The Oxford Flood Network is making a flood detection network in the UK, using low cost sensors and volunteers. They are sharing their code on Github and their results on the Flood_Network Twitter account.
They encourage you to join their effort, and no high technology is necessary. The network incorporates both readings from automated sensors (about £250) as well as manual readings from gaugeboards or photos.
New as of December 2015 is an interactive flood map. A post from Nominet describes the effort:
Nominet, in association with the Flood Network, is today launching an interactive, online map which visualises river and stream levels around Oxford. The map, showing how technology can be a part of flood defence systems anywhere, has been developed following a successful pilot project with the Oxford Flood Network. The project has been focused on exploring the potential of the Internet of Things (IoT) to create an extensive, localised, early-warning system for flood-prone areas for the first time in the UK.
The system is using TVWS (“TV white space”) as its wide area backhaul network for these sensors for hard-to-reach devices that are outside of the range of wifi. Cost-effective and reliable access to remote small sensors is one of the tough spots in Internet of Things development, it’s interesting to see TVWS as a possible solution to this issue. The other relevant technology for low-cost metro area networks for sensors is Lorawan, more about which later.