Towards flood-proof sanitation (Zimbabwe)

This study applied earth observation and hydraulic modelling techniques to map flood-prone areas of Chimanimani District. The study used GRACE satellite 0.5° · 0.5° spatial resolution to map the spatial variations of groundwater levels in the study area. Hydraulic modelling HEC-RAS 2D framework was applied to compute flood depth and extent for 10, 50,100 and 1,000-year return periods. The model was validated using past inundation maps, flood marks and stakeholder consultation. A 1,000-year flood covers areas which are more than 50 meters away from the rivers, and a flood depth of over 2.8 m inundates approximately 75 % of the conventional sanitation facilities. Furthermore, water quality sampling carried out on the water sources within the flood inundated areas indicated a positive test for faecal coliforms. These were attributed to the sanitation facilities within the area. According to the analysis of the period from 2002 to 2022, or the GRACE mission’s lifetime, there is no change in groundwater level from 2002 to 2010, but there is a sharp increase in storage in 2021, which can be partially explained by increases in average rainfall patterns due to Cyclonic activities from 2019. The GRACE-derived groundwater level variations data indicates areas located in shallow and high groundwater levels. Based on the hazard maps and the mapped groundwater table, Chimanimani was divided into three regions and sanitation options were proposed for each region. The study recommends the use and introduction of dry composting toilets for holding and processing waste material and to capture the nutrients in human waste, such as nitrogen and phosphorus, for local reuse.