Where will it flood?

Flooding brings with it more than the risk of excess water. There are potential financial and social costs resulting from inundation whether refurbishment of buildings or temporary shelter for displaced persons as well as the health risks from the transmission of water borne diseases and effluent. PLACE data can be used assess the risk and determine the impact of flooding.

The first example is from the Turks and Caicos Islands (TCI), where PLACE collected new aerial imagery in early 2023. Here flood risk was assessed for a small community in Dockyard on the island of Providenciales (Provo). The study sought to estimate the number of people and number of properties at risk of flooding, ranking this from high to low (as shown below). Using this type of analysis means planners can prioritize mitigation works in those places that need it most:

We also used PLACE imagery acquired in Anguilla in late 2023, to assess flood risk in the country's capital, the Valley. The Valley is located in the middle of Anguilla island and even though its low lying, it’s still prone to flooding.

We started with elevation information, or the height of objects above ground. Elevation information is derived from processing PLACE imagery. As a result all objects, whether trees or buildings are assigned a height in meters. As shown below this information can then be color coded with reds and oranges representing higher areas and greens lower areas:

With elevation comes the ability to view scenes in 3D:

Next using Esri's ArcGIS Pro we identified catchment areas or natural boundaries, delineated by ridges or hills within which surface water will drain into a common channel forming a river or stream. Below you'll see the catchment areas (colored polygons) and channels (blue lines) for the Valley. While channels will not always visible, especially when dry, when it does rain these are the courses that water will likely follow as it seeks a route to low lying areas:

So how do you go about assessing flood risk? Well as we saw in Zomba, Malawi, you can use models to detect buildings from PLACE imagery. As shown below it means planners can quickly see if a building is in a water channel, or close to one. The pooling of water means buildings at the ends of channels are going to more adversely affected than those further upstream:

And as buildings are often underwritten by loans and insurance recording building characteristics, a task facilitated by combining PLACE street imagery means it is possible to make a determination of the financial impact of flooding as well by assessing things like number of floors, construction material and building condition:

So even in this small area of Anguilla the likely cost resulting from flooding to buildings, and damage to fixtures and fittings can be expected to run into 100’s of thousands of dollars. And this can all be done, quickly, using PLACE imagery.