FLOOD10216

• County: Statewide
• Basin: Statewide
• Title: Method for Estimating the Magnitude and Frequency of Floods at Ungaged Sites on Unregulated Rural Streams in Iowa
• Date: 1/1/1987
• Prepared For: State of Iowa
• Prepared By: USGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

Hvdrolo2ic Re2ion 1

Hydrologic region 1 (fig. 1) extends north and south along the bluffs
that border the Missouri River valley, with limits approximating those of
the physiographic area known as the Western Loess Hills (Prior, 1976). The
landscape has a corrugated appearance of alternating waves and troughs.
Hills are sharp-featured, with narrow broken ridge-crests. intersecting
spurs, and steep-sided slopes; the landscape is conducive to rapid runoff.
The western border of the region is well defined and easily distinguished
on topographic maps and in the field. The eastern border is more difficult
to define and merges gradually with the landscape of hydrologic region 2.

Hvdrolo2ic Re2ion 2

The bluff area that borders the Mississippi River valley is typical of
the landscape in hydrologic region 2 (fig. 1). The landscape can vary
from rugged to rolling topography, where runoff may be rapid, commonly
causing flash flooding. Bluff-like areas are not only located in the
vicinity of the Missisippi River, they also are present along the divide
between the Mississippi River and Missouri River basins; in parts of the
Iowa and Cedar River basins, in areas that border the Western Loess Hills,
and in the headwater parts of basins of streams in south-central Iowa.

Hvdrolo2ic Re2ion 3

Hydrologic region 3 is the largest hydrologic region (fig. 1). Most
of the area in this region is typical of landscapes in Iowa. The
topography of this region can be described as steeply to gently rolling
hills interspersed with areas of more subdued topography. The area has a
well-established drainage system. Physiographically, it covers most of the
Iowan Surface, a large part of the Southern Iowa Drift Plain, and the
Northwest Iowa Plains (Prior, 1976).

Hvdrolo2ic Re2ion 4

This hydrologic region, which is located in west-central Iowa (fig.
1), is characterized by level terrain and a poorly developed drainage
system. The region coincides approximately with the southern two-thirds of
the Des Moines Lobe (Prior, 1976). Many clusters of ponds and marshes with
no drainage outlets are present in this region. Small streams in level
areas are shallow and sluggish.

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