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<br />The Pueblo Reservoir JUP (PRIUP) study con-
<br />sisted of two major components: (1) Frequency analy-
<br />sis of recorded daily mean discharge data for selected
<br />streamflow-gaging stations (stations) upstream and
<br />downstream from Pueblo Reservoir, and (2) implemen-
<br />tation of the extended streamflow prediction (ESP) pro-
<br />cedure for the Arkansas River basin upstream from
<br />Pueblo Reservoir. Upstream from the reservoir, the
<br />objective of the frequency analysis was to derive an
<br />estimate of the 0.01 ~xceedance probability (EP),
<br />April15-May 14 daily inflow discharges; this EP was
<br />considered in design of the flood-storage capacity of
<br />Pueblo Reservoir. Downstream from the reservoir, the
<br />objective of the frequency analysis was to derive esti-
<br />mates of 0.01 EP discharges for two tributaries, Foun-
<br />tain Creek and the Sf. Charles River.
<br />
<br />Frequency analysis for the tributaries was
<br />needed because channel capacity of the Arkansas River
<br />in the vicinity of Avondale (about 20 miles downstream
<br />from the reservoir) is limited to about 6,000 ff/s; the
<br />operating procedures of Pueblo Reservoir require
<br />that this discharge criterion be maintained, if possible.
<br />Because discharges in Fountain Creek and the
<br />St. Charles River affects discharge in the Arkansas
<br />River at Avondale, discharge in the tributaries can .
<br />affect operation of Pueblo Reservoir, including the
<br />JUP. The study area has an area of 4,669 mi2 upstream
<br />from Pueblo Dam and 1,658 mi2 downstream from
<br />Pueblo Dam. Most discharge is derived from snowmelt
<br />in mountainous headwaters during spring and early
<br />summer.
<br />The frequency analyses were made by fitting the
<br />data to the 10g-PearsQn type-ill distribution. Station-
<br />skew coefficients were analyzed for selected stations to
<br />determine an appropriate generalized-skew coefficient.
<br />Preliminary analysis of the April-May discharge vol-
<br />ume at six stations on the Arkansas River was made to
<br />evaluate the adequacy of record length and effect of cli-
<br />matic variations. This analysis indicated that the near-
<br />Pueblo station, which had a 79-year record, could be
<br />used to reliably estimate the 0.01 EP reservoir inflow
<br />volume. However, because this station was discontin-
<br />ued after completion of Pueblo Dam (in 1975) and
<br />because some large discharges were recorded on the
<br />Arkansas River during the 1980's, the record for the
<br />near-Pueblo station was extended for water years
<br />1976--90.
<br />
<br />The record extension was made by two methods.
<br />The first method con$isted of using a linear least-
<br />squares regression bcitween discharges for the near-
<br />Pueblo station and the at-Portland station (about 20 mi
<br />upstream from the near-Pueblo station). The second
<br />method consisted of lIdjusting the discharge record for
<br />
<br />the above-Pueblo station (immediately downstream
<br />from Pueblo Dam) for the effects of reservoir regula-
<br />tion. In both methods, discharge data also were
<br />adjusted for the effects of diversion. Results from the
<br />two methods were averaged for use in the PRIUP
<br />study.
<br />The 0.0 I EP discharges from the frequency anal-
<br />yses were routed through Pueblo Reservoir to estimate
<br />evacuation dates for the JUP for the corresponding
<br />inflow volume. The frequency analyses alsq were used
<br />to derive additional sequences of daily inflow dis-
<br />charges for which evacuation dates also were esti-
<br />mated. A relation was indicated between the April 15-
<br />May 14 inflow volume and the estimated evacuation
<br />date; the date ranged from about April 23 for an inflow
<br />volume of about 168,800-acre-ft to May 5 for an inflow
<br />volume of about 20,000 acre-ft,
<br />To apply the study results, only a forecast of the
<br />April15-May 14 inflow volume to Pueblo Reservoiris
<br />needed; the relation derived between inflow volume
<br />and evacuation date then is used to estimate the evacu-
<br />ation date. To provide the capability to make forecasts
<br />of April 15-May 14 reservoir inflow, the operational
<br />capability of the National Weather Service River Fore-
<br />cast System (NWSRFS) model was applied for the
<br />PRIUP study. The operational capability of the
<br />NWSRFS model is applied by personnel of the
<br />National Weather Service, which maintains and
<br />updates the model and the associated data bases.
<br />The ESP procedure, which is an integral part of the
<br />NWSRFS model, is used to make probabilistic fore-
<br />casts of reservoir inflow volume.
<br />
<br />REFERENCES
<br />
<br />Abbott, P.O., 1985, Description of water-systems operations
<br />in the Arkansas River basin, Colorado: U.S. Geological
<br />Survey Water-Resources Investigations Report
<br />85-4092, 67 p.
<br />Anderson, B.A., 1973, National Weather Service river fore-
<br />cast system-Snow accumulation and ablation model:
<br />Silver Spring, Md., National Oceanic and Atmospheric
<br />Administration, NOAA Technical Memorandum
<br />NWS-HYDRO 17, 217 p, [Out of print. Available only
<br />from the National Technicallnfonnation Service,
<br />Springfield, VA 22161 as acquisition no. COM-74-
<br />10728.]
<br />_1986, The National Weather Service river forecast sys-
<br />tem and its application to cold regions, in Santeford,
<br />H.S., comp., Proceedings of sixth international northern
<br />research basins symposium/workshop-Field measure-
<br />ments under winter conditions: [Houghton, Mich, ?],
<br />U.S. National Committee for Scientific Hydrology,
<br />p.219--237.
<br />
<br />REFERENCES 45
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