The Algerian experience in the domain of small dams studies
The objective of this paper was to summarize the information obtained from studies of small dams in Algeria from 1987 to the present With the growing consumer demand, Algeria chose to maximize its surface water resources by the construction of small dams. Following the inadequate performance of these projects, the public administration re-evaluated its responsibility for designing small dams. The lack of experience with such studies resulted in a big investment in dam design. To improve this situation, the Algerian consulting engineers developed their own calculation methodology. In contrast to big dams, small dams are unique due to their particular characteristics. The studies have become more consistent and as a result the construction delays have decreased from 12 to 6 months, thus reducing the overall cost, which passed from 2 500 000 to 1 200 000 DA ($50 000 to $25 000) without affecting the quality and the reliability of the design. These improvements have been achieved thanks to a certain normalization of the studies and a rationalization of the tasks, such as the hydrological study, the geological and geotechnical investigations (bores, excavations, laboratory tests), the hydraulic design of the construction works, the calculation of the reinforced concrete works and the drawings. The reduction in delays was obtained thanks to technical improvements and computing tools. The working studies were divided into six distinct projects: topographical; hydrological; geological and geotechnical; feasibility; planning; and call for tenders. The hydrological study highlights only essential parameters that are required for the continuation of studies. The geological and geotechnical study, performed on the basis of data collected in a reconnaissance campaign and data from limited laboratory tests, defines the type of embankment required, considers the possible treatments for the foundations, and generates the geotechnical parameters needed for scaling the hydraulic structure. The choice of type of embankment, which is linked at the availability of construction materials of suitable quality, is limited to either a homogeneous or zoned embankment. The details of the embankment are derived from the application of a standard execution plan, which is valid for all projects involving small dams; only the local geotechnical levels need to be specified. The choice of spill wall mainly depends on the relief. Two types of spillways are recommended: lateral with frontal entry; and lateral with lateral entry. The heights of the spillway walls are standardized, and plans for an iron framework with different heights are developed, ready to be adapted to the specific project. USBR types stilling basins are recommended. Two standardised outlet types have been selected and designed, to be applied to all the small dam sites, and the implementation plans are developed and ready for a wide use. To better understand these studies, a sample of more than twenty small dams currently in operation, in five Wilayases in northern Algeria, is presented. Our experiences, although limited when compared to certain countries in the Mediterranean basin, deserve to be taken into consideration and can contribute in improvements in the security and performance of small dams.