ETL 1110-2-540
30 Sep 96
Figure 4-2. Relative accuracy raingage network
a gage network will generally require a downward
Terrain slope and orographic effects
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revision of the initial estimate of the number of
gages. Example costs of flood warning - prepared-
Potential usefulness for other purposes
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ness plan components for a typical ALERT type
system are shown in Appendix E. The location of
Location of existing gages
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the rain gages, described below, will likely further
modify the selected number of gages.
Gage redundancy
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(b) Location of raingages. Once the number of gages
Necessity for monitoring storms before the reach the
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needed is estimated, the location of the gages is determined.
watershed - (When warning times are very short, it
The initial estimate of the number of raingages based on
may be desirable to sample storms before they reach
watershed size and rainfall variability will normally be revised
the watershed. In this case, it may be prudent to
based on gage location. The following factors should be
locate gages outside the watershed. Due consid-
considered when determining the location of raingages.
eration for the likely tracking of storms across the
area is important in determining the location.)
Hydrologic engineering judgement, knowledge of
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storm and rainfall-runoff characteristics
Appendix C provides additional information on raingage
siting as related to gage exposure (NWS 1972).
Requirements of line-of-sight radio telemetry to base
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station
(c) Types of raingages. The most common gages
measure rain by volume or weight. The most popular rain
Gage accessibility for maintenance and potential for
measurement device for automated measurement and
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vandalism at the site
detection systems used for flood warning is the "tipping
4-4
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