Percentage of Surface Drinking Water from Intermittent,
Ephemeral, and Headwater Streams in Illinois

Key:

Intermittent, ephemeral, and
headwater stream miles as
percentage of total stream
miles contained in all SPAs
for a given county

~	0.01% - 44%

~	45% - 56%

~	57% - 69%
70% - 86%
87%-100%

^ No Data

Legend: This map highlights
regional patterns of
dependence on intermittent,
ephemeral, and headwater
streams for surface drinking
water in Illinois. In Illinois,
9,894 total miles of streams
provide water for surface water
intakes supplying public
drinking water systems; of this,
5,688 miles, or 57%, are
intermittent, ephemeral, or
headwater streams. Over 1.6
million people in Illinois
receive drinking water from
public drinking water systems
that rely at least in part on
intermittent, ephemeral, or
headwater streams. This
analysis compared the stream
length of intermittent,
ephemeral, and headwater
streams to total stream length
within all mapped Source
Protection Areas (SPAs) for
each county. A SPA is an area
upstream from a drinking water
source or intake that
contributes surface water flow
to the drinking water intake
during a 24-hour period. This is
based on data that generally do
not include streams less than
one mile in length. Intermittent
streams are streams containing
water for only part of the year.
Ephemeral streams flow in
response to precipitation
events. First-order streams have
been used to represent
headwater streams.

Data Sources: National
Hydrography Dataset Plus at
medium resolution; Federal
Safe Drinking Water
Information System 4th Quarter
2006 Data.

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