WSPC07372

• File Number: 8040.950
• Description: Section D General Studies - General Water Studies
• State: CO
• Basin: Statewide
• Date: 9/1/1981
• Author: Colorado DNR
• Title: Colorado Water Study - Background Volume - Preliminary Review Draft - Report
• Water Supply Pro - Doc Type: Report/Study

001256

Draft - 9/81

Varlabll i ty

The fundamental hydrologic fact about Colorado's renewable

water supply Is that it is highly variable.

The amount of pre-

\'. cipitat ion that falls on the state varies greatly in respect to

both time and place.

ThIs can be illustrated most simply by the

, following:

Figure 1, whIch shows the outflows of the South

Platte Ri\er at the Julesburg gauge in northeastern Coiorado,

clearly illustrates variability from year to year.

Table 1 shows

both snowfall and normal total precipItation at various stations

in each of the state's four major river basins. It clearly

illustrates variability from place to place within the state.

Consumption vs. Use

Perhaps the most important distinction fundamental to this

~
,~.,

analysis concerns the concept of "consumption." Generally, when

water is diverted a certain percentage is consumed and the rest

is returned to the source.

In simple terms,

diversion = consumption + return flow

A farmer who applies one acre-foot of water to a gIven crop may
,
find that 50 percent of that amount Is returned to the stream and

the other 50 percent is lost to further uses because of evapo-

transpirat ion or evaporat ion from the so i 1.

Simiiarly, someone

who takes a shower using water from a municipal water system

consumes only that water that ~ ~ flow down the drain. The
rest can be treated and reused later by others; it has been used

but not consumed.

For our purposes, water is consumed only when

it is evaporated, evapotranspired, or chemically or physically

incorporated into a product.

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