Mapping Drainage

This is part of a series on the Industrial Training of Students on Zanzibar by Spatial Collective. You can read parts one, two, three, four, and five here.

As mentioned in previous blog posts, at the start of the training, the students met with the stakeholders from the civil society, government and the private sector to determine what are their key data needs. During these meetings, the following themes continuously came up in the conversation: creating a base map, mapping roads and drainage, and conducting a household survey in the Zanzibar City’s Urban West.

Drainage mapping was likely the most complicated task performed during the training. This is because the building materials, shapes, and sizes of drainage lines and accompanied infrastructure often change rapidly as they make their way downstream towards the sea. For example, a concrete, rectangular, closed drainage of 1-meter in width and depth can suddenly transition into an open, informal, 25 cm deep ditch made of dirt.

To make sure everybody collects the same data, in the same way, we set up precise data collection protocols and spent a lot of time practicing with the students in the field.

We decided to collect the following data and attributes on drainage infrastructure:

• Type of drainage: [ditch, drain, undergroun]
• If underground: [culvert]; Profile: [round, boxed]
• Built from the material: [concrete, steel, asphalt, sand, plants, trees, gravel, dirt]
• If covered, by material: [concrete, grating, metal, wood]
• If blockage: [dirt, concrete, rubish or solid waste, grass or plants[
• Width: [top, bottom]
• Depth
• Profile: [open rectangular, tabulated, trapezoid, elliptical, trapezoid eliptical]
• Infrastructure: manholes, drainage outlets, and inlets, bridges, etc.

In less than two weeks, the students collected about 35 kilometers of drainage lines and more than 650 drainage related points of interest. A map and the list of some of the data collected can be found below.