WSP00880

• File Number: 8441.100
• Description: Colorado Big Thompson Project - Project Description
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 12/1/1982
• Title: Colorado - Big Thompson Project
• Water Supply Pro - Doc Type: Project Overview

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I . ~ systt'm. Projl'Ct water released from Lake Estes flows
~ through Olympus Siphon and Tunnel and Pole Hill Tun-
.......:i nel and Canal into Pole Hill Penstock and Powerplan!.
'Waler al50 can be released from Lake Estes 10 tht' Big
Thompson Rher. u.aving Pole Hill !'owerplant After-
bay. the water enters Rattle~nake Tunnel and flows into
Pinewood Lake forme-d by Raul....;nake Dam. Bald
)Iountain Tunnel carries the water into th.. Flatiron
Pemtocks and Powerplant which di,;eharges into Flatiron
Beservoir. where it is .~tored for irrigation ll!'t'. Pole Hill
Pow('rplant operates under an average n('t hf'ad of 815
feel with a I!!t'nt'rating capacity of 33.250 kilowall$.

.

ColorlJdo-lJig Thomp$on Project

The Flatiron Powerplant operates under an averagt' net
head of 1.055 feet. with a gt'nerating capacity of 71,50n
kilowatts. The powerplant contains two main power units
and a rt'ver~ible 13.000-horsepower pump-turbine unit
which lifts water !iOuthward from Flatiron Heservoir to
Carter Lake. This unit is capable of discharging a max-
imWll of 370 cubic feet per second into Carter Lake and
normall~' opertltes on surplus or off-peak powt'r gent'ralt"()
by other I>owt'r units of the projl'Ct system.

The pumping unit at Flatiron Powerplant pumps from
Flatiron Re,.;ervoir to Cartt'r Lake through a 1.4-mile-
long ronnl'Cting pressure tunn..1. The pumping lift
through this tunnel ranges from 200 to 300 ft'et. depen-
din/{ on the water surface elevation in Carter Lake. Dur-
ing pt'ak load demands on till' projl'Ct s)"Stem. water can
be released from Carter Lake to flow back into Flatiron
Heservoir. and at such times the pump-turbine operat..s
in rever!'t' to gem'rate 8..')00 kilowatts of power.

Flatiron Dam provides aftt'rba~' ..torage for watf'r
di.schar!lffi from the powf'rplanl. The water then flows b~'
gravity northward throuKh the Charli"!' HnnSt'n Fet>i.li"r
Callal. to and acro!lS the Big lllOmpson Bin.r. and on to
Hor~tooth Ri"!'t'rvoir for delhery to tht' Poudre River.
Poudre Valley Canal. and. by t'xchange. to tht' :'\orth
Poudrf' Supply Canal.

Watt'r pumpt'd southward into Cart",r Laki" is "tort>i.) fOf
irrigation delivl;"rie~ to th", Little TIlOmp!'On Hi\'er. St.
\'rain Crt't"k. Boulder Cr('{'k. and tht' Soulh Platt... Hi\"f'f.

Carh'r Lake Dam and H""enoir

Carter Lakt' is one of the two main project "toragf' re~r-
mir!' in dlt' Ea~t Slope- di...tribution ~ptt'm, \\' ater is
!<toroo in Ihi" re!'t'rmir for dt'liwry to the Little Thomp-
50n Riwr. 51. \'rain Cret'k. Boulder Crft'k. and the
South Platte Ri\,t'r. {or rt'turn to Flatiron Rel't"rvoir for
ust' in the Big Thomp>'On or Cache la Poudrt' \'alleys. Of
for power ~eneration.

Cartt'r ukI' Rf''''t''r\"oir is formed in a natural ba"in in the
foothill!' b~ a ::?1.J..foot.high t'arthfill dam and two smaller
dams across low saddlt's in th", surrounding hilk Tht'
reservoir has a total capacity of 112.::?30 acre-ft't't,

\lar}-81.ak..Pm,,'r"'"11l

St. \'rain Supply Canal

Leading from th!" Carter Lakl" outlet. the SI. Vrain Sup-
ply Canal exti"nds t'Outhward 9.8 miles to St. \'rain
Crt't'k nt'ar Lyons. It consiMs of an open canal. siphons.
tunnt'ls. drops. and flumes designed to con\'t'~" 625 cubic
feet per second of water to the Littl", Thomp,;on HiWf
turnollt and 575 cubie fef't ()(Or !ll;'Coml from the turnoul
to St, \'rain Crt'f'k.

HClulder Cr_k Suppl~' Canal

Anulder Creek SlIppl~' Canallwgins at the turnout near
th(' f'nd of the St. \'rain Supply Canal. crO.'l:<es 51. \'rain
Creek b~' a "iphon. and extends sollthea"terl~" 15.7 miles.
h di~hargf's into Boulder Cr",ek ahout 6 mile~ east of
Boulder. Tht' eanal has a carrying capacity of 200 ctiliic
fef't per *Cond.

:\"'ear the lowt'r end of Ihe canal. the city of Boulder con-
structed Boulder Rt'sen'oir to be u~1 for stnra~e and
regulation of the city's water for replacenwllt watt'r car-
rif'd in tht' canal. This reservoir was built nnd!"r all
agTet'ment hetwet>n th(' city and tht' :\orthern Colorado
U'att'r Con.......n.ancy District. LJnclt'r the agreem",nt. the
re"'t"r\-oir provide" 175 cubic feet per second of flow for
tht' SOllth Platte Suppl~" Canal.

South Platle Supply Canal

Thi" canal extends from Boulder Crf't"k gt'nt'rall~ north.
east to the South Plalle Ri\'er. a distanct' of about 32.2
miles. Tht' capadty of thf' canal i:< 230 cubic ft'et per