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Western Dam Engineering <br /> <br /> <br /> <br />16 <br />You Con-du-it; How to Fix a Leaky <br />Pipe <br />Introduction <br />A key component in operation and risk management of <br />small to medium sized embankment dams is the outlet <br />conduit(s) that provide the means to control the <br />reservoir level. Maintenance of conduits through <br />embankment dams is essential to the overall reliability <br />of the dam facility. Conduit deterioration such as joint <br />offsets, cracks, and voids behind the conduit develop <br />for a variety of reasons. This deterioration can lead to <br />the inability to operate the conduit or to excessive <br />seepage into, out of, or along the conduit, which could <br />endanger the integrity of the entire dam embankment. <br />This article presents investigation techniques and <br />common methods for in-place outlet pipe repairs that <br />can extend the life of the outlet conduit and possibly <br />provide an alternative to conduit abandonment or <br />replacement. <br />Outlet Conduit Inspections <br />Typically, dam safety organizations and embankment <br />dam owners will conduct a variety of inspections <br />throughout the service life of a conduit. Regulatory <br />requirements, dam hazard classification, conduit <br />condition, and access dictate both the scope and <br />frequency of the conduit inspections. <br />Dam inspections, and therefore outlet conduit <br />inspections, generally fall into four different <br />categories: formal, intermediate, routine, and <br />emergency. For additional detail regarding each type <br />of outlet conduit inspection, refer to Table 1 below. <br />Table 1: Types of Outlet Conduit Inspections <br />Type of <br />Inspection <br />Frequency <br />Interval <br />Inspection <br />Team <br />Inspection Scope <br /> <br />Fo <br />r <br />m <br />a <br />l <br />1 <br />4-6 yrs - High Hazard <br />10 yrs - Low Hazard <br /> <br />Often performed in <br />conjunction with formal <br />inspection of entire dam <br />facility. <br />Owner Representative <br />Qualified Engineer <br />Regulatory Agency Rep <br />- Prepare inspection plan & checklist2 <br />- Review all available data (design reports, drawings, <br />instrumentation data, current and historic operating data) <br />- Check operability of all mechanical equipment associated with the <br />outlet works, through its full range of operation <br />- Perform external conduit inspection <br />- Perform internal conduit inspection <br />- Document findings in inspection log4 <br />- Develop inspection report5 <br />In <br />t <br />e <br />r <br />m <br />e <br />d <br />i <br />a <br />t <br />e <br />1 <br />1 yr – High/Sig Hazard <br />3-5 yrs – Low Hazard <br />Owner Representative <br />Qualified Engineer <br />Regulatory Agency Rep6 <br />- Prepare inspection plan & checklist2 <br />- Review current operating and instrumentation data <br />- Perform external conduit inspection <br />- Check operability of critical mechanical equipment for outlet works <br />- Perform internal conduit inspection3 <br />- Document findings in inspection log4 <br />- Develop inspection report5 <br />Ro <br />u <br />t <br />i <br />n <br />e <br />1 <br />Conducted in conjunction with <br />other routine inspections of <br />the dam facility <br />Owner Representative <br />- Prepare inspection plan & checklist2 <br />- Perform external conduit inspection <br />- Perform internal conduit inspection3 <br />- Document findings in inspection log4 <br />- Develop inspection report5 <br />Em <br />e <br />r <br />g <br />e <br />n <br />c <br />y <br />1 <br />Conducted when an immediate <br />dam safety concern is present <br />or an adverse loading condition <br />has occurred <br />Owner Representative <br />Qualified Engineer <br />Regulatory Agency Rep6 <br />- Perform external conduit inspection <br />- Perform internal conduit inspection3 <br />- Document findings in inspection log4 <br />- Develop inspection report5 <br />1. More detailed information regarding inspections can be found in Technical Manual: Conduits through Embankment Dams, produced by the Federal Emergency <br />Management Agency (FEMA 2005). <br />2. Develop a detailed inspection plan & checklist to identify the features to be inspected and the objectives of the inspection. <br />3. Based on the results of the external inspection, state or federal requirements, and general facility maintenance, an internal visual inspection may be warranted. <br />4. It is good practice to maintain an inspection log documenting the historic inspections and their associated findings for reference during future inspections. <br />5. After an inspection has been completed, an inspection report should be developed documenting the findings and any recommendations for repairs. <br />6. As a courtesy, an invitation is typically extended to the regulatory agency but the presence of the regulatory agency is not required.