Percentage of Surface Drinking Water from Intermittent,
Ephemeral, and Headwater Streams in Idaho
N
+
Coeur d'Alene
Salmon
Pocatello
Legend: This map highlights regional patterns of
dependence on intermittent, ephemeral, and
headwater streams for surface drinking water in
Idaho. In Idaho, 8,043 total miles of streams
provide water for surface water intakes supplying
public drinking water systems; of this, 4,816
miles, or 60%, are intermittent, ephemeral, or
headwater streams. Over 250,000 people in Idaho
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 4 th Quarter 2006 Data.
Key:
Intermittent, ephemeral, and
headwater stream miles as
percentage of total stream
miles contained in all SPAs
for a given county
45% - 56%
57% - 69%
70% - 86%
87% - 100%
No Data
240
3 Miles

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