the
underlying physical basis for the observed characteristics of the flood series
in the modern, historical, and paleoflood records.
This study of the Verde River basin will relate paleoflood information and associated evidence of hydroclimatic variability to conventional practice in river basin management involving issues of flood-frequency forecasting, and long-term planning. The results will be useful for flood control and water supply management on the Verde River, an important sources of municipal and agricultural water supply for metropolitan Phoenix and surrounding rural areas. The research strategy that we will employ will be applicable to other large drainage basins in the western U.S. Water supply management and flood control strategies in the region will benefit from improved flood-frequency assessments and increased understanding of the effect of global climate variability on flood characteristics. Understanding of linkages between climate and floods will improve the ability of water-supply managers to foresee the local and regional consequences of hemispheric to global scale climatic phenomena, an important component of long-term planning in the face of uncertain future climatic characteristics. Additionally, realistic characterizations of the largest floods that have occurred on each stream in the past several 100s to 1000s of years provide a basis for estimating the maximum flood potential of each stream. This information has particular relevance to theoretical models of extreme flood runoff such as probable maximum flood (PMF) estimation. Information about extreme floods based on the analysis of evidence for the largest known floods in a given river basin has critical importance for evaluating safety issues involving dams built for multi-use objectives, notably hydropower and irrigation prior to the recognition of long-term variability in flood magnitude and frequency. Because of the potential high cost of remediation, information about the most extreme flood phenomena is critical for sound management decisions.
U.S. Department of the Interior, U.S. Geological Survey
URL: http://water.usgs.gov/wrri/96grants/wr3nv.htm
Maintained by: John Schefter
Last Updated:
Wednesday March 23, 2005 9:17 AM
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