Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Damsdeteriorating conduit is cleaned without the benefit of CCTV inspection, the conduitmay become unknowingly damaged.Indications of obstructions within the conduit may include reduced outlet flowcapacity, etc. If obstructions are found during the CCTV inspection, the method ofcleaning can be evaluated and a preferred method selected. Sometimes, CCTVinspection and cleaning are done on the same day. Some cleaning services havelimited CCTV inspection equipment. Any cleaning should be attempted only in thepresence of qualified and experienced staff representing the agency/owner of theembankment dam. Complete documentation (including photographs) of all activitiesat the site is highly recommended.The success of any conduit cleaning depends upon accessibility, type of cleaningrequired, and the cleaning method used. A variety of cleaning methods are available:230• Flushing.—If debris and sediments are not significant, adequate cleaning may beobtained by merely flushing the conduit with water. Flushing can beaccomplished by opening a gate or valve and allowing water to flow throughthe conduit or by inserting a flexible hose and pumping water into the conduit.In many cases, volume and low pressure is all that is needed to adequately cleanthe conduit.• Pressure washing.—Pressure washing (figure 133) involves the use of a flexiblehose attached to a metal nozzle that directs jets of water out in front of it toloosen debris and sediments in the conduit. The jet is created by a shapedrestriction in the flow channel that forces water to accelerate and convertspotential energy (pressure) into kinetic energy (velocity). The nozzle ispropelled forward by reverse angle jets. The reverse angle jets also push debrisand sediments backwards toward the end of the conduit, where the flexiblehose exits. Pressure washing is best suited where biomasses or mineralencrustation are to be removed. The pressure selected for cleaning should fullyconsider the condition of the types of conduit material, age, and type of joints.The lowest possible pressure that effectively cleans the conduits should be used.The jets on the nozzle should be angled no more than about 30 degrees, so thejets are not aimed directly at the conduit wall. The nozzle should be keptrotating and moving and should not be allowed to remain in one spot duringjetting.• Mechanical.—Mechanical cleaning utilizes rotating brushes.• Cleaning pig.—Cleaning pigs have wire brushes to scrape the walls of theconduit. A variety of brushes are available, depending on the type of cleaningrequired and the existence of any coatings on the interior surface of theconduit. Cleaning pigs are generally available in diameters up to 48 inches.