2015-12-30_HYDROLOGY - M1983090

• Permit No: M1983090
• IBM Index Class Name: HYDROLOGY
• Doc Date: 12/30/2015
• Doc Name: Substitute Water Supply Plan
• From: DWR
• To: DRMS
• Email Name: ECS
• Media Type: D
• Archive: No

Poudre Pits Combined SWSP
December 28, 2015
Page 4 of 10
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 and is projected to occur during this plan period, lagged accretions at the North
La Poudre site will total 41.19 acre-feet in 2016. Combined, the dewatering/recharge operations at
the La Poudre and North La Poudre pits will result in a net depletion of 40.15 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 Dewatering Impacts (acre-feet)
Site Name
2016 Direct
Accretions
2016 Lagged
Accretions
2016 Lagged
Depletions
Net Balance
Firestein-
120,000
0.48
-0.64
-0.16
Tigges-
0.20
8.32
-13.69
-5.37
Roberts-
La Poudre
2.51
-3.34
-0.83
North La Poudre-
2,500
64.46*
-23.27
41.19
La Poudre-
2.27
-83.61
-81.34
Total-
78.04
-124.55
-46.51
* Excludes accretions from any dewatering recharge that may have occurred in
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 the table below.
Table E - Glover Parameters (Dewaterin
Site Name
X (ft)
T (gpd/ft)
S
Firestein
1,035
120,000
0.20
Tigges
3,600
120,000
0.20
Roberts
3,435
120,000
0.20
La Poudre
1,500
50,000
0.20
North La Poudre
2,500
50,000
0.20
The lagged combined evaporative and operational depletions in 2016 will be 177.00 acre-feet.
The lagged combined post dewatering depletions and accretion from the stated recharge creates a
net depletion in the amount of 46.51 acre-feet. Therefore the total depletions owed to the river for
this SWSP approval period are 223.51 acre-feet. See Table 10 column 2a for the monthly distribution
of the total losses.