WSP03577

• File Number: 8281.300
• Description: Colorado River Studies and Investigations - Colorado River Consumptive Uses and Losses Report
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1991
• Title: Colorado Population Estimates and Projections 1980 - 2015
• Water Supply Pro - Doc Type: Report/Study

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of the region were distributed to the respective counties in a manner consistent
with the distributions developed by the Denver Regional Council of Governments
in their 1988 projections update and with the 1990 census counts. Accordingly,
net migration for the counties within the region was adjusted to achieve these
projected population totals.

For the Denver metropolitan area, the age-sex migration pattern was determined
first for the area as a whole in the manner described in the paragraph before
last. From this set of net migrants a certain number of net migrants by age and
sex were assigned to Denver County in a manner consistent with that county's
age-sex specific migration pattern and with the total required by the ORCOG
projection. The remaining net migrants for each age-sex group were then
distributed to the other five counties in proportion to the total net migration
required by those counties to be consistent with the DRCOG totals.

The general method of scaling the 1970 - 1980 age-sex specific net migration
patterns and then the special treatment of the counties within the Denver
metropolitan area were used to create the age-sex distributions of net migrants
for each of the estimate years (1981 through 1990). The total number of net
migrants .for each of these years was calculated as the difference between the
estimated total population and that which would result with zero net migration.
This difference for each county was multiplied by the respective age-sex
distribut~on (in proportions) to achieve the age-sex migration pattern in each
of the estimate years.

Base Year. pooulation. As described above, the projections are based on a July
1, 1990 extrapolation of the total population counted in the April 1, 1990 Census
of the Population. However, the estimates and projections by age and sex from
1980 onward are projected from the 1980 Census. The Demographic Section intends
to incorporate the 1990 Census age-sex data in a revision of the projections
later this year.

The Treatment of "Soecial" Poculations. In eighteen counties, the model
recognizes the existence of "special" populations whose demographic behavior is
different than that assumed for the general population. These special
populations include college students, state prison inmates, temporary ski resort
employees, and military personnel. In the case of all but the military, these
special populations -- by age and sex -- were estimated and projected on the
basis of 1980 Census data and on known or expected changes in the populations.
As they are considered to be temporary residents, these populations neither give
birth nor survive to upper age groups within the projection model. Instead they
are merely added to the general population each year after the model has been run
for the year.

The counties regarded as having these special populations are:
COLLEGE: Alamosa, Boulder, Gunnison, La Plata, Larimer,
Pueblo, and Weld.
STATE PRISON: Chaffee, Crowley, and Fremont.
SKI RESORT: Eagle, Grand, Pitkin, Routt, San Miguel, Summit.
MILITARY: Denver and El Paso.

Treatment of Elderlv Populations. For the estimate years 1981 to 1988 the
population 65 and over is adjusted to be consistent with data on medicare
enrollments. The basis of this adjustment is the ratio of the population 65 and
over to medicare enrollment at the time of the 1980 Census. For each estimate
year tqe total population 65 and over is calculated by multiplying the 1980 ratio
times the number of that year's medicare enrollees. The population 65 and over
that is projected by the model is adjusted to be consistent with this total.