In flood prone areas, it is important to adjust sanitation solutions, to avoid the health risks associated with flooding or overflowing pits and septic tanks, causing the release of wastewater and faecal sludge into the environment. Also, flood resilient sanitation infrastructure prevents damage due to flooding, and ensures sanitation services can continue to be used during flood events.
The main aim is to prevent rainwater from submerging the equipment (raised floors, non-return valves, etc.), to reinforce the resistance of the equipment and to limit the infiltration of wastewater near water tables (watertight pits, urine diversion, etc.).
- Step 1: Evaluating the flooding risk.
Characterize the flood risk by collecting the following data:the area affected by flooding (linked to topography)
- the intensity of flooding (shallow or deep water? slow-moving or fast-moving flood water?)
- the frequency of the flooding event
- the duration of the event.
The aim is to establish a zoning of the territory, distinguishing between areas that are safe for sanitation systems, and those where more or less extensive flood protection measures will be required.
- Step 2: Designing or adapting sanitation systems to withstand flooding
The aim here is to choose sanitation systems which can be operated without interruption, and which do not risk discharging effluent into the environment.
The SPHERE standards recommend “making the excreta containment infrastructure watertight to minimise groundwater contamination” or “building toilets or septic tanks raised”.
Different options should be considered:
- Raising toilets and pits above the highest level of floodwater;
- Reinforcing the walls of latrine pits (lining them with erosion-resistant materials);
- Waterproofing sludge and wastewater containment facilities where they cannot be raised above the maximum flood level;
- Limiting the risk of effluent infiltrating the soil by separating urine from feces (UDDT: Urine-Diverting Dry Toilets);
- Installing non-return valves on septic tanks.
The effectiveness of all of these measures can be enhanced by designing the adaptation measures for wastewater and storm water management together.
Step 3: Taking into account the constraints associated with technical solutions
- Additional construction costs: masonry work on pit walls, raising latrines or tanks;
- Additional operating costs: lifting wastewater if storage or treatment facilities are raised, more frequent emptying of pits if they are sealed;
- Adapting technologies to people’s practices: use of urine-diverting toilets, accessibility of elevated toilets for people with reduced mobility, etc.
- Equipment maintenance capabilities: ability to ensure regular emptying of watertight pits, maintenance of urine-diverting latrines, etc.
Climate change and urbanization are significantly increasing the frequency of intense flooding events. Flooding of sanitation infrastructure, like latrines, toilets or treatment plants, gives rise to two types of problem:
- Disruption of sanitation services
Flooding can lead to the destruction of sanitation facilities: a frequent problem is the collapse of simple unlined pits, which are the most common type of latrine in low-income countries. Disrupted sanitation services can force people into unsafe alternatives, like open defecation, which increases public health risks.
Floods can also cause hydraulic overloading and make wastewater treatment systems (such as septic tanks or activated sludge plants) ineffective.
Lastly, flooding can disrupt pit-emptying services (inaccessible areas, increased demand for emptying as rainwater fills the pits).
- Environmental contamination
The flooding and/or overloading of sanitation systems (including treatment plants) leads to the release of untreated effluent directly into the environment. Untreated waste water and faecal sludge in the environment increase the public health risks and pollute the environment (potentially causing significant ecosystem degradation).
Existing flood-prone sanitation solutions can lead to higher investment costs. Also, flood-prone solutions can be considered less user friendly and require additional maintenance.
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Bibliography
A review of sanitation technologies for flood-prone areas
WASH Services and Climate Change: Impacts and Responses
Technical Brief: Climate Resilient Sanitation in Practice
WASH Climate Resilient Development - Linking risk with response: options for climate resilient WASH
The SPHERE Handbook, 2018 – see “excreta management, p.115
Key Resources and Tools
Strategic Framework for WASH Climate Resilience
This strategic framework provides guidance on the main areas to be considered when planning and…
Compendium of Sanitation Technologies in Emergencies
The Compendium lists technologies that are suitable or not for flood prone areas. See “Sanitation…
WASH FIELD NOTEDevelopment of a Disaster-ResilientToilet: lessons from the States ofAssam and Gujarat, India
This Field Note describes the development process of designing a Disaster-Resilient Toilet (DRT) whichwas carried…
Designs
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