Your Dam Your Responsibility (PDF~1.2MB)
Your Dam Your Responsibility (PDF~1.2MB) Your Dam Your Responsibility (PDF~1.2MB)
Appendix B utlet Works and Concrete Structures Problem Possible Causes and Potential Harm Outlet Releases Eroding Toe of Dam Piping Along Outlet Note: Do not allow anyone to enter the water to try and block the outlet when water is flowing. Outlet Pipe Damage (these can be difficult to diagnose because of occurring internally within the embankment) Cause: 1. Outlet pipe too short. 2. Lack of energy-dissipating pool or structure at downstream end of conduit. Harm: 1. Erosion of toe over-steepens downstream slope, causing progressive sloughing. 2. Eroded material causes environmental damage. Cause: 1. Fracture or joint failure in outlet pipe. 2. Seepage along outside of pipe (poor construction). Harm: 1. Will get progressively worse and cause embankment failure. 2. Can be difficult to stop once it progresses beyond a seep. Cause: 1. Settlement; impact. 2. Rust (steel pipe) pitting. 3. Settlement or poor construction practice. Harm: 1. Excessive seepage, possible internal erosion. 2. Provides passageway for water to exit or enter the pipe, resulting in erosion of internal materials of the dam and possibly dam failure. Action Required B Action: 1. Extend pipe beyond toe (use a pipe of same size and material, and form watertight connection to existing conduit). 2. Protect embankment with riprap over suitable bedding. Action: 1. Investigate cause by probing and digging. 2. Determine if leakage is carrying soil particles and monitor flow rate changes. 3. If flow increases lower dam water level as quickly as possible. 4. A suitably qualified engineer should inspect the dam and recommend further actions to be taken. Action: 1. Check for evidence of water either entering or exiting pipe at crack/ hole/etc. 2. Tap pipe in vicinity of damaged area, listening for hollow sound that shows a void has formed along the outside of the conduit. 3. If there is any suspicion at all of a progressive failure, request urgent engineering advice from a suitably qualified engineer. 4. Install upstream valve to isolate pipeline and enable inspections. 71
72 C Appendix C Standard Design Guide for Farm Dams Application These guidelines are meant for dams not exceeding 3 metres in height and 20 megalitre in capacity, and for which the consequences of failure are reliably assessed as low (ie. in the ‘low hazard’ category). Note that these size limits are less than those set out in Section 3.2 of this booklet. Warning These guidelines are given in good faith only as an outline in principle as to how a safe and durable dam may be designed. They are not intended as a manual giving explicit instructions which may be applied to any given dam, to do so requires professional appraisal of the dam site, proposed materials and construction procedures, as well as any relevant features of the site-specific hydrology, meteorology, operation of the dam and any other relevant matters. As stated elsewhere in this booklet, a dam must be matched to its site for assuring performance, and the relevant expertises to do that adequately, even for small dams, are typically outside the expertises of dam owners. The state of Victoria and the authors of these guidelines do not accept any responsibility for application of these guidelines, in whole or in part, to any particular dam, and owners are warned that professional advice from a suitably qualified engineer is required for that purpose. General It is beyond the scope of this booklet to cover all aspects of the design of larger or complicated dam sites. So if there is any doubt about the circumstances or the nature of the materials or site on which the dam is to be constructed you will need to seek professional advice from a suitably qualified dam engineer. Generally the dam design and construction can be broken up into the following four areas: • foundations; • embankment; • spillway; and • outlet works. The following is an outline of ‘good practice’ criteria in designing and constructing such a dam. Foundation The first step is to strip the total foundation area, on which the dam is to be placed, of all topsoil and organic material. Stockpile topsoil separate from other materials so that it can be spread on the finished surface of the dam and spillway chute to encourage grass re-growth and provide protection from erosion. All soft material and pockets of sand or other permeable material should also be removed from the foundation and replaced with sound compacted material. If on stripping the topsoil from the foundation the surface has voids and cracks, advice should be sought. Foundations must be stable and not excessively steep. On steep sided abutments against which the dam is to be placed do not leave vertical or overhanging material. Cut back preferably to a slope of 1 Horizontal (H) to 1 Vertical (V) but do not have any surface steeper than 0.5H to 1V. The core trench located under the centre of the dam should have cut slopes of 1H to 1V and have a base width of 3 metres.
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72<br />
C<br />
Appendix C<br />
Standard Design Guide for Farm <strong>Dam</strong>s<br />
Application<br />
These guidelines are meant for dams not exceeding 3 metres in height and 20 megalitre in capacity, and<br />
for which the consequences of failure are reliably assessed as low (ie. in the ‘low hazard’ category). Note<br />
that these size limits are less than those set out in Section 3.2 of this booklet.<br />
Warning<br />
These guidelines are given in good faith only as an outline in principle as to how a safe and durable<br />
dam may be designed. They are not intended as a manual giving explicit instructions which may be<br />
applied to any given dam, to do so requires professional appraisal of the dam site, proposed materials<br />
and construction procedures, as well as any relevant features of the site-specific hydrology, meteorology,<br />
operation of the dam and any other relevant matters. As stated elsewhere in this booklet, a dam must be<br />
matched to its site for assuring performance, and the relevant expertises to do that adequately, even for<br />
small dams, are typically outside the expertises of dam owners. The state of Victoria and the authors of<br />
these guidelines do not accept any responsibility for application of these guidelines, in whole or in part, to<br />
any particular dam, and owners are warned that professional advice from a suitably qualified engineer is<br />
required for that purpose.<br />
General<br />
It is beyond the scope of this booklet to cover all aspects of the design of larger or complicated dam sites.<br />
So if there is any doubt about the circumstances or the nature of the materials or site on which the dam is<br />
to be constructed you will need to seek professional advice from a suitably qualified dam engineer.<br />
Generally the dam design and construction can be broken up into the following four areas:<br />
• foundations;<br />
• embankment;<br />
• spillway; and<br />
• outlet works.<br />
The following is an outline of ‘good practice’ criteria in designing and constructing such a dam.<br />
Foundation<br />
The first step is to strip the total foundation area, on which the dam is to be placed, of all topsoil and<br />
organic material.<br />
Stockpile topsoil separate from other materials so that it can be spread on the finished surface of the dam<br />
and spillway chute to encourage grass re-growth and provide protection from erosion.<br />
All soft material and pockets of sand or other permeable material should also be removed from the<br />
foundation and replaced with sound compacted material.<br />
If on stripping the topsoil from the foundation the surface has voids and cracks, advice should be sought.<br />
Foundations must be stable and not excessively steep. On steep sided abutments against which the dam is<br />
to be placed do not leave vertical or overhanging material. Cut back preferably to a slope of 1 Horizontal<br />
(H) to 1 Vertical (V) but do not have any surface steeper than 0.5H to 1V.<br />
The core trench located under the centre of the dam should have cut slopes of 1H to 1V and have a base<br />
width of 3 metres.
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