Environmental Engineering Reference
In-Depth Information
Short Exercise 10: Measurement of Groundwater Flow Using a Half-
Barrel Seepage Meter
Seepage meters were used to quantify rates and distribution of exceptionally fast
flow through a lake bed (Rosenberry
2005
). In this exercise you will use data from
that report to determine groundwater-surface-water exchange and also compare
standard flow measurements with those based on connecting multiple seepage
cylinders to a single seepage bag.
Mirror Lake is a small, 10-ha lake in the White Mountains of New Hampshire.
A dam built in 1900 raised the lake level by about 1.5 m, increasing the lake surface
area and inundating what had previously been dry land. Water leaks out of the lake
through a portion of the southern shoreline that, because of the stage rise following
dam construction, has been covered by water for only about 110 years. More water
is lost as seepage to groundwater than from the lake surface-water outlet
(Rosenberry et al. 1999). Seepage meters were used to determine where rapid
rates of seepage were occurring and to determine the rates of seepage from the
lake to groundwater.
DatashowninTable
3.10
were collected from 18 seepage meters that
wereinstalledintheareashowninFig.
3.39
. The photo inset shows the
locations of some of the seepage cylinders that were installed prior to the
installation of seepage bags and associated bag-connection hardware. Most of
themeasurementsweremadefromstandard seepage meters similar to Fig.
3.25
.
However, two sets of measurements were made from four seepage cylinders that
were all connected (ganged) to one seepage bag. Your task is to fill in the
missingdatainTable
3.10
for meters 3 and 13 and then answer the following
questions. To convert from ml/min to cm/day you will assume that 1 ml
1cm
3
of water. You will divide your result in cm
3
/min by the area covered by the
seepage cylinder (2,550 cm
2
) and then multiply by the number of minutes in a
day to obtain units in cm/day.
ΒΌ
1. What are the averages of seepage measurements made at each of meters 3, 4, 5,
and 6? Values for 4, 5, and 6 are already provided. What is the range in seepage
rates at these 4 m? How does the variability in seepage among these 4 m
compare with the ranges of values at each meter based on repeat measurements?
2. Repeat this analysis for meters 13, 17, 18, and 20. How do these seepage rates
compare with meters 3 through 6? How does the range in seepage among meters
compare with the ranges of measurements at individual meters?
3. Calculate average values for the two sets of ganged measurements (13, 17,
18, 20 and 3, 4, 5, 6). How do these values compare with the sums of seepage
rates based on measurements made at individual meters? What can you say
about summed versus ganged measurements for areas of slow versus fast
seepage?
