2018-01-16_HYDROLOGY - M1983090

• Permit No: M1983090
• IBM Index Class Name: Hydrology
• Doc Date: 1/16/2018
• Doc Name Note: Approved SWSP
• Doc Name: Approved SWSP
• From: DNR Water Resources
• To: DRMS
• Email Name: ECS
• Media Type: D
• Archive: No

Poudre Pits Combined SWSP
Plan IDs 3218, 3589 Et 4585
January 16, 2018
Page 4 of 10
the stated recharge that occurred, the lagged depletions to be replaced in 2018 equal 0.66 acre-
feet. Combined, the dewatering operations at the Firestein/Tigges/Roberts Pit have resulted in a
lagged depletion of 4.37 acre-feet that must be replaced in 2018.
Dewatering operations at the La Poudre Pit occurred from January 1995 through December
2002, and during October and November of 2014. The Lee Parcel is projected to be dewatered at
an initial rate of 500 gpm for the first three months (March - May 2018), decreasing to 250 gpm for
the following seven months (June - December 2018). Fifty percent (50%) of the dewatering water
delivered to recharge in the West Lake and fifty percent (50%) will be delivered directly to the
river. Combining the lagged depletions and net accretions from the stated recharge with projected
dewatering depletions and accretions, dewatering activities at the La Poudre Pit site will create a
net accretion of 83.91 acre-feet during 2018. At the North La Poudre site, dewatering operations
occurred from September 2002 through March 2003 and recommenced from April 2012 through July
2014. The 2012 dewatering was not metered therefore no recharge credit was given. Instead, all
2012 dewatering was assumed to be discharged directly to the river creating no lagged accretions.
The operator installed meters at this site by January 2013 and starting January 2013 the actual
meter readings are used in the dewatering analysis. Dewatering that occurred throughout 2013 was
returned directly to the river through an unnamed slough located above the Whitney Ditch. With
the stated recharge that occurred in the past, the lagged depletions to be replaced in 2018 equal
5.85 acre-feet. Combined, the dewatering/recharge operations at the La Poudre and North La
Poudre pits will result in a net accretion of 78.06 acre-feet.
For this SWSP and any future approvals, actual monthly meter readings must be used to
determine the true dewatering rate, and to determine how much water was delivered to recharge
versus being directly returned to the river.
Table D below summarizes the impacts past and projected dewatering operations at each pit
will have on the stream system during this SWSP period.
Table D - Summary of Dewaterinia Impacts (acre-feet)
Site Name
2018 Direct
Accretions
2018 Lagged
Accretions
2018 Lagged
Depletions
Net Balance
Firestein
-
0
-0.60
-0.60
Tigges
-
5.58
-8.69
-3.11
Roberts
-
1.99
-2.65
-0.66
North La Poudre
-
4.27"
-10.12
-5.85
La Poudre
219.38
134.10
.269.57
83.91
Total
219.38
1 145.94
1 -291.63
73.68
Excludes accretions from any dewatering recharge that may have occurred in 2012
AWAS was used to determine the lagged depletions to the Cache La Poudre River from past
and projected dewatering operations at each site. The following parameters were used in the
model with the infinite aquifer boundary condition: the distance (X) from the centroid of the
exposed ground water surface to the river; the transmissivity (T); and the specific yield (S). The
Glover parameters used for each pit are shown in Table E below.
Office of the State Engineer
1313 Sherman Street, Room 821, Denver, CO 80203 P 303.866.3581
www.water. state. to. us
rets