dams are 15 meters or more in height. Dams that are between 10 and 15 meters in height are treated as large dams if they present special design example, an unusually large flood-handling requirement, location in a zone of high seismicity, foundations that are complex and difficult to prepare, or retention of toxic materials. Dams under 10 meters in height are treated as large dams if they are expected to become large dams during the operation of the facility. Information in this guide concerns small dams that do not meet the ICOLD (1974) definition of a large dam given above. It does not provide guidance for excavated ponds as they do not represent a safety concern and they generally do not have an embankment associated with them. Dam Management in In , the Ministry of Natural Resources (MINIRENA) is in charge of water resources. It defines national water policy and establishes a national master plan and management of water resources. The Ministry of Agriculture and Animal Resources (MINAGRI) and the Ministry of Infrastructures (MININFRA) are the main institutions using water resources. MINAGRI, is responsible for the planning and design of dams for Agriculture purposes while MININFRA is responsible for the planning and design of dams for Water Supply and Hydropower purposes. However some dams are planned as multipurpose in both Ministries. During the design phase, the Ministries usually adopt industry accepted standards of dam design. No formal guideline/document has been prepared about how dams are designed, operated and maintained. For the dams under MINAGRI, operations of schemes and maintenance of irrigation infrastructures are planned to be handled by the farmers through Water Users Associations (WUAs). Minor maintenance works such as removal of silt and weeds from canals and rebuilding of temporary diversion structures are done by the users’ own initiatives at the beginning of the irrigation season. Major maintenance works that require input of experts and materials are handled by MINAGRI. In 2010, the Irrigation and Mechanization Task Force was established under MINAGRI to carry out the operation and maintenance of water and irrigation infrastructures among other duties. Dam ownership Dam owners are responsible for the safety and the liability of the dam and for financing its upkeep, upgrade, and repair. The common legal understanding is that the dam owner is the developer of the dam, and is therefore responsible for the potential impacts, which the impoundment of water may have on upstream or downstream life, property and environment.
Impervious core and shell Seepage control, filter and drainage Wave protection Freeboard Allowance for settlement width and crest protection Embankment vegetation, and The design has to ensure: It is impermeable enough to prevent excessive loss of water from the reservoir. all conditions of construction, reservoir operation, and seismic activity, the embankment slopes, foundation, and abutments must remain stable. Seepage through the embankment, foundation, and abutments must be properly controlled and collected to prevent excessive pore water pressures, piping, sloughing and removal of material by solution or erosion of material by loss into cracks, joints, and cavities. Settlement of the dam and foundation must not be excessive so as not to reduce the freeboard of the dam. The upstream slope must be protected against erosion by wave action, and the dam crest and downstream slope must be protected against erosion due to wind and rain. A sufficient bond between the embankment and its foundation must exist to prevent the development of seepage paths; excessive hydrostatic uplift must be controlled by proper drainage. The single most common cause of earthen dam failures is overtopping of the embankment. An undersized spillway will lead to overtopping; therefore spillway design is critical to reservoirs. The spillway must be located such that discharge will not erode or undermine the toe of the dam. If the banks of the spillway are made of erosive material, provision must be made for their protection. Consideration must be given to the hazard to human life and potential property damage that may result from the failure of the dam or excessive flow rates through the spillway. Further consideration must be given to the likelihood of downstream development that may result in an elevation of the hazard classification. Such developments should be monitored and pointed out in dam safety reports. Concrete Gravity Dam Design The major concepts and criteria in designing a concrete gravity dam are that it has to be: Safe against overturning at any horizontal within the dam. Safe against sliding at any surface within the dam and its foundation. So proportioned that the allowable stresses in both the concrete and the foundation shall not be exceeded.
Crest •Deteriorated joints •Cracking/Spalling •Poor alignment Downstream Face • Deteriorated joints • Cracking/Spalling • Seepage Abutments • Vegetation/erosion • Sloughing/slides/cracks • Seepage/wetness Toe • Erosion/undermining • Seepage/wetness • Foundation drains Gallery • Deteriorated joints • Cracking/Spalling • Seepage Inspection Procedures Getting the most out of an inspection requires some preparatory work: Figure 1 Successive passes The previous diary entries should be reviewed first to note any areas which will require special attention; and If the purpose of the inspection is to re-evaluate suspected defective conditions discovered during the last inspection, any available construction drawings should first be examined for a possible explanation of the situation ( but do not speculate, obtain professional advice if the is any doubt or ambiguity in the situation).