Your Dam Your Responsibility (PDF~1.2MB)

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Appendix C The width of the discharge channel must be sized to suit the gradient. This is required to make sure the water flow will not be too fast or restricted. Table C-1 below provides the discharge channel width required for the slope of your channel. Table C-1 for Up to 25-Hectare Catchment Discharge Channel Slope (% vertical to horizontal, or fall in m. per 100m) 3% 4% 5% 6% 7% 8% 9% 10% 15% Discharge Channel Width in metres 4 4 5 6 7 7 7 10 13 For dams that have a catchment greater than 25-hectares and less than 50-hectares, the following size may be used: Figure C-3 Where a long entry channel is required this channel width must not be less than the width the spillway crest and the level must not be higher than the crest section. C The width of the discharge channel must be sized to suit the gradient. This is required to make sure the water flow will not be too fast or restricted. Table C-2 below provides the discharge channel width required for the slope of your channel 77
78 C Appendix C Table C-2 for over 25 up to 50-Hectare Catchment Discharge Channel Slope (%) 3% 4% 5% 6% 7% 8% 9% 10% 15% Discharge Channel Width in metres 6 8 9 11 13 14 15 17 22 In some cases there may be some potential for trimming of the spillway size if a suitably qualified engineer is engaged to consider all the factors relating to your specific dam site. Outlet Pipe General Outlets should be constructed in undisturbed ground in the foundation. The outlet pipe may be a welded steel (preferred), polyethylene or ductile iron pipe below the embankment to discharge the stored water for supply or environmental flow purposes. The type of pipe selected should be able to take the embankment and water pressures. Taking into account a minimum service life of around 50 years, some wall thickness allowance for corrosion should be made for steel and ductile iron pipes. PVC pipe is not considered suitable due to its potential for cracking. Many failures occur along the outlet pipe due to lack of compaction around the pipe particularly under the lower third of the laid pipe. The outlet pipe should be concrete encased because it is very difficult to get suitable soil compaction around a pipe. The trench for the outlet pipe should have vertical sides up to the top of the pipe then battered 1H to 1 V side slopes to allow good compaction of backfill. (Note that this requires careful attention to detail: seek advice). Installation The pipe should be laid in the trench supported at intervals off the floor of the trench (75mm high concrete blocks) to ensure that concrete can flow under the pipe to fully encapsulate it. Prior to pouring the concrete the pipe should be filled with water to test for leaks. When the outlet pipe is being encased, care should be taken that it is not only supported from the floor of the trench but that it is also held down at intervals to stop it floating in the fresh concrete. Filling the pipe with water will help in this regard. Size of Pipe The minimum size should be 200mm to protect against blockage. This size of pipe is also useful should you need to lower the level of the water if an embankment problem develops. The diameter of the outlet pipe should also be large enough to provide adequate supply and environmental flows. Pipe manufacturers have strength and flow chart information readily available.
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Irrigation and Commercial Farm Dams
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ii Published by the Victorian Gover
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iv Contents 6 Safety Surveillance .
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1 Introduction It makes good busine
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2 Risks Posed by Dams 2.1 Owner’s
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2 Risks Posed by Dams The most comm
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2 Risks Posed by Dams 2 Note: The r
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3 Licensing Requirements for Farm D
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3 Licensing Requirements for Farm D
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4 Planning to Build a Dam It is imp
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4 Planning to Build a Dam 4.3 Types
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4 Planning to Build a Dam 4 2. Turk
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4 Planning to Build a Dam becomes a
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4 Planning to Build a Dam 4.6.2 Ext
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5 Construction of a Dam Mixing tops
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5 Construction of a Dam is inviting
Page 34 and 35: 6 Safety Surveillance 6.1 Purpose o
Page 36 and 37: 6 Safety Surveillance QUICK VISUAL
Page 38 and 39: 6 Safety Surveillance 6 Warning: If
Page 40 and 41: 7 Operation and Maintenance of Dams
Page 48 and 49: 8 Dam Failure Emergency Section 8 i
Page 50 and 51: 8 Dam Failure Emergency Action 4. I
Page 52 and 53: 9 Decommissioning of Dams 9 The sit
Page 54 and 55: 10 Glossary of Terms Cut-off An imp
Page 56 and 57: 10 Glossary of Terms Monitoring Rec
Page 58 and 59: Publications directly relevant to f
Page 60 and 61: Appendix A A • probe - a ten-mill
Page 62 and 63: Appendix A Inspection Procedures Ge
Page 64 and 65: Appendix A A and the resistance to
Page 66 and 67: Appendix B 1. Seepage Problem Possi
Page 68 and 69: Appendix B Problem Possible Causes
Page 72 and 73: Appendix B 2. Cracking, Deformation
Page 76 and 77: Appendix B 3. Miscellaneous Problem
Page 78 and 79: Appendix B utlet Works and Concrete
Page 80 and 81: Appendix C The depth of the core tr
Page 82 and 83: Appendix C will be needed. In stabl
Page 86 and 87: Appendix C Other Pipe Details At th
Page 88 and 89: D Figure C-4: Design guide for a fa
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