WSP05388

• File Number: 8449
• Description: Platte River Projects
• State: CO
• Basin: South Platte
• Date: 9/9/1980
• Author: USGS
• Title: Hydrologic Analysis of the Proposed Badger-Beaver Creeks Artificial-Recharge Project, Morgan County, Colorado
• Water Supply Pro - Doc Type: Publication

Development of Ground-Water Models

'.

To predict the effects of artificial recharge on the aquifer system, a
ground-water model of each of the two alluvial valley aquifers was construct-
ed. These models consist of a unique set of input parameters describing the
j~spective aquifer systems and a digital computer program which approximates
the solution to the ground-water flow equation. The program used is a modi-
fication of the standard U.S. Geological Survey two-dimensional, finite-dif-
ference model using the iterative, alternating direction, impl icit solution
techn i que (Trescot t and others, 1976).

,:

To model the aquifers, maps of the areas of interest were fir~t subdi-
'vided into a rectangular network of nodes'. Beaver Creek valley was subdivided
into 37 rows by 27 columns with the largest node representing an area of'
0.5 mi2 and the smallest node an area of 0.08 mi2. Badger Creek valley was
subdivided into 33 rows by 24 columns with the largest node representing an
area of 0.3 mi2 and the smallest node an area of 0.04 mi2. The input param-'
eters to these models included the hydraulic head, hydraul ic conductivity"
specific yield of the aquifer, altitude of bedrock surface, and altitude of,
land surface at each node. In addition, al I the stresses to the aquifer were,
specified. These stresses included boundary fluxes, pumping, recharge, and'
discharge to the stream.

All of these stresses are input to the model except discharge to the'
stream, which is computed by the model. Discharge to a stream was simulated'
by defining a node to be constant head if the water level at a stream node
rose above the bottom of the streambed (as defined by the altitude of land
surface). The discharge to all constant head stream nodes was accumulated and,
accounted for as the surface streamflow leaving the modeled area. If the
flow to a stream node reversed directions as water l~vels in the aquifer de-'
clined, thus making the stream a source of water, the designation of a con-,
stant head node was discontinued and that node would no longer be considered
a part of the flowing stream.

Data Availabi lity

. !
i
i.

The most abundant data available for ground-water modeling are water,
levels. In Beaver Creek valley, south of Brush, water-level data for at least
15 years were available for 24 wells (fig. 14). The hydrographs of these,
wells (fig. 15) illustrate some interesting trends. Little change in water,
'levels is noted in the southern end of the valley (higher alti tudes) since
about 1955-60. The date of the initial water-level declines cannot be deter-:
mined from the avai lable data for that part of the valley. In the northern i
end of the valley (lower altitudes) the date when water levels began declin-:
jng moved steadily forward in time. Thirteen wells within the modeled area of i
Badger Creek valley have at least 10 years of data (fig. 16). Unfortunately, I
most of these wells are considered part of the South Platte River alluvial:
~quifer and are in areas that are irrigated by surface-water supplies. The I

I i

i
,
I'
j
'j

33