WSP12310

• File Number: 8221.110.J
• Description: Juniper-Cross Mountain Project
• State: CO
• Basin: Yampa/White
• Date: 7/21/1984
• Title: Yampa River Reservoirs No. 1 and No. 2 - Water Yield Analysis
• Water Supply Pro - Doc Type: Report/Study

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Baseline hydrologic data for the Yampa River Reservoirs were
derived frOlll discharge records for the Yampa River at Maybell.
Recorded streamflows were adjusted slightly downward for
Reservoir .b. 1, which is a short distance upstream M ".the
Maybell gage. 'rhe Reservoir No. 2 site, is several IIliles
downstream of the Maybell gage and recorded streamflows were
adjusted slightly upward.

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'rhe period of stream discharqe records ranged from a
durat;ion of 73 years at the Yampa River at Steamboat to only 8
years at the Yampa River at Craig. 'rhe average period of :record,
,for the stream gaging stations was 33 years. Since long-term -
streamflow data was not available for several of the gage sites,
data was sometimes missing for a particular year being modeled.
In this instance, the relationship between the gage with missing
data and a near!:?y gage with long-term data was determined for the
period of record. 'rhe missing year's data was then calculated
with actual data from' the nearby gage and with the defined
relationship.

For the three accounting points at which gaging has not been
conducted (Yampa River above Blacktail Reservoir"and 'rrout Creek
at the P&M and Energy Fuels reservoir sites), discharge data was
derived by 'another method. Runoff-elevation relationships were
developed using a procedure outlined in the hydrology chapter of
EPA publication 600-8-80-012.' Precipitation and tem~erature data
were retrieved from local climatic stations in order to derive
mean annual runoff for different elevation zones according to the
above methodology. 'rhe watershed area, by elevation zone, above
each of the three ungaged sites was measured. 'rhe calculated
runoff coefficients were applied to each elevation zone to
estimate mean annual runoff at each of the three sites. 'rhe mean
annual runoff was adjusted to reflect actual conditions of the
particular year being modeled based on nearby gage records. The
runoff was distributed on a monthly and weekly basis also
according to nearby gage data, and was adjusted to account fOI:
existing diversions and return flows.

f!:2ject Bypasses. 'rhe strearnflo~1 that must be present to
sa tisfy existing senior water rights and miniClum streaJ:lflow
requ~rcments below each project was estimated for input into the
;;'Iodel. It was assumed that these bypasses C1ust be met before a
proj ect can divert or store water. While the Sta te's J:li.nimum
flow decree~ are junior to most of the water rights for the
modeled projects, it was felt that the Federal, State and local
permits that must be obtained prior to construction of any
storage project would,require that applicable minimum flo,'1s be
satisfied. In most cases, the nlinimum flo\'1s reco::Jmended by the
Colorado '''ater Conservation Board for fishery maintenance would
also satisfy downstreao senior water rights. The tiypass criteria
utilized in the model are listed in 'rable 2.

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