The art of drainage mapping in Dar es Salaam

One of the main goals of Ramani Huria 2.0 is to scale up all drainage mapping efforts that were previously executed during the project’s pilot. Students have now been grouped into specialized groups to ease coordination and delegate according to skillset. These groups include: Drainage Team, GIS Team, Open MapKit Team, Community Outreach team and Remote Mapping Team.

There was no clearly identified method for mapping drains, so our team had to test most of the known field mapping applications. After testing these applications, the GeoTrace feature, coupled with its ability to enable the creation of customized surveys, placed the OpenDataKit  (ODK) tool on top of all tested applications. This is a free and open-source Android application that helps organizations to gather data and manage mobile data collection. A data collection form or survey is built (XLS Forms is recommended for larger forms) and collection of data is done on a mobile device. It is then sent to a server, which aggregates the data and makes it available for extraction in a useful format.

After creating the appropriate form, students were trained to use ODK on their own Android phones. OSMAnd is another application that helps field mappers to properly orient themselves as they move around the city mapping, and the GeoTrace functionality is incredibly helpful for mapping of drains, ditches, and culverts, and accurately taking coordinates as a mapper moves along the feature being mapped.

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 A student tracing a drain.

Additionally, while mapping, mappers use ODK to take GeoPoints to accurately locate features in or along the drain segments. These points include: drain beginning point, drain damage or blockage, point where drain connects to private property, spillways, silt traps, drain outflow point, and many others.

In order to accurately acquire measurements of the different details of the drains, ditches or culverts, tools fit for this purpose were sought. These include tools like tape measures and custom-made measuring sticks (designed by our own Tanzanian team!) to measure depth and width of drains and diameter of culverts. Drainage data needs to be measured accurately since the goal of Ramani Huria is to improve the city’s flood resilience, and drainage is plays a critical role in this. 

Students measuring depth of the drain using custom-made measuring stick

As a test of the students’ understanding of this mapping process we took them to Hananasif ward for real field data collection. Students divided themselves into groups according to the sub-wards and then scattered to collect data. The process was a bit challenging since it was the first time for these students to collect drainage data in the actual field and some community members viewed the process as a political move, but students were very keen to explain the aim of the Ramani Huria project to any inquisitive parties.

Another challenge that came up surrounded the direction of water flow in the drains. Sometimes it is very difficult to see which way a drain flows. This problem was solved by asking community members about the direction of flow of a specific drain or by looking carefully at the sediment record. 

There were also some accuracy challenges with smartphone GPS systems. Some of these issues were solved by visiting local computer programmer, Ka-Ping Yee, but certain locations remain problematic as they they struggle to allow for accurate GPS reception on a mobile phone. 

Very occasionally, students encountered resistance from community members who were not well informed about the project. This particular issue justifies why Ramani Huria has such a strong emphasis on community engagement. 

Students in the field at Hananasif Ward.

Despite these few difficulties, students collected as much information as they could. Their reports shows that there exist a lot of unconnected drains, drain segments filled with garbage, and streets with no drainage at all – perhaps the main cause of disastrous flooding. 

The data collected from these areas is analysed for accuracy and worth using QGIS. While visualizing data through QGIS software some errors were found such as missing data and inaccurate information. In theses cases, students had to re-collect the data. As the process evolves, they are becoming increasingly aware of the importance of quality checking their information during data collection. 

Drainage data of Kisutu Sub-ward in hananasif visualized on QGIS

Our students are will continue with their training and practice to make sure they are well equipped with the necessary skills required to undertake the official mapping process.