WSP03745

• File Number: 8111.815
• Description: Arkansas River Compact Administration
• Basin: Arkansas
• Date: 4/1/1990
• Author: UCACOE
• Title: Drought Contingency Plan - John Martin and Trinidad Lake - Appendix D
• Water Supply Pro - Doc Type: Publication

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312,000 acre-feet (Apr-Sept). The average inflow at John Martin Reservoir is
.165,500 acre-feet (Apr-Sept). The average inflow during the Apr-Sept time frame
at John Martin Reservoir and at Trinidad Lake is approximately 70 percent of the
total inflow for the whole year. Snowmelt runoff has been chosen as a primary
indicator of actions needed during a drought, because of the dramatic impacts
associated with it.

(4) Surface Water Supply Index. The Surface Water Supply Index
(SWSI) is a weighted value derived for each major basin in Colorado, which
generally expresses the potential availability of the forth coming season' 5 water
supply. Development of the SWSI is a cooperative effort between the Colorado
State Engineers office and Soil ~onservation Service. The components used in
computing the index are reservoir storage. snowpack water equivalent. and
precipitation. The SWSI number for each basin ranges from a -4.00 (prospective
water supplies poor) to a +4.00 (prospective water supplies plentiful). The SWSI
number is only a general indicator of surface water supply conditions. The SWSI
scale along with the Soil Conservation Service (SCS) characterization of the
corresponding supply status is shown in Table 3-5.

Table 3-5

Surface Water Supply Index

SWSI
4.0 to 2.0
2.0 to -2.0
- 2.0 to - 3.0
-3.0 to -4.0
< -4.0

Class
Abundant Supply
Near Normal
Moderate Drought
Severe Drought
Extreme Drought

(5) Lake Levels. The amount of water stored in Corps reservoirs
in the Arkansas River Basin will also be used as an indicator of the severity
of the drought. The reservoir level cannot be used as a sole indicator of a
drought, because many other factors affect reservoir levels. Foremost among
these is water supply demand for irrigation, which can severely reduce reservoir
levels. As the water level drops, water suppliers are forced to institute
conservation measures during high-water-use periods of the irrigation season.
The lower lake levels result in a lower quality of water. As the lake continues
to fall water supply for irrigation is inadequate and many crops in the Basin
may fail. Because of the dramatic impacts associated with the pool levels, they
are chosen as the other primary indicator of actions needed during a drought.

b. Drou~ht Action Levels. For management purposes, four action levels
have been designated in this plan based on the duration of drought and the
percentage of storage remaining in the conservation pool versus percent snowmelt
runoff. The rationale for selecting the upper and lower limits of the drought
levels is based on an attempt to group anticipated impacts as the drought
severity increases. The four levels provide a guide for a response that is
consistent with the magnitude of the drought and its resultant impacts. A
detailed description of the four levels of drought response actions are located
in Section VII. For the purpose of this plan, drought severity is indicated by

3-6