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W.01 Engineered Dams
Introduction
Dams, dikes, and levees are engineered structures with an impervious core (which, in most cases, makes the difference with vernacular dams) that support flood control and the protection of built and agricultural areas. They are usually located along or across rivers, deltas, or seashores (see also Measure W.06 ).
Dams:
Dams represent engineered, mostly large barriers for water control, storage, and supply during drought. Dams can also impound other liquids, such as wastewater. They often come with complex control systems (e.g., spillways or control gates). This compendium does not refer to dams for hydroelectricity production.
Dikes and levees:
Dikes and levees (also: embankments) aim to act as a barrier for diverting, redirecting, or confining flood waters. In contrast to dams, dikes, and levees usually do not have complex water control mechanisms. Some non-engineered dikes and levees do not have an impervious core (see Measure W.02 ). The impervious core, which is built deeper than the dike base, aims to avoid water infiltration through the soil. The crest and the inner wall must be designed (at least in some strategic places) to withstand the submersion, avoiding a total collapse of the dike during a flood. Moreover, geotextile containers and tubes come increasingly into use as a hybrid form of embankment or to support the structure of dams, dikes, or levees (see Measure W.03 ). Note that the goal of the dike contradicts the drainage necessities (see Measure S.07 ) and therefore must be carefully designed.
Check Dams:
Check dams represent a simpler type of dams and describe barriers across channels or rivers. They aim to reduce erosion and sediment accumulation and fix the stream axis during a flood event. However, in contrast to other dams and dikes, check dams continuously operate and do not only come into effect during flood events. Wooden structures and gabion retention walls can also be used as check dams (see Measure W.05 ).
Benefits & Risks
In general, the construction of dams, dikes and levees should consider the effects of the changing climate and the linked hydrological events. The failure of a dam could cause severe floods. To ensure the safety of dams, it is crucial to apply structural, operative, and emergency planning. Large and concrete dams need comparatively strong monitoring and maintenance. As a result, the risk of failure can be higher regarding smaller dams due to sometimes neglected maintenance and design standards.
Environmental Impact
Depending on the scale, type, and location of a dam/dike/levee, the structure can cause the loss of ecosystems and habitats, submersion of large areas of land, the disruption of natural water flows and quality, and the fragmentation of river systems.
Good Practice
Dike Construction along the White Nile, South Sudan
Heavy rains caused severe floods and resulted in the collapse of a dike along the White Nile in 2021. The incident left the South Sudanese town of Bor in the east of the White Nile wetlands devastated. Most of the town’s residents lost their homes and agricultural fields. As a response, the works involved the youth of Bor to fix around 90 spots along the dike with sandbags. In addition, a new dike of 9.4 km has been constructed with the help of excavators while the existing embankments have further been reinforced. Lastly, community-based disaster risk management committees were formed that received training in emergency preparedness and were equipped with response toolkits (Loyce 2021).
References
Forestry Blog (2023): Different Types of Check Dams & Design Procedures
Loyce, Nabie (2021): Construction of Dike Brings Hope to Flood-Affected Communities in Bor , IOM South Sudan
Martinez, Maria; Bakheet, Ramez; Akib, Shatirah (2021): Innovative Techniques in the Context of Actions for Flood Risk Management: A Review , Eng
Ward, Philip J.; Ruiter, Marleen C. de; Mård, Johanna; Schröter, Kai; van Loon, Anne; Veldkamp, Ted et al. (2020): The need to integrate flood and drought disaster risk reduction strategies , Water Security
Score Card
Environmental Impact
Risk Protection
Affordability
Durability
Criteria
Scale of Intervention
Shelter-Plot-Block Settlement Supra-settlement
Type of Intervention
Engineered Nature-based Hybrid Non-structural
Targeted Natural Hazard
Pluvial Flood Coastal/Riverine Flood
Strategy Type
Relocate Reduce Hazard Magnitude Reduce Asset Vulnerability Reduce Casualties
Implementation Time
Short (1 day ‐ 1 month) Medium (1 month ‐ 1 year) Long (> 1 year)
Effect Duration
Short‐term ( <1 year ) Medium‐term (1 year to 10 years) Long‐term (>10 years)
Targeted Vulnerable Assets
Buildings Transport Technical Infrastructure Land Cover
Investment Costs
Low Medium High
Maintenance Costs (yearly)
Low (<10% investment costs) Medium (10-50%) High (>50%)
Materials
1. Concrete, Rock, Earth-Fill, Timber, Gravel, Sand, Steel (Selection for Dams) 2. Earth-Fill, Compacted Soil, Wood, Sand, Clay, Concrete, Timber, Steel, Rocks, Gravel, Riprap (Selection for Dikes and Levees)