WSPC02224

• File Number: 8408
• Description: River Basin General Correspondence
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 5/16/1991
• Title: Platte River Evaluation: USBR - Platte River Evaluation Update - Publication
• Water Supply Pro - Doc Type: Publication

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flow needs would be determined. Reclamation responded that threatened and
endangered (T & E) species flow needs for the Central Platte are being
developed for the Platte River Management Joint Study, and the flows needs
T & E species on the North Platte and South Platte will be developed by
Reclamation and the US Fish and Wildlife Service (Service). It was noted
mandated minimum flows for some reRr.h~B of th~ Pl~tte Ri~e~ such as belo~
Reef and Miracle Mile exist to date.

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The third agenda item was to discuss what Study Period should be used for the
water operation studies. Mike Ouever started off the discussion by presenting
a paper that displayed work from other studies he had reviewed on long term
river flows and precipitation (see attached paper). He concluded from the
various data sources, that for an extended period before 1900, flows in the
Platte basin were in an average range followed by a period of high flows from
1900 to 1930. Low flows followed throughout the 30's. During the 40's to
present, a period of average flows have occurred. Studies in the Colorado
River basin whi9h also receives much of its runoff from the Rockies shows a
similar period of high and low flows. Some members of the group did not
believe the Colorado and Platte Rivers should be compared.

Reclamation explained that operation studies like the NPRSH model used the
study period 1951 to 1983, the North Platte River Management model went back
to 1929, and the Central Platte study uses the period from 1941 to 1989. It
was discussed that the period of study used to do a water supply yield for a
basin area may not be necessary for a evaluation study where comparison of
changes in durations will be assessed. For example doing a yield study on a
enlargement of a dam would require defining the critical inflow and outflow
period while a evaluation assessment is analyzing changes in all flows so it
may not be necessary to have a critical period represented. Also noted was
that a critical period would vary with total system reservoir storage
capacity, and that the conditions of storage prior to the start of a study
needed to be taken into account. It was suggested that total storage capacity
of the system be considered for this long term study since short periods of
drought may not affect all storage and that initial reservoir contents could
be varied in runs to simulate different starting conditions.

It was pointed out that it would be difficult to go back further than 1930
based on available data for most areas ,of the Platte Basin but also noted that
good data was available going back to 1900 for the upper North Platte basin
area. It was suggested the 1931-1971 period could be the critical period when
evaluating yield in the North Platte basin. It was decided to try and take
the study period back to 1931 and run it to present. Study team members noted
operation analysis may need to be considered before a final decision is made.
It was recommended the study period should start with the reservoir storage
full or make sure the system filled before the critical period. The
suggestion was also made to make runs starting empty, half full, and full to
show the resulting effects on water use, flows and storage.

The fourth agenda item was to discuss the development of the North Platte
River operation study model. Reclamation reviewed for the group that the
North Platte River Simulation Model (NPRSM) had been purchased from the
Wyoming Water Development Commission in March and Reclamation's modified
Seminoe Enlargement version was what had been distributed to the study team.
Reclamation's intent in purchasing the model is to have the study team assess