The following words or phrases have the following meanings
in this subchapter unless the context clearly indicates otherwise:
(1) Average condition--for all measurement points,
the hydrologic condition that would occur approximately 50% of the
time.
(2) Climatic division--a geographic area defined by
the National Weather Service.
(3) Dry condition--for all measurement points, the
hydrologic condition that would occur approximately 25% of the time
and that is intended to represent the driest periods.
(4) Lower Basin--the geographic area of the Brazos
River Basin which includes all watersheds below Lake Whitney Dam,
and the San Bernard River and coastal watersheds, and which is defined
for the purpose of calculating hydrologic conditions as described
in §298.470 of this title (relating to Calculation of Hydrologic
Conditions).
(5) Middle Basin--the geographic area of the Brazos
River Basin which includes all watersheds draining into the Brazos
River and its tributaries downstream of Possum Kingdom Dam and upstream
of Lake Whitney Dam, and which is defined for the purpose of calculating
hydrologic conditions as described in §298.470 of this title
(relating to Calculation of Hydrologic Conditions).
(6) PHDI--the Palmer Hydrological Drought Index, based
on a scale from -6.0 to 6.0, and representing the severity of moisture
conditions from extremely dry to extremely wet.
(7) PHDI Index--a regional PHDI, calculated for the
Lower Basin, Middle Basin, and Upper Basin, based on ranked values
for a period of record from 1895 through 2010, and which is defined
for the purpose of calculating hydrologic conditions as described
in §298.470 of this title (relating to Calculation of Hydrologic
Conditions).
(8) Spring--the period of time March through June,
inclusive.
(9) Sound ecological environment--characterized by
fish, macroinvertebrate, and riparian vegetation species assemblages
that remain relatively intact compared to historical records.
(10) Summer--the period of time July through October,
inclusive.
(11) Upper Basin--the geographic area of the Brazos
River Basin which includes all watersheds upstream of and draining
into Possum Kingdom Lake, and which is defined for the purpose of
calculating hydrologic conditions as described in §298.470 of
this title (relating to Calculation of Hydrologic Conditions).
(12) Wet condition--for all measurement points, the
hydrologic condition that would occur approximately 25% of the time
and that is intended to represent the wettest conditions.
(13) Winter--for all measurement points, the period
of time November through February, inclusive.
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