1. STREAM SEDIMENT SAMPLING
Hydrography Skills Set Training
Course No
June 2012

2. WHAT IS SEDIMENT?
Definition: “Sediment is any solid matter eroded, transported or deposited by flowing water”
‘Silt’ denotes a size range of material to 0.062mm

3. Sedimentation Processes
Erosion: The wearing away of the earth’s surface by surface water runoff
Transportation: Movement of eroded particles through stream channels to the point of deposition
Deposition: Deposition of eroded particles in stream channels, flood plains, reservoirs, harbours, canals etc 3

4. Why is Sediment a Problem?
Reservoirs:
Loss of potential water storage due to sediment accumulation
Further reduction by evaporation due to change in lake surface area from sediment accumulation
Irrigation Canals:
Generally constructed in erodable material, so scour and sediment deposition can occur
Degradation Below Dams:
Potential dam failure due to undermining causing lowering of bed level downstream of wall
Power Station Turbines:
Sediment can damage blades and bearings 4

5. Why Sediment Samples are Required?
Quantity and particle size of sediment is required
Quantity:
Determines necessity for and type of sediment removal devices
Particle Size:
As sediments of different size act differently, data for particle size is important
Samples should be taken regularly and at different gauge heights (full range) 5

6. Theory of Sediment Transport
Contact Load:
Material that rolls or slides along bed of stream
Suspended Load:
Material that moves along the stream in suspension
Saltation Load:
Material ‘bounding’ along the stream bed, in contact with bouncing particles which may force other particles upwards for a short period of time
Bed Load = Coarse material moving near the bed (i.e. Contact Load and Saltation Load and other particles that cannot be sampled by a suspended load sampler) 6

7. Effects of Sedimentation7

8. Sampling Equipment Depth Integrating Type:
By traversing the stream at a uniform speed the sampler is moved through each vertical to receive a sample proportional to stream velocity
Sampler is designed to fill at a rate proportional to the velocity of the approaching flow
One sample per vertical is taken by lowering and raising the sampler to and from the stream bed to achieve a representation of mean concentration and particle size in each vertical
Attached to a gauging rod or handline
DH-59
DH-48 8

9. Depth Integrated Sampling9

10. Sampling Equipment Point Integrating Type:
Sampler remains stationary at each point on the vertical with electrical activation of sampler at specific point on vertical
Samples are integrated or ‘added-up’ on each vertical over a period of time
Allows mean concentration of sediment to be determined
Usually suspended from a gauging winch
P 61 10

11. Sampling Equipment Bed Load Samplers:
Designed to sample sand, silt, gravel or rock in close proximity to stream bed
Samples collected in a polyester/monofilament bag or scoop
Suspended from either a gauging rod or winch
BLSH
BLS30 / BLS48
Van Veen Grab 11

12. Bed Load Sampling 12

13. Sampling Equipment Static Samplers:
Free standing or mounted on trees, bridge piers, gauge posts to obtain discreet samples at set gauge heights
Sample bottles are replaced after flood events
Rising Stage Sampler 13

14. Sampling Equipment Grab Sample: Water ‘pumped’ into plastic bladders
Water scooped up in bottle manually
Water ‘pumped’ into plastic bladders
Sample preservation and chain of custody 14

15. Sampling Equipment Automatic Sampler:
Water pumped from stream and bottles filled
Available as refrigerative or non-refrigerative
Configured to sample at critical gauge heights or flow proportional 15

16. References
Snowy Mountains Hydro-Electric Authority – Hydrographic Course (September 1966), Volume 3
United States Geological Survey ‘ Field Methods for Measurement of Fluvial Sediment’, Book 3, 1982.

17. Questions ?