A dike is an engineered barrier, typically a long embankment, constructed to manage and control the flow of water. This artificial structure is designed to prevent water from inundating adjacent low-lying land. Dikes represent a fundamental technology in human settlement, historically enabling civilization to flourish in areas near rivers or coastlines.
Defining Dikes and Levees
The terms “dike” and “levee” describe the same basic artificial embankment built to hold back water, though their usage depends on geography and purpose. In North America, the term levee is predominantly used for embankments built alongside rivers to prevent overflowing during high water events, protecting land susceptible to riverine flooding. Conversely, the term dike, especially in European contexts like the Netherlands, is associated with coastal defense and land reclamation projects. Dikes protect land that is naturally below sea level or the high-tide mark. Both structures are linear earthen or concrete walls that run parallel to a body of water, holding water on only one side, unlike a dam which creates a reservoir.
The Primary Roles in Water Management
Dikes serve two primary functions in water management: flood control and land reclamation. For flood control, dikes act as a first line of defense, containing water within its natural or controlled channel during periods of high flow or severe weather. River dikes prevent rivers from spilling over their banks and devastating communities and farmlands in the surrounding floodplain. Coastal dikes and seawalls are engineered to withstand the powerful impact of storm surges and high tides, protecting coastal infrastructure from erosion and saltwater intrusion. The protection they offer is calculated based on the maximum expected water level to ensure safety for the area behind the barrier.
The second major role is land reclamation, often seen in the creation of polders, particularly in the Netherlands. A dike is built to enclose an area of water, which is then drained to create new, usable land for agriculture or habitation. Since these reclaimed areas are permanently situated below the water table or sea level, the dike system must act as a permanent barrier against the water.
Structural Variations and Materials
Dikes and levees are not monolithic structures; their composition and design are dictated by the environmental stresses they must endure. The most common form is the earthen dike, constructed primarily from compacted local materials such as soil, clay, and sand. Clay is a valuable component because its low permeability helps to limit water seepage through the structure.
River dikes are typically broad, gently sloping earthen mounds designed to withstand hydrostatic pressure and may incorporate grass surfaces to prevent erosion. Coastal dikes, which must contend with the dynamic force of wave action and saltwater, often feature robust construction. These may include rock revetments or concrete seawalls on the waterside to dissipate wave energy and resist physical damage.
Modern designs often incorporate geosynthetic materials like clay liners and geotextiles to enhance stability and control water movement. These materials help prevent the internal erosion of fine-grained soil, a process known as piping, which can lead to rapid structural failure. The design must also account for internal drainage to manage the seepage that naturally occurs when water levels remain high for extended periods.
Maintenance and Risk Management
Dikes require constant surveillance and maintenance because they are subject to continuous degradation from hydraulic forces and environmental factors. Routine monitoring involves inspecting for signs of erosion on the slopes, checking the stability of the foundation, and detecting potential seepage issues. Subsidence, the gradual sinking of the dike or the protected ground, is also a concern, especially in areas with unstable or reclaimed soil.
Seepage, where water slowly moves through the dike body, must be managed carefully to prevent the washing out of fine soil particles which weakens the internal structure. If seepage pressures become too high, they can cause a phenomenon called a sand boil on the protected side, which is a precursor to catastrophic failure. Risk assessment is a continuous process that involves evaluating the dike’s current condition against the projected threat from future extreme weather events and rising sea levels.
Failure of a dike system can result in catastrophic flooding. Consequently, maintenance plans often include structural reinforcements like the installation of cut-off walls, drainage trenches, or the use of impermeable sheeting to reduce internal water pressure. The viability of these structures depends on a sustained commitment to inspection, repair, and upgrade.