WSP01376

• File Number: 8142.700
• Description: Trinidad Project - Annual Operating Plans and Reports
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 12/1/1988
• Author: US DoI BoR
• Title: Review of Operating Principles Final Report
• Water Supply Pro - Doc Type: Operating Principles/Plan

2~6()

Discussions' with the District revealed that no attempt has been made to deter-
mine the irrigation requirement for any year. In addition, there is no evidence
that the District has limited the headgate diversion based on an irrigation
requirement. A comparison of 1985 headgate diversions (only year with suitable
irrigated acreage data) with the irrigation requirement computed using methodo-
logy of the 1961 Study shows that the 1985iheadgate diversion exceeded the require-
ment by 14,210 acre-feet.1/

To gain insight into the impact of excess diversion, the previously described
Baseline study (lH and 1R) and variation studies 5H and 5R were modified to
reflect assumed increases in headgate diversion. This included established cri-
teria for calculating return flow from diversions in excess of ideal requirement
as described in the 1961 Study. Sever;al runs were made, each reflecting an
incrementa 1 increase in headgate di vers i on (above idea 1) . Excess di vers i on
increments ranged from .1 to 1 foot of addit i ona 1 water per acre. When an
increment resulted in a negative effect on John Martin Reservoir inflow, no
analysis was done of the higher increments.

This range of excess diversions represents an increase in headgate diversion
requirement of from 1,972 to 19,717 acre-feet per year(example - 19,717 acres X
0.1 foot per acre). In order to simulate a more realistic water management pro-
cedure, excess diversions were allowed, to occur only in those years of above
normal water supply.

The modified Basel ine study shows the direct effects of the excess diversions.
The modified 5H and 5R show the cumulative effects of excess diversions,
transfer of water out of the Model decree and wi nter storage under joi nt use
decree.

A few of the key results of this analysis are displayed below:

Effect of Excess Diversion on Baseline Study

Item
(Units 1000 Acft.)
Total Bypass/Spill
Total Return Flow
Total Irrigation Shortage
Net Effect on J .M. inflow
compared to historic Model
reservoir operation (lH)

Net Effect on J.M. inflow
compared to rehabilitated
Model Operation (lR)

1H/1R
Baseline

Foot/Acre of Excess Diversion
0.2 0.3' 0.4 0.5 1.0

0.1
13.3
17.7
11.8

13.0
18.0
12.1

12.6
18.2
12.3

12.4
18.6
12.6

12.2
18.9
12.9

11.0
20.3
14.0

13.6
17.3
11.5

0.5

0.3

0.2

-0.7

0.8

0.7

1.0

3.3

3.2

3.0

2.8

2.7

2.6

4/ It must be noted that 1985 is not within the study period and
- the first year that Model lands were back to full irrigation.
the example of effect of excess diversions, .it is appropriate.

that 1985 is
However, for

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