Environmental Engineering Reference
In-Depth Information
the average infiltration rate by channel width.
The calculated number, 0.09 m
3
/s/km, is about
half of that estimated by the stream water-
budget method (Hoffmann
et al
.,
2007
), a dis-
crepancy attributed to the fact that channel
width at the transect location was less than
the average width for the reach over which the
water-budget method was applied.
mining, agricultural, and municipal interests
in the region, a study was conducted to esti-
mate loss rates from Trout Creek (Prudic
et al
.,
2007
). Stream water-budget and heat-transport
methods were applied. Streambed temperatures
were monitored at seven locations. At three of
these locations, temperatures were monitored at
depths of 0.1, 0.2, 0.5, 1.0, and 1.5 m beneath the
stream channel.
At one of the measurement sites, infiltration
was estimated for a 7 day period in April 2000
by using the VS2DH model for simulating water
and heat transport in the subsurface. The model
was set up to simulate water and heat flow in
a two-dimensional section perpendicular to the
stream channel. Lateral boundaries extended
15 m on either side of the stream to allow
horizontal flow within the unsaturated zone.
The water table was set at a fixed depth of 30 m,
consistent with water levels in a nearby observa-
tion well. Stream stage was assumed constant
throughout the simulation. Stream tempera-
tures were set equal to measured temperatures,
which were allowed to change every 30 min.
The PEST parameter estimation program
(Doherty,
2004
) was used to determine the
value of saturated hydraulic conductivity that
produced the best agreement between simu-
lated and measured temperatures at depths of
0.2, 0.5, and 1 m. All other hydraulic properties,
as well as the thermal properties, were held
constant and are found in Prudic
et al
. (
2007
).
Example: Trout Creek, north-central
Nevada
Trout Creek in north-central Nevada is typical
of streams in the Basin and Range Province of
the western United States (Prudic
et al
.,
2003
;
2007
). Throughout much of its reach, streamflow
is ephemeral; most days of the year there is no
flow. Following periods of extended snowmelt
or rainfall, streamflow can occur for periods of
several days. Because of limited groundwater
supply and increased demands for water from
22
20
18
16
14
12
10
0.75
1.50
6
7
8
9
10
11
12
13
14
15
April 2001
Figure 8.6
Measured (solid line) and simulated (dashed
line) temperatures at depths of 0.75 and 1.50 m beneath
Rillito Creek in April 2001 (after Hoffmann
et al
.,
2007
).
Stream, measured
0.2 m, simulated
0.2 m, measured
0.5 m, simulated
0.5 m, measured
20
15
10
5
Apr 13
Apr 14
Apr 15
Apr 16
Apr 17
Apr 18
Apr 19
Apr 20
2000
Figure 8.7
Measured and simulated temperatures at
depths of 0.2 and 0.5 m beneath Trout Creek in April 2000
(after Prudic
et al
.,
2003
).
