C153607L Feasibility Study

• Contract/PO #: C153607L
• Contractor Name: Trinchera Irrigation Company
• Contract Type: Loan
• Water District: 35
• County: Costilla
• Bill Number: SB 92-87
• Loan Projects - Doc Type: Feasibility Study

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A summary of the water storage records for Mountain Home Reservoir is shown on I
Figures IV-I for the years 1946 through 1989. The highest recorded storage
volume was 13,500 acre-feet in 1948 and the iowest fU level was 1,700 acre- I
feet in 1951. The average filllE!~el_!~pproximatelY 000 acre-feet for the 44
years of record.------~--.-.- ~ '--:-~,-;. c" ;0"'"1 I,t;. ~r:;.7 ~Iooo....e ,.....~, .'
/~---- iZe.. .(\11 It.-~~ ,t()I\ly !1()o..Il~<;:' ~(I~~ I"",....~, ""<'j\.~Y,~. I
Mountain Home Reservoir is c llntly operating under restriction imposed by the.(: 1\.
Colorado State Engi~' ce, This restriction is at Gage Height 87.5 feet for c~~ .
.!l total capacltv ot( ~'!1!.9 _~ re-feet of storage which is a 10ss of 7,351 acre-feet wi {,.." ."'
~ storage. The storage restrIction has been placed on the reservoir aueto an r<-<"- .." '" I
inadequate spillway.

All water diverted, stored, and used by the Trlnchera Irrigation Company is under
existing water rights held by the Company and under existing State of Colorado
laws and regulations. The water rights are administered by the Water Commis-
sioner based on the volume of water available in the system. Copies of the
decrees, as supplied by The Trinchera Irrigation Company, are included in
Appendix C of this report,

The purpose of the rehabllltation is to upgrade the spillway such that the
restriction can be remove and full storage reinstated.

Figure IV-3 shows the water delivered by the Company throughout the district
from the surface rights. The average inches per share delivered from 1959 to
1989 is 11.2 inches which corresponds to approximately 11,200 acre-feet of
water,

B. Water Utlllzation. Mountain Home Reservoir is an on-stream reservoir that is
fili from water rights from Trinchera Creek, The reservoir is the main water
storage faclllty for The Trinchera Irrigation Company. The past and current use
of water stored in Mountain Home Reservoir has been to irrigate lands that lie
below the reservoir. No municipal or industrial water use has ever been
provided from the reservoir except for a smail amount of replacement water for
land development projects in the watershed, The water use is not expected to
change in the future and would be expected to be used primarily for irrigation.

C, Firm Yield. The firm or safe yield of a reservoir is generaily defined as "the
maximum quantity of water which can be guaranteed during a critical dry period".
The safe yield of Mountain Home Reservoir was not evaluated by analysis of the
available fiow of water in Trinchera Creek and its tributaries, It was evaluated
only by a review of the past history or record of fUling of the reservoir, A
summary of the water records are shown on Figures IV-I.

'1 From a review of Figure IV-l it can be seen that Mountain Home Reservoir has
. ~en filled to near "...paclty IIIQsL:l!'!lar.!L.and significantly drawn down during most
:r-,. '.'j b<<A of the years. The maximum fUl level recorded for Mountain Home Reservoir is
'~'{"-oo"-( during the years 1946 to 1989 at Gage Height 90 feet for a storage volume of
('i c_.) ""~ 13,500 acre-feet. The reservoir has been fUled to a storage volume of 4,000
acre-feet or above in 30 of the 44 years or 70 percent of the record studied;
fUled to a volume of 5,000 acre-feet in 50 percent of the years of record; and,
filled to a volume of 2,400 acre-feet 40 of the 44 years or 90 percent of the

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PAGE IV-2
CIapter IV - Ibmtain JbDe Reservoir

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