1. Project Title: Construction of Self-Cleaning Spawning Substrate
2. Contact
Doug Geiling
Great Lakes Laboratory for Fisheries and Aquatic Sciences, Department of Fisheries and Oceans, 1 Canal Drive, Sault Ste. Marie, Ontario P6A 6W4
Tel.: (705) 942-2848; FAX: (705) 941-3025; E-mail: Geiling@ssmare.ssm.dfo.ca
3. Agencies Involved
North Shore of Lake Superior Remedial Action Plans*, 1194 Dawson Road, Thunder Bay, Ontario P7B 5E3
(* Includes Environment Canada, Great Lakes Cleanup Fund, Ontario Ministries of Natural Resources and Environment and Energy)
Department of Fisheries and Oceans, Great Lakes Laboratory for Fisheries and Aquatic Sciences, 1 Canal Drive, Sault Ste. Marie, Ontario P6A 6W4
4. Restoration Goal
Provision of spawning substrate which will remain free of fine sediment deposition.
5. Project Type
Construction of an upwelling through a man-made spawning bed.
6. Background and Rationale
Fish spawning habitat has been rendered inaccessible or degraded in quality by anthropogenic influences including deposition of fine sediments. Barrier construction, urban and agricultural development may cause increased erosion and sedimentation of spawning habitat. In many cases, correction of sedimentation problems in spawning habitat may require extensive and costly rehabilitation of not only spawning habitat, but also the upstream sources of increased sedimentation.
Construction of self-cleaning spawning habitat may be a localized alternative to extensive riverine rehabilitation. By creating an upwelling through man-made spawning habitat it is possible to locate spawning habitat in zones of fine sediment deposition. The force of upwelling water will prevent sedimentation of the spawning habitat itself, without altering significantly the hydrologic characteristics of the reach in which the habitat is constructed.
7. Regulatory Considerations
Compliance with Provincial, State, Federal, Municipal, or other environmental assessment regulations as they apply to instream works (intake site and distribution system) and terrestrial works (pipeline). In Ontario this will include compliance with the Navigable Waters Protection Act, the Fisheries Act, and the Ontario Ministry of Environment and Energy's Lake Filling Guidelines.
8. Criteria
The force of upwelling must repel fine sediment deposition while not dislodging deposited eggs. The system should be as close to maintenance-free as possible. Thus, available hydraulic head must be utilized to drive the system rather than pumps or other mechanical means. The area of spawning habitat will vary according to head available. Spawning habitat design should allow for placement in a range of depths (usually < 3.0 m) with substrate particle size tailored to the species targeted.
9. Project Design
The self-cleaning substrate system consists of a water intake connected by piping to a distribution manifold. The distribution manifold, or network of piping which contains small diameter orifices, underlies a man-made spawning bed with particle sizes tailored to the requirements of the targeted species. High density polyethylene pipe (HDPE) is recommended while polyvinylchloride pipe (PVC) is an acceptable alternative.
Flow through the system is continuous but will vary according to available hydraulic head and base flow at the intake. As the spawning substrate will be free from sediment initially, the up-flow needs only to maintain suspended particles in the water column. The up-flow velocity to accomplish this is significantly less than that required to flush substrate laden with fine sediment, thus reducing the size (and expense) of the piping and trenches required.
An up-flow velocity of 0.07 m/s has been assumed in design calculations. This velocity is sufficient to maintain in suspension particles approximately 0.6 mm in diameter and smaller. Also assumed is a porosity value of 15% on a horizontal plane for the spawning substrate. Using these assumptions, a minimum 0.6 m hydraulic head is required to provide sufficient flow volume from the distribution network to the spawning substrate. The hydraulic head is defined as the difference in elevation between the surface of the water at the intake site and the spawning habitat.
The maximum area of the spawning bed can be estimated from the availability of flow at the intake location. Select two locations on the stream, one above and one below the candidate intake site. The locations should be at least 50 m apart unless the stream is very steep. Measurements for base flow calculations should be taken during a period of low flows to ensure that adequate water is available to the intake year round.
To calculate base flow, measure the cross sectional area of the
stream and wetted perimeter at both locations. Also required is
the difference in elevation of the surface of the water and the
distance between the locations to calculate the slope of the water
surface. Base flow is then calculated
as follows:
Base Flow (m3/s) = 28.6 (A)1.67 (S)0.5/(P)0.67
where: A = Average Cross Sectional Area (m2)
P = Average Wetted Perimeter (m)
S = Slope of Water Surface (m/m)
Maximum spawning area size (m2) can be estimated by multiplying
the base flow value by 22.5. Having measured the available hydraulic
head, final size and location of the spawning area can be determined
using cost/benefit analysis. Costs will increase with distance
between the intake and spawning area as well as with pipeline
diameter required. Benefits may increase with increasing spawning
area size.
Table 1 provides a condensed version of the range of man-made spawning bed sizes which are possible given various hydraulic head and pipeline diameter values. An expanded version of this information can be found in Wm. R. Walker Engineering Inc. (1994).
10. Implementation
The intake consists of two concentric sections of corrugated steel culvert pipe (1.2 and 1.8 m diam.) which are welded to a 6 mm plate steel base. A length of steel bell-mouth pipe, equal in diameter to the pipeline leading to the manifold, penetrates through both culvert walls. The culvert sections should be 0.9 m long if the pipeline diameter is 300 mm or less, otherwise they should be 1.2 m. The space between the culvert pipes should be filled with rock to sink and anchor the intake. The opening above the inner culvert should be covered with 25 mm mesh fibreglass screen.
The pipeline connecting the intake with the distribution manifold should be buried in a trench. Width of the trench should be at least 0.8 m plus pipe diameter, while the depth should be at least 1.35 m plus pipe diameter. The pipe should be laid in a compacted sand bedding which is at least 150 mm thick below the pipe and 300 mm above the pipe. The balance of the trench may be backfilled with compacted native material. The pipeline should have a downward gradient along its entire length, although the slope need not be constant.
Geotextile filter fabric should be laid on the stream bed prior to substrate placement. The filter fabric should be overlain with a 150 mm layer of granular material (max. particle diam. 25 mm) to provide a bed for the distribution piping. The distribution manifold can consist of a single pipe supplying a 1.0 m wide rectangular spawning bed, or it may consist of a series of paralell pipes spaced at 1.0 m intervals. In the case of a single distribution pipe, the pipe diameter will be the same as the pipeline from the intake. In multiple pipe systems, the product of the length of the spawning bed and the 1.0 m width of substrate the pipe is to supply is termed the contingent area. Using the contingent area as the equivalent of bed size and the known hydraulic head, Table 1 can be used to determine the diameter required for the distribution pipes.
Two lines of orifices (25 mm diam.) should be drilled into each
distribution pipe. One line of orifices should be drilled on each
side of the pipe half way between the top and the maximum horizontal
width of the pipe. The orifices in each line should be spaced
150 mm apart, and the two lines should be offset such that one
orifice is present for every 75 mm of pipe. Granular material
(37-75 mm diam.) should be placed around each pipe to prevent
clogging. A layer of spawning substrate extending to 0.5 m beyond
the edge of the outermost distribution pipes can then be added.
The spawning substrate layer should be 200 mm thick above the
tops of the pipes, and can be comprised of stone ranging in sizes
from 10 to 125 mm.
The outer slopes of the spawning area should be armoured with 100 to 250 mm rock. The armouring should extend from the top of the spawning area to the stream bed at a slope of 3:1 or greater (horizontal:vertical).
11. Degree of Environmental Intervention
The degree of intervention will vary between application sites. Some trees may have to be removed to facilitate trench digging but the effects of these losses on the stream can be minimized by locating the trench away from the stream bank. Construction of the in-stream components will likely displace a small amount of sediment, but this too can be minimized by construction during a period of low flows. Significant direct negative impacts on biota are not expected.
12. Cost
The following unit costs have been provided by Wm. R. Walker Engineering Inc. (1994). All costs quoted are estimates in 1994 Canadian dollars. Actual costs may vary significantly depending on the characteristics of the site selected.
Piping: HDPE pipe, includes installation and all fittings.
Pipe Diam. (mm) Cost per metre
150 $ 74 315 $ 86 630 $132Intake:
- Inlet pipe diameter 315 mm or less: Allow $1 500
- Inlet pipe diameter greater than 315 mm: Allow $2 500
Substrate Bed:
- Material sourced on site: $ 12 per m3
- Material trucked to site: $ 18 per m3
Thus, the approximate cost of a 25 m2 (5 m by 5 m) spawning bed constructed with trucked-in materials and located 100 m from the intake (315 mm pipe) would be:
Intake: $1 500 Piping: Pipeline 100 m @ $ 86 /m $8 600 Distribution 6 * 5 m @ $ 86 /m $2 580 Substrate Bed: 25 m2 * 0.7 m @ $ 18 /m3 $300 Armouring allowance (est.) $300 $13 280
13. Biological Assessment
Measurement of egg deposition and hatching success prior to and
following construction
are suggested.
14. Measures of Success
The project can be considered a success if the following conditions are met:
1. Egg deposition and survivorship are increased on the man-made spawning area as compared to the same area of substrate before construction,
2. Sedimentation of the man-made spawning area does not occur, or occurs so slowly that the area remains viable for many years without requiring maintenance, or
3. If periodic, but infrequent, flow dependent flushing is sufficient to provide sediment free substrate during critical spawning periods.
An alternative method of measuring success would be to monitor fish production on the spawning area over time. Economic value of the fish produced over time could then be compared to the cost of construction and subsequent maintenance.
Success Rating: 1
The system described herein has yet to be tested in the field. However, similar but less rigorously designed systems have been constructed in the Nipigon River (Savioja and Kushnier 1991, Ont. Min. Nat. Res. unpubl. report). Results from these trials have been mixed, but evidence of brook trout (Salvelinus fontinalis) spawning on portions of one of the two project sites has been reported. Lack of success at one site was attributed to overly strong flows through the substrate while sedimentation occurred on portions of the other project site. It is possible that the Nipigon River results could have been improved had flow rates through the spawning substrate been more tightly controlled.
15. Key References
Wm. R. Walker Engineering Inc. 1994. Report on Self-Cleaning Stream Substrate System. Job # 93/74. Sault Ste. Marie, Ont.
Correct citation for this contribution:
Geiling, D. 1995. Construction of self-cleaning spawning substrate, p. 32-38. In J.R.M. Kelso and J.H. Hartig [editors]. Methods of modifying habitat to benefit the Great Lakes ecosystem. CISTI (Can. Inst. Sci. Tech. Inf.) Occas. Pap. No. 1.