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Brian Reed gravatar image

What Liz proposes is a cess pit - basically a large bucket latrine. Cheaper to build but higher maintenance with very regular emptying. A sealed tank may float if (partially) empty during floods. Raising the whole thing may help emptying and avoid the floatation.

The septic tank option (assuming you have a sufficient water supply) may work with tweaks. The floatation thing will still be around, but as the tanks are only emptied infrequently (longer than a year), this can timed for the dry season. A bigger problem is the soakaway. High groundwater tables will mean there is nowhere for the effluent to infiltrate to. One way to cope with this is to use trenches rather than deep soakaway pits. These maximise the wall area of the soakaway trenches and they can be shallow, above the groundwater if possible. This can be arranged as a “herring bone” pattern to save space. Planting large leaved plants in the area may help increase evapotranspiration.

Another alternative is to go for a constructed wetland. This can cope with flooding! A granular soil is planted up with local wetland plants and the effluent flows through this. The final effluent could be discharged into a pond or stream, as long as it’s not directly used as a water supply. Having this at the end of a soakaway trench means that the effluent can infiltrate if possible but the wetland acts as an additional stage.

The septic tanks will still need emptying periodically.

On a wider scale, you have to ask the question why people are living in an area that floods. This really isn’t suitable as combatting the floods is very very very expensive. Improving transport links may help people to live elsewhere but still get to work and this may be more sustainable than trying to improve an area that floods.