FST- hemispheres
The hemisphere method describes near-bottom flow
conditions in watercourse. The method is based on a
simple concept:
Which weight of a hemisphere exposed to a flow is moved
by a given current from a reform plate.
The set of hemispheres consists of 21 identical
hemispheres with different specific gravity.
The set of hemispheres
with transportation kit and bottom space plate.
Ordering no. 27.000 (Complete
set)
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Preparing for hemispheres
measurement.
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The modern description of the quality of running
waters requires a solid understanding of physical
conditions.
Modern conservation of running water and restoration of
nature aims at natural variation of the physical
environment of running water, considering channel form,
as well as discharge and bottom space sediment.
This complicates the use of traditional methods of
measuring flow for example propeller instruments, well known
to be unreliable for measuring current in weeded running
water or near the stream - bottom.
The hemispere method is an attractive alternative /
supplement for a detailed evaluation of the physical
environment when restoring running water, establishing
spawnbanks, etc.
The method is especially suitable if the flow forces
prevailing at the stream - bottom are of interest.
SPECIFICATION :
| Material................. |
Pressure molded polycarbonate
thickness 2,5 mm |
| Calibration............. |
No. 1 - 21 star metal with
screwed and glued bottom plate. |
| Tolerance.............. |
Specific gravity better than 1% |
| Capsuling.............. |
Hermetically welded in plastic |
| Baseplate.............. |
PVC with ballast inlay (lead)
and inlayed tube level for correct horizontal
positioning |
| Surface.................. |
Sprayer sealed (algare-fusing
surface) |
| Transportation....... |
Alloy transport box with plastic
inserts. |
| Application: |
|
| Current velocity.... |
0 - 4 m/sec. |
| Temperature......... |
- 10 to + 40Cº (storing: -20 to
+50Cº) |
| Maintenance......... |
None - or simply wipe off. |
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Field
Procedures for FST Hemispheres
From Statzner, B and
R. Müller. 1989. Standard hemispheres as indicators of flow
characteristics in lotic benthos research. Freshwater Biology 21: 445-459.
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- Place
the Plexiglas plane in a shallow (ideally 1.8 cm deep)
horizontal pit dug in the stream bottom (Fig. 1).
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-
- Make
sure the plane is level (a slope of less than 2.5% in
each direction). Place small stones under the corners
in coarse substrate to make the plane horizontal.
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- Place
the hemispheres on the plane, one after another,
noting the densest hemisphere that moved.
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-
- The
placement procedure for each hemisphere is as follows:
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- Hold
the hemisphere with one hand slightly above the
plane with the brass wire loop facing downstream and
the monofilament line loosely held by the other hand
(Fig. 1).
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- Bring
the upstream edge of the hemisphere into contact
with the plane.
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- Allow
the hemisphere to drop down between the fingers
completely to the plane – do not press the
hemisphere down onto the plane.
-
- Slowly
remove the hand from the area.
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-
- Note
the heaviest hemisphere that moves on the plane (short
movements of less than 2 cm should be considered
artifacts and should be neglected).
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-
- The
density of the hemispheres can be found in Table 1.
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Sphere #
|
Density (g m³)
|
|
Sphere #
|
Density (g m³)
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|
Sphere #
|
Density (g cm³)
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1
|
1.015
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8
|
1.439
|
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15
|
3.361
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2
|
1.031
|
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9
|
1.624
|
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16
|
3.795
|
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3
|
1.063
|
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10
|
1.834
|
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17
|
4.284
|
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4
|
1.095
|
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11
|
2.070
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18
|
4.836
|
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5
|
1.129
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12
|
2.337
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19
|
5.460
|
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6
|
1.199
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13
|
2.637
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20
|
6.166
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7
|
1.274
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14
|
2.987
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21
|
6.958
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Table
1 - density
of the hemispheres
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LITERATURE:
Standard hemispheres as indicators of flow
characteristics in lotic bentos research.
Bernhard Statzner & Rainer Müller, Zoologisches
Institut der Universitat Karlsruhe, W.Germany, Freshwater
Biology (1989) 21, 445 - 459
Calibration of FST-hemispheres against bottom shear stress
in a laboratory flume.
Freshwater Biology (1991) 26, 227 - 231
Frutiger, A. & Schib, J.-L. (1993) : Limitations of
FST-hemispheres in lotic benthos research. - Freshwater
Biology 30, 463 - 474
Statzner, B. (1993) : Response to Frutiger & Schib
(1993) "Limitations of FST-hemispheres in lothic
benthos research". - Freshwater Biology 30, 475 -
483
Dittrich, A. & Schmedtje, U. (1995) : Indicating
shear stress with FST-hemispheres - effects of
stream-bottom topography and water depth. Freshwater
Biology 34, 107 - 121
B. Statzner * F. KoPunann ** and A.G. Hildrew. ***
* URA CNRS "Ecologie des Eaux Douces"
University of Lyon 1, France.
** Bayerisches Landesamt für Wasserwirtschaft München
Germany
*** Queen Mary and Westfield College, London U.K.
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