Summary Report ‎(Working Draft)‎ Modeling of Reservoir Management Strategies for Lakes Powell and Mead December 2005

• Description: Summary Report ‎(Working Draft)‎ Modeling of Reservoir Management Strategies for Lakes Powell and Mead December 2005
• State: CO
• Title: Summary Report ‎(Working Draft)‎ Modeling of Reservoir Management Strategies for Lakes Powell and Mead December 2005
• Water Supply Pro - Doc Type: Meeting

Modeling Results for
Colorado River Basin States' Modeling of
Colorado River and Reservoir Management Strategies
One drawback to the ISM approach is that each trace repeats the annual sequence
of inflows as they occurred in history — annual sequences not seen in history are
not generated. High -flow periods follow droughts with the same frequency and
magnitude as the historical record. Reclamation is actively pursuing research
projects to develop alternative ways of quantifying the uncertainty of future
Colorado River inflows.
Probabilistic Output - Percentile Analysis
The result of ISM is 90 possible inflow scenarios. Thus, a range of probabilistic
output is generated for each modeling result (i.e. reservoir elevation), for each
year of simulation. This output is managed and displayed graphically by GPAT,
an Excel -based tool developed specifically to analyze RiverWare model outputs.
Statistics used in this report to present results of elevations, shortages and releases
are percentiles, exceedance and non- exceedance probabilities.
Percentile analysis is a statistical method used to view the results of all hydrologic
traces in a compact manner yet maintain the fluctuations at high and low reservoir
levels that would be lost by averaging the results of the 90 traces.
Figure A -1
Lake Mead Elevations under the Powell Normal — Step Short Original Strategy
90th, 501h and loth Percentile Values and Representative Traces
230
180
130
)50
--0-10th Percentile
—50th Percentile
030
- - - 90th Percentile
— Trace 20
r —Trace 47
050
------Trace 1
2005 2010 2015 2020 2025
Figure A -1 illustrates the range of possible Mead EOCY elevations for the period
of analysis (2006 to 2025) under this particular strategy. Within a given year, the
reservoir is projected to fluctuate from nearly full to very low as shown by the
90th and 10th percentile lines (respectively). The median elevation is shown by the
50th percentile line. For example, in the year 2015, the 50th percentile value is
approximately 1115 ft, meaning an equal number (50 %) of the 90 possible traces
were above and below 1115 ft. In that same year, the 10th percentile value is
approximately 1038 ft. — 10% of the traces in year 2015 were at or below 1038 ft.
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