Gage Gap Analysis (View)

<p>This layer shows California flowlines and their status with
respect to stream gage coverage.<span>  </span>The
Gage Gap Analysis is part of the <a href='https://www.waterboards.ca.gov/waterrights/water_issues/programs/stream_gaging_plan/' rel='nofollow ugc'>Senate
Bill 19 Stream Gaging Plan</a>, which seeks to identify and prioritize areas
for additional stream gaging efforts.<span>  </span>The
<a href='https://gispublic.waterboards.ca.gov/portal/home/item.html?id=32dfb85bd2744487affe6e3475190093&amp;view=table&amp;sortOrder=desc&amp;sortField=defaultFSOrder#overview' rel='nofollow ugc'>stream
gage dataset</a> is a snapshot of gages from the fall of 2020, consisting only
of USGS and CDEC gages.<span>  </span>The flowlines dataset
is based on the <a href='https://www.epa.gov/waterdata/get-nhdplus-national-hydrography-dataset-plus-data' rel='nofollow ugc'>National
Hydrography Dataset (NHD) Medium Resolution Version 2.1</a> and associated <a href='https://www.usgs.gov/national-hydrography/value-added-attributes-vaas' rel='nofollow ugc'>Value-Added
Attributes</a>.<span>  </span>Modifications include
adding and removing attributes from the base dataset and filtering to remove flowlines
that lack information on upstream drainage area, nearly all infrastructure and
coastline flowlines, and flowlines under large waterbodies.<span>  </span>Finally, attributes that designate the gage
coverage and gap status (Gage Gap Analysis) were added to every flowline. <span> </span>A flowline is considered covered (or gaged) if
its upstream drainage area is greater than 50% and less than 150% of a stream
gage as a stream gage directly downstream or upstream.</p><p><b>Data Dictionary:</b></p><table border='0' cellpadding='0' cellspacing='0' style='border-collapse:collapse; width:576pt;' width='767'><tbody><tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; width:110pt;' width='146'><u>Field
Name</u></td>
<td style='border-left:none; width:48pt;' width='64'><u>Range</u></td>
<td style='border-left:none; width:418pt;' width='557'><u>Description</u></td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>comid</td>
<td style='border-top:none; border-left:none;'> </td>
<td style='border-top:none; border-left:none;'>Common identifier of
an NHDFlowline feature</td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>gagegap_status</td>
<td style='border-top:none; border-left:none;'> </td>
<td style='border-top:none; border-left:none;'>indicates if the
stream segment is well-gaged, almost well-gaged, inactive gage, or never
gaged </td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>gage_comid</td>
<td style='border-top:none; border-left:none;'> </td>
<td style='border-top:none; border-left:none;'>comid of the gage
that covers this steam segment (if any)</td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>site_id</td>
<td style='border-top:none; border-left:none;'> </td>
<td style='border-top:none; border-left:none;'>site_id of the gage
that covers this steam segment (if any)</td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>drainage_area_sqkm</td>
<td style='border-top:none; border-left:none;'> </td>
<td style='border-top:none; border-left:none;'>drainage area
upstream of this stream segment, in sqkm</td>
</tr>
<tr height='20' style='height:15.0pt;'>
<td height='20' style='height:15.0pt; border-top:none;'>stream order</td>
<td style='border-top:none; border-left:none;'>0 - 9</td>
<td style='border-top:none; border-left:none;'><a href='https://en.wikipedia.org/wiki/Strahler_number#River_networks' rel='nofollow ugc'>Modified
Strahler Stream Order</a></td>
</tr></tbody></table>