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FST- hemispheres

FST 1

The hemisphere method describes near-bottom flow conditions in watercourse. The method is based on a simple concept:

The 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 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 bottom of the stream.

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.

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.

  1. Place the Plexiglas plane in a shallow (ideally 1,8 cm deep) horizontal pit dug in the stream bottom (Fig. 1).
  2. 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
  3. Place the hemispheres on the plane, one after another, noting the densest hemisphere that moved.
  4. The placement procedure for each hemisphere is as follows:
  5. 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).
  6. Bring the upstream edge of the hemisphere into contact with the plane.
  7. Allow the hemisphere to drop down between the fingers completely to the plane - do not press the hemisphere down onto the plane
  8. Slowly remove the hand from the area.
  9. Note the heaviest hemisphere that moves on the plane (short movements of less than 2 cm should be considered artifacts and should be neglected).
  10. The density of the hemispheres can be found in table 1.

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.

 
 
27.000 - FST Hemispheres.
 
 
27.021 - Plastic tray with support for 12 hemispheres.
 
 
27.020 - Base plate.
 
 
27.030 - Container.
 
 
27.020 - Base plate with spirit level.
 
 
Lines used for FST Hemispheres.
 
 
27.040 - Single FST Hemispheres, all sizes can be bought separately.
 
 
Fig. 1 - Preparing for hemispheres measurement.
 
Specificatins
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 (algae-fusing surface)
Transportation: Alloy transport box with plastic inserts
Application:
Current velocity: 0 - 4 m/sec.
Temperature: - 10 to + 40 Cº (storing: -20 to +50 Cº)
Maintenance: None - or simply wipe off

 

Sphere #

Density (g m³)

Sphere #

Density (g m³)

Sphere #

Density (g cm³)

1

1.015

 

8

1.439

 

15

3.361

2

1.031

 

9

1.624

 

16

3.795

3

1.063

 

10

1.834

 

17

4.284

4

1.095

 

11

2.070

 

18

4.836

5

1.129

 

12

2.337

 

19

5.460

6

1.199

 

13

2.637

 

20

6.166

7

1.274

 

14

2.987

 

21

6.958