PROJ00518

• Contract/PO #: C153484
• Contractor Name: San Luis Valley Water Conservation District
• Contract Type: Grant
• Water District: 0
• County: Rio Grande
• Bill Number: FSG
• Loan Projects - Doc Type: Feasibility Study

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VI. RIVER BASIN MODELING

Given the complexity of water supplies and uses in the Rio Grande Basin and the

number of potential reservoir sites under investigation, a computer tool to organize

and analyze the collected information was warranted. The following sections briefly

describe aspects of modeling the Rio Grande Basin performed for this study.

VI.l SELECTION OF A HISTORIC MODELING PERIOD

One of the first work items was the selection of a suitable period of historic

record for data collection and the modeling effort. A historic modeling period

for the Rio Grande Water Supply Study was selected based primarily on a statistical

review of unadjusted gaging records for the Rio Grande near Del Norte (USGS number

08220000). Annual flows for the calendar years of 1890 to 1985 were collected from

the USGS's WATSTORE system and are presented in Table VI-I. The mean annual flow

for the Rio Grande near Del Norte, Colorado is approximately 654,000 af. A graph

of the annual flows is presented in Figure VI-I.

Other factors considered in the selection of a modeling period were the availability

of diversion and water use records, inclusion of drought years, consistency with

previous studies in the Basin, public perceptions of the study period and the

desirability of including recent years to make best use of the most reliable data

relating to water supply and use.

The most valuable statistics for the evaluation of study periods were found to be

the arithmetic mean, median, standard deviation and skewness. No recent time

interval of 10, 20 or 30 years has a mean flow similar to the 1890 through 1985

average due to an extremely wet period from 1905 through 1929. The 1909 through

1977 or 1909 through 1985 periods have means similar to the 1890 through 1985 mean

but because of their length (more than 60 years) and lack of data availability they

were not considered viable study period candidates.

For the 25-year wet period from 1905 through 1929, the annual flow is less than

the 1890 through 1985 average in only three years. Since wet conditions prior to

1930 are not representative of long-term flow conditions, time periods starting i::

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