365
find it important to forge strong agreements to limit large scale water diversions from sources within the basin.
(b) Declaring and canceling a DWDR occurs when an ongoing drought has a
real likelihood of becoming a new Drought of Record. A DWDR declaration
would trigger action to cut off interruptible stored water and implement
mandatory pro rata curtailment of Firm Water demands. The LCRA requirements for declaring a DWDR are given by the following metrics:
• Drought duration of at least 24 consecutive months.
• Drought intensity greater than that of the Drought of Record, as measured by inflows into Lakes Buchanan and Travis.
• Combined storage in lakes Buchanan and Travis of less than 600,000
acre- ft. (Note that the LCRA uses the value of 600,000 acre-ft as a safety
factor to account for the uncertainty inherent in the hydrologic modeling
of firm yield, helping to avoid the triggering of a DWDR in the event of a
repeat of historic hydrology.)
2. The WMP sets the “Evaluation Dates” of March 1 and July 1 when the LCRA
determines the water supply condition, the interruptible stored water available
for agriculture, and effective environmental flow criteria.
3. The WMP allows the LCRA to stop releasing interruptible stored water for agricultural operations, even in the middle of a crop season, if reservoir storage
drops below certain predetermined levels.
Thus, the Lower Colorado River Authority Water Management Plan uses a combination of different metrics that are most relevant for meso/macro-scale management: absolute–extensive and relative–extensive metrics.
Of the metrics mentioned above, relevant absolute–extensive metrics include the
following:
• Firm Yield (acre-ft/year).
• Water Inflows into the lakes (ft
3
/s or acre-ft/month).
• Environmental Inflows into Matagorda Bay (cumulative flows over 1-, 3-, and
6-month spans).
However, it is probable that the reference of drought plans to the Drought of
Record is the most critical metric driving not only the LCRA WMP but also the
WMP of the entire state.
For Texas, the drought of record occurred during the 1950s, with water planning
and water curtailment operations ultimately based upon the relative–extensive
metric of how similar current conditions are to the conditions that would come
about from a repeat of this drought of record.
In the event of a drought triggering the curtailment of interruptible water rights,
primarily irrigation, the plan also indicates pro rata, or proportional, cuts in water
access based on the total quantity of surface water rights, another relative–extensive
metric to govern water allocation.
13 Metrics
find it important to forge strong agreements to limit large scale water diversions from sources within the basin.
(b) Declaring and canceling a DWDR occurs when an ongoing drought has a
real likelihood of becoming a new Drought of Record. A DWDR declaration
would trigger action to cut off interruptible stored water and implement
mandatory pro rata curtailment of Firm Water demands. The LCRA requirements for declaring a DWDR are given by the following metrics:
• Drought duration of at least 24 consecutive months.
• Drought intensity greater than that of the Drought of Record, as measured by inflows into Lakes Buchanan and Travis.
• Combined storage in lakes Buchanan and Travis of less than 600,000
acre- ft. (Note that the LCRA uses the value of 600,000 acre-ft as a safety
factor to account for the uncertainty inherent in the hydrologic modeling
of firm yield, helping to avoid the triggering of a DWDR in the event of a
repeat of historic hydrology.)
2. The WMP sets the “Evaluation Dates” of March 1 and July 1 when the LCRA
determines the water supply condition, the interruptible stored water available
for agriculture, and effective environmental flow criteria.
3. The WMP allows the LCRA to stop releasing interruptible stored water for agricultural operations, even in the middle of a crop season, if reservoir storage
drops below certain predetermined levels.
Thus, the Lower Colorado River Authority Water Management Plan uses a combination of different metrics that are most relevant for meso/macro-scale management: absolute–extensive and relative–extensive metrics.
Of the metrics mentioned above, relevant absolute–extensive metrics include the
following:
• Firm Yield (acre-ft/year).
• Water Inflows into the lakes (ft
3
/s or acre-ft/month).
• Environmental Inflows into Matagorda Bay (cumulative flows over 1-, 3-, and
6-month spans).
However, it is probable that the reference of drought plans to the Drought of
Record is the most critical metric driving not only the LCRA WMP but also the
WMP of the entire state.
For Texas, the drought of record occurred during the 1950s, with water planning
and water curtailment operations ultimately based upon the relative–extensive
metric of how similar current conditions are to the conditions that would come
about from a repeat of this drought of record.
In the event of a drought triggering the curtailment of interruptible water rights,
primarily irrigation, the plan also indicates pro rata, or proportional, cuts in water
access based on the total quantity of surface water rights, another relative–extensive
metric to govern water allocation.
13 Metrics