SOIL SAMPLING

Soil Sampling– Ramani Huria partnered with JBA Consulting  (specialized in understanding geomorphological features) all funded by the World Bank and worked on developing a surface soil dataset that will be used for geomorphological assessment and soil characteristics of Dar es Salaam in comparison with future flood risk studies in the region. Soil and/or sediments were sampled from Dar es Salaam and nearby districts that border the city because most of the sediments that flow to the city are from the upper catchment areas which are not likely to be within the city. In order to get a complete dataset of sediments form, these areas needed to be examined too.

Our partner, JBA Consulting, created 731 sample points on a map using a 2km by 2km regular grid to make sure we get samples for the whole of the Dar es Salaam catchment area. A team of 12 field mappers was then trained in the data collection, with an offset policy in place for points where a sample could not be taken due to inaccessibility. Each sample site had its unique code to identify it, date of sample collection and the name of the mapper to avoid any inconvenience that might occur during the analysis.

In case the sample point was hard to reach or a sample could not be collected for some reasons like paved areas, the mapper had to move about 500 meters north and collect the sample. In order to reach the points for taking the soil samples, mappers were used MapHub on their phone to guide them. When connectivity became an issue the team switched to the Maps.Me application, which allowed them to navigate to points offline simply relying on the GPS on their phones.The collected sediments were then sieved to determine grain size distribution. Before sieving, the sample is supposed to weigh 500g, and after sieving, the mass of the soil was recorded on a spreadsheet according to the layers of the sieving tool. There was also a prepared ODK form which was being used to fill in the sieved data to make sure that the data is safe in a server.Now that we have soil data of the city and the drainage data is underway to be completed, we will then be able to create an accurate flood model of the city by layering the sediment data and drainage channels data of the city and obtain a more complete understanding of flooding in Dar es Salaam.