Design of a Flood Early Warning System Using Water Level Sensors for Coastal Communities in Bayelsa State

Bayelsa State, located in the South South geopolitical zone of Nigeria, is among the most flood-prone states in the country, with coastal and riverine communities regularly experiencing devastating inundations that destroy property and displace populations. This project presents the design of a low-cost flood early warning system using ultrasonic water level sensors and a GSM-based community alert network. The system measures water levels at a river monitoring point using an ultrasonic sensor calibrated against a physical staff gauge. An Arduino Mega microcontroller processes water level readings and compares them against user-defined alert thresholds corresponding to advisory, warning, and emergency flood stages. When thresholds are exceeded, a SIM800L module broadcasts pre-programmed SMS alerts to registered community leader phone numbers and activates a local siren. The system was prototyped and installed at a monitoring point along the Ekole Creek in Yenagoa Local Government Area. During a four-month monitoring period that coincided with the 2023 rainy season, the system generated warnings with a lead time of 3 to 6 hours before observable community flooding events in all six recorded flood episodes. False alarm rate was 8 percent, primarily caused by debris interference with the ultrasonic sensor. A weatherproof enclosure and solar power supply ensure continuous unattended operation. This study provides a practical, low-cost early warning framework deployable across Bayelsa's riverine communities without dependence on national meteorological infrastructure. Keywords: flood early warning, water level sensor, coastal community, GSM alert, Bayelsa State