In many cases, inappropriate siting, or leaks in water-supply system components, can cause landslides that damage a given component or even render an entire system inoperative. (Slide 56)  This slide is animated and takes one minute to view.

Landslides are generally the result of cumulative changes over weeks, months, even years.  Water companies often have enough time to take precautionary measures to prevent damage to the system (Slide 57). However, landslides caused by unpredictable natural phenomena such as earthquakes or heavy rainstorms (Slide 58) do not allow for preventive actions—unless these were taken at the time the system was designed.

Several measures are available to reduce vulnerability to landslides. They vary depending on the particular needs of each case (Slide 59):

• Reforestation campaigns.
• The construction or reinforcement of retaining walls and drainage components.
• Slope stabilization.
• When pipes have to be laid on slopes, use of materials appropriate to the contours of the terrain.

Volcanic eruptions

Volcanic eruptions differ in their effects depending on the type of emissions that occur, the viscosity of the magma, the quantity of gases released, the flow of lava (which varies in volume, extension, thickness, and speed of movement), the type of ashes ejected, and the areas subjected to lava flows and ash fall. (Slide 60)

Although the frequency of eruptions is notoriously erratic, historic and even prehistoric records provide clues to the recurrence of this phenomenon. Most active volcanoes in Latin America and the Caribbean are monitored in some fashion, allowing for the adoption of preventive measures before the most critical stages of the eruptive phase.

Generally, volcanic eruptions unleash a chain of disasters—landslides, mudslides, avalanches and rock flows due to the extreme heat and vibrations, as well as emissions of ash, dust or gases.

Impact areas may be covered by lava or affected by acid rain and ashes.  The waterways, treatment plants and pump-houses located in such areas are most at risk.

Volcanic eruptions can affect water and sanitation systems (Slide 61) in several ways:

• The total destruction of system components in areas of direct impact. (Slide 62)
• The obstruction by ashes of catchment facilities, silt basins, water mains, flocculators, and filters. (Slide 63)
• Degradation of water quality due to ashes; pollution of rivers, brooks and water bodies in the areas where ashes fall.

To reduce such risks, the following measures should be taken:

• Protecting reservoirs and other water storage facilities by covering them either permanently or temporarily. (Slide 64)
• Building alternative (redundant) water-supply and sewerage systems.

Drought

Drought is a reduction in the water or humidity available that brings about a decrease in the normal flow rate of surface and ground water sources. The precise definition of drought varies depending on whether it is viewed as meteorological, hydrological, or agricultural (Slide 65).

Areas most vulnerable to drought are those with a predominantly dry climate where soil does not retain much humidity.  Drought may bring about a reduction or even extinction of the water supply from habitual sources.  Surface water sources such as rivers and lakes generally suffer the effects of drought much earlier than groundwater sources.  Drought may affect the drinking water supply (Slide 66) in the following ways:

• Loss or decrease in the flow of surface or ground water.
• Degradation in service quality or increases in operation costs.
• Rationing or suspension of the service.
• Inability to rely on the current system.

Certain prevention and mitigation measures can be taken (Slide 67):

• Assessing the conditions of existing wells.
• Assessing the quality and volume of underground water, and having the equipment needed to facilitate operations in the event of a decrease in volume while preventing pollution of water sources.
• Establishing alternative sources and interconnecting them with existing systems; considering the possibility of emergency drilling.
• Rationing water consumption.

Disaster prevention and mitigation (Slide 68)

Vulnerability reduction can be achieved through the use of prevention and mitigation measures that help correct deficiencies before disaster strikes and minimize the risk of failure in normal conditions.  Mitigation and prevention is the product of interdisciplinary efforts by professionals with experience in the design, operation, maintenance, and repair of the system components.  It is therefore not an isolated task, but an integral part of all planning and development decisions regarding water and sanitation systems.

Mitigation and prevention is practiced (see Slide 69):

• In new works, by applying prevention criteria in the design, choice of site, selection of materials, grid design and incorporation of redundancy components.
• In existing works, by engaging in conservation and maintenance activities, repairs, replacement of old components, relocation of incorrectly sited components, and new projects aimed at increasing redundancy.

Priority must be given to those actions that take into account:

-  The Magnitude of the Decrease in Supply (MDS) with respect to total supply volume.

-  The Time Needed to Repair the component that is out of order (TNR).

The units of measure to quantify risk are Lost Production Days (LPD), equivalent to the decrease in the total capacity of the system while repairs are carried out.  This indicator is independent of the frequency of the hazard; in relation to reserve capacity, it makes it possible to characterize existing risks and define mitigation measures.  As a top priority, those components should be considered in which total LPD is greater than reserve capacity.

The purpose of this prevention and mitigation strategy is to counter the weaknesses in the system based on the frequency and intensity of the phenomena that may occur.

In most cases, the problems that cause damage to water and sanitation systems are not exclusively related to the disaster itself, but rather reflect insufficient consideration of natural phenomena as a variable in the planning, design, construction, operation and maintenance of such systems. (Slide 70)

Most hazards can be mitigated by decentralizing water and sanitation systems; for instance, by establishing alternative water sources so as not to disrupt the service.  One way of achieving this is to incorporate redundancy into the systems.  Should damage occur to a component or system, another connection is available that can be brought on line promptly so that services can be restored without delay.  Special emphasis must be placed on the desirability of having control valves in strategic locations. (Slide 71)

Interconnected systems and redundant components increase the reliability of the system as a whole and provide greater flexibility even when engaging in routine tasks such as maintenance.

Operation and maintenance activities are an ideal opportunity to work on reducing systems vulnerability (Slide 72).  However, some situations call for the execution of special works and projects aimed exclusively at vulnerability reduction (Slide 73).