VOLUMES OF RECENT FLOODS AND POTENTIAL FOR STORAGE IN
UPLAND WATERSHED AREAS.

Robert Buchmiller 1 and Andrew Manale2
1U.S. Geological Survey,400 South Clinton St., Iowa City, Iowa 52244,  2U.S.
Environmental Protection Agency, 401 M Street SW, Washington, DC. 20460

Substantial flooding at various locations throughout the United States,
particularly during and after the Great Midwest Flood of 1993, resulted in large
disaster payments from both public and private sector institutions. The financial
impact of these floods has increased the discussion of alternative flood mitigation
methods that rely on non-structural approaches or approaches that do not require
expenditures of new capital. During the autumn of 1997, the U.S. Geological
Survey, in cooperation with the U.S. Environmental Protection Agency, began an
investigation to determine the volume of water associated with recent flood
events in the Midwest and a preliminary evaluation of the potential areas for
storage of floodwaters within the watersheds where flooding occurred. Flood
volumes for 11 flood events that occurred between 1990 and 1993 in eight
watersheds in Iowa are presented. Flood volumes greater than the respective
recurrence-interval discharges for these events are totaled for discharges above
the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year floods. A Geographic
Information System (GIS) analysis of watershed land-surface elevation and
topography was used to identify potential upland areas within each watershed
where floodwater might be stored. The volume of upland storage was estimated
by assuming various depths of inundation within the identified storage areas.
Comparison of estimated potential flood-storage-area volumes with computed
flood event volumes indicates that areas with less than 2.5% land-surface slope
and an inundation depth of 1 foot would contain the hypothetical 10-year
recurrence interval excess flood volumes for 7 of the 11 flood events analyzed.
Increasing the estimated potential flood-storage-area volumes to include areas
with less than 5% land-surface slope and inundated to a 2-foot depth would
contain the hypothetical 10-year recurrence interval excess volume for all 11
flood events analyzed. This preliminary study did not address the hydraulics of
reducing flooding by storing excess water in upland areas.

Keywords: flooding, flood storage, Geographic Information System


Robert Buchmiller, USGS, P.O. Box 1230, Iowa City, IA 52244 (319)337-4191 
rcbuchmi@usgs.gov FAX(319)358-3606 

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