BOARD00632

• Board Meeting Date: 8/16/1972
• Description: Agenda or Table of Contents, Minutes, Memos
• Board Meetings - Doc Type: Meeting

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water of a different quality, will ultimately have an effect upon the
stream itself.

(Slide) This next slide presents a simplified flow chart showing the
steps taken in the calculation procedure itself. First of all, we
must be able to describe the system we are modeling. This requires a
knowledge of the boundary conditions, the boundaries of the aquifer,
a knowledge of the hydraulic properties of the aquifer materials, and
also, some knowledge of the chemical quality of water in the aquifer
at the start of the simulation period. The model can be run on any
time basis, actually. We ran a model on a monthly basis, telling us
this would suffice, would be adequate, to describe any seasonal trends
of changes occurring in water quality. For each month then, we had
to determine all stresses, hydrologic and quality stresses, on the
system. This would include such factors as precipitation, changes in
river stage, potential evapotranspiration, all pumpage from the aquifer,
all recharge to the aquifer, diversions from canals, and so on. Then
with the knowledge of the model knowing the properties of the system
and the stresses placed on the system, it can then calculate new water
table elevations at the end of that month, the end of the time period.
From this data the model then has the hydraulic radiants throughout
the aquifer and this in turn is used to calculate the velocity of
ground water flow in any direction at any point in the aquifer. This
data then, is in turn used to calculate the changes in dissolved
solids concentration throughout the aquifer and in the stream due to
the transport and dispersion of these dissolved solids. This .eries
of steps is then repeated for each month of the simulation period.

(Slide) To take a closer look at the study area itself very briefly.
First of all, I could point out that the Fort Lyon canal diverts a
large percentage of the flow from the Arkansas River at a point west
of La Junta and flows along the northern boundary of the aquifer.

Our stream gaging stations were maintained on both the canal and the
Arkansas River at both ends of the study reach, and also recording
conductivity meters. So we had a measure of both the flow and salt
content entering and leaving the study area. In addition, we main-
tained a series, or a network of observation wells in which water
quality samples and water level measurements were made on a monthly
basis. You can see for one thing that the data requirements for this
model are not simple, not easy to fulfill, and it takes quite a bit
of work to just collect the data needed to run the model.

(Slide) Now, we ran the model for a one-year period, starting on
March I, 1971, that was the beginning of our study period. This map

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