Environmental Engineering Reference
In-Depth Information
References
Lee DR (1977) A device for measuring seepage flux in lakes and estuaries. Limnol Oceanogr
22:140-147
Lee DR, Cherry JA (1978) A field exercise on groundwater flow using seepage meters and mini-
piezometers. J Geol Educ 27:6-20
Stonestrom DA, Constantz J (2003) Heat as a tool for studying the movement of ground water near
streams: U.S. Geological Survey Circular 1260:96
Field Activity 4: Stream Gaging Techniques
Stream inflow or outflow may be the dominant component of a wetland water
balance, in which case it is important to measure stream discharges as accurately as
possible. The following field activities will provide values of stream discharge
using three different methods. These measurements are ideally conducted in a
relatively small stream with a well-defined channel that is safely accessible by
observers.
First, identify a suitable stream reach that satisfies the conditions listed in the
first paragraph of the “Discharge measurement” segment of Sect.
3.4
. Following the
procedures described in “Velocity-area-method” of Sect.
3.4
, a measurement section
perpendicular to the flow direction should be set up. One observer wades into the
stream with a current meter and a device to measure the depth of water (e.g., a wading
rod), while the second observer takes notes on the bank and also takes necessary
precautions for the safety of the observer in the stream. Depending on the type of
current meter used, the velocity is measured at a prescribed depth (e.g., six-tenth
point for the Price-type meter), or averaged over the entire depth profile in a
subsection. From the depth and velocity data for individual subsections, the total
discharge is calculated using Eq.
3.22
. Repeat the same measurement two or three
times, preferably moving the cross section upstream or downstream by several meters,
and compare the results to assess the repeatability and errors of the method.
Next, measure discharge in the same stream reach using the float method
described in the section “Other methods of discharge measurement”. This method
usually is not as accurate as the velocity-area method, but it provides a useful
alternative when a current meter is not available. Any floating objects that are
clearly visible and are relatively unaffected by wind can be used. Subsections
should be determined in a manner similar to the velocity-area method (but usually
with coarser spacing of measurement points). Once points are determined, float-
velocity measurements simply replace measurements made with a current meter.
The profile-averaged velocity can be estimated by multiplying the surface velocity
determined with the floats by 0.85.
The tracer-dilution method provides a third value of stream discharge at this
stream reach. First, select a suitable location upstream of the measured cross section
for release of the stream tracer. This location should be sufficiently far upstream to
ensure complete mixing of the tracer solution. This may require preliminary release
of tracer at several upstream locations, along with accompanying downstream
measurements of tracer concentration at several locations, to confirm complete
