# Flash Flood Early Warning System in Colima, Mexico
## 2 Materials and Methods
### Sensor and Processing Considerations
The actual implementation of the RiverCore fixed node, which has been deployed in the experimental network, has inbuilt libraries for RS-232, Analog, I2C, and SDI-12 devices; however, different libraries can be developed to include compatibility with a wide range of hydrologic devices. The drifter node integrates a GPS module, which retrieves location, time, and speed variables. It also contains a physical storage card slot to retrieve measured data. This device is sealed inside a waterproof enclosure that holds a magnetic switch, which powers the data logging mechanism while it flows through the river basins. These data are stored inside the MicroSD card and can be analyzed by the EWIN data acquisition platform. Drifter nodes add radio communication capabilities to transmit information to other devices like a fixed node and a sniffer. The above-depicted hardware components are shown in Figure 7.  
The electronic components are sealed into a spherical lightweight plastic container using polypropylene material. The device's mainboard is 8 cm long and 5.1 cm high; a bright color is recommended to facilitate the search and recovery of the equipment. The drifting device operates using a magnetic, normally closed switch, allowing it to be turned on after it is sealed by removing a previously attached magnet. Current river conditions present challenges due to constant changes in current velocities, water level, the presence of vegetation, rain, and other environmental factors. Drifters have been used in many countries, making them a popular platform used to collect river parameters, such as the direction of the river's water flow path. The proposed technological solution uses a drift network through various sections of the river. Similar technology solutions were published in [22; 23; 24; 25; 26; 27]. The drifter has the possibility of integrating other sensors to measure variables such as water quality or depth. The RiverDrone platform is a combination of software and hardware aimed to be mounted onboard other mobile exploring methods, such as drones (UAV) or other mobile infrastructure, adding an aided method to find as many drifters as possible when deployed. The RiverDrone hardware can be mounted on any drone that can support a weight of 400 g. The type of drone is not described because RiverDrone hardware is not connecting to the drone hardware at this time. The software constantly broadcasts a message searching for drifters. When a drifter is found, the software will report the sniffer and drifter location to the EWIN web platform via the 3G cellular network using MQTT communication protocol. Natural water channels like rivers have many obstacles, cavities, and uneven shapes that may cause the drifters to get stuck; therefore, a tool like the RiverDrone is required to facilitate the retrieval process of such devices. The sniffer is physically composed of five different devices: a microcontroller unit, a 3G cellular modem electronic board, an XBee (802.15.4) or LoRa radio, a regulated power supply, and a LiPo battery (Figure 8). It contains the proper materials and components to localize the mobile nodes throughout the river and send these data to the server (Drifter Id, Latitude, Longitude, RSSI (\"Received Signal Strength Indicator\"), and Speed). Figure 8: Sniffer hardware components. Figure 7: 3D model and picture of drifter electronic components.